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  #141  
Old 08-25-2022, 04:03 AM
swift12 swift12 is offline
 
Join Date: May 2021
Location: Palmerston North
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Quote:
Originally Posted by airguy View Post
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.
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  #142  
Old 08-25-2022, 06:41 AM
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plehrke plehrke is offline
 
Join Date: Sep 2006
Location: Defiance, MO
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Quote:
Originally Posted by swift12 View Post
“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.
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There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact. —MARK TWAIN
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  #143  
Old 08-25-2022, 07:56 AM
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airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
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Quote:
Originally Posted by swift12 View Post
“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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Last edited by airguy : 08-25-2022 at 08:02 AM.
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  #144  
Old 08-25-2022, 08:10 AM
BillL's Avatar
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
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Default Let's look at this a different way.

Quote:
Originally Posted by airguy View Post
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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Last edited by BillL : 08-25-2022 at 08:21 AM.
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  #145  
Old 08-25-2022, 08:14 AM
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airguy airguy is offline
 
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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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Last edited by airguy : 08-25-2022 at 08:17 AM.
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  #146  
Old 08-25-2022, 08:26 AM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by swift12 View Post
...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.
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  #147  
Old 08-25-2022, 08:34 AM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by BillL View Post
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.
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  #148  
Old 08-25-2022, 09:16 AM
Robert Sailor Robert Sailor is offline
 
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Location: Nanaimo BC Canada
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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.
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  #149  
Old 08-25-2022, 09:58 AM
jask jask is offline
 
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If the 14 rudder will fit on the 7/9 and is the latest design, why hasn’t commonality of parts dictated a change?
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  #150  
Old 08-25-2022, 10:14 AM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
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Quote:
Originally Posted by swift12 View Post
“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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