How Much is Three Degrees?

Jan (of Viking Engines) was here in the Seattle area recently, and upon looking at my plane, commented that the engine sure looked like it was “drooping” down in front more than it should.  I shrugged and told him it was down three degrees, not a big deal.  But the more I looked at it, the more I agreed with Jan that it really didn’t look right.  But measuring again showed me that yes, it’s only down three degrees.  Figured tightening a few bolts would sort that out in a hurry.  After all, how much is three degrees, really?  Well, more than you’d think, actually.  Turns out the front of the engine is about 65cm from the firewall where the engine mount attaches.  If you take the tangent of 3 (0.05240779) and multiply it by 65cm, you get 3.4cm.  So a droop of three degrees means the front of the engine is down 3.4cm.  Wow, three degrees is more than you’d think.  So today’s project was propping the engine up to where it’s supposed to be.  And there the fun started.

The Zenith CH-750 is a really well-designed kit.  For the most part, it’s very well thought-out, and the parts just fit.  Building one almost feels like cheating most of the time.  But the lower engine mounts (above) are just plain asinine.  The bolt you see going forward (which is the lower engine mount bolt) has a 9/16″ head.  But guess what?  You can’t get a 9/16″ wrench or socket into the steel channel to hold the bolt while you tighten it.  When I originally put the bolts in, I jammed a screwdriver into the space between the bolt head and the steel mount to hold it while I tightened the nut.  Guess what?  That didn’t work to remove the bolt.  It took two of us (my neighbor and myself) almost two hours to get that bitch out.  We tried everything.  I even resorted to grinding a slot in the head with a Dremel to try to get a large screwdriver into it to hold it.  No joy (see below).  My neighbor finally ended up using a “disposable” 9/16″ wrench that came with some piece of equipment he had in his shop and grinding it down until it fit in the tiny space.  Needless to say, the old bolt is unusable.  I also managed to mangle a brand new Craftsman screwdriver along the way (something I don’t make a habit of).  Very frustrating.

Anyway, in the end, it took three stainless steel washers on each side to prop the engine up to the proper angle of about 1.5 degrees nose-down (below).  No, those aren’t the washers that will be in there for flight, and the bolt isn’t even inserted in this photo.  But now at least I know the angle (see bottom photo).  Long day today without a lot to show for the effort.  Oh well, it all has to get done, and it can’t all be fun.


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