Define loads/Engine mount

[transall]

Hello,

I have some probleme to determine the loads acting on an engine mount.

I have an engine mount which bears a 91 kg engine with 4 attachment point,at each corner of the engine. I am studying the lower attachment point of this mount. The engine is in cantilever.
From my point of view I have define as loads:
- The engine's weight
- The moment due to the cantilever
- A starting torque
- And a compression loads because if I look the engine on one side we can see the two attachment points and the engine's centre of gravity between the two points (on the middle line). If there weren't the attachment point, then the engine would rotate around its center of gravity, consequently there is a couple, and on each attachment point we have: compression load for the lower point and tractive effort for the upper point.

Do you think my argument is good?

Thanks for your help,

Mickaël

 

[GregLocock]

Is the frame stationary?

How is the motor coupled to its load?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[transall]

it's an helicopter engine mount.
The frame is stationnary for this analysis. the engine is attaches to the engine using tubes with rubber shock mount.
you can have an idea with this picture:

http://www.cozygirrrl.com/images/parts/conical.gif

Thank you,

Regards

Mickaël

 

[GregLocock]

Then you have other loads to consider.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[JStephen]

The torque exerted by the engine has to be resisted somewhere. Since the frame actually isn't stationary, you'll generate loads due to movement or rotation of the frame and the inertia of the engine and spinning components. You'd want the motor mounts to survive a very hard landing.

 

[rb1957]

a picture says a thousand words ...
as greg succinctly posted "you have other loads" ... you've got a good enough handle on the weight of the engine, but you have to consider the engine output (torque) has to be reacted at the motor, plus i think you need to think about the dynamic forces involved (due to all the bits and pieces whirling about) and how about the imbalance within the engine (as different cyclinders fire) ...

you also need to consider the fact that you've got two different styles of mounts. two mounts are supported by a tripod of struts, good for reacting load in pretty much any direction; but two mounts have only a single strut, good only for axial load (as these struts react load in one direction they induce loads in the other two directions, and these induced loads have to be reacted at the other mount).

 

[mechengdude]

As others have stated, I think you need to consider your dynamic loads. seems that resonanant frequency of the engine and fatigue issues would be of larger concern. Additionally if this is for an aircraft, don't you have load requirements like "must withstand 9g crash load" etc.