Re: Wing Load Testing


Mike Perry
 

Jay:

First, I probably am splitting hairs. The 1 G load on the wing is probably between 32 and 38% of the weight; I am trying to get a more accurate number but it is a small difference. The 1 G load would be between 320 and 380 lbs; the 12 G load would be between 3840 and 4560 lbs. (based on the original gross weight of 1000 lbs.) If I split the difference the 12 G load would be 4200 lbs. -- probably adequate for our purposes.

Second, The angle of attack changes the center of lift, but only by a small percentage.

Third, I am not aware of the effects of "pitching moment" but I don't see how any force can transfer load from the wing to the canard in stable flight without a shift in CG. Certainly not a large percentage of the gross weight. The center of lift for the entire airplane must act at the CG in order to support the airplane ("center of lift for the entire airplane" includes lifting surfaces, trim and control surfaces and other effects like P-factor).

Mike Perry

JAY SCHEEVEL wrote:


Hi Guys,

I think you may be splitting hairs here. Jason Kramb, please correct me if I
am wrong:

I believe that the percentage of load carried on each wing is a function of
airspeed. This is because of the pitching moment contribution of each wing.
The influence of pitching moment is significant and has been neglected in the
discussion so far. Both airfoils (wing and canard) are assymetric (top to
bottom), they have trailing edge upward pitching moments that varies as a
function of angle of attack and airspeed.

Because of the contribution of pitching moment, the "effective" load transfers
progressively to the canard with increasing airspeed. This means that at the
lowest airspeeds, the highest load percenteage is on the rear wing (probably
around 35%) and at the highest airspeeds, the highest load is on the canard (I
have heard some on the Q-performance list say it is as high as 90%, but I have
not verified..I think this number comes from X=plane). So I think the effort
to pin an exact percentage on each wing the is a fruitless exercise.

As far as the chord at which you find the "center of lift", again this is only
a number that is significant if there is no pitching moment contribution.
Since the wing is likely to fail by fiber crushing ion the top surface (not by
torsion), it probably does not matter where on the cord the loads are placed
as long as they don't fall off during the experiment. To simulate a trailing
edge up pitching moment, assuming that the wing is inverted for the
experiment, you would want to bias the weight toward the trailing edge as you
load it.

Cheers,
Jay Scheevel -- Tri-Q still building

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