By Gp Capt Kapil Bhargava (Retd)
Acquisition of the Gnat by IAF resulted in a number of benefits. It not only got our fighter pilots a fantastic Sabre Slayer, it also gave the aviation industry many other associated benefits. We will look at what the airframe side did for us a little later as we try and build up the authentic history of the Gnat. In my opinion an aircraft designer needs to consider the engine as soon as he thinks of creating a new aircraft,if not sooner. An aircraft project will go nowhere unless an engine matching the designer’s aspirations is either already available or is about to arrive on the scene.
The engine selected by Ted Petter for the Midge was the Saturn being developed by Bristol Aero Engines Ltd. But the project was aborted after the British Government decided against it. Petter had to use the Viper which powered the Jet Provost.
Fortunately for Petter, even this lower power engine on the Midge gave it very nippy performance, including supersonic dives. This proved that his concept of the Gnat as a light (Low Cost Aircraft = LCA!) fighter was viable. Coincidentally, the Orpheus engine appeared on the scene exactly at the time it was needed for the Gnat. The aircraft was designed to intercept incoming attackers before they crossed the English Channel. After the British Government rejected the Gnat, even more fortunately for Petter, we bought the aircraft. With it came the Orpheus to India to be produced under license in the country.
Contrary to much of our R&D efforts, I do not believe copying a product really helps us. The industry neither learns how to design such an item nor gets the production technology to do a proper job at the correct price. My thesis was and still is that we should take a licensed item and develop it to the next level. This is what the Japanese did, starting with textile machinery from Manchester. We have done this in a very limited way.
Let us now list the applications to which the Orpheus was applied. First of all, it helped create an Engine Division within HAL. Apart from its use on the Gnat, the same engine powered the HF-24 and the Marut Trainer. Its de-rated version is still in use on Kiran Mk II. A re-heated version, so-called developed by GTRE was used to power the HF-24 Mk IA, IBX and IR. But its most daring application was on the C-119G Fairchild Packet. The best person to describe it is Group Captain Jacob Chakko, the brains and the working hand almost solely responsible for the success of the project.
Orpheus Jet Pack on the Packet
By Gp Capt Jacob Chakko Tech (Eng)
Fitting Orpheus Engine Jet Pack on the C119-G was indeed very interesting. It was a challenge at ‘that’ time to suggest that the Orpheus could be used as a Jet Pack because there were too many ‘nay-saying wet blankets’ who had doubts whether that engine could also run on the 115-Octane fuel used by the Packets.
So here is a short summary of the Orpheus installation and a little of what was involved, engine-wise. Yes, my technical paper had riled a lot of people in high places. But once AVM Pinto and the CAS Air Mshl Aspy Engineer had okayed it as an Operational Requirement, and AVM Ranjan Dutt at HAL was given the task, I had quite a lot of support for its quick ‘denouement’.
Orpheus to run on Packet’s High Octane Fuel.
The IAF Orpheus Engine was only cleared to run on JP-4 for us. For the Jet Pack we had to clear it for use with the Packet’s 115 Octane fuel. Special tests were run at the Engine Factory for 400 hours plus. The engine was inspected every 100 hours or so. There was a micro-thin greenish-yellow coating of a ‘lead oxide deposit’ on the hot parts from the combustion of the High Octane Fuel. But it was decided that the engine’s performance was not affected in any way. So the TBO for the Orpheus Engine was retained at the normal at 400 hours (as I recall) on this installation.
Orpheus Fuel Pump Life
However, since the Fuel pump was also running on this high octane fuel which had less lubricity than JP-4 kerosene, it was decided that the fuel pump would be mandatorily inspected and changed at 200 hours. I believe this figure was later changed to 250 hours. My memory fails me a bit now. (He is 84 now- KB).
Orpheus on a Hydraulic Starter
The Orpheus at that time could only be started with compressed air from those massive high pressure cylinders on the ground. These cylinders weighed a whopping 1750 pounds each. These Packet aircraft had to land and take off from airfields where such facilities were not always available. It was therefore decided that 2 such cylinders would be installed in the Packet’s Aux Deck to give the aircraft total independence from ground equipment. The Orpheus could be started in the air by wind-milling it but it became an IAF requirement that the jet had to be running at take-off also. Missing this installation would have meant a reduction of nearly 3500 – 4000 pounds in payload capacity. An alternative Engine starting system had to be found asap!
The ‘designers’ went on a rampage for a few months to find an alternative electric or hydraulic starter from the international market. A suggestion that the extant Hydraulic Starter on the Westinghouse J-34 Jet Engine would do the trick was rudely ridiculed. Discussions were held ‘in camera’ with Air Cdre S Rikh of the Engine Factory who, being convinced that this could be done, took it on himself to produce the very simple modifications. Having been done (hubba hubba) and having proved itself totally successful in the Engine Test Bed, Air Cdre Rikh called AVM Ranjan Dutt and requested him to come and start the Orpheus with the Hydraulic Starter by himself. Having satisfied himself that this was a successful mod, the AVM called the CAS from the Test Cell itself and said to him,”Sir, we at HAL do the impossible, miracles take a little longer”! This was ‘a la AVM Harjinder Singh’ for those who know the allusion!
The result of this modification was immediately felt by the Packet Aircrew who straight away had an extra 3 – 4 thousand pounds extra in payload carrying capacity. And the increased factor of safety in flying in Ladakh will always be remembered also by a single episode where ” Air Marshal PL Purohit and Winco HB Singh flew a Packet on the Orpheus Jet alone, with both piston engines feathered, from Zojila to Srinagar, a distance of over 100 miles, losing height in a powered glide from 18,000 feet and maintaining level flight at approx 7,500 feet over Srinagar.
I am told these modifications of the Orpheus Jet Pack not only extended the Service Life of the Packet C-119G aircraft by 20 odd years, from 1964 to 1984, but also gave HAL a whopping order for over 150 Orpheus Engines plus oodles of work in overhauling Packets and the Jet Engines over the years.
I hope this is useful information.