Reflections – Bristol Sycamore

The history of the RAN’s association with helicopters goes back just on 40 years to the time when HMAS Sydney was operating her three squadrons off the west coast of Korea. The USN very kindly lent us a Sikorsky S-51 Dragonfly, plus crew, to act as plane guard while deployed in the theatre. Up to this time we had relied on the time honoured destroyer as Resdes.

Good old UP-28 (its side number) really earned its keep, including carrying out the longest rescue mission of the war when one of our Fireflies was shot down well inland and the crew was extracted under enemy fire. I doubt that the RAN would have got into the helicopter business as early as it did if it hadn’t been for that experience. In those days, the helicopter was avoided by all fixed wing pilots as being not quite respectable.

In line with the policy of the time of “buy British”, it was decided to purchase a number of Bristol Sycamores to act as plane guard and these duly arrived in 1953 with HMAS Vengeance, which had been taken on loan from the RN while we were waiting for HMAS Melbourne to be completed.

The aircraft were soon proving their worth, in particular in the SAR role ashore, and carried out many civilian rescues, the most noteworthy being in the floods of 1953. One incident which is amusing in retrospect, was the time two foolhardy souls ventured out to sea off Jervis Bay in a small aluminium boat. When they hadn’t returned on time, the distraught wife of one of them rang NAS Nowra pleading for help. It was that time of the year when howling westerly winds blow for days on end at Nowra, however the duty SAR crew bravely got airborne and commenced to search. They fairly rocketed out to sea with a 30 knot tailwind and pushing their luck, went further out than prudence dictated. Lucky for the fishermen they did so as the latter were found miles to seaward, having run out of fuel. After winching aboard the survivors, the SAR crew then had a battle to get back to the shore as their ground speed was only about 30 knots. They made it only to have the wife ring the following day, to berate the duty officer because the SAR crew hadn’t saved the boat!

Following the 1959 decision (the first of many) to disband the FAA, a few dedicated staff officers managed to achieve a reprieve by proposing and having accepted, a policy of converting Melbourne into an ASW helicopter carrier, operating Wessex ASW helicopters.

As a result of this fairly dramatic change in the way we were to operate in the future, it was decided that all pilots would be converted to helicopters in readiness for the new aircraft. The obvious aircraft to be used for the conversion program was the Sycamore and we began to be processed through in batches.

I must admit to being in two minds at the time about the move to an all helicopter FAA; on the one hand it would mean the end of my fixed wing flying career, but on the other it opened up the new world of hovering flight which had always intrigued me.

As to the aircraft itself, shortly after the war Bristol Aircraft bravely decided to enter the helicopter market and to design and build a completely new aircraft. It did however, incorporate proven helicopter principles, particularly the fully articulated rotor head with feathering, flapping and drag hinges.

A pecularity of the design was that the head was tilted six degrees forward and one and a half degrees to the left, the aim being to obtain a level fuselage in cruising flight. This had to be compensated for on take off by moving the cyclic back and to the right to level the disk. At the same time the collective had to be raised at a rate which increased rotor RPM from 250 to 269. There was no governor to control rotor RPM, however the collective had the usual throttle/pitch cam which increased engine power as the collective was raised, but you had to be on the ball with the throttle twist grip to trim to the desired rotor RPM. The twist grip was rotated away from you to increase power and a common problem with anyone who had ridden motorbikes was to rotate the grip the wrong way. This, as might be expected was known as “motorbiking”.

The tilted rotor head, apart from making life difficult for us helo tyros was the cause of at least one prang when a takeoff was attempted without first levelling the disk. It was also to cause innumerable scares with passengers trying to embark from the front, when only the quick reaction of the pilot in tilting the disk saved them from being decapitated.

One unusual fitment in the Sycamore was a collective pitch angle of attack indicator; this was interesting to observe in a climb to height as the pitch angle increased. Another unusual feature was the fitting of ballast tanks in which water( from memory), could be pumped from front to rear and vice versa to maintain the c of g in limits.

The Sycamore was powered by a 520hp Alvis Leonides 7 cylinder radial air cooled engine which had a centrifugal clutch which automatically engaged as the throttle was opened. Being a wheeled helicopter, care had to be exercised when engaging the clutch and hence the main rotor that it was done quickly and smoothly to prevent ground resonance or “padding”. This could develop very quickly if there were any out of balance forces in the rotor system. Because of the dangers, we were given a demonstration of ground resonance as part of our introduction to the wonders of rotary flight. This was done with the aircraft sitting on the ground and the main rotor at takeoff RPM. The cyclic stick would then be deflected sideways and back to the centre without damping the lateral movement of the aircraft, which would then start to rock from wheel to wheel, the motion rapidly accelerating as it bounced from tyre to tyre. The only way to stop the aircraft from shaking itself to pieces was to lift it into the air. It was a very convincing demonstration and made you very conscious of the need to check the rotor system thoroughly on pre flight and also of the need to check that the tyres were correctly inflated.

The aircraft was trimmed manually via large trim wheels at your left hand and these had to be used constantly to counteract the large trim changes that occured between hovering and forward flight. There was a particularly large lateral change of trim, which in the Mk50, which was flown from the left hand seat and therefore had the trim wheels on the right, required some rapid changing of hands both to and from the hover. The technique, as I recall, was to let go the collective, grab the cyclic with your left hand and madly trim with your right, reversing the procedure after trimming.

I found cruising flight reasonably “normal” but my first attempts at hovering were confidence shattering. My instructor was an old friend who had undergone the flying instructors course with me which made my miserable performance even harder to bear. I well recall his comments about the Mississippi Paddle Steamer which had enough steam either to turn the paddles, or to blow the whistle, but not both at the same time! I would get the hover height right only to have the aircraft drift off from the hover spot. Next it would be rapidly decaying rotor revs as I pulled too much collective without trimming with throttle.

Needless to say, I slowly improved my hovering skills and got it down from “county” to “parish” to “field” and in the end could maintain a respectable hover on the spot.

Having finally soloed, we proceeded to learn how to use the aircraft which of course included winching. Many hours were spent “box knocking” where a box would be placed on the ground in a remote part of the airfield and we would practice making approaches conned by a crewman in the back.

The culmination of all our efforts was wet winching in Jervis Bay where we winched a live body, and in turn were winched by our fellow course members. The performance of the Sycamore was not exactly startling and on one occasion, on being given the order “up gently” which meant the survivor was in the sling and that he should be lifted out of the water by raising the collective, I found that there was nothing left as I pulled power. As we began to lose rotor revs, all I could do was to “milk” the revs by lowering the collective a fraction and as the revs slowly built up, move forward to try and gain translational lift. The poor old survivor on the end of the cable had to endure being dragged through the water but it was a better option than having a flaying Sycamore settle on top of him!

One of my most exciting moments in a Sycamore was the occasion when I experienced vortex ring (or settling with power) a few feet over the intersection of the two runways at Nowra. This is normally caused by too steep an approach where the aircraft’s rate of descent starts to match the inflow of air through the rotor giving rise to loss of lift. The Sycamore was susceptible to this phenomenon and we were given an early demonstration of its effects, but it was not easy to appreciatejust what was going on at the safe altitude at which it had to be demonstrated.

On the occasion in question, I reduced power to commence the approach and on coming up on the collective as I commenced the flare, experienced a strange noise, and felt the aircraft starting to settle. There was no response to the increase in collective pitch and it didn’t take too many nano seconds to work out what was happening, but the question was what to do about it? Once again good briefing, and the fact that I had hoisted it in, came to my rescue. There was only one way out and that was to lower the collective and to push forward on the cyclic to slide off the mass of disturbed air. This was no easy thing to do at 50 odd feet above the ground, with an already high rate of descent. With the nose pointing at the concrete intersection, I came up on the collective and to my immense relief, the aircraft responded normally. My passenger, a young chap who had completed the previous course, sat there oblivious to what was going on. He commented later that he thought I was throwing it around a bit!

We did most of our flying at the Jervis Bay airfield to keep us away from the real aeroplanes back at Nowra. It was strange to be bepracticing hovering on the airfield on which I had spent countless sorties doing dummy deck landings. Amongst other things we were shown was the effect of weight on performance. This was done by stabilising (as best we could!) the aircraft in a low hover and then have fellow course members climb on board one by one. The aim was to maintain the hover height as the load was varied, no easy matter. Another demonstration was of the Sycamore’s tendency to pitch nose down if it was flown too fast in backwards flight. This was done by rapidly backing up in a rearwards climb when suddenly you would find yourself looking at the ground as the nose pitched down.

Exploring the limits of the rotor head in sloping ground landings also provided its share of excitement, particularly when you exceeded them on lowering the collective! During confined space landings, clipping the tips off small gum trees also proved to be interesting.

Finally, as we gained experience and confidence in our ability to fly the aircraft, we were introduced to quick stops into and downwind. This put to the test the skills we had acquired in controlling rotor revs with the throttle and collective.

To my regret, I only managed to fly the Sycamore a few times after completing the conversion, having by then commenced the Wessex course, so once again I can’t profess to being an expert on the marque. However, I acquired sufficient experience in the machine to be confident that I could fly it within the permitted limits of its flight envelope, which I think is essential to be able to do in any aircraft.

In conclusion, there is no doubt that having learnt to fly rotary wing in the Sycamore, there were very few surprises to be found in any other helicopter (except perhaps. the Belvedere!) and hence it proved to be an excellent training vehicle.

The next aircraft is the Wessex which served the RAN well in its long career