"BSH structure": "Brick S**t House", as in really darn stout.
And if you over tighten the diagonal wires, the wing will snap to a shape with compression ribs alternating between nose up and nose down as you go along the wing. Not making this up, folks have applied too much torque to the system and "pop" the wing.Regarding the structure you posted, the diagonal wire bracing is for drag/anti-drag, and does nothing for preventing the wing cell twisting in the vertical plane, i.e: chord-wise.
put in a small twist
for wing at limit .....the loads are pretty straight forward....a tilt of 15 Degree is recommended for a load of 25% in the forward direction......one could also measure twist at max aileron load of 9 PSF for my speed. ....but it is going to twist no matter what and how much is too much seems to be my problem.....calculating deflections
have I missed this spec. somewhere in all the design guides (part 23, Glider Criteria, etc.)The torque divided by the twist is torsional stiffness
Well, you know when you are one the edge when you give right aileron, and the plane rolls left...
I distinctly remember large opposite aileron deflection required to maintain the bank in the 1-26.....is this what you are talking about and is it normal in other gliders?I could grab the tip and crank in a couple degrees of washout or wash-in with relatively little effort,
Spec for torsional stiffness? Not usually specified directly. There are several things to be taken into account:have I missed this spec. somewhere in all the design guides (part 23, Glider Criteria, etc.)
Right. FAA Basic Glider Criteria page 79.I believe the old FAA glider standard does give a stiffness criteria that relates the twist/deflection to 200/Vd^2.
The glider manual explains this. You apply a torque (any reasonable amount that results in measurable twist) close to the tip of the wing. You then measure the unit twist (radians per ft lbs) at multiple points (say 4 points) across the span where the ailerons are. Unit twist is the twist you measure in radians divided by the torque you applied. You then plot a curve - x axis is aileron span and y axis is UnitTwist*chord^2. You then measure the area under this curve. If that area is less than 0.053 you meet the criteria. Usually for 61mph Vd airplanes, assuming conventional structures, you should have no problem with flutter, but with as with all things flutter you can never be sure.When I do the calculation for 61mph Vd...I get .053 which I am going to have to figure what that means exactly.
I had not been concerning myself with flutter for that very reason......Usually for 61mph Vd airplanes, assuming conventional structures, you should have no problem with flutter,