Friday, March 21, 2008

Origins of the Velocette swinging arm frame

Looking at the 1936 works Velo racer frame debuted in the Ulster GP, IOM TT and other continental races that year and the Mk.8 KTT frame which was its derivative, you can’t help noticing that it was the same as the twin shock frames used up to and still often today…..
How did this occur?
Ivan Rhodes and I have discussed the matter on numerous occasions and in correspondence and the consensus between us seems to be that either Harold Willis, Charles Udall, possibly Phil Irving and others or all in discussion came up with the idea of removing the rear fork section of their current rigid frame, welding a steering head casting across the rear down tube and fabricating some arms that initially were internally splined and slid onto a splined trunnion shaft ( some accuracy needed here to here to ensure the axle slots at the end of the forks were dead in line…). The “bearings” were the actual cup and cone steering head races.
Ivan has the one of the first frames made, designated SF2 and the picture clearly shows all the above.
The oleo rear struts were needed to form the other vital part of the change and as Harold Willis flew his own aircraft a DH60 Moth known by him as “Clattering Kate”, he obviously read the flight magazines of the day, “Flight” and “The Aeroplane”, as well as technical society papers and according to Charles Udall in an interview with Ivan late in Udall’s life , Willis was the one who came up with the idea and visits to the Dowty company in Glostershire, presumably with Percy Goodman, and perhaps Udall followed.
George Dowty, later knighted for his services to the British aviation industry, worked initially at A.V.Roe and then in the mid 1920s at Gloster Aircraft Company. He presented a paper in 1922 to the Royal Aeronautical Society on the subject of oleo undercarriage design and then in 1926 a second paper “Aircraft Alighting and Arresting Mechanisms” and followed with articles in Feb.1929 in “The Aeroplane” and others in “Aircraft Engineering”.
He was unable to convince aircraft manufacturers and others of the time to take up his ideas and in Jan.1931 formed a company “Aircraft Components Company” and from this the huge Dowty Organisation followed which is still a major player in aviation today.
Willis and Goodman obtained from Dowty experimental rear oleo legs which were used on those early spring frames in 1936. Eventually Dowty went into limited production with the rear units for the Mk.8 KTT and following WW2 supplied front oleomatic forks as replacements for the Webb girders to Velocette, Scott and Panther.
The top photo is Ernie Thomas on his 1936 350 DOHC TT machine. Thomas was a comfortable 2nd during the race until he fell on the 5th lap, remounted and finished 3rd..a nice debut for Velocette for their new DOHC engine and swinging arm frame.Photo credit to S.R.Keig Ltd, Douglas, IOM.
The photo in the centre is Stanley Woods 1936 500 SOHC factory Velocette seen in IOM at the TT, it shows one of the prototype rear oleo suspension legs. The photo credit is to "MotorCycle"/Mortons Media Group.
In the lower left photo the cup and cone bearing are clearly visible as is where the rear part of the original rigid frame was cut off.. Photo credit.Ivan Rhodes.
The lower right pic is from a prewar Mk.8 KTT I had, showing the name plate...Aircraft Components Ltd., "The Dowty Oleopneumatic Strut". Poor quality pic, but the struts are gone....
This item in part was originally written & published by me in FTDU330, p.24, Summer 2004 edition & published by the Australian Velocette Owners Club.
Left click on photos to enlarge.

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