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Post by matthorr on May 12, 2015 14:03:56 GMT
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Post by Br. Marius on May 12, 2015 14:13:34 GMT
Ahh...much appreciated. The link is good.
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Post by matthorr on May 12, 2015 14:15:11 GMT
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Post by matthorr on May 12, 2015 14:25:14 GMT
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Post by Br. Marius on May 12, 2015 15:57:14 GMT
Where are you finding these?
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Post by matthorr on May 12, 2015 16:09:23 GMT
I got them from other students in my lab group (and the older test they got when they took the course).
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Post by trdodge on May 12, 2015 17:54:39 GMT
Very helpful Matt, much appreciated.
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Post by matthorr on May 12, 2015 20:57:32 GMT
For the 2012 Final Question #6, does anyone know how to find the rotating damping ratio?
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Post by trdodge on May 12, 2015 22:10:09 GMT
I haven't done that problem exactly, but one similar to it in the 2013 exam. You'd use the typical I*(rotating frequency)*(damping ratio)*omega = constant equation. You're given the new damping ratio, I and omega are constant (assume blade geometry doesn't change). Your two rotating frequencies are the new one you just calculated, and the old one which, even though isn't given explicitly, is found the same way as the new one without the alpha_4 coupling. I'm sorry I haven't learned the mathematical formatting for the forum, but I hope this helps.
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Post by matthorr on May 12, 2015 22:41:00 GMT
Thanks, that's close, I think - neither the 2012 or 2013 exam had the right answer... The lag perturbation equation has an extra term in it \(\gamma\left(\frac{C_d\sigma}{4a}+\frac{\lambda\theta}{6}\right)\) but you don't have enough information to calculate the \(\theta\), or the first fraction, either. Your approach was only -1/2 point (the other "wrong" answer used the non-rotating frequency for a full point off).
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Post by trdodge on May 12, 2015 23:14:39 GMT
I'm not sure what you mean? As far as I can tell, you don't actually need the full theta, you just need the change in theta due to the pitch-flap coupling. That, along with the lock number, inflow ratio, and hinge information should give you enough to determine the lag frequencies.
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Post by matthorr on May 12, 2015 23:32:48 GMT
In these problems, the C coefficient changes with trim inflow and blade pitch theta (not constant like most problems). Damping ratio zeta is from /(C=2/zeta/omega_n/). I'll probably go for the ½ point off though
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