On figuring main wheel weights for ordering spry shocks. I have my empty weights and can figure cg's but how do you get to main wheel weights from there without scales?

narm*nwt + 2*Marm*Mwt = Moment

nwt + 2*Mwt = Weight

Moment/Weight = CG

Record your cruise speed in furlongs per fortnight.

 

Where, with the longerons level:

CG = center of gravity measured from reference point (BL0, usually the aft side of the firewall).

arm = measure point - BL0

n = center of nose wheel axle

M = center of main gear axle (Note, for this example it is ok to assume the weight is equally distributed between the mains)

 

Let A = the absolute distance (narm - Marm)

Let B = the absolute distance (Marm - Harm) where Harm is the BL distance of the Horizontal Stab main Spar from the firewall.

 

With a support below the tail, stack known weights (taken from the local exercise gym) on a cushion above the H-Stab Spar nearest to the vertical stab.  When the nose wheel just begins to lift off the ground, record the weight as Hwt.  This is an approximate balancing weight (about 150 lbs) because the longeron will not be level unless the mains are raised somewhat on blocks.

 

Hwt * B = nwt *  A    or     nwt = (Hwt*B)/A

 

Mwt = (Weight - nwt)/2 (approximately)

 

Check using the moment calculations.

 

Ignore the cruise speed.

 

Grayhawk

 

PS Hint: empty, each main should statically be supporting about 430-450 lbs, depending.