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  #111  
Old 08-22-2022, 01:59 PM
RV8JD RV8JD is offline
 
Join Date: Jan 2005
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Quote:
Originally Posted by DanH View Post
Sharp guy, just didn't know. He said he would change it when he returned home.
Glad to hear that. Thx!
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Last edited by RV8JD : 08-22-2022 at 02:35 PM.
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  #112  
Old 08-22-2022, 02:07 PM
RV8JD RV8JD is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
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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Last edited by RV8JD : 08-22-2022 at 02:11 PM.
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  #113  
Old 08-22-2022, 02:51 PM
RV7A Flyer's Avatar
RV7A Flyer RV7A Flyer is offline
 
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Location: US
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Quote:
Originally Posted by scsmith View Post
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")?
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  #114  
Old 08-22-2022, 03:34 PM
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rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
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Quote:
Originally Posted by RV8JD View Post
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.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 460.7 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #115  
Old 08-22-2022, 03:57 PM
RV8JD RV8JD is offline
 
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Quote:
Originally Posted by RV8JD View Post
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.
Quote:
Originally Posted by rv6ejguy View Post
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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Last edited by RV8JD : 08-22-2022 at 04:22 PM.
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  #116  
Old 08-22-2022, 04:54 PM
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BillL BillL is offline
 
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Default Exactly!

Quote:
Originally Posted by scsmith View Post
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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Last edited by BillL : 08-22-2022 at 05:07 PM.
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  #117  
Old 08-22-2022, 04:57 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by RV8JD View Post
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.
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  #118  
Old 08-22-2022, 05:33 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
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Default 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.
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  #119  
Old 08-22-2022, 07:10 PM
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rv6ejguy rv6ejguy is offline
 
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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."
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 460.7 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #120  
Old 08-23-2022, 02:53 AM
swift12 swift12 is offline
 
Join Date: May 2021
Location: Palmerston North
Posts: 169
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Quote:
Originally Posted by RV7A Flyer View Post
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….
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