The Foxwell Su­per­charger

Classic Racer - - MACHINES -

The un­usual su­per­charger that Messrs Irv­ing and Willis chose for their ex­per­i­ment was a prod­uct of Daniel Foxwell and Son of Chea­dle, Man­ches­ter. The main in­ter­est for this long-es­tab­lished com­pany was tex­tile ma­chin­ery and the Foxwell blow­ers ap­pear to have been a side­line, ap­par­ently in­tended for use with in­dus­trial vac­uum clean­ers. How­ever, it was a com­pact unit, suit­able for the ini­tial pur­pose and, even­tu­ally, rel­a­tively easy to install on a mo­tor­cy­cle. This one com­po­nent sets Clara apart from any other KTT Ve­lo­cette. While Ivan Rhodes could gather all the other bits he needed for the restora­tion from var­i­ous sources, with­out a re­place­ment su­per­charger it looked as if the project would stall. Sal­va­tion ar­rived cour­tesy of Ve­lo­cette en­thu­si­ast Den­nis Frost, who had man­aged to track down some orig­i­nal Foxwell draw­ings. Fel­low en­thu­si­ast Chris Wig­gins did some up­dat­ing to the de­sign and his brother Rob pro­duced the cast­ing pat­terns. An­other en­thu­si­ast, Harold Beal, of­fered his ser­vices and even­tu­ally took over the cast­ings for fin­ish ma­chin­ing, as well as deal­ing with the other in­ter­nal parts. The sup­port of the vanes is un­usual on the Foxwell unit. A cir­cu­lar, alu­minium bronze plate lo­cates within each end cap. Each plate has a cir­cu­lar groove that de­ter­mines the path of six alu­minium seg­ments. Each seg­ment has a cir­cu­lar hole to sup­port a round piece of brass. Each brass piece has a slot to lo­cate the end of a vane, but the de­sign also per­mits a cer­tain amount of float. It leaves a min­i­mal clear­ance be­tween the vanes and the hous­ing. Com­pared to other cen­trifu­gal com­pres­sors, the un­usual bear­ing de­sign re­duced some fric­tional losses, but cre­ated oth­ers. While the draw­ings that Den­nis Frost had lo­cated had en­abled the cast­ings to be made, there were no pre­cise di­men­sions for the ma­chin­ing of the su­per­charger. Harold is a re­tired engi­neer, but he also has a com­pre­hen­sive home work­shop and a knowl­edge of CAD (com­puter aided de­sign). He worked his way through the com­po­nents un­til he could prove, in the­ory, that ma­chin­ing ev­ery­thing to the pa­ram­e­ters he had worked out, the su­per­charger should do as its de­sign­ers in­tended. The clear­ance be­tween the vane and the hous­ing was just one-thou­sandth of an inch! It took many hours of work­shop time to com­plete the work but, even­tu­ally, it was time to put the re-cre­ated su­per­charger to a ‘dry test’. Ivan sup­plied a Best & Lloyd oil pump, which was the same as that fit­ted orig­i­nally to Clara.the rest of the trial jig in­cluded a 2hp elec­tric mo­tor to drive the su­per­charger. Ap­par­ently, used in this ap­pli­ca­tion, the me­chan­i­cal op­er­a­tion of the vanes ab­sorbs a lot of power. In Harold’s opin­ion, the orig­i­nal set-up was prob­a­bly worth no more than an ad­di­tional three or four horse­power. The su­per­charger was run for an hour, dis­man­tled and checked, then run for a fur­ther hour. With noth­ing un­to­ward, it was handed over to Ivan for him to carry on with the re­build.

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