Wing taper best at L.E. or T.E.?

[turbojoe]

Take a look at my scratch built Eastwind Models Gemini Twin. It's a great flier but is prone to nasty, no warning tip stalls when flown too slow even with washout. I flew the original 30-40 times and knew it's limitations. The original fuse was destroyed in a non flying incident. I built a new fuse and made very minor repairs to the wing. On its re-maiden it was flying as good as ever but I insisted on flying low and slow even after 4 saves from tip stalls. The last time I got bit and the wing was broken in half. It's been sitting on the shelf for a month or two and I just drug it out for a look see. The fuse is perfect and the wing while pretty torn up is repairable. I want to keep the flat center section as is but modify the outer panels to be less tip stall prone. I could just build "square" outer panels but I like the looks of a bit of taper. There is approximately 3 degrees dihedral in each outer panel. I plan to stay with at least that much. Given the high wing loading (30 ounces AUW) I'm not certain whether the taper should be at the LE or TE. I'm thinking TE as it would seem the TE would be best being straight as it gives more exposed wing area at high angle of attack. Kind of like adding more washout. Am I right? I plan to fly this plane at the Arizona Electric Festival and I don't want to embarrass myself in front of hundreds of people by stuffing it in again.


Joe

[Sparky Paul]

At that wingloading, you're fooling yourself to think that plane can fly slowly.
The only cure is more wing area, not washout or sweep.

[turbojoe]

Nah, I know I'm not going to get really slow flight. Just looking for a less violent tip stall.


Joe

[BMatthews]

Use washout and add some turbulator strips to the upper surface for the last 30% of the span on each side. The strips can be two layers of masking tape or electrical tape or car pin stripe tape. Slit the tape so it's only 1/8 inch wide. You want it to be about the thickness of two business cards. You should stick them to the upper surface about 10% of the chord behind the leading edge.

These turbulator strips will help delay the stall but they won't eliminate it.

Also you want to be sure that your airfoil has the proper leading edge shape sanded into it. If you left it sharp or overly squareish due to not properly shaping the leading edge that can often cause a harsh stall depending on the type and degree of the error. Use a small thin plywood or sheetmetal template as a guide for the shaping.

Taper in this case won't do anything other than reduce the reynolds number of the tip and help promote even worse tip stalling.

Adding a downturned tip plate may help delay the tips stalling as well. Like this....

[turbojoe]

Adding a downturned tip plate may help delay the tips stalling as well. Like this....

Kind of like the [GASP] GWS E-Starter? I added winglets to the original but the downturned plates will probably look and work better. I will try them in addition to the turbulators. I may make the tips attachable with magnets so I can try the up and down turned as well as none to see what the differences are. Now all I need is a chance to get back to building.... :rolleyes: Thanks for the tips guys.


Joe