A Polymorph for the Future? a
review of inherent upgradability and the pontoon “chassis”
Prof.Prodyut Das.
Poly morph –literally “many
forms” here is taken to mean an airframe that is inherently suitable for
“infinite” modifications and up gradations. Should design for upgradability be
a conscious part of the design requirements for combat aircraft? Given the technological factors that are shaping
the conceptual design of combat aircraft and India’s own lack of infrastructure which
keeps the Industry at the mercy of foreign vendors, the answer is definitely a
“yes”. Strategically this overdependence on vendors for key aggregates is an
unacceptable situation that must be compensated by technological innovation as
represented by the “Ponton” (pontoon).
The question of inherent
upgradability to alternative engines and systems arose after Prof. KK Sarma of
Guwahati ( to whom thanks) wrote to me about considering the possibility of
using the AL 41 F with thrust vectoring for the LCA which, like all pretty
young things, has with time, transformed from a maidenly LCA to now a more
matronly MWF.
As a knee jerk reaction we
both agreed that the engine was “impossible” but further prodding by Prof. Sarma
triggered the search. What emerged is a discussion on upgradability with some
conjectures as to meeting the MWF ( Prof. Sarma’s original query) and AMCA
requirements with a Ponton/AL41F based solution a solution whose aim is to be
inherently upgradable..
The story is told in the
backrooms of Aeronautical bars about the chap who designed the perfect
aeroplane. He had to be sacked because he had violated a basic rule of aircraft
design- his aeroplane could not be improved! Perhaps there is wisdom in old wives tales and bar room ditties that one does not
pick up elsewhere because even a casual look around will show that the
commercially successful warplanes were always “developable” or “upgradable”.
A short resume of upgradability
Until the 1930s upgradability
was not to be considered. Wood and fabric aircraft structures would decay in normal service within a few years and in
any case the pace of aeronautical development was so furious that the airframes’
aerodynamics was obsolete within months. The Albatros D III was formidable when
it entered service with Herr Rittmeister Manfred von Richthofen’s Jasta 11 in
1917 but by June 1918 the Fokker D VII’s amazing- what is now called high AoA ability- enabled
the Fokker, even at high altitude, to
hang on to its prop and pour fire into its opponent from behind ( Note 1). The
Fokker was such a sensation that it was required in the terms of the Armistice
for Germany to surrender “alle apparte DVII”. The Albatross was obsolete within
a year.
The advent of all metal
monoplanes of the mid 1930s was the first time that upgradability tip toed onto
the scene. Final versions of the fighters like the ME 109 had three times the
power and perhaps 12 times the firepower of the first prototypes and pointed
the way to the future.
After a point aircraft design
subsumes Aeronautical Engineering and Science and gives precedence to the
global scenario. One cannot design an useful aircraft by focusing just on the
engineering. The early German Jet aircraft designers were probably conscious of
the need to make the aircraft upgradable. The early German jets- the Arado Ar
232 Blitz, the ME 262 Schwalbe, the Heinkel He 280 and even the projected
Messerschmitt Me P1101 all had under slung jet position which, given the state
of flux the German jet engines development was at that time, was a very
sensible engineer like decision despite the drag penalty. The under slung
engine layout made re-engineering for another type of engine relatively less
disturbing. Boeing’s under slung engine was a more modern avatar. Imagine what
would have happened if the B 737 was designed to have the elegant De Havilland
Comet’s “buried- in the wings” type of engine location. The Boeings could
remain in production for long because the pylon mount for the engine could
handle engines of more than twice the power and size engines than of the
prototypes.
It was with the coming of the
transonic and supersonic fighters that upgradability should have been
considered as a design requirement.
Transonic flight required enormously strong airframes at Mach 1.2 low
level- which as fast as anyone would wish to go at low level ,the fuel
consumption being 300kgs per minute or roughly 20 litres per kilometer- puts on dynamic pressures in the region of
3.5 atmospheres. Designing for such
dynamic air loads meant that the strength of the airframes were close to what
would any way be required for having a life where the airframe fatigue life and
the operational life-the life at which the airframe would be written off due to
accident, wear and tear and in- service degradations. (Note3) This bonus could not be reaped because at that
time, the SAM was not yet perfected for the all weather point defence tasks the
airframe performance demands were still creeping up for the Mach 2 regime so
the aerodynamic design of the airframe was “unstable- going upward”. Therefore
even in the sixties the “inherently upgradable airframe was not easy to
practice. (Note 4) What actually happened was as below:
The service life of an
aircraft is not entirely decided by airframe fatigue. The “other” factors
determining the retirement of aircraft are:
i)
Difficulty in
obtaining “running” spares- tyres, brake pads rubber seals etc.
ii)
Difficulties in
replacing major aggregates such as engines and such type specific items as the
Hobson unit etc which are particularly difficult to get in the open market.
iii)
Operational attrition which reduces fleet size
which makes maintaining the fleet difficult or uneconomical.
The succeeding generation of
engines, avionics and accessories were smaller and lighter yet upgrading often
faced problems. The item not only had to match the performance but also the “shape”
for a successful fit without too much engineering. For example upgrading the
engine of the Hunter/ Lightning with the suitable versions of the RB 199 was
possible in theory and would give a significant all round improvement in range
but unfortunately the aircraft had ”tubular”
semi monocoque fuselages which is a “hard” skin making changes difficult. If
the outer skin did not take the entire load it would be easier
to modify the aircraft significantly. It was economically impossible to
“rebore” the fuselage to take the new engine and its ducting.
Engineers beat this
constraint by designing the replacement as a”drop fit” or specific to type
item. A handy example would be the MiG 21. Given the enormous production run of
about a thousand for the plain vanilla Mig 21 F for example the Russians
developed the rather natty GSh 23 mm for
the MIg 21 M which gave the aircraft the roughly the same weight of fire as the
Vulcan six barreled but of course at the cost of thermal stability. For the engine
they had the R 13 and the R25 to replace the R11. This put constraints on the
extent of upgradability. One remarkable
example of an “inherently upgradable” design of the era was the Douglas A4 Skyhawk where of course the
one piece low wing acted as a” Ponton” (pontoon) foundation which is almost a halfway
house for the concept of the polymorph.
The Ponton.
The Ponton (“pontoon”) is a
concept known well enough in Automobile design and indeed the Mercedes Benz 220
was nicknamed “Der Ponton” though for my money the little Citroen 2CV was a more
brilliant example of the true “pontoon”. I had the opportunity to tape and
micrometer an old 2CV for one of my projects (what one had to do to make a
living as an engineer!ah, me!) and came away very impressed. The chassis, which
used rolled sections and did not require heavy presses to make, was brilliant. It
permitted the little Citroen’s coach work to be made from steel tube and
corrugated sheet- again without needing heavy presswork. Though the design is
over eighty years old, as an example of frugal engineering, its study was a
humbling experience. If the idea of the Ponton were to be translated into
aeronautical engineering terms what we will have is the use of the wing and stabilizer and the connecting structure to form
a ponton which will carry the cockpit, fuel tanks, equipment on the top and the
engines underneath all faired by unstressed composite panels. This would
allow infinite upgradability because much of the fuselage volume would be
accessible..
A current example of the
“Ponton” approach is the Russians. A look at the photos of MiG 29 under
production shows how easy it is to upgrade the aircraft because the centre
section acts a “ponton”. Perhaps the Russians, who examined several
conventional “tubular” semi monocoque layouts, realized that requirements were
uncertain and were changing sufficiently to make sense to have future
upgradability in mind ab initio. In the MiG 29 for example
the changes to the systems or to the engines or a more “stealthy” configuration
at a future date will be easy to engineer when compared to equivalent western
types. The FGFA is but built on on a Su 30 Ponton.
The “Ponton” has its draw
backs. Greater cross sectional area which will limits its supersonic acceleration
and the greater wetted area which will increase drag but current engines say
the RD 33 in comparison to the Avon have about two and a half times more power
per unit cross section. This additional power enabled Northrop for example to
do away with area ruling in the F20 or for that matter the “conformal” packs on
the F 16 are examples of how advanced engine capabilities can allow “abuse” of
aerodynamics. The structure will be heavier but as the Russians have shown, this
is within manageable limits.
India and the “Ponton”
For India the Ponton concept
is an imperative for our future
combat aircraft and I am including the AMCA and the MWF as “future “fighter
projects. The caution that these two projects are “Future” is because:
i)
the dates of the
first flight are being given by people who will have retired before those
dates. The present concept may require major redesign amounting to “new” design
by the time the prototype flies.
ii)
The aircraft is
very likely to fail to meet the basic performance parameters- I am just going
by the way the development cards are being played. Too many new technologies in
being tested on a new unknown test vehicle – the AMCA. Even the US did not go
for the moon ( F 117) without an intermediate tes vehicle- the “Have Blue”.
iii)
The major vendors may increase prices to
unacceptable levels.
We have been up these streets before. We must have inherently upgradable fighter designs
for several compelling reasons.
Resistance to sanctions and
arm twisting- is that we have had experience of a vendor upping the price of a
product forcing us to choose an alternative at the last moment. In the case of
the HJT 36 for example the Larzac had to be replaced by the NPO Saturn AI 55
fairly late in the day for reasons which included commercial unviability.
Earlier with the HJT 16 the Viper had to be replaced by the de-rated Orpheus.
Who will guarantee that it may not happen a third time? I have just heard that
the planned re-engining of the Jaguar has run into “commercial difficulties”
and may have to be dropped. Upgrading the Jaguars would have been an economical
but effective solution. The problem of a ”tubular” semi monocoque is that outer
load bearing skin is wrapped around the engine and ducting. The accessories are
then fitted into various nooks and crannies and upgrading them with better is
not always possible. Those who can make afresh design after twenty years but
what about those who are trying to keep a leash on budgets?
Whilst vendors are offering
airframes with 6000 hrs life this
feature is meaningless without inherent upgradability as offered by the
“pontoon”. Statistics show that about two thirds of the fleet will be
written off- depending on the role – between 2300 hours and 3000 hrs which is
about 15-20 years.
The MBT and the AMCA
The second reason is that
Combat aircraft concepts and design is at a point that Tank design was in the
early 1940s. Four unrelated changes- radio telephony, track metallurgy, the
high speed Diesel engine and dual purpose main armament converted the “infantry”
tank to the MBT. In fighter aircraft design we are also at such a point. The
concept of the fighter being marketed may have changed by 2025 to that of a ”carrier”
relying more on GW, AI and systems to do the job-that is if that job is not
already been taken over by UAVs and SAMS, when we fly the prototype AMCA- if on
time.
The potential for a
significant change in the concept and specifications of the fighter has been
long overdue but this has been always stymied by a lobby which wants to push
the most complex and expensive specifications that the market will bear. The
impact of the following uncertainties
and new technologies has to be noted.
i)
Is “stealth”
i.e. the F 117 style total stealth achievable for frontline fighters
o[operating say from Ambala or Jorhat or it will be a specialist “hush hush”
weapon operating from special bases and requiring may be only two percent of
all combat sorties flown ? The rest 98% can be flown by vanilla warplanes. This
question has to be settled because “stealth
– as marketed- will make the aeroplane both inefficient and technologically an
insuperable challenge to master. Things are made worse by the fact that stealth
itself may also become obsolete/ obsolescent by 2025. Old stagers will say
that that many of “must have “features
of today are just very good marketing.
ii)
To what
extent will thrust vectoring and HMDS and the R 73 style “cueable” CCMs render
traditional “aerodynamics based maneuverability” obsolete? Yes the technology
exists to have the aerodynamics based maneuverability but it is not the least
expensive “solution”. Meeting India’s
defence needs by conventional i.e. Western-’ thinking is unaffordable. New
thinking, starting from fundamentals is
imperative.
iii)
People
are tiptoeing around the “Vartamaan “combat. Was the result of that combat an
“outlier” or was it the proverbial “you can tell from a single grain if the pot
of rice is done”. Let me put it more bluntly. Could an aircraft even simpler,
smaller, cheaper and lighter than the MiG 21- i.e. inherently less
detectable by eyeball, radar or IR with only ,say Mach 1.3 aerodynamics but
capable of cueing the R 73 CCM and replicating the aerodynamics performance of the MIG Bison to the extent as actually used on that day- have
done the job? The answer is obviously “Yes” and a (relatively) low performance
but smart platform with lower signatures is actually be a better solution given
the fearsome proven reliability of the CCM though there will always be more
expensive and “safer” ways of fighting a war. I concede there can be no perfect
decision in procurement. We can play “safe” and order the same as everyone else
until we skid to the borderline of dangerously
low fleet sizes which without a doubt will be unsustainable in
war.
iv)
What is the
impact of sensor fusion and artificial Intelligence on Combat aircraft design?
For example designers have always returned to the all round vision canopy after
going on for “flush” canopies e.g. Mc Donnell F 4 Phantom to Mc Donnell Douglas
F 15 but today but can rearward facing cameras and “facial recognition”
techniques with promptings from ADGES do the job?
v)
Finally there is
the undeniable truth that Mach 2 plus capability was an old Western requirement to supplement the
failings of the early SAMs and plays
havoc with “sensible” airfame design. The English Electric Lightning design
sacrificed range dramatically to boost climb rate and speed so that it could
back up the Bristol Blood Hound for the point Defence tasks. It also had some
undesirable servicing and safety features. (Note 4).Today the point defence
tasks for VPs and VA should mainly be shouldered by the SAMs . We should trade
supersonic aerodynamics for “fuselage volumes” which augurs well both for range
– always a most useful feature for warplanes- and upgradability. As an example,
the useful fuselage volume of the MiG 21 , that is the fuselage volume
theoretically available after deducting the engine and duct volumes is for
example only is 49 percent. The pontoon is around 63 percent and can be
expanded with penalties. Even if the figure is approximate the fact that the
“Ponton” is both practicable and “infinitely”( within limits of logic)
modifiable is undeniable.
vi)
These questions cannot
be ignored anymore by India which has limited design capabilities and limited
budgets. Again let me repeat – there can
be no perfect decision. The Japanese sacrificed “recklessly” by Western
standards-battle damage resistance to get range. It was to the IJN an arguably sensible decision and if Japan lost it was not
because of its design philosophy but because its industrial potential was
limited. To cut myself short- if we do not examine the possibilities of the
polymorph- what will happen is that, even
if the AMCA and MWF programmes are on time, we will have produced
aircraft that are not modifiable or upgradeable to the extent required. Nor can
they stand up to commercial or political arm twisting. The Designer cannot
estimate the likelihood of such an event but he can provide in his design
features to reduce the impact of such moves.
The danse Macbre
Aircraft
design is not just a three legged race of the junior schooldays but probably a
five legged race where the lengths of the legs- i.e. the development cycles of
all the various systema are all very different. In the case of this category of
combat aircraft the “legs” comprise of:
i)
Airframe
aerodynamics
ii)
Propulsion
Technology. People are working now on variable cycle engines ( we should not
even think of such things!)
iii)
Airframe
materials
iv)
RAM coatings ( applicability, maintainability
and disposal)
v)
Radar reflecting
geometry i.e. robust stealth.
vi)
Control technology-
FBW, FBL, “Puff Pipe” e.g Harrier,
vii)
Artificial
Intelligence
viii)
Radar and
avionics
ix)
Power and power
control systems- hydraulics, FBW, FBL, electrics.
Only the first- aerodynamics-
is now relatively “stable”. Indeed it is regressive- top speeds are coming down
and high AOA is less in demand than two decades ago but the rest have changes
which can make significant impact on future configurations.
Aircraft Engineering is
Technology but Aircraft Design is Humanities and is strongly linked to the
technological environment .Indian designers must keep “sanctionability” or
vulnerability to sanctions very much more in their minds than others. The LWF
is coming in a big way once the last F 35 has been “flogged” and suppose then
there was a genuine shortage of the F 404/ F 414 engines in the market. Where
will we be then with the AMCA? As mentioned earlier It has happened to us
before and who can take the responsibility if it happens again once we have say
perfected the AMCA? The present people would have long retired.
A different way of doing things
We will also have to change
the way we develop aircraft. The idea that if we tinker around long enough we
will somehow come out with a trouble free aircraft does not work. (Note4), The
successful method is to cobble together
something promising and get it flying within 3 or 4 years of “go ahead” and
then patiently squash all the inevitable worms that crawl out of the
woodwork. At present there is a great
reluctance to do so and first flights are usually planned to coincide with the
project Chief’s retirement.
The “pontoon” for the AMCA/MWF?
With all that as a part of
what is going on in my mind I will propose the design.
We begin by accepting that we
do not have the time to do ab initio design and the aircraft must
be cobbled together using known and proven sub assemblies and come to a firm
base which is flexible enough to develop further. This is the historical
process. We have the following options:
Wings:
i)
MiG 21 wing and stabilizer.
ii)
LCA wings and
since I dislike tailless deltas awe pickup the tailplane of the MiG 27
iii)
MIG 29 wing and
empennage. I prefer a “tailed” layout as they are less draggy and we do not
need STOL as much as the Swedish AF plans for.
iv)
The Su 30 wing
and empennage to be scaled down to around 35 M2 wing area.
v)
The AMCA wings
and empennage presuming that the documents are prototype ready.
It will be noticed that only
aerodynamics that are “available” to us is being considered
In the engine we have a
choice of four contenders.
i) )
The RD 33
ii)
The AL 41 F / AI31F with thrust vectoring
III) The Eurojet 2000
iv)
SNECMA M 88
In avionics the electronic
suites to be considered are those of the Mig Bison, , the MiG 29 the Sukhoi 30
and the LCA.
Thus we have the set of 5 wings X 4 engines X 4
avionics suites X 4 other systems and i.e. 320 options. Many of these 320 options will
automatically discarded after cursory examination and tabulation e.g. the MiG
21 wing with RD 33 and the Su 30 systems This option will require a “new”
centre section to be developed and give a wing area a shade too small whilst
the potential
for further development will be marginal. Nevertheless these have to be
rejected only after due diligence. Record
of the discards and the reason thereof is important. We will end up with about
12 or so near feasible solutions. It will not be possible to discuss all the
twelve or so possibilities. Two of the possibilities stand out by “gut feel”
and in no way dismissing the others will discuss these two in some more detail.
The MWF ponton
The first possibility is to
use the wing panels of the LCA as available at the moment along with its
systems and avionics assuming these are acceptable as is and creating
a “pontoon” to pick up the two panels and the stabilizers. Since I
dislike tailless layouts for their “finnickyness in terms of developability-’ a
suitable stabilizer is mandated. The
stabilizer of the MiG 27 is in terms of area more or less “right” and probably
has sufficiently low aspect ratio not to stall before the wing! These will be
attached to a pontoon which will carry the SU 30 nacelle for the AI 31/41 F
underneath and the LCA MK1A cockpit and systems are attached to the pontoon. (
Fig1) The thing will look something like shown in the sketch. I expect that the disadvantages of the
1.76 AR wing will be compensated in combat by thrust vectoring and HMDS/R 73
systems so we have a possible solution- even with the present very low aspect
ratio of the wing and its consequent high induced drag in a turn is negated by
TV.
The MiG 29
Ponton
Another probable solution is based on the
MiG 29’s with a single AL 41 F TV. (Figs
2, 3.) The basis of the aircraft will be the MiG 29 ponton which consists
of the wing outer panels the tailplanes and the centre section which also
carries the cockpit. There will be temptation to redesign the MIg 29s wing by
replacing the R 177 aerofoil with something “more suitable” for the Mach 1.3
range- the promise of having 20 percent fuel volume in the wings is alluring
but this goes against the philosophy of “make do and mend” type of design and
will hamper the target of getting something into the air as fast as possible.
The centre section whilst based on the
existing MiG 29’s centre section (CS) with such “irrelevant- for the flight
test aircraft- features as the louvered intakes etc deleted will have to be
remanufactured to replace the two tunnels that are used by the RD 33s and
replaced with a single larger central tunnel for the AL41F- as per Prof.
Sarma’s original surmise. The centre section will also carry hard mounts so
that the engines position relative to the CG can be shifted longitudinally for
the the flight trials. The entire engine nacelle of the SU 30 is the basis of
the propulsion “egg” and is slung under the CS as mentioned. ALL systems and
aggregates are identical except the change in loom length as dictated by the
change. The MiG 29’s undercarriage will not reach down sufficiently to cater
for the 200 mm bigger diameter of the AL31/41 engines and so the solution will
be re-examine the MiG 27’s undercarriage and “appliqué” them, to use a term in
dressmaking, on to the sides of the nacelle or shift the datum of the tunnel upwards
for the AL41 by the same amount.. The nose wheel and the brakes of the MiG 27
will be used and the nacelle will have to be modified accordingly or – at least
for the prototypes -a 4 wheel undercarriage where the nose wheel is also
appliquéd onto the front of the nacelle can be considered. The existing twin
fins , though probably slightly excess in area , can be retained for the
prototypes.
Each of the solutions have their problems.
The MIG 29 based solution is good because the development and detail design
work will be the least but the problem is that the Russians may need to be placated with license. The LCA
based solution is free from such hazards but will mean more engineering work.
It is always thus- no prefect solutions. The test aircraft will not be built to
any operational requirements or comply to any standards being in the “X”-experimental-
category. The aim is to clear the aircraft for about 500 hours of testing to
see if the idea has promise.
The
DASA/Rockwell X31
Of course no one builds an aircraft as
described above- like a patch work quilt- in India! Elsewhere “patchwork
quilting” method is standard. Fighter designers always minimize risks ( because
of the pressing need to be commercially successful, by using proven ,yawningly
familiar systems and aggregates to build a trial quick build “canter horse”
e.g. YF 17, EFA etc usually without a very formal “specs”. This is what
Rockwell DASA did for the X (note “X”-experimental) 31 and we will see a
marketing shift to hyper-manovreabilty some time soon..
i)
A new cranked
Delta wing and long moment canard by MBB who had developed it for the EFA- note
again- the precursor for the Eurofighter.
ii)
Thrust Vectoring
system –with paddles that had been developed for the F 14 Tomcat’s spin
testing. To be noted was that it was “good enough” TV – certainly not as good
what could have been done later or the AI 41F- but it worked!.
iii)
Landing gear
adopted from the F 16 with wheels from the Cessna Citation and Vought A 7
tyres. Note the extent of “scrounging around” for ready- made task reducing
parts!
iv)
Ejection seat, instrument
panel ,stick and throttle taken directly from the FA 18
v)
GE 404 GE 400
engine taken from the F 18
The
entire aircraft as made with aluminum except for the Wing skins but as already
noted the entire wing was a “bought off the shelf” item from MBB.
The
aircraft had no specifications but explored what was possible in terms of
supermanouvreability -AOA of 700
and low speed handling at 28kts and a turn radius of 100mts. The technology
developed has been salted away and will reappear as tehnew “wonder formula” for marketing at a future date. The flight
test programme was limited to 500 sorties- pl. also note. It was destroyed in
the last flight under circumstances which to me at least sounds so careless as
to be fishy. Except for the last flight we can faithfully follow the American
approach.
Summary
Aircraft
design is different from aircraft engineering and the Chief Designer’s ability
to “read the situation” makes all te difference between an effective warplane
and a lemon. It is an admittedly difficult task. The West has employed –
particularly in America- thousands of talented people over the years to predict
what kind of wars will be fought and therefore the kind of equipment that
should be procured. By a process that is not clearly understood the Americans
,in particular, has always chosen solutions that involved manufacturing the
most expensive ( as opposed to useless) equipment which could at apinch do the
job. I am not being uncharitable. The Americans, in the ‘fifties developed the
F 105 for nuclear strikes against the CCCP whereas they should have developed
low cost equipment to knock out NV truck parks, power stations and bridges
,preferably at Night and in bad weather which in Vietnam was really bad. That
they have not lost the proclivity is seen by the fact that they are extremely
cautious about where and how they
use the F 22 and the F 35 for reasons that do not make common sense to the
Taxpayer. They developed theB!,B1A and the B2 but its affair bet that the B 52 will see the younger
aircraft off-( especially if the Americans can think of refurbishing theB52s in
India!) . Why they do such things is a topic in itself but I will caution that
in following American procedures beyond a certain point means that we are going
for a very expensive way to meet our defence needs. The Americans have always
survived by their unfettered “thinking –on the- feet” ability and we must do so
too. Aircraft Marketing is very incoherent. Take the case of airframe fatigue
life where 6000 hours is being now flouted and talks are going on for 10,000
hours- anything you can do I can do better is the game!. My studies show that
50% of a fleet will have been written off by about 1500 hours to 2300 hours
depending on the operational profile flown.
The
pontoon chassis concept allows for easy upgradability of engines and systems
over the years For India, with no base in terms of engines and upgradability
the study of the pontoon concept deserves particular emphasis.
The
pontoon also is relevant because as discussed above it can be an “experimental”
aircraft to serve as basis for our AMCA and MWF aircraft.
|
Sl.no
|
Parameter
|
LCAmk2
|
MiG 29
|
MiG 29 Polymorph
|
AMCA
|
MWF
|
LCA Polymorph
|
Boeing X32-JSF
|
|
1
|
Length
|
14.2
|
17.61
|
17.61
|
17.6
|
14.55
|
14.8
|
13.72
|
|
2
|
Span
|
8.2
|
11.41
|
11.41
|
11.13
|
8.2
|
8.2
|
9.14/10.97
|
|
3
|
Ht.
|
4.4
|
4.357
|
4.357
|
4.8
|
4.4
|
4.357
|
4.02
|
|
4
|
Wing area
|
38.4
|
38
|
38
|
55
|
40.4
|
38.4
|
54.8
|
|
5
|
Empty weight
|
7700
|
10,800
|
10,200
|
12,000
|
7700
|
8100
|
10,000
|
|
6
|
Clean TOW
|
11,400
|
15,800
|
13,780
|
12,000
|
11,000
|
11,400
|
18,144
|
|
7
|
MTOW
|
16,500
|
18,500
|
23,900
|
20000/,25000*
|
17,500
|
20,600
|
22,680
|
|
8
|
T/W
|
0.86
|
1.05
|
0.97
|
1.02/0.81
|
0.89
|
0.93
|
|
|
9
|
SFF
|
0.366
|
0.255
|
0.218
|
0.255
|
0.336
|
0.269
|
|
|
10
|
Engine thrust
|
1xGE 414 – 98kN
|
2x RD 33
2x83kn
|
1xAL41F(TV)142.2/ 86kN
|
2x98kN
|
1x98kN
|
122.4/76.2AL31F
|
P&W F119 -156kN
|
|
11
|
Aspect Ratio
|
1.75
|
3.4
|
3.4
|
2.25
|
1.8
|
1.9
|
|
|
12
|
Internal Fuel
|
3300
|
3630
|
3630
|
5000
|
3300
|
3300
|
8618
|
|
13
|
Payload
|
5500
|
3600
|
10,000
|
1500/5000
|
6500
|
|
|
Note 1
The Fokker D VII sturdiness
and tractability and sturdiness came from Goettingen 298 aerofoil of 14.5 percent
thickness not only give immense structural strength – spar bending
strengths go up as the cube of the depth and torsional rigidity is proportional
to the enclosed area - but also the thick rounded aerofoil with its large nose
radius worked better at the Reynolds Numbers involved than the earlier thin
“clutching hand” aerofoils- based on
birds wings of the earlier aircraft. There is some dispute about the
nomenclature of the aerofoil. Some say the nomenclature is Go 298 and others
say that the aerofoil upper surface is Go387 and the lower surface is Go 418
with 14.5 % at the root tapering to 9% at the tips. The confusion is because
the aerofoil actually came “out of the head” of Rheinhold Platz and was later
formalized by Goettingen. Rheinhold Platz, Fokker’s talented Chief Designer,
was a welder by trade, had like his contemporary Sydney Camm of Hawker’s , a
flair for aerodynamics. Platz went on to design many of Fokker’s thick wing
monoplane airliners after the war. It so happens that Einstein (yes! HIM!) also
designed an aerofoil “ Die Katzenbuchenflache ” ( Cat’s back) which was so
weird that it is perhaps better that he stuck to Relativity!
One interesting side show to
this is why the German’s did so considerably in advance to the British in terms
of theoretical aerodynamics even though it was Stokes who formulated and first
proposed the circulation theory ( the Navier’s Stokes equation) . I would
cautiously suggest 400 pages 280 odd differential equations (easy ones) that if
you get a chance to read Prof. Bloor’s “The Enigma of the Aerofoil” don’t miss
it. The politics and personality clashes that affect scientific development has relevance to our
situation and brings to mind the old adage that Science progresses by Deaths!
Note 2
When the Lightning was a
gleam in Petter’s eyes he was looking for an aircraft that would be a
supplement to the Bloodhound SAM i.e. a point defence interceptor. The
Light5ning was of the manned missile genre of its contemporaries eg F 104, F
106 etc. After examining several dozen
possible configurations, Petter chose the vertically and longitudinally staggered
engine layout. The two Avons and their afterburners were thus behind the
Pilot’s “shadow” and thus the cross section – critical in supersonic flight
-was at a minimum. On the flip side it was a headache to maintain and any
leakage of fluids from the upper engine or hydraulics would result in an inflight
fires – a great plague in Lightnings.
Note 3
One is reminded of an old
cartoon strip where a scientists is seen busily scribbling data – humidity, density, hardness and many
complex equatiosn on the side of a large block of marble in his laboratory. He
then after much further scribbling marks appoint “x” on the side of the marble
with a plumb line and with achisel gives atap. A rubble of marble falls away
and there is revealed a magnificent horse, rampant, on apedestal that Cellini
would have been proud to have produced . However the Scientist is distraught
and is seen wailing “No!No! there was supposed to have been a rider on the
Horse!”. In aircraft design also it is proven fact that there is a limit to what
can be done by theoretical studies. Getting the first prototype up in the air
is the job to do.
