dimachorny
New member
- Nov 3, 2007
- 31
Dear friends,
My helicopter with a teetering rotor and two composite blades is not stable enough and has very bad autorotation characteristics.
To improve these properties I decided to add mass to the blades by injecting epoxy to the tips. Total addition of the weight was 28%, but in the terms of moment of inertia this added 60% to each blade.
After injection the difference of the mass is about 0.01%, and 0.04% difference in moment of inertia between two blades. Also the span wise CG is almost the same (0.05% variance).
There is a relatively big change in the chord wise CG: 2.74% toward the trailing edge. There is also a small change in the airfoil profile in the range between 75%-95% of the blade radius. The variance is relative to the original blade and to the each other (there is a mismatch in thickness of about 2% in the skin of the upper blade surface).
On the ground there is a good tracking of the blades, but when hovering, the helicopter starts to vibrate, I think laterally, nevertheless perfectly balanced blades.
Does anybody have the idea what can cause these vibrations?
Thanks a lot.
My helicopter with a teetering rotor and two composite blades is not stable enough and has very bad autorotation characteristics.
To improve these properties I decided to add mass to the blades by injecting epoxy to the tips. Total addition of the weight was 28%, but in the terms of moment of inertia this added 60% to each blade.
After injection the difference of the mass is about 0.01%, and 0.04% difference in moment of inertia between two blades. Also the span wise CG is almost the same (0.05% variance).
There is a relatively big change in the chord wise CG: 2.74% toward the trailing edge. There is also a small change in the airfoil profile in the range between 75%-95% of the blade radius. The variance is relative to the original blade and to the each other (there is a mismatch in thickness of about 2% in the skin of the upper blade surface).
On the ground there is a good tracking of the blades, but when hovering, the helicopter starts to vibrate, I think laterally, nevertheless perfectly balanced blades.
Does anybody have the idea what can cause these vibrations?
Thanks a lot.