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Holes for Fittings In Solid Wood Spars

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Zoomzoooie

Well-Known Member
Joined
Feb 14, 2011
Messages
170
Location
BC Canada
I have been trying find information or standards for holes in solid wood spars for fittings, but haven't been able to find anything so I hope someone hear can help.

I am planning on converting my wings to have flaps for my 85% Cub and am concerned about the new hole size, distance from other holes and quantity of holes for new fittings in the 3/4" x 3.5" solid spruce rear spar with 1mm ply reinforcement around the holes. The existing fitting bolts are 5/32" and the new ones will be the same.

I plan to use three hinges to mount the 7ft flaps, with the pushrod attachment hinge in the center area. There will be 2 bellcranks. One horizontal mounted, from the flap handle cable, which will be attached to a second vertical mount bellcrank with a pushrod attached to the flap which has to clear the top of the spar. The bellcranks will be mounted to inside of the spars because of limited space from the rear of the spar to flap. I will try to use one bracket and existing holes if possible.

The problem is that the compression tube is in the bay where I want to mount center hinge and bellcrank bracket to equalize force or the flap span. I have worked out a way to fit everything in this bay adding 2 or 3 more holes for the mounting bracket which will use an existing hole presently used for a cable fairlead. The fairlead can be remounted to the new bracket. I the attached image, this is in the 4th bay from the root.

The other option is to mount bellcrank bracket in the 5th bay and make use of the holes for jury strut mounts for one end bracket and add 1 or 2 new holes to secure the other end of the bracket.

The additional holes will be for the end hinges adding 4 more holes in those sections. All new holes will be ply covered.

ZZ
 

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