Originally Posted by
rwaltman
Using the formula from the video and plugging-in Geowitz numbers:
m = 17.5 lb = 7.95 Kg
b = 6" = 0.1524 m
L = 72" = 1.829 m
T = (165 + 170) / (2 * 30)
T = 5.58 sec
Pi = 3.1416
g = 9.81 m/sec^2
I = (m * g * T^2 * b^2) / (4 * Pi^2 * L)
I = (7.95 Kg * 9.81 m/sec^2 * 5.58^2 sec^2 * 0.1524^2 m^2 ) /
(4 * 3.1416^2 * 1.829 m)
I = ((7.95 * 9.81 * 5.58^2 * 0.1524^2) /
(4 * 3.1416^2 * 1.829) ) Kg m^2
I = ( 56.40 / 72.21 ) Kg m^2
I = 0.7810 Kg m^2
I = 7810 Kg cm^2
Note that the video defines L not as the string length, but as the distance from the upper attach point to the plane of the center of gravity of the body being measured. Also I believe the 20 degree oscillation angle described in the Rotax paper is too much, I would aim for no more than 10 degrees.
Roberto.