Constraint set for accelerating aircraft?

[MBD26]

I'm trying to wrap my head around what a reasonable constraint set would be for an accelerating body. I have a helicopter that will be accelerating upwards, and the acceleration load will be applied to the entire body. I'm struggling with the idea that I would just apply a typical 3-2-1 constraint like a body in equilibrium, or clamping it at some reaction point. Just doesn't seem that realistic, and I'd get huge artificial constraint forces in either case. Is there a more accurate way of doing this kind of analysis?

 

[IRstuff]

Why would you need to constrain it? The aircraft pushes the body and the body moves with the aircraft with a slight lag, to account for the continued acceleration until it stops.

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[MBD26]

Because you need constraints to run FEA. Maybe I should have been more clear... the aircraft is the body. I want to know what the peak stress in the airframe is due to this vertical acceleration. If you don't constrain the model, you just get rigid body motion and the model flies off into space. If I do constrain it, though, I'm going to get artificial constraint forces in the model

 

[jhardy1]

Does your software support "Inertia Relief Analysis"?

http://julianh72.blogspot.com

 

[MBD26]

jhardy, I think that's exactly what I'm looking for. Thank you!

 

[rb1957]

you need to restrain rigid body motion ... sure te body can react some applied force with inertia acceleration, but the math doesn't understand the real world; so you have to restrain the 6 dof to hold the model. it shouldn't matter much where or how you restrain them, so long as ...
1) you restain only 6 dof, and
2) the structure around your constraints is stiff enough to effectively transfer the constraint into the bulk of the model.

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