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Rudder flutter and added weight. Adsb tail beacon

Turbo69bird

Well Known Member
So in reading one of the accident reports where rudder flutter was the cause and a little body filler blamed it occurred to me that the weight of something like a tail beacon ADSB solution could be a factor.
Any thoughts on rebalancing or of would cause issue would be appreciated.

I already have the old style rudder without the counter balance. Not sure how that adds to the situation.
 
flutter

So in reading one of the accident reports where rudder flutter was the cause and a little body filler blamed it occurred to me that the weight of something like a tail beacon ADSB solution could be a factor.
Any thoughts on rebalancing or of would cause issue would be appreciated.

I already have the old style rudder without the counter balance. Not sure how that adds to the situation.
I am no aero engineer, but from what I have read about flutter any kind of change can have a positive or negative impact on flutter, and even both depending on the speed of the airflow over the surface.

The accident where the body filler contributed, there was also high speed involved.

At the time of the vertical stabilizer and rudder separation, the aircraft was at or near 234 knots, exceeding the 200 knot Vne and the speed at which the aircraft was shown to be flutter free. The theoretical flutter onset speed was 300 knots. Adding extra weight (paint and filler) can reduce the speed at which flutter onset occurs by 50 knots or greater. It is possible that the manoeuvre overstressed the rudder, reducing its stiffness, which further lowered the flutter speed.

http://www.vansairforce.com/community/showthread.php?t=72316

http://www.vansairforce.net/safety/G-GNDY.pdf
 
Anyone know the rebalance
Procedure my field A&P says the way they want it done is manufacturer and mode specific.
 
There are 5 RV7's that have had inflight failures, all were the tall rudder shared with the 9. All the rudder pieces looked much the same but the causes were different, as listed in the reports. Several of the HS spars were failed (maybe all but don't recall), and the VS broken.
1- Canada, 3 USA, 1 NZ.

You should call Vans for your specific situation and get an official recommendation.
 
There are 5 RV7's that have had inflight failures, all were the tall rudder shared with the 9. All the rudder pieces looked much the same but the causes were different, as listed in the reports. Several of the HS spars were failed (maybe all but don't recall), and the VS broken.
1- Canada, 3 USA, 1 NZ.

You should call Vans for your specific situation and get an official recommendation.

It's worth noting that most if not all of them involved speeds above Vne when a tail failure was present.
 
I have often wondered if this was the delay in the approval of the certified version of the "rudder trim tab" version of Uavionics ADS-b.
 
Re-balancing alone may not be an adequate compensation for added mass at the trailing edge. Control surface stiffness is also a factor, and ultimately strength. Here we're talking about adding more mass at two ends of the same structure in torsion.

As a homebuilder lacking the tools and knowledge to do a flutter analysis. I wouldn't add anything significant to the trailing edge of a surface.
 
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It's worth noting that most if not all of them involved speeds above Vne when a tail failure was present.

In my case, the odds of me accidently exceeding vne during nanuvering would be much greater than accidently entering a spin. If I am dumb enough to enter a spin in a landing attempt, they aren't recoverable anyway. I am undergoing cancer treatment and if or when I resume building, I will install the early rudder.
 
Difference in wt between Whelen tail position light (0.14 lbs) and the replacement Tailbeacon (70 grams or 0.154 lbs) is 0.014 lb.
 
Many RV's (everything after the 6) have a rudder based beacon installed and presumably tested by vans. I would compare the weight of the adsb beacon against the standard whelen fixture.

I know many people put tail beacons on 6's (both small and large rudder) that weren't designed / tested for them and many different tail light units are used in the field and I am sure the weights vary significantly between them.

It would seem from anecdotal evidence that these variations across 1000's of planes aren't impacting safety.

Larry
 
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Hang in there!

What I have is really aggressive so it looks like the only two options available are being able to able to return to work on my project or an estate sale.
Jim, good luck with the treatment. No idea what you've got, but my mom had it really bad and pulled through. They are getting better at every day, so hang in there.
 
tailBeacon

So, notwithstanding this discussion, have you, or anyone you personally know, replaced an existing rudder-mounted tail light with a uAvionix tailBeacon? Was re-balancing the rudder required?

Thanks
 
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I am undergoing cancer treatment and if or when I resume building, I will install the early rudder.

For what it's worth, even though my Dad got his cancer successfully treated into remission, a few years later passed away for not doing his required followups (his choice).

My Mom on the other hand has had 4 different types cancers and has beat them all, in fact today is her 83rd birthday !!

It can and is done on a daily basis, good luck buddy !
 
So, notwithstanding this discussion, have you, or anyone you personally know, replaced an existing rudder-mounted tail light with a uAvionix tailBeacon? Was re-balancing the rudder required?

Thanks

I replaced my Whelen strobe and position light on my RV7A with a Uavionx tail beacon and no rudder re-balance. The weight difference is negligible. PS the Uavionx tail beacon was an easy installation and works great
 
I just finished installing a SkyBeacon on my wifes Decathlon. The weight of the skybeacon was about a half ounce less than the piggyback combo position/strobe fixture that was removed. The real weight change was being able to remove the left wing tip strobe power supply that was just over one pound. Since it was nearly right on the C/G; there was almost no change in EW C/G station.
 
In my case, the odds of me accidently exceeding vne during nanuvering would be much greater than accidently entering a spin. If I am dumb enough to enter a spin in a landing attempt, they aren't recoverable anyway. I am undergoing cancer treatment and if or when I resume building, I will install the early rudder.

Do you feel the early rudder is less prone to balance issues?
 
For what it's worth, even though my Dad got his cancer successfully treated into remission, a few years later passed away for not doing his required followups (his choice).

My Mom on the other hand has had 4 different types cancers and has beat them all, in fact today is her 83rd birthday !!

It can and is done on a daily basis, good luck buddy !

Sorry to hear that about your dad but happy to hear your mom had her 83rd bday.

Wonder what the thought was on the early rudder if he?d felt it had less issues with balance.
 
I replaced my Whelen strobe and position light on my RV7A with a Uavionx tail beacon and no rudder re-balance. The weight difference is negligible. PS the Uavionx tail beacon was an easy installation and works great

This was the larger counter balanced rudder. For what it’s worth I currenly have the original small rudder without any counter balance
 
What I have is really aggressive so it looks like the only two options available are being able to able to return to work on my project or an estate sale.

Well I sure Hope you beat it. Sorry to hear that what you have is agressuve have you seen what they are doing with the taxis plant ?
What about stem cells or gene manipulation or something else like that. You hear about all these new things maybe one will work out.
 
Well I sure Hope you beat it. Sorry to hear that what you have is agressuve have you seen what they are doing with the taxis plant ?
What about stem cells or gene manipulation or something else like that. You hear about all these new things maybe one will work out.


I am on the EPOC chemo and they are telling me my blood work is looking good. Every one with my condition who used the normal RCHOP before this stronger chemo was developed died. This really torches the immune system so that's my main danger. So far, I'm tolerating the stuff pretty well but it gets more difficult if I catch any bugs.
 
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Uavionix tailBeacon

I replaced my Whelen strobe and position light on my RV7A with a Uavionx tail beacon and no rudder re-balance. The weight difference is negligible. PS the Uavionx tail beacon was an easy installation and works great

Thanks for the response. As has been mentioned here, there are two different rudders. Mine is the larger. Yours?
 
If you have ever seen some of Rick Gray?s control surface work and how he ?boxes in? his surfaces it looks like a work of art. I wanted to try to do the same but was a little concerned about flutter margins. I emailed Vans and the reply was that mass balance of the surfaces on an RV wasn?t necessary as long as gross amounts of weight were not added and the surface remained ?in trail? I was alright. I added nut plates to the elevator horns to add weight as needed after painting. Everything I have read on guys that have run into flutter problems in RVs have been when they exceeded TAS margins.
 
Carl, thanks but no I meant exactly what I wrote. Mass balancing is a procedure performed on all certified aircrafts individual surfaces after repairs or paint work with the limits spelled out in the AC maintenance manual. Here is the email from the mother ship.

Mark,

There typically isn't an issue doing this sort of modification on the elevators & H/S. The
weight of the foam and epoxy isn't that much. The counterbalance weights are designed to
simply bolt on an fly. There doesn't have to be a 'mass balance' procedure done on them
although you are welcome to do it though.

The only down side I can see is that you can really look under the foam to inspect for
corrosion.

Thanks


My concern was that of the OP that altering the weight of the control surfaces would have dire consequences. I wanted the peace of mind knowing that the final outcome is that they remain ?in trail? per the plans and there?s no problem even with a little more weight. It seems in reviewing the flutter accidents and incidents that over speeding these aircraft are more critical that a little added weight on the control surfaces.
 
I replaced my Whelen strobe and position light on my RV7A with a Uavionx tail beacon and no rudder re-balance. The weight difference is negligible. PS the Uavionx tail beacon was an easy installation and works great

Once again....with feeling. Is yours the larger or smaller rudder?

Thanks.
 
Guys, frequency issues are also a factor.

Weight placement and its overall distribution can be a factor.

Interesting thing about adding trim tabs not included in original is that few, if any, follow the FARs and repeat the Vd-Vne series with the tab control detached and the tab trailing in the wind.
 
I have a friend with a RV-6.5A (RV-6A with larger RV-7 vertical and rudder). The trailing edge of the rudder has a tail light mount area but it is not used as the aicraft uses combination lights on the wing tips.

The owner was interested in the tailBeacon but I pointed out there would be an addition of the entire weight of the tailBeacon at the rudder trailing edge which is a more extreme weight add than when replacing an existing nav light assembly where the net weight change is less. Also, new wires would have to be run from front to back since there was no existing wiring.

In the end I talked him into the EchoUAT which is hundreds of dollars cheaper and provides both in and out.

Now I am reading about RV7 tail flutter failures and am glad he went with the Echo UAT. I know most failures occurred at over Vne but who doesn't like a little more safety buffer built in? Flutter is one thing that scares the bejeezus out of me. I am a stickler for control balancing and having no slop in hinge lines and trim tabs.

Maybe it's just me but I really don't think an Echo install is much more work than a Beacon install, especially if exiting strobe power packs need to be removed or bypassed and wing tips need special accessory fairings for the unit to mount and look right (I did a Cessna 172 and the SkyBeacon didn't fit or look well until we ordered a $90 acessory from uAvionics which was a chunk of plastic trim).

Jim
 
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There are 5 RV7's that have had inflight failures, all were the tall rudder shared with the 9. All the rudder pieces looked much the same but the causes were different, as listed in the reports. Several of the HS spars were failed (maybe all but don't recall), and the VS broken.
1- Canada, 3 USA, 1 NZ.

You should call Vans for your specific situation and get an official recommendation.

The -7 and -9 only share the VS and rudder. The HS and elevators are very different.
 
That makes sense to me

This may be an underappreciated difference between RVs and traditional trainer/budget GA aircraft.

After transitioning from a Warrior to a -9A, it dawned on me that although the -9A is (like the Warrior) forgiving and easy to fly, it IS in fact capable of exceeding VNE in flight regimes where the Warrior would have been far too draggy to get into trouble.

Everything I have read on guys that have run into flutter problems in RVs have been when they exceeded TAS margins.
 
There are 5 RV7's that have had inflight failures, all were the tall rudder shared with the 9. All the rudder pieces looked much the same but the causes were different, as listed in the reports. Several of the HS spars were failed (maybe all but don't recall), and the VS broken.
1- Canada, 3 USA, 1 NZ.

You should call Vans for your specific situation and get an official recommendation.

BillL do you have a list or the accident references. That sounds like a lot. I heard of one HS failure... (turbulence and high speed may have been factors) Appreciate it.

BTW: RV-7 completed in Sport class at Reno and had qualifying speeds close to 250 MPH.... Rockets with basically stock RV-4 tails also have been going fast for a long time. If you are worried about at near Vne put your feet on the rudder pedals, that will dampen as well as keep hand on stick...


EDIT: I went and looked up all the fatal RV7 or RV-7 accidents. I found about 25. Of those I found something to do with structural failure in flight or possible in 5. All of them seem to be related to over speed (botched Aerobatics), Loss of control (IMC) or Bird Strike. One is undetermined but reading the text they state loss of control. Feel free to look at these and give your analysis. There is of course fatigue crack SB from vans on the Horz stab.

Registration Number Make Model Fatal Injuries Weather Condition Broad Phase of Flight
N731RV JORDAN JOHN RV7 2 VMC Vert Stab Failure possible BIRD STRIKE (feathers in cockpit) or maneuver to avoid over stressing
N307AB BARNETT ALLEN S RV7 2 VMC CRUISE /Performance/control parameters - Not attained/maintained (Cause) / Turbulence - Effect on Equip & operation (Cause) / Gusts - Effects on HORZ STAB FAILURE operation
N174BK BROWN ROBERT K RV7A 1 VMC Loss Control In Flight - Airspeed - Capability exceeded (Cause) / Incorrect action performance - Pilot (cause) Botched Aerobatics
N747BA ALEXANDER RV-7 1 VMC MANEUVERING Parts Separation from AC Structural (Radar Info Indicates Aerobatics… high descents/climbs and speeds…)
N774US NOLES VANCE L VANS RV7A 1 IMC MANEUVERING VFR INTO IFR Vert and Horz Tail Separated Thunderstorms.
 
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Vne

Putting your feet on the pedals and hand on the stick will not necessarily prevent nor stop flutter of flight controls; the best way to avoid it is to stay within the design parameters of the aircraft. Vne is there for a reason, and flutter is not something to take lightly...and it doesn't matter how good of a pilot you think you are...
 
Putting your feet on the pedals and hand on the stick will not necessarily prevent nor stop flutter of flight controls; the best way to avoid it is to stay within the design parameters of the aircraft. Vne is there for a reason, and flutter is not something to take lightly...and it doesn't matter how good of a pilot you think you are...
For the record I did not say this guarantees flutter prevention, but it helps, nor did I say or imply to exceed the operating limits. I think that is a given every pilot should know.. ... Thanks.

Flutter test they hit the stick and let go.. hands off. Trust me hands/feet on controls does increase flutter margins. I am not a test pilot but have known a few who do or did flutter test, even broke a plane in flight doing one of these tests during certification of a STC modification... If the control system is stiff (like it is on the RV) feet and hands on stick does change the dampening, but NEVER exceed limits of aircraft. Vibration (flutter or "aero-elasticity") of structure is complicated and unpredictable.

EDIT: Added new video from my favorite instructor: www.youtube.com/watch?v=f7tg94QflBY

To scare you all watch this (skip to 0:50): https://www.youtube.com/watch?v=qpJBvQXQC2M

Resting feet on rudder has a lot of benefit even for reducing dutch roll in turbulence. On larger aircraft the yaw dampener actuates the rudder to give less rock and roll automatically...
 
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Agree!

"...I think that is a given every pilot should know..."

We are on the same page. The only reason for my comment is that, unfortunately, I think a lot of people DON'T know...and think flutter is just a nebulous concept that engineers talk about.

The fact is, it CAN kill you. Years ago, I had an Aero Prof that was a project engineer doing flutter testing on one of the big name certified GA aircraft who related his story to us. Long story short, an elevator entered a divergent flutter mode, destroyed the stabilizer...and the aircraft crashed. The test pilot was killed.

More recently, we owned a C-421 that experienced an elevator flutter, due to the loss of a trim tab cotter pin. Luckily, the bolts connecting the left and right elevator torque tube halves sheared. My Dad was able to land the aircraft with only the left elevator being controlled...
 
N174BK-RV7A

This accident report is an interesting read. There was well documented evidence that the pilot was attempting to learn aerobatics on his own. Evidence of him falling out of previous roll attempts.
The wreckage path started with the lower half of the rudder and progressed thru the various portions of the tail.
The pilot was not the builder. He had repaired wind damage to the rudder some time previously.
 
Tough

It?s tough to re read those accidents since some were folks we knew here. I never liked the zipper edge rudder. If made and maintained right, it?s safe and fine within parameters. Exceed parameters and the data suggests that it doesn?t have as much margin as say the folded -8 rudder. Want more margin and willing to sacrifice 1 to 1.5 turns in a spin, put the -8 rudder. If you are a spinner and really need that 1.5 less turns and willing to accept less margins, then put the zipper edge rudder on.
Choose your poison. It?s all a trade off.
Me personally I?m a non spinner and went with the folded edge and mass balanced it and I have the tail beacon.
Best wishes in your endeavor!
 
mass balance with tail beacon

...
Me personally I?m a non spinner and went with the folded edge and mass balanced it and I have the tail beacon.
Best wishes in your endeavor!
Did you have to add much to offset the tail beacon?
 
Rudder light

I mass balanced mine with a standard light assembly. Later when the tail beacon came out I removed the standard tail light and installed the tail beacon assembly. I did not rebalance the rudder because the weight removed from that location was not statistically significant to what I reinstalled. Nevertheless, I was glad that I mass balanced the rudder to begin with.


Did you have to add much to offset the tail beacon?
 
Putting your feet on the pedals and hand on the stick will not necessarily prevent nor stop flutter of flight controls; the best way to avoid it is to stay within the design parameters of the aircraft. Vne is there for a reason, and flutter is not something to take lightly...and it doesn't matter how good of a pilot you think you are...

I always heard flutter can happen so fast it can feel like an explosion. I remember seeing a story about a Beaver (I think) in Alaska that nearly vibrated the wing off, from an unbalanced aileron if I recall.
 
I remember seeing a story about a Beaver (I think) in Alaska that nearly vibrated the wing off, from an unbalanced aileron if I recall.

It may not have vibrated the wing off, but it probably caused enough localized damage that the rest of the wing could no longer support flying loads. A local owner of a wooden amateur-built found that out when one aileron attach point failed due to undetected dryrot in the rear spar. The flutter that followed caused the control cables to saw through the rest of the aft spar, and with that gone the outer half of that wing folded up and departed the aircraft. As the aileron was cable-controlled and on a single loop, that meant he had no aileron control on the other side either. Needless to say, he didn't make it.
 
I seem to recall a momentary incident where a T-18 pilot developed blisters on his palm that was explained as caused by a flutter incident.

Flutter is an aero-elastic condition, it's hard to understand how feet on the pedals, when you consider all the links and, tolerances and/or elasticity of the control linkages, can act to prevent flutter. Might help to dampen the positive divergence until the airplane can be slowed below excitation speed, but I don't (personally) have much confidence in the explanation.

FWIW
 
Umm

?...It may not have vibrated the wing off,...?

Hard to say but it could be possible...

You want to see what flutter can do? Search for the Tacoma Narrows Bridge...

In an aircraft it happens much faster. In the case of our c-421, it sounded like an explosion...and there were hands on the yoke; it didn?t make any difference at all...
 
Ah, it was a Beaver. And yes, it nearly vibrated the wing off.

"The right-wing aft attach point was completely severed and held in place by lift of the wing."


https://www.aopa.org/news-and-media/all-news/2006/march/01/never-again-online-denalis-rough-ride

"The FAA engineering team concluded that one aileron was 17 ounces out of balance"- Well there's your problem.

"An FAA inspector who did the investigation stated — with no supporting data — that I had exceeded the aircraft's V NE speed and caused this to happen, a statement that caused me considerable hardship. I have since been totally exonerated from any wrongdoing, and I actually have been credited with a save of the three lives and my own, with my correct and swift response to the emergency."- Oof.
 
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Flutter is an aero-elastic condition, it's hard to understand how feet on the pedals, when you consider all the links and, tolerances and/or elasticity of the control linkages, can act to prevent flutter.

Flutter is a coupling of two (or more) damped-driven systems. Airspeed provides the ?drive? and a number of things act to dampen oscillatory movement. Anything that increases dampening will increase the critical flutter velocity. Keeping your feet on the pedals will increase dampening, but it?s more of an academic point. As you, George and Bob all imply, the real-world effect is not likely to be much.
 
It's always interesting to read about flutter conversations. There's a lot of misinformation about what flutter is, even in this thread. I'm definitely not an expert, but I did loads/flutter/structures testing for over a decade with the air force and as a contractor. I was also a weight and balance guy for a few years on a modern fighter platform.

Just because a control surface vibrates without any control input does not mean you have flutter. True flutter only occurs in a negatively damped system. You can get oscillations on underdamped and neutral damped systems which don't result in flutter. The F-16 has a known vibration mode on the wings:
Research Paper: https://arc.aiaa.org/doi/abs/10.2514/2.2696?journalCode=ja
Video: https://www.youtube.com/watch?v=1DK-zGLK6GQ

While this isn't true flutter, it should scare the **** out of anyone in a GA aircraft, especially an experimental with no published guidance on under-damped or known LCO modes. When you move beyond LCO and into a negatively damped regime, the oscillations increase uncontrolled, and almost always end with pieces of the aircraft coming apart. There's fractions of a second to slow down/pull-g in order to catch a true flutter event before things break. When things go negatively damped, every oscillation adds energy to the system, and it takes as few as 3 oscillations before the magnitude has increased enough to exceed the load limits and break things. All you can really hope for in a true flutter event, is that the aircraft breaks in a way that's still flyable.

As far as changing out the beacon to the ADS-B unit, if vans said it wouldn't need a rebalance, I don't see a reason to argue with them. Just like the entire airplane has a weight and balance envelope, each control surface has a weight and balance envelope. It's not an exact number that can't be deviated from. You can have a theoretical "perfect" surface, or a heavy/light surface, or a forward/aft surface. As long as you're in the envelope the surface won't impact flutter below Vne in any significant way. I've seen control surfaces that were out of limits be approved for full envelope flight after a few more hours of "sharpening the pencil" to determine flutter impacts. If Vans looked at the weight difference and placement of the ADSB beacon and said no rebalance was required, its likely because the change in W&B was so small that 99% of the surfaces out there will still be inside the W&B envelope after the swap. If you've got 9 different coats of paint on there, or for some reason have added a whole bunch of doublers and inspection plates and have a crazy heavy control surface, and then did the swap, maybe its worth reweighing and rebalancing because you might have a fringe case control surface. Chances are though, you have a control surface that was built within spec, and falls somewhere in the middle of its weight and balance range, and adding 0.1 lbs to the aft end of it won't pull it out of limits.
 
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