Why Not?

So how come none of these hot rod machinists have offered us maple motor mounts bored from the back to save weight? ie: a 3/8" hole in a 1/2" square piece would be stronger and a bunch lighter, yet exhibit none of the tendancies that cross drilled pieces show?

BTW, go to the Smokey Yunick web site http://www.smokeyyunick.com/ and tell me how that works?
(Finally finished the book?)
See Ya

If I understand your question correctly, you want a motor mount drilled lengthwise? I suppose it could be done but from my years of woodworking I have found that drilling lengthwise (IE with the grain) is a trying experience to make it work correctly. The problem is that the drill bit point tries to follow the softer part of the grain and then "tunnels" down that pathway. Usually the result is a drill bit that comes out the side of the wood. I have done it but only by taking more time than most people would want to pay for. Jigging on a drill press works but even then the bit wanders. Removing wood in either direction would result in a lightening. I suggest that you go behind the motor - say an inch and thin the mounts down to half the thickness. Start your drilling at this point and use a small drill and increase the diameter as you go toward the rear of the plane. With the doublers there the strength should not be effected that much.

I just clamp a fence on the drill press, use a sharp 1/4" drill and Swiss cheese the aft part of the motor mount. I think it is adequate for sport flying and the putzing around I do. Simple and effective.

The hot rod guys are using Titanium!!. Rich , I looked for you at nats, but they said you left . I brought an extra speed limit pig for ya.
I just drill the heck out of the maple, behind the spar. I weigh the thing and I loose about 4 grams. I have never broke the maple behind the engine tho. Must need to be lighter. Now I only crash every third flight!!!!!!!!!!!!!!. MM

You can take a router bit and route a slot in the engine mount behind the engine and it still leaves three sides intact. Matthew does this and then puts a sheet of cross grain balsa right in the slot to make the crutch. A piece of 1/8 inch balsa underneath (between the bearers) finishes it off for a smooth tank "floor". Simple and effective.