Wing Tips

[Bob Axsom]

Has any one tried making basic minimum teardrop wing tips for speed? If so what were your test findings? I have airfoil conforming tip tanks that extend the wingspan by 1.5 feet. I am toying with the idea of making new tips over the next winter that might stick out 2" beyond the basic wing or the tip tanks (blunt like the Mustang for example). The idea would be to install the them on the end of the wing for short races like the Taylor 100 and on the end of the tip tanks for longer races like the AirVenture Cup Race. If there is actual experience with with this type of wing tip on an RV, I would like to hear about it.

Bob Axsom

[Bob Axsom]

I am surprised that no one seems to have tried this as you should be able to clip the wing span by a foot or more this way. That's OK, I appreciate you taking the time to read the question. I'll probably make a couple of foam tips as layup molds since I alraedy have the blue foam from Aircraft Spruce. This will probably happen around December.

Bob Axsom

[N908RV]

Bob,

Glad to hear you are trying this - have often wondered what impact tiny wingtips would have. Curious both about the speed increase potential and also interested in what this does for your stall speeds/characteristics.

Your posts are always thought provoking - nice to see some old school experimenting going on.

Happy modifying,

Rob

[Tom Martin]

Bob
The EVO wing kit comes with a flat aluminium wing tip. Aesthetically I wanted a different shape, something that would go with my camouflage paint scheme. I modeled a set after the wing tips of a 337 Cessna and they looked great. After flying the plane for a while I started to wonder if the tips were having any affect on speed so I took one off and installed one of the supplied flat tips.
With a flat tip on the right wing and my beautiful tip on the left side I went for a flight. As soon as I levelled off I could actually feel a difference. The plane was yawing and correcting continuously. The right wing would move ahead, or more correctly the left wing would lag until the plane got to a point where either the dihedral effect, or the fuselage drag caused the plane to bump back to straight flight. It was quite interesting to experience and it was obvious to me that my tips were causing more drag than I had expected. I removed the left tip and installed the other supplied flat tip. I would estimate, based on my three leg gps trials, that I gained between one and two knots. After telling a few people about my test I was informed that Steve Wittman used to do exactly this type of testing on his wing designs.
I may have given up a bit of low end lift and a better look, but that amount of speed loss was too much for me to pass on so the flat tips have remained. Now that I have gotten used to them I kind of like the look and it has made me wonder about the glass tips on the tail surfaces?.

[pierre smith]

Bob,
Have you considered upturned tips like most of the Formula One guys run? Only the trailing edge, or more correctly, the last foot or so is upturned.

I suspect that your/my exiting air is so disturbed by all those tubes holding the nosegear in place that the best alternative would be to go to a Taildragger. I think we give up a lot in drag with a trike because the lower firewall is so much cleaner on the TD's with much more potential for aero cleanup.

Two cents,
Pierre

[Bob Axsom]

Pierre,

If I saw an advantage to the turned up tops I would do it but I have lived through so many airplane fashion fads that I just wouldn't do it without clear evidence that there is a significant performance improvement.

Probably like you I have looked at that nose gear structure and I have fretted over it and I have modified the area to try to improve it but I have been totally unsuccessful in producing any improvement. I put a flush plate of top of the Filter Air Box and closed off the base of the inverted pyramid (support tube web structure) and I appeared to lose speed. Then I added a baffle extending across the front of the lower cowl curved back under the engine and above the filter air box to the front of the NLG structure above the closed inverted pyramid. I got one invalid test in that configuration that looked good but it was not repeatable and must be considered inaccurate. Then I added smooth curved extensions from that baffle down to the lower lip of the outlet - looked fantastic but it reduced the speed. I believe the exit air was following the curved surface into the airstream aft of the cowl and causing drag. I removed the baffles and got the speed back but more work can be done to achieve success I think. A cowl flap would help I believe but the structure really makes it difficult to implement. When I was talking to Tom Martin on the telephone the other day we talked about this a little bit and the idea of extending the lower cowl aft of the firewall and adding a flap in there seemed like a possibility. There is no doubt at all in my mind that you are correct in saying the best answer is conventional (tail dragger) landing gear. When I look at the unobstructed cowl outlet it makes me drool.

Bob Axsom

[kentb]

I was talking to the friend with the BT 13 this weekend and he was telling me the the plane was certified to fly without the wing tips, but the gross weight would be decreased by 900 lbs with them removed.

Kent

[Bob Axsom]

The reduced wing tips will most certainly effect flight characteristics and capability and should not be done for normal operations ... however, I plan to give it a try later on.

Bob Axsom