Tail Section Weight Changes and Flutter 1

[SAITAETGrad]

A colleague and I are at odds about how concerned we should be with regards to the dynamic effect of removing an APU from the tail section of a commuter aircraft. The APU is a light modern design (~100lb) but is at the extreme aft location. The mode we would be most concerned about would be the empennage vertical bending.

At what point would you be concerned about dynamic effects from a similar design change? What would warrant investigation to you.

 

[MiketheEngineer]

First of all it will change the CG - so I would be concerned right there. After all it is 100 lbs about as far from the existing CG as possible.

How does it affect the structure - does it somehow stiffen or strengthen something? Obviously, we don't know but depending how it is installed, it could??

 

[SAITAETGrad]

cg limits are not affected.

Mounted in isolation. Does not carry any loads.

 

[MiketheEngineer]

Then I have no clue if it will affect anything - but my gut reaction is that it will.

 

[berkshire]

Check to see if it changes the natural frequency of the fuselage in yaw. With that weight removed, the frequency may go up. Then look to see if it couples with anything.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[rb1957]

and pitch ... had a case where we had to ballast a plane ('cause sales effed up, and sold a configuration with out of bounds cg). dynamic landing analysis showed that the ballast was going to feel Huge accelerations, way more than the rigid airplane flight envelope.