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Flutter of AST in Flight

Crafting N112DR

Well Known Member
I have been documenting my test flights extensively using a 360 camera mounted on the tail tie down. I have noticed that the the AST tends to flutter in flight. This it not notable whatsoever in the stick in flight. I have the older style AST trim with no bend in the rod. There is a very small amount of play when you hold the stabilator stationary on the ground and then flex the AST. I have looked at three other RV-12?s and they seam to have to same amount of static play. I made a 1 min video so you can all see what I?m talking about. Anyone have any insight on this?


Here is the Link


https://youtu.be/hG2BrVRO3eg
 
Looks like rather stable flight conditions. The trailing edge of the tab appears always in the "up" direction, zoomed in at .25 speed.
 
Looks like some oil canning of the skin, even on the area outside the aileron. Watching the TE, I don?t see any movement...
 
I think I'd focus on calling it "vibration" rather than flutter.

Not being picky, but flutter, in airplane context, usually suggests divergent occillation (increasing in amplitude). This appears steady state.

In a gross sense, anything totally rigid to flight loads would probably be too heavy to get off the ground.
 
Comparing the outboard trailing edge of the AST to the trailing edge of the
stabilator, I can see the relative motion between the two surfaces, especially if
the play back speed is reduced to 25 percent. We need Van's opinion on this.
 
Man!! I even can see the skin of the elevator vibrate - it looked like it's alive. Ho wonderful these pics are - where's the rest of the 360 movies?
 
It appears to me to be a vibration induced movement of the tab, and not unusual. One reason I say this is that the movement doesn't appear to have a constant / steady frequency.
Another reason is that the variation of the reflection on the outboard stabilator skin right beside the AST seems to mimic the reflection rhythm of the AST skin.
 
Vibration

Thank you all for your opinion, my main concern is safety of fight. This vibration could lead to wear of the AST components down the road. As Scott has said he thinks this is not unusual so I'm good with the knowledge that its safe. Has anyone else experienced this in flight?

Thanks
 
Pretty sure what you are seeing here is vibration and not flutter. Having survived wing flutter on a motorglider, I've seen what it can do first hand. The flutter was so intense that it ripped up the wing skin and actually broke the rear spar at the fuselage attach point. Fortunately, I got the airplane slowed down to about 80 mph and the flutter stopped, so I got on the ground safely. The wing flutter was aileron induced. Witnesses on the ground said that the wingtip was oscillating at least 2' vertically.
 
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The tail surfaces are in the slipstream of the fuselage and turbulence (P-factor) from the prop. Air flow at back of fuselage is probably pretty turbulent ? cabin entrance steps, canopy release handle, a couple thousand rivets, comm and xpndr antennas, fuel tank vent tube, and even the round OAT sensor all cause disruption in airflow which will be noticed by lightweight AST hanging out the back. Not exactly stealth?
 
I checked mine this morning and I agree <1/16"


I think all of our 12's AST vibrant in flight. Thats just how it is.

If anyone else can install a camera looking back at the AST that would confirm my theory that all 12's AST vibrant in flight. If only we could get a couple.
 
Based on my limited experience with flutter if you are not sure if it is flutter it probably isn't. With flutter you hit a certain frequency and the whole structure comes alive and starts feeding off itself. Quite terrifying and destructive. Rivets get loose, skin cracks and ultimately the whole thing flies apart. I agree with the other posters who identified this as buffeting. Check your shorts. If there are no fresh stains it's likely not flutter.
 
Based on my limited experience with flutter if you are not sure if it is flutter it probably isn't. With flutter you hit a certain frequency and the whole structure comes alive and starts feeding off itself. Quite terrifying and destructive. Rivets get loose, skin cracks and ultimately the whole thing flies apart. I agree with the other posters who identified this as buffeting. Check your shorts. If there are no fresh stains it's likely not flutter.

Good to know, will sleep and fly better at night.
 
Maybe it?s because I?m a lowly RV-8 driver and I don?t get out much, but... what the heck is AST?? I figure it?s something at the back of the aeroplane, but I have no idea what you guys are referring to. A little help?
 
Maybe it’s because I’m a lowly RV-8 driver and I don’t get out much, but... what the heck is AST?? I figure it’s something at the back of the aeroplane, but I have no idea what you guys are referring to. A little help?

Anti-servo tab used on a plane fitted with a stabilator. Moves in the same direction as the stabilator but at a greater rate, and being aft of the stabilator hinge line it opposes the effect of the stick force to help return the stab to a neutral position.
 
AST

Maybe it?s because I?m a lowly RV-8 driver and I don?t get out much, but... what the heck is AST?? I figure it?s something at the back of the aeroplane, but I have no idea what you guys are referring to. A little help?
I had to google it as well. "anti-servo tab"
 
Buffet of AST in Flight

What you are seeing is buffet, as others have pointed out.

Below is a link to a pitch I put together a few years ago. It describes different aeroelastic phenomena, including buffet, divergence, control reversal, control surface buzz, forced vibration, flutter, and aeroservoelasticity.

"An Introduction to Airplane Flutter":


Enjoy!

(BTW, I would suggest a Moderator change the title of the thread to "Buffet of AST in Flight", so no one thinks it's flutter.)

Your Right but look how much discussion I have created by accident.
 
Remember that the .020 aluminum that much of the RV-12 control surfaces are made of is very thin. I would characterize the vibrations you see as simply "oil canning" and nothing to be concerned about. Also, how is your camera mounted? Is it possible that you are inducing turbulent flow behind the camera?
 
Remember that the .020 aluminum that much of the RV-12 control surfaces are made of is very thin. I would characterize the vibrations you see as simply "oil canning" and nothing to be concerned about. Also, how is your camera mounted? Is it possible that you are inducing turbulent flow behind the camera?
If you watch the Video you will see the camera is as smooth as butter. Please look at the area in the video denoted by the red arrow, you will see it is not oil canning but the AST is actually vibrating.

oDC.png


and here is the video link incase.

https://youtu.be/hG2BrVRO3eg
 
No problem at all. Air rejoining at aft end of fuselage is turbulent. Air has to spread, go around a bunch of stuff, and try to rejoin as airplane goes on its marry way...
 
No problem at all. Air rejoining at aft end of fuselage is turbulent. Air has to spread, go around a bunch of stuff, and try to rejoin as airplane goes on its marry way...

I'm sure it's good, just wish it was as stable as the stabilator.


Thank's everyone for there input.
 
Cameras everywhere

If you watch the Video you will see the camera is as smooth as butter. Please look at the area in the video denoted by the red arrow, you will see it is not oil canning but the AST is actually vibrating. ...
The proliferation of cameras everywhere on an aircraft will probably show us some things we didn't know, and some things we didn't want to know.
 
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