ARMSTRONG WHITWORTH SISKIN
The Siskin started life in 1919 as the single-seat Siddeley-Deasy SR2 biplane of fabric and wood construction with wings of unequal span, it was initially powered by an A.B.C. Dragonfly engine with an expected power of 320hp. The prototype Siskin displayed excellent handling and stability outmatching its Dragonfly-powered contemporaries. However, the engine was a disaster, it only provided 270hp and had a very short service life.
By 1920 the Dragonfly engine was replaced with a Siddeley-Deasy Jaguar radial engine, this gave the Siskin performance qualities that impressed the Air Ministry to the extent that they encouraged Armstrong Whitworth (who had absorbed Siddeley-Deasy) to develop the aircraft further. There was one caveat applied to any orders being placed, all future R.A.F. aircraft had to be of an all metal construction.
In response to the Air Ministries directive on all-metal aircraft, a halfway house version of the Siskin was produced with an all-metal fuselage but having wings of conventional wood construction, this became known as the MkII Siskin.
A MkII Siskin aircraft, piloted by Frank Courtney, was entered in the 1922 Kings Cup air race which had to retire after flying some 575 miles because of broken centre section fitting. The following year the same aircraft was again entered in the race which was run over a course of 809 statute miles, it won the race at an average speed of 148.7 mph. However, it was a close run thing as the undercarriage, which had survived several intermediate landings for refuelling, collapsed as the aircraft was being wheeled to a hanger at the end of the race.
For the1923 race Frank Courtney was again piloting the MkII Siskin and was the odds-on favourite to win the race, but Frank had to and yet again retire the aircraft apparently with a broken spinner on the propeller. This was almost certainly not the real cause of the retirement, see Frank Courtney's version of this in his article below.
Further development work, together with lessons learned in competition flying, resulted in the much improved MkIII Siskin entering service with the R.A.F. in 1923. This was an all metal aircraft fitted with a 325hp Armstrong Siddeley Jaguar radial engine and armed with to .303 Vickers machine guns. When the Siskin was retired from service with the R.A.F a total of 385 aircraft had been produced.
Frank Courtney's take on the 1924 Kings Cup air race.
As has been mentioned above, the AW Siskin MkII entry in the 1923 race was retired very early in the race with the official reason given by AW as "the aircraft had a broken propeller spinner".
The aircraft was the one that had won the race the previous year with a number of modifications, including a large diameter air-intake pipe to the carburettor leading vertically down through the bottom of the engine cowling, instead of the earlier twin small diameter intake pipes that had fed horizontally from each side. According to Frank the retirement was almost certainly caused by this modification, please read his version of events of the day:
"On tests everything seemed fine. I was odds-on favourite to win the race. I took off on signal and levelled off at a thousand feet, and headed with wide-open throttle for Newcastle, the next stop. It was a cloudless August morning with a moderate summer haze that left plenty of visibility. After 15 minutes or so something that looked like a small sheet of metal flew back past my head, coming from some unseen spot in front. Nothing seemed to develop from that, so I just kept it in mind and went ahead.
After a while I got the impression that the engine was slowing up, and soon my tachometer showed that it really was. I couldn't think why; it was running smoothly enough' I checked everything I could, but now the loss of power was getting serious; with no other indication of trouble, the engine was acting as though I was slowly closing the throttle.
At last I couldn't even maintain altitude, and saw that I would have to land. I tried to reach the Blackburn Companies airfield at Brough, near Hull, about 130 miles from the start, but I couldn't quite make it and I had to land in a field a mile or so away. I was chagrined and mystified.
I switched off the engine, climbed out, and walked around the front to look things over. The first thing that I noticed was a hole about eight inches square, in the propeller spinner, which explained the piece of metal that had come adrift. But this could have had nothing to do with my engine trouble; I could have left it as it was or else removed the whole spinner with no measurable effect on the engine performance.
I was still puzzling when I heard something 'plop' on the ground. I glanced down to see what looked suspiciously like a large lump of ice that must have fallen out of the vertical intake tube. I picked it up. It was ice, all right. Ice-on a sunny August morning? Absurd! Ridiculous! Impossible!
After some time, a group of Blackburn mechanics came strolling over. I told them about the ice. they looked at each other, evidently not sure whether I thought I was being funny. The ice, unfortunately, was no longer available as evidence. They went over the engine with me, but couldn't find any particular trouble. One of them swung the propeller and I ran up the engine. Perfect.
It was now much too late for me to get back into the race, so I flew over to the Blackburn field, went to an office, and telephoned the Armstrong Siddeley factory at Coventry. I was put through to tough Mr J.D. Siddeley in person. When I told him about the ice he blew up. He said that he would discuss with me later my real reasons for quitting the race, whatever they were, but why did I have to tell him that silly story about ice?
So a report was issued to the press that I had retired from the race due to a broken spinner, and for all I know that story still stands. Nobody who knew my record believed either the spinner story or the ice story. So it was generally assumed that I had hastily invented a feeble cover-up for some serious failure of the Jaguar engine.
However, the companies design engineers were not so sceptical. They made studies and concluded that it was possible in some circumstances, even on a fine day and in the heart of a hot engine, for ice to build up in the carburettor and choke it. Today carburettor heaters are standard installations"
From 'Flight Path' by Frank Courtney.