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| HAL HF 24 Marut |
This is the story of India's first indigenously designed jet fighter the HF-24 Marut. It was a landmark achievement for the 1950s and 60s and I don’t wish to take anything away from that. Nevertheless this tale is narrated with what I hope is a balanced objectivity and not a nostalgic applaud. I have tried to balance between things we can be proud of, things we didn't do so well and lessons we ought to have learnt but may not have.
CONCEPTUALIZATION
India, in 1955, was a young nation full of enthusiasm for building the economy. A lot of projects were tried for the first time under the national objective of creating our own manufacturing and design capabilities. One such endeavour was to design and build in India, for the first time, our very own jet fighter. This was ambitious to say the least at a time when we had just started assembling diesel locomotives, had never built a major ship, had just started assembly of motor cars, possessed little aluminum smelting capacity etc etc. This was Pandit Nehru's vision and the IAF (Indian Air Force) enthusiastically went along. At the time of the Marut's conception, the domestic aviation industry's only design experience amounted to designing and manufacturing the HT-2, a piston engine propeller driven trainer. Whatever aircraft manufacturing capability existed resulted from the license assembly of the Vampire Fighter Bomber FBMk.52 and Trainer TMk.55. To have considered building a supersonic capable aircraft, given such limited capabilities, bordered on audacity. The only aircraft manufacturing capability lay in Hindustan Aircraft Ltd (HAL) set up by Walchand Hirachand in the 1930s and nationalized by the Government subsequently.
The HT-2 propeller driven primary trainer, this represented the only indigenous design capability in India at the time of the decision to design & build the Marut. The HT-2 was designed by Dr VM Ghatge and served the IAF and the Army Aviation Corps for 25 years. 172 were manufactured of which 12 were exported to Ghana.
The building of the Marut (Spirit of the Tempest), as this aircraft was to be called, was the first attempt of its kind anywhere outside the four major powers of USA, USSR, UK and France to build a supersonic jet fighter. Whatever else one might say the gumption deserves admiration. The political, bureaucratic and I dare say military hierarchies did not have a proper appreciation of the supply chain infrastructure and quality control challenges that would need to be overcome.
AIR STAFF REQUIREMENT
The Marut was conceived to meet an Air Staff Requirement (ASR), that called for a multi-role aircraft suitable for both high-altitude interception and low-level ground attack. The specified performance attributes called for a speed of Mach 2.0 at altitude, a ceiling of 60,000 feet (18,290 m) and a combat radius of 500 miles (805 km). Furthermore, the Air Staff Requirement demanded that the basic design be suitable for adaptation as an advanced trainer, an all-weather fighter and for 'navalization' as a shipboard aircraft. It was directed that this aircraft be developed within the country. Nations with advanced military design and manufacturing capabilities rarely, if ever, put out specifications that are such all singing all dancing renditions. A military aircraft is designed to play one role well, a second role moderately well and sometimes , only sometimes, a third role in a limited form. Unfortunately out of lack of experience (and in my opinion a willingness to apply common sense) the Air Staff Requirement was too wide and reflected lack of clarity of aims and a complete lack of understanding of what it takes to design and build a fighter as opposed to flying one. It is like saying - I want a car that drives like a BMW 3 (Mach 2.0), suitable for both high and low altitudes (drive well on a race track as well on Delhi's rutted roads), can carry payload like a Isuzu D-Max pick-up (low level ground attack payload) and have the toughness of a 4-wheel drive cross country mud slogger (capable of all weather capabilities & navalization). The combat radius of ~800 kms was beyond the ken of the most efficient fighter turbojet even in the USA of the 1950s. These ranges were not achieved till military turbofan engines like the Rolls Royce Spey (on the Hawker Buccaneer, 1960s) or Rolls Royce Adour (Sepecat Jaguar, 1970s) amongst others came into play. All weather was at best in an experimental rudimentary stage even in USA and USSR in 1956 and no IAF aircraft of 1956 even carried a gun ranging radar let alone a search & track one. While I don’t wish to be too critical these were overly ambitious specifications for 1955 even for the UK, France or USSR. As an aside, it might be worth noting that the ASR for the current Light Combat Aircraft (LCA), Tejas, in mid-1980s, followed the same concept of all singing all dancing and (partly due to that) it is sadly still some way off from full operational service 30 years later. The only other aircraft of the 1950s and 1960s that was designed to similar specifications as the Marut and carried a requirement for navalization + all-weather was the legendary McDonnell Douglas F4 Phantom of the US Air Force and Navy. And let's remember the Americans were then and today the foremost in aviation R&D, design and production know-how. And even with the Phantom the Americans lost out on maneuverability.
Dr VM Ghatge, India's senior most aeronautical designer was the only voice against the Marut. He prescribed a more balanced step by step approach to building the nation's aviation industry by first designing & building propeller trainers, then basic jet trainers, then light attack fighter-bombers and then a more advanced light multi-role fighter and to do this in stages over 2 decades. In retrospect his was, in my opinion, the more sensible approach. But Ghatge's voice was drowned out.
Nehru tried to attract leading aeronautical designers from the west to work for India on this project. It was to his credit that he convinced Dr. Kurt Tank (of Focke Wulf fame) to take up this assignment along with his able deputy Engineer Mittelhuber. Both arrived in Bangalore in August 1956. As head of the design team it was Kurt Tank who would give the design shape and substance.
HAL in 1956, possessed only three senior Indian design engineers and the entire design department boasted only 54 personnel. It had no hangar space for construction of prototypes, no machine shop for prototype engineering, no suitable test equipment, structural test rigs or a flight test laboratory. In fact even the runway length was inadequate for a jet fighter prototype. It is to the credit of HAL team of that era that all this was created from scratch while Kurt Tank built up the design & prototype team of over 850 personnel including 18 German designers.
DESIGNING & BUILDING THE MARUT
A full scale representation (wooden glider) of the projected fighter was ready by early 1959. A test program was initiated with this glider on 1 April 1959. The new design was given the designation of Hindustan Fighter 24 or simply HF-24.
Glider tests for aerodynamics started in April 1959. 78 test flights were conducted with the gliders which were released between 12,000 and 15,000 feet altitude. Use of wooden gliders was an integral part of Kurt Tank's style of design testing.
Assembly of the first HF-24 prototype (HF-001) began in April 1960 and after a comprehensive three month ground test programme, HF-001 (later re-numbered BR 462), with the late Wing Commander (later Group Captain) Suranjan Das at the controls, flew for the first time on 17 June 1961. In the circumstances this was a commendably short period of 15 months from starting to put together the prototype to first flight.
HF-001, the first prototype was first subjected to several days of ground run testing to check if at a basic level the controls, engines, fuel systems, hydraulics, electrics actually work in co-ordination.
Wing Commander (later group Captain) Suranjan Das, India's foremost test pilot, flew the HF-001 for the first time on 17th June, 1961. He led the test flying on the Marut as well as the later Kiran jet trainer. Earlier he had led the test flying for the Gnat. Tragically, he was killed in 1970 when testing a more advanced version of the Marut.
On 27th June 1961 they built up enough confidence and test hours to show case the prototype to Prime Minister Nehru. The prototype was re-numbered BR462. By November 1961, a structural test airframe had been completed and was subjected to extensive structural and functional tests in rigs designed and fabricated at Bangalore. On 4 October 1962, a second prototype (BR 463) joined the flight development programme and the two prototypes were extensively tested by Das and a team of three Air Force test pilots for aerodynamics & stability, engine protocol, armament, instrumentation, emergency procedures etc. It was a remarkable achievement for its era. India became only the 6th country to design and fly its own supersonic jet combat aircraft after USA, UK, USSR, France and Sweden.
SEARCH FOR A SUITABLE POWER PLANT
The design of the HF-24 had been based around the expected availability of the 3700 kgf (kilogram force) afterburning Bristol Siddeley (later Rolls Royce) Orpheus engine which the British planned to develop. An after burning turbo jet is one in which fuel is injected and exploded in the hot exhaust of the jet (behind the turbines) which still has some oxygen in it. The resultant combustion of pure vaporized fuel into a red hot efflux blasting rearwards at hundreds of metres per second results in a rocket like acceleration and very high power to weight ratios. Afterburners consume prodigious volumes of fuels and are usually used when high thrust is needed for a few minutes. Unfortunately, the British requirement for this power plant was discarded and the Indian Government in a short sighted decision declined to underwrite its continued development (to Rolls Royce) even though the budget was only £13 million not a large sum even by the standards of 1961. This decision was to bedevil the Marut programme permanently. The design team was forced to adopt the non-afterburning 2200 kgf Orpheus 703 which powered the Gnat as an interim solution. It was an utterly reliable engine but with inadequate power for the Marut. We evaluated the Soviet Tumansky RD-9F that powered the contemporary Mig-19. The Tumansky powerplant had a full thrust of 3750 kgf with afterburners and put it just right for the Marut. But for reasons I don’t fully understand the Tumansky engine was rejected on grounds of surging and limited MTBO (Mean Time Between Overhauls). Speaking in favour of the Tumansky RD9F it was a rugged engine, had great acceleration, was resistant to ingestion of dust, mud and ice and went on to power the Soviet Mig-19, Yak-25, the Chinese Shenyang J-6 & Nanchang Q-5. It is popular in Western literature to decry the old Soviet engines as having a lower MTBO. What is less understood is that between the two MTBO points this Soviet engine needed little care & maintenance. However, I don’t want to be harsh in judging those who took these decisions as I have not stood in their shoes.
The lack of an appropriate power plant meant the Marut could not fulfill its role as an interceptor though the scope of being a reasonable ground attack fighter-bomber was very possible. A lot of hard work by Kurt Tank and team, by HAL and by Suranjan Das who led the team of test pilots did help mature the Marut into a flyable aircraft. Despite IAF reluctance and unwillingness to understand that it was in its own interests to support a fledgling home industry the Government sensibly ordered 18 pre-production aircraft and 62 operational ones to arm 2 or 3 squadrons. In fairness to the IAF there is a long journey from an aircraft that flies to an aircraft that fights and does so consistently in adverse conditions. In 1963 the Marut development efforts had not traveled that distance and the IAF was justified in not being keen to take an immature product into operational squadrons. In fact it would be 1971 by the time most defects were ironed out.
AIRCRAFT DESIGN & FEATURES
Marut's wing was highly swept and thin and large - all three characteristics for an interceptor. The sweep and thickness together determine the planes ability to fly across the speed of sound - greater the sweep and thinner the wing the lower is the thrust to weight ratio needed to get the aircraft supersonic. However, on the flip side, the greater the sweep and thinner the wing the higher becomes the landing speed and the less stable and maneuverable is the aircraft at low speeds below 250 knots (450 kmph). The Marut wing is a well balanced compromise of adequate sweep to get supersonic (provided the engines develop the thrust) and the thickness was enough to maintain moderate landing speeds and low speed stability. The wing bestowed on the HF-24 an acceleration and low altitude speed that the Pakistani Sabres and Indian Hawker Hunters could not match. In fact the Marut was one of the few, if not the only, frontline aircraft that could cross Mach 1.0 without afterburners - albeit just about at high altitudes.
The wings were designed to carry 4 pylons (or hardpoints) rated at 454 kgs each (1000 lbs). In addition each wing carried about 700 litres of fuel in the integral tanks. An integral tank means the internal space within the wing is sealed up and filled with fuel floating between the structural members. This means each wing carried a payload of about 1425 kgs of fuel and weapons. Think of it as carrying four Maruti 800s, two under each wing and clipping away at 550 knots (~1000 kmph).
TECHNICAL DETAILS:
General
Crew: 1 in the fighter-bomber; 2 in the conversion trainer
Length: 52' 1"
Wingspan: 29' 6"
Height: 11' 10"
Wing Area: 301 square feet (~28 sq metres)
Wing Sweep: Approximately 52 degrees
Weights
Empty equipped: 6195 kgs/13,658 lbs
Loaded Clean: 8951 kgs/19,734 lbs
Fully Loaded: 10925 kgs/ 24,085 lbs
Power Plant
Type: Two 2200 kgp (4850 lbs) Rolls Royce Orpheus 703 turbojets
Size & Weight: These were a variant of the Gnat powerplant. Small & compact at 75" length and 32" diameter. Weight = 379 kgs Power to Weight ratio of 5.9 kgp/kg of weight.
Fuel Consumption: Specific fuel consumption for the Orpheus is 1080 grammes/kgp/hour. At full thrust for the Marut this translates to 106 litres per minute flying at 600 knots in clean condition … 175 metres per litre … this is just a rough calculation to tickle the petrolhead in all of us.
Performance
Maximum Speed: 1112 kmph / 600 knots* or Mach 0.91** at sea level; 1086 kmph/ 586knots or Mach 1.02 at altitude
* a knot = 1 nautical mile per hour i.e. 1.852 kmph; a nautical mile equals 1 minute of arc of any meridian of the earth
** Mach 1.0 is the speed of sound at a given altitude; Mach 2.0 by inference is twice the speed of sound. At sea level Mach 1.0 = ~1225 kmph; at 36,000 feet altitude it is ~ 1054 kmph.
Stall Speed: 248 kmph / 133 knots
Initial climb rate: 6000 feet/min or 30 metres/second at sea level
Range/Radius: 396 kms / 214 nm lo-lo-lo with a 1800 kgs warload
lo-lo-lo is the typical fighter-bomber flight configuration it means ingress, attack and egress are all at low altitudes typically below 500 feet or 1000 feet, depending on terrain, to avoid radar detection; similarly you can have configurations such as lo-lo-hi or hi-lo-hi. Ferry flights by nature will be hi-hi-hi to get the best fuel economy
Wing Loading: ~66 lbs/ square foot in clean loaded condition; 80 lbs/ square foot at maximum weight.
The first figure is one factor on its ability to dog fight out of enemy territory after releasing its warload on target. 66 is a lightly loaded wing supporting maneuverability. Corresponding figures for the Gnat are 57 lbs/ square foot and that for the very capable modern F-16 is 88.
The latter figure of 80 indicates how well the wing will take to heavily loaded low level attack. Here we need a highly loaded wing to reduce the gust response (or bone jarring bumps) the aircraft encounters when flying at 550 knots below 1000'. Here The HF-24 doesn't do so well. Classic lo-lo-lo attack aircraft like the Sepecat Jaguar have wing loadings as high as 130 lbs/square foot
You can design a wing for interception - large, triangular, low loading, highly swept, thin or for low level attack - small, long chord (length at the root), high wing loading, moderate sweep to enhance lift and low speed control and thicker for aerodynamics and greater fuel.
Power Loading: 0.50 at clean weights; 0.41 at full weight
These were moderate power loadings even for the 1960s. It reflected the unsuccessful hunt for the right engine or given the engine you had asking too much in the Air Staff Requirement. Normally for the 1960s the desired power loading in clean condition, for an interceptor, would have been 0.60 to 0.70 compared to Marut's much weaker 0.50. On the other hand in that era a dedicated ground attack aircraft (such as the McDonnell Douglas A4 Skyhawk) would have a maximum power to weight loading of 0.33 to 0.45. Here Marut's 0.41 ratio was in the right spot.
Service Ceiling: ~ 45,000'; as it was primarily used as a ground attack aircraft in combat it would usually fly at low altitudes below 1000' to avoid detection by radar.
Armament
Four 30mm Aden cannons with 130 rounds per gun; combined rate of fire 2400 rounds per minute ie 40 rounds per second. Some reports talk of blanking out two guns to reduce vibrations while firing. This was an issue in the 1960s and even cost the life of one test pilot. I don’t know if this was a temporary problem or a permanent issue.
4 underwing pylons rated for 1000 lbs /454 kgs each; typical loads were bombs of 1000lbs, 500 lbs & 250 lbs, 68mm SNEB rocket packs typically of 18 or 36 rockets per pack & napalm bombs. Not known if the HF-24 was configured for cluster munitions such as Hunting BL755 which was (and is) in common use by the IAF
50 French SNEB 68mm ground attack rockets in internal pack behind pilot; The French rocket is used even today and is the world's most widely produced unguided rocket armament. The rockets can be fired in ripples with a spacing of 0.33 milliseconds. Typical warheads, amongst several variants, were high explosive, fragmentation & anti-tank. By possessing an internal weapons bay the HF-24 could carry these 50 SNEB rockets without their carriage inducing drag. This gave it greater flexibility in how the 4 pylons would be used to carry fuel or weapons for greater payload on target or a greater range for a given payload.
SQUADRON SERVICE
HAL & IAF conducted 1800 test flights, between 1962 and 1967, to iron out the defects of the Marut. In April 1967 No.10 Flying Daggers Squadron became the first unit to be equipped with India's first indigenous combat aircraft. Close liaison between the IAF and the Hindustan Aircraft (as HAL was then named as) continued to progressively modify the Marut for the lo-lo-lo attack role.
During the early years Maruts with the IAF suffered from the non-availability of spares which in turn adversely affected serviceability. These chronic shortages affected the Marut fleet between 1965 and 1968, however as production picked up the situation improved markedly. But the aircraft had teething troubles that were not solved until 1970, and only a very meticulous reporting of problems and the professionalism of the pilots and engineers, prevented any fatalities from occurring.
There is wide consensus about excellent handling characteristics of the aircraft. Most pilots who have flown the aircraft describe it as pleasant to fly and excellent for aerobatics with fine control responses. And its ability to out-accelerate the Sabre jet, especially at low levels, was a useful asset in 1971. The Marut offered a stable weapon delivery platform and packed a formidable punch. While the Marut's pilots expressed an understandable desire for more thrust than the Orpheus 703 offered, they were unanimous in their view that the aircraft proved itself a thoroughly competent vehicle for the low-level ground attack profile. One defect which, I believe, remained was malfunction of roll control aerodynamic surfaces and the canopy flying off when all four 30mm cannons were fired simultaneously and the impact the recoil had on the electrics of the aircraft. HAL, I believe, claimed to have cured the problem but the IAF decided to be safe and blanked off the two upper cannons and operating only with the lower two in squadron service. The Marut was a robust aircraft with extremely good visibility for the pilot, and was aerodynamically one of the cleanest fighters of its time.
The Marut eventually equipped three IAF Squadrons. No.10 Squadron was the first to convert in April 1967, the No.220 the Desert Tigers converted in May 1969 and the No.31 The Lions in March 1974. Of the 145 Maruts produced, 130+ entered squadron service the rest were used for testing & development
PERFORMANCE IN COMBAT
Both Squadrons mounted on the HF-24 operated from Jodhpur in December 1971 and served exclusively in attacking enemy ground targets such as fuel dumps, lines of supply, communication nodes, Pakistani airfields, railway junctions, armoured vehicles and troop concentrations. The HF-24 also took part in the battle of Longewala providing support to the 4 Hunters from Jaisalmer, that led the Indian offensive, by attacking the supply lines to the Pakistani tank brigade. About 100 enemy tanks were destroyed or damaged and their bid to attack Jaisalmer was subverted.
The Marut's flew approximately 200 combat sorties during the two week war. On one strike mission they flew 200 nautical miles (~370 kms) into enemy territory to deliver their goods. The Marut also demonstrated that when flown clean it could tackle a Sabre jet. A Marut flown by Squadron Leader KK Bakshi of 220 Squadron also shot down a PAF F-86 Sabre on 7th December 1971 (Flying Officer Hamid Khwaja of 15 Squadron PAF). No aircraft were lost to air action although by the end of the war three Maruts had been lost to ground fire and one lost on the ground.
Maruts constantly found themselves under heavy and concentrated fire from the ground during their low-level attack missions. On at least three occasions, Maruts regained their base after one engine had been lost to ground fire. On one of these, a Marut returned to base without escort on one engine, from about 240 kms inside hostile territory. Another safety factor was the automatic reversion to manual control in the event of a failure in the hydraulic flying control system, and there were several instances of Maruts being flown back from a sortie manually. Throughout the December 1971 hostilities, the Marut squadrons enjoyed extremely high serviceability rates (in contrast to the late 1960s), this undoubtedly owed much to an improved spares situation and the original design's emphasis on ease of maintenance.
CONTINUED DEVELOPMENT
Dr. Kurt Tank and his team returned back to Germany in 1967 and the leadership for developing the Marut further passed onto Group Captain Suranjan Das who also served as the Chief Test Pilot. The Indian team at HAL successfully developed a two seat conversion trainer which moved into squadron service as the HF-24 T Mark 1. A prototype with an Indian developed experimental after burning Orpheus engine designated Mark 1R was lost while being test flown by Group Captain Suranjan Das. His death and challenges with the afterburner led to the demise of this line of development.
A PRE-MATURE END
The Marut served on in the IAF through the 1970s. The IAF developed two Air Staff Requirements namely the Deep Strike Penetration Aircraft (DPSA) and the shorter range Tactical Attack & Strike Aircraft (TASA). The IAF was not interested in waiting for HAL or DRDO to develop the Marut further to meet either of these requirements although with the right effort and sans the bureaucracy the TASA requirement could have been met by a Marut powered by the Rolls Royce Adour that powered the Sepecat Jaguar. The IAF went on to select two very fine aircraft to meet these requirements - the Sepecat Jaguar for the DPSA and the Mig-23BN followed by the Mig-27M for the TASA. Unlike the Indian Navy and the Chinese Air Force who both supported their home industry with orders for step by step improvements the IAF chose not to do this. Speaking in favour of the IAF - those days the Indo-Soviet friendship was at its peak and the Soviets were offering license production for the Mig-27M, a superb tactical attack aircraft, with Rupee trade payments and the IAF must have felt this was a better alternative than to spend yet several more years dealing with HAL's development journey. Maybe HAL was not to blame. Maybe the early demise of the Marut was sown in the overly ambitious specifications laid out in 1956-57. The last Marut was withdrawn in 1990. Today one can only wonder what could have been possible if HAL and other development agencies like DRDO had the focus and competence of ISRO and the IAF had a long term view like the Indian Navy which working with Mazagon Docks & Cochin Shipyard has built up some meaningful indigenous capability in design and construction after having started in the early 1960s same as the HF-24. To develop a nations aviation industry you have to think in terms of a 50 year horizon and go step by step.
THE PATH AHEAD
In mid-1980s the ASR was laid out for the Tejas Light Combat Aircraft. Once again it was an ambitious set of specifications calling for capabilities and technology such as fly by wire flight control systems, multi-mode pulse doppler radar and an afterburning turbofan engine in the 10,000 kgf class. These were technological assets which only the Americans (F-16 & F-15) had successfully put into service at that time, the French were about to (Mirage 2000) and the Soviets were still developing. Partly due to, once again, putting out highly stretched specifications and partly the bureaucratic approach of the agencies involved the Tejas took three decades to develop, has just been inducted into the IAF for operational breaking-in and is still maybe a year short of full scale operational service. The more things change the more they stay the same.
The current generation of engineers & designers working on the Tejas cannot be blamed for woolly headed thinking of 33 years ago. We should cheer them and support them as they work to put the country's second indigenous fast combat aircraft into full operational service this year. Aerodynamically speaking the Tejas is a superb design and this time around with the adoption of the General Electric F404 afterburning turbofan we also have a winner of an engine.
