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Community RV-10 Flutter Analysis Project

digidocs

digidocs

Well Known Member
I have recently spoken with Martin Hollman of Aircraft Designs Inc. about doing a flutter analysis on the RV-10. Martin is FAA DER and is very experienced in computer FEA flutter analysis. He has analyzed designs including the Lancair IV-P, 360, Wheeler Express (post-crash), and BD-10 (post crash).

I am very curious about the flutter characteristics of the RV-10 at speeds beyond Van's 200 knot Vne. By understanding these characteristics the RV-10 speed envelope may be able to be significantly extended. For example, Van says that a turbocharged 260hp RV-10 would be able to exceed 250mph in level flight. Furthermore, even if you don't plan to go that fast, knowing exactly where the limits lie could enhance your safety and peace of mind.

Here's my proposal:
A group of us band together to generate the required funds to have Martin (or a similarly qualified individual) perform a finite element analysis of flutter in the RV-10 wing and empennage. This model would be tuned with actual structural measurements from an RV-10 to ensure validity. This study would determine the critical flutter speeds and modes for the aircraft. Analysis would be also be conducted with fuel loads ranging from empty to full and also with extended range tanks. Martin gave me a quote of $8000 to perform this study. I envision having Doug or another trusted third party hold accumulated funds in escrow until we reach the required amount or an agreed upon "expiration" date arrives. If we fail to raise the funds by the expiration date, then all funds would be returned.

That said, I propose the following sponsor levels:
Silver - $250+
Gold - $500+
Platinum - $1000+

We'd only need 32 Silver or 16 Gold sponsors to proceed. Imagine getting a 50mph speed increase STC for the cost of a tank of gas!
Donors would, of course, be recognized for their contributions to the community.

If this sounds interesting, please indicate your interest/comments and how much you would be willing to donate.

Thanks,
David Carr
 
The only problem I have is that every RV-10 is not exactly alike. One little twist in an elevator or aileron just throws the whole finite analysis out the window! I think the only true way to know your Vne is to slowly increase the flight speed until you have the early warning signs of flutter. I would also suggest having a very experienced pilot test this. I also don't think Doug wants to play bank. Sorry about the negativity but I believe finite analysis is good for a lot of things but I am not willing to bet my life and my plane on it because I can't say I built a perfect plane. For all I know my Vne might be 200mph.
 
just curious

I have a friend that flies an RV10 and he never flies at full throttle. He doesn't want to pay the price so flies a little slower.

So the question is: How many RV10 fliers are using full throttle now?

Kent
 
Todd,

The point of the finite element analysis is to determine the oscillatory modes/frequencies of the structure. This mode data is then further processed to determine which modes will be excited at the lowest speed --- the critical flutter speed.

The resonance frequency of a structure is almost exclusively determined by it's mass and stiffness. In the fleet, I believe you'll find relatively little difference (percentage wise) in the mass of the wings/tail and even less difference in the stiffness of these structures. If this were not the case, and there were major differences then much of Van's engineering data would not apply to the general fleet. So, in short your slightly warped trailing edge or your wingtip antennas are not going to have much effect.

-DC
 
I don't want to sound harsh here, but food for thought. Perhaps those few who want/need a turbo-super-charged airplane to go 250 mph in the flight levels should look at aircraft other than the RV-10. We've already had substantial accidental impact to the RV-10 fleet that could begin to adversely affect our insurance premiums. Yes-- I know it's experimental aviation, and I fully support it. Van has always been conservative, and overall we have a pretty good safety record and can feel good about having an airplane, that if built correctly and flown within the recommended operating envelope, will give us and our friends/families/loved ones lots of enjoyment.
I also question if the finite analysis done on one RV-10 in a standard configuration would really behave the same with a totally different engine/prop combination, in the flight levels, perhaps with some ice on it, etc.
NOT meant as a flame.... just food for thought.

Vic
 
DC
The problem again is everybody's is different. Mine is completely different. I have an extremely heavy engine and airframe. The analysis would be useless to me. I don't have the need to over 200 mph and just like having a little extra power to climb out of anywhere I want at any DA. If you could get similar planes together then it might be worth it but your fuel consumption is going to go through the roof.
 
I think it's an excellent idea.

....and then let it be applicable to only standard RV 10's, not V-8 or Subes, as few are.

As far as incrementally testing at progressively higher airspeeds until you see the initial onset of flutter, could be suicide. As you've read in some of my earlier posts, I visited with Nick Jones last week and he bailed after his Cassutt instantly, without warning, shed its wing skins, the speculation being that it was aileron flutter from torsionally weak stiffness.

IMHO, $8000 should be spread among those expecting to go faster than Van's numbers.

Regards,
 
commuity rv 10 flutter analysis project

I cant find any step by step procedure on bal. any of the control surfaces .sticking some lead on a contol surface make no sence . If a procedure for bal. could be done with this analysis sign me up
 
testing at progressively higher airspeeds until you see the initial onset of flutter, could be suicide.
Click to expand...

I'll 2nd Pierre's comment.

During phase I in my plane I kept landing with only 1/2 of my gearleg fairings intact. Kept beefing them up and they kept ripping off. Finally I had a set survive a 1 hr flight and thought the problem was fixed. Next flight I did a nose down descent and heard/felt a buzz then heard/felt two loud bumps.

The time duration of the buzz to bumps was probably less than 2 seconds.

The noise was clearly flutter from the fairings and the thumps where when they ripped off.

I had built the fairings per spec and just like the prototype which never had a problem. The final fix wasn't more beef only realignment by about 2 degrees.

In any event had it been control surface flutter there would not have been enough time from first warning till death to do anything about it. Also of note is my Vne for the fairings was significantly lower than the prototypes even though I thought I had built it exactly the same.

I would not suggest trying to sneak up on flutter to see where it is. As Pierre said this could be suicide.
 
N395V said:
I would not suggest trying to sneak up on flutter to see where it is. As Pierre said this could be suicide.
Click to expand...

And I'm aware of a warbird replica that picked up flutter on a high speed pass, with un-balanced ailerons. It only took a few seconds to shed a wing.

L.Adamson
 
Pierre: I wasn't aware that you know my buddy, Nick Jones. If anyone can discuss flutter with some authority, it would be Nick. I think his Cassutt is not the only airplane Nick has bailed out of, or dead sticked, or...etc.

Nick is the real deal...what a character!

Regards,

Lee...
 
I'm not sure FEA can reliably predict flutter but ground vibration testing can these days. This is far safer. Ultimately though, the envelope should also be validated by flight testing. I second the other comments here about sneaking up on it in flight to find the limits. Bad idea.
 
I'm not sure many designers actually test until flutter is reached because it is just as dangerous for test pilots. They probably pick a reasonable speed given the application, design, power and altitude it is operated at and flight test to 110% of that. Van's designs may have a small or big margin from their posted Vne.
 
A few comments on issues that have been raised so far:

This analysis won't apply to my non-stock airplane
The analysis I proposed is to specifically study the flutter characteristics of of wing and tail. Flutter frequencies and modes are primarily determined by the stiffness and mass of these surfaces. In general, I suspect that most -10 wing, tail, and control surfaces are very similar in terms of mass and stiffness. These are simply not the parts of the airplane that people choose to modify extensively (unlike the fuselage). The fall out is that the results of this study would be widely applicable, even to modified -10s like Todd's airplane.

A FEA model will not match my airplane
As I mentioned above, flutter behaviors arise out of the stiffness and mass distributions of aircraft surfaces. Conseqently, a flutter FEA model doesn't include every rivet and wire but rather includes relevant structural elements of the aircraft like spars, ribs, skin thickness, fuel location, etc. Most RV-10s, including those with an oops or two, will still look alike from the flutter model perspective.

A FEA model won't predict all flutter modes, how about a GVT?
While I am not a flutter expert, I have read a few books on the matter and understand the basic physics. The primary advantage of using a FEA model is that it enables you to identify all of possible vibrational modes of the structure. Some of these modes are quite complex, and would be difficult to identify using manual measurement/computation methods. During a GVT, transducers are placed on the aircraft to stimulate and measure a certain vibrational mode. However, the test will only demonstrate modes that you have previously identified. For this reason, GVT is best applied as a verification step for some other sort of analysis. If you haven't already predicted the mode, you may not see it in the GVT.

I've seen some good comments so far, glad to see that. If we'd like to make this reality though, we need some real contributions.

I'll start out by pledging $500. Who else would match that?
 
You left one out

#4 -- What are you going to do with the information?

As a point of curiousity, it might be interesting to mathematically determine the ultimate theoretical flutter point of the design. It's certainly not worth to $500 me, but to each his own, I guess.

I do have a concern about what people would do with the information. I'm sure Van's knows the number because they've told us that the limiting factor for the design is flutter. They probably don't publish the number because they don't want some idiot to rip off his tail in a 230 mph dive in HIS plane just because he read somewhere that the design was theoretically capable of 300 or some such.

Lots of RV's have been built that routinely fly well above the VNE. If you built a 10 carefully, you could probably put a turbine in it and get pretty close to 300 mph cruise. The problem isn't the theoretical number -- it's that you'll have to actually flutter test whatever number you pick as YOUR VNE. If you want to complete at Reno, or go into business selling upgrades, that's one thing. But I can't imagine risking a $200K pleasure plane that you probably spent years building (not to mention your life!) just so you can get to your weekend burger 10 minutes quicker. And if you want to compete at Reno or go into business, it wouldn't be ethical to ask the community to chip in without telling them why.

So, what are you going to do with the information?
 
Jon- Thanks for saying what I tried saying earlier. You still have to test it at small increments regardless of what anybody or any report says. I will stick to 200 mph.
 
I'll stick with Van's numbers!

jonbakerok said:
#4 -- What are you going to do with the information?
Click to expand...
And if you DO publish the information, what are you going to say to the jury in front of the Widow who says that her husband was using your data when he died?
Personally I'll stick with Van's numbers.
 
I give up.

The RV community clearly is not interested in understanding the flutter behavior of the RV-10 beyond the bare minimum data provided by Van.

Other aircraft communities have banded together to further understand and improve their aircraft in a collective manner. The KR2 guys are a good example of this. My goal was simply to study our aircraft and release the results. I am disappointed that we were not able to do that.

Oh well,
-DC
 
I don't think it's that anyone is terribly uninterested, it's just that unlike some of the other kitplanes out there that have had this data and test performed have had a number of incidents caused by such things - whereas I'm not aware of any RV (There probably is, I just don't know about it) that has flown apart as a result of flutter. There are 5K+ of these things flying and I think that's why you get the response you do. We all know of certain fast glass airplanes that had known flutter problems, others that were discovered later on in their lives...but overall as a percentage was a bigger problem than the RV's in general have experienced. Couple that with the fact that there are many RV's that've already pushed the envelope so far beyond what normal paramenters are, that people are just pretty comfortable with things. I'm not saying this makes the airplane flutter proof, or anything like that. I'm just saying that most people are comfortable with their planes. As a percentage RV's are probably some of the safer kitplanes out there...some of the fast glass birds have not had a good track record this year at all!

Also, I'm dead against usings the theory of "testing in small increments" for flutter. On these sizes/speeds/design of planes, it's unlikely that us as normal human pilots will be able to detect where the "increment is" that induces flutter. As most know, the majority of the times where there is flight control flutter, there is a quick buzz and then a "BANG" as the flight control/wing/whatever suddenly and violently departs the plane long before the pilot ever realizes what the heck just happened.

In the end I think you're seeing that people think this would be an creating a solution for a problem that doesn't really exist. I don't think anyone was trying to be particularly negative...just honest and pragmatic about it.

My 2 cents!

Cheers,
Stein
 
I agree with Stein. Even though the cost of gas has come down, it will go up again at some point in time. I want to get my three passengers and baggage from point A to B as cheep as possible. I plan on flying LOP pulled way back, not pushed up to see how fast I can get there. I am comfortable with the high side limits from VANS, I will probably only see it in the Phase I testing and feel that I will never see it again.
This is why I didn't reply.

In my openion, I am finishing building a Transport, not a Fighter. :D
 
Me too

I have to agree with all the prior statements about "sneaking up" on flutter.

It usually happens so fast that there is no turning back------or to put it another way, it is like being pregnant------no such thing as "just a little bit"

One of my neighbors just had a flutter incident recently (bottom of an outside loop, 180Kts, in a Yak 52)----luckily it only ripped the trim tab off the plane and destroyed half of the elevator, so he could get back safely. He said it was over before he could even react.
 
I would love to see the analysis even though I don't any plans to build an RV-10. I think it would be 'fun' to see what kind of margin there is in the design. I imagine there is a pretty large margin, but without an analysis like this there is not much of a way to know.

It is unfotunate the nay-sayers are the loudest to voice there opinion about this.
 
Pitch in and you will see it.. the "nay sayers" aren't stopping anyone from doing it.. simply expressing the "it's not worth it.." opinion...
 
The problem with building-up in flutter testing is that you might be approaching flutter onset and never notice the signs. I was a test conductor on a military fighter aircraft test program, and flutter testing was performed with a control room with ~30 engineers (probably 4 or 5 were dedicated strictly for flutter) looking at real-time test data. Any hints of flutter onset that were not expected, or not understood, caused an immediate halt to that line of testing until further analysis could be completed. The indications the control room engineers were seeing would not be noticeable to the pilot.
 
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