My first thought was to stiffen up the new steel mounting bracket, but I thought I would go after the trigger wheel runout first and see if that yielded any results. Depending which document I am looking at, the allowable runout for a 7 1/2" trigger wheel should be .003" - .006". My initial check seemed to put it at .006.
I got hold of a dial indicator clamped it in the bracket and filed each tooth until now I am about .0025" of a perfect circle.
I test flew it today and the miss was still there, but it seemed to kick in at 2,870, rather than the former 2,820 RPM. Again, I am looking for 3,100.
Now, it's time to see about stiffening up the bracket.
Wish me luck. I am so tired of all this.
4 comments:
Just a quick thought on vibration. A bolted stiffener may be more effective than a welded one because it will provide more damping. Also, try to add torsional and not just bending stiffness.
I was planning on welding a gusset along one edge of the bracket. Perhaps .050" x 3/8" stock.
I understand what you are saying about the torsional stiffness.
Why would a bolted support provide more damping?
A bolted joint allows microscopic motion creating friction.
How much damping you get is unknown, the only way to know is to do a modal analysis after you built the bracket. Boeing does it all the time but they can afford it (even for the whole airplane in a ground vibration test, GVT, before a first flight of a new model).
http://en.wikipedia.org/wiki/Modal_analysis
I would try to put gussets on both edges or one in the middle to put the mass in the center of the beam. How thick is the current bracket? The natural frequency goes up with the square root of the stiffness so a 50% increase in stiffness only gives you about 22% increase in freq.
The support bracket is 1/8" 4130 steel. Yes, I thought I would try some gussets or stiffners
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