(From AM Shashi Ramdas, by email)
Gp Capt Kapil Bhargava has written a detailed account on the tragic accident, in which Sqn Ldr “Saper” Sapre was killed, during 4-gun trials, on the Marut (HF-24), in Jamnagar in November 1971 and some background information on the way the installation had been “cleared” for live trials.
I would like to add some information/comments which may shed some more light on the subject, even though it may be of only academic interest today.
I do not know when the very first 4-gun trials were carried out but I had heard that “the entire instrument panel fell into the pilot’s lap” as soon as he pressed the trigger!! I presume, the truth is what AM Jayal relates in Groupie Bhargava’s post on S/L Sapre’s accident.
However, I can personally vouch for the veracity of what happened when 4-gun trials were carried out, in Jamnagar, in 1967. An HAL aircraft had been flown out from Bangalore, specifically for these trials, together with a full team of engineers and technicians. Chuchu Tilak was detailed for the trials . As far as I can recall, the initial trials were to be carried out at a “safe” altitude to check the vibration levels.
One fine morning, “Chuchu Tilak took off and, as soon as he pressed the trigger, the canopy flew off!! He promptly returned to base and a whole team of HAL personnel swarmed round the aircraft trying to figure out what had happened, and why. In spite of every effort, nobody could figure out why the canopy had flown off. Another canopy was then flown out from Bangalore, installed on the same aircraft and extensive checks carried to ensure it was properly fitted. The aircraft was then loaded up and cleared for another sortie. Chuchu Tilak got airborne and, having climbed to altitude, pressed the trigger. Again, the canopy flew off!!!
This time there was very serious consternation and even more HAL personnel swarmed all over the aircraft to find out what had happened. Again, nobody could figure out what had gone wrong. The only clue was that, in both cases, the canopy had jettisoned cleanly. The entire canopy jettison system had worked beautifully, but nobody could figure out the reason for this inadvertent jettisoning.
Then, some bright lad decided to check the entire canopy jettisoning system, from start to finish. Actually, he started the other way round, ie from “finish” to “start”. Finally he arrived at the “start”, which was the external canopy jettison button situated on the left of the nose cone. The plastic cover, protecting the button, was intact and the button looked perfectly okay. Even an in situ electrical test showed that there was nothing wrong with the jettison button. Luckily, this lad didn’t give up then. He decided to remove the entire external jettison button and look at its innards. What he found inside was an eye-opener. The bakelite parts of the push button had broken up into small pieces and the metal piece that was meant to complete the electrical circuit across the two terminals was lying loose! In this condition, the external canopy jettison system was “safe” and everything was normal. However, as soon as the trigger was pressed, the excessive vibrations made that loose metal piece jump around and make contact across the two terminals, resulting in the jettison circuit being completed and the canopy being jettisoned. It was surmised that the jettison button had broken internally, due to excessive vibrations, during the very first sortie itself.
As far as I know, that was the end of the 4-gun trials and the aircraft was thereafter restricted to firing only two guns at a time.
I can only guess why the 4-guns trials were taken up again in November 1971, and that was the imminent expectation of hostilities with Pakistan. The Marut squadrons were based in Jodhpur, at the time, and their operational location was a satellite airfield in the desert. It was expected that they would be the first to go into action, and so they did.
Marutfans 
Assuming that original HF-24 design had the 30mm Aden guns, it is surprising that it turned out to have such extreme vibration levels during 4-gun firing. But what is more disturbing is that there seemed to have been no noticeable improvement in the vibration levels as further gun firing trials were carried out. The very severe vibration levels were reported prior to mid-1967 (when Chuchu Tilak lost his canopy on two successive sorties in Jamnagar), and there was no apparent improvement 3½ years later when Saper Sapre lost his life in that tragic accident in Nov 1970. It would be interesting to know what improvements/modifications were carried out on the gun installation in the interim period. Surely there are some people still around who could shed some light on the subject.
AM Ramdas has this discussion further and sent his comparision between the gun system on the Hunter and Marut.
More on the Marut Aden Gun Installation
and Loss of Lateral Control
The inability to clear the Marut for 4-gun firing has been a very sore point with the aficionados of the aircraft. There were two major reasons why the aircraft could not be cleared for 4-gun firing. The first was the unacceptably severe vibrations. The second was the possibility of loss of lateral control that resulted in the late “Saper” Sapre’s tragic accident in November 1971.
To start with, it would help if the Aden gun installation and aileron control system on the Marut were studied and compared with the corresponding installations on the Hunter which also had four 30mm Aden guns.
The four Aden guns on the Hunter were carried in a removable gun pod, complete with ammunition tanks. (Only the gun barrels remained with the aircraft when the pod was removed). Vibration levels, while firing four guns, were acceptable. The Aden gun installation on the Marut was a “fixed” one. The question then arises as to why the vibrations levels on the Marut were so “dangerously” high. Having brought up this comparison, I am not qualified to comment on the design/manufacturing deficiency of the Marut installation. Would it be possible for those in the know to describe the differences in the two installations and also to explain what remedial actions were taken by HAL to reduce the vibration levels on the Marut? I have brought up this controversial matter because, as far as I am aware, one of the reasons why the Marut aircraft was scrapped was its inability to fire four guns simultaneously.
Did the “original” Marut design, as initially envisaged by Dr Kurt Tank, have a four 20mm gun installation? I had heard that Dr Kurt Tank had conceptualised the Marut design long before he came to India. The 30mm Aden gun came into service only with the Hunter/Gnat generation of aircraft. If this trend of thought is reasonable (and I am open to correction), was the “original” design of the Marut re-designed to accept the 30mm Aden gun? If not, did HAL make any study of the Hunter gun installation and see whether any improvements could be made in the Marut?
The aileron hydrobooster installations on the earlier series of Hunters and on the Marut were different. Though the basic hydroboosters were similar (both made by Fairey Hydraulics), there was a differnce in the way the ram was anchored to the airframe when the controls were in “power”. The Hunter hydrobooster ram was anchored by a single pawl mounted integrally in a fixed unit through which the ram moved longitudinally when the controls were in “manual” and gripped the ram when the controls were in “power”. On the other hand, the extreme end of the Marut hydrobooster ram was attached to a swinging pendulum which was anchored by two pawls which gripped the end of the pendulum when the controls were in “power” and allowed the pendulum to swing freely when the controls were in “manual”.
However, the major difference in the installations was that the Hunter hydroboosters were located in the mainplanes and directly connected to the ailerons. On the other hand, the Marut hydrobooster was located in the fuselage and connected to the ailerons through a number of linkages. It is understood that, in the early days of the Marut, there was some problem on aileron flutter due to this chain of linkages downstream of the hydrobooster.
The main problem on the Marut installation, however, was that the aileron hydrobooster was located directly above the Aden guns, between the ammunition tank and the fuselage skin. Thus, it was directly subjected to very severe vibrations whenever the guns were fired. Gp Capt Kapil Bhargava has mentioned disengagement of the hydrobooster pawl as being the cause of loss of lateral control in the case of “Saper” Sapre’s fatal accident. Presumably the disengagement of the pawl was due to these very severe vibrations in the region of the hydrobooster installation.
Re-location of the aileron hydrobooster may not have been a practical alternative (though every engineer and airframe technician would have welcomed it), but substitution with a bypass hydrobooster (as introduced by a retromod on Hunters) may well have been possible, and could have prevented loss of lateral control durng gun firing.
The bypass hydrobooster did away with the pawl arrangement. Instead, the hydrobooster ram was permanently fixed to the airframe, whether the controls were in “power” or “manual”. But the chambers either side of the hydrobooster were interconnected (hence the term “bypass”) when the controls were in “manual”, and isolated when in “power”. The absence of the pawls meant there was a smooth transition in switching controls from “manual” to “power”, and vice versa. Those pilots who had flown the modified Hunters will vouch for this.
I have been in love with the Marut ever since I first set eyes on her. My harping on some of her shortcomings is only out of a feeling of immense sadness that she was given a premature burial without, apparently, any worthwhile effort in trying to fix her problems. More of this on another day.
——– Shashi Ramdas
Sent by Groupie Bhargava through email.
“I am quite incapable of commenting on Air Mshl Ramdas’ description of the gun installation. All I know is that four 30mm Aden guns were intended to be installed right from the start. There was no late change in plans at any time.”
Ravi,
You are so right!
Dara
The repository of episodes of the four gun trials are indeed awesome and in most distressing ! But one can vouch for the potency of the following later day two gun configuration of the Marut. With the beautiful and effective ISIS sight, a well harmonized pair of Marut guns were deadly and accurate. Even rank younsters during our time routinely notched up some fine scores with the RSO frequently lamenting the total destruction of the range gun firing screens. No doubt a befitting tribute to the spirit of the past masters of the gun trials especially the ones who made the supreme sacrifice at the alter of their testing. May they ever rest in peace with their lovely Marut in the affirmation that their sacrifice was not in vain but gave in full measure to the gennext of the IAF.
“Dara, Shashi”
“Yes sir”
“Dara, goof up big time on that article of the four gun firings.”
“It wasn’t Pop Ashoka but Chuchu Tilak.”
“Right sir will edit it. We’re all getting old!”
“Just do it and save the wise cracks!”
Groupie Bhargava has sent an extract of this article to Wg Cdr Ashoka and hopefully we will be able to get his reaction too.
However, more pertinently, Groupie has this to say about the author:
“Note: As far as I know, Shashi Ramdas is the only engineer to have flown the Marut and in fact acquire proficiency on it, You risk serious trouble for yourself if you denigrate the Marut and he gets to know of it! – Kapil Bhargava”