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If You Have Flutter-Tested Your RV-3 --

David Paule

Well Known Member
As I slowly get closer to getting the RV-3B kits that I've got on order, I was wondering about the lack of mass balancing on the tail. Hence this question for those of you who flutter-tested your aircraft:

How fast and at what altitude did you clear it? I'm interested in actual testing conditions, not a knock-down speed for the ASI gauge. Obviously, if you actually encountered flutter or buzzing, please report that, too.

And were there any modifications to the tail of your plane of the aft fuselage?

Feel free to PM me if you'd rather not make your results or test conditions public, but if there are some replies to this, then other builders in the future will be helped by it, too.

Thanks!

Dave
 
I flutter tested mine to 220 ias at 5000ft pressure alt, worked out to 230 tas as I recall. Stick raps for the ailerons, elevator doublets, pulses on the rudder.
Dive tested to 230 ias at 5000 pressure alt.
Mine would indicate 220 flat out at 3000 feet.
No structual mods to the tail but minimum paint.
Standard disclaimer applies...every aircraft is different.
Mike

Ed. These #s are in MPH
 
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You guys are nuts. Flutter is usually one of those once in a lifetime events you encounter, because it's so destructive you shouldn't survive it.

The occilations are typically divergent, and usually rip the structure apart before you ever know it started. There are several examples of flutter testing on youtube that should scare the **** out of you.

Not saying it CAN'T be done, but Vne is there for a reason. Keep it in the published limits, why is this a constant debate? I've never met an old pilot that colored outside the lines.
 
In answer to David's question, I did not do any flutter testing on our new RV-3 because I am comfortable operating within Van's limits.

In my mind, the problem with flutter testing (sorta' like Sig pointed out), is that in a small-scale test program, flutter testing doesn't really prove that you don't have a problem - it simply proves that you didn't have a problem on that day (or on that test). There are so many variables that go into flutter that it's hard to prove (beyond a shadow of a doubt) in a few tests that you are truly "flutter-proof".

Building a balanced tail SHOULD move you in the direction of goodness...but how would you know for sure unless you did a FULL test program - and risked your entire one-plane investment in the process.

It's a tricky conundrum, so I just choose to live within the designer's limits.
 
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You guys are nuts. Flutter is usually one of those once in a lifetime events you encounter, because it's so destructive you shouldn't survive it.

Amen. I am the "wrong kind" of engineer to understand this point intuitively, so my big breakthrough came when someone smart told me the problem starts with the word "flutter":

Flutter makes us think of a butterfly when we should be thinking of an explosion.

--
Stephen
 
I've posted before

You guys are nuts. Flutter is usually one of those once in a lifetime events you encounter, because it's so destructive you shouldn't survive it.

.

100% with Sig on this one. I've posted about Nick Jones before, who's Cassutt's ailerons fluttered and disintegrated the wing, in Texas. He bailed but was extremely lucky.

Going to, or past redline, and "pulsing" any control is suicidal! You may not live to report your findings.

Best,
 
Other ways to test...

Found this article interesting, "Why Flutter is a 4-Letter Word." states their is other ways to test for flutter, not just an increase in speed.

http://www.wired.com/autopia/2010/03/flutter-testing-aircraft/

We've all seen the NASA Piper Commanche flutter video, funny that was in 1966.

I would love to know where flutter would begin on my plane, but its like knowing how close you can get to the edge of a cliff before fallling off...you dont know till you fall.

I agree with most, build it properly and stay in the envelope.
 
It bothers me when a poster comes here with a very specific question on data, and gets chastised for asking it.

He did not care to know what flutter is, or why it exists, or need another link to dead fluttered planes and pilots. There are a ton of threads on that. He simply asked for data and environment.

Flutter testing is not "making it flutter", it does not have to be in excess of Vne, it does not have to be dangerous or questioned as idiotic or debatable. Its a perfectly worth while exercise in every plane that is built.

He asked a simple question that has not been answered here before. If someone did their tests at 100mph great. 200? Fine. But why on earth is a simple flight test question challenged like this?
 
It bothers me when a poster comes here with a very specific question on data, and gets chastised for asking it.

He did not care to know what flutter is, or why it exists, or need another link to dead fluttered planes and pilots. There are a ton of threads on that. He simply asked for data and environment.

Flutter testing is not "making it flutter", it does not have to be in excess of Vne, it does not have to be dangerous or questioned as idiotic or debatable. Its a perfectly worth while exercise in every plane that is built.

He asked a simple question that has not been answered here before. If someone did their tests at 100mph great. 200? Fine. But why on earth is a simple flight test question challenged like this?

Well said.

And remeber that we all choose to be test pilots. If the plane has a flutter tendency I would rather figure it out when I'm by myself, regardless of outcome, than when I have my kid in the back seat.
 
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But why on earth is a simple flight test question challenged like this?

Challenged? Because this thread is going to be archived forever. The question should be challenged, so that the vast majority of pilots like me who read it won't think they should just add flutter testing to their test cards without understanding what they're risking.

I agree David shouldn't be "chastised" for asking the question, but I didn't see any of that here. However, if this thread had only the original question followed a few answers like Mike's, that is, just a request for data followed by data, then one expected outcome at some point in the future would be an RV crashing, where we read a fatal incident report (again) and shrug our shoulders wondering how the pilot got himself killed.

Your point about low-risk NDT flutter testing is great, but would you have made that point if we worry-warts hadn't added our "don't try this at home kids" boilerplate?

--
Stephen
 
And remeber that we all choose to be test pilots. If the plane has a flutter tendency I would rather figure it out when I'm by myself, regardless of outcome, than when I have my kid in the back seat.

Agreed, Robert. To a point.

But accepting some risk for being test-pilots in our planes is not the same as accepting any risk. So I think it's perfectly acceptable that every discussion about dangerous test regimes include warnings about their dangers, just like every Team RV performance begins with a briefing. If they dropped their briefings just because they became monotonous, people would eventually die.

--
Stephen
 
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The question is valid and appropriate in that testing to red line is testing for flutter. There's no other reason to do it.

Unfortunately (theoretically) the positive responses are presented, the negative ones not because the pilot did not survive.

Burt Rutan, at one of his grass sessions under an airplane wing at OSH in the good ol' days, once responded to the question of red line testing - approach it one knot at time. The canard on his airplanes was very critical and elevator balance a major major deal. I was surprised with the RV's we do not measure elevator balance in degrees as we did with the canards.

Fortunately, the Vans aircraft design is thoroughly tested and approaching the red line is no big deal - if it is built according to plan. (i.e., the elevator balances in trail - a rather loose tolerance) The counter balance features of aircraft coming after the RV-3 are just more assurance things do not come apart unexpectedly in flight.

We do know adding stuff to flight control surfaces, like a ton of filler and paint, can change all that.
 
Just how do you find the flutter point of a control surface without actually taking it there?

We need a Vg diagram and we could put the "whys" to be real quick. Anyone know if Van even publishes one for each model?
 
Well said.

And remeber that we all choose to be test pilots. If the plane has a flutter tendency I would rather figure it out when I'm by myself, regardless of outcome, than when I have my kid in the back seat.

No...........the outcome might only last a second or two. An acquaintance of mine, experienced severe aileron flutter. The ailerons (non-RV) really needed some attention. He's not here anymore. At least the Van's planes have had plenty of precedent, through thousand of hours, by the pilots before us. We're not "testing" unknown designs, by any means.
 
Just how do you find the flutter point of a control surface without actually taking it there?

We need a Vg diagram and we could put the "whys" to be real quick. Anyone know if Van even publishes one for each model?

BINGO! Flutter testing is not going to an airspeed, not encountering flutter and saying "I'm Good!" It involves very carefull buildup, with instrumented structures, flight test engineers monitoring those structures in REAL TIME and as the parameters build calling the pilots off. . This is the only way you can reach a flutter limit without crossing over to fully developed divergent flutter in which you become a lawn dart and make people sad.

All that has been done in the example above is shown on that day, under those flight and ambient conditions (exactly those and no others), flutter did not occur at those airspeeds. Twist a fraction of an inch-pound greater on an aileron hinge nut and you'll have to redo the test...

If these planes were production built to the approved plans you could reasonably fly right out to Vne without much worry. Considering the vairability in balance, trailing edge radius, attachment torque, auto pilot servo connections, etc... We should approach Van's VNE cautiously every time until the full enviromental and aircraft CG/GW envelopes have been probed.

If someone proposes to do something dangerous and unecessary I'd say we should absolutely chime in...
 
This is the only way you can reach a flutter limit without crossing over to fully developed divergent flutter...
I've been involved in a lot of flutter testing, on instrumented and non-instrumented airplanes, but I've never been on a test that set out to *intentionally* reach a *flutter* limit. I doubt anyone in this thread was suggesting going out and explicitly determining the flutter boundary.
 
I've been involved in a lot of flutter testing, on instrumented and non-instrumented airplanes, but I've never been on a test that set out to *intentionally* reach a *flutter* limit. I doubt anyone in this thread was suggesting going out and explicitly determining the flutter boundary.

nor was I. The instrumentation and support team is there to help prevent it - Pilot always had final say. YMMV depending on test philosophy and mission.
 
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Thanks to Mike for actually responding to my request and thanks to Paul for giving us a succinct, sensible comment about the standard approach and why it makes sense.

If anyone wishes to let me know of their own experiences off-line - if there are any more, relating to flutter testing the RV-3 - either send me a PM or an email.

Thanks,
Dave
 
flutter

Please correct me if I'm wrong but I believe that ground vibration testing is the modern protocol for insuring that a particular aircraft is safe from flutter. This was done on the Stephens Acro derived airplanes after a fatal flutter accident and revealed a problem that would not have been found by any other method.
Diving to an arbitrary speed and "batting" the stick proves little if anything.
Flutter problems are mostly related to ailerons. However there were at least two fatal accidents in the early history of the Thorp T18 that involved flutter of the stabilator. Lots of history available on the T18 issues.
Just to clarify a point-Nick Jones's Cassutt accident was a one of a kind wing that Nick had designed. Significant airspeed errors led Nick to dive the airplane to a true airspeed that was far beyond the requirements for race testing. There was no published airspeed limit that I know of for the Cassutt. Tom Cassutt stated that the fuselage fabric would come off somewhere around 400 m/h.
 
Challenged? Because this thread is going to be archived forever. The question should be challenged, so that the vast majority of pilots like me who read it won't think they should just add flutter testing to their test cards without understanding what they're risking.

I agree David shouldn't be "chastised" for asking the question, but I didn't see any of that here. However, if this thread had only the original question followed a few answers like Mike's, that is, just a request for data followed by data, then one expected outcome at some point in the future would be an RV crashing, where we read a fatal incident report (again) and shrug our shoulders wondering how the pilot got himself killed.

Your point about low-risk NDT flutter testing is great, but would you have made that point if we worry-warts hadn't added our "don't try this at home kids" boilerplate?

Stephen



Stephen, according to your above response we will need a 3 paragraph disclaimer carefully written by some law firm from every request for information regarding questions and advice asked on this forum. Anyone know a good lawyer?--
 
Please correct me if I'm wrong but I believe that ground vibration testing is the modern protocol for insuring that a particular aircraft is safe from flutter.

You are incorrect. GVT only tells you the excitation frequencies of the structure. You need wind tunnel, CFD, and analysis to know the aero characteristics and local flow fields around the aircraft. Flutter (or explosion term used in an earlier post) is a combination of aero and control surface inputs exciting the structures natural frequencies.
In today's airplanes GVT is done after every flight control software update and any structural chanes that may effect structural modes. Since software is flying most modern commercial and military jets, the control loops and actuator responses are major contributors to excitation frequencies. Remember Pilot moving the stick is only one input into what the control surfaces are doing.
 
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Stephen, according to your above response we will need a 3 paragraph disclaimer carefully written by some law firm from every request for information regarding questions and advice asked on this forum. Anyone know a good lawyer?--

Yeah, I suppose you're right. But it's not about legal liability for me, more like moral liability. I'm a bit over-sensitive to the risk/reward value proposition right now. Last week, I visited the crash site of a friend who died on takeoff with his wife and two kids last fall. Preliminary facts look like a W&B miscalculation at high DA.

Please forgive me for my petulance on this issue. I'm really tired of losing pilot friends and pilot could-have-been-friends.

Robert's point of discovering boundary anomalies for our aircraft without our kids aboard is a good one, but our kids would prefer we don't do it with ourselves aboard either.

I'll shut-up now. Instead of getting cranky as I age, I'm just getting weary.

--
Stephen
 
Yeah, I suppose you're right. But it's not about legal liability for me, more like moral liability. I'm a bit over-sensitive to the risk/reward value proposition right now. Last week, I visited the crash site of a friend who died on takeoff with his wife and two kids last fall. Preliminary facts look like a W&B miscalculation at high DA.

Please forgive me for my petulance on this issue. I'm really tired of losing pilot friends and pilot could-have-been-friends.

Robert's point of discovering boundary anomalies for our aircraft without our kids aboard is a good one, but our kids would prefer we don't do it with ourselves aboard either.

I'll shut-up now. Instead of getting cranky as I age, I'm just getting weary.

--
Stephen

?Knowledge is safety?. I?m sure I?m not the only one that learned allot about flutter from the original post. There was never any implication initially about introducing flutter testing into a flight test plan like you had mentioned.
 
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