I have an ultimate biplane and tha elevator and stab have a gap larger than i wanted but the linkage and setup is solid like a rock. Do gaps produce that much flutter. All edges are knife edge and linkage is solid will there be flutter problems.

fainjon,

Seal that gap. Use Monokote or some kind of hinge sealing tape but don't fly with a large hinge gap on your control surfaces. 3M makes a very nice repair tape that I use on my racers. This stuff would be really great for sealing the gap.

What do you mean? if i use monokote should i only adhear one side of it so the other can slide on the control surface. Sould you adhear both sides when the surface is at full throw, which it will wrinkle. Give more specificity.

fainjon - bend the surface all the way up and put some clear packaging tape or iron on film in the gap underneath. It should be about 1 1/4" or so wide so you can get at least 1/2" ironed on each surface. The gap only needs to be sealed on one side.

You can also put it on top. Either side is the same, but it generally looks better where you can't see it.

if you do the covering yourself then make it continuous over the top of the gap. bend the control surface down and use a thin straightedge to stuff the covering into the gap. looks good, works great


dave

The question missed by everyone: How big a gap and what type hinges?

You can get away with a 1/4 inch gap (a bit extreme) if the hinges are solid, preventing a floppy hinge line. You can't get away with 1/8 inch with CA hinges, as you wll have a floppy hinge line, introducing a way for flutter to get started.

The gap sealing is MORE for improving the control responsiveness than for flutter prevention. It also reduced drag a tiny bit.

So... if you can easilly move the TE of the control surface without moving the servo... you may need to rehinge it.

Remember that RCers flew with big gaps for years, I have seen some extreme cases (of course not on mine!) and the airplane flew fine. As mentioned it just reduces control effectiveness some. In a racer it is important because the drag goes up with greater deflection required. With any other airplane you just add a little more deflection. In the case of ailerons though if the gaps from left to right side are different it might give a roll when hard elevator is commanded.

Mr. Hubber and Mr. Lanterman gave you some good info. The only way a gap contributes to flutter is if the hinge line (like when using CA type hinges) is limber or limp and lets the surface bend or oscillate when excited by the turbulence in the air stream. Usually, gaps only desensitize the control response.

I apologize for my brief reply and I understand your frustration with me. ZAGNUT and CafeenMan have described what I failed to iterate. If both the elevator and stab are already covered, a strip of iron on covering like Monokote or Ultracote about 1.25" wide and as long as the span of the elevator can be ironed into the gap providing a seal. Start by using a piece of tape to hold the elevator at full deflection. Then with the iron at low temperature, tack the strip to either the stab or the elevator--whichever is easier for you. Using a straight edge or ruler, push the strip into the gap down to the hinge line. Use the iron to tack the strip along the gap and onto the other surface. Once everything is tacked down you can increase the temp on the iron to seal everything in the normal iron-on-film technique.

If you haven't already covered the surfaces, a lot of times you can modify the above technique to cover everything all at once. You're just using a bigger piece of covering rather than a strip. With this technique, you can eliminate hinges entirely and the covering material becomes the hinge. This is known as a Monokote hinge. I've used Monokote hinges on planes up to 1.20 size without any problems. If you're into bigger planes than that, I would be leery of using just the plastic film as my hinge.

Does this help or do I need to explain further?

Thanks,

did I understand you correctly to say that you use the covering as the hinge on planes?

tph1 - Yes, that's what he said. It's common practice on smaller planes to use iron-on covering for the hinge. Kills two birds with one stone - hinges and seals. Personally, I wouldn't use it on anything more than a slow .40 size plane, but that's just me.

ok thanks for clearing that up. I'm just getting back into this after about a ten yr. lay off and was just curious if things had changed that much.

I don't know when the Gentle Lady glider kit came out... but the instructions call for use of the "monokote hinge" Its been out at least 22 years. (thats about when I got my first Gentle Lady...)

The Monokote hinge is better than you might think... it can withstand the stresses of a Sig Kougar with a .61 on the nose. But it has a flaw... if it starts to tear at all, the control surface rips free VERY fast on a high speed airplane.

Great for slow flight... not so good an idea for a speedy airplane.