HF 24 Marut: Some Technical Notes

 Summary

The HF 24 airframe was a masterpiece in aeronautical design .It is the finest platform the IAF has ever had in this category of aircraft. It is even today more suited for actual combat conditions. A resurrected, re-systemed Marut is a very low cost, guaranteed platform that can supplement our efforts to increase our air strength as a supplement to the LCA,MWF, and Jaguar aircraft.

The original aircraft was produced with very limited resources and a capital outlay of only 16 crores in less than five years 1956-1961. The revival of its proven airframe will take a fraction of the time and resources of usual programmes.

Its aerodynamic performance is acceptable even today and can be improved by small changes. The consequence is that it will demand less from our engine development efforts.

Its strongest points were simplicity; high performance on low power, very good handling but most of all was it was a very balanced design giving versatility and very high levels of upgradability.

. The HF 24 design makes eminent sense as a platform for meeting both the MWF requirement as well as a supplement to the LCA programme as well as the Jaguar replacement need..

 Its upgradability as regards additional future equipment will exceed both the LCA and the projected MWF.

The proposal deserves consideration as a guaranteed economic and rapid solution with respect to meeting the Air Force’s squadron strength needs.

Given the firm base and the anticipated low development costs the project should be handled by the Private sector particularly the Indian Automotive Industry which has the skills for much of the detail engineering. It is a resource we are not utilizing at present.

INTRODUCTION

India is the only major economy which faces apart from state sponsored terrorism the threat of armed attack by conventional forces from powerful neighbours. These aggressions are a part of long term plans. India thus has to maintain large and powerful conventional forces to deter the adventurousness of its neighbours.

The Indian Air Force has a sanctioned strength of 42 squadrons. For reasons this needs to be reviewed and upgraded to 50 squadrons (Appendix). This numerical strength can be achieved with an atmanirbhar Industry at a fraction of the cost of imported solutions .

 

 

 

ATMANIRBHARATA

Atmanirbharata is not just self -reliance it is self -confident self–reliance. This means that we have the ability to not only set up, tailor and manufacture to our own specifications but also to modify our equipment to reflect the lessons learnt from active service.

AN ASSESMENT OF THE TEJAS SITUATION

The following is an independent, open source assessment of the Tejas situation. The self-contradictory information has been filtered by applying engineering common sense. The intent of the assessment is to highlight the risks with IAFs fulfillment plan and building an alternate option while keeping the focus on timely delivery of current indigenous fighter programmes. 

1.  The project was very badly begun and it has continued to suffer from that bad start.

2.   The standard of detail engineering was very poor made worse by glacially slow rates of correcting them.

3.     It appears that the first series aircraft have an empty weight approaching 8 tons making them useless for any realistic purpose except trials and training.

4.     The current utilization rate is around 50 hrs. / yr. per aircraft confirming pt.2 above.

5.     Low production rates even after 2 IOCs / FOC indicate that the design is still not satisfactory.

6.    If the above (2, 3) is true then any claim to speed rate of climb range etc. being satisfactory is untrue.

7.     The design lacks “balance”. In trying to make the smallest airframe the aircraft has thrown away “upgradability”.

8.  Even if successfully developed to meet FOC standard, which is unlikely, this lack of upgradability will dog the design.

9.  The MWF configuration as projected  is extremely cluttered and almost certainly end up with a situation where the additional power of the F 414 is frittered away by more weight and drag.

It is quite possible that simple fixes and attention to detail may improve the present performance of the LCA Mk,1 &1A by about 7 to 15 % but unfortunately that attitude of “Caritas” – a word meaning care, love compassion and interest -is lacking in the concerned Organizations. The aircraft does not need so much technology as “Caritas”.

Whatever the deeper reasons, the situation is that we have a bad airframe with possibly good systems. Therefore combining the proven excellence of the Marut airframe with what is usable of the developed systems is worth a re- look.

AN ASSESMENT OF THE MARUT AS A JAGUAR REPLACMENT

The Jaguar has been serving in the punishing low level cross country role for over forty years and will need replacement as serviceability and airframe life begins to reach their limits. Though the DARIN III upgrades has been a matter of justifiable pride for the IAF the airframe is old. More tellingly the Jaguar was designed for the low level attack role by keeping the wing area as low as possible. This works fine in NATO because the air temperature in North Europe ensures about 7 to 10 % more lift and thrust. Under Indian conditions the combination of low wing area and lowered thrust means the airframe is reaching the end of its potential. As the Table shows the HF 24 airframe gives the same utiizable volume – possibly slightly more-and being a low technology aircraft it is going to be substantially cheaper than the Jaguar. Its performance as a platform will be superior to the Jaguar in every way and we have in the IAF very highly developed upgrading skills.

The HF 24 MARUT AIRFRAME

The Marut airframe has the following commendations:

1.     It is totally Indian as regards intellectual property rights are concerned.

2.     The design is all metal and the technology is sixty years old yet its performance on even modest engine technology is completely relevant today and its upgradability is high.

3.     It was built at a project cost of Rs.15 crores and less than 5 years which included capability to build at a modest rate of 16 aircraft per year.

4.     Its re-creation will not need large sums of money or “sanctionable” resources.

5.     Over 100,000 hours was flown on the type. It has proved to be strong and reliable.

6.     It is possible to manufacture single and two seat versions.

7.     Its performance as a platform is up to current needs and there is scope for further improvements by simple fixes.

8.     It has proven super cruise abilities being known to do Mach1 at 5000 mts. on the limited power of the B.Or.3. It should do Mach 1.2 - 1.3 with the simplest of the proposed engines.

9.     The aerodynamics of the aircraft made it a true “pilot’s aeroplane” - safe stable pleasant to handle and easy to land.

10.  For the same reason it requires less engine power to meet a set of performance requirements. This puts less stress on our engine design capability.

11.  Like all great designs it is naturally upgradable.

12.  It has almost double the “real estate” i.e. volume for stowage of future equipment of the LCA Mk1A making future addition of equipment quite easy to accommodate.

13.  It can accommodate a larger radar dish about 10 cms larger than the Tejas.

 

TWO PROJECT STUDIES

There should be two different project studies:

1.   To make use of the systems developed centered around the F404/414 engine based LCA. This will save a lot of the work. The flip side is that the rear fuselage of the aircraft would have to be almost totally re-designed following the F 5E/F20 process to eliminate a lot of unnecessary flight testing w.r.t. spinning.

2.   The second project study should aim at keeping the original airframe envelope as intact as possible and modify the above systems/engine gearbox etc as required as the engine outlet pressures and rpms would be different.

WEIGHT CONTROLAND THE POSSIBILITY OF NEW EQUIPMENT

Weight estimate: The HF 24 with the Orpheus B.Or.3 weighed 6150kgs.

The following obsolete will be stripped from the old aircraft:

i)               ADF                                                                                        11.44 Kgs

ii)             VHF ( 9XM2)                                                                         23.00

iii)           Radar Ranging                                                                        45.46

iv)            IFF                                                                                          22.00

v)             Gun Top pair                                                                             174.00

vi)            Gun Bottom pair                                                                        174.00      

vii)          Gun Camera                                                                            3.40

viii)        Gun Sight ISIS                                                                        14.75

ix)            Ammo.Box Top pair                                                               16.30

x)             Ammo.Box Bottom pair                                                         16.30

xi)            Ejection chute Top pr.                                                              3.09

xii)          Ejection chute Bottom pair                                                       5.09

xiii)        Feed Chutes Top                                                                         2.88

xiv)         Feed Chute Bottom                                                                    5.28

xv)          Link Chute                                                                                2.144

xvi)         Link Chute                                                                                2.144

xvii)       Pressure Box                                                                             43.50

xviii)     Floor                                                                                         16.50

xix)         Ballast                                                                                     134                                                                                                                     

The total saved would be around 712 kilos and another 50 kilos can be saved by changing the design of the pylons which were unnecessarily deep to accommodate the ML MK1A ejectors.  This weight savings will bring the aircraft empty weight 5430 kilos. Keeping a target empty weight of 6800 kilos for the Super Marut there is thus a prospect of 1400 kilos to be used to upgrade the engines and new NavAttack equipment on the first twenty aircraft. After fitting the upgraded engines (Up rated Orpheus) there would still 1100 kilos for new equipment. All this is without using a single gramme of composites whose reliable Indian supply is uncertain. With weight saving using composites (250 kilos), FBW (100 kilos) Carbon brakes, new electrical harness, 115 v A.C. systems there would be a further 500 kilos available for new equipment and 5^thgeneration systems. Beyond an empty weight of 6800 kilos recourse would have to be taken in cutting the fuel load down from 3300 kilos. In sum allowing for even the Modified Orpheus (aatmanirbhar, developable without consultancy) engines there is about 1100 kilos available to the designers to upgrade the aircraft nav. attack capabilities and about 1500 kilos if the HTFE 4000 meets timelines.

ENGINES

The engine problem, self- created, killed the Marut programme because the platform performance          was then too indifferent to urge its further development.

The engine therefore is going to be as important in the remanufacture programme as with the                  original programme. As can be seen in Tables 1 &2 there is a wide choice of engines that are                  commercially available. These foreign engines must be seen as “back- up” or supplementary to the         several potential “atmanirbhar” engine possibilities, namely:

1.     The Kaveri GTX

2.     The Kabini core of the Kaveri.

3.     The HTFE 4000

4.     The Orpheus B. Or. 12 redux

5.     The core of the Pegasus used by the Indian Navy. This is an “üp-to-date” (1970) version of the Orpheus compared to the 1955 version of Orpheus that we have.

A SHORT NOTE ON THE ORPHEUS AS THE PREFERRED ENGINE

There is a popular mis-conception that the fighter engine has to be a turbofan to be fully efficient. In fact the bypass ratio is way below anything to be effective and the two spool engines is chosen for other reasons  the “turbofan” thus being only a by- product..

A developed Orpheus engine is a strongly preferred option for the Super Marut second only to the lighter and smaller HFTE 4000 when it gets ready. At the speeds that the Marut operates there is little to choose between a “leaky” turbojet/turbofan especially if one considers the factor of Atmanirbharata” and the simple single shaft turbojet has much to commend it under combat conditions whilst the simplicity of the design assures low costs and assures good response to upgradations e.g. Electronic Fuel Control not necessarily FADEC. The following engineering packages are anticipated.

1.   Improvement of fit finish tolerance, reduction of tip clearances, change to a bigger fuel pump, and a “look” at the combustion chamber aerodynamics plus greater care and documentation during assembly should push up the thrust to 5600-6000 lbs (25-27kn) . Even without afterburner this will allow the Marut to supercruise at Mach 1.1 at 5000mts. Since this engine will only be Bench tested as a proof of concept engine and it may be possible to rebuild an existing engine (s) to the new standard.

 

2.   This would be followed by a more comprehensive modification of the engine and would include redesign of the turbine stage to take a higher TET so that a slightly higher mass flow and Pr. Ratio can be achieved resulting in a cold Military thrust 6600 lb.st (30kN)

 

3.     Second stage would be to develop an afterburner and to replace the mechanical AFRC with an electronic fuel control system, particularly for the “root T” parameter of the AFRC. Better control and less weight is expected. FADEC can wait at the initial stage.

 

Notes on the Super Marut specifications ( pl also see Table 1)

 

Dimensions: Both aircraft have the identical dimensions in terms of span, length Height and wing area. The following are the differences.

 

Engine Power : Prototype and systems test Aircraft approx. twelve will be equipped with Improved non after burning  Orpheus  of 6600 lbs thrust or 30kN. Production aircraft will be equipped afterburning Orpheus of 39 kN. Final engine –which can be fitted to earlier aircraft also will be the HTFE 4000.

 

Equipment fit: The HF 24 has the advantage over the other designs in having one of the biggest utilizable volumes. This is sufficient to incorporate all the Avionics and systems planned for the MWF/ AMCA. viz :

LRG

GPS

MC1 /MC2,

Cockpit MFD,

HUD,

Digital Moving Map,

Autopilot,

HOTAS,

TACAN,

IFF,

Secure Comm.,

VHF,

OBOGS,

RWR, 

AESA radar,

NVG,

HUMS,

TCAS,

GWPS.

 

A further conformal pack on the dorsal spine will increase this by another 1 cu.mts. Features of the design and the sturdy structure allows for designing highly serviceable access to all LRUs.

 

Weapons stations.

The Marut has four pylons stressed to 500 kgs loads. The design is weak and using modern concepts the weights and drag can be reduced. Another three pylons can be added in the fuselage centre section these can carry various pods though the Undercarriage will need redesign to allow full length stores to be carried. Over wing pylons for CCMs can be easily integrated.

 

Fixed Armament

Two GSh-1-30 30 mm cannons will be carried semi externally (MiG 21M/Bis style) under the fuselage with 125 rounds per gun 

Table 1: Super Marut Engine options:

1.     Twin engine (existing) aerodynamic configuration

Sl.No	Type	Thrust (kN)	Length (mm)	Dia. (mm.)	Weight (Kg.)	Mass flow (kg./sec)	PR.Ratio
1	Orpheus B.Or.3		1916	822	379	38.1	4.4	For reference only
2	Orpheus B.Or.12 modified	30.3/39.5	1916	822	460	43	6-10*
3	Honeywell F125	28/43.8	3150	914	521.6		25
4	AI-222-22F	25/42	3138	624	560	50
5	Adour		2971	762	809	50
6	Pegasus Core	?	?	?	?	?
7	Kabini	?	?	?	?	?
8	HTFE 4000	25/40	1730/?		350	43

 

·       The small pressure rise results in a bigger engine but makes for very stable operations and fewer technical development challenges whilst providing an adequate engine.

·        

Table 2: Engine Options

2. Single engine configuration

Sl.No.	Type	Thrust (kN)	Length (mm)	Dia. (mm)	Weight (kgs)	Mass flow (kg/sec)	Remarks
1	Kaveri	52 / 72	3490	986	1235	78
2	F404		3912	889	1036	70
3	F414	58 / 98	3910	890ivses	1110	77.1
4	M 88	50 /75	3538	696	897	65

 

The Orpheus max. diameter is 835 mm and the two engines together weigh about  the above table is an indication of the amount of “deepening” the Marut airframe will require to accommodate the single engine in the F5/F20 resurgey style. Reductions of weight and drag is expected even with the heavier Kaveri.

 

 Table 1: Marut permutations and comparisons

Sl.	Type	We.(Kg)	Thrust (kN)	Disp. Load (kg)	T/W (Clean)	Fuel Fraction	Fixed Guns	A.R.	W.L. (kg/M2)	VMax.SL(kts)	GIUV M3	Remarks
1	HF 24.Mk.1	6150	2x21.6	4713	0.49	0.54	4x30	2.9	310  / 387	600	15.8
2	MiG 21 FL	5100	39.5/61.20	3450	0.85	0.57	Nil	2.22	310  / 370	610	8.3	a)
3	HF 24 Mk.2	6450	2x27.4/36.3	8400	0.76	0.6	4x30	2.9	328  / 530	610	15.8
4	Jaguar	7000	2x 24.56/37.3	8400	0.68	0.7	2x30	3.12	408  /  637	713	16.3	b)
5	Kaveri Marut	6800	49.84/79	8600	0.76	0.76	GSh2-30	2.9	367  / 550		16.3
6	Marut F 124	6500	28/44.5	8600	0.85	0.78	GSh2-30	2.9	357 /  546		16.3
7	Tejas Mk1A	7040	50/78	6400	0.78	0.46	GSh 23	1.7	264 / 370	n.a.	8.25	c)
8	MWF	7700	58/98	9800	0.9	0.59	GSh 23	1.7	310 / 426		9.8

 

Notes:

a)      The development of the HF 24 Mk.2 would have made the import/production of the MiG 21, Jaguar and the Hunter F56A –about a thousand aircraft - unnecessary. Compared to the HF24 Mk2 the MiG 21 FLs load- range was pathetic.

b)      GIUV is the volume of the airframe available for storage of fuel and equipment after subtracting the volume required for the cockpit and the propulsion system i.e. engine inlet, engine and jet pipe. It is an index of upgradability. The Marut’s “balance” of design is reflected in the figures. It can be “expanded”or “upgraded”.

c)      The MWF has a lower wing loading but the amount of space is much lower and its prospects is not confidence inspiring. The Marut is a happy balance.

d)    Specific Fuel fraction is total internal fuel divided by total full cold thrust.

Remarkably both the Marut and the Jaguar have approximately the same GIUV. The Jaguar, optimized for the low level DPSA role is on its last legs because of its high wing loading. This may have been a factor in non-selection of the Honeywell F124 upgrade because the “small wing”. would have not been able handle to the full the improvement offered, as was the case of the F 20 by the F 404. The Marut’s wing is 16% bigger in area. In the 1980s BAC had proposed a big wing Jaguar!  The HF 24 of course could increase its MTOW by at least another ton.

Table 1: Super Marut Engine options:

2.     Twin engine (existing) aerodynamic configuration

Sl.No	Type	Thrust (kN)	Length (mm)	Dia. (mm.)	Weight (Kg.)	Mass flow (kg./sec)	Remarks
1	Orpheus B.Or.12	30.3/39.5	1916	822	379	38.1
2	Honeywell F125	28/43.8	3150	914	521.6
3	AI-222-22F	25/42	3138	624	560	50
4	Adour		2971	762	809	50
5	Pegasus Core	?	?	?	?	?
6	Kabini	?	?	?	?	?
7	HTFE 4000	25/40	1730/?		350	43

 

Table 2: Engine Options

2. Single engine configuration

Sl.No.	Type	Thrust (kN)	Length (mm)	Dia. (mm)	Weight (kgs)	Mass flow (kg/sec)	Remarks
1	Kaveri	52 / 72	3490	986	1235	78
2	F404		3912	889	1036	70
3	F414	58 / 98	3910	890	1110	77.1
4	M 88	50 /75	3538	696	897	65