Left break on stall with new VGs.

[pokekey]

We recently installed Vortex Generators (VGs) on a Maule M7-235 (1994). On flight testing we found that a mid-power stall constantly breaks to the left. (Power off just results in a mushing decent - no real stall). It is not a minor break; the plane rolls 90 degrees left and then dives toward the ground, much like a spin entry. This happens in a coordinated stall. Heavy right rudder will prevent (or minimize the break).

We would like to eliminate the potentially dangerous characteristic. Anyone with VGs have a similar experience? Any suggestions on what to adjust?

Thanks,

Tom
Seattle

[maules.com]

If you are in a power on stall with not enough rudder input then it would want to break left. If you have adequate right rudder in then is your aileron in a cross control position. If so then the washout on the wings may not be rigged correctly, so the left is stalling when the other is not ready to let go yet. The vortex generators increase effectiveness of the ailerons at slow speed which is one of their advantages so the above may be why this showed up after installation of VGs.

[pokekey]

Thanks Jeremy.

Both my partner and I have tested this. Event with ailerons flat and plenty of right rudder it breaks left. That would implicate wing rigging, right? e.g More washout in the right wing than the left. This leaves the left tip with greater angle of attack and this causes it to stall first.

Before VGs we had adjusted the rigging by adjusting the flap setting. The plane tended to roll right so we added flap to the right wing. This seems to agree with more washout in the right wing than the left.

Tom

[maules.com]

Assuming the plane fuselage has not been rebuilt from an accident, the best way to rig it is to start from scratch. Level it laterally and chock the gear to eliminate depression of tyres. Check hinge line of elevator and leading edge of stabilizer and balance horns of elevator for lateral alignment with tube under the front of the seats (gear truss) and with the carrythrough tube at top back of windscreen. Next check vertical of rudder post to be 90deg to lateral alignment. Next check extended line forward of rudder/vertical fin to a point on top of windscreen to be 1.75" left of centre. Then stretch a stringline wingtip to wingtip and tape it to the skin over the sparcap and measure for laterally level plus a dihedral lift in the centre of the top rear of windscreen of 2.75" +/- .25". Set dihedral with forward struts and then the washout with rear struts. Now rig flaps, ailerons, stabilizers, rudder, and rudder servo interconnect tab, and rudder trim. Don't confuse servo tab with rudder trim. Your maintenance manual has most of this info. If you don't start at ground zero, its like a dog chasing its own tail.
Jeremy