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Bottom hinged ailerons

Posted: 14 Mar 2019, 10:24
by StephenB
The Mike Trwe design Fauvette I'm currently building calls for bottom hinged ailerons, presumably to emulate the full size although I can't find any reference to this. Included in this is a purpose made control horn which fits within the aileron, this would entail exiting the control linkage through the trailing edge of the wing leaving it hidden from view. All very neat but it does involve some constructional difficulties for me.

My preferred method of hinging would be self adhesive wing tape on the lower surface and a sealing strip along the top surface. However, it appears that this may not work with the purpose made control horn which relies on the pivot point being more rearward than my wing tape method would allow.

Any suggestions?

Aileron detailJPG.JPG

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 12:29
by Peter Balcombe
I think that you will find that the Mike Trew plan details the ailerons as Frise ailerons which are hinged at the bottom.
The idea with Frise ailerons is that they are bottom hinged behind the aileron LE, thus an up-going aileron deflection causes the bottom LE to project below the wing surface, creating drag on the down-going wing to counteract adverse yaw.
The aileron bottom LE doesn’t project on the down-going aileron side and is hidden.

I fitted 3 small vertical brass sheet hinge strips in my wings which linked up with short lengths of brass tube set into the ailerons via separate wire hinge pins at each hinge point. The aileron is fully removable.
See pics below which show the underside of the RH wing at tip hinge point when the aileron is a little down & partially up.

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 15:08
by StephenB
Peter, thanks for the reply. I'd guessed that they were probably Frise ailerons and have deliberated over using Robart hinge points but I think it may be quite a tricky job getting them set up correctly, there isn't a lot of meat in the ailerons and cutting biggish slots for the Robarts worries me. Given how the Frise are designed to work it obviously rules out my wing tape method and the construction of the aileron and wing trailing edge doesn't, on the face of it, leave many other options open.

The much shallower wing section, compared to the original scale section doesn't leave a lot of space or material to work with, the two aileron spars are only 3/16" square balsa, very close together and apart from that not much else to work with!

I need to get my head around how you've done it as a possible option for me, it appears from your pictures that you used the hidden linkage and horn as per the plan?

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 16:08
by chris williams
Stephen, what you have here is the classic scale glider dilemma... Whether or not to worship the scale gods, or the gods of practicality. Such decisions are more critical the smaller the model gets, so in this instance I would strongly recommend simple top hinged ailerons, with tape on top to seal the gap, and then a Mylar strip underneath to seal the lower gap. This will make your wing more efficient in a Reynolds regime where efficiency trumps scale fidelity...

Just don't tell Vince

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 17:03
by Peter Balcombe
Stephen, using simple top hinged ailerons would certainly be easier, although that would also mean that you would probably have to bring the aileron pushrod out of the bottom of the wing to connect to a bottom mounted horn - although this could possibly be relatively hidden.

I agree that there isn’t too much meat, but as I glassed my wings & ailerons, they are plenty strong enough.
Yes, my linkage is hidden & the clevis for this is connected up to the aileron (pushrod at full down aileron position to give more of clevis visible) before the aileron hinge points are moved into position & the hinge pins slid into place. Removal is in the opposite order.

If you go for the scale Frise ailerons, then I advise installing the hinge plates to the hinge spar by assembling the plates to the aileron hinge points, inserting pins & checking each hinge for free movement before offering the plates up to the wing hinge spar slots & fixing in place with epoxy on the inside of the hinge spar once happy that everything is in the right place. The aileron can then be removed after withdrawing the hinge pins.
My aileron hinges were formed by having two short lengths of brass tube at each hinge point - spaced apart slightly to allow the vertical hinge plate to fit in the gap & the two tubes aligned with the hinge pin whilst fixed into position.

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 17:07
by StephenB
Thanks for the reply Chris, at this point in time I am edging towards siding with the gods of practilcality as I know my options are compromised by the relatively diminutive scale and the much thinned wing section.

I'd love to top hinge, it's long been my preferred method but, given the wing/aileron is well on the way to being completed and I can't easily alter the structure, would that work with the "upside down" chamfered aileron (see above pic)? It would leave a hell of a gap at the bottom with up aileron. I'd also have to lose the hidden linkage and control horn to get the correct geometry. Suggested control throws on this are 1/2" up and 1/4" down.

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 17:56
by chris williams
Not sure what you mean, Stephen... Do you mean simple hingeing at the bottom with a gap on top, in which case up aileron would close the gap?

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 18:44
by Peter Balcombe
Chris, I think what Stephen means is that given the fact that the aileron is designed for an inset bottom hinge, it’s LE is angled back from the bottom rather than the top & a top shroud normally fills the gap for a down going aileron
The upper LE moves forwards & under the shroud for up going aileron deflection.

Stephen, have you considered adding a wedge to the aileron LE to make the LE square & then plane an angle on the LE for normal top hinging? Then the aileron shroud can bee removed & theaileron top hinged with tape etc. as normal.

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 21:43
by StephenB
Thanks Peter, you've explained it correctly and more concisely than me!

I have in fact as a result of this discussion considered doing what you suggest, I haven't yet glued on the top spruce shroud so could indeed modify it by adding to the LE of aileron. I've even thought of replacing the whole aileron with TE stock :o It also crossed my mind to do as Chris suggested - leaving the structure as is but hinging the bottom of the aileron and sealing the top gap.

Re: Bottom hinged ailerons

Posted: 14 Mar 2019, 22:29
by RobbieB
Stephen, good advice there from Peter and Chris - on reflection I wish I had 'sided with the gods of practicality '! :o

...........and that was before I spotted the deliberate mistake the other day. :oops: