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Load Test Failure Aluminum Dragon

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proppastie

Well-Known Member
Joined
Feb 19, 2012
Messages
6,391
Location
NJ
Check build log for pictures. As there is no substitute for experience, and it is practically impossible to obtain the experience short of a lifetime of work in the aerospace industry, I am not that upset......Its a retirement project, I have a excellent aircraft to fly when I want and am living the dream.

Possible Reasons for failure:

FEA model wrong...yes. Perhaps....

Inability to accuratly do a complicated "method of joints" by hand or spread sheet.....yes. However I have loaded Bruhn/Peery examples into the FEA (grape) and solved correctly .

The design is not properly executed so that the ribs do not flex and shift under load, which causes a condition/failure mode not properly modeled.

After spend the last 2 days playing with the model to remove excess constraints..... adding hinges, changing load conditions to accurately reflect the failure I understand a little bit more.

I am still not able to model the failure without adding additional constraints where I know the failure occurred. Currently the failure model shows PSI of 9K when the crippling failure of my angle is 18K.

Is it reasonable to change my allowable based on this test?....It does not seem correct to me.

As an additional data point....the original in wood has 2x the number of ribs...which in my hubris I only noticed about 2 weeks ago.
 
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