Hinge slotting for dummies...
 

Hello everyone,

I'm just starting out building my first plane, a Midwest Aero-star, and already I think I've whoopsed up something. The instructions start out with the Stabilizer/Elevator, and after being very proud of my sanding job, I've made the mistake of attempting to hinge it all together... without a hinging tool. So now I need some help fixing my mistake.

First, about the stab: It's constructed in 4 pieces: leading edge, trailing edge, and two small blocks at both tips.

The elevator: It's the entire length of the stab and is attached with 5 hinges (I bought dubro hinges).

The mistake: I think my slots are not centered right, and one or two might be slightly angled into the balsa. When I insert the hinges in the slots (or rather force them in, the slots are very thin and I have to wiggle the hinges into the slots), and attach the elevator, the stab gets bent slightly, so that the elevator can't be straightened out: it either snaps up, or down.

What can I do about this? I'm assuming that the slots I've cut are not perfectly centered, causing the stab to warp, but when sanding the elevator, I also noticed that there was a very small (almost unnoticable) warp in the elevator.

I've already decided to buy myself a hinge slotter and try to 'fix' the slots, but this brings me to another question: How 'loose' should the hinge be in the slot?

Also, if with the hinge slotter I can't 'fix' the slots, would it be better to buy myself some balsa with the same grain as the stab and elevator and just 'start over'. Or can I fill the slots with balsa filler and either redo the slots at the same location or cut some new slots beside the old ones?

Any help will be appreciated!

Savi "Slot dumb" Savard.

Hinge slotting for dummies...
 

Best bet:
Get a hinge slotting tool/blade kit and put new slots beside the bad ones. If the original slots are "thick" fill then my sliding in some 1/32 (or thicker if neded...) balsa sheet and CA'ing with thin CA.

If you want to put the hinges n the original slot locations... fill the slots... but use yellow gluye, which is muh easier to cut through (even then you'll need the GP power hinge slotter to cut proper slots in it.)

The angled and offset hinges will cause significant loading of the servos, and can cause you to drain the RX batteries in less than 1/3 normal amount of flying. The loaded servo is going to be less resistant to control flutter, it could wear out faster (due to the loads making it "hunt" for its desired position, making a buzzing noize.) If the binding is severe, you could cause fatigue failure of the hinges in just a couple of flights and might even break the balsa stabilizer/control surface framework.

The elevator warp (asuming solid balsa) can be steamed out. I it returns when covering, then you can heat and bend to remove the warp again. balsa is fairly easy to bend with heat and a bit of moisture.

The good thing is... you saw there was a problem, and are going to get it fixed rather than try flying the plane anyway. A lot of beginners would have decided to "live with" the problem... and thier planes wouldn't survive long.

Hinge slotting for dummies...
 

fhhuber:

I think there's enough space around the slots I made to make new slots, so instead of having 5 hinges, I'll just end up with 6 (three each side of the center line) and fill the old slots with the balsa sheeting like you've said. But this time, I'll make sure that the slots are perfectly centered using the hinge slotting kit.

It's a little dissapointing that I've managed to fudge this up so soon in construction, especially after that sanding job, but well, at least it's fixable.

When I get the hinge slotting kit, I think I'll pick up a sheet of balsa as well for some practice. One of the nice things about that Midwest Aero-star is that quite a bit of it comes precut, but that also means that I don't have much in terms of scrap balsa to practice on.

thanks for the advice,
Savi.

Hinge slotting for dummies...
 

Later, when the hinges do wear out, you may find you need to replace wood to put in new hinges. When I do that, I strip off 3/8 inch of the TE of the fixed surface and completely replace the control surface. (solid balsa tailplanes)

that of course assumes the plane slast a LONG time.... The hinges take many hours of flying before they fail.

Hinge slotting for dummies...
 

By the way, the hinges I'm using are the pin kind: two pieces of plastic held together with a small pin. Can these fail? They seem pretty darn resilient from the way I pulled, pushed and wiggled them to fit in those dreadful slots I made.

I had originally thought of buying the Great Plane's PT-40, but when I went to the LHS, the owner recommended the Midwest aero-star instead saying it was better. She was kind enough to have the patience to assemble everything I would need from glue to hinges to wheels (even suggested a slightly bigger size than called for). She's the one who suggested the dubro pin hinges.