Rounded trailing edge vs. Blunt (AEX wedge RV-9/10 style)

I am about to start building my TE control surfaces for my HR2 and I have come to a crossroads, so to speak. I either have to buy the thicker .020 skins from Van's at $300 plus shipping or...I could buy some .020 stock metal and make them myself using the TE method that Van's now uses on the -9/-10 and later model -7 (I think?). The tail kit I own was "previously enjoyed" so I wasn't able to select the thicker skins from Van's when purchased.

I really like the look of the two piece skins utilizing the AEX wedge and double-flush rivet method but, I am concerned about control feel. From the little bit of research I have done online, it appears that the sharper, more blunt contour of the AEX wedge style TE produces a higher stick force. Not having any time in a RV-7/9/10 I have no way to compare it to the RV-4 that I am flying now. I also realize that the ailerons and elevators would be the most critical as far as control feel is concerned. Perhaps a mixed bag of the two methods would be the best combination. AEX wedge rudder and rounded elevators and ailerons??? Just a thought.

Does anyone out there have some concrete evidence to say one way is better than the other? Flying characteristics being my most important quality. I know I can build them either way to be very strong, I just don't want to sacrifice the amazing flying qualities the RV-4 style rounded TE has for something "less desirable" just to save a few bucks on some metal.

Any input would be greatly appreciated.

Thanks,

Mark

Rounded vs tapered trailing edges has been discussed lots here before.
Try grabbing the search function and read away at the pros and cons of the design options.

I did that.

Perhaps you could re-post one of those discussions for me because all I get when I search for that topic is the post I submitted? Changing the words a bit yields a few more results but not much info out there when I search....hence the forum post.

"Aileron Trailing Edge" search:

http://www.vansairforce.com/community/showthread.php?t=57684&highlight=aileron+trailing+edge

May not be exactly what you are looking for but it might get you closer..

Found some info

Helps if you check spelling. Still would love any input that folks may have on this topic.

Thanks!

Squared vs. Rounded?

Thank you bkilby. That actually did shed some light on my question. In fact, one of the posts in that thread posed the exact question I was trying to convey.

Jconard posted this comment but unfortunately he did not get a response.

Has anyone considered a squared off trailing edge? I have in mind, making it from the AEX wedge or similar. I understand that this is also drag reducing.

Any thoughts from the brain trust?

That is exactly what I am considering with my control surfaces. If you look at any high performance aerobatic airplane ie: Extra, Edge 540, Cap, etc. you will notice they all have blunt trailing edges. They are plastic airplanes but I doubt mother nature cares. I am starting to think the radius has less to do with the control feel. It really has more to do with how smooth that transition is from the leading edge to the trailing edge.

blunt vs sharp

The key question you are asking should be posed as blunt vs. sharp. There are really 3 things going on here.

The rounded edge is actually somewhat undesireable from both drag and control-feel standpoint, but is easy to manufacture. In the case of most RV models, the adverse affect of the roundness is offset by the beneficial effect of the bluntness.

A square-edged, blunt trailing edge will have much lighter stick force, but is still consistent, crisp, self-centering, and linear (proportional) feel. In some flow regimes, the blunt trailing edge can have lower drag, but probably not for our GA airplanes. There is some drag penalty, but it is modest. Control force probably decreases roughly linearly with trailing edge bluntness height. A good square-edged trailing edge with a 3/16" base height will have nice light forces. 1/8" base height will be nice too. If you look at competition aerobatic planes like Extra's, their ailerons are something like 1/4" base height. But always crisp, sharp corners.

A sharp trailing edge will have the lowest drag for GA airplanes. It will have very crisp, self-centering, "linear" control feel, but the control forces will be higher. But the control force depends on other things too - aerodynamic balance tabs, hinge offset, type of control seal, if any. And of course the control force you feel at the stick also depends on linkage geometry (mechanical advantage). So it is hard to say on a particular airplane if the control forces will be too heavy or not. Experience with RV's is that if you make sharp trailing edges, the stick forces are noticeably heavier. Are they "too heavy"?, thats probably a matter of personal taste and intended mission. RV-9's and -10's aren't intended as aerobatic machines, and stiffer controls may make a more stable instrument platform.

The round, folded trailing edge on most RV's is easy to build. We got lucky that the 3/32"-1/8" bend radius, with straight contour leading up to it, gives nice control feel. But it is right on the ragged edge. If you under-bend the radius so it is 3/16" radius, or if you have somewhat curved contours running to the radius, you will get very light, sometimes vague, squirrelly control feel. Sometimes it will show up as having two stable points on either side of centered, but will not like to center.

I hope that helps your decision.

Thanks

Thank you Steve for the great response. That kind of information from an engineer is exactly what I was hoping to obtain.

I have several ideas floating in my head as how to best attack my problem.

1. Bite the bullet and just buy the metal from Van's at nearly $400 plus shipping and go with a proven design.

2. Use a wedge to connect the TE skins with possible "less than desirable" results due the the sharp TE.

3. Design my own TE insert out of metal or some very dense plastic that will still allow me to rivet the two skins together and also give me the nice 1/8" to 3/16" blunt edge.

I think I'm gonna pull out the RV-4 from the hanger and go for a ride up to Oshkosh and do a few laps...looking (and taking pictures) of everything I see with regards to TE design.