The Direction the Indian Private Sector may take to Build up an Indian Military Industrial Complex (MIC): The Bee, the Fly, and the Bottom of the Pyramid?!

The Bee and the Fly

It appears if one puts a bee in an empty glass jar and the glass jar is put in a dark room with its bottom facing a strong source of light the bee- logically equating light with an opening – will repeatedly try to “fly out”  through the bottom until it dies of exhaustion. Interestingly, a fly, being illogical, will zip around in all direction and very quickly fly out from the open end of the jar. Our Private Sector, I feel, is emulating the bee. It is being “logical”, the hope of a logical big launch order blinding it against an invisible and possibly an extremely resilient obstacle.

Am I being unduly pessimistic? A practicing engineer always has an ingrained dour pessimism regarding the cost of money and unlike the PSU the Private sector cannot run on infinite delays and overdraft. (Note. 1)

What we wish to analyse is the role the Indian Private sector can profitably play and if it may not be more fruitful if some apparently radical line of thought is pursued. The illogic of “Latest and Best” Western weaponry must be accepted (Note 2). There are limitations in the capabilities of the Indian Industry and we have to carefully study these contradictions and anomalies to produce weapons which are different, marketable and yet within our present capabilities. (Note 3)

Because Weaponry is per se “useless” no country supplies more than “venture Capital” for any Weapons development programme. That venture capital, too, comes from the earnings of the previous successful weapons programme. No previous exports - no new programmes. China was in the past a possible exception but then the Chairman was spending thirty times more on his MIC alone than what he was spending on his Urban development. Such deprivation is not an option for us. We therefore have to plan for weapons export as an Integral plan right from the start. The idea of funding development of weaponry with the sole objective “to save foreign exchange” is naïve or whitewash. As a corollary the constant moan of lack of funding is appalling. Free funded weapons development is unsustainable. Earn it first!

It is nobody argument that the selling of weapons is a National effort. Every President or Premier that visits New Delhi comes with an appendage of Hawks or Howitzers to sell. So ideally we should have a situation where the Cabinet, the PMO, North Block, DRDO the PSU, the Armed Forces and the Private Sector should be working in close co-operation and harmony creating a National effort to build and export Weaponery. One will instinctively notice how long the chain is.

It is in this idée fixe of somehow everyone should work as a team that I am skeptical of and it is this idea that the Industry must sideline if it is to succeed. Two primary factors come to the fore in any success

a) The quality of the decisions taken and
b ) The quantity of the orders expected.

Let us examine the quality of decision making in matters related to Defence which are in Public Domain:

1. The failure to wake up to the Chinese threat even after the Chip Chap Valley incident in 1959. The troops had to face Chinese PPShs with bolt action SMLEs in 1962.

2. The failure to fund the development of the Orpheus B.Or.12 at the rate of 1 million GBP/ year for two years. This later hobbled the Marut project. Mind you we found money to buy an aircraft carrier and it complement of aircraft about the same time i.e. 1957.

3. Though the Orpheus was for two decades numerically the most important engine in the IAF (Marut. Gnat, Kiran Packet) no attempt was made to develop/improve the engine in terms of thrust, SFC, TBO. One “Science Lab” afterburner programme (Note 4) was closed down with alacrity once the daring test pilot was killed in what may have been a Pilot Error situation. Money was of course made available for a GTX project which had no immediate application.

4. Repeated efforts by HAL to develop the HF 24 –HF 73,GAF, ASA, and HF 25 at costs of around Rs. 70 crores were not funded in circa 1971-1976. In 1983 we funded a “Rahu” Organization –ADA-(For Non Indian readers!-Rahu in Indian astrology is dissatisfied head without a body) to the tune of Rs. 565 crores for the crucial MiG 21 replacement plan. At that time the earlier HAL proposals were not revisited and refunded to keep as a “second string” given the obvious and glaring weaknesses of the venture.

5. The somewhat arbitrary manner in which both the Gnat/Ajeet and the Marut were retired even though it was clear that the Hunters, particularly the T66s were going to the scrapper‘s yard very soon.

6. The incredible seventeen years delay in ordering the AJTs.

7. The delay in following up the HDW submarine programme- resulting in all the skilled manpower retiring out- before taking up the Scorpene programme.

8. Someone sat on the Bofors 155/39 drawings for Twenty years. By that time the fashion had changed to 155/45 calibre. Given this litany why should one be optimistic?

The reasons for such contrariness in decision making are not the present issue. The issue is that in the Indian Techno structure, read Raisina Hill, will not provide the Private Sector speedy logical decisions. The private sector cannot afford delay. Has there been any reliable indication that things are about to change and change very dramatically, for the better?

To be sure the New Government has been remarkably “sure footed” in its pronouncements so far but caution suggests that we do not plan on the basis of anticipated change for the better. There are two very important reasons for ignoring, as of the present, of a “helpful” Government Techno structure. One is from the past. You will note that many of the above weird decisions were taken during the Nehru/ VK Krishna Menon watch where sincerity of aims was unquestionable. The other reason is pragmatic. You may have noticed it is remarkably easy to change one’s plans when the circumstances suddenly change for the better. So whilst optimism about the new Government is to be retained such hope must not find a place in the Private sectors plans. Better prepare as if Raisina Hill will be ready with the spokes and spikes.

The Bottom of the Pyramid

The second area we must look at is the value of the order- particularly the annual production order. Presuming the Private sector has survived the first hurdle above what will it get anyway? What have been the procurements over the past 30 years or so? 3-500 combat aircraft, 2500 tanks, 500 field guns, a million rifles in several varieties and so on. The Navy’s procurements have been better but again the annual value would still probably be sub profitable. Whilst the figures look impressive prima facie they work out a miserable production rates which is what the Industry will have to factor in. ( Note 5) Between the long delays pending a (possibly) weird decision it is quite possible that the Private sector will realize the wry truth of Northkote Parkinson’s dictum that delay is the deadliest form of denial. I may add that according to Parkinson we may find that strong support and enthusiasm at one level of Government is usually replaced by ridicule and harassment at the next level.

To sum up this section we may conclude that:

a) The Indian decision making process is “unreliable” for business planning.
b) The Indian market is too small to tailor our products to the Indian Armed Forces need
c) And finally- the Indian Private sector is still not ready to produce competitive weapons- i.e. products that can match the big Five (US, Russia, China, Europe, France!). It has the POTENTIAL to do so but potential is so different from reality.

So what would be a summary?

1. What the present Government is doing-Make in India” is extremely welcome but it still remains a “Hygiene”- it will improve the situation, it will create a base, but it will not transform our capability.

2. Our present capabilities in the Private Sector is not still sufficient to “create” new weapons. It is still some time away from making competitive “big league” equipment.

3. Fortunately there is a vast untapped equipments market worth- my conservative guess is about USD 10 billion per annum for appropriate equipment which the Private sector can supply.

4. The CII and similar such bodies must resolve to do what the Government has failed to do i.e. to develop a comprehensive set of weaponery and equipment which is specifically suitable for fighting the Third World’s wars”. Today the Third World is equipped with expensive unsuitable equipment developed for fighting the White Man’s wars or making do with “Grandfather’s Generation “equipment!.( Note 6, 3)

5. Do an analysis of the economic conditions of these countries and how much money they are spending on Defence and what are they getting for it, what we can buy from them and what can they buy from us. (Note7)

6. Accept as an axiom that an Indian designed weapon, built with Indian or local labour, to Indian standards, and Indian materials will be two to five times cheaper. (Note7)

7. Set up a Think Tank of independent (note) experts who would be able guide what kind of equipment should be developed. 8. Do Professional market research.

9. Set up Test Standards that realistically reflect Third world Warfare conditions rather than the Global Market/Temperate and Arctic zone conditions.

Can the Private Sector develop a MIC without any Government aid ? I am reminded that the Germans-after the First and Second World Wars formed offshore enterprises in Denmark, Sweden and Spain to keep their MIC intact under the noses of the victorious Allies Commissions. I have absolute confidence given our ancient Mercantile skills we can do better.

Notes

1. The delay in clearing the F 35 and the F 22 Raptor may spell a period of great difficulty regarding US dominance in the Aerospace market because of Commercial failure of the product. The B 787 Dream liner may be giving nightmares in Seattle not because of the Technical problems which Boeing will definitely solve but because of red ink in ROI. Convair went with the Coronado CV990, Douglas went with the DC 10, is it now Boeing’s turn, I wonder ? I just want to illustrate the harsh realities of the real world as compared to the world of PSUs.

2.Take the case of the so called Mine proof vehicles. It was a Western “latest and Best” idea that is less than successful. Is that the best for counter Insurgency? It’s weak point is that it is confined to the motor able road. The Maoists know they are safe in the jungles. Would not an armed and lightly armoured (STANAG1 level) All Terrain Vehicle e.g a Bren Gun carrier or a Kettenkrad that can get off the road and give them hot chase be more useful.

3. I was looking up at random about the Republic of Salvador. The GDP is USD 50 billion and it’s armed forces is about twenty thousand personnel who are engaged in-what else- counter insurgency. We can presume that it’s defence budget is around 2 billion annually of which perhaps 300 million USD is for new acquisitions. Now there are eighty countries which represent an Arms market of may be 24 billion USD. Is it not worth looking into?

Salvador’s armed forces are equipped with guns of 120 mm caliber maximum, light armoured vehicles, and the Airforce uses 40 Vietnam era Helicopters, 10 Basler modified Dakotas and 16 Cessna T 37 jet trainers for their strike duties. Until the ‘90s I think they used to use ex- Israeli Ouragans. Their heavy truck is a MAN, perhaps similar to our Shaktiman. .What is the equipment we can supply to Salvador to upgrade their combat capabilities? Similarly when we talk about Tanks we think automatically of super power MBTs. What about the old concept of the “Infantry Tank”?. Surely the Abrams or Arjun tank- good as they are -is not the best equipment for Salvador! A modernized Stuart -that did so well in the Burmese terrain- or perhaps a KPzW IV with all the mod cons which can be afforded in large numbers may be more suitable than the incomparable Leopard or Abrams in a country where the max vehicle load for bridges is thirty tons. It should be possible for Indian Industry to develop very simple but modernized replacements without risk of great additional investments.. The best part is there are 77 countries like Salvador’s and even trickle orders can keep the lines busy and profitable.

4. I can’t remember to have seen a variable area nozzle of any sort on the surviving HF 24 R prototype in HAL’s flight test hangar.. If this is indeed so then the jet pipe must have been enlarged to the higher after burning jet pipe temperature. This would have meant a modified ‘fatter” rear fuselage. This would have increased the “base” drag- no wonder she performed badly when the Afterburner was not “on”. I can’t myself believe this but that is what I had seen- oh! so many years ago! Notes/ corrections anyone?)

5. The production rates of the Chinese make for sober thinking. In 1961 they were producing thirty MiG 17s a month! Their current production rates – witness the line ups of J10s – means they have not lost the habit!

6. The Tamdaw Lay ( Burmese AF) flies the MiG 29. What they probably needs is a simple close support aircraft more in line with a “baby” A-10 or Su 25. Across the world the G77 countries are “making do” with over potent platforms with watered down equipment or weaponery where one has to buy the spare parts from museums or from David Monathan AFB boneyard!!

7. We may buy to re- export or assist to export I think it is Chad which makes an excellent cheese out of Camel’s milk. It cannot be exported to the Euro zone because the Euro zone wants fully automatic milking machines (in Chad! Lieber Gott!) What we can do is to see if Amul will help the Chad people to use Indian expertise to export the product so that they can buy from us.

8. In the HJT 16 Kiran after setting the cabin pressurization capsule setting ( at 7000’?) the setting screw had to be held in place by a small collar which slipped over the hex. Head to prevent it from rotating. The hex head was slightly smaller than the hex. Hole in the collar and did not come even in contact with the collar. Yet the collar had to e made from imported “S1” steel- which is exactly ordinary mild steel ut made in a :certified” factory in the UK. The Russians don’t have this business of “certified” materials and GOST standards are sufficient. The MiG 21s spars are made from ΧΓСΑ30 material the A denoting not Aerospace as is sometimes mistakenly assumed but that it is an economically valuable material and is to be used with reserve! My experience in production of high tech licensed engineering products was that our manufacturing prices were one fifth of their selling prices!

Prodyut Das

Professor

Prodyut Kumar Das is an Alumnus of St.Xaviers’ Hazaribagh, IIT Kharagpur, and IIM Kolkata. He started his career with Aircraft Design Bureau HAL and for twenty years worked and led various vehicle related Product Development Projects with leading Indian and multi National Companies.

He left Industry to join IIT Kanpur in 1993 as a Professor in the Department of Mechanical Engineering. There he won a prize of the Royal Aeronautical Society of UK for his design of a light sports aeroplane using grants given by ARDB. He also did a project study on “The design of a Light Car costing less than 1 Lakh” which was a Ministry of HRD funded project IDICM 36 and started his research on Stirling Engines in which the IN was keen.

When IIT Kanpur did not renew his 5 year tenure he returned to the  Industry as a Vice President Technical and finally retired as Advisor Aerospace in the e- Engineering Division of a Leading Indian Engineering Company.

He currently teaches Engineering in a Private Engineering College in his hometown and continues his Research as a Consultant. He has been writing on matters related to Defence Engineering since 1990s.

Some Notes on the Forthcoming Spin Trials of the HJT 36 - Part 2

In the first part of this series we had published an analysis as to what is the possible areas of problems with the HJT 36 which has been withering on the vine since a spectacular launch in 2003. There have been some reader’s responses and since they raise important points or suggestions I thought I would put in part 2 as a conclusion.

Before I go on to the Technical portion I have a bone to pick with Indranil Roy because he has touched upon a very important point. He said, whilst agreeing with my prognosis, that (and I am quoting from memory) “what Professor Das has said is actually what  is taught in Second and Third year Aerodynamics” How I wish this were true! No! Indranil, very unfortunately this is not what the Second and Third years learn.

What they learn in Second and a Third year is this:

-T = Iθ^"́+ KAθ^́́

They will learn why there is a negative sign on the LHS and how to solve the equation by “substitute tan θ by R” and whilst the teacher will do several blackboards of derivation to obtain the equation (which is in the book in any case!) he will be unable to explain that what the equation means is “this” - this being what I have written in the earlier part. Harsh? Those of you who have done IC engines will remember the painstaking derivation of the Thermal efficiency formula of IC engine but no teacher discusses the physical phenomena and the co-relation behind Thermal efficiency and compression ratio. Any wonder we then have overweight engines?

The portmanteau explanation is “lack of time and vast course” but someone who wastes time will never have enough of it. In trying to teach everything our Institutions finally teach nothing. Unlike the Germans- who introduced the Sciences based Engineering in Prussia in the 1880s with great emphasis on the Physics of things -“Technische Mechanik” - we have replaced the Physics with Mathematics and preen ourselves on “Science based Engineering! Back in Berlin or was it Potsdam – one had to have “real” Industrial experience to be considered a Professor. Kurt Waldemar Tank , an electrical Engineer by the way, was Professor Tank.

Let us revert:

In the earlier part we put forward the hypothesis that there are three problems:

1. Engine flame out at the spin

2. Possible difficulty/delay in spin recovery due to suboptimal location of the tailplane.

3. Wing drop at the stall.

If the above hypothesis is true we now have to test the hypothesis and recommend a possible course of correction. Let us start with the easiest one first.

Wing Drop Correction

First we have to test the hypothesis that lack of “washout” and not say the engine gyroscopic moment due to sharp pull up at the stall is indeed the cause of the wing drop. This means “wool tufting” the prototype and exploring the airflow separation behavior at the tip as stall approaches. CFD and wind tunnel testing can follow if it is possible to organize quickly. The appropriate “washout” has to be introduced.

The simplest is to introduce some kind of a turbulator or a vortex generator. You must have seen them on the Boeing 737. The Brazilian AMX also has prominent vortex generator on the outer span. Did they have a similar problem?

Here I must mention a very interesting solution proposed by Mr. Mukut Pathak who suggested a “dog tooth”. If we overlook the terminological inexactitude” (A dog tooth is a local extension of the leading edge used in swept wings to break up the span wise flows) the suggestion is very good and I have improved on it. Instead of the local slat as MR has suggested I would use a “banana wing” i.e. a wing where the local L.E. sweep near the outer semi span is reduced. That way you increase the aerodynamic “washout” as also it is a good way to introduce the conical camber to solve the problem. The sketch at the end of this note clarifies the idea. Instead of plunging into massive redesign and tooling it may be just possible to prepare a new leading edge in wood (teak,  if spruce is not available) as on the lines shown hack off the existing leading edge at the appropriate location and attach the wooden L.E. segment to the existing wing with suitable brackets and bolts. The expected loss in performance will be negligible. The loss in the lift will be insignificant as towards the tips the wing will not be producing so much lift (elliptical lift distribution) and the drag will be not too much. An excellent solution possibility.

Wooden bits on a jet aircraft?! Now! Who has heard of that? Well the Canberra-larger and faster than the Sitara had a wooden fin and rudder! The story goes that to get the aerodynamic balance of the rudder right W.E.W Peter’s people would shave away at the profile until the control Harmonization felt good. Prototype aircraft are like musical instrument - they love being “tuned” and then what music they make!

Tail Plane Location

Many have suggested the cruciform tail-I presume like the MiG 15/17. This is indeed the simplest engineering solution though one would have to put in an “acorn” fairing a la Hawker Seahawk because at the junction the airstream separates into four parts and that did cause severe vibrations until “fixed”. Also the fin will require stiffening (thicker gauge fin skins will probably do). At the end of it all because the HJT 36 is short coupled like the MiG 15 and the cruciform tail will blank out a fair portion of the fin the spin recovery will still be a “white knuckles “affair. I have seen films of MiG 15 (at a presentation by the legendary Rostislav A Belyakov no less!) spinning and recovering but the problem was known to exist. No, I think I would like to go for the full treatment as I have in mind of lowering the datum of the Tail plane and pushing it back as far as possible - and if that does not work then we may be looking at anhedral on the stabilizer to get it out of the wake. That can be done in six months if we get a move on. If we don’t, it will take forever. 

Inlet Location and Engine Flame Out

The more one thinks about it the more one suspects the inlet position. I can imagine that in a fully developed spin the inlet will be “behind” the wake being shed by the thick (NACA 23015?) wing. One hopes we have data as to at what point of the spin the engine flamed out? This would be crucial to the reconstruction of the problem and rectification. Crashes during the development of an aircraft are quite acceptable but it is criminal treason if the relevant data is not available because “someone” did not “think”. I mention this because I have found we sometimes do tests without sufficient planning and foresight of what we may want.

Assuming that the prognosis IS right then we have to increase the length of the inlet until it is out into the “clear” air. Whilst CFD/wool tuft studies will no doubt be made perhaps the quickest solution would be to “jury rig” a new extended lip inserts over the existing one and do confirmatory tests. This is not alarming as it sounds because most of the tests will be done at speed of around 100-120 kts and at 2000-3000 mts the dynamic pressure will be still lower. The point is not to waste time fiddling around trying to get the best pressure recovery or whatever. It is sufficient that the rig up shows that the extended intake works and the engine does not flame out. IF that works then the solution is to refine the design and standardize the extended lip for the first batch because the best solution, the intake lowered to the level of the wing L.E will be a bit of a job and delay things too much. What HAL can promise is that if the IAF will accept the first lot with the extended lip- it will curtail the downward view somewhat for the rear cockpit- then HAL will remanufacture the fuselage to the final configuration when it comes back for its 1000 hour overhaul or whatever is the set period.

Reader Gupta has demanded as to why this happened in the first place? This is a very relevant question. One reason, though obviously not the only one, is the element of passion. It is my view that vehicle design involves more than the basic knowledge. It requires passion. Companies such as Ferrari or Porsche or AVL are not large companies nor are they financially powerful. Yet the Giants of the Automobile Industry speak of them in whispers. As a Nation our Aeronautical men know less about Aeroplanes than our Footballers know about football. If you look at the AMCA in its last public Avatar you might agree with me.

The second is a lack of conviction of one’s own decisions. Redesign is onerous but if one is sure it will work it becomes a mission. In the Government this spirit is significantly lacking because everyone is on drip feed. Why do anything non routine? You will only be blamed if things go wrong. So don’t move away from the Glucose bottle. In the private sector –where people are arguably less qualified- the very question of survival- spurs people on to try alternatives. Assuming they are not morons they then very quickly arrive at some “effective” solution.

These are my views based so far away in Kolkata.

16 August 2014

Some Notes on the Forthcoming Spin Trials of the HJT 36

Introduction

These notes are being put up for those who may be following the forthcoming spin trials of the HJT 36 Sitara. There is some Physics/Math but it is High school stuff and helps in understanding the conclusions given. No claims are being made as to accuracy of prediction though some of the points are interesting and indisputable.

A quick review of the Programme

The HJT 36 programme is another of those Defence related mysteries. Here was a programme which showed, briefly, what standards we are capable of. Excellently managed (Take a bow, Yogesh Kumar!) it went from sanction to first flight in 3 years which is about good as it gets, only to hit a sandbank when the engine was changed. Talk of changing horses in midstream! Mind you, the idea was not bad. The French, seeing an opportunity, reportedly wanted higher prices for their Larzac and as usual there was some weight increase/specifications change. The Saturn AL-55I was chosen but things then began to unravel. The original design and project management leaders retired practically en masse. There was no system of retaining them. The engine was delayed by two years over the scheduled delivery and when installed it reportedly would flame out during spins and the TBO was only 250 hrs. To add to the above delays the prototypes suffered two accidents – in one the canopy came off and the Aeroplane skidded off the runway during takeoff. The other –a proper crash- was due to some engine related problem. If that was not enough I believe somehow an ejection seat fired during final assembly damaging and delaying the prototype. I think HAL made a classic mistake of following the specifications and did not allow enough “let” in the design. As the great Sydney Camm used to say “Follow the specifications too exactly and you are a “goner” most of the time”.

The present problems on the HJT 36

My sources- no more than newspapers and what go on in the www. - indicate the following “problems”:

i. Engine flame out during spins
ii. Poor engine TBO.

iii. Wing drop

iv. Spin trials not yet carried out

Engine flame out and TBO. Very little actual details are known but it is surprising to hear of a TBO of 250 hours. This is what was normal with Russian engines some 60 years ago. I cannot believe Saturn cannot do better than that today. They have been in this business for over 60 years. Regarding flame out it is true turbofans are more sensitive to non uniformity of flow across the compressor face. The Y intake duct will have the “in-spin” inlet getting some useful side flows but the ‘out-spin” side will be sucking in a lot of vortices shed by the slab sided front fuselage which is not a help. Both aircraft have a similar height of forward fuselage but I wonder if the Hawk’s lower inlet position is not better for taking in some undisturbed air from the sink velocity flows. Another point you might want to take note of is that the HJT 36’s inlet is bang in line with the wing L.E. Somehow most people try to keep the inlet lip a bit forward by at least a foot or so of the l.E. -Kiran, Hawk, Galeb, Aviojet et al. What might be happening is that in a proper spin with the AOA hitting 50-60 degrees the intake may be full of eddies being shed by the L.E. Is there anything in that I wonder? The Aero L 39 has an exactly similar relative location but the Czech aircraft has a much more slender forward fuselage of more oval cross section so the yaw related eddy would be much less. Of course putting the inlet forward may require a new design for a boarding ladder for the rear cockpit but c’est facile! Scarf the intake lip by 45º may be another idea.
A longer inlet duct always helps to smoothen out the flow. Going by the 3 view available on the net the designer has an estimated 5130 mm between the air inlet lip and the engine exhaust. Take away 1210mm (?)  for the engine leaves 3920 which is about six inlet diameters for the Y and flow stabilizing portion. It would mean that the engine has to be mounted fairly far back to have a reasonable amount of stabilization of the flow. All this, from so far away, of course is conjecture but I know some simple solutions can be thought of.

Wing drop

Wing drop at low airspeed is not really a problem unless it is vicious i.e. the whole wing drops suddenly and without any warning. The idea is to delay the stall at the tip which should stall only after the wing root has stalled so the pilot gets a “sink” rather than a wing drop. There are several standard cures for wing drop at the stall.

i) Keeping the tip chord at a lower incidence than at the root so that the wing root stalls first. Called ‘washout”, it is the aero modeller’s equivalent of the “one eighth packing under the T.E.” during building. In fact with straight unswept L.E.s there is a certain amount of aerodynamic “washout” due to tip vortices and viscosity and thus special “twist’ at the tip is often not needed in light planes.

ii) A change in the tip aerofoil. The designer will sacrifice maximizing lift to choose an aerofoil which is happier at low Reynolds numbers. The Australian Victa had a sharply tapered wing and the designer Henry Millicer had a NACA 23012 at the root and a NACA 4412 at the tip. Our well beloved Gnat had the RAE 108(?) at the root but a deeply cambered thin section (RAE ??) that spoke of circulation theory if you even looked at it. That “conical cambered L.E.” only partially cured the problem because at low speed i.e. on the approach, the Gnat would rock gently from side to side as she came in over the fence.

iii) Automatic slots on the tips like the Me109. But one wants to be careful with that because if un damped, one of the slots may open a little earlier than the other and give one a bit of jerk or spoil one aim in a combat turn.

Seeing how close the IJT 36 is to the HJT 16 it is a wonder that the design team did not use the earlier aircraft’s flying surfaces and saved themselves a lot of time, bother and expense. As a bonus they could have used the old undercarriage also. Using existing sub assemblies happens often enough in Aeronautics. The Beaufort used the Blenheim’s wing and the Supermarine Attacker jet used the propeller driven Spiteful’s wing and the American High manoeuvre test prototype used bits from a lot of other aeroplanes.

Stall

The stall is the first step of the spin. As is well known the flow breaks away causing loss of lift. Expanding a little on this what we can say is that at low velocities the flow lacks the momentum (you can use that lovely onomatopoeic Hindustani word “dum”, if you like!) to overcome skin friction and begins to break away near the trailing edge. It is only on the blackboard that the flow over the wing is ‘homogeneous”. In reality it has micro variations so the breakaway point will shift nearer and further away from the trailing edge causing the often described judder near a stall. Once the speed i.e. momentum of the stream is well below the requirement the breakaway will start close to the leading edge and you have a full developed stall. I will mention here Dr. Winter’s Zaunkoenig , a little 35 hp Zundapp engine parasol monoplane of the ‘40s which had a wing so slotted and slatted that it was apparently impossible to stall the entire wing at any one time and it could almost hover in a strong wing and be flown controllably at as low a speed as 35 mph. Of course one must realize that at those low energy and momentum levels the margins are paper thin. Many young gentlemen wrote themselves off exploring the low speed characteristics of   “harmless” slow flyers such as the Westland Lysander and the Fieseler Storch.

Spin

A spin is NOT a spiral drive. It occurs when one tries to turn at low airspeeds such as in a dog fight or turning off the downwind leg and manage to stall the aeroplane. The following things happen.

i) The aeroplane stalls and because of the turn the “inner” (to the turn) wing is flying at a lower speed than the ‘outer” wing tip. It will stall first, lose lift and go down there by pushing up the  local angle of attack thus stalling it properly.

ii) The outer wing will go up thus reducing its local angle of attack. It is also moving slightly faster the stall speed and so is generating some lift.

iii) The aeroplane now has its two wing halves, one generating slight lift (remember that the mean airspeed is near the stall) and the other no lift. Lifts and drags are related so the two panels have different drags thus yawing the aeroplane.

The aeroplane is at now at a slow forward speed, slowly (relatively) sinking due to loss of lift and slowly rolling and yawing due to the asymmetric and weak lift and drag. Mind you though the wing has stalled the tail plane and the fin are still ‘flying” i.e. it is not stalled. Thank God for small mercies! The empennage do not stall as they are usually of lower aspect ratio than the wing and the tip vortices “wash” over more of the span keeping local angle of attack down below the stall. However there is the danger that if – as in low sectional density aircraft e.g. light planes, the forward speed will decay rapidly below the “flying speed” of the tailplane.

At this point we can make a simple mathematical model to give ourselves some figures and then use an analogue so that we can compare the figures and draw some conclusions that is not all hunch.

The spin model is simple:

The forward speed V_H is equated as the stall speed which is calculated using standard formulae. This speed will decay slightly with time as the engine is throttled to idle and because of the cranked up attitude at the stall, the wing and the fuselage acts as a large air brake. The sink speed V_V is obtained approximately by calculating the flat plate area of the plan view of the aeroplane. We can calculate the increase and the terminal sink speed V_V. It is possible to calculate the rate of increase of the V_V with time and in combination with behavior of V_H   get the instantaneous flow vector of the aeroplane. The final AOA w.r.t. to the airstream in a spin is usually in the range of 40-70⁰

The yawing and rolling rates can be approximated by knowing the aerofoil characteristics of the aircraft concerned. They are very slow about 0.25-1 turn/sec. and is ignored in this exercise.

So now we can visualize the aircraft as if trapped in a bubble of sluggish, disorderly air, from which it must break out if it is to recover. It is now easy to understand why spins in light aeroplanes can be very disconcerting. The aerodynamic forces are high relative to the inertia forces so they spin quickly and also snap out of the spin rapidly. My favourite story is about the Bucker Jungmann biplane which could be spun rapidly but once the correct procedure was followed it would snap out of it so promptly that it often left the tyro pilot “shattered”.! In light planes the low sectional density means it will lose way quickly and so one could get into a flat spin from which recovery is more difficult. BTW there were aircraft which could not be “spun”. The Erco Ercoupe was one –achieving that by the very limited control movements giving rise to the dreadful pun “No(vices)can’t spin!” and there was the “unspinable” Australian CAC Winjeel. (Young Eagle) which was embarrassing because it was the basic trainer of the RAAF!

Recovery from the spin

Once the pilot realizes he is in a spin and if he is not doing show aerobatics he will first put anti-spin rudder. Apart from subtle and interesting points such as “freeing more of the rudder area” the opposed rudder removes two disconcerting motions i.e. the roll and the yaw thus allowing the presumably frightened pilot to reorient him with the world. He would then push the stick firmly forward to “unstall”’ the aeroplane and recover normally. Just as prototypes have refused to come out of spin - the prototype Fairey Swordfish was one such – despite the pilot’s best efforts - many aeroplane will also often come out of a spin if its controls are kept at neutral. The aerodynamic damping will slowly remove the yaw and the roll and the natural stability will re assert itself but prompt recovery action is recommended to reduce the considerable height loss.

Some physics and maths

One would need proprietary software and huge computers to model and predict spin behavior-and even then get them wrong! There is a much cheaper way of being “wrong” and that is by using fundamentals of Physics and some arithmetic to calculate the relevant parameters. If we can then set up an “analogue” - an aircraft whose configuration and spinning characteristics are ‘known” we can make a reasonable prediction of the new aircraft’s spin behavior or some kind of a figure of merit as a comparison. Here goes!

We need to know:

i) The pitch inertia PI. In this class of aircraft it is approximated by 0.7 ML2. Why 0.7? Because the fuselage is taken to have 0.7 of the mass M and the wings plays no big role. The M is the clean half fuel weight.

ii) The roll (RI) and yaw (YI) inertia. 0.7 ML2 + 0.3M. WS2. L is the length and WS the span.

iii) The tail volume TV which is the area of the tail plane and the moment arm of its centroid with the Cg. This will give the comparative rate at which nose will be pushed down given the pitch inertia.

iv) The Fin volume FV. As above

v) This is the horizontal component of velocity. It will start as the stall velocity and decay with time. The time decay can be approximated by assuming a Cdo.

vi) Vv. The vertical velocity again can be calculated as indicated earlier.

vii) The tail angle θ is the angle that the leading edge of the tail plane makes with the wing trailing and leading edges. The tail plane must be clear of the wing wake to be able to unstall the aeroplane.

viii) The Fin coverage Fθ is the amount of the fin that is covered by the tail plane during the spin. The yaw inertia approximation divided by the blanket factor will give the yaw correction time comparison.

ix) In all cases the height is taken as 2000 mts because the air density ISA is 1.00 and it is the minimum height you would want to spin this class of aeroplane –when in service.

x) The fuselage side area moment which will indicate the damping available for opposing the yaw?

We will now select some aeroplanes which are in service and compare the factors to see where the IJT 36 stands.  Our choices are as follows.

i. The HJT 16. The side by side sitting is an obvious disparity

ii. The Aero L29 which is remarkably similar configurationally.

iii. The Hawk because it is here even though the slight wing sweep adds to stability.

Finally I decided to compare with the Hawk because despite the slight swept wing it is one whose spin characteristics we know. The Aero L 39 Alabatros was actually the better choice but I could not get all the details I needed to compare.

So the results:

Assuming that the empennages are equally efficiently exposed to the resultant airflow, then:

i. Compared to the Hawk the HJT 36 will lose less height during the spin at approximately 60% of the value of the Hawk’s and pushing my luck the IJT 36 will stabilize in a spin in about 4 second compared to the Hawk’s 7 – both times should be treated as comparative rather than actual.

ii. The rate of yaw will be slower at 60% to that of the Hawk due to greater damping.

iii. On application of opposite spin rudder the HJT 36 will recover 15% faster than the Hawk.

iv. On application of forward stick the HJT 36 will be in the correct attitude to recover by a time 30% less than the Hawk.

Whilst the figures are derived from a very simplified model they seem to be sensible. After all the HJT36 is a smaller lighter aircraft than the Hawk.  By the above approximation the figures are excellent because the young gentlemen can have a foretaste of milder jet spin of the IJT before going on to the harder stuff of the AJT.

Uh! Oh!

There is however one little fly in the Ointment. It always struck me that the HJT 36 was “close coupled’ as control line model flyers used to call the Peace Maker or Mercury Matador designs. This close coupling CAN affects the airflow over the tail plane and fin at the stall. If that is so the above results - where I assumed that fin and tail plane effectiveness is same in the analogue as well as the specimen aircraft - may not be obtained despite the potential to do so being definitely there. 

The desirable situation is that when the aircraft stalls the tail plane is clear of the wing wake and the fin is clear of the wake of the tail plane. It is then that the recovery actions will be most effective. I calculated the position of the wing wake at the stall and it appears that the HJT 36 stabilizer is deep within disturbed air shed by the L.E and T.E. of the wing (tail angle 27 degrees minus stall angle 14 degrees equals 13 degrees on the wake whereas in the HJT 16 it is clear and in the Hawk it is 2 degrees in the wake). As a result, the controls of the HJT 16 will not be effective for the first 3-4 secs after the aircraft enters the spin during which the aeroplane may lose about 100 meters in height. This can critical in case of a spin at low altitude. With the Hawk or the Kiran, the tail moves down and out of the wing wake. The sketch at the end of this note makes things clear. Actually in the Hawk the tail stays within the wake at the root - giving good stall warning - but because of the anhedral most of it is below the disturbed wake and therefore effective. Wicked thought! Did BAC make the same mistake as HAL and corrected it with the anhedral or it was a case of force majeure - there was no place else to put the tail? Old Sir Sydney (Camm) would never have allowed that even in his sleep!

The table below is interesting as it compares the angle the Tail L.E. makes with the Wing’s L.E. and T.E. for comparable types.

Type	Angle between Wing L.E. and Tail plane L.E	Do for Wing T.E.
Aero L39	9.5º	18º
Hawk	9.0º	16º
HJT 16	7.125º	13.4º
HJT 36	15º	27º

“Bobbery”? (Hobson Jobson- derived from Hindustani ‘Baap re’ and indicating consternation!)
There is really no need to panic, even if the above prognosis is true. A prototype crashing during spin trials is yawningly boring. The HT-2 had spin related crash. The French Epsilon had a spin related crash but, after Gallic shrugs no doubt, they simply sawed off the old tail and fitted a completely new fin which was as effective as it was elegant! BTW the location of the HJT 36 fin w.r.t. the tail plane, is pretty good.

The above model of the wing wake is true at the stall when the nominal angle of attack is circa 14 degrees. As the aircraft begins to sink faster with time this wake will move counterclockwise and the tail and fin will move into clear air after 3-4 seconds. The total height required to recover from a spin may still be less because inherently the HJT 36 should recover faster than the Hawk.

The real problem is human -psychological and cultural. We have great faith in rigourous analysis and so when things go wrong there is shock induced paralysis. Much time, I have seen, is spent in fixing blame rather than fixing the problem! In the “feel” based approach, which is sometimes, treated as a disability with sophistication, however, the Designer is not only acutely conscious of possible failures but also he has subconsciously prepared several “what if “ scenarios so the nettle is grasped firmly and quickly.

Solution

What I have said is not a judgment but rather a starting focus. What needs to be done now is perhaps to go down to the flight Hangar and “talk” to the aeroplane, noting the subtleties of its contour and using the rough figures of velocities to imagine how the air would sluggishly flow around the nose, the intakes, the wings and from the bottom of the rear fuselage upward towards the fin and tail. One would also imagine how a strake or under fin would behave and on which longeron and frame the strake could be riveted etc.  This is to be followed up using CFD ‘snapshot” assuming the proprietary spin software is not available.

If major corrections are indeed required then HAL Design team may have to accept to make a three four small changes rather than try and cure by a one-step major change solution. The former will be faster!

The HPT 32 Crashes - An Alternate Logic

Professor Prodyut Kumar Das

The recent article in Vayu V/2012 Requiem for the HPT 32 was carefully researched and provoked thought.  The fuel divider and the Collector tank location and capacity are the prime suspects. However there appears to be some uncertainty; The article mentions that at one stage the Fuel Divider was taken off the list of suspects by the investigators and there was the case of an engine stoppage on the ground. There is a certain uncertainty.

The uncertainty could be from the following. It is true that unless the fuel supply is smartly cut off, a warm fuel injected engine will continue to “diesel” even after the ignition is shut off. This “cut off” is one of the major functions of the fuel divider. However this function “gets out of the way”, so to speak, when the throttle is opened beyond idle or near idle. If the fuel divider is the culprit all the seventy odd incidents of engine stoppage would have occurred at idle or near idle conditions. Also, if maintenance is a problem NO failures should have occurred with a new/ “not overhauled” fuel divider. Has this been indeed the case? 

Regarding the fuel pipe line being not as per FAR standards the usual requirement is that the pipeline should be able to handle one and a half times the TO fuel flow rate. For the engine in question the TO fuel flow is approximately 1.3 litres per minute or 20 ml per second corresponding to fuel flow velocity of about 0.7 metres /sec which is also not too bad. In any case the main restriction to flow would be the filter just upstream of this line and increasing the pipe diameter will not make a decisive difference. Mind you at the idle case the fuel flow would be around 200 ml per minute so both the usable header tank capacity and the pipeline would be unlikely to be a prime suspect. By my estimate, even with the usable 3.5 litre capacity quoted  the engine could chunter on for a quarter of an hour at flight idle or three minutes full chat –both times more than enough to get the aeroplane at least into level circuit if not on the ground. That too under flight conditions of no bank or turn during the descent because a bank would recharge the header! It is also to be noted that there was an engine stoppage on the ground-when the aeroplane was near as level and  feed / collector capacity problems could not have occurred. Finally it is bemusing to accept that a failure rate of 77 failures in 400,000 flight hours-that too in a system that is “on” every minute of the flight- if a single component or system is at significant fault. In my view there is clearly room for an alternate hypothesis.

Let me say my Mea Culpas right in the beginning. I had no chance to see the aeroplane or have access to the data and the hypothesis is based entirely on conjecture and my experience as an Engineer and I.C. Engine man. The starting point of the alternate construct is that considering its usage the rate of failure is very low. Could the failure be due to the fact that there are a fairly large number of random factors which almost never occur at the same time. When they occur together, however, they cause an engine “failure”. The “rare random combination” better explains the one failure every 5000 hrs. What could be these factors?

a)      The poor engine is suffering from the “Glider tug” syndrome. A high power –low air speed combination as in towing gliders have been known to cause engine failure. The HPT 32 does not tow gliders but it is an extremely “draggy” aeroplane.  If you visually compare the HPT 32 with the similarly powered SF 260 you will get the point. If you are one of those who will point out that the Italians will get “style” into concrete “tie down” blocks then look at the Finnish Vinka or even the Bravo or the Bulldog. In the HPT 32 the contours of the cowling and the canopy, the untidy undercarriage linkages and the huge fin hurt the eye. One must mention the oversize fin. The excess wetted area results in excessive parasite and induced drag leading, again, back to an overworked engine. The engine has to operate at a few notches higher throttle setting compared to other installations and yet not get enough cooling air.

b)      The cooling of the last row of cylinders in a horizontally opposed engines requires, as the Germans say, “Patience, experience and maturity”. Particularly the rearmost cylinder opposed to the direction of the propeller rotation is, cooling wise, in a severely unfriendly environment. Thus the fitment of the cooling baffles and its maintenance is of greater than usual relevance in this case.

c)      In India the cooling air itself is 20 to 25 degrees higher than ISA. This would rob it of about thirty percent of its cooling capability. Bidar is notably dry.If this is combined with the occasional less than “normal” humidity we can see problems lurking around the corner. I dare say that if the HPT 32 operated above 35° N we may not have seen this problem at all!

d)      The dust and the dirt. The metered fuel supply system takes input from the static and rams pressures. If this is not “klim bim” perfect then the mixture would lean out to the point when the engine would starve and stop. Dust would also reduce the cooling heat transfer.

So what could be happening? We have an older (somewhat dented and battered and the cowling and canopy rattles a bit in flight!?) aeroplane flying a sortie on a dry dusty day with some prolonged spirited flying at high power. The engine is hot. As the power is reduced and that aircraft is gliding back the cooling flow is reduced by the low airspeed; the heat accumulates under the cowling. May be the baffle seals are just a little aged. All add up to –in those rare occasions- leading to a local overheat, distortion and “incipient seizure” in the engine. The high oil temperature and hence reduced viscosity of the lube oil would be additional contributor in this construct.

For reasons too boring to detail here I once had a car that had 90,000 kms on the clock. It had this trick of the engine suddenly “seizing” yet when I let the old girl be for some time -this was in Daman where chilled liquid coolants for me were easily accessible!- it would restart as if there had been no quarrel. There was another case when a students’ designed racing car that would stop suddenly due to over heating. A better designed duct for the radiator cured the problem very satisfactorily. Perhaps our engine is having the same problems?

Incidentally the HPT 32’s wing and span loadings are some 40% higher than the HT2s and so the glide ratio and minimum airspeed would be that much poorer. At low altitudes the pilots have that much less a chance of a safer landing or a pancake.

If the above construct is a possible model then what is to be done?

In the immediate term:

1. To increase the routine maintenance quality. The baffling of the engine is a prime suspect and so must come for close inspection at suitable intervals. Cylinder fins and the static and pitot ports for the AF system to be checked for dirt and should be inspected for cleanliness as per flying conditions. I mention routine maintenance and preflight checks only because a recent issue of a NTSB bulletin mentions fatal crash at take off killing six people because the pilot had failed to drain the fuel tanks of accumulated water. In his previous company someone else used to do this for him.
2. The quality of fit of the cowling and the canopy joints and panels to be improved by the fitters to the extent possible to reduce drag. Older airframes to be examined for the usual dents, bumps, loose fittings with the above prognosis in mind.

 In the medium term the following studies to be made.

3. An OR study into the accidents based on the above assumption that “an unfortunate combination of circumstances” rather than major system fault is the cause of the “engine failure”.
4. Initiate the design of a neater cowling and canopy. The cowling lines of the SF 260- which incidentally has the same engine - is the work of a Past Master (Stelio Frati) and could be an inspiration. These could be retrofitted at the FTS .
5. Do a CFD study of the through flow and back flow on the oil cooler. I have seen significant improvements with some very simple “fixes” and better lubricant viscosity would be a definite palliative.
6. Do a study to find out how difficult it would be to fit a semi-retractable undercarriage as in the Yak -18 and if there would be any benefits.

The real “de luxe” solution is economically unviable but is mentioned for the completeness of the discussions. It is entirely a personal view that HAL spoilt itself by the success it had with the big fin to improve the spinning characteristics of the HJT 16 which I have seen has very reliable spinning characteristics. What worked for the Kiran was possibly tried again on the HPT 32 but the balance was lost. Optically the HPT 32’s fin is huge resulting in excessive weight and drag. Others rely extensively on strakes to generate flow across the fin and rudder in a spin. The German Grob is of course  typically Teutonic in its determined application of strakes and under fins but the Bulldog, and the Vinka not to mention the SF 260 all use strakes quite discreetly with success to achieve  desirable spinning characteristics. The gains of using strakes for good spin recovery are in weight and drag which seems to be the root problem here.

Prodyut Das

Professor

Prodyut Kumar Das is an Alumnus of St.Xaviers’ Hazaribagh, IIT Kharagpur, and IIM Kolkata. He started his career with Aircraft Design Bureau HAL and for twenty years worked and led various vehicle related Product Development Projects with leading Indian and multi National Companies.

He left Industry to join IIT Kanpur in 1993 as a Professor in the Department of Mechanical Engineering. There he won a prize of the Royal Aeronautical Society of UK for his design of a light sports aeroplane using grants given by ARDB. He also did a project study on “The design of a Light Car costing less than 1 Lakh” which was a Ministry of HRD funded project IDICM 36 and started his research on Stirling Engines in which the IN was keen.

When IIT Kanpur did not renew his 5 year tenure he returned to the  Industry as a Vice President Technical and finally retired as Advisor Aerospace in the e- Engineering Division of a Leading Indian Engineering Company.

He currently teaches Engineering in a Private Engineering College in his hometown and continues his Research as a Consultant. He has been writing on matters related to Defence Engineering since 1990s.

The Ails of the LCA

Professor Prodyut Kumar Das

Kolkata, June 2014

I wish I had a guinea every time ADA missed out on a Date. I would have been, if not rich, at least well –to-do. I say this because recently, this last December , I think, one of the key figures of the programme- one might say- the Father of the LCA- stating that we would have two LCAs more by March and, if I remember a right- half a dozen before the year is out. The Ides of March have come and gone, “April, the Cruellest of Months” has gone and now even “the Darling Buds of May” have wilted. “June is ready to bust out but nary a sign of them those Airplanes!

It is worrisome when ADA repeatedly fails on dates because these are symptoms of  cluelessness. The highly qualified gentleman in the above paragraph must have had access to the proverbial “Horses Mouth” and yet, not for the first time, he has been hopelessly wrong. Is it really so difficult to predict the future events?

 In India we have a culture of very accurate predictions based on informal methods and folklore. The apparently “stupid” farmer kicking the dust as he chews slowly on a dry rice stalk may predict the Weather quite accurately. The old Crone sitting under the Neem Tree as she berates her newest daughter- in -law will still be able to predict whose Bahu is going to be a Mother -sometimes even before the poor girl herself is aware! Neither the Farmer nor the Crone has any “scientific” qualifications but they still come pretty close to the truth. So why not try applying those techniques on the possible date for the LCA?

Let me say before I begin that I have no access to “inside” facts. I am a very seasoned Engineer and I like machinery. That is all. What I am writing is therefore a construct. Of course ADA may, (out of sheer spite!) come out with a squadron of LCAs by December along with a chorus of well trained mechanics and a well organized stream of spares etc just to prove me wrong. That would be quite nice. In any case if people speaking from the Augean stables are so repeatedly wrong I am in “eminent” company if my here predictions are wrong. Of, course, mark my word; I fear I shall be proved right!

Let me put down the more important tasks remaining for the LCA to get FOC.

a) Opening the full envelope of positive and negative ‘g’

b) weapons firing particularly of the 23 mm GSh.

c) Spin trials

d) Missile Launching.

e) Proving of remaining systems.

Missile Launching: Pakistan managed to jury rig the AIM9 onto the MiG19 in a matter of months there is no reason to expect that the same cannot be done onto the LCA. I am referring only to CCMs. It will be a brave Air Marshal who will refuse the LCA solely because the aeroplane cannot fire BVRs for the moment.

GSh 23 firing.

The problem of gun firing is “old hat”. The Chemistry is Class 9. The gun propellant gases are ingested by the engine and that affects the air fuel ratio as the propellants gases displace the oxygen in the air causing the engine to flame out through “over richness”. This is aggravated by the pulsations of firing which will tend to “blow out the candle”. This is particularly true at high altitudes where the air is “thin” causing both effects to be amplified. The old trick is to “dip” or reduce the fuel to the engine automatically when the gun is fired. In the LCA, a one second burst will release about five kilos of gun gases into a region of inlet flow of 4 kilos of air over the same period at high altitudes. Vibration is of course a problem but the GAST system (look up!) of the GSh 23 means the recoil loads are much less. I do not think the horrible memories of the HF24 -where I still believe the concerned German Engineer probably put a “bug” into the design- will be repeated here, especially if ADA has had the wit to use the forged aluminum cradle or its derivative the MiG Bureau used for the MiG 21M’s mounting.

24⁰ AOA

This is the old Phantom joke now gone sour. I would like to meet the person who will refuse the LCA simply because the aircraft won’t do 24^0.

Proving of remaining systems

Thirteen years after the first flight there would be very few things that require major tweaks so there is very little that remains to be done.

Does that mean then we can see a FOC by December and a steady stream of LCAs from 2015. No, definitely not, because I guess the Mk1 is still a ”lemon”. It is not combat worthy. I am on shaky grounds here because I am making the previous statement entirely on what is available in “open source”. The LCA was “officially” declared to be about 1300 kilos overweight by ADA. Subsequently there has not been any announcement about the weight being corrected. Certainly the weight correction would have been noised about. If you have “inside” confirmation that the basic empty weight of the LCA is around 5100 kilos don’t read the remaining portion because everything written below is then irrelevant.

Why is weight important?

Airframes will tolerate a fair amount of abuse but they cannot tolerate excess weight. Let us take the MiG 21 Bison. Despite its age it is still relevantly “sprightly” as Cope India showed. The MiG 21 is of the same thrust to weight class as the LCA. Now imagine we poured in 1300 kilos of lead (Plumbum!) into the airframe. Immediately all critical parameters- take off run, acceleration, climb rate, radius of turn, range, ceiling and top speed will fall below current designed figures. In short the MiG 21 will not be fit to fight. In summer thrust and lift reduces by about ten percent and things would be worse! Exactly the same is happening to the LCA. Until the weight has been corrected the aircraft cannot even complete its flight test programme. My Farmer’s guess is that ADA should have an airframe weight of around 2300 kilos and an undercarriage weight of around 300 kilos to come out shouting winners. Mention has been made of the LCA requiring ballast. Aeroplanes sometime require ballast to get the CG right. The HF 24 needed 134 kilos about 2 % percent of the basic empty weight. This was in the days of wooden slide rules but evidently someone cared. How much ballast does the LCA need? Given the use of CAD it should perhaps be no more than half that figure.

“Opening up the envelope”.

This cannot happen safely because the “g”s to be applied requires acceleration and lift. Unfortunately lift means drag particularly in AR Deltas whose induced drag is almost double of comparable swept wings. Given the combination of excess mass and drag the F 404 just may not have enough “urge” to pull the little aircraft around a turn at 8.5 G i.e. the aircraft is power limited and lift limited to pull the required “Gs”. One could of course dive the aircraft and do pull ups but I think it would be a pointless exercise because one would have to do it again when the definitive airframe is available.

Spin Trials.

This is also held up because of weight. A spin is a combination of a stall and a turn at low airspeeds. The aircraft sinks because of the stall and it yaws and rolls (slowly) because of differential lift and drag caused by the different airflows due to the turn over the two wing panels. The forces at play are the above aerodynamics loads and the inertia of the aircraft which depends on the weight of the aircraft. Given these basics the LCA will be reluctant to spin because the Delta wing is usually difficult to stall. Given the excess weight/ inertia it will take a long time to stabilize the spin. Height loss in recovery will be “interesting”. It may be recalled that the Mc Donnell Phantom II was so difficult in spin recovery that if the crew had not recovered from the spin by 10,000 feet the drill was to eject. Well that is a precedent anyway!

So unless you have tackled the weight you can’t do the spin trials. What happens to the FOC? Please do try and not have FOC 1,2 etc.

Intake Problems

There have been persistent reports of “intake matching” problems. What happens is the take off requirements of the intake are in direct contradiction to those required in transonic flight. You either accept poor take off and climb or face high spillage drag and engine surge at transonic speed. The solution is conceptually and mechanically very simple. Aeromodellers flying ducted fan models (PE Norman’s ducted fan MiG 15 of happy memory!) used them. We used to call them “cheat intakes”) .Spring loaded “blow in” and “dump out” doors are generally used. Even the dear old Hunter of Good Queen Victoria’s times (well, almost!) had them. You could see them on the wing intake lips. As I write about this I realize that I have not seen any photos of such doors yet on the LCA . Perhaps some reader can post?

Aerodynamics

I have elsewhere mentioned that the LCA is aerodynamically blunt, its comparable equivalents being almost a meter longer. Any Aerophile will remind you the Douglas A4M with the 10% more power was actually 0.1 Mach slower than the less well powered Hunter Mk6 which had a longer fuselage and better entry Supersonic wave drag depends on the maximum cross sectional area and its position along the longitudinal axis as well as the entry aerodynamics i.e. from the radome tip to somewhere behind the rear cockpit bulkhead. ADA needs to go over the contour and the cross section centimeter by centimeter. I am not exaggerating because it is so easy to end up with excess weight and wetted area if one becomes too enthusiastic. It is not for me to dare suggest but for God’s sake use some “feel” along with the Analysis.

Maximum speed.

My betters have said that the aircraft has reached Mach 1.4 -(or was it Mach 1.6?).). Sorry, Guv’nor but the facts don’t tie up! We seem to have on our hands an overweight aeroplane that is significantly stubby and has inlet problems and yet it reaches its design speeds? Cap in hand, with fingers touching my forelocks (Alas! Long gone to happy hunting grounds!), I would say no, Sors, this bain’t true! What may have happened is that the claimed speed has been achieved in a dive of around 30⁰.

The Prognosis

Common sense is that if the LCA Mk1 is reasonably well designed it should be in the same class as the early Gripens i.e. definitely superior as a replacement to the early Mig 21s which have begun to retire. The LCA Mk1 should be clear for super priority production. Somehow that is not happening and, going by precedent- not going to happen. The horrible suspicion is that we will see only “token” numbers of the LCA Mk1on v pretexts of manufacturing difficulties etc as a rearguard action until, hopefully, the LCA mk2- which will be an almost new airframe design, - is ready. We will, of course be relying on an organization, which could not correct an overweight problem it itself acknowledged in near twenty years (1996-2013). I am so glad I am not the Air Chief!

The interest expressed by the IAF in the AJTs is perhaps a corroboration of the above. The YAK 132 is a fairly useful LCA if you look at it carefully and indicates how little was actually wanted by the customer before ADA went gaga over Technology. Reminds one of Tacticus who had said so long ago “The enthusiasm for war is highest amongst those who have the least experience of it”. Replace “war” with “Technology” and you have the gist of the situation.

Prodyut Das

Professor.

Prodyut Kumar Das is an Alumnus of St.Xaviers’ Hazaribagh, IIT Kharagpur, and IIM Kolkata. He started his career with Aircraft Design Bureau HAL and for twenty years worked and led various vehicle related Product Development Projects with leading Indian and multi National Companies.

He left Industry to join IIT Kanpur in 1993 as a Professor in the Department of Mechanical Engineering. There he won a prize of the Royal Aeronautical Society of UK for his design of a light sports aeroplane using grants given by ARDB. He also did a project study on “The design of a Light Car costing less than 1 Lakh” which was a Ministry of HRD funded project IDICM 36 and started his research on Stirling Engines in which the IN was keen.

When IIT Kanpur did not renew his 5 year tenure he returned to the  Industry as a Vice President Technical and finally retired as Advisor Aerospace in the e- Engineering Division of a Leading Indian Engineering Company.

He currently teaches Engineering in a Private Engineering College in his hometown and continues his Research as a Consultant. He has been writing on matters related to Defence Engineering since 1990s.

The Aerodynamics of the MiG 21 Accidents

A fighter pilot flies a wing and an Engine. The qualities of the wing like the wing loading, span loading, aspect ratio, section profile of the wing and the qualities of the engine such as power loading and response time determines the flying qualities of a Fighter.

Fighter flying is one of the most hazardous occupations known to man. It is hazardous because the very high speeds, low level flight over inhabited areas in an airspace often attractive to large birds means that both the reaction times and the options available to a pilot in an emergency are often dangerously limited.

This spate of MiG 21 accidents caused much anguish and was widely written about. This paper is an analysis the technical and statistical aspects of the accidents and has some suggestions of future importance.

The MiG 21: a Technical appreciation

It is significant that for 50 years the MiG Design Bureau were at the forefront of fighter design and yet they never used anything but "yesterday's" proven technology to set and maintain the pace ( Note 1).

There is a lesson in that for Indian aircraft designers..

Coming from such a distinguished pedigree it is not surprising that the MiG 21 was remarkable. It combined low cost proven technology with brilliantly innovative and insightful application of the physics to produce at lowest cost the solution of a high altitude bomber interceptor.( Note 2 ) At the time of its induction into the IAF the MiG with its auto stabilization, radio altimeter, fully duplicated controls and general reliability introduced new standards of safety and reliability .Pilots converting to the MiG 21 were universal in their praise for its ease of piloting and safety and the reliability and the functionality its systems. 'Safe as a bullock cart" was how the aeroplane was described in the late '70s.

The Aerodynamics of the MiG 21 in low level flight.  

Unfortunately all fighters are designed primarily for air superiority but end up in the more hazardous low level close support role.

This was also the case with the MiG 21.From the 1980s the MiG switched to the close support role. New upgrades to make the type suitable for close support also meant a steady increase in weight. The aircraft became more sluggish and unwieldy particularly during the landing and take off and in circuit where the aerodynamic control forces decline as a square of the flight velocity but the inertias remain the same. The weight increase affected the wing, power and span loadings (please refer toTable A- for the MIG the figures on the top of each box are for the FL those below are for the Bis).

The span loading increases is a good indication of how much more angle of attack has to be generated at a given speed to maintain height. Increase in the angle of attack in turn means more power to stay aloft.

The wing loading increase shows how much more speed has to be increased to maintain level flight. A doubling of wing loading would mean a 40% increase in flight speed. This also means a doubling of the power required.

The power loading indicates how much power is available to accelerate the aeroplane should the airspeed fall too low. I have computed the figure for max dry thrust as in a crisis there would not be those few seconds available for the afterburner to kick in before the aircraft impacted.

A special mention must be made of the low aspect ratio of the MiG 21. The low aspect ratio makes the aircraft "alpha "sensitive. The CL /Cd curve becomes unfavourable in low aspect ratio wings. In other word unless the pilot gets the angle of attack right he may see a very great increase in the drag of the aircraft without any corresponding increase in lift. His total energy would decay preventing the aircraft from accelerating. Translated into reality it means one of the following scenarios: During take off "over rotation" -too much nose up-would mean poor acceleration due to high induced drag and failure to lift off with the aircraft running into the overshoot area at high speed.

During landing the misjudged alpha would increase the induced drag causing the aircraft to slow down, lose lift and hit the ground before reaching the touch down area.

During turn into the finals ( or during low level aerobatics) the aircraft is pulling more 'G"s with corresponding increase in induced drag slowing down the aircraft which is already side slipping because of the turn and losing height over ground. A combination of side slip during a turn with high induced drag reducing speed caused unforeseen height loss and a "controlled flight into terrain".

Very many of the MiG 21s lost were in these three regimes of flight. Even in civil airliners most accidents occur during these three phases but:

1) The alpha sensitivity of the MiG21 ,because of the low aspect ratio of 2.2, requires much more precision than the same maneuver when executed in an aircraft with a aspect ratio of 5.6 as in a basic trainer.

2) The continual, if inevitable, weight increase in the MiG 21 meant that the approach speed in the later marks had to be made at a higher and higher speed. This reduced the amount of surplus power available to accelerate away from a "coffin corner "situation". In India the hot weather meant the engine was producing about 12%less thrust and the wing was producing about 12% less lift to begin with.

3) In case of an emergency, to gain height, the pilot in a Hunter or a Kiran would open up the throttle and pull back the stick- things which are instinctive even in a rookie pilot. Ina MiG the pilot has to push the stick forward, build up his energy and then after a delay of several seconds, pull back the stick to climb away. He may simply not have the time when flying close to the ground.

4) The CK ejection seat, one of the best for high speed high altitude ejection simply was not good enough for low level by modern standards. One of the clever features of the CK seat was that as the seat left the cockpit the canopy- which was hinged to the front of the windshield in the FL - attached itself to the top of the ejection seat and rotated itself until it covered the entire front of the ejection seat- thus giving unparalled blast protection when ejecting at supersonic speed. I remember a Martin Baker engineer getting very interested in how the thing worked. I had seen the seat but he had not! Unfortunately I was not able to help him. The semi -encapsulation feature delayed ejection in that it took too long to get rid of the canopy after clearing the aircraft and this delayed clear release and deployment of the Parachute. The 300 kmph, 100 meters minimum parameters meant that many low level ejections were unsuccessful.

The span loading, wing loading the power loading and the aspect ratio of a series of aircraft flown by the IAF is tabulated at Table A.

Accident rates in supersonic fighters

The accident rates in supersonic fighters of the same generation as the MiG 21 makes for relevant comparisons.

Starfighters.

The German Luftwaffe flew about 950 F 104s from about 1960 to 1987 and lost about 292 of them during the same period. Average loss rates were thus about 11 per annum though the peak loss rate was 28 aircraft in 1965 and about the same in 66. The ejection seat of the F104 was even worse that the MiG 21 for low altitude flying. The Germans corrected that by switching over to the Martin Baker GQ 7 seat sometime in the mid sixties.

The Canadians lost half of their fleet of 200 CF 104s during a similar period of service. Training was admittedly a problem with the German Luftwaffe which was barely ten years old at the time of the induction of the F104 but the same could hardly be true about the Canadians.

The true master of the F 104 was the Spanish Ejercito d Aire who never lost a single Starfighter in seven years of service. People said it was due to fine weather over Spain! This usually made the Spanish AF indignant! The British RAF lost over a hundred of their 297 Lightnings in about 25 years of service- a number of them to engine fires which was probably due to a flaw in the detail design. Our MiG losses have been at a much lower rate.

Flying fighters is a hazardous business and continual stress and training on flight safety and discipline without killing the spirit of the Fighter Pilot is a difficult and skilled art.

Interestingly the Pakistan Air Fore lost 23 F-7s ( Mig 21 equivalents ) in 10 years which approximates the IAFs loss rates, given their smaller fleet size. It is stated that the PAF possibly reports only those crashes which are in populated areas. In fact the PAF is extremely touchy about anything that shows it in a bad light and it would possibly be that their actual crash rate is higher than the IAFs MiG 21s.

About their image consciousness I remember in the mid 80s there was a review on the PAF in Air International and there were these enormously dirty and dusty MiG 19s with chipped yellow and red paint and oil streaked fuselages and generally looking very neglected though the MiG 19s were right there on the flight line. Someone obviously got (and deserved ! ) a "rocket" because since then I have never seen a PAF aircraft in any magazine that did not look as if it has just come out of the paint booth.

One notes that there are 4 mid air collisions in the 23 PAF losses reported- the MIGs outward view was never its strong selling point. I feel the mid air collisions were more for this type. A switch to a glass cockpit and bulged hood ( to raise the pilot's eye line) may be useful at least in improving forward view.. Another reason could be due to the very small wing span in comparison to the fuselage length. In formation flying the aircraft would be that much closer together. In a turn, with the poorer visibility sometimes the collision was inevitable.

What should be the accident rates? Ideally zero.

However this is not possible in a profession where getting back with a tale to tell or making a hole in the ground can depend on decisions made with a difference of hundredth of a second or a few meters difference in position or height.

The Western world considers acceptable an accident rate of 1 in 10,000 hours as an 'acceptable". If we can accept this figures at a face value then a simple set of "expected number of accidents " could be created by assuming the number of squadrons and assigning a certain percentage of availability and a certain number of flying hours. This would work out to about 7 aircraft per annum in the 80s and thereafter. The fact that in the tropics the aircraft is flying in a non ISA atmosphere means that the engine thrust and the lift available is lower than available to a European pilot. In addition the flying environment- the ratio of open to densely populated areas, the number and size of birds at low level can alter the accident rate in spite of identical standards of training and maintenance.

Table A .

Comparative parameters of IAF aircraft and also the Chinese FC 17

Type	Power Loading N/kg	Wing loading Kg/sq.M	Span Loading Kg/M	Aspect ratio	Aerofoil Thickness	Pitch Inertia Kg.m*mX10e6
Harvard	2.75	93.3	172	6.96	15% (?)
Vampire	3.8	159.8	355	5.51	12% ( ?)
HJT 16	3.71	157	280	6.025	15%	0.309
HJT 36 IJT	4.6	183	324	5.56	15% ( ?)
Hunter	6.0	228	722	3.24	8 %	1.16
MiG 21	5.6/8.2 (with a/b)	279 334	897 1076	2.2 all models	6 %	1.18(FL) 1.39(Bis)
Su 7	7.3/10.5	274	1019	2.65	10.9 %	2.2513
F 104	6.94/10.41	417	1142	2.44	3.5%	2.12
HF 24 Marut	6	256	799	2.89	6 %	1.387
Hawk	5.4	254	458	5.2	10.9 %	0.5359
FC 17	6.6/ 11	319	816	3.52	6 %

Discussions

1. The above table gives a good insight to the problem. In the earlier days the pilot progressed through the HT 2 to the Harvard and Vampire to the Hunter. The critical parameters of Wing, power and span loadings and the aspect ratio progressed gently and even at the then top of the line aircraft the Hunter the aspect ratio was relatively modest.

As long as the Hunter was there in service a kind of de facto advanced trainer available to stream in the pilots to the tricks of "power flying". The pitch inertia figures are approximate but shows why pilots translating from the responsive Kiran would have found the MiG 21 slow to respond in pulling up or down. Criticism of the Marut and the Su-7 in terms of slow pull out after a close support run can also be found in their relatively high pitch inertias.

With the phasing out of the Hunter the pilots translated directly from the HJT 16 Kiran to the MiG 21 where the figures increased several times. The pilot had to be alert to keeping his energy levels within bounds. Whilst this was also generally managed, it meant, in a case of a mistake, the pilot was skating on thin ice.

2. The accidents were evenly distributed between seniors and rookies. Of the100 cases of accidents where the pilot is identified by name we have 36 accidents where the pilots were Squadron Leaders and above and 24 were of the level of Flight Lieutenants. Only 40 of the accident cases were below these ranks and one could ascribe inadequate experience as a cause. To note however is that 60 % of the accidents, in a sample of 100, involved senior pilots.

3 Of the 164 losses between 1962-2004 that is recorded in the Warbird of India records the main categories were:

Cause	Nos Lost
Mid Air Collisions	10
Bird Strikes	10
Take Off or Landing Phase	29
Combat Related	11
No details in Public Domain	rest

The numbers may appear inadequate as a statistical sample. However one has seen or dealt with an infinite sample (so beloved of statisticians!) but in practice the laws work as well for a sample of 50 as for infinity! Even if we take the first three cases ( leaving the combat losses out) it is statistically reliable. It clearly shows that accidents where that low aspect ratio was a factor ( i.e TO & landing ) dominate with 29 cases out of 49 i.e greater than 60%.

Is the general accident level too high? According to the MOD the IAF lost a total of 315 MiG 21 were lost from all causes in 40 years. Taking out the combat losses this is less than 30% of the MiG fleet in 40 years. Compared to the Canadian losses of 50% and the German Losses of 292 out of 915 F104s in a much shorter period of operation and the fact the percentage of Lightning losses for the RAF were just as high would indicate that losses were not unusual.

The figures from Warbirds of India are likely to be incomplete, especially in the pre 90s figures. However there are some statements made by the MoD that might help us. Using the figures the Warbird's loss records can be modified as follows.

The loss as recorded in the Warbirds site:

Financial Year	No of Aircraft Lost
92-93	6
93-94	10
94-95	6
95-96	4
96-97	5
97-98	7
98-99	10
99-00	13
00-01	12
01-02	8

The figures would indicate that the losses from 98 to 01 are "out of control" But if we modify the figures by using some figures later given by Mr. Pillarisetti (Source: the Warbird thread quoted by Mr. Pillarisetti http://www.warbirdsofindia.com/forum/forum_posts.asp?TID=59&PN=1) and the statement by the MOD about the MiG 21s lost during the period we can construct a closer model of the actual aircraft losses .

In this model the numbers "missing " in the Warbirds site with respect to the MOD statement are equally distributed into those years of the Warbirds site which showed a lower number. The actual crash figures would thus be:

Financial Year	No of Aircraft Lost
92-93	11
93-94	10
94-95	11
95-96	9
96-97	10
97-98	7
98-99	10
99-00	13
00-01	12
01-02	8
02-03	11
03-04	5
04-05	2

(Thanks to Jagan Pillarisetti for this table)

Looking at the revised figures we can say that the losses whilst regrettable do not reflect any sudden decrease in quality.

There are many press reports that said that the dip in 1997-98, where only 7 were lost could be because of ACM Sareen's measures of reduced flying efforts, which was the butt of much criticism. 01-02 drop also indicates some kind of "interference". The view was that the high value for 98-99 was due to Kargil which meant extra flying and the state or readiness thereafter.

The sudden decline of crash rate après 2003, is statistically speaking, "out of control" and indicates the presence of a new factor which powerfully reduced the trend.

The reason for the crash rate as also the sudden decline in recent times can only be conjectured. The popular press mentioned everything from inadequate training (which was probably not true) to spurious engine parts from ex- Soviet Republics to combustion cans losing their enameling. None of this can be verified.

According to Western rates the loss rates should have been around 5to 7 aircraft a year but one must remember that they do not have to contend with large birds and high runway temperatures. Pilot attitudes may play a major part in accidents. "Disciplining" pilots may reduce the accident rates but break the spirit of the fighter pilot which is counterproductive. Somehow the RAF manages to maintain a balance in an understated way and one expects the IAF has its own methods.

Thoughts on Future training equipment

4. The induction of the Hawks will be warmly welcomed but judging by the parameters in table A and the above para 2. It would be unwise to expect any dramatic reduction in accident rates because of the introduction of the Hawks per se.

It is interesting to conjecture whether HAL should prepare a few IJT with a thin, low aspect ratio wing as a Mk 2 IJT. This should have a 6% wing and an aspect ratio of around 3.2 and a smaller area which would improve the thrust to weight ratio and push up the wing and span loadings but keep the same basic systems. Pilots qualifying on the IJT could then easily change to the Mk2 to extend their training envelope by flying a relatively more "snappy yet similar" machine before proceeding to the AJT.

The LCA has an unusually low aspect ratio of 1.9. It will inevitably put on weight in mid life. Unless it has been tamed by the FBW software, the LCA , will be requiring much careful handling at low speed low level flight. It is also a single engine machine. Will it repeat the MiG experience? May be but the loss of life will be less as it has a very good ejection seat.

5 The importance of having the best ejection seat possible cannot be overstated. It is noteworthy that the Pakistan Air Force retrofitted their MiG 19s with the Martin Baker MK 10. Such a seat in the MiG 21would have saved many of the 70 pilots killed. Wg.Cdr Gautam, MVC and Bar who died "dead sticking" a MiG 21 FL during take off at Lohegaon is one name, of the many, who come to mind.

6 HAL made many valiant attempts to revive the HF 24 Marut. The table does show what a good potential it has as an advanced trainer. With the same Saturn AL 55 engine possibly with an afterburner and systems aggregates as the HJT 36 and the avionics of the MiG Bison for commonality and a modest use of composites in non critical parts it is almost spot on advanced trainer cum long range strike aircraft. It has a lot of room for modern avionics. .A time to first flight of 36 months and an IOC of 54 months should be achievable. How about involving the private sector? 7. An investigation of the accidents of supersonic fighters shows the need for a twin engine configuration. Almost all the next generation combat aircraft are twins. This is no coincidence. Since fighter engines are "state of the art" ( sales jargon for "doubtful reliability") it is important to have twin engines so that the plane can get back to base. The number of Starfighters which crashed due to engine related problems is shocking to any investigator. The reported engine related failures in the MiG 21 is noteworthy.

Northrop once published a study where it was claimed that the peacetime loss rate of a twin engine fighter was one fifth of a single engine fighter. This would be true only for a very high and rigid standard of flying discipline but no doubt many of the losses are due to pure engine trouble. In the case of the MIG 21 crashes some 40-50 losses would have been avoided had the aircraft been twin engine.

8. The Chinese FC 1/FC 17 is probably the most intelligent development of the MiG 21 The lateral intake allows for a decent size of radar without obstructing forward view - something that declined with each new mark of the MiG -21. The high aspect ratio larger wing of the FC 17/ FC1would improve both low speed and combat handling as t would bleed off less energy and the lower wing loading would mean that the blistering landing speed would have been tamed to a reasonable figure. We should have had an alternative LCA project along similar lines. It is cheaper, more economical and faster to have two competing projects until a clear winner emerged.

Given the expected delay in the LCA induction the IAF could do a serious contingency study about rebuilding their time expired fleet of the MiG 21Ms. Aircraft are not like the fabled "one Horse shay" in that they don't fatigue all over at once. Life expired means usually the wings have no life left in them. Usually some 8 to 10 other components of the air frame suffer the rest are usually quite good for another 3000 hours. This would essentially mean remanufacturing the centre fuselage carry over structure and the wings and some of the empennage fittings. The RAF is "re-winging" its Hawks which is a good precedent.

Conclusions

1) The MiG 21 is a sound and excellently engineered design by one of the most respected design bureaus in the domain of fighter design.

2) The loss rate of the MiG 21 is in no way worse than any similar fighter of its genre and better than most.

Applying western accident rates is also somewhat unrealistic because of significant decay in thrust and lift due to high air temperatures. A 12% decrease in lift or thrust can lead to a 100% difference between crashing or getting back safe. There being no easy mathematical co-relation.

3) The design of fighters for mach 2 flight makes them difficult to handle during take off and landing. This is traditionally the most accident prone regime of flight- even in civil airliners operated by highly seasoned crews under vary benign flying conditions.

4) Statistically at least there is no conclusive evidence that poor training was a major contributor. Highly seasoned aircrews were involved in a significant number of accidents. Fighter flying is a hazardous job.

5) The ejection seat's performance left a lot to be desired. It may well have been worthwhile to develop a specifically tailored seat once the aircraft was switched to a role involving low level flights. Possibly the licensing agreements did not cover such a case.

6) The sudden decline in the crash rate of the MiG 21 après 2002 cannot be explained with the current level of published information.

7) Twin engine equipment and redundancy of systems, despite a higher first cost, may be essential in the future and may actually be economical during the life of the fleet

8) With innovative engineering the MIG 21 M and the Marut can be the basis of future equipment as a low cost supplement.

-Prodyut Das M.Tech M.Ae.S.I

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Notes:

The MiG philosophy of simple technology and advanced concepts

1. Some schools think of the Fighter as a showcase of technology, others differ.

The MiG Design Bureau, which set the world standard in high performance fighter design, for fifty years belonged to the second. The remarkable fact of the MiG fighters was the stead fast use of only proven ,decade old technology to achieve phenomenal performance which often the rivals equaled only by much more costly unproven and sometimes ineffective technologies.

The MIG 1/ MiG 3 used steel tube and wood structure in 1941. Despite a heavy engine it was the fastest fighter in the world with an unrivalled high altitude performance.

The MiG 15 used a ten year old centrifugal flow engine design copied from the Nene and yet it not only completely outclassed all other opponents ( Meteor, Panther etc ) having similar engines but also was a very worthy foe to the much more advanced F 86 Sabre.

The MiG 25 Foxbat used steel instead of Titanium and a simple engine that could be described as a large version of the Bristol Viper. Yet by clever but simple design of its intake system it was the fastest and highest flying fighter /interceptor/ PR aircraft for a very long time.

The MiG 29 was clearly set the standard in fighter maneuverability when it appeared yet it neither used FBW nor any composites initially.

A comparison of the design approaches of the MiG 21 and the F104

2. Of the five Mach 2 jet fighters - Draken, Lightning, Mirage III, MiG 21and the Starfighter the MiG 21 was the lightest, simplest and the most widely used. It saw combat in the Vietnam, Indo-Pak and Arab Israeli conflicts where it acquitted itself very well against much more sophisticated adversaries. A technical comparison between the MiG 21 with its adversary the Starfighter F104 A is interesting as it shows how superior packaging concepts permitted the avoidance of expensive technology.

In the F104 Starfighter was definitely the more sophisticated Aircraft. The brilliant Clarence Johnson, possibly spoilt by an abundance of technology and resources, used a combination of a 3.5% thick straight wing with a state of the art J 79c engine wit a 17 stage compressor giving a pressure ratio of 12. The 3.5 % thick wing required CNC milling which was cutting edge technology in 1950s. The wing was cutting edge in a literal sense also. On the ground the leading edge had to be capped to prevent damage and injury. Interestingly the intake was fixed geometry which meant that the intake was inefficient at off design conditions. The tyres, which could not be fitted into the thin wings were of extra high pressure and had to be fitted into a narrow track fuselage mounted undercarriage. The ejection seat was of a downward ejection type which must have been unnerving. The fact that the wings were almost solid meant that all the fuel was carried in the fuselage. This must have lengthened the fuselage considerably increasing its pitch inertia.

The MiG 21 team chose the innovative tailed delta concept. Initially derided by the West it was proved to be the best solution for the supersonic combat role. It combined lowest wave drag and yet avoided the problem of high induced drag of the pure delta which had to use "up" elevon" resulting in loss of lift during take off or a turn. Engineering wise the Delta plan form of the tailed delta meant a reasonably thick wing which could be manufactured by traditional sheet and rivet methods.

The engine compressor had only six stages but two spool technology (first used in the Daimler Benz ZKL in 1944 !) allowed a pressure ratio of 9. This combined with a conceptually sophisticated but engineering-wise simple translating intake cone allowed better ram pressure recovery. With typical MiG Bureau simplicity the cone was three position rather than being continuously variable. The overall pressure ratio was thus pretty close to the F104s but the fewer engine stages meant a much cheaper and lighter engine.

The MiG 21 is till date the lowest powered Mach 2 interceptor in service despite a profusion of bulges and scoops and having mushroom head rivets towards the rear.

The undercarriage was a brilliant design which allowed a wide track undercarriage with low pressure tyres for ease of ground handling. The ejection seat not only equaled the performance of the contemporary seat but the semi encapsulating feature gave an outstanding protection for high speed bailout Unlike many of its contemporaries all systems were duplicated.

The MiG 21 went on to successful service with both large and small, relatively obscure and new air forces which speaks well of its serviceability and reliability.

Whenever used in combat (Indo-Pak, Vietnam and Yom Kippur) the MiG 21was a very respected opponents to warplanes several times more expensive. Pakistan lost 3 Starfighters to the MiG 21 in 71 and the Israeli Air Forces had greater respect for the MiG 21 in the Yom Kippur war. The F4s and Mirage 3s usually avoided dog fights with the MiG-21.

Western Industry found the selling price of a MiG 21 unbelievably low and politically motivated but sheer good engineering and ruthless standardization kept prices down. Low prices led to mass production. If prices were indeed subsidized the amount would not be as much as is made out to be.

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References and acknowledgment;

This is to thank Jagan Pillarisetti of Bharat Rakshak and Warbirds of India for allowing me to use the data on his Warbirds site as well as supplementing the data with further information and comments.

Wg. Cdr. Sekaran ( Retd) of MOFTU for his inputs in discussing the accidents listed in the Warbirds of India site.

The reader is also directed to search the following websites through any search engine. I used Google.

1. Bharat Rakshak
2. Warbirds of India
3. Greg Goebels website on Fighter aircraft
4. www.-916 - Starfighter for Starfighter losses and operational history
5. Encyclopedia of Fighters Gunston for basic details of the Aircraft.
6. Air International
7. Air Forces Monthly
8. http://mod.nic.in/pressreleases/content.asp?id=119 mentions that a total of 315 MiG-21s were lost in about forty years - Oct 63 to end of July 2003 The MOD also stated that between April 1992 to March 2002 , a total of 102 MiG-21s were lost in accidents and 39 Pilots killed. We have records of 81 of these Mig-21 mishaps.

The opinions expressed in this piece are personal and do not reflect the opinion or policies of the organization I am currently employed in.

Prodyut Kumar Das is an Alumnus of St.Xaviers’ Hazaribagh, IIT Kharagpur, and IIM Kolkata. He started his career with Aircraft Design Bureau HAL and for twenty years worked and led various vehicle related Product Development Projects with leading Indian and multi National Companies.

He left Industry to join IIT Kanpur in 1993 as a Professor in the Department of Mechanical Engineering. There he won a prize of the Royal Aeronautical Society of UK for his design of a light sports aeroplane using grants given by ARDB. He also did a project study on “The design of a Light Car costing less than 1 Lakh” which was a Ministry of HRD funded project IDICM 36 and started his research on Stirling Engines in which the IN was keen.

When IIT Kanpur did not renew his 5 year tenure he returned to the  Industry as a Vice President Technical and finally retired as Advisor Aerospace in the e- Engineering Division of a Leading Indian Engineering Company.

He currently teaches Engineering in a Private Engineering College in his hometown and continues his Research as a Consultant. He has been writing on matters related to Defence Engineering since 1990s.