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 3rd
generation
The 3rd
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 3rd
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 3rd 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 2nd generation. The 3rd 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 “5th 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.
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—17stage
compressor and a 3- stage turbine. The French went in for a single
spool 8C plus 1T ,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+1T.
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 R11 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 table2) 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 R11 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+3C, 1+1T |
1040/1205 with A/B |
8.6: 1 |
1170 |
0.95/ 1.96 |
3880/ 5110 |
2 |
GE J 79-7 |
17C,3T |
1532/1745 |
13.5: 1 |
1210 |
0.84 |
5361/ 8500 |
3 |
ATAR 9B |
8C+1T |
??/1155 |
6.1: 1 |
|
0.97 |
4150/ 5900 |
4 |
Avon 300 Srs |
15C+ 2T |
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 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 4th generation 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 turbocooler 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 and 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 re-designedd 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 sstory,
7. Canberra B ( I) Mk58 being trialed possibly for the Rushton Towed target
8. DH Tiger Moth ( scrapyard)
9. HT2
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.
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