Control surface design

[Deskpilot]

Will it or won't it work. This is my latest atempt to design a simple control surface for an ultralight 3 axis machine. Nothing fancy, reasonably straight forward to make, I think, and strong enough for 'average' flying.

 

This is intended to be covered with a Stits type skin.

 

 

 

 

[old man emu]

I'd ditch the semi-circular bits and replace them with triangular block running vertically. The triangular block will give more surface area between the rib and face of the spar. This will result in a stronger glued joint. Also, it's easier to cut lengths of triangular block than semi-circular bits.

 

I guess that the control surface is going to rotate around a torque tube? If so, I'm OK with that.

 

OME

 

 

[Deskpilot]

More surface area for sure, but also more weight, and it'd a damned sight easier to cut the disks with a disk saw than it is to cut and shape a corner block. With the blocks you're relying on surface contact only but with the disks, there's a mechanical link as well as they're inserted into a groove in both the leading and trailing edges.

 

The use of the half tube is as a substitute for a torque tube. The assembly will rotate on pivots inserted into the larger hole and corner blocks at both ends. I've just realised that I've forgotten to add the far end one.

 

Thanks for your comment OME

 

 

[geoffreywh]

You might take a The German "iron on " fabric.. ORA Cover...Just like covering a model aeroplane. About 8 colours available..I saw it on the EAA website. Lots lighter than Stitts... Plus...those half discs don't do anything for torsional stiffness as they lie on the "neutral" line. The triangular blocks suggested is a sooo much better idea....or put the half discs on the surface

 

 

[Deskpilot]

Thanks Geoff, hadn't heard of it before. Did a search but couldn't find anyone using it on full size aircraft although it is sold in rolls up to 1800mm wide. One disturbing post stated that it deteriorates after about 2 years, used or not, and the colour separates from the sub-film.

 

I think I might give it a miss.

 

 

[geoffreywh]

That's the model stuff. For more look at "EAA top ten"...I've copied a part of it

 

HERE............Lanitz-Prena Folien Factory Oratex (Leipzig, Germany, www.oracover.de)—Known among model airplane enthusiasts in the U.S. as Ultracoat, Lanitz-Prena’s Oracover was first used on the advanced, foot-launched Swiss Archaeopteryx in 2001. The success of this effort led the manufacturer to develop a new line of iron-on coverings for full-scale manned aircraft, starting with Oratex 600 for planes with gross weights up to 600 kg (1320 lbs/LSA category). Oratex 3000 will soon be released for aircraft weighing up to 3,000 kg (Cubs, Pitts, homebuilts, etc.) and later will follow Oratex 6000 for heavy aicraft such as the large An-2 biplane. A key advantage of Oratex is how it’s applied—a liquid adhesive is brushed or sprayed onto the aircraft surface to be covered, allowed to dry, then the fabric is applied with a simple iron. Once the heat-sensitive coating cools and cures (in about an hour), the fabric is shrunk to its final form with an hot air gun. No other paints or coatings are required, and the fabric may be removed easily with the application of heat. Officials from The Light Aircraft Company (TLAC) of Norfolk, England, who displayed their Sherwood Ranger kit biplane in the Oratex display at AERO, reported a savings of over 30 pounds using Oratex 600 compared to conventioned Stitts-like covering systems. Oratex is “self-colored” and available in eight classic aircraft colors. While not yet available in the U.S., it is supplied by several kit makers, such as TLAC, who export to the U.S.

 

 

[geoffreywh]

This is from the Users website in pommieland....Quote:.....................

 

"The oldest actual aircraft covered in the material is approx. 3 years, the material is as good as the day it was applied, the accelerated lab tests indicate we are certainly no worse and could comfortably be well in excess of Stits, Diatex and Ceconite. Pinked edge stick down is outstandingly good, and that was an area of great concern with one of the UK’s highly respected builder."

 

 

[rgmwa]

The use of the half tube is as a substitute for a torque tube.

It's very easy to twist a half tube along its length compared to a full round tube, so a half tube may not be a good substitute if you need a torsionally stiff structure.

 

rgmwa

 

 

[old man emu]

the fabric may be removed easily with the application of heat.

Hmmm.

 

Coloured, heat applied material. Aussie Summer Sun. My guess is that structures would start warping before the material let go. That's a problem faces by model aircraft fliers.

 

OME

 

 

[djpacro]

Its common to have diagonal braces in the end bays to prevent the fabric bending the ribs however, those disks would seem to provide some lateral stiffness.

 

The ribs primarily carry vertical shear and bending to the spar hence the usual vertical corner blocks. I guess that your airloads are not large so may not be needed.

 

I agree with rgma about the stiffness (or lack of) of an open tube.

 

 

[Deskpilot]

Originally I didn't have the tube, just wood, but I thought there was a possibility of the LE bending under high deflections. Sure, a mid point hinge would fix that but it would mean splitting the LE if it was to rotate around the circular center as in my design. Plus, it would be a nightmare to assemble/disassemble when needed. With the current design, simply pull the pivot pin at each end and the assembly is off.

 

Twisting could occur with wood only as well, unless it's anchored along one edge (piano hinge for example). For a simple plane that's ok, but I'm thinking of something a little more advanced. I doubt that the tube and wood filler, would twist very much. The tube cannot twist by itself due to the wrapped over sections. These, btw, would be more flattened in reality, it was just easier to model them as half circles.

 

Re Oartex 600, certainly has its good points, but why haven't we heard much about it before? I've never seen it mentioned on any builder blogs etc..

 

 

[geoffreywh]

the covering film was amongst the top ten innovations from the EAA...I'll see if I can get a sample. I have an elevator to recover. It would make the job sooo much simpler

 

 

[RickH]

Hey Doug

 

seems like your trying to re-invent the wheel(in this case control surface) and causing a lot of unnecessary work into the bargain.

 

Attached is a photo of the control surface frames for my Texas Parasol (mine is a mid wing)

 

Regards RickH[ATTACH]12836.vB[/ATTACH]

 

 

 

[facthunter]

If its metal skinned (or ply for that matter) the twisting is thereby taken care of. Barnes Wallace used geodetic design. (See Wellington bomber). IF the ribs meet at a common point at the trailing and leading edges (thereby triangulating it) would that do the trick? Nev

 

 

[Guest Maj Millard]

Having your lever bracket-angle basically attached to the end rib like that concentrates a lot of the loads locally in that area. Those loads need to somehow be transmitted and shared by a larger portion of the surface, not just at the end. The first and maybe 2nd bay at least, need to have some cross angle braces to take that load down along the surface a bit. Remember loads transmitted through the pivot bracket work in both directions, particulary when gust loads hitting the surface are felt back at the stick.

 

I agree with the previous, in respect to the half tube vs the full tube. You loose a lot of strength and torsional stiffness with only the half tube.........................................................................................................................................Maj...

 

 

[Deskpilot]

wow, I'm surprised to see this thread suddenly come to life again. All I'm going to say is,'there's more than one way to skin a cat' or a wing for that matter. My original intent was to make something cheap and aerodynamic for slow flying.