Reflections-Westland Wessex

The aircraft was a turbine powered version of the Sikorsky S-58 built under licence by the United Kingdom firm of Westland and first delivered to the Royal Navy in 1960 as the Wessex Mk1. The engine was a Napier Gazelle gas turbine. Amusingly, when Napier was taken over by Rolls-Royce, the latter removed most of the fuel control system with its many half ball valves and bell cranks and not surprisingly the engine ran better as a result!

The rotor system had a conventional fully articulated head with four folding blades and a folding tail cone which carried the tail rotor. A wheeled undercarriage was fitted to enable the aircraft to be moved around the hangar and flight decks.

The one aspect of the aircraft which was new to us all, was the automatic flight control system (AFCS or “system”) which, with the press of a button, would fly the aircraft into a 35ft hover, and then control it over the submerged sonar ball. It was of vital importance that we learn how this functioned as we had to trust it at night, often in bad weather and with no horizon. However, more of that later.

After the Sycamore (refer p. 44 Mar 92 AA), the Wessex was easy to fly. It had a fully governed engine and rotor system which maintained the rotor revs dead beat even with coarse movement of the collective lever. In addition it had, relatively speaking, plenty of power so you could get yourself out of trouble with a hand full of collective.

After the usual period of ground school, we commenced our conversion. My initial dual was not without incident as I was to learn the hard way about the torque system going into “open loop” with the flight control system engaged when high power was pulled. I think it was about my second ride and the aircraft for some reason was parked fairly close to the hangar. I had yet to get the feel of the collective and was a little fast in lifting the aircraft into the hover We normally flew with the flight stabilisation system engaged which meant that the aircraft would hold heading with your feet off the rudder pedals. If you wanted to change heading it was only necessary to touch the pedals and micro switches would cut the system out. Because of the limited authority of the flight control system and the large range of movement that had to be catered for in the anti torque system, the latter would go into “open loop” when it had reached the then limit of authority and reposition itself for another bootfull. This meant that the rudder pedals actually moved under the authority of the system. It was SOP to take off with your feet off the rudder pedals and in this instance, as I had pulled a lot of collective, the system put in a rapid bootfull of rudder to hold heading moving the pedals as it went into open loop, causing the latter to touch my foot. The system immediately kicked out and we went up in a screaming torque turn. My instructor thought I was being really fancy in my flying doing a torque turn out of the hangar dispersal area!

With a few hours dual we were soon all off solo, but then generally flew two up on mutual exercises to get to know the aircraft; this included the usual confined spaces, sloping ground, autorotations etc. One aspect of the aircraft that I didn’t like was the flight control/trim system. Trim was controlled by a four-way button on the top of the cyclic stick which was very slow in operation. The cyclic control had what I considered to be too heavy a breakout force so you were constantly having to use the trim release button on the stick. This released all trim forces and repositioned the trim to the new position of the stick. Formation flying with this arrangement was a pain and I usually switched the stick force off and flew with no load at all on the stick. The only snag with flying without stick force was that if you let the cyclic stick go it would literally fall to one side. This was not normally a problem but I once let go of the stick on the ground in this condition and the blades were instantly on the droop stops on that side!

An interesting question; I don’t know how other people react, but I always developed an itchy nose when ever flying a helo in formation. I put it down to a psychosomatic reaction to not being able to let go of the controls with either hand.

My only other problem with the aircraft was with the seat. In the conversion phase of our flying we used a back cushion but this was replaced by a back pack dinghy once we started over the sea work. It was fine with the back cushion but my behind used to spill over into the space below the dinghy, which sat in the middle of your back, and I found myself sitting on a very hard and painful cross bar. I was the only oneon course to suffer this problem (perhaps I had the biggest behind!) but I soon found a ready solution by having a horse hair oblong pack made up to fill the space. It worked fine.

Instrument flying followed next and proved to be much more demanding than in any fixed wing aircraft I had flown because we had to be capable of monitoring the AFCS as it flew the aircraft into and out of the hover. As well as that, we had to learn to fly the aircraft in the hover itself with the instruments essentially static, no easy matter. We used two stage amber which consisted of amber screens covering the front and side of the cockpit and amber goggles for the pilot flying the aircraft. It worked fine except for thelack of screensin the overhead panels which when turning, let a bar of sunlight move across the instrument panel which was inducive to vertigo. I guess the problem never arose with the Royal Navy because the sun never shines in the UK!

The AFCS was programmed to fly a set pattern which would take the aircraft into a “doppler” hover from which a “cable” hover could be captured. The aircraft would be flown from “jump” to “jump” at 125ft with the barometric height hold controlling height. It would then be turned into wind, and the first pilot would call for the second pilot to “engage”. The latter would engage the AFCS and the first pilot would then take his hands and feet off the controls. The AFCS would lower the collective, raise the nose and take the aircraft down to the height selected, normally 35ft. The system would then bring the aircraft to a hover using the doppler return from the sea surface. Once in the hover, the sonar ball would be lowered and when completely steady, the hover would be transferred to the cable. It was important that the ball not be dragged through the water as this degraded the sonar’s efficiency. The system’s aim was thus to maintain the aircraft vertically over the ball which it did by a set of sensors in the form of fingers through which the cable passed. Should the aircraft drift forward, the cable would touch the rear sensor which would send a message to the flight control system to back the aircraft up. Equally, if the aircraft drifted to the right, the cable would touch the left sensor and the system would fly the aircraft back to the left. The system was designed to handle left/right and forward/back at the same time and would adjust accordingly.

All this sounds fine but it must be remembered that this was a system designed in the fifties employing very basic technology. Often, the practice was vastly different to the theory!

Firstly there was the problem of the system just not staying in tune and not being able to cope with the conditions. This could occasionally be overcome by pilot input, that is, taking over from the system, steadying it down, and then handing back to the cable hover.

One thing the AFCS didn’t like was making an approach out of wind and then attempting to hover. To overcome this, we used to fly with the side doors open so that we could feel the wind in the hover and correct if needs be.

As outlined above, the transition between jumps was made at 125ft with the barometric altitude hold engaged. I once had an aircraft that was a bit ropey on holding height so I tried to help it with a bit of collective. It didn’t likeit, and when I tried to hand the aircraft back, it attempted to wipe off the error I had induced, all in one go; the collective felt like a piece of limp spaghetti as we made a dirty dart for the sea.

Another thing the system didn’t like was lack of doppler return as it was endeavouring to bring the aircraft to the hover. This could happen with a glassy sea when the doppler signals sent by the system reflected off the water and didn’t return to the aircraft. The aircraft would then just drift aimlessly forward without coming to a hover. Should the system suddenly get a doppler return, it would try to correct all the errors induced in one go, backing the aircraft up alarmingly and sliding backwards out of ground effect in the process. I had this happen to me early on in my introduction to the marvels of night ASW work when we were trying to get the aircraft into a hover in the middle of Jervis Bay on a very still night. We were not achieving a hover when suddenly we got a doppler return from our rotor downwash. The nose pitched up 10 degrees and the aircraft started madly backing up, and descending backwards as it did so. I can assure you that this is not a manoeuvre to attempt to recover from on instruments so I hit the “pickle” button under the collective which was designed for just such an emergency. The “pickle” button system was programmed to apply up collective and fly the aircraft out of the hover. I hadn’t practised this emergency procedure before and as a consequence wasn’t ready for the large amount of collective applied by the system; I learnt afterwards that you were meant to restrain the lever! As a result of my hitting the button, we went up in a screaming torque turn, with full power on, so fast that the ball was flicked off the end of the cable. To my knowledge I am the only pilot to have castrated a Wessex!

Hovering over the sea in daylight was a piece of cake after the odd hairy ride on a dark and stormy night. However, on one day trip when I was just sitting there enjoying the view I happened to look down and there was the biggest Hammerhead shark I ever hope to see. It was cruising around under the aircraft and had obviously come to see what thenoisewas all about. My immediate thoughts were “please engine, don’t quit now!”. Fortunately it didn’t and we rapidly recovered the ball and found ourselves another bit of ocean less crowded to play in.

The hover height when cable hovering was determined by the system measuring the water pressure at the ball depth. It knew that there was a total cable length of 90ft, so if you had dialled in a hover height of 35ft, it determined that the ball should be at 55ft. This was of course with the British 194 sonar and not the later American AQS-13 variable depth sonar in the modified Wessex MK31B.

I have often remarked how fate rules our destiny. During a day trip with the AFCS engaged, I suffered a ball depth sensing element failure which went to zero depth generating an immediate down collective signal. I grabbed the collective just in time to prevent us from ending up in the water. This was a rare occurrence; I can’t recall us experiencing a previous failure. A week later, as we were in the hover at night, the dome submerged light flickered. I had my hand under the collective as usual but just beat the system as a massive down collective signal immediately followed. Maybe we would have been OK but the experience of the week before had prepared me.

As things turned out, just before the end of the course I was selected for promotion and as a result was posted off to other things so I never did get to fly the aircraft under frontline conditions. I did however as a result get to fly the Mk2, Mk3 and Mk5 versions of the aircraft in the UK. The Mk2 was the RAF version and the Mk5 the RN version of the twin Gnome troop carrier/ commando aircraft. You could tell the difference between the single engine version and the twin by the fact that the former had two exhausts each side and the latter one!

The Mk3 was a later version of the ASW aircraft with 195 sonar. The RAN looked long and hard at fitting 195 when the Mk31 was updated to the Mk31B but instead opted for the American AQS-13, a fatal mistake. This was because AQS-13 was designed to go into the USN SeaKing with a much larger opening in the floor which meant the system had a better cable movement to control deflection ratio. When it came time to fit AQS-13 into the Wessex, because of the smaller hole, the AFCS had up to its electronic design limit and as a result it never functioned satisfactorily.

There is no question that the Wessex served the RAN well. For a single engine helicopter operating over the sea at night it is remarkable that so few were lost. In its later years it continued to serve in the utility role and did a fine job.

For my part, I enjoyed my time flying the Wessex; it was certainly a challenge operating it in the ASW role but otherwise it was a pleasant and reasonably comfortable aircraft.