Stiffness of Aircraft Structure at attachment point to Landing Gears

[feajob]

Hi Guys,
I understood that if we have a Nastran Model of Aircraft then one way to find out stiffness of Aircraft Structure at attachment point to Landing Gears is using following cards:

ASET1 123 GRID1 GRID2 ... GRIDn (to have 3 x 3 stiffness matrix)
PARAM,EXTOUT,DMIGPCH

I also think that we should put the constraints far away (by our engineering judgment) to obtain more realistic stiffness matrix in the punch file. What do you think? Is there any better way?

Thanks,

 

[rb1957]

if you've a FEM of the plane, and you want the stiffness at the LG attach points, apply unit loads in each direction … deflections will give you stiffness.

another day in paradise, or is paradise one day closer ?

 

[feajob]

Thank you rb1957. Unfortunately, we don't have access to FEM of Aircraft. I proposed both above approaches to our customer. I thought that they should be able to assume some reasonable boundary conditions to estimate reasonably the stiffness of Aircraft Structure at attachment point to Landing Gears. Meanwhile, I thought to double check with experts here.

 

[rb1957]

Ok, I took my lead from "if we have a Nastran Model of Aircraft" …

so, what are you trying to do ? model a gear ??

if so, support the three (typically) attachment points on finite stiffness springs (you can use CBUSH, I prefer three RODs) 1E7 or 1E6 is a typical stiffness.

another day in paradise, or is paradise one day closer ?

 

[feajob]

Yes, basically, customer is asking for deflection of LG by including the flexibility of backup structure. So, we need to have their feedback to include the appropriate stiffness (using CBUSH or ...) into LG FEM at attachment points.