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  #51  
Old 02-20-2017, 02:43 PM
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airguy airguy is offline
 
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Quote:
Originally Posted by RV8JD View Post
Based on the 217kt number in the report, it appears that Van's did flight test the RV-7A to approximately Vd. I wonder which rudder (-8 or -9/-7) was installed during the flight test.
The report said it was done on the 7A Prototype, so it would be the earliest rudder version shipped with the 7/7A kits. I don't have personal knowledge of that, do you know which rudder was on the early kits?
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  #52  
Old 02-20-2017, 03:39 PM
Robert Anglin Robert Anglin is offline
 
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Default Carl and Greg.

It has been a long time now and we did not fallow the 7 as close as we did the 8, so you would have to check with Van's for a good answer. Best I can remember the 7 had the 8 tail to begin with. It was when they got to spin recovery that they did not quite like the recovery and wanted to get a little better response. So the 9 ruder was put on and the fallowing testing show a better result. I think that is how we got the bigger surface area ruder to be implemented for the 7. I really don't know for sure, but they had a contract test pilot doing the testing at the time if I remember correctly so there may be test results from that refit and I just don't know about it. I most often find that Van's try's to get to certified standards with their prototype testing so they have a record of it on the books. You mite E-mail Scott Ryson and ask.
Yours, R.E.A. III #80888
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  #53  
Old 02-20-2017, 07:04 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by RV8JD View Post
I feel sure "rvbuilder2002" (Scott M.) is following this thread and was hoping he might add some facts to the discussion. But I understand that he might feel he would be getting into a hornet's nest, and given the accidents that have occurred, may not want to comment for legal reasons.
And you might be right......

I will say that it is incorrect to assume that all testing (old rudder, new rudder, or otherwise....) done by Van's was only done with N137RV.
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  #54  
Old 02-21-2017, 08:07 AM
Mudfly Mudfly is offline
 
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Quote:
Originally Posted by RV8JD View Post
Thanks for this link. It verifies (for me) that the current -7 rudder is identical to the -9 rudder.
Quote:
Which I believe I remember reading somewhere is also the same as the 14 rudder.
UPDATE:Correction..It was brought to my attention the -14 and -9 rudders are not the same. Sorry. My Mistake. I read that from one of the -14 builders blogs and did not have correct information.

BTW RV8JD, and others, thanks for all the info in this thread. While I'm completely satisfied and comfortable with Vans designs (when operated within their limits), it's nice to hear some of the "behind the scene" physics that make up these limitations. Like most probably, I've been flying airplanes for many years, but didn't know some of this information. Very interesting.
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Last edited by Mudfly : 02-21-2017 at 12:53 PM.
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  #55  
Old 02-21-2017, 08:46 AM
BillL BillL is offline
 
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Location: Central IL
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Quote:
Originally Posted by Mudfly View Post
Which I believe I remember reading somewhere is also the same as the 14 rudder.

BTW RV8JD, and others, thanks for all the info in this thread. While I'm completely satisfied and comfortable with Vans designs (when operated within their limits), it's nice to hear some of the "behind the scene" physics that make up these limitations. Like most probably, I've been flying airplanes for many years, but didn't know some of this information. Very interesting.
Absolutely not. Your 14 rudder has the stiffeners attached to each other like ribs. The 6-8-9 rudders have free floating stiffeners. Look close at the post above to see that.

"Jackie Stewart and Graham Hill would walk through the paddock after the F1 races and the drivers (who lost) would say - if I had one more lap, if i had 3 more liters of fuel I would have won, I am the best . J & G, joked sure, and we could have strawberries and cream, if we had some strawberries . . . . . . and some cream. "
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Last edited by BillL : 02-21-2017 at 11:36 AM.
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  #56  
Old 02-21-2017, 06:15 PM
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DanH DanH is offline
 
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I'm going to link two old posts, since we have lots of readers who fly things other than RVs. High speed is not necessarily required to find flutter.

http://www.vansairforce.com/communit...9&postcount=40

http://www.vansairforce.com/communit...8&postcount=18
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  #57  
Old 11-13-2017, 12:45 PM
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grubbat grubbat is offline
 
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Default -7 vs -8 Rudder

Finally got around to building a -8 folded edge rudder and put it on the static balance table (just for information purposes) only to find that the weight supplied in the kit doesn't come close to keeping the rudder neutral. It was tail heavy. I took the -8 rudder off the table and put the -7 zipper edge rudder on the balance table and it was even more tail heavy than the -8. I certainly wasn't expecting that. In addition, the -7 zipper edge rudder could be flexed enough to cause the skin to oil can. The -8 folded edge rudder was stiffer and oil canning wasn't noticed.

Decades ago I used to balance the control surfaces of commercial jets after they were worked on or after they came out of paint shop. Out of balanced meant they were sent back to have have some paint removed or the repair repaired.

Interesting note is that balancing the rudder isn't a requirement per the plans, just use the weight that is supplied. I'm guessing that attempting to static balanced the rudder to a neutral setting may open up another can of worms such as reinforcing the rib holding the lead and so forth. All things being equal, the -8 rudder looks like a more robust design. I guess if I were rebuilding a -6 or a -7 rudder, I would probably go with the -8 rudder.
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  #58  
Old 11-14-2017, 08:20 AM
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airguy airguy is offline
 
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Are you going to paint before first flight? If so, that will change the balance point, I would wait until paint to balance the control surfaces. If you balance them carefully prior to paint, then you'll add weight aft of the hinge point during paint and end up needing to add a little counter weight back. I flew mine for 160 hours prior to paint and had to use a little double-sided sticky tape and lead sheet to rebalance.
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Greg Niehues - PPSEL, IFR, Repairman Cert.
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N16GN flying 500 hrs and counting! Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
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  #59  
Old 11-14-2017, 09:39 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by grubbat View Post
Finally got around to building a -8 folded edge rudder and put it on the static balance table (just for information purposes) only to find that the weight supplied in the kit doesn't come close to keeping the rudder neutral. It was tail heavy. I took the -8 rudder off the table and put the -7 zipper edge rudder on the balance table and it was even more tail heavy than the -8. I certainly wasn't expecting that. In addition, the -7 zipper edge rudder could be flexed enough to cause the skin to oil can. The -8 folded edge rudder was stiffer and oil canning wasn't noticed.
Normal, typical on both counts, lots of previous discussion in the archives. The rudder is not 100% static balanced.
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  #60  
Old 02-23-2018, 05:56 PM
Wiley Wiley is offline
 
Join Date: Jul 2005
Location: Brownwood TX
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Default recent KitPlanes article

I just read the kitplanes article on the supercharged RV8. It is obviously a very well built example, built from a quickbuild kit without other deviations, according to the article. It was reported going 272 mph during one portion of the race.

I have always densely adhered to the Vne in terms of TAS per the Van's article. The previous discussions and the article, given the elevation at Reno, make me feel I am leaving something on the table in elevations up to 8-10000 feet.

I am not an engineer, so I will not try to convince myself I understand better than the next guy that I can exceed the recommendations. I will continue flying the way I do, but, makes you think.........
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