Aileron Linkage & I-struts

2/16/2008

I-struts

I was hoping to utilize salvaged I-struts, but I decided it wasn't to be, there was just too much fudging to be done to make them work, I could have made them fit and everything would have looked good due to fabric covering and fairings, but all the fudging was making me feel uncomfortable and sort of goes against the grain. So I ordered some material and started heat bending the box sections, forming them around a rib template. The upper box sections were cut to length + 1inch, clamped in place, then I mark-drilled the steel by drilling down through the hole in the spar. The 1/4 holes were drilled on the drill press slightly under-size, cut to length and angled, clamped back in situ on the spars, then a reamer was fed through everything.

Due to the curvature of the box section where the 1/4 bolt passes thru, washers have to be wedge shaped in order to sit snug up behind the bolt head. I had some 4130 steel square washers left over from when I made some for the drag wire blocks. So, how to handle them when grinding to form a wedge shape? I glued each one to a 3/4 x 3/4 x 2 block of wood [so my hands had something to hold on to], shaped them on the disc sander, then chiseled of the washer afterwards.

I am still looking for streamlined tubing, but at $40/ft, I was hoping I could shop around...seems there isn't much choice out there due to such a small market, so it looks like I'll have to bite the bullet.

Slave Struts

I had bought the slave struts in basic form a couple of years back. They did need some tweaking however: Every plane is different, so the angle from the lower aileron slave attach point to the upper aileron is going to be a variable. I suggest drill one side of the upper fork, dry fit the slave strut, check for freedom of movement where the strut exits the lower wing trailing edge, then match drill the upper fork.

Bell crank to Hinge Pushrod

On the plans, this calls for a 1/2 tube with hollow rod end/riveted bearings each end. After a bit of head scratching, I decided that one of those bearings needed to be adjustable. If not, the only fine tuning available is the bearing rod end at the stick, this causes me a problem, because I am fitting a stop at the bell crank, and I see fine adjustment after that location advantageous down the road.

Roll Wire Fitting

This Skybolt is utilizing the older method of flying wires with the brackets mounted externally, i saw no reference for a certain fitting that was required to mount the rear flying wires. Neil from biplaneforum.com helped me out with a sample drawing of a roll wire fitting from the Acrosport plans, which I then based my fitting upon.

Aileron Linkage

When trying to fit the straight pushrod from the torque tube to the idler in the wing, the tube clashed with the 1/4 inch drag wire, so I had to put a slight dog leg in the tube to miss it. After a little digging around and obtaining feedback from biplaneforum.com and local sources, I decided to go with this route after ensuring that no binding would occur if there was the unlikely event of the lock nut loosening thus allowing the pushrod to move.

There are two variables that decide whether there is sufficient clearance or not.

1. Wing dihedral.

2. 1/4 anti-drag wire location:

Some background stuff on this: the drag/anti drag wires cross over and under each other in the center of each bay. When drilling through the spars for these wires, you have to identify at the inboard bay whether the first wire will be an 'over' or 'under' wire, then the rest of the wires are governed by this sequence. Choosing 'over' for the first 1/4 anti drag wire (that is near the aileron pushrod) will give nice clearance, but can/will cause a wire clash at the bell crank location. Choosing 'under' will make it of course, good for the bell crank travel, but potentially tight for the aileron pushrod: why, if dihedral is properly set?... because.. the 2 1/4 inboard wires start out inboard at the same center line, but have to miss each other at the cross over, so they have to travel up and downhill so to speak, this is difficult to drill accurately in the first drag blocks. If off a little, you could end up having less window for the aileron pushrod. Phew.. 'sorry it was long winded...