Vincent tried for a government contract supplying motors for the ML Aviation U120D target aircraft. The motor had to be capable of passing prolonged full power operation tests. This was called the Picador project. The Vincent motor was upgraded with a better crankshaft, Scintilla magneto, double speed oil pump and fuel injection. They did not get a contract. (Russel Wright's record breaking bike was fitted with a Picador crank and oil pump, by Vincent, while in England for Earls Court, shortly after the 1955 record attempt.)
The following article is by Roy Harper from his book The Vincent H.R.D Story published by the Vincent Publishing Company in 1975 and 1979.
Around the beginning of the 1950 decade Vincents learned of an interest at the Air Ministry in producing a powered target aeroplane to be operated by radio control and to possess a consistently higher speed and climbing ability then the Tiger Moth, which was normally the target aircraft in those days and was restricted to straight and level flight at a limited range of speed and altitude towing sleeve targets. Another disadvantage of the Tiger Moth, to quote from Flight dated August 28th 1953, was 'the psychological discomfort of the aircrew which makes their task an unpopular one.' P.C.V. got in touch with the department concerned and continues the story:
"I succeeded in interesting them in a tuned-up version of the Black Shadow engine suitably modified for installation in the aeroplane they were having designed for them by the M.L. Aviation Company Ltd., of White Waltham, a very insignificant village in Berkshire possessing a very important airfield. My main interest in this contract was a strong hope that if we could gain the order for supply of engines for these target aeroplanes we might have a steady demand for our vee-twin engines, which might enable production of the motor-cycle to continue on an economic basis long after it would otherwise have been discontinued. I also hoped that such a contract would afford us an opportunity of developing the engine to a relatively long life at high power output as these engines were intended to run flat out for the majority of the time that they were flying. The M.L. designers of the aeroplane favoured a back-to-front layout completely reversed from the normal motor-cycle position with the exhaust ports located in the rear side of the heads, where they received reduced cooling. We were not unduly concerned about this because we expected that practically all of the time that the engine was in flight it should be travelling at upwards of 190 miles an hour, which is slightly more draught around the heads than the poor old bicycle has a chance of creating."
"We envisaged a new crankcase in which the parts around the engine flywheel and timing gear would remain substantially unaltered while an entirely new bevel gearbox was added to replace the four-speed gearbox used for the motorcycles. This gearbox would be driven by a triplex chain from the crankshaft with an overall reduction of 2 to 1."
The development work on the Picador was carried out by C.J. Williams and Alec Mitchell, firstly at the works and later in a hanger at de Havillands.
As the specification requirements meant that the U120D would be shot off a ramp (by three rockets) at an acceleration of 10g, conventional carburetters could not be used and Jack Williams designed the fuel injection system in which the output of a C.A.V. pump was related to the throttle opening while a barometric aneroid control ensured that the air/fuel ratio was constant at different heights. Both throttles were operated by a common shaft and were kept fully open by a spring. For starting the throttles were held in a slow-running position by a peg, which was removed immediately the Picador engine had been turned over by an electric starter motor on the launching ramp engaging a starting dog on the drive side end of the crankshaft. When the enginie fired the rockets were automatically ignited and the U120D accelerated into the air.
In flight, the aeroplane was controlled from the ground by radio and could perform a variety of vertical and horizontal manoeuvres. When it was time for the U120D to be landed a radio signal released an Irvine triple-parachute and at the same time a flotation bag and a shock absorbing cushion were inflated, thus enabling the aircraft to descend in a horizontal position and make a gentle touch-down on land or water. The command to release the parachute also cut the magneto and switched off the fuel.
The control system had several built-in emergency devices. A "memory" retained knowledge of straight and level flight during the various manoeuvres commanded by ground control and these movements were opposed by feed back to eliminate instability and hunting. Should the engine stop unexpectedly, the parachute was automatically relased; if radio control were lost, or the aeroplane descended to a preset height, its radio equipment released the parachute and also switched of the engine and fuel.
The life expectancy of the aeroplane was 12 hours but as it was constructed in three all-metal sections, with the engine held in position by four simple mountings and the electrical equipment coupled to an adjacent section by plug and socket connections, replacement of the engine or damaged section was quick and easy and would have extended the life of the U120D.
After several months development work the Picador engine, which weighed 200 lb. and incorporated Mk II cams, Scintella magneto and K.L.G FE102 sparking plugs, had an output of 65-70 b.h.p at 5,000 r.p.m. with a compression ratio on 10 to 1. It was installed in the U120D and preparations were made for the target aircraft's maiden test flight at Tenby, Glamorganshire. Jack Williams was present and describes the occasion:
"The weather that day was not too bad but there was a very low cloud base. In the afternoon the place became absolutely stiff with high-ranking officers. There were admirals, air-marshals and impressive-looking gents in bowler hats. Then cam the time for the flight test of the aircraft. My mechanic got things under way; the starter flew in, the engine fired, the rocjets automatically ignited and the aeroplane shot into the air."
"For some reason, the chief designer of M.L. Aviation had decided that he would fly this aircraft himself and he'd got the box (with the strap around his neck) in which the controls were mounted like an aircraft's - stick and rudder, etc. He had got at his ear an army captain who was watching the instruments from the predictor telling him exactly were the aircraft was and what it was doing but unfortunately because of the low cloud base the U120D promptly disappeared into the clouds and we couldn't see it. The chief designer probably thought 'That's bad because all these high-ranking officers have come here to see the aeroplane and the thing is up above the clouds' so he decided to bring it down but, panicking a little perhaps, he ignored the instructions from the army captain standing by the side of him. As far as I could tell, he must have flown it by ear because there was the sound up above while I was looking out over the sea. I said to my mechanic, who was standing next to me: "Jack, for goodness sake don't look now but it's gone into the drink." The sound was still above us of course. Meanwhile the poor old army captain first went red in the face, then he went white, because he was doing his level best to tell this chap who was flying the aeroplane not to fly it by ear. Anyway there it was, it went into the drink. There was a dreadful hush. Then a high-ranking officer said to a colleague: "Well, see you in the Pall Mall, old boy" and the gold braid just disappeared."
After the failure at Tenby, the Air Ministry decided that the U120D should not be flown in England again. The aircraft were taken to Castel Benito in Libya, where they couldn't do much harm, and Jack told me that "they flew very well indeed, except for the loss of two when radio contact was lost".
I asked him how many Picador engines and M.L. aircraft were made and he put the totals at ten and six respectively before he left the company in 1953. About thirty engines were made altogether.
The Picador, which was a high compression racing engine running continuously on full throttle, had an excellent reliability record and there is no doubt that had the U120D overcome its radio control difficulties and had been ordered in quantity by the Air Ministry, motor-cycle production at Stevenage would have continued for many more years.
Source: Roy Harper from his book The Vincent H.R.D Story published by the Vincent Publishing Company in 1975 and 1979.