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Hanging Flaps

Hanging flaps was not a hard process, but it took a lot of time.  The big steps, fitting the flap to the fuselage and installing the pushrod, were both a series of installing, measuring, removing, trimming and repeating.  But I would rather take it slow and end up with a good fit than move too fast and end up with a big gap because I removed too much metal.

Fitting to the Fuselage

To begin the process of hanging flaps, I set the ailerons in the trail position by installing the W-730 bellcrank jig.  I also checked that the tooling holes in the wing tip and aileron lined up.  Then I installed the flaps, sliding the hinge pin in from the inboard side of the flap.  An alternate method that might be a little easier if you have help is to make two small hinge pins.  Have your help hold one end of the flap and slide the pin in a few inches while you do the same on the other end.  Since you just need the flap in position to check for fit, you really don’t need to install the entire hinge pin.

Flap with templateI started this step by marking and trimming the top skin with the cutout template from the plans.  Then I repeatedly installed the flap, looked at the fit, marked where it needed more trimming, removed the flap and trimmed.  I got pretty good at installing the hinge pin, and found that a shot of WD-40 made a huge difference.

I did most of the trimming with a cutoff disk on an angle grinder.  I then polished Flap in full up position.the edge with the course scotchbrite pad on the grinder.  Once I was down to minor trimming, I used just the course scotchbrite pad.  I didn’t bother with final edge dressing until I was done with all the trimming.  The aft end of the flap with the tight bend radius was a little tricky to trim.  I used the scotchbrite pad as far aft as I could, but finished the aft end with round files and emery cloth.

Flap seen from under fuselage.Trim just enough to keep the top skin of the flap from scraping the side while the bottom skin of the flap lightly touches the bottom fuselage skin. 

Now mark and trim the bottom flap skin to match the F-826 and F-827 skins.  I used a cutoff wheel with the flap on the bench to initially cut the large piece off.  Then I cleaned up the edge with the scotchbrite wheel.  I did the final trimming to make the edge parallel to the F-826 and F-827 with the flap installed, using just the scotchbrite pad.  This made hanging flaps go a lot faster.

If you haven’t already set the ailerons to neutral, you will need to do it now before you install the pushrod.

Installing the Pushrod

Flap rod hole.I started with the pushrod the length called for in the plans.  I disconnected the WD-806 flap control from the motor so I could move the flap up and down by hand.  I installed the pushrod by just pushing a bolt into the holes; I didn’t bother with nuts just yet.  Then I moved the assembly through the up and down motions until the pushrod touched the skin.  Then I marked where it touched, removed the pushrod, trimmed and re-installed for another check.

I used a rotary file bit on the angle grinder to do most of the trimming in the holes.  Then I used a piece of emery cloth to smooth and dress the edges.

I repeated this process on one side until I could move the flap assembly through its full range of motion.  Then I did the other side of the airplane.

Final Installation

After completing these hanging flaps steps, ensuring everything fit without interference, I then connected the WD-806 to the flap motor and ran it full down.  I adjusted the down stop on the motor until the bottom of the WD-806 stopped ¼” from the floor as called for in the plans.  Then I connected the F-847 pushrod to the WD-806 and the flap.  I checked that the flap was between 40 – 45° down, and adjusted the length of the pushrod if needed.

Then I ran the motor until the flap was full up, and adjusted the up stop to get the flaps to just touch the belly skins.  As I ran the flaps up, I moved very slowly, ensuring the pushrod didn’t scrape anywhere.  I actually had one spot that I had to trim again.

I wanted to run the flaps full up and down a few times to check everything, but I wasn’t sure how many times in a row I could run the flaps without overheating the motor.  So I only ran them one direction and checked for fit.  In the full up position, I checked that the flap was flush in trail with the aileron and flat on the bottom of the fuselage, and full down, I checked that it was between 40 - 45°.  Then I waited a little while before I ran them the other way.

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