Dan Ruggirello wrote:

Paul,
Here are the normal modes results for the MMP.  Not sure I modeled the aft mount very accurately
though.  It is fixed in X,Y,Z  and free to rotate in RX,RY,RZ.  You mentioned that the Questair is
only fixed vertically though.  I could go ahead and release the X and Z directions and see how it
behaves - let me know your opinion.

The mass I used was 265 lbs for the remaining engine and it is at 8" behind the MMP.  The
PSRU/prop mass is 70 lbs and 6" in front of the MMP.

The mpeg file names specify mode number and frequency.  The first three modes are from the barry
mounts, 10hz, 13hz and 64hz.  The last two modes are psru/prop/MMP modes.  The 118 hz mode is the
psru/prop bending mode against the MMP, and the 143hz mode is the prop/psru moving against the
MMP.

So, if the model is correct, you wouldn't want to operate the engine or prop continuosly near 1100
rpm (118 hz) or 1370 rpm (143 hz)  (ideally we would slap a few accelerometers on and gather some
test data).  But, if the rear mount were free in Z, you will likely see a small frequency increase
in the 118 HZ mode and a larger increase for the 143 Hz which means moving closer to the common
operating frequencies.  Also, the MMP geometry in this model is a bit different than what was
tested - much different than what is being built?

Sorry if the mpeg files are too fast, I can't figure out how to slow it down.  If you set your
mpeg viewer to repeat you can get an idea of what the mode is doing though.

Next step would be to put a sine prop force and/or peak engine torque at the operating rpm's to
see how the applied loads excites the last two frequencies.

I would like to take a look at the ultimate bell housing eventually to see how it compares.  Can
you export two IGES files - a solid and surface model?

Also, I looked at the other redrive design you sent.  How expensive do you suppose it would be to
get one built?  How about the weight?  I would change the housing in that design to something like
the ultimate bell housing though instead of using struts.  It would be easier to install and maybe
stiffer in torsion.

Dan

OK folks I need your feedback on this. Are you learning anything from this?
Is it clear what is going on?

Paul Lamar
 
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