Sharp guy, just didn't know. He said he would change it when he returned home.
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Sharp guy, just didn't know. He said he would change it when he returned home.
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.
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.
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")?
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.
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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.
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."
"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."
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.
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.
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’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.
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.
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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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 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.
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...
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.
sailsunfurled
Member
Did the pre 2002 -7 come standard with -8 rudder?
Yes, it came with the 8 rudder.
sailsunfurled
Member
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.
Good plan.
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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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?
PilotjohnS
Well Known Member
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.
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.
Speculation
Nope. You said it. I was trying to say that without my usual obnoxiois opinion. Thx
Nope. You said it. I was trying to say that without my usual obnoxiois opinion. Thx
“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.
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.
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"
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.
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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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.
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.
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.
I wonder if any of the Reno-racing RV modified the vertical stabilizer by making it shorter or smaller. It seems the large standard kit size is for aerobatic flying and spin recovery but I suspect it works against the high top speeds that are seen at Reno. I've seen some of the Reno specific racers (non-RV) that have very diminutive tails.
FAR Part 23 requires 15%.
Tandem46
Well Known Member
Yeah, EXCEPT this is not happening to the RV-3, RV-4, RV-6, RV-8, or even RV-7s equipped with the -8 rudder. Only RV-7’s with the -9 rudder.
Yeah, I don’t think that’s the issue here.
Dive Testing
There is of course no requirement for EAB to test to part 23 or part 25 requirements.
The Wittman Tailwind in 1953 was the first EAB to be allowed to carry passengers. The CAA(FAA) requirements were a dive test to 110% of Vne and a 4G test while loaded to gross weight.
The first five Tailwinds were tested to this standard.
On one of those tests a sandbag slipped out of place and pushed against the stick. The resulting dive was near 300 statute indicated and the G meter showed plus 8.3 and minus 3.8. Minor bend in windshield support, no other structural damage.
The elephant in the room is the question: was the RV7 ever dive tested with the RV9 rudder???
Why has Van's and or the FAA not canceled the aerobatic certification for the RV7 with the RV9 rudder?? Why have they not reduced the Vne of the 7 with 9 rudder as a safety precaution?
RV4 and 6 zero structural breakups. RV8 one wing failure caused by G load far in excess of design limits.
There is of course no requirement for EAB to test to part 23 or part 25 requirements.
The Wittman Tailwind in 1953 was the first EAB to be allowed to carry passengers. The CAA(FAA) requirements were a dive test to 110% of Vne and a 4G test while loaded to gross weight.
The first five Tailwinds were tested to this standard.
On one of those tests a sandbag slipped out of place and pushed against the stick. The resulting dive was near 300 statute indicated and the G meter showed plus 8.3 and minus 3.8. Minor bend in windshield support, no other structural damage.
The elephant in the room is the question: was the RV7 ever dive tested with the RV9 rudder???
Why has Van's and or the FAA not canceled the aerobatic certification for the RV7 with the RV9 rudder?? Why have they not reduced the Vne of the 7 with 9 rudder as a safety precaution?
RV4 and 6 zero structural breakups. RV8 one wing failure caused by G load far in excess of design limits.
After watching this thread grow to 16 pages with great interest, I've decided to chime in with a few thoughts, in no particular order;
if you beef up one area, you are frequently just transferring the initial failure to an adjacent area
slippery airplanes can reach Vne in a heartbeat if you're inattentive, especially when you are coming out of something that can't reach Vne unless you point it at the center of the earth.
flutter margins aren't something to be trifled with, nor are they something to be improved upon unless you have a big brain plus the ground and flight test equipment to back up your proposed fix.
A few of the modifications that are being talked about here aren't something that we would do in the certified world without a ton of modeling and static test articles, followed up by flight testing with an emergency egress system, pilots with chutes, and sometimes spin chutes on the flight test plane.
Yeah, I get that with a big enough statistical sample, you can predict X number of events over time, and this statistic seems to say that if you overspeed an RV7 you can rip the rudder off before the rest of the tail comes apart.
This set of statistical data would also seem to indicate that the builder has a choice; he can either install a big rudder and have smaller flutter margins (maybe) or install a small rudder and have poorer spin recovery characteristics. Pick one-live within the constraints of your choice. It's obvious where Van stands on this because back in the day they ponied up free rudders for everybody.
I'm going to take the stance that there isn't anything inherently unsafe about a well proven design, and be thankful that it's been in service long enough to identify potential danger areas to stay away from. Is it as forgiving as a 172? In this particular area, probably not. But you know what, it's not as forgiving of being left out in the rain either. That doesn't make it a bad airplane, just different considerations.
I could look at any two airplanes and pick them apart as to which one is better and which one is worse. A lot of you guys are old enough to remember when the first Citation came out and the Lear guys started saying that it was so slow that it was going take bird strikes from the rear. It wasn't very long before the Citation guys started saying that a Citation was doing everything it could to keep you alive and a Lear was doing everything it could to kill you.
My point is that like most things in life, you have to weigh the pro's and cons, mitigate the cons while being confident that the cure isn't worse than the disease, then live with the result.
This is an interesting discussion for sure, but as for me, I'm going to accept that my airframe has some well documented areas that need to be respected, with different considerations that a Cessna (or whatever). I'm building the airframe to it's well proven design, with the big rudder that Van's recommends/supplies and will try to live within those constraints.
edit- I have one final thought here; I've seen some comments about modifying stuff and the rebuttal has been "you're going into test pilot mode" followed by somebody else chiming in; "you're in test pilot mode when you're in phase 1" or something to that effect, implying that these two things are somehow equivalent.
I'll respectfully opine that no, in phase 1 you're in CONFORMITY pilot mode. You're confirming that your particular airplane behaves the way everybody is expecting it to, because that's the way it was originally designed and built to behave. If it's out of conformity with the rest of the fleet, then you try to figure out why and fix it, but it's extremely unlikely if you build to plan that something is going the be catastrophically out of whack.
In this case, it would seem to hold true whether you use the small rudder or big one you're in safe, well documented territory. They are both known quantities with known characteristics. But, If you go off the reservation with extra stiffeners or balance weights or otherwise start monkeying around with your own "improvements" without knowing what you're doing, you're truly in test pilot mode, which isn't where most of us want to be without significant training and safeguards in place.
if you beef up one area, you are frequently just transferring the initial failure to an adjacent area
slippery airplanes can reach Vne in a heartbeat if you're inattentive, especially when you are coming out of something that can't reach Vne unless you point it at the center of the earth.
flutter margins aren't something to be trifled with, nor are they something to be improved upon unless you have a big brain plus the ground and flight test equipment to back up your proposed fix.
A few of the modifications that are being talked about here aren't something that we would do in the certified world without a ton of modeling and static test articles, followed up by flight testing with an emergency egress system, pilots with chutes, and sometimes spin chutes on the flight test plane.
Yeah, I get that with a big enough statistical sample, you can predict X number of events over time, and this statistic seems to say that if you overspeed an RV7 you can rip the rudder off before the rest of the tail comes apart.
This set of statistical data would also seem to indicate that the builder has a choice; he can either install a big rudder and have smaller flutter margins (maybe) or install a small rudder and have poorer spin recovery characteristics. Pick one-live within the constraints of your choice. It's obvious where Van stands on this because back in the day they ponied up free rudders for everybody.
I'm going to take the stance that there isn't anything inherently unsafe about a well proven design, and be thankful that it's been in service long enough to identify potential danger areas to stay away from. Is it as forgiving as a 172? In this particular area, probably not. But you know what, it's not as forgiving of being left out in the rain either. That doesn't make it a bad airplane, just different considerations.
I could look at any two airplanes and pick them apart as to which one is better and which one is worse. A lot of you guys are old enough to remember when the first Citation came out and the Lear guys started saying that it was so slow that it was going take bird strikes from the rear. It wasn't very long before the Citation guys started saying that a Citation was doing everything it could to keep you alive and a Lear was doing everything it could to kill you.
My point is that like most things in life, you have to weigh the pro's and cons, mitigate the cons while being confident that the cure isn't worse than the disease, then live with the result.
This is an interesting discussion for sure, but as for me, I'm going to accept that my airframe has some well documented areas that need to be respected, with different considerations that a Cessna (or whatever). I'm building the airframe to it's well proven design, with the big rudder that Van's recommends/supplies and will try to live within those constraints.
edit- I have one final thought here; I've seen some comments about modifying stuff and the rebuttal has been "you're going into test pilot mode" followed by somebody else chiming in; "you're in test pilot mode when you're in phase 1" or something to that effect, implying that these two things are somehow equivalent.
I'll respectfully opine that no, in phase 1 you're in CONFORMITY pilot mode. You're confirming that your particular airplane behaves the way everybody is expecting it to, because that's the way it was originally designed and built to behave. If it's out of conformity with the rest of the fleet, then you try to figure out why and fix it, but it's extremely unlikely if you build to plan that something is going the be catastrophically out of whack.
In this case, it would seem to hold true whether you use the small rudder or big one you're in safe, well documented territory. They are both known quantities with known characteristics. But, If you go off the reservation with extra stiffeners or balance weights or otherwise start monkeying around with your own "improvements" without knowing what you're doing, you're truly in test pilot mode, which isn't where most of us want to be without significant training and safeguards in place.
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Thanks Steve for that info. I think Van's mentioned testing to 220 KTAS AFAIK so that's a bit short of the FAR 23 requirement.
There's an awful lot of talk about statistics and failure rates and whatnot, but you know what I haven't seen?
Actual statistics and failure rates and other numerical data.
How many RV-7s are there? How many with each rudder option? How many RV-8s?
Now, the claim is that there are 0 RV-8 rudder flutter-induced fatalities. Maybe, but let's accept that for now.
How many RV-7 flutter-induced fatalities? Below Vne? Above Vne? With which rudder?
I've seen nothing to convince me that there's any problem with the larger rudder other than when a pilot grossly exceeds Vne there's an increased risk of flutter-induced failure. No s**t, Sherlock, as we used to say.
I'm with the poster who asked to see any evidence of rudder issues on any aircraft flown within the envelope. Haven't seen it yet.
Actual statistics and failure rates and other numerical data.
How many RV-7s are there? How many with each rudder option? How many RV-8s?
Now, the claim is that there are 0 RV-8 rudder flutter-induced fatalities. Maybe, but let's accept that for now.
How many RV-7 flutter-induced fatalities? Below Vne? Above Vne? With which rudder?
I've seen nothing to convince me that there's any problem with the larger rudder other than when a pilot grossly exceeds Vne there's an increased risk of flutter-induced failure. No s**t, Sherlock, as we used to say.
I'm with the poster who asked to see any evidence of rudder issues on any aircraft flown within the envelope. Haven't seen it yet.
Quote:
The kit manufacturer had conducted flight testing of the RV-7A prototype. No indications of flutter were encountered at a speed of 217 knots. Additional theoretical flutter analysis was done where the flutter speed was calculated to be 300 knots for the baseline design
This is from a previous thread. It looks like the initial testing with the 8 rudder looked pretty good.
The kit manufacturer had conducted flight testing of the RV-7A prototype. No indications of flutter were encountered at a speed of 217 knots. Additional theoretical flutter analysis was done where the flutter speed was calculated to be 300 knots for the baseline design
This is from a previous thread. It looks like the initial testing with the 8 rudder looked pretty good.
Arlington, AZ RV7
Some interesting highlights from the NTSB Probable Cause:
"cockpit canopy, vertical stabilizer and rudder were found about 1 mile from the main wreckage".
Probable Cause:
Inflight overstress separation of vertical stabilizer and rudder during flight-----Contributing-----was an inflight collision with a bird. (end)
"The RV7 is a two place, tandem seat,------(can't they do any better than this??)
Comments: No discussion of why canopy and vertical tail were all found together. No discussion of how bird feathers might have gotten under the passenger seat. No discussion of size/weight of bird which was identified as Rock Pigeon which is under one pound. No discussion of aircraft speed but a detailed discussion of ground track.
They do mention that the overstress could have been a startle reaction to the bird(s)
Some interesting highlights from the NTSB Probable Cause:
"cockpit canopy, vertical stabilizer and rudder were found about 1 mile from the main wreckage".
Probable Cause:
Inflight overstress separation of vertical stabilizer and rudder during flight-----Contributing-----was an inflight collision with a bird. (end)
"The RV7 is a two place, tandem seat,------(can't they do any better than this??)
Comments: No discussion of why canopy and vertical tail were all found together. No discussion of how bird feathers might have gotten under the passenger seat. No discussion of size/weight of bird which was identified as Rock Pigeon which is under one pound. No discussion of aircraft speed but a detailed discussion of ground track.
They do mention that the overstress could have been a startle reaction to the bird(s)
