C. Beaty;n1131849 said:
I realize that rotation raises the frequency but don’t know how much.
The resonance of 6Hz you obtained with your the jig saw is ω[SUB]NR[/SUB]. To know the natural frequency during the rotation, you must apply the formula: ω[SUB]R[/SUB][SUP]2[/SUP] = ω[SUB]NR[/SUB][SUP]2[/SUP] + KΩ[SUP]2[/SUP] with K = 1.9 (I hope it true)
For example, with ω[SUB]NR[/SUB] = 6 Hz, a rotation of 300 rpm changes the natural frequency so that ω[SUB]R[/SUB][SUP]2[/SUP] = 6[SUP]2[/SUP] + (1.9 * 5[SUP]2[/SUP]) Hence ω[SUB]R[/SUB] = 9.1 Hz
Since it the spinning drag shakes the rotor at 5Hz, the vibratory motion is not amplified.
You can check this formula has no solution that gives a natural frequency equal to the frequency of rotation, therefore the amplitude of the motion is never very affected.
For both the cantilever and free-free modes, hub stiffness plays a leading role since most inplane deflection occurs at the hub rather than along the blades. This being the case, centrifugal stiffening plays a smaller role than would be the case for a beam of uniform stiffness.
I had already shown that an articulated beam at the root still has the own frequency equal to twice the frequency of rotation
dinoa;n1131861 said:
Working backwards, solving for Force at .07" deflection, 2 X 0.065" 4130 mast, 36"cantilever gives 25lbs.
Despite all its advantages steel is heavy.
If you are looking for the softer mast, to avoid vibration are transmitted from the rotor to the airframe, then we must reduce his diameter and the elasticity modulus. It seems like you're doing the opposite.
A link showing its use in sailplane wing spars . It would seem an ideal material for rotor spars as well.
A blade has other requirements than a sailplane wing, Dino. Of course, it must be rigid to allow the larger aspect ratio. But we need enough weight, because the centrifugal force decreases the coning