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RV-7/7A In-Flight Breakup Accident Information

At the end of the day I don't think it's been shown that an RV-7/7A operated within the published design/performance envelope is at any risk.

No one disagrees.

Trouble is, despite good intentions, sometimes they get outside the envelope. The plain truth is everyone makes a mistake from time to time.

BTW, I met a fella at OSH with an RV-7 rudder installed on his beautiful new RV-8. He said he thought it would give him more control authority.
 
If there was a systemic fault here….

Arguably if flown within limits, there is nothing unsafe about the -9 rudder on the -7. But as Dan pointed out and we all know…we all make mistakes. In the last 15 yrs, every single catastrophic RV rudder flutter failure has been a -7 with the -9 rudder. Not the RV-3. Not the RV-4. Not the RV-6, not the RV-8.

Makes one think…hmmm.
 
BTW, I met a fella at OSH with an RV-7 rudder installed on his beautiful new RV-8. He said he thought it would give him more control authority.

This is distressing information. I hope that individual reads this thread and retrofits an RV-8 rudder to his RV-8.
 
No one disagrees.

Trouble is, despite good intentions, sometimes they get outside the envelope. The plain truth is everyone makes a mistake from time to time.

So if you "beef up" the design, however you do it, and enlarge the envelope, won't you still have the problem of people making mistakes and exceeding it?

How far do you go to ensure that no pilot ever violates a design constraint?
 
So if you "beef up" the design, however you do it, and enlarge the envelope, won't you still have the problem of people making mistakes and exceeding it?

How far do you go to ensure that no pilot ever violates a design constraint?

This excerpt is from my post #16:

"The problem appears to be that there are small rudder strength margins and small fin/rudder flutter margins outside that envelope when (the RV-7/7A is) equipped with the -9/-7 rudder. Note that RV-8s are not coming apart in-flight with the same regularity and for the same reason that RV-7s are. And I don't think RV-8 pilots are any better or more careful than RV-7 pilots."


There have been approximately 8 RV-7/7A accidents involving the rudder, with 11 fatalities. None for the RV-8/8A that I know of. The simple retrofit of the -8 rudder to the -7 gains a significant amount of safety margin, with no appreciable change in spin recovery characteristics.

Post #16 has some other useful information.
 
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Accident Record

What I can find:
RV4 structural failures zero
RV6 structural failures-one that was called a RV6 but was not built to plans. Modified RV3 wings among other poor choices. Continental six cylinder engine.
There are 4's and 6's that have been intentionally operated in excess of Vne, primarily for racing.
Racing at Reno is very likely to mean moderate turbulence, sometimes severe.
Many would contend that operation in moderate or greater turbulence should be limited to Va, which at Reno means one should not even bother starting the race.
 
We don't have the luxury of full FDRs showing control inputs in any of these accidents so you can't say what might have initiated overload or flutter.

I know of 2 stock 7s (turbos) which have been over 210 KTAS in level flight.

Straight and level flight in smooth air is a lot different than flight with a bunch of rolling G thrown in and coarse control inputs as far as structure deflection goes.

I assume Van's has tested to 220 KTAS? How far do you design or test to? 240 kts? 250? That still doesn't guarantee the structure is safe at those speeds when flown by hamfisted pilots.

You can't expect to do stupid things in airplanes, even if by mistake and survive all of them.
 
So if you "beef up" the design, however you do it, and enlarge the envelope, won't you still have the problem of people making mistakes and exceeding it?

How far do you go to ensure that no pilot ever violates a design constraint?

The key point here is to increase the margins and then DON'T enlarge the envelope. Enjoy the existing envelope with increased margins.
 
You can't expect to do stupid things in airplanes, even if by mistake and survive all of them.

So are you saying RV-7 pilots are the only ones that are doing stupid things and making mistakes?

As I said earlier, I don't think RV-8 pilots are any better or more careful than RV-7 pilots, and RV-8s are not coming apart in-flight due to the failure of the rudder.
 
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The key point here is to increase the margins and then DON'T enlarge the envelope. Enjoy the existing envelope with increased margins.

Ah, but now you're doing what engineers don't normally do, which is *over*-design to beyond the requirements. Speaking of which, what *are* the requirements here? In my view, any design beyond that set is, in some way, sub-optimal (usually in terms of weight/mass, but sometimes in other ways). How's that old expressions go? A design is optimized not when there is no more to add, but when there is nothing left to take away?

An engineer *could* design to a higher Vne, and then just tell the customers that Vne hasn't changed from the original, lower value, but what do you do when they find out you've lied to them? (and when they do, and start flying at the new, higher Vne value because "now we know the REAL value")?
 
So are you saying RV-7 pilots are the only ones that are doing stupid things and making mistakes?

As I said earlier, I don't think RV-8 pilots are any better or more careful than RV-7 pilots, and RV-8s are not coming apart in-flight due to the failure of the rudder.

Not all all, just where do you draw the line at Vne over margin, flutter and structural strength on any aircraft, not just RV7s?

The demo RV-8 lost a wing due to overstress. Do we condemn the design because of that one accident saying it should be stronger?

Van's can't be expected to make their designs fool proof in every situation and still meet the design mission. It looks like Van's has done substantial testing with other rudders and published the results. For anyone who is worried about this, they can change the rudder and maybe widen the margins. Kudos to Van's for doing the test flying and putting the results out.
 
So are you saying RV-7 pilots are the only ones that are doing stupid things and making mistakes?

As I said earlier, I don't think RV-8 pilots are any better or more careful than RV-7 pilots, and RV-8s are not coming apart in-flight due to the failure of the rudder.

Not all all, just where do you draw the line at Vne over margin, flutter and structural strength on any aircraft, not just RV7s?

The demo RV-8 lost a wing due to overstress. Do we condemn the design because of that one accident saying it should be stronger?

Van's can't be expected to make their designs fool proof in every situation and still meet the design mission. It looks like Van's has done substantial testing with other rudders and published the results. For anyone who is worried about this, they can change the rudder and maybe widen the margins. Kudos to Van's for doing the test flying and putting the results out.

I think this is a different situation. In the case of the RV-7s, Van's took the unmodified RV-9 rudder and put it on the RV-7 later in the history of the RV-7. The RV-9 rudder is designed for the -9 which has lower Va and Vne speeds than the -7 does, thus reducing structural margins when installed on the -7s.

The -9/-7 rudder is weaker and less stiff than the -8 rudder, which was designed for the same Va and Vne speeds that the RV-7 airplanes are designed for, since the RV-8 and the RV-7 have the same structural design speeds.

It's hard to get by the fact that there have been approximately 8 RV-7/7A accidents involving the rudder, with 11 fatalities. And they continue to happen with some regularity (see Post #1). There have been none for the RV-8/8A that I know of.

The simple retrofit of the -8 rudder to the -7 gains a significant amount of strength and flutter safety margin (similar to what the RV-8s have), with no appreciable change in spin recovery characteristics.
 
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Exactly!

The key point here is to increase the margins and then DON'T enlarge the envelope. Enjoy the existing envelope with increased margins.

Well said, that is all one could expect.
 
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But in the case of the RV-7s, Van's took the unmodified RV-9 rudder and put it on the RV-7 later in the history of the RV-7. The RV-9 rudder is designed for the -9 which has lower Va and Vne speeds than the -7 does, thus reducing structural margins when installed on the -7s. The -9/-7 rudder is weaker and less stiff than the -8 rudder, which was designed for the same Va and Vne speeds that the RV-7 airplanes are designed for, since the RV-8 and the RV-7 have the same structural design speeds.

It's hard to get by the fact that there have been approximately 8 RV-7/7A accidents involving the rudder, with 11 fatalities. And they continue to happen with some regularity (see Post #1). There have been none for the RV-8/8A that I know of.

The simple retrofit of the -8 rudder to the -7 gains a significant amount of strength and flutter safety margin (similar to what the RV-8s have), with no appreciable change in spin recovery characteristics.

Two things:

1. Do we *know* the root causes of all of those accidents? Not hearsay, not some of them, actual causes of every one? Are they ALL the same failure modes? All the same flight regimes? Absent some clear engineering evidentiary trail that points to a common cause, that being a rudder that is underdesigned, this is all just conjecture.

2. It doesn't matter much if the "margin" you're talking about is 10 knots or 100 knots...the *pilot in command* is not supposed to be messing around in the margin area. That it appears that the margin is somewhere around 40 knots or so, anecdotally, it seems like Van's has done their part, now we should do ours by staying within the envelope.
 
Sequence of failure

I have posted what I know about the sequence of events in some of the accidents as well as what is not know in the case of the WA accident. Read the NZ and Atlantic City reports to understand more.
 
This, right off Van's website clearly states their design philosophy:

"Based on the results of our various design and testing programs, we determine and publish do-not-exceed limits for calculations such as max gross weight, max G-loading, etc. When we publish specification numbers for our aircraft designs, we expect that people will stick by those limits when they build, certify and fly their airplanes. While we do, of course, build in a certain safety margin or “buffer,” it’s very important to understand that these margins “belong” to the engineer – not to the builder. Pushing the limits is just that. So, unless you are fully and uniquely qualified to assess your own custom design (in which case you’re on your own, of course) we will tell you — quite directly — that the published limits are the limits. Period."
 
Two things:

1. Do we *know* the root causes of all of those accidents? Not hearsay, not some of them, actual causes of every one? Are they ALL the same failure modes? All the same flight regimes? Absent some clear engineering evidentiary trail that points to a common cause, that being a rudder that is underdesigned, this is all just conjecture.

2. It doesn't matter much if the "margin" you're talking about is 10 knots or 100 knots...the *pilot in command* is not supposed to be messing around in the margin area. That it appears that the margin is somewhere around 40 knots or so, anecdotally, it seems like Van's has done their part, now we should do ours by staying within the envelope.

All wonderful stuff. Staying within the envelope is the brightest thing to do for sure but we are humans and stuff ups can happen. We train for jet upsets for that very reason….maybe even not our fault and wake, clear air turbulence, hitting unforeseen turbulence near coffin corner…(ok the rv’s shouldn’t have a problem with that!) but the point is….if a mistake happens and an rv8 rudder is less likely to come apart or flutter one wonders wether it may actually be better than a rudder designed for a slower aircraft even if you take another half turn to recover from a spin….which is less likely to get into versus an over speed in a fast flush riveted design.
I think I’ll be looking hard at an rv8 rudder for my 7. Not because I want to push the envelope at all….I merely think the design is lighter and stronger….the spin recovery is a minor issue….
 
I an 77 now and have owned a 7A Kit for several years. I haven't done much on it for the past 4 years since being treated for cancer. Soon after my initial purchase, I put an 8 rudder on my kit. I had read all accident reports because it is a good method of learning. The 9 rudder was installed for better spin recovery but since I do not intend to do any intentional spins, that didn't bother me. If I spin unintentionally, it would be at pattern altitude and I would probably die regardless of the rudder installed.

The cancer treatment was not kind to me and a few years ago I went looking to buy a 6A. My wife is a really good pilot and I just fly the right seat now. We both love the 6A and have finally got the Dynon for a panel upgrade. We sure enjoy the airplane and I still work slowly on my kit. I was at Anti Splat recently getting the bearing upgrade. He has some fixes for the 7/9 to strengthen the forward vertical spar attach point. He feels that is the failure point in a rudder event. BTW, I have toyed with being a novice machinist for the past 20 years and Allan is really good. He also gave me some #9 lead shot to put in my steps.
 
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Data says it all

In my humble opinion, having to use TAS when flying a RV coupled with a narrow margin rudder is a recipe for more inflight failures in future. Data is not emotional and it’s going to happen. That’s just the way it is. Education to individuals may slow the occurrences but relying on human memory is just not good mistake proofing. How far does one go? Well, if a rudder change will bring the inflight failure rate of the -7 down to the -8, then that’s all one can expect. Trying to educated all the pilots about watching TAS and not exceeding it has not been effective.
 
…. I was at Anti Splat recently getting the bearing upgrade. He has some fixes for the 7/9 to strengthen the forward vertical spar attach point. He feels that is the failure point in a rudder event. BTW, I have toyed with being a novice machinist for the past 20 years and Allan is really good. He also gave me some #9 lead shot to put in my steps.

I’m building a 9A and intend to put shot or sand in the steps. How will you seal the drilled hole?
 
I think this has been a educational thread, both about the importance of airplane limits and what can be done should you wish to increase margins on a -7.
 
I’m building a 9A and intend to put shot or sand in the steps. How will you seal the drilled hole?

I used sand in mine for a "dead blow hammer" effect to dampen the vibrations. I sealed the hole with some epoxy, and then put a strip of non-slip material on top of that.
 
I think this has been a educational thread, both about the importance of airplane limits and what can be done should you wish to increase margins on a -7.

The two primary ways to increase the margins of ANY aircraft...

1) Hire a competent engineer to find the weak points, and be ready to write the check.
2) Buy an airplane with the flight envelope you want, and be ready to write the check.
 
I agree.

There are aircraft better suited for aero and high speed than RVs if you're looking for higher margins.

Looks like the 2 high profile -7 breakups were caused by pilots hooning around with nary a thought of any airframe limits- 234 and 244+ knots respectively- WAY over Va and Vne.

If you want to do aero, get some training first. Things can get out of hand fast with the nose pointed down if you screw up.
 
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He has some fixes for the 7/9 to strengthen the forward vertical spar attach point. He feels that is the failure point in a rudder event.
While the vertical stabs have failed in these accidents, it's happened after other items failed first (ie. the rudder). The forward spar on the vertical stab is a red herring. Reinforcing the attach point of the vertical stab as AntiSplat suggests just creates stress concentrations elsewhere.
 
In my humble opinion, having to use TAS when flying a RV coupled with a narrow margin rudder is a recipe for more inflight failures in future. Data is not emotional and it’s going to happen. That’s just the way it is. Education to individuals may slow the occurrences but relying on human memory is just not good mistake proofing. How far does one go? Well, if a rudder change will bring the inflight failure rate of the -7 down to the -8, then that’s all one can expect. Trying to educated all the pilots about watching TAS and not exceeding it has not been effective.

I think most modern EFISes can display the correct IAS redline for any altitude. I know my Dynon does. And it will yell at me if I hit that speed.

I also don't know that the flutter margin is "narrow". Seems like the two incidents with the most data were at least 15-20% over Vne. How much margin do you need? The Canada incident occurred around 2000', so TAS ~= IAS anyway. The NZ one was between 2000 and 4000 feet, from what I can glean.

This is not a matter of training, it's a matter of pilots grossly exceeding the design limitations of the aircraft. Trust me, if you somehow create a 50% flutter margin (flutter onset at 300 knots), somebody out there is going to go out and find that limitation and kill themselves.

You simply can't engineer away all risk. Stay within the envelope.

Unless and until someone does a better job of *actual* engineering and analysis than the aeronautical engineers at Van's did with their design, all the rest is really just TLAR guesswork.
 
Looks like the 2 high profile -7 breakups were caused by pilots hooning around with nary a thought of any airframe limits- 234 and 244+ knots respectively- WAY over Va and Vne.

LOL! I hadn't heard this expression, and actually had to look it up, but I like it! Something about it makes me laugh out loud...
 
While the vertical stabs have failed in these accidents, it's happened after other items failed first (ie. the rudder). The forward spar on the vertical stab is a red herring. Reinforcing the attach point of the vertical stab as AntiSplat suggests just creates stress concentrations elsewhere.

I agree with this. In at least one of the two cases, the attach bracket that Anti-splat replaces with a stainless steel one was NOT the final failure point either. The fwd fin spar actually tore right above the attach bracket. I think BillL has a really good photo showing this.

Although this point was not the initial failure (other stuff broke first), the stiffness at this point may contribute to the flutter boundary. In Rockets, and several Reno-racing RVs, the fwd fin spar gets a doubler that runs part way up (to the middle rib IIRC) which stiffens the fin in torsion (and also somewhat in bending). With this added thickness from the standard fin spar plus the doubler, a thicker attach bracket should also be used. The rear fin spar also gets additional strengthening/stiffening.
 
Yes, it came with the 8 rudder.

Thanks for verifying what I thought I read sometime ago.

I took over a -7 build this past year (wings and tail partially built). It had the original rudder, 2001 was the year of the tail kit order. While waiting for my fuselage kit, ordered Nov. 2021, I requested the free larger rudder mentioned in Van’s service bulletin to make some movement on my build.

I am in the middle of building the new rudder when I noticed this thread. I will finish the larger rudder for the practice and to hone my skills but install the original “8” rudder.

Informative thread and reading, thanks all for your contributions and view points.
 
Thanks for verifying what I thought I read sometime ago.


I am in the middle of building the new rudder when I noticed this thread. I will finish the larger rudder for the practice and to hone my skills but install the original “8” rudder.

Good plan.
 
Although the RV-10 and -14 rudders still have riveted trailing edges, the internal structure is different from that in the-7/9. Stiffeners are tied to the rudder spar with shear clips, and the stiffeners themselves are much more robust - the horizontal flanges are joined to their mates on the opposite side with a rivet about halfway down the rudder chord. Also, the counterweight skin is integral to the rudder skin and not riveted on as with the -7/9.

My professional flight test work has only dealt with structures and flutter at a conversational level, but my sense is that these changes make the rudder quite a bit stiffer. Only Van's can say whether those changes were remedies for a weakness in the -7/9 rudder design, or if they were done for another reason.

This is a thread that seems worth pulling on. The numbering of the individual components that comprise the RV-14 rudder are similar enough to the corresponding RV-7 rudder parts that it leads me to think that an RV-14 rudder ought to bolt right on to an RV-7 VS. Assuming that's true, it would be interesting to explore why two in-production aircraft designs use rudders that are the same external size but have different parts and internal structure... especially considering that there haven't been any known in-flight breakups of RV-14s
 
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Vans

14 pages of comments.
Numerous posts about changing Vans design or components.
Did I miss a Vans comment?
Seems like they would have something to add.
 
14 pages of comments.
Numerous posts about changing Vans design or components.
Did I miss a Vans comment?
Seems like they would have something to add.

If there were something noteworthy to add, yes.

So far this is nothing but conjecture that "something is wrong" - but it's all based on pilots exceeding the published limits of the airplane. Vans will most likely not make any comment at all on accidents where the pilot exceeded the limits of the airplane - the cause of the problem there is obvious. Don't do that.

Is there any evidence at all that shows a failure while WITHIN the published limits of the airplane? Did I miss something?
 
Before we leave this topic

In my model airplane days, I was always trying to get my control surfaces stiffer for no added mass. I found that offsetting the tail ribs so the were not parallel increase the stiffness immensely with very little weight gain. When I started playing with real airplanes, I was surprised to see all the tail surfaces ribs running parallel based on what I “knew” from models. Perhaps the analysis tools are better now and non-parallel ribs can be assessed for if they provide greater stiffness with only minimal weight increase.

OK I am done with this topic, you may close the thread now. Because it is all about me anyway.
 
If there were something noteworthy to add, yes.

So far this is nothing but conjecture that "something is wrong" - but it's all based on pilots exceeding the published limits of the airplane. Vans will most likely not make any comment at all on accidents where the pilot exceeded the limits of the airplane - the cause of the problem there is obvious. Don't do that.

Is there any evidence at all that shows a failure while WITHIN the published limits of the airplane? Did I miss something?

“Don’t do that” is very simplistic. I’m sure those that have oversped their aircraft had not done it intentionally and may have some inexperience or had made a critical error. It is true these aircraft are slippery and point the nose downhill for an aircraft cruising reasonably close to VNE puts it in a “be very careful camp”…..so the question remains why have 7 rudders fallen apart in high speed events due flutter but not on 8’s as I am sure many 8’s have experienced overspeeding but none have crashed? Are we ok to ask the question does the 9 rudder actually suit the 7 given the different speeds these aircraft fly at? Is the 8 rudder stronger….putting aside the spin characteristics……it’s a fair question.
 
“Don’t do that” is very simplistic. I’m sure those that have oversped their aircraft had not done it intentionally and may have some inexperience or had made a critical error. It is true these aircraft are slippery and point the nose downhill for an aircraft cruising reasonably close to VNE puts it in a “be very careful camp”…..so the question remains why have 7 rudders fallen apart in high speed events due flutter but not on 8’s as I am sure many 8’s have experienced overspeeding but none have crashed? Are we ok to ask the question does the 9 rudder actually suit the 7 given the different speeds these aircraft fly at? Is the 8 rudder stronger….putting aside the spin characteristics……it’s a fair question.
Fair question in the experiment world but as stated before several times in this thread just be aware you are now a test pilot. And for sure you need to go back to phase 1.
 
“Don’t do that” is very simplistic. I’m sure those that have oversped their aircraft had not done it intentionally and may have some inexperience or had made a critical error. It is true these aircraft are slippery and point the nose downhill for an aircraft cruising reasonably close to VNE puts it in a “be very careful camp”…..so the question remains why have 7 rudders fallen apart in high speed events due flutter but not on 8’s as I am sure many 8’s have experienced overspeeding but none have crashed? Are we ok to ask the question does the 9 rudder actually suit the 7 given the different speeds these aircraft fly at? Is the 8 rudder stronger….putting aside the spin characteristics……it’s a fair question.

Why do high school kids wreck the Shelby Mustang that daddy bought them on their 16th birthday? Should we put age/experience restrictions on the things we want to buy/use? Minimum 200 hours in a Cessna 150 before being allowed to buy a tail kit from Vans? Without going far enough into politics to excite the moderators - we don't want to go there.

This is not a Vans problem. This is a piloting problem, and you can't fix that. There will always be the bottom 5% of any population of people that cause problems for the rest, no matter how selective you are for the group as a whole.

If the 7 scares you, don't fly it.
 
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Let's look at this a different way.

If there were something noteworthy to add, yes.

So far this is nothing but conjecture that "something is wrong" - but it's all based on pilots exceeding the published limits of the airplane. Vans will most likely not make any comment at all on accidents where the pilot exceeded the limits of the airplane - the cause of the problem there is obvious. Don't do that.

Is there any evidence at all that shows a failure while WITHIN the published limits of the airplane? Did I miss something?

Yes, but you are not alone. Many here strongly see it the same way. The concept of statistical variability is inherent to all things. I speak about this from production design experience and having dealt with many many production field problems as a result. Some have commented about the flutter margin. That is simply a failure margin and all designs have many of them. There are variance of loading, shock, vibration etc, many of which are unexpected. The unexpected in the case of a since serial number product in the field on one thing but when there is a population group of many identical products, the difference of the margins become more evident. The higher production numbers cause even a low failure rate to become significant in accumulated failures. This is why the 6-sigma programs (lean production - many names) made huge headway in product reliability improvement.

So here what we have is a product with the same specifications but which stands apart from it's brethren in a particular failure. It is used, and respected equally by the user population but has a higher failure rate. This is not conjecture it is a statistical fact.

This will yield a continuing count of failures and close to the statistical pattern. One about every 12 months based on the flying hours for the worldwide fleet. The question is, how long, how many will fail before it is accepted that there is something different. 10-20? Beech had 44 V tails go before addressing the issue, and that was done by the FAA and NTSB performing the testing. But we should keep in mind it is but one of a list of causes of fatalities, and not necessarily the greatest.

As individuals we don't have privy to the core engineering issues and details. So can only blather about the whole thing. The same crappy pilot theories were voiced about the V tail too. It just has to be viewed with a different and statistically/mathematically valid lens. This lens is in widespread use in industries where volume production is high. They don't always fix the problem, just make a new product that does. It is a $$$ and liability tradeoff.

If we knew the first flights per year for the product, a survey can tell us what the typical usage is and then it is a simple matter to calculate the failures/100,000 flight hours. That can replotted on Weibull and pretty accurately predict when the next failures will happen.

Meanwhile, users will do what they think is best to avoid this potential failure, however small.

My final engagement with this subject. Ref: "The Orville - Majority Rule"
 
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Do you want to end up paying V-tail prices for a Vans airplane? Because that's exactly where you'll end up, by treating them like a V-tail and expecting the same standards.

It's part and parcel of the experimental world - we accept a higher level of risk (and the accompanying higher level of responsibility) in order to do it ourselves, the way we want it, at a lower cost. If you want to guarantee you'll never have tail flutter, fly a Cessna 150.
 
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...so the question remains why have 7 rudders fallen apart in high speed events due flutter but not on 8’s as I am sure many 8’s have experienced overspeeding but none have crashed? ... Is the 8 rudder stronger….putting aside the spin characteristics……it’s a fair question.

It's only a fair question if you want to be exceeding the design limits of the aircraft. It's pretty clear that both rudders are adequately strong if you stay within the limits.
 
So here what we have is a product with the same specifications but which stands apart from it's brethren in a particular failure. It is used, and respected equally by the user population but has a higher failure rate. This is not conjecture it is a statistical fact.

You're missing one important factor: These are not the first failures in the accident chain. They are not the "root cause", using the same failure analysis/production engineering language that you used. The rudder failing is a result of an earlier failure, the overspeed/overstress of the aircraft. You can't identify the rudder structure as the primary concern when it's not the primary failure mechanism.
 
Why don’t 6’s suffer similar failure rates?. There are many more flying and it isn’t reasonable that this model doesn’t have pilots that exceed the red line as often as 7’s.
 
If the 14 rudder will fit on the 7/9 and is the latest design, why hasn’t commonality of parts dictated a change?
 
“Don’t do that” is very simplistic. I’m sure those that have oversped their aircraft had not done it intentionally and may have some inexperience or had made a critical error.

Critical errors are often fatal in aviation.

Make it safe to 250 knots might save a few but someone will still exceed that limit one day. If the two high profile -7s hadn't broken when they did, they were both on the way past 250 a second or two later.

Testing to 10% over Vne is pretty standard in the industry and Van's has done that. They have also offered up the flight test data on other rudders.

Builders should hopefully understand the importance of control surface weight and balance and that wide variations there and in construction quality can put you at more risk of flutter (Canadian accident). Margins can be eaten up here.

Full control deflection over Va can cause structural failure as well as we've seen in other RV accidents. It's important to be aware of all these limits when flying if you don't want to your RV turned into aluminum confetti but we can see that some pilots are oblivious when they are having fun yanking and banking.
 
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