The Mig 21 – a tribute to its engineering                         Prof. Prodyut Das

 

05 October 2025

 

The STC or the State Trading Corporation - one of whose activities was to collect cars left behind by “posted out “diplomats from the Embassies and organize their auction- paid their GETs a basic pay of Rs.950. We, the PGETs of the Design Bureau of the Hindustan Aeronautics Limited (HAL) were paid a basic of Rs.550. In the Orwellian society of Socialist India, all were equal but PGETs in Aircraft design were less equal, than the Raisina nephews working as GETs for STC. However, if you were crazy enough about aeroplanes the HAL job, though barely affordable to keep, had its compensations. You could slip off your stool any time and walk through the hangars and workshop and it was like walking through the caves of Ali Baba. One saw unicorns (note 1) and the work of legendary Masters- Mikoyan- Gurevich, Petter and Tank. Not only did you wonder at the genius of the overall solution but also you could compare their solutions to particular problems. To purge the gun gas from the gun bay Tank used an electrically actuated scoop and a timer. MiG – used fixed scoops and vents and Petter used the 19 mm recoil of the Aden to kick open a “door closer” type aggregate. But I am getting carried away. The retirement of the MiG 21 has brought forth an outburst of deserved gratitude and affection. I did not work the work that the pilots and groundcrews did but “they also serve who stand and wait” so here is my tiny salute to a masterpiece by pointing out some of the thinking.

The 3^rd generation

The 3^rd generation included the 4 single engine aircraft, F 104. MiG 21. Mirage 111 and the Draken. In addition, there were two twins, the EE Lightning and the HF 24 Marut. I have no hesitation to say that the HF 24 Marut was the masterpiece of them all. If we had a professional led aeronautical Industry what Indians would have done with that magnificent airframe beats thinking.

The 3^rd generation was a “mongrel” generation- partly conventional fighter, partly a manned SAM. Its “fighter” part of the specifications were compromised to include a very high rate of climb, a Mach 2 capability and the capability to destroy large structures as in Jet bombers i.e. be a fall back in case SAM development were delayed. This led to the frequent appellation of “a missile with a man in it”. The distinguishing marks of the 3^rd generation were – a search and ranging versus the earlier ranging only radar, heavy cannon, IR missile capability, M2 speed and climb rates in excess of 7000mts/min with the addition to receive GCI instructions. all needed to destroy jet bombers like the TU 16 and the B 52 under all weather.

This capability came at the cost of a 30 to 40% increase in weight, size and power an increase, over the typical 2^nd generation. The 3^rd generation was also a totally European requirement, The IAF had no need for a nuclear bomber interceptor capability and therefore for the argument’s sake, no need for the M 2 speed in the specification of the HF 24. Did it affect us? It did. Remember we rejected the free of cost tech transfer for the eminently suitable Tyumanski RD 6 because it was stressed only to M 1.6 and the Russians - quite understandably- point blank refused to develop (the engine they were going to “scrap”!)  to our “needs” of M 2.  An early example of how we screw up our own development task. The current nonsense about building an “US specifications -world class ” AMCA without knowing or attempting the first thing about how we can have a “5^th generation Indian” stirs the old wounds of shooting oneself  in the foot.

The Brute Force Aeroplane.  

The MiG 21 was the first IAF aeroplane with an afterburner and so we had the “Ignorami” (yes! We had them even then!) who would cockily say “MiG 21?! Russians! Brute force aerodynamics!”  Nothing could be further from the truth. It was a most carefully thought-out design, undoubtedly different but full of careful, stoic Slavic common sense. The loud braying “Experten” completely overlooked that the allegedly brute force MiG 21 was, in fact, the lowest powered, lightest “Mach 2” fighter in the business. The Table below is indicative.

Table1.

All units MKS

Sl.No	Aircraft	Thrust (D/AB)	Dimensions	Dry Weight empty
1	MiG 21F	3880/5740	7. 15  x 15,76 x 4,1 ,  23 m2	4871
2	Dassault Mirage IIIA	4150/5900kg	8. 22  x  14.73  x 4,253 Wing area   34,85 m2	5300
3	Saab Draken A	5640/7280	9.40 x 15.35 x 4,2 Wing area 49 m2	5800
4	Lockheed Starfighter F 104A	5361/7850	6.63 x 16.66 x 4.09 19.6m2	5788

 

The approach to the problem

Given the identical same task the different approaches to the solution is extremely interesting. France, lacking any SAM, focused on the bomber intercept role. It selected a tailless delta, pretty inadvisable for most roles but perfect for this high altitude, low STR work with its large wing area for low density atmosphere at 15000mts, excellent fuel volume and low supersonic drag besides being easy to fabricate, The Swedes went pretty much the same way i.e. tailless delta but having a STOL requirement threw in another 14 sq. mts. of wing area and one and a half ton more thrust. The Americans in the F 104 apparently forgot about the wings until quite late; It was an intrinsically limited aeroplane and when the USAF lost interest (they bought only about 290) they conned everyone else to buy this under winged thing in the close air support role.  Most of the 2500 plus built went to others via NATO which is the marketing arm of the US Banks who, it seems to me, if not actually writing the specifications, probably gives the approval. The Russians recognized the advantages of the delta but ameliorated its weaknesses by fixing a stabilizer. Decried in the Popular Mechanics and Popular Science of that time for being “draggy” the arrangement was in fact, a war winning solution- a stunning performance, adequate equipment and capability at an affordable price. A little tit bit: The TsAGI tried out the tailed delta concepts and gave the data to the OKBs. Apart from MiG, Sukhoi used the data for the configurationally identical Su- 9 and the same tradition of hard headed applicable research continues, witness the similarity between the MiG 29 and the Su 27/30. TsAGI does not dabbles in mainline projects leaving it to professionals with facilities.   

Intakes

The MiG 21 was the lowest powered and lightest of the “genuine M 2 single engine brigade” of third generation fighters. One of the reason the MiG 21 could return a phenomenal performance at low power was a simple but highly developed intake system. It had a three position two shock cone right in the nose which, for a reduction of over the nose visibility (not something the average Spitfire pilot would have at all minded) gave very high ram pressure recovery, and a simple but carefully thought-out intake system that ensured the engine got exactly the amount of mass flow it could handle -there were three dump door and two plus two suction doors all spring loaded. This improved supersonic performance at low cost in terms of weight. How much did that help? I don’t know for the MiG 21 but I read that the early Mirage III when fitted with a – now hear this – manually-adjusted “Souris” (mice’} shock cones in the intakes the speed achievable went up from M 1.5 to 1.8! I have emphasized “manually” because it highlights the “suck and see” nature of design refinement. The French did not spend time pondering and then further time developing a final automatic extension system straight away. They rigged up a system to see if the idea worked then threw in the resources to formalize it for production. Funds? Funds are needed / useful only if you have the ideas, the attitude and something tangible in terms of practical data to back your demand for further funds.

The Engine

The difference between the West and the USSR again shows the stoic Slavic approach to the engine design. The West wanted the best, the USSR - something that would just do the job reliably. The Americans used the J 79 for their Starfighter and to wring the best sfc went in for 17 stages compressor, yep you heard that right—17 stage compressor and a 3- stage turbine. The French went in for a single spool 8 C plus 1 T ,essentially the much modified BMW 003 ( shows how much TLC works in turbine engine development) and the Swedish chose to use the RR Avon which, similar to the J 57, with a 15- stage compressor and a 3- stage turbine. The Russians? They knew of the two- spool technology, possibly from the Germans and used a two-spool layout 3+3 C+,1+1 T.  Result the Russian engine was about a 100 to 260 kilos lighter than the French and British engine and about 700 kgs lighter than the US. The US engine had the lowest sfc at 0.84 as compared to 0. 95 of the R. 11 but who was right? The 0.11 s.f.c. reduction was important if your sorties have a heavy load of Transcontinental positioning flights; a 4 hr flight, gave half an hour extra may be one less “hook up” so the J 57 with its 17-stage compressor made sense. USSR was planning to have 45 minutes sorties a 0.11 kg/kgp improvement would perhaps give 5 mins more, the two-spool turbojet of lighter weight made sense. The much lower compression ratio and TET of the R 11 (see table 2) also made for the lower efficiency but how much? After all these two parameters contribute only as their reciprocals i.e. a case of diminishing returns. The R 11 made more sense because it was “good enough” for the job and yet was lighter, cheaper and could be developed quicker with less problems as it was challenging the current “safe” zone less. They say that the R srs, even the R 25 had fewer parts than the little GE J - 85 series. Another interesting point was that the Russians focused more on getting the dry thrust portion “happy” and relying on up to 3 stages of afterburner to get the desired max. thrust levels which are in any case used sparingly. Never mind what I think. What seems more sensible to you?

 

The other point is that the engine TBO was low may be about 250 hrs but mathematically it was such that, should a conflict break out the probability of having to change an engine during the conflict would be almost nil. The aircraft would be lost in combat before that. I have put it down the table at the end and you can mull over it. Believe me it is full of interesting dialectics and conflicts of interests!

 

Sophistications amidst allegedly crude design

 

One small point. The R 11 engine had an oxygen relight system. To ensure relight, especially at high altitudes, the engine was fed with gaseous oxygen to ensure a relight. A quiet sophistication I am not aware of in its contemporaries. Talking of sophistication of thinking I have in my earlier writings mentioned the CK (Seydla Katapultiniy) 270-300 mt seat. Despite its low altitude restrictions, if you were going to attack a B 52 at 13000m and had to bail out at M> 1, you couldn’t ask for a better seat in terms of reliability or blast protection. The B 52 had a Gatling “stinger” in the tail so perhaps the need for hi- altitude bailout was more than the need for low altitude bailout. The later KM_1M was something like a Douglas Escapac but the shoulder restraint arms were formidable.

 

Table 2

ALL units MKS

 

Sl. No.	Engine	Configuration	Weight dry/with AB	C.R.	TET 0C	s.f.c. dry/AB	Thrust Dry/AB
1	R-11-30	3+3 Ç, 1+1 T	1040/1205 with A/B	8.6: 1	1170	0.95/ 1.96	3880/ 5110
2	GE J 79-7	17 C,3 T	1532/1745	13.5: 1	1210	0.84	5361/ 8500
3	ATAR 9B	8 C+1 T	??/1155	6.1: 1		0.97	4150/ 5900
4	Avon 300 Srs	15 k+ 2 T	1310 /	7.45: 1		0.932/ 1.85	4895/6535

 

 

The undercarriage

 

A M 2 warplane will have an aerofoil t/c of less than 6%. In the Starfighter that works out to be about 250mm. Too thin for anything, even fuel. The consequence was a fuselage mounted undercarriage of poor track width. Imagine landing at 300 plus kmph in a cross wind on a narrow track. The MiG 21 wing thickness was slightly better but brilliantly concepted. The broader chord of the Delta permitted a thickness barely sufficient for the u/c strut to retract inward. This was done and the wheel, which rotated to remain vertical, was tucked into the fuselage hard against the engine inlet duct. In doing so the top and bottom of the tyres “broke” through the tubular fuselage surface which was about 1.3 mts diameter at this point. The “breaks” were faired over by local streamline bulges. The effortlessly  confident ,flow of problem solving was almost like watching Grandma cook. The arrangement resulted in the MiG 21 having both relatively low-pressure tyres and a wide track – always a welcome feature when landing.  Another interesting “deviation” was that even the nose wheel had brakes. It probably reduced the turn around time in waiting for the brakes to cool but I don’t know.

 

The ECS approach- a comparison

 

The joke was that if the Gnat and the MiG 21 had air conditioning, it was secret. The Gnat and the MiG 21 had the identical a/c system- a “turbo fan” circuit. The bare bones of it was that the Engine air was bled off a choke, passed through a heat exchanger, and fed into a inward flow radial turbine. The turbine was connected to a fan which loaded the turbine which caused the air enthalpy and therefore the temperature to drop to about 4 ⁰ C which was then was passed into the cabin after extracting the condensed moisture. The output of the fan was used to cool the engine bay. You will note the Gnat does not have any ram air scoops for engine bay cooling. The simple layout had problems. At high altitudes the air density goes down and the turbofan, rotating at 95,000 rpm would overspeed. The trick was to use a pressure reducer but that was wasteful and added weight. The Gnat didn’t need it because the Orpheus had a PR of only 4.4 which was pitiful to begin with. In the MiG 21 the engine had a PR of 8-10 so the problem would have been encountered. The MiG 21 countered the problem by i) using a cantilever inward flow turbine which has self- regulating overspeed characteristics and ii) the brake fan plenum was connected to the engine intake duct so that it was always working at a pressure in sync with the engine bleed pressure. It was brilliant see all all by detail thinking that worked even if the execution was “crude”. The 2130 model Turbocooler had hammer tone finish!

 

Every aspect of the MiG 21 showed deep thinking and left lessons for the aspiring designer. My list would be;

 

1.      More is not better. There is always a price.

2.      As the 4 examples shows the identical problem can have several solutions. All must relate to the user’s local scenario.

3.      The MiG 21 was ridiculed when the first example was examined in 1967. Its differences with Western ideas were held up as crude engineering and it’s different approach was publicized as lack of capability. This was Western Marketing.

4.      The MiG 21 combat record when flown by pilots of widely varying levels of skills showed the excellence of the design, its versatility and developability.

5.      The excellence came from very profound application of basic science with frugal engineering.

6.      Lessons specific to India? An aircraft cannot be good merely by bringing several advanced technologies together into one airframe. As the example of the undercarriage or turbo cooler shows the features must be adjusted to accommodate one another into a harmonious whole.

7.      The comparison of weights indicates that the Tejas MK1A needs further weight improvements . It would become another class if the weight is brought down to around 5500 kgs.

                                                                                                                 

Note 1

Amongst the aeroplanes I saw and could examine in detail at HAL- and by detail I mean literally crawling over them were:

1. Curtis Commando belonging to a Latin American airline

2. Noordyun Norseman- stripped off its covering or possibly a local copy thereof.

3. The HA 31 Basant 1. It failed to move out of ground effect but was quickly designed to ger teh MK 2 of which 32 were produced

4. Zlin Trainer 146(?)

5. de Havilland Dove

6. De Havilland Vampire - the security guard caught me but that is another story,

7. Canberra B ( I) Mk 58 being trialed possibly for the Rushton  Towed target

8. DH Tiger Moth ( scrapyard)

9. HT 2

10, Marut incl the surviving reheat version

11. Gnat

12. HSS 73 mock up

13, MiG 21

the  first two were rare as unicorns !

 Of aircraft in transit- any number- AN 12, Alize, Harvard, Avro 748, Hunter ( this one had downed a Sabre) Su 7s. I remember crawling around in teh AN 12 turret almost sea sick with teh lurching when anxious feet scrambled up to me. "I have left some custard apples here" the Engineering Officer of teh flight that had jut parked teh aircraft said. I thought he was more worried about the safety of  his precious custard apples than teh giant 4 engined aircraft for he left me alone to continue with my examination.