Friday, March 21, 2008

ORIGINS OF THE SWINGARM FRAME

by Dennis Quinlan

When looking at the frame of the 1936 works Velocette racer, which debuted in the Ulster GP, Isle of Man TT & other continental races, you can’t help noticing that it (and the MkVIII KTT frame which followed) was the same arrangement as the twin-shock swingarm frames still in use today…..
How did this occur?
Ivan Rhodes & I have discussed the matter on numerous occasions, and our consensus seems to be that Harold Willis (development engineer at Veloce), Charles Udall (Chief Designer for Veloce), possibly Phil Irving & 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 & slid onto a splined trunnion shaft. This required accuracy in machining and assembly, to ensure the axle slots at the end of the forks were dead in line. The “bearings” used to hold the trunnion shaft were the actual cup & cones used on Velo steering head races. Ivan has the one of the first frames made, designated SF2, and the photos show clearly all the above.

springing arrangment, which is in fact the novel factor in the equation, as swinging arm suspension had been imperfectly applied to motorcycles since the very earliest days. WhatOleo hydropneumatic rear struts were used to form the other vital part of this new rear was the inspiration for the use of these 'shocks'?

Harold Willis (who had joined Veloce in 1927 as a works racer, and who applied the first successful positive-stop footshift to a motorcycle) flew his own aircraft (a DeHavilland DH60 Moth, known by him as “Clattering Kate”); being an engineer, he obviously read the flight magazines of the day (Flight & The Aeroplane), as well as technical society papers. According to Charles Udall, in an interview with Ivan Rhodes late in Udall’s life, Willis was the one who came up with the idea for the rear springing, and made visits to the Dowty company (maker of Oleo landing gear for aircraft) in Gloucestershire, presumably with Percy Goodman (son of John Goodman, founder of Veloce), and perhaps Udall.

George Dowty, and inventor of hydraulic landing gear for aircraft (and later knighted for his services to the British aviation industry), worked initially at A.V.Roe, 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 & then in 1926 a second paper “Aircraft Alighting and Arresting Mechanisms”, followed with articles in Feb.1929 in The Aeroplane & others in Aircraft Engineering.
He was unable to convince the aircraft manufacturers to take up his ideas, and in Jan.1931 formed Aircraft Components Company, and from this the huge Dowty Organisation followed, which is still a major player in aviation.

From Dowty, Willis & Goodman obtained experimental rear oleo legs, which were used on their first spring frames in 1936. As they were successful, Dowty went into limited production of the rear units for the MkVIII KTT. Following WW2, they supplied telescoping oleomatic front forks (as replacements for Webb girder forks) to Velocette, Scott & Panther.
The top three photos show Stanley Woods' 1936 'works' Velocettes, with the top pic a dohc 350cc, seen at the Isle of Man TT, using the prototype rear oleo suspension legs (photos from TheMotorCycle/Morton's Media Group).

In the bottom photo, the cup & cone bearings are clearly visible, as are the sawn-off lower frame lugs, which originally connected to the rigid rear end (Ivan Rhodes photo).

This crux of this article was originally written & published by Dennis Quinlan, in FTDU330, p.24, Summer 2004 edition.

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