GyroKit library and GyroRotor program

kolibri282

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Thank you for providing a full example, Jean. I have entered the values in my program and the results are below. It's a sort of quick check, since over the weekend I actually wanted to make progress with my implementation of Nikolsky's autorotation report but was not very successful. I will analyse the differences more thoroughly next weekend. Several of our derivative values are fairly close and the real part of the short period mode as well as the frequency are very close indeed. It's all the more surprising that the imaginary part of our short period solution differs by an order of magnitude. As for the trim solution, is your disk angle of 3.91° the angle between relative wind and no feathering plane? My rotor speed is slightly higher at 350 rpm, but this is probably due to my use of a three term drag polar. I'll leave it at that for the moment since I should have gone to bed some time ago, so everything else will have to wait.
 

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Jean Fourcade

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Yes, 3.91 deg is the angle between relative wind and the no-feathering plane.
Be aware that my imaginary part of the roots are in cycles/s. So you have to multiply it by 2*pi to get rad/s.

I don't understand why your frequency in rad/s is different from your imaginary value ?
 

kolibri282

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The values in question are the result of the octave/Matlab damp function. It had never occurred to me that the imaginary part and the frequency in rad/sec should be the same, seems I took my control theory class a bit too long a go....;-(
In the example below the difference is after the decimal point, I take it that there is some sort of small bug in said damp function.

-25.634551......3998.175630i.....0.006411....3998.257808
-25.634551.....-3998.175630i.....0.006411....3998.257808

Multiplying your imaginary parts by 2*pi reduces our difference to about a factor 1.8. This seems reasonable taking into account the slightly different values for the stability derivatives.
 
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