What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV-7A Flutter & In-Flight Breakup

P

Pitts

Member
I might humbly suggest all RV builders and pilots obtain and read the TSB report A10O0018 concerning the causes of a fatal crash of an RV-7A on 23 Jan 2010.

I was amazed at the effect of paint/filler on the rudder flutter speed.

One must wonder how many people here are close to flutter, and don't even know it.
 
I found the report very sobering. It was also very well written and understandable. I applaud the Canadian authorities on this report.

The thing that struck me is the airspeed. These airplanes pick up speed very quickly when pointed downhill.
 
Where's the report? Uh...your planes are about to disintegrate..............
 
Last edited:
Check the front page...

Hey guys, check the front page. Doug put a link to the report under the Saftey heading. (Its located a little ways down the front page - below the "Calender" and above the "Misc./Overtime" section)

Hope this helps!
 
Thanks, found it!

Wow, I wish NTSB reports were so well written.

I wonder how many guys using on board video realize how many more "G's" they have to pull than the person they are following to keep the person in view?
 
Interesting.

I have been waiting for this report for a long time. Sobering.

The data that can be collected from an EFIS and a camera...amazing post crash. I do know that my dynon skyview captures and keeps the MAX G load plus and minus the airframe has encountered in its memory unless I go in and reset it. Might be wise for some pilots having fun out there to check that every once in and while and see what they are really loading on the airframe. If an event like this with a good detailed report can keep one of us from following that path...it served its purpose.

Andrew was a great guy who loved his plane, very sad.
 
Very, very interesting. This should be required reading.

A couple of points I took away from reading this:

Technology helps: The Canadian TSB had some remarkably good empirical data to work with given the recovery of the EFIS logs and the video.

Relief: Any in-flight breakup of an aircraft should raise the hair on the back of your neck if you fly the same type of aircraft. I think the Canadians did a fantastic job of determining that this accident wasn't caused by an inherent design flaw. As with most accidents it was multiple factors, including a heavy rudder and overspeeding the aircraft.

Condolences to Andrew's family.
 
WOW-

Gee---ok--for those of us that fly right seat, or back seat, this sure does get my attention. Ive been asking alot of "dumb" questions about Vne, and stuff for a 9A, and the real differences in the 7A/9A flight packages.
This report seems to answer alot of questions. Like Randy said--sobering-especially from the passenger point of view.
Tom
 
For the moderators, I think any reference to the TSB # and the name of the pilot should be removed from this thread. This thread shows up when you Google the TSB #.
 
apkp777 said:
Wow, I wish NTSB reports were so well written.
Click to expand...

My thoughts exactly, a very detailed and more importantly useful report. Safety would improve dramatically if we had reports like this coming out of the NTSB on accidents.

First and foremost, my thoughts go out to the family.

In addition, I have filler on my rudder (not flying yet) and this report sure does give me something to consider.
 
Thanks for posting that. This really raises a question for me (and I'm hoping I'm not the only one) regarding rudder balancing. I've read more than one post that stated you don't need to balance your rudder because it's in the vertical plane. I actually believed that to be true until now.

So my new question is, how do you balance your rudder?
 
Balance

lostpilot28 said:
.

So my new question is, how do you balance your rudder?
Click to expand...

I would think that you'd do it the same as the elevators------on the centerline of the hinges.

This means you'd have to build a fixture to put the rudder in the horiznntal plane.

Anyone with a better idea????????
 
I believe the rudder is not 100% mass balanced, and as far as I know Van has not given us an acceptable imbalance amount.

I've seem numbers for the RV-10, and would sure like to see the published numbers for other models.

Any one out there have these numbers?

Roger Bloomfield
 
apkp777 said:
For the moderators, I think any reference to the TSB # and the name of the pilot should be removed from this thread. This thread shows up when you Google the TSB #.
Click to expand...
Since the subject of this thread references a finding report of an RV accident that is a matter of public record, it should stay. The actual document, its information, and findings are important.
 
Kahuna said:
Since the subject of this thread references a finding report of an RV accident that is a matter of public record, it should stay. The actual document, its information, and findings are important.
Click to expand...

I was only suggesting the TSB# be stricken, not the report. As you remember, when this accident first took place, the discussion turned ugly and finally had to be closed.

I am sure that yours is the right decision. Although, I think some of our opinions will be tempered, which are equally valid in this discussion, out of respect for the pilot and his family.

This accident is part of the "full" circle which includes D.R.'s "safety missive".
 
Curious ...

I haven't finished reading the report, but one thing struck me as unusual, given that rudder flutter seems to have been the culprit.

The report states, "...The rudder was badly bent along its length, twisted chord wise, and the riveted joint at the trailing edge was split open ..."

Maybe the RV-7 rudder construction is different from that of the -8, but in the -8, there are no rivets in the rudder's trailing edge.

This may have already been discussed, and if so, disregard. It just struck me as curious.
 
The later and larger RV7 rudder is built like the 9 rudder with two skins and a trailing edge wedge. The forces required to do that to that rudder would be off the chart but flutter is more than capable of producing such forces...

N8RV said:
I haven't finished reading the report, but one thing struck me as unusual, given that rudder flutter seems to have been the culprit.

The report states, "...The rudder was badly bent along its length, twisted chord wise, and the riveted joint at the trailing edge was split open ..."

Maybe the RV-7 rudder construction is different from that of the -8, but in the -8, there are no rivets in the rudder's trailing edge.

This may have already been discussed, and if so, disregard. It just struck me as curious.
Click to expand...
 
Brantel said:
The later and larger RV7 rudder is built like the 9 rudder with two skins and a trailing edge wedge. The forces required to do that to that rudder would be off the chart but flutter is more than capable of producing such forces...
Click to expand...


Ahhh ... thanks, Brian. I knew that something that obvious wouldn't have been overlooked.

And, for some reason, I was of the understanding that the RV-7 used the same, larger empennage as the -8, as an improvement over the RV-6. Apparently, I was misinformed.

Thanks for the clarification.
 
It did in the begining but Van did not like the slow spin recovery and had them send out new larger rudders for everyone that wanted them. New kits get them by default. I still have the first one I built.

N8RV said:
Ahhh ... thanks, Brian. I knew that something that obvious wouldn't have been overlooked.

And, for some reason, I was of the understanding that the RV-7 used the same, larger empennage as the -8, as an improvement over the RV-6. Apparently, I was misinformed.

Thanks for the clarification.
Click to expand...
 
AND abrupt change changes of direction/atitude

Jamie said:
Very, very interesting. This should be required reading.

A couple of points I took away from reading this:

...

Relief: Any in-flight breakup of an aircraft should raise the hair on the back of your neck if you fly the same type of aircraft. I think the Canadians did a fantastic job of determining th...at this accident wasn't caused by an inherent design flaw. As with most accidents it was multiple factors, including a heavy rudder and overspeeding the aircraft.
...
Click to expand...

I seriously doubt that this would have happened in steady state flight with this aircraft.

Bob Axsom
 
The report refers to some Lab reports that were generated as a result of this investigation, and says that they are available upon request. I have asked an acquaintance at the TSB whether they are "generally available" and if so whether we could get a copy and perhaps post it. I'll forward anything I receive.

This does reinforce my desire for a good helmet-mounted camera though.
 
I disagree with the findings of the report (page 11).

1. Exact balance is not required of a control surface to prevent flutter.
2. There is no evidence provided that flutter occurred.
3. Not reweighing after paint did not cause this accident.
4. Being over gross did not cause the rudder to fail.

The #1 cause of this accident was doing acro well beyond Va and Vne. This is pure speculation on my part but if they were rat racing, well beyond Vne, its easily possible that the rudder/VS failed when this aircraft entered turbulent air or the wake of another aircraft.
 
Very sobering report indeed.

During construction my final assembly, I called Vans and asked them about rudder balancing and they said is not required. Also, during construction I trimmed my elevator weight so the elevator was leading edge heavy, counting for the paint. Well after painting the elevator, I found that I needed to add about 5.5 oz of weight to have a balance elevator. I was very surprised as how much the paint had affected the balance.
 
Very good report

Interesting but sad report. I learned some things for sure - which should be the point in such reports.
I wish our own government took the time to disect light GA accidents. I image they don't even know that many of our airplanes now have what amounts to multichannel flight data recorders by virtue of our EFIS systems.
 
panhandler1956 said:
Interesting but sad report. I learned some things for sure - which should be the point in such reports.
I wish our own government took the time to disect light GA accidents. I image they don't even know that many of our airplanes now have what amounts to multichannel flight data recorders by virtue of our EFIS systems.
Click to expand...

Almost every modern NTSB report I have read say that they shipped the GPS's and EFIS units (if equipped) to the manufacturer to try to retrieve data.

Another take-away from this accident (at least as far as the Dynon units are concerned), you have to manually enable data recording in the config screens.
 
2. There is no evidence provided that flutter occurred
Click to expand...

Clearly, de nile isn't just a river in Egypt. Nothing is certain in this life, but from the wreckage, the rudder was torn to bits as if a stick of dynamite had gone off inside it.

3. Not reweighing after paint did not cause this accident
Click to expand...

True, but it was interesting to note that because of the excessive weight of paint and filler on the entire aircraft, he was almost certainly doing aerobatics outside the aerobatic W&B envelope.

4. Being over gross did not cause the rudder to fail
Click to expand...

Ok, at least you now admit that the rudder failed, for some reason. According to your investigation, why did the rudder fail?

Note that the TSB report contains several apparently orthogonal findings, such as the fact that they were doing aerobatics illegally at low altitude.

While you might argue that the altitude probably directly didn't cause the accident, the required maneuvering to avoid hitting the ground might have. Wasn't there a recorded descent rate of over 10,000 FPM shortly before the rudder and fin separated?
 
Last edited:
The title of this thread seems to be misleading, the Tsv conclusion is that flutter OR overstress occurred, not that flutter was the cause.

The aircraft encountered either flutter or overstress of some rudder components.
Click to expand...
from findings number 3.

am i reading the report incorrectly? It seems to say flutter limits were reduced due to the paint imbalance, but there is no proof flutter was the cause of the problem. The definitive point seemed to me to be the 234 knot speed in finding number 2.
 
rocketbob said:
I disagree with the findings of the report (page 11).

1. Exact balance is not required of a control surface to prevent flutter.
Click to expand...

And the RV-3,4,6 don't even have rudder counterbalances.
I've often wondered about the torsional twist loads on those surfaces, usually when I'm slipping hard or doing coordination exercises, which I do below Va. For some reason the rudder always concerns me the most.
 
Brantel said:
The later and larger RV7 rudder is built like the 9 rudder with two skins and a trailing edge wedge.
Click to expand...

The RV-10's rudder is also the same way.

It's got to take some truly violent action to split apart such a riveted seam as the trailing edge on those types of rudders.
 
Hmmm....

After reading the entire report, I have to agree with RocketBob on this. There are some conclusions based on information but nothing conclusive. Since a video was running, what was shown at the moment of the first harmful event? I would think there would be some evidence on the video of a buzz, yawing etc...

Could this have been a fastener failure, metal failure, skin failure? Unfortunately, although eye opening, I think there are more questions than answers.

Regarding filler, I would think from an aerodynamic standpoint (beyond the weight added) that smoothing the trailing edge or skin would assist in preventing flutter by smoothing the air leaving the TE. I'm not an engineer so I'm just thinking out loud. The balancing is another issue.

Finally, with 1000's of these airframes flying, I believe this is the first confirmed problem with tail group. So, what happened?

Prevention- (not saying anything was done improperly here)

1) proper fasteners
2) proper thread clearance
3) proper torque
4) on going inspection
5) proper balance
6) current weight and balance data after painting

Just some thoughts guys. This is very sad and my thoughts are with the family. Lets keep this discussion going to the benefit of everyone.
 
Pitts said:
Ok, at least you now admit that the rudder failed, for some reason. According to your investigation, why did the rudder fail?
Click to expand...

Well, the rudder WILL fail if the VS is torn off first. Judging by the pictures in the report, this is entirely possible. Pure speculation on my part.
 
Pitts said:
Clearly, de nile isn't just a river in Egypt. Nothing is certain in this life, but from the wreckage, the rudder was torn to bits as if a stick of dynamite had gone off inside it.



True, but it was interesting to note that because of the excessive weight of paint and filler on the entire aircraft, he was almost certainly doing aerobatics outside the aerobatic W&B envelope.



Ok, at least you now admit that the rudder failed, for some reason. According to your investigation, why did the rudder fail?

Note that the TSB report contains several apparently orthogonal findings, such as the fact that they were doing aerobatics illegally at low altitude.

While you might argue that the altitude probably directly didn't cause the accident, the required maneuvering to avoid hitting the ground might have. Wasn't there a recorded descent rate of over 10,000 FPM shortly before the rudder and fin separated?
Click to expand...

The tsv report states
Therefore, the possibility exists that the vertical stabilizer and rudder separated as a result of overstress.
Click to expand...

and also is clear to say there are no proof of flutter in the damaged parts...

for me the conclusion is that the failure was the result of EITHER overstress OR flutter, or combination of the two, with no way to definitively say it was one or the other. That is the way i read the report, i believe that is the plain language conclusion...
 
Indeed

a very informative, sobering, thought provoking.....and sad read.

I have some thoughts to add to the general discussion:

The early RV-6 rudder ("small tail") as previously mentioned is not balanced at all. To my knowledge, there are no reported cases of rudder flutter in these totally un-balanced rudders of similar (usually lighter) construction.

The investigators do not mention, and may have no knowledge of, the common practice of attaching rudder trim tabs to these rudders. Does anyone have knowledge of whether this -7 had a rudder trim tab?? What type it was, how mounted etc??

The area of the rudder failure in the photos coincides with the typical location for mounting these tabs.

Can any experienced aero engineer (Van or Kevin or other) address possible rudder structure effects and flutter effects that these tabs might have??

Might it be possible that a rudder trim tab was a factor in this incident?? If so, it would seem we need to look critically at these common installations.
 
Last edited:
The NTSB is extremely good at getting data from the EFIS units, they have the tools to get the data from what we would have considered a destroyed memory IC.


Rob Hickman
Advanced Flight Systems Inc.
 
Here?s my theory:
At way past Vne, the rudder counterbalance tore off, maybe due to a bit of flutter and the resulting aerodynamic load on the surface ahead of the hinge line when it got in the slipstream.
After that, things rapidly went from bad to worse.
As that happened, it overstressed the vertical stab, which broke off and ripped off the top half of the rudder, explaining the damage to the middle part of the rudder.
Otherwise, the damage to the top of the rudder makes no sense. It did not get damaged in the separation or ground impact. It had to be the initiating event.

discuss
 
gereed75 said:
Might it be possible that a rudder trim tab was a factor in this incident?? If so, it would seem we need to look critically at these common installations.
Click to expand...

As to trim tabs, the 7 has a built in offset in the vertical stab ( I believe), where the 6's original design were straight. This would make a difference, to having a tab at all.

L.Adamson --- RV6A
 
So I have this airplane project and the <strike>rudder</strike> elevator is not perfectly balanced. Why? Who knows why but it is aft heavy and when you add in the manual trim cable it is even more aft heavy. It's not painted, of course, but the tips are done.

Should I be cracking those emp tips open and starting over with adding more weight?
 
Last edited:
Ron Lee said:
I have ZERO concern after reading this.

My opinion: Gross pilot error.
Click to expand...

Which translates too:

RV speeds can build up VERY fast on the downhill! So keep it in mind! Reports such as this, tragic as they are, at least remind us.

L.Adamson
 
RV7Guy said:
After reading the entire report, I have to agree with RocketBob on this. There are some conclusions based on information but nothing conclusive. Since a video was running, what was shown at the moment of the first harmful event? I would think there would be some evidence on the video of a buzz, yawing etc...
Click to expand...

The report was quite clear in this regard.

Top of page 4:

During a pull-out from a rapid descent, there was a sudden onset of an airframe vibration
(shuddering around the longitudinal axis), which was followed by a yawing motion, a roll and
ground impact.
Click to expand...
 
I treat VNE like it is a wall.

It seems a lot of this discussion is analyzing the report to come to some conclusion that even those that wrote the report and studied the accident where unable to come to. As some have noted in their comments, "pure speculation".

Bottom line; If you exceed VNE, in any flight condition, structural damage can occur. Throw any kind of manuevering, and certainly aerobatics, and wow, recipe for a disaster. We all believe Van's published numbers to be conservative but I dont treat them as such. I have flown to VNE in Phase I. I have ventured a bit above it a few times, usually letting down from up high, pretty easy to do on the 6 with a lower VNE. But, I treat it like if you go there, something bad WILL happen. I treat the yellow arc with the same care.

The simplest take away here is that as good as these machines are, they have limits. What those are may be up for debate, but I believe if you go beyond Van's published numbers you are taking your life into your hands. Don't put yourself in a position knowingly unless you are willing to take that risk, and if you unknowingly get into that position, fly the airplane and correct the condition.
 
Last edited:
I am sure you are not alone....

Bob Collins said:
So I have this airplane project and the rudder is not perfectly balanced. Why? Who knows why but it is aft heavy and when you add in the manual trim cable it is even more aft heavy. It's not painted, of course, but the tips are done.

Should I be cracking those emp tips open and starting over with adding more weight?
Click to expand...

...and of the hundreds of machines flying none have failed with the few exceptions of gross over stress (a few is an assumption, perhaps only one?). As mentioned, can't balance a 6 rudder.....Might be a good poll; who has balanced their rudder? I suspect very few....
 
fl-mike said:
Here’s my theory:
At way past Vne, the rudder counterbalance tore off, maybe due to a bit of flutter and the resulting aerodynamic load on the surface ahead of the hinge line when it got in the slipstream.
After that, things rapidly went from bad to worse.
As that happened, it overstressed the vertical stab, which broke off and ripped off the top half of the rudder, explaining the damage to the middle part of the rudder.
Otherwise, the damage to the top of the rudder makes no sense. It did not get damaged in the separation or ground impact. It had to be the initiating event.

discuss
Click to expand...

Very interesting theory. Could just the aerodynamic load alone be enough to rip away just that top portion of the rudder? Just how strong is that part of the structure up there?
 
My free 2 cents.
The picture shown in the report reminds me of a video posted here a while back that scared me to death. I see that picture and my heart sinks. Bad geometry. Trouble pending.

Tail chasing aerobatics in the hands of a low time pilot can be disasterous.
My Theory...
Im picturing -2 going down hill, bad geometry on lead, speed of heat, heat of the moment, suddenly in the wash, pulling G or not, seeing his lead approaching quickly, panic sets in, stomping on controls, nothing happening, and wham, outta the wash, flight controls in some mis-controlled manor, tail over stresses. Game over.
Or in the wash at high speed, exits in unusual attitude, then pilot induced overstressed VS with rudder to recover.

Had he been by himself, Id have more faith in the flutter. Given where he was and what he was doing, my bets on overstress pilot induced.

I probably have about as outta balanced rudder as you could have with my -8tail and a servo and tab electric in the aft of the rudder. While ive been at his speeds. I have not done it in any kind of turbulence, wash, or G. Course my tail is not his.

Just one mans opinion
 
RV7Guy said:
...
Regarding filler, I would think from an aerodynamic standpoint (beyond the weight added) that smoothing the trailing edge or skin would assist in preventing flutter by smoothing the air leaving the TE. I'm not an engineer so I'm just thinking out loud.
...
Click to expand...
I think this is like thinking that, if you smooth out all the parts of a whistle enough, that it won't make a noise when you blow it. I believe there's always enough turbulence to start the resonance of you exceed the flutter margin. If for no other reason, the empennage is running in the propwash. (I'm not an aeronautical engineer, either, though.)

- John
 
rudder design

This could have been caused by simply not holding both rudder cables tight. ( and exceeding Vne) I believe it was a flutter failure.

Chris M
 
You must log in or register to reply here.
Back
Top