RE: Elevator Flutter ?

[fstringham7a]

It sure has been fun to be at the airport and putting all the parts together that I made during the past 4.5 years. I installed the elevators today which brought up the age old balance / flutter question.

I reread the forums on balancing the elevators and reviewed Van's info on the subject. Pretty straight forward stuff.......

But, I did a google search and also some general surfing to find info on any RV accidents caused by elevator flutter and other control surfaces in general. I came up empty.....realize I am real poor at his high tech info gathering. My memory though vague, but remembers an accident a few years back that an RV accident may have been caused by flutter.

What do you deep knowledged base folks have in this area........


Frank @ 1L8 ...RV7A... @ the airport NDY ( not done yet )

[pierre smith]

I posted that incident about a -4 that augered in in Oz. The two guys were over gross, aft of the aft CG limit, and doing aerobatics when something went wrong. Witnesses saw parts coming off while it was vertical...could have been the rudder but there was no confirmation. Yes, two fatalities.

Regards,

[plehrke]

Originally Posted by pierre smith

Witnesses saw parts coming off while it was vertical...

Pierre,

If you mean vertical to be when they where nose pointed at the earth then it could have been over "G" and not flutter as I would imagine they where pulling pretty hard with the stick and, being over gross and picking up speed, you can easily over "g" the plane. What did the NTSB report say?

True flutter is quick, happens in milliseconds.

[Aviator168]

Can true flutter be tested in a wind tunnel on the ground? I know that is not the same as real world situation.

[DGlaeser]

Originally Posted by Aviator168

Can true flutter be tested in a wind tunnel on the ground? I know that is not the same as real world situation.

Flutter can definitely be tested in a wind tunnel. Many years ago (in school getting my BSAE) I saw a number of videos showing flutter in wind tunnels. I saw some wind tunnel testing on rotor blades when I worked at Boeing Vertol that would make your hair stand on end

[pierre smith]

Originally Posted by plehrke

Pierre,

If you mean vertical to be when they where nose pointed at the earth then it could have been over "G" and not flutter as I would imagine they where pulling pretty hard with the stick and, being over gross and picking up speed, you can easily over "g" the plane. What did the NTSB report say?

True flutter is quick, happens in milliseconds.

It was reported by the Australian equivalent of our NTSB.

Still seems to me it was a piece of rudder....perhaps some of the guys from Oz would chime in.

Regards,

[flyboy1963]

always pays to treat the flutter issue serously, at any speed!

..but has anyone noticed on their walk-around that the elevator trim tab is not all that solid!?!? ( manual trim)
A little slop in the various connections adds up to more movement than I like to see.
Trim flutter becomes elevator pretty quick I'd assume.
I know some guys have beefed up the trim arm, and/or hinge.

any observations?

[Aviator168]

There was a debate on which trim is better, manual trim tab or electric spring type. I was leaning to trim tab. Its advantages are 1) no load on the push rod and 2) you can still move the control surface if rods are broken by using the trim. Now I've taken a second look. I might go with electric spring type trims for both the aileron and the elevator. Advantages 1) one less moving part 2) puts a load on the rod and 3) the spring on the device gives more stiffness to the control surfaces.

[L.Adamson]

Originally Posted by Aviator168

There was a debate on which trim is better, manual trim tab or electric spring type. I was leaning to trim tab. Its advantages are 1) no load on the push rod and 2) you can still move the control surface if rods are broken by using the trim. Now I've taken a second look. I might go with electric spring type trims for both the aileron and the elevator. Advantages 1) one less moving part 2) puts a load on the rod and 3) the spring on the device gives more stiffness to the control surfaces.

My preference is neither manual or electric spring. I have servo operated tabs for both the elevators & ailerons. The servos are mounted inside the elevator/aileron & have no slop. The aileron tab, which is a 1"*6" piano hinge was an older method when I built my 6A; but I still prefer it over the spring setup. As to more stiffness on the control surfaces, I don't see what an advantage would be. They feel and work great, just as they are.

L.Adamson --- RV6A

[Aviator168]

L.A,

Your setup is great. But have you think about adding mechanical trim wheels just in case those servos quick. The investment just goes up and up, doesn't it.