The Indian 5^th generation- an axiomatic review

Part 2 of 3. The glister of technology engine power vs supercruise

Prof. Prodyut Das

23rd January 2026

 

Super cruise

Super cruise is not new. It is being repackaged. The HF 24 with its ancient Orpheus engine could do about M 1.1 and the GAMD Super Etendard reached M 1.2 without afterburning for its ATAR 8K 50 both aircraft having simple “fixed” intakes. With variable intakes that could go up by another 0.1- 0,15 M i.e. M 1.3- 1.4 is possible. So if you want super cruise, you don’t need wonder engines. The old ones would do. (see table later)

The catch is that if you add “stealth” to the menu it needs an internal weapons bay of at least 1.0- 1,6mts x 3,5 mts x 0,5 mts; Supersonic aerodynamics is “funny”- apparently the drag penalty of the “sow belly” is not so much as you expect but the thrust required would go up by another about 30kN over and above the installed thrust of a HF 24 or a Super Etendard. So if you re-designed a Super Etendard or Marut airframe to have the internal bomb bay you would need 80 -90 dry instead of 50kN and 40 kN. Getting 80 kN dry out of Kaveri technology is possible.  This is where the knife twists.

Super cruise is defined as > Mach 1.6. not by me or the holy Angel Gabriel but by Western Journals who have decreed that a “pedestrian” Mach 1.1 or 1.2 is not super cruise why so being un-explained. Now as a rough mental calculation that M 1.6 on the top of a sow belly would add another 32 kN. You are now looking at needing an engine with a dry rating of 112 kN to 102 kN respectively. The snag is that 120 kN is beyond the Kaveri’s and our technology reach.

If on the other hand we accept M 1,2 the Kaveri, with new management can handle the required growth. Who inserted super cruise at M 1,6- M 1.7? It made foreign collaboration necessary. Why? Was it debated and the IAF asked how M 1,6 was vitally necessary and M 1.2 unacceptable? I say it does not add value in India’s context. It is also my doubt that these kind of discussions and options and tradeoffs do not take place because these are the soft knowledge “buttresses” that our scientists leading the serial failtoo projects evidently lack.

Some very basic engine fundas relevant to this case given below. The explanations are:

i)                  Any engine with a certain level of thrust/ engine frontal area and thrust to mass flow ratio can be made to super cruise. Once such engines became commercially available the rest was marketing.

ii)                What is hidden in discussions, is the engine at super cruise, even though not using reheat will still burn much more fuel than in subsonic cruise. Super cruise requires tanking up roughly every hour. Without strong FR ability it is an fancy feature. The cost of the IFR capability should be added to the project cost.

iii)              The development of a “super cruising” engine will require very difficult technologies. Who will we approach for an alternate to the failed engine?

iv)              Supercruise is “better” but not to the same degree for India as against the US which must post over land and sea in haste?

v)                Super cruise at M 1.6 has to be ruled out except on a small simple “Sniper” where the Kaveri base will do.

Table 1 An index of engine development challenges

Sl.No	Parameter	A	B	C	D	E
	Engine	Orpheus	Atar 8	F 404	Kaveri	PW F119
0	Build year	1950	1960	1970	1990	1990
1	Aircraft fitted	HF 24	Super Etendard	Tejas	n. a.	F 35
2	Mach no./ dry thrust	1,1	1.2	?	n. a.	1.6
3	C.R. (x:1)	4.4	6.15	26:1	21.5	25*
4	Dry Thrust kN	22	49	49	52	116
5	Impulse kN /kg m.f	0,56	0,68	0.7	0,66	116
6	TET (0 K)	920	1170-1220	1390	1487-1750	1922
7	kN /Frontal Area m2	40	60	78.7	79	107

 

These tables derided as “school boy” (by some) have their utility in placing the picture squarely. the comments are indicative.

If you look at Sl. Nos 5 and 6 of engines B, C, D it shows:

a) the Kaveri in spite of its advanced mechanicals is at the technical level of the simpler single spool 1960s French engine rather than the 1970s US . I mention this not for criticism but to show room exists for improvements without collaboration.

 b) the Kaveri “as is” should easily go to about 56 kN. from the present 50 kN. 6 shows the level of the shortfall and the certainty of achieving it.

 c) 6.7. C, D indicates the possible culprit; the efficiency of the spools of the Kaveri well is below the ATAR and F 404’s. It is absorbing too much energy for the job it is doing, Turbine and brake power mismatch is a well-known and common problem in compressor turbine assemblies. May be this is a bad case.

It is my hunch that this extra energy absorbed by the blades leads to rupture of the blades through vibration which the Kaveri has stubbornly displayed. If we improve the rotor efficiency the blades will stop rupturing. We do not need foreign collaboration; Engineering is not all slide rule and computers. It is also guesses, hunches and day dreaming. We may need funds but most of all need engineers who think.

d) The Pratt & Whitney F 119 has an output 107 kN/M^2. To get 120 kn dry from the same size as the Kaveri we will be looking at a specific output of 184 kN/M^{2 i}. Who is fooling whom? Is the collaboration going to end up in “Sorry, we overpromised and under delivered”. On the other hand, a Kaveri enlarged (from 989 to 1200 mm dia.) to the size of F 119 will, at the present level of technology will give us 100 kN. The other is to re look at the Bristol Pegasus samples (now in museums) which gave 100kN with 1965 technology and should go up to a cold thrust of 120 kN after treatment with Kaveri technology? Who proposed collaboration?

 We have many safe options based on engines already existing in hardware form. This collaboration is technically unjustified. Who proposed or advocated such a proposal.

The need to analyse the specifcations

 A high super-cruise speed is better – if politically possible. Post 1971 the IAF insisted on “supersonic” performance for its front- line aircraft. They cite examples e.g. the loss of Sqn. Ldr.  Jal Mistry (KIA), whose Hunter was shot down by a pair of Mirages whilst returning from a strike on Kohat which is a deep strike mission at the limits of the “Blue” Hunter’s (F Mk.56A) range. How much can be blamed on the speed difference between the Mirage IIIs and the Hunter and how much should be blamed on other factors- in this case numerical inferiority and the high risk of the deep penetration sortie itself? Performance in one area comes at the cost at loss of performance elsewhere.

Sqdn. Ldr. Mistry took off alone and after successfully completing his mission was bounced by two Mirage IIIs. Once engaged, Sqn. Ldr. Mistry’s chances of survival were one fourth because he was outnumbered two to one. He would have a four times better chance to survive had he flown with a wing man. Note at no time did any of the aircraft involved go supersonic. So can we review the super cruise speed. Just for the history buffs- Saiful Azam, flying a Hunter in Iraq downed two Isr.A,F, Mirages, a Super Mystere and a Mystere IVA under a more even tactical situations.

Quiz means to teach by asking questions. The important idea is not to thwart the customer but to learn from each other so that the best solution can emerge. What I emphasize is that every customer demand has to be examined and debated the price in terms of performance, availability and costs shown to him. This is a capability which the defaulting DRDO labs. and ADA lacks,

Stealth

It is possible stealth was prioritized after the Isr.A.F was thrashed in the opening phases of the 1973 Ramadan War. They lost 110 aircraft in 48 hours. The US started the stealth programme in 1974. The following are some general fundas about stealth.

1.      Stealth extracts a serious penalty in terms of cost performance and serviceability.

2.      It is a restricted use scenario and capability. This is why very few true stealth aircraft are produced and not all countries have them.

3.      100% stealth is available only for night operations. In day operations the stealth aircraft is handicapped and in WVR combat it is severely handicapped.

4.      Stealth is compromised very rapidly with diminishing distance- close enough and even a Ghost will be seen.

5.      A fifth generation by logic cannot destroy another fifth generation. BVR missile are useless as an anti -5^th gen armament.

6.      A fifth generation operating singly against a fourth generation high over a flat earth will massacre the 4^th generation. However, factors like Terrain, supporting AWACS, the sensor fusion level of the 4^th generation all will diminish the difference. The degree has to be worked out by informed discussions.

7.      Stealth design is misunderstood. Some small aircraft have naturally low RCS e.g. MiG 21 and Gnat but some aircraft like the Avro Vulcan of 30 mts wing span had low RCS despite not being made to stealth standards.

8.      Stealth extracts a severe penalty in small fighters because of the need to carry missile internally but the penalty diminishes as the aircraft is larger. The Chinese have used this physical factor in their large J 20 and H 36 and having developed the technology applied it to their Dolly 5^th J 35.  We should try a large subsonic true or prime 5^th gen instead of AMCA.

So in sum

1.      Engine collaboration is not indicated.

2.      Our present situation has been arrived, in the defaulting cases almost by plan. Amateurs playing with public funds, without accountability and any fear of reprisals and callous of the customer have led us to this present where imports are necessary whereas the professed vision was of avoiding future imports.

3.      The fact that there has been remarkably excellent products developed means that the system can work. Local failure of leadership is to be blamed.

Whatever has been achieved has largely been by using only a part of our Industrial strength. What we can achieve by professional re- organization is bey