Author Topic: Douglas Patents of Note 01  (Read 5011 times)

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Offline Doug

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Douglas Patents of Note 01
« on: 19 Oct 2007 at 04:21 »


Improvements in or relating to the Frames of Motor Bicycles

Patents of Note: 01
Patent No.: 290,825
Application: May 17, 1927
Complete: Feb. 15, 1928
Accepted: May 24, 1928


The object of the present invention is to provide a construction having a very low centre of gravity and equal weight distribution between the two wheels; which will result in a machine which will steer and corner well at high speeds. 

This unusual frame was patented by Douglas Motors Limited and Cyril George Pullin.  Noted features in the claim is a lower frame member that …extend in a straight line from the rear axle lug to their forward ends… and …an upper frame member (or members) extending straight from the top of the steering head to the rear axle lug.  Sounds like a Cotton frame!  More to the purpose, the lower frame rails were to be …adapted to have suspended beneath them an engine with horizontally arranged cylinders…  This was to be connected via the frame lugs 16 in the patent drawing- though if via the horizontal or vertical holes shown in the lugs- is not stated.  While further elaborating The engine (not shown) has two cylinders… in a fore and aft direction… it is also mentioned the connection could be via lugs on the crankcase or ‘crankcase covers’.  In addition The gear box is preferably integral with, or attached to, the crankcase, and is arranged low down behind the back cylinder, still further lowering the centre of gravity.  It is not clear if this means below the back cylinder (like the 3-1/2hp Sports) or above (like the RA.) Probably the later as the RA also had the transmission mounted off of the crankcase. It is unlikely it was truly behind or aft of the rear cylinder as done with the side valve machines; the length of an OHV unit would preclude such. 

It would appear to be a design inspired by the by then obsolete Sports models of 1922/23, in which the lower frame rails were rather high off the ground.  A small step then to sling the engine under, rather than on top of, the frame tubes.  Though by 1927 Douglas was well down the other path with the RA and subsequent TT/I.o.M. racing models as well as the OB/OC road models, with the engine sitting on top of very low, lower frame tubes.  The gearbox integral would reappear in the Ascot-Pullin, though on that machine there was no rear cylinder to contend with.  Where as Although the frame of completely tubular construction has been described, the horizontal member or members… to which the engine is attached, need not be tubular and may be of pressed steel. reflected Pullin’s love for stamped sheet metal in general. 

Apparently there was such a thing as too low.  Rather than using an oil sump, the brackets 15 are provided to hang the oil tank from the lower tank rail.  The purpose of the tube projecting down vertically from the one lower frame rail is unexplained.  If it were only on the other side, it might be a low attachment point for a sidecar. 

Just such an experimental machine is mentioned in The Best Twin by Jeff Clew. Developed in about 1926 by Cyril Pullin as a special TT model, it was tested at Brooklands by Jim Whalley, Rex Judd, and Graeme Brown. The engine was equally unorthodox (for Douglas) as notable features mentioned are leaf valve springs, primary drive via helical gears, and a four-speed gearbox. No picture of the machine or engine has been yet seen by the author.

© 2007 D. Kephart, Glen Mills, PA, USA
« Last Edit: 26 Oct 2007 at 03:17 by Doug »