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Date: Sat, 11 Sep 2004 03:06:29 -0500
From: David Staten <Dastaten@earthlink.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Engine off the floor
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Ernest Christley wrote:

> Ed Anderson wrote:
>
>> Looking good, Ernest!
>>    Not quite certain I understood your pan attachment arrangement, 
>> but you
>> want to make certain that the Pan is structural quality steel - which 
>> being
>> an oil pan it may not be.  You may need something like the 1/4" plate to
>> carry the load.
>>
>> Ed
>>
>
> Having cut a slice from the pan, I can vouch that it cheap steel.  But 
> it is THICK and it is steel. A picture should clear any confusion.  
> The red areas of the attached sketch would be the 1/4" plate.  The 
> arms would be long enough to catch a reasonable number of bolts.
>
> The way I'm seeing it, the block sits on a plate that sits on the 
> mount pads.  Because the mount pads are not directly under the block, 
> there is a torque moment on the ear with the fulcrum at the corner of 
> the block.  As long as the ears don't bend (I'll have to run numbers 
> to determine if 1/4" is enough to meet that demand),  then the arms 
> simply have to counteract that torque moment.  I just don't see what 
> all the metal in the middle is doing except weighting the aircraft down.
>
> Paul Lamar's sight has a tutorial that quotes 800ft.lb. as the maximum 
> torque pulse from the engine.  I'll need to add that to the maximum 
> 10G load limit (situation: trying to pull out at the last second with 
> full power, but slamming the nose in anyway). It's too late tonight, 
> but I'll take measurements and try to run some numbers tomorrow to see 
> if this is even worth pursuing, but it sounds good at this late hour 8*)
>
> In the likely chance that I'm missing something, I'm all ears 8*)

What are you trying to accomplish by NOT using a sandwich mount.. save 
money? Save weight? If you aren't conducive to using a sandwich mount 
like the others, I would err towards using the original mounting 
hardpoints on the engine block, or use some of the other 10x1 stud 
holes... AND perhaps the pan based mounts for some sort of torsional 
stability.. but NOT the proposed pan mounts as sole support. You are 
dealing with not only torque (which you appear to be cognizant of) but 
also G-loading (both positive and negative)... I would be interested in 
seeing what this sort of pan mount would withstand with regards to 
ultimate g-loading.. Normal Category is 3.8 g if I remember (and thats 
considered normal bounds.. I dont recall what the design factor is above 
and beyond that. Aerobatic is something like +9 and -3 or -6... it would 
be interesting if this 250 pound motor on a pan mount will remain in 
position without deformation at loading approaching 1000 (normal) or 
2000 (approaching aerobatic) pounds of load x factor.
 
Engine mounts are a major structural item, and failure WILL likely mean 
loss of the aircraft, and landing in an uncontrolled manner (engine 
comes off and then you have a really unfavorable CG).. this is where you 
want to OVERBUILD (if you are going to err), not underbuild.. a stamped 
oil pan is hardly a structural item....
 
Fly SAFE,
Dave