A few months ago, Super Troll expressed skepticism/called several of us fabulists (in his own inimitable and hopefully unique style) for claiming we built the airplanes with removeable flaps. Since then, I developed a minor problem and have had to remove the flaps again (for the 4th time since June 2020), so here are some pictures of it (below).
Note that the reason I had to do this was interesting and superficially disastrous. I noticed after our Stunt Farm session the other day that the airplane was making a lot of rattling noise while I was carrying it down the road. When I got home, I grabbed the leadouts and tried moving the flap, and there was some minor slop. This is a potential catastrophe, because using the original Rocket City ball links I have airplanes 35 years old with at least 1000+ flights that still have nearly no slop at all in any of the control connections.
This was not a lot, maybe 1/32" at the TE of the flap, but doing the math in my head, that might mean that one or the other of the screws holding the link to the bellcrank or flap horn might be moving 1/16-3/32" in the hole. The hole through the bellcrank faces and insert is a #33, which gives about .002" of clearance, and should have been filled with JB weld, so if the nut was loose, it must also have banged the hole bigger and was probably tilting, which will degenerate quicky and eventually fail. The control horn upright is drilled and tapped 4-40, then has a nyloc jam nut, also staked with JB Weld.
If either of these was the problem, then the only solution is cutting into the airplane and fixing it. I spent the last few days figuring out how I might do that, it was certainly doable but very, very ugly.
As it turns out, the slop is where the horn goes into the flap. For removable flaps, this has to be a slip fit so you can get them off again. I have had no end of problems with the horn jamming in the slot, (usually from rust), and once, from the hardwood swelling up from water exposure. That time I had to cut it loose. It was particularly bad because it happened between round at the 2006 NATs, which I ended up winning! We were in the Signature fixing at 1 AM Thursday morning.
While I have always managed to get it loose, I spent extra effort making darn sure that the clip was going to have clearance even after paint, and by sealing the wood up extra-well. It was just fine when I started, but it has now pounded itself out. The quick fix for now is to wrap the arm with FASCAL to take up the extra space. I am still working on a longer-term fix, with the leading candidate being cutting off the existing aircraft ply clips, and machining new clips out of 6061, and tapping that for 2-56 set screws on the bottom to bear on the arm.
At any rate, it is little things like this that people spend their time on - details matter! 1/32" of slop doesn't sound like much, and I can fly it that way with reasonable success (after finally solving a bunch of other trim and engine setup problems at the Golden State contest), but it was definitely triggering a few little mistakes here and there.
Brett
p.s. Two additional things. While he normal Klett hinge pin is 1/32 (.032) wire, you only use that to set it up and install the hinges. Once you are done and the hinges are installed, get the next size down (K&S the nearest common size is 0.025") and use that. That will remove any possibility of binding.
Another thing is that, while it used to be great, the Scotch Clear Mylar tape used to pull off with no residue. But the recent rolls I have gotten leave a sticky mess behind, just like FAS-CAL. You can clean it off of *my* finish with Acetone but if you use dope you would have to use something like mineral spirits/paint thinner, which takes much longer. If anyone knows of a good alternative clear plastic mylar tape to use for this, I am open to ideas.