Not mass balanced & cable failure

[SteveJeff4567]

I found that many certified LSA aircrafts and some standard FAR 23 certified don't have mass-balanced surfaces. I'm interested in how they are designed to show freedom from flutter, especially control surface flutter and if these aircrafts can handle a disconnected freefloating surface emergency (due to cable failure, for example).

If they are not prone to develop flutter in normal operation, how things may change if, for example, the aieron cable fails?

Thank you very much!

 

[mohr]

Hi SteveJeff4567 :

Some manufacturers under the LSA rules, have made ​​some aircraft without mass balancing in the ailerons control system.
Even have conducted studies and tests showing that it is not necessary such mass balance.
It is clear that the tension in the control cables of the system must be the recomended by the factory and
without any free play in the system because if that happens, may occur catastrophic effects.
Anyway in this case counterweights was installed later in the ailerons....

I enclose two links of the Hamburg Institute of Technology reports that may help you.

Link
Link

Cheers

 

[SteveJeff4567]

Ok, in generally, how at risk to flutter is a control cable failure? The study doesn't seem to take care about this problem.

 

[mohr]

Hi SteveJeff4567:

You are right. The study does not take into account even the risk of losing some cable tension or cable break.
The control cable without correct tension or failure may be one of the flutter issue specially if the ailerons
are not mass balanced. Remember the flutter ia a very complex phenomenon.
Read specially from page 4 of this NTSB report

http://www.ntsb.gov/doclib/recletters/2009/a09_30_37.pdf

This report is a good approximation to the truth.
Regards

 

[SteveJeff4567]

Not really the main topic of this thread, anyway, actually the study posted above, this one, take into account the risk of losing some cable tension and as I found in the study there is no flutter even at low cable tension. So, it is somehow confusing. If there's no flutter at low cable tension, what caused those crashes? The NTSB report says that low cable tension.