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  #101  
Old 08-22-2022, 08:54 AM
Mikeyb Mikeyb is offline
 
Join Date: Nov 2018
Location: Pasadena ca
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Default Vans comment on rudder balancing

https://vansairforce.net/community/s...Balance+rudder
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  #102  
Old 08-22-2022, 09:56 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Snowflake View Post
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.
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  #103  
Old 08-22-2022, 11:00 AM
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Tandem46 Tandem46 is offline
 
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Location: Colorado
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Quote:
Originally Posted by rv6ejguy View Post
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.
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  #104  
Old 08-22-2022, 11:44 AM
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RV8JD RV8JD is offline
 
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Quote:
Originally Posted by DanH View Post
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.
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  #105  
Old 08-22-2022, 11:46 AM
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RV7A Flyer RV7A Flyer is offline
 
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Location: US
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Quote:
Originally Posted by DanH View Post
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?
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  #106  
Old 08-22-2022, 11:56 AM
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RV8JD RV8JD is offline
 
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Quote:
Originally Posted by RV7A Flyer View Post
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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Last edited by RV8JD : 08-22-2022 at 12:04 PM.
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  #107  
Old 08-22-2022, 12:03 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
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Default 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.
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  #108  
Old 08-22-2022, 01:29 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by RV8JD View Post
This is distressing information. I hope that individual reads this thread and retrofits an RV-8 rudder to his RV-8.
Sharp guy, just didn't know. He said he would change it when he returned home.
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  #109  
Old 08-22-2022, 01:42 PM
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rv6ejguy rv6ejguy is offline
 
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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.
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  #110  
Old 08-22-2022, 01:53 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
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Quote:
Originally Posted by RV7A Flyer View Post
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.
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