Below is a look at making a one of a kind Corvair mount.
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The elevation of the engine in the airframe is set by several factors like specified thrust line. On some designs you can alter this with caution, ie, my Pietenpol mount as 3.5″ higher than BHP’s because I deleted the cooling fan. But I wouldn’t try that trick on a tandem wing plane like a Dragonfly, because it has no elevator to counter act the potential pitch change.
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A very important cosmetic issue: The cowl must slope down from the base of the windscreen to the spinner. May sound dumb, but Dan Weseman and I have discussed countless times that an upslope there is a mortal design sin. Along with this, the tops of the main gear tires must point outboard slightly, otherwise the plane looks stupidly heavy. (there are also important dynamic reasons for this) Dan always adds that all fixed gear planes must also have wheel pants, but I don’t agree, but he is too big to argue with.
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Above, down slope to the spinner being assured. This give about a plans height thrust line anyway. The distance from the firewall to the motor is set by CG calculation. This plane had previously been finished and briefly flown on a C-90-12 by a meticulous builder……who made a colossally stupid error on his CG, weighing the plane in a 3 point attitude... it took me 5 minutes looking at his numbers to spot this, his main gear moments were in the wrong place by 1.5″, but his DAR never saw this. Lesson: Trust your own training, don’t assume another homebuilder got anything right.
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If you compare this picture with the previous one, we spent 3 hours yesterday correcting the sag in the main gear which gave the wrong camber to the wheels. The rubber bushings in the Starlet’s suspension design were motor mounts from a popular 1960s car……..The Chevy Corvair.
