Control Surface Balance Checks

[PT20J]

The interesting thing about Mooneys is that the control surfaces are all underbalanced — in other words, trailing edge heavy — opposite of what you would expect to prevent flutter.

[A64Pilot]

1 hour ago, PT20J said:

The interesting thing about Mooneys is that the control surfaces are all underbalanced — in other words, trailing edge heavy — opposite of what you would expect to prevent flutter.

The few aircraft I have experience with their flight controls when hung level from their attachment points also have weight on the trailing edge, (under balanced) of course there are usually limits you must be between, and the aircraft we manufactured also had a max weight allowed as well. So there was a max amount of weight you were allowed to add. Every instance of a flight control that you couldn’t balance that I saw had either a repair or usually someone repainted over the existing paint instead of stripping.

On my little C-140 the ailerons must be balanced, but not the elevators or rudder. I don’t know why?

Edited October 3, 2021 by A64Pilot

[Raymond J1]

On 10/4/2021 at 12:18 AM, PT20J said:

The interesting thing about Mooneys is that the control surfaces are all underbalanced — in other words, trailing edge heavy — opposite of what you would expect to prevent flutter.

There are two reasons for this:

- The controls are rigid, there is no elastic tension in the connection with the control stick or pedals (for cable controls, there is an elasticity depending on the tension of the strands)... And this elastic bond is an aggravating factor when the rudder flutter is servicing.

- The manifestation of the flutter must be manifested before the aeroelastic deformation of the surfaces (wing or tail fix surfaces)... A good aircraft is therefore a machine that warns its pilot that it is reaching a critical speed. A bad plane, is one that deforms aeroelastically while its moving surfaces do not know flutter.

 

And the Mooney is a good plane...

Edited October 5, 2021 by Raymond J

[A64Pilot]

Respectfully, flutter doesn’t necessarily have anything to do with cable or push pull tube, in fact a flight control doesn’t even have to be movable to flutter.

Thst bridge that galloped itself to death for instance didn’t have any aerodynamic moving parts, nor do these glider wings.

Flutter is a harmonic vibration that occurs or is exacerbated when vibrations occur at the natural resonance frequency of an object, think of pushing a kid in a swing, you time the pushes right and the kids gets swung high.

You test an aircraft for flutter by shaking it at different frequencies and watching with accelerometers to see if the amplitude grows. The flutter DER that shook ours used huge JBL drivers to shake the airplane with it on jacks at different loadings, he said that with it being shaken that sand can be thrown onto the surface and where it gathers together can be a trouble spot, but we didn’t throw any sand on it, our flutter margin was huge, but it still has to be validated if any significant changes are made to the design, especially if V speeds are increased.

https://youtu.be/kQI3AWpTWhM

Edited October 5, 2021 by A64Pilot

[Raymond J1]

https://www.aviation-pilote.com/2020/12/22/le-flutter-par-airbus/