Reflections – Fairey Gannet

There is an old maxim that says a new engine should never be married up with a new airframe. This was true for the Gannet, which had the unproven Armstrong Siddeley Double Mamba installed. We suffered continuous problems with engine/propeller vibration, the cause of which was never properly determined. There were something like thirteen standard fixes for the problem and at times all of them would be tried without success. I can recall suffering itch round my shin bones due to the flesh having been subjected to constant high frequency vibration!

The Double Mamba had been developed from an idea by Faireys which envisaged two engines mounted as a single unit, driving separate propellers through co-axial shafts, with either engine capable of being shut down in flight. I saw the original Fairey piston engine, the P24, when visiting the Fairey factory at Hayes. It had been developed during the war and sent to the USA for further development but nothing came of it.

The Single Mamba was an axial-flow propeller turbine which powered a few aircraft in the early fifties, but it soon faded from the scene. It was installed in that remarkable aircraft the Short Seamew, which fortunately never entered service, although whole squadrons of them were built. I happened to chance on long lines of Seamews at Lossiemouth in Scotland in the aircraft graveyard, where no doubt they had been sent to be out of sight. (December ’90 issue Yesteryear noted the sale of 19 Seamews with less than two hours’ flight time each).

The Double Mamba consisted of two single Mambas mounted side by side, joined by a common gearbox at the front. The port engine drove the front airscrew and the two airscrews were contra-rotating. The engines were constant speed turbines running at 15,000rpm, with power variations being determined by varying the pitch of the airscrew blades. This arrangement was necessary in order to provide instant power for over shoot on deck landing. The engines were controlled by separate throttles and high pressure cocks, the latter being multi function, controlling the feathering and unfeathering of the airscrews during starting, and relighting in flight. The the throttles had ground idle and flight idle positions and were spring loaded to the right. Once past the flight idle gate they could only be returned to the ground idle position by pushing them to the left to clear the gate.

The high pressure cocks had three positions, and a button which controlled the feathering and unfeathering of the airscrew blades. The lowest position was ‘feather and brake’ which if selected, and the button pressed, would shut the engine down, feather the blades and apply a brake. The next position was ‘off’ which if the button was pressed would unfeather the blades. The up position was ‘relight and on’ which released the brake, unfeathered the blades if the button was pressed, directed fuel into the engine fuel system, and operated the engine ignitors To start the beast, the throttle of the engine to be started was placed in ground idle. The HP cock was moved to the ‘on’ position to release the brake, and then to the ‘off’ position. The blades were then unfeathered by pressing the button; the pump note would audibly rise when the job was done. With the starter fuel pump on, the HP cock would be placed in the ‘on’ position and the starter button pressed. This would fire a cartridge about the size of a Bofors shell which in turn would spin up the engine. Now it was a fact of life that the Double Mamba would not start on one cartridge on the first start of the day no matter what the time or conditions! A non start would be indicated by the RPM not reaching self sustaining revs with the JPT continuing to rise; the HP cock would then be put to ‘off’. On passing 800rpm, the second cartridge would be fired which would push the revs well above self sustaining. Every subsequent start of the day could be achieved with one cartridge!

The second engine would be started by windmilling it from the first engine with the latter at full power. The start would be made using the relight button.

Engine power was indicated on torque meters which were fed from torque pots which resisted the rotation of the engine in the airframe. There was an arrangement in the system which would automatically feather an engine if there was reverse torque of minus 50 psi, ie, if the propeller was attempting to drive the engine, which is a sure indication of engine failure.

The final links in the engine/propeller control system were the flight fine pitch stop (FFPS) and the ground fine pitch stop (GFPS). The GFPS was a fixed stop set at 6 degrees which enabled the blades to be fine enough to permit a start and also to allow the engines to run at idle for taxying. The more important stop was the FFPS which was set at 21 degrees and would engage once the undercarriage had been retracted. This stop would prevent the blades fining-off below 21 degrees in the event of propeller malfunction; at this setting there was enough power on one engine to sustain flight against the windmilling prop. There were switches in the cockpit to hold the FFPS in, in the event of propeller malfunction. Failure to make this switch following a propeller failure and with the engine shut down, would mean that the blades would go to 6 degrees as soon as the undercarriage was lowered which had an effect like hitting a brick wall.

We had one such case in the RAN in a Gannet trainer, when a propeller ran away and could not be feathered. The aircraft safely returned to the circuit but the pilot in the front cockpit failed to make the switch to hold the FFPS in. As soon as he lowered the undercarriage, the blades went to full fine pitch and the aircraft literally fell out of the sky, ripping off the entire under surface of the fuselage. Fortunately they were at a relatively low height when it happened and they only sustained minor back injuries.

As the then resident Gannet instructor (unqualified at the time), I decided that I should demonstrate what happened to all future students to ram home the need for a clear understanding of the engine/propeller system. I did this by shutting an engine down and letting it windmill on the 21 degree stop. We would return to the airfield at about 7,000 feet, and over the top, I would lower the undercarriage. The effect was dramatic indeed as the aircraft literally ran out of airspeed. The nose had to be lowered to about 30 degrees to maintain a speed of 140 knots which is what I guessed would be necessary to land the beast. I must admit to breathing a small sigh of relief each time the dead engine feathered after the demo.

The Gannet had an internal bomb bay which was required to take the new homing torpedo, Pentane. It so happened that the weapon and aircraft were in the development stage at the same time. As Pentane increased in length, the Gannet’s bomb bay had to match it, which produced a rather strange numbering sequence for the bomb stations. Subsequently, as the squadron Airwarfare Instructor, I had the task of ensuring that all pilots knew that station ‘F’ came before station ‘E’!

There was a radar installed in what was known as ‘the dustbin’, which retracted into the rear fuselage. The wings folded in three sections on each side and there were interlocks to prevent the wings from being folded with the flaps down, or conversely, the flaps being selected down with the wings folded. The interlocks, as we discovered, only worked with the wings actually folded and did not defeat one chap who selected flaps up and immediately selected wings fold. The resulting mess was a sight to behold!

It is perhaps hard to believe, but a Royal Navy Gannet was successfully landed after losing both outboard wing sections during the recovery from a rocket attack. The aircraft hit the slipstream of the aircraft ahead just as the pilot applied maximum ‘g’ for recovery. The resulting overload tore both sections off at the wing fold joint, removing both ailerons which were installed on the outboard section. With that big fat wing there was plenty of lift still available and evidently, the aircraft was quite controllable in roll using rudder.

Surprisingly, despite the sheer bulk of the aircraft, it handled remarkably well, having light, well coordinated controls. A fair comparison would be the fat lady who you find yourself forced to partner in the barn dance who surprisingly is very light on her feet! The ailerons were particularly effective due to the spring tab arrangement adopted by Faireys and the aircraft had a very good rate of roll. The youngsters in one RN squadron foundthat it barrel rolled with ease, until wrinkles in the inner wing panels began to develop and their illegal aerobatics were brought to a sudden stop.

The normal anti submarine patrol routine was to feather an engine once cruising height had been gained and to swap engines every half hour. The beast would cruise comfortably at 140 knots on one engine, but it would slowly lose airspeed with the the radome-down at maximum. Landings were alway sdone on two engines as it was not possible to overshoot on one below 100 knots and 100 feet. I was forced to disprove this on a number of occasions when students let the airspeed drop on commencing a single engine overshoot. The trick was to gently trade height for airspeed until things were back under control.

Despite all our engine problems, I was lucky enough to have only two experiences worth noting. The first occurred shortly after I hadconverted to the aircraft and was on an anti submarine exercise over the Irish Sea. I had just shut the starboard engine down but noticed the JPT was reading as if the engine was stil running. In time honoured tradition I tapped the gauge but as it remained reading, I assumed the gauge had failed. I continued with the flight until my observer remarked that he could detect a strong smell of kerosene, followed by the statement in a slightly higher key that he could smell burning. I concluded that something had occurred with the starboard engine but could not determine what. We were in cloud at the time and the weather at base was not the best. I called for an emergency GCA and can remember vividly to this day the rare attack of vertigo I suffered on the final stages of the instrument approach with all my senses telling me I had 90 degrees of bank on. Needless to say I managed to ride it out, but we broke out at a couple of hundred feet in pouring rain and no sight of the runway. I did a fairly rapid single engine circuit and found the runway, maintaining a continuous turn until touchdown. Just as I was relaxing on the roll out, all hell broke loose with the JPT overtemperature warning bell ringing its head off in my earphones. I looked down at the engine instruments and there was the ‘dead’ engine JPT off the clock! I looked back over the side to see smoke and flames pouring out of the starboard jet pipe. I shut the other engine down and turned off the electrical master switch and we all three evacuated the aircraft just as the fire tender arrived to smother the starboard side with foam. Subsequent investigation established that the starter fuel pump had continued to run after the starboard engine had been started (it was meant to automatically shut down after seven seconds) and had continued to run after the engine had been shut down in flight. The effect was like a ramjet, which is what the JPT gauge had been trying to tell me!

The second engine incident occurred a year or so later on a hot summer’s day when the starboard jet pipe separated immediately under my cockpit; that was one of the hottest flights I’ve ever experienced!

The aircraft was very easy to deck land, having a very good view over the nose and in any case, with the new angle deck, if you missed the wires you bolted, with nothing damaged but your ego.

As the aircraft had not been cleared for catapulting when we did our initial deck landings with the RN, we were forced to do free takeoffs. The aircraft was not known for lightning acceleration and on one occasion taking off from HMS Bulwark I found that my speed was stabilised at 70 knots half way down the deck due to the ship pitching (the stalling speed was about 76 knots). Fortunately it picked up speed just before we were due to fall off the front end but it was a little scary for a while.

Shortly after the RN cleared the aircraft for catapulting, one was lost due to engine failure immediately after the cat shot. Investigations disclosed that the recuperators, which had been fitted to ensure positive fuel pressure on a cat shot, weren’t doing the job. As luck would have it, I was on a deck landing refresher sortie with HMAS Melbourne, having just flown out from NAS Nowra, when a signal was received clearing the aircraft for catapulting. The procedure devised by the RN was to turn each low pressure fuel cock off in turn for seven seconds at full power and if the engine didn’t stop, the recuperator was OK. Naturally the ship was keen to try it and as they had a live bunny onboard, why not now? The only snag was that Melbourne had never launched a Gannet before and I had not done a cat shot in the aircraft either.

I hastily consulted the pilot’s notes and was reasonably happy except for the recommended elevator trim setting which I thought was not enough nose down. As I sat on the cat, half of me was saying more forward trim and the other was saying there must be a trick in it somewhere. In the end I compromised and put the trim half way between what I thought it should be and what the pilot’s notes recommended. At the same time the ship was making certain that all factors were on the plus side. The end result was that I went off like an express lift, with full forward stick and winding on trim for all I was worth!

In summary the Gannet was easy to fly, had no real vices apart from engine problems and served the RAN reasonably well, but it was never in the same league as the Tracker as an anti submarine aircraft. Where it really shone was at air displays! You could really ring the changes shutting down and relighting engines, bomb bay doors opening and closing, radome up and down, wheels and flaps for a slow flypast; the combinations were endless with lots of noise and the crowds loved it.

Finally, the aircraft is perhaps best summed up by the reaction of a team of Indonesian naval aviators who were visiting NAS Nowra some years ago. As they were still operating the Gannet, I jokingly suggested that they might like to take our remaining aircraft off our hands. There was no doubt from the expression on their faces what they thought of the idea!

The aircraft next month is the Sea Venom, a solid dependable machine in which I spent most of my time leading an aerobatic team.