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  #291  
Old 11-14-2022, 04:29 PM
AndrewR AndrewR is offline
 
Join Date: Jun 2017
Location: Ballarat, VIC
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Quote:
Originally Posted by airguy View Post
From a strict engineering and evidentiary perspective, that answer is just as likely as the one about poor design.
The common failure involves a joint that doesn't exist in the RV6/8, so I think the evidence is much stronger than for RV6/8 pilots being smarter.

But I wouldn't call it poor design (is that what people are upset about?)

I would say it is discovery of a common first point of failure that doesn't exist in the RV6/8. Evidence from the RV6/8 suggests there is a fix that would improve margins enough to avoid these in flight breakups and save lives.

The looming question is what about the RV-14? I don't think there are enough flying yet to be confident it won't see the same failures. I know the rudder structure is different, but is it different enough to avoid the problem?
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  #292  
Old 11-14-2022, 04:56 PM
RV7A Flyer's Avatar
RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by Thermos View Post
Maybe.


Your assumption that flutter is the first failure mode/limitation past Vne, isn't necessarily correct. Vne is defined as 90 percent of Vd, the design dive speed that the manufacturer chose to demonstrate. The hazards past that could be buffeting/vibration, increasing structural loads, etc. If I screwed up on a downline and went well past Vne, I'd like to know that the failure mode was "gradual", to use your words, or something I had some limited control over - like keeping the wings and stab on by gentle use of the stick.

ds

ps - Tagging on to Carl's words, I'm an engineer as well. I spent a fair chunk of the Air Force and FAA portions of my career as a Flight Test Engineer and Test Director in fixed and rotary wing aircraft. I'm also a consultant DER. I've intentionally been past Vne more than once in high-risk tests, which is more than enough. I learned enough about margins around Vd to pay attention to the flutter/aeroelastic experts; Carl's position as the FAA's flutter specialist for transport category aircraft is all I need to know about his expertise.
Thanks for the info in the 1st paragraph. I'm an engineer as well, 30+ years, but not aero (rather, systems, in aerospace). So my preferred verification method is Test, followed closely by Analysis. Somewhere lower down is Inspection. And way down (like off the list) is "Seems as if...", TLAR, etc. I'll certainly defer to an aero engineer's overall assessment.

Still seems to me that this is a solution in search of a problem. Don't go VFR into IMC, get aerobatic training before you do aerobatics, and know your V-speeds seem to be correct answers to "how do I not go so fast that I break the airplane?". THOSE are the root causes of the failures, not the hardware.
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Last edited by RV7A Flyer : 11-14-2022 at 06:00 PM.
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  #293  
Old 01-14-2023, 03:31 PM
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Mark33 Mark33 is offline
 
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This has been a really good thread. I kind of view the “potential” problem/solution as money in the bank. Yes, if you have enough money in the bank to pay your bills every month, you’re probably in pretty good shape….but it never hurts to have a little extra emergency funds.

I posted in another RV-7 thread with similar questions. In that thread the OP raised the question and wondered if the 14 rudder would fit/work on his 7? He felt as though the 14 rudder offered a better/stronger internal structure and decided to give it a try. He reported that he really liked the results and that the 14 rudder was working well on his 7. So that does bring up the question as to why the 14 rudder isn’t standard equipment on the 7/9? Even if the 14 rudder becomes standard equipment on the 7 and 9, I’m still personally firmly in the 8 rudder camp and think it’s a better choice. If for no other reason, it looks a lot better.

Quote:
Originally Posted by AndrewR View Post
…..snip…..The looming question is what about the RV-14? I don't think there are enough flying yet to be confident it won't see the same failures. I know the rudder structure is different, but is it different enough to avoid the problem?
The pros and cons have been argued pretty thoroughly in this thread and everyone has their own reasons for liking one flavor or the other.

Now this brings me back to the question I asked in that other 7 thread: How would the 14 fly with an 8 rudder? I know it’s never been done before and you’d be a “test pilot”, but the question still remains. Not being an aeronautical engineer, I’m merely looking at it and asking the questions from a novice point of view. This is how I see it:

1. It’s known that the 8 rudder works perfectly fine on the 7/9 and many people, including myself, argue it’s superior to that of the 9.

2. It’s known that the 14 uses the 9 VS and rudder. Yes, there may be some internal structural differences, but for arguments sake, they’re the same.

3. It’s known that the 14 flys perfectly fine with the 7/9 rudder so one could easily conclude that the overall aerodynamics/flight characteristics of the 14 are similar enough to that of the 7/9 that the 7/9 VS and rudder works well on the 14.

4. I know it’s never been attempted before, and you’d be a “test pilot”, but with the known facts listed above, it’d be an interesting discussion and to point to specific things , compare and contrast, that would be detrimental if attempted.
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RV-7- IO-360, EFII, Whirl Wind C/S, (Built and sold)
RV-4- O-320, Catto three blade, P-Mags (Sold)
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Last edited by Mark33 : 01-14-2023 at 05:55 PM.
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  #294  
Old 01-14-2023, 03:46 PM
MED MED is offline
 
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Quote:
Originally Posted by Mark33 View Post
How would the 14 fly with an 8 rudder? I know it’s never been done before and you’d be a “test pilot”, but the question still remains.
My question is why bother? The 14 flies just fine with the 14 rudder that comes as part of the kit.
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  #295  
Old 01-14-2023, 03:55 PM
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Mark33 Mark33 is offline
 
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Quote:
Originally Posted by MED View Post
My question is why bother? The 14 flies just fine with the 14 rudder that comes as part of the kit.
I’m not saying anyone “should”….I’m just asking the question. As discussed throughout this thread, there’s different schools of thought. I’m firmly in the 8 camp (money in the bank) and believe it’s a better design and offers a safety margin. On top of that, I think it looks a lot better. 😎
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Mark H.
RV-7- IO-360, EFII, Whirl Wind C/S, (Built and sold)
RV-4- O-320, Catto three blade, P-Mags (Sold)
RV-8- IO-360, Hartzell C/S (Flying)
RV-7- Sold project
RV-14- Building

Last edited by Mark33 : 01-14-2023 at 03:57 PM.
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  #296  
Old 01-14-2023, 09:31 PM
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RV8JD RV8JD is offline
 
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Quote:
Originally Posted by Mark33 View Post
I posted in another RV-7 thread with similar questions. In that thread the OP raised the question and wondered if the 14 rudder would fit/work on his 7? He felt as though the 14 rudder offered a better/stronger internal structure and decided to give it a try. He reported that he really liked the results and that the 14 rudder was working well on his 7. So that does bring up the question as to why the 14 rudder isn’t standard equipment on the 7/9? Even if the 14 rudder becomes standard equipment on the 7 and 9, I’m still personally firmly in the 8 rudder camp and think it’s a better choice. If for no other reason, it looks a lot better.



The pros and cons have been argued pretty thoroughly in this thread and everyone has their own reasons for liking one flavor or the other.

Now this brings me back to the question I asked in that other 7 thread: How would the 14 fly with an 8 rudder? I know it’s never been done before and you’d be a “test pilot”, but the question still remains. Not being an aeronautical engineer, I’m merely looking at it and asking the questions from a novice point of view. This is how I see it:

1. It’s known that the 8 rudder works perfectly fine on the 7/9 and many people, including myself, argue it’s superior to that of the 9.

2. It’s known that the 14 uses the 9 VS and rudder. Yes, there may be some internal structural differences, but for arguments sake, they’re the same.

3. It’s known that the 14 flys perfectly fine with the 7/9 rudder so one could easily conclude that the overall aerodynamics/flight characteristics of the 14 are similar enough to that of the 7/9 that the 7/9 VS and rudder works well on the 14.

4. I know it’s never been attempted before, and you’d be a “test pilot”, but with the known facts listed above, it’d be an interesting discussion and to point to specific things , compare and contrast, that would be detrimental if attempted.
I think your question was thoroughly discussed in the RV-7 subforum when you posted it there. Let's not rehash it again in this Safety subforum thread.
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Last edited by RV8JD : 01-14-2023 at 09:39 PM.
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