ORIGINAL: F86_SABRE
Hi,
I would like to enquire whether there is any form of calculator that caters for the optimum landing gear position in relation with the aircraft's CG.
At the moment I am designing a Pilatus PC-21 and would like to properly locate the best location for its landing gear. As you may be aware the PC-21 landing gear is of the L type (as I call it) as the wheel shaft is rearward to the main strut. In my case, the wheel's shaft centre is about 2.5'' (circa 63mm) behind the centre of the vertical main strut. Consequently, should the main strut be on the CG since the main wheel is rearward by the quoted amount?
Any assistance will be appreciated.
With thanks
Reuben
I do not know about the PC-21. I have observed a few Pilatus aircraft so from that and your description, I take it the landing gear is a tricycle gear. Now since you seem to be willing to have the mainstrut located for active flying rather than exact scale, here are some suggestions from many years experience.
TRI-Gear: The wheel axle should be behind the wing center of gravity (actually the aircraft CG as per da Rock) by a small portion of the chord. If you get it really back, like half way between the CG and the TE of the wing, you will have difficulty during the rotation part of the take-off. That will cause the take-off to be like a model that sets nose-low. It will take too much speed to rotate and when the wing goes from negative lift to positive lift Angle-of-Attack the model just leaps into the air - not good - better is a slow rotation to a lift-off at good flying speed.
Tail-Dragger Gear: The best choice for the wheel axle is just about the leading edge of the wing or very slightly forward. Way back many years ago, modelers wanted the gear well forward. Two things: 1. The airplane flies off too slow (high AOA) because the speed is not yet sufficient to lift the tail up. Generally that causes the proverbial "tip-stall". 2. The model hits a slight bump (especially on landing) and all that
weight behind the wheel axle-line rolls over, i.e. a nose over. Kind of like landing with the brakes applied - not good!
Finally modelers realized that a more aft gear position was far better and both take-offs and landings smoothed out.
No scientific formulas here , just simple "That Works."
