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  #21  
Old 08-17-2022, 06:05 PM
BillL's Avatar
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
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Default Clarification

Quote:
Originally Posted by Taltruda View Post
If I had a -7, that’s what I would do.. especially because that -9 rudder feels just too big and stiff. Those folded trailing edges feel sweeter. Isn’t the vertical different too? Like the -7 crowd would need to change the stab and the rudder together? I thought the -8 balance tab was smaller and doesn’t fit the -7 stab..
The original 7 release came with the same-as-the-8 rudder also the same as counterweighted 6 rudder with .020 skin. Let's call it the 7Short. The vertical on the 7 does not change with the rudder. I have both, the 6-8-7short hanging in my basement, 7tall/9 on the plane.

Vans shipped free tall (aka -9) rudders for early 7 serial numbers after they did spin testing and a test pilot did not like the recovery response.

A number of the inflight failures, broke the rudder, broke the forward VS spar, and folded down the HS spar - -maybe in that order the first pieces to hit the ground were the upper section of rudder w/counterweight.

These are all facts listed in reports.

What I would like to know: How much flutter margin (if that is the real issue) changes with the rudder change on a 7? I get vertigo just reading about flutter.
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Last edited by BillL : 08-17-2022 at 06:15 PM.
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  #22  
Old 08-17-2022, 06:41 PM
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grubbat grubbat is offline
 
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Default Margins for the zipper rudder

Every design if operated within the design margin is safe. HOWEVER, some designs have narrower margins. The unzipped rudder seems to have a rather unpleasant consequence if the design is exceeded.

I removed the -7 /-9 zipper rudder from my -9 and installed a balanced -8 rudder. It was easy peasey. Probably an overkill for a non-aerobatic -9.
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  #23  
Old 08-17-2022, 06:47 PM
PhatRV PhatRV is offline
 
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Default Aftermarket RV7 Folded Rudder?

What if some people with the equipment can build the folded rudder like the RV8 but with the larger size for the RV7 and sell them? I am sure some of the RV7 owners are willing purchase a stronger design that is less prone to zipping.
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  #24  
Old 08-17-2022, 08:11 PM
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BillL BillL is offline
 
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Default

Quote:
Originally Posted by PhatRV View Post
What if some people with the equipment can build the folded rudder like the RV8 but with the larger size for the RV7 and sell them? I am sure some of the RV7 owners are willing purchase a stronger design that is less prone to zipping.
I bet some would if it was lighter (like the 8), carbon fiber, stronger/stiffer in torsion and bending. Then counterweight factor could be better. Reno/racers might want it.

Can this be done in carbon?

Edit: Why lighter and stiffer? Nice discussion of flutter.
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Last edited by BillL : 08-18-2022 at 05:57 PM.
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  #25  
Old 08-17-2022, 10:48 PM
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Roadjunkie1 Roadjunkie1 is offline
 
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Location: Erie, Colorado
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Default Fly within the design limits of the airplane...

......about the most common cause of RV-4 wings parting company with the airplane. As I remember, it was pilots newly acquiring an RV-4, not builders, that would execute a fast low pass with a zooming pull-up.

Quote:
Originally Posted by RV8JD View Post
The RV-7/7As are not coming apart in-flight because of wing failures.
My post was referencing exceeding the design limits of any airplane, but sited the cause of some -4 incidents. I did not infer that the -7 had a wing failure, just that it was a common cause of RV-4 wing failures as this discussion was referring to exceeding design limits during flight, a possible cause. At this juncture, we do not know the cause of the most recent referred to incident.
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  #26  
Old 08-17-2022, 11:04 PM
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Untainted123 Untainted123 is offline
 
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Default

Quote:
Originally Posted by grubbat View Post
Every design if operated within the design margin is safe. HOWEVER, some designs have narrower margins. The unzipped rudder seems to have a rather unpleasant consequence if the design is exceeded.
It seems like once you go past the margins and unzip the rudder, the rest of airplane or at least the tail is not far behind it.

Does any one know if it would be possible to land or fly an RV with only the rudder unzipped/departed, and the rest of the tail intact? Otherwise I would think having a “stronger” -8 rudder just moves the failure to somewhere else on the tail, and the (tragic) results are the same once you go past the point of no return.
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  #27  
Old 08-18-2022, 01:06 AM
Stewbronco Stewbronco is offline
 
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Location: Langley BC
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Default RV4 structural failure

Quote:
Originally Posted by Roadjunkie1 View Post
There was a post a while ago, possibly referring to a Kitplanes article, about the most common cause of RV-4 wings parting company with the airplane. As I remember, it was pilots newly acquiring an RV-4, not builders, that would execute a fast low pass with a zooming pull-up. Easy to overstress any airplane. The RV series is very responsive without being twitchy but even SMALL stick inputs can results in LARGE changes in attitude. Pull the stick back half an inch at cruise and see how fast you are suddenly at another altitude.

Ya'll be careful out there now.....
I would be VERY interested in that article if you can .....in all my investigations,I could only find one structural failure of an RV4 ( in Australia) and after reading the report and looking at pictures of the wreckage ,it couldn't be blamed on the design ( operating outside the design limits ) and the failure was not the wing
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  #28  
Old 08-18-2022, 05:06 AM
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plehrke plehrke is offline
 
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Default

Quote:
Originally Posted by PhatRV View Post
What if some people with the equipment can build the folded rudder like the RV8 but with the larger size for the RV7 and sell them? I am sure some of the RV7 owners are willing purchase a stronger design that is less prone to zipping.
Quote:
Originally Posted by BillL View Post
I bet some would if it was lighter (like the 8), carbon fiber, stronger/stiffer in torsion and bending. Then counterweight factor could be better. Reno/racers might want it.

Can this be done in carbon?
I don’t think adding a new untested rudders into the mix without it going through Vans engineering would satisfy my worries if I had a -7. Changing stiffness and mass will change the aeroelastic axis and with out proper engineering may actually reduce flutter margin.
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Last edited by plehrke : 08-18-2022 at 05:09 AM.
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  #29  
Old 08-18-2022, 07:23 AM
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BillL BillL is offline
 
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Default Education Please

Quote:
Originally Posted by plehrke View Post
I don’t think adding a new untested rudders into the mix without it going through Vans engineering would satisfy my worries if I had a -7. Changing stiffness and mass will change the aeroelastic axis and with out proper engineering may actually reduce flutter margin.
Could you help the flutter-ignorant engineers with some understanding please. I thought that decreasing mass, moment, and increasing stiffness of a flight control would always extend the flutter speed. Given fixed design otherwise.

I do understand the aft fuse, HS, VS structures are all involved the dynamics, and one time at low altitude I hit a burble at 130kts (straight and level) and the tail seemed to shake like a wet dog. Nothing like this has happened in 250 hrs since. It would make me happy if there was a full ground vibration test performed, but that is out of my control.

Edit: Here is a reference for the combination of lower mass, stiffer torsionally, and stiffer in bending.
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Last edited by BillL : 08-18-2022 at 05:58 PM.
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  #30  
Old 08-18-2022, 08:27 AM
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jeffw@sc47 jeffw@sc47 is offline
 
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Location: Simpsonville, SC (SC47)
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Default Thank you

What a great thread for a safety discussion regarding aerobatics in RV's.

I'm glad that VAF has not found reason (so far) to close or delete the thread for any presumption of speculative comments relating to a specific incident. Reader/Contributors - Please refrain from making that sort of comment on this thread.

I have been considering, with some apprehension, getting some instruction/introduction to some gentlemanly aerobatics in my recently completed 14A. This thread and some of the embedded links make good reading and provide much appreciated guideance.

EDIT > One question I have about aerobatics, and instruction in aerobatics is "Are parachutes required?". You can't or it isn't a recommended procedure to eject the canopy in-flight in an RV-14A, so what does a parachute do for you if they are required?
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Last edited by jeffw@sc47 : 08-18-2022 at 08:32 AM. Reason: parachute question
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