Gap Tape Worsen Drag?

[green66]

Hi all,

I normally use hinge gap tape on gliders to reduce drag at control surface hingelines, but now question the rationale of it.

When a control surface deflects in the direction making the gap wider, i.e. a top-hinged surface deflecting upward, the gap tape overhangs the gap, acting as a fence preventing air from following around the hingeline and staying attached to the deflected surface, which I'd think would create a large wake, high drag, and reduced control response.

Provided the hinge gap is sealed to prevent air from blowing through, the gap region is a stagnation zone where air doesn't want to enter anyway, so it seems air would flow smoothly over the gap regardless whether the surface is deflected or not.

Am I missing something? Comments / enlightenment appreciated.

TIA

[Ollie]

If the gap tape is inserted in a narrow slot opposite its attachment point, when the control surface is deflected the tape will slide in the slot and bend to form a smooth bridge across the hinge line. Otherwise a gap will be produced as you describe and drag will be created rather than avoided.

[Antonsoarer]

To keep it simple I use tape top and bottom as shown in picture below. Tape for the hinge as usual and another peice over the resulting gap. My soarers are quieter with the gap cover in place. I don't think leaving the gap open (on the other side from the tape hinge) would result in lower drag even during control surface deflection.

Tony.

[Weisse Luft]

I camber the gap tape to follow the control surface deflection for recommended throws save flaperon/crow positions where deflection addition is considered. I do this prior to removal of the backing tape and it seems to work well except to increase servo effort and require thicker hinge tape to offest the shear forces on the hinge line.