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David Staten wrote:
Ernest Christley wrote:
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?
Well...yeah.
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.
Normal Category is certified to 3.8g positive and negative is 1.52g.
For airplanes, the standard design safety factor is 1.5. I believe most of the composite designs use a factor of 2.0, due to the wide disparity in quality between hand layups made by different people (but don't take my word on that one.)
Not worried about aerobatic manuevers, since I'm putting it in a non-aerobatic, VFR aiplane, but my design criteria has been 10g with a working weight of 350lb.
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
Overbuilding is definitely one approach, but not the one I'd prefer to use. The problem is that just adding more metal won't necessarily make the structure stronger, but it ALWAYS makes it heavier (and more expensive). Very often it can actually make the structure weaker (though, a full plate wouldn't).
That being said, I have not set a goal to err or underbuild. I have set a goal to eliminate several pounds of expensive steel (or aluminum), IF POSSIBLE. A stamped oil pan can be as structural as anything else, IFF it is used within it's capabilities.
I have been having trouble finding some information. Unfortunately, I don't have the luxury of hanging weights from the bottom of my engine until a bolt gives up, so I'm looking for published numbers. The closest I've been able to find is that a 6mm bolt should have a load rating of at least 650lbs (the load ratings for is eye bolts, and there is no way to tell if the limitation is on the eye or the bolt). Does anyone have a table of working load limits for various size bolts?
--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber
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