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03-13-2012, 08:17 PM
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Join Date: Sep 2006
Location: Defiance, MO
Posts: 1,674
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Quote:
Originally Posted by paul330
STRUCTURE - VANS tests the aircraft at the appropriate weight and G using a 50% safety factor. The wing must support this without permanent deformation.
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Incorrect. 50% Safety factor is to failure. Permanent deformation is allowed to occur anytime after design limit load (6 gs for the RV-6) and failure is allowed after ultimate load (1.5X design limit load or 9 gs). If you surpass 6 gs then you ought to inspect the aircraft for permanent deformation.
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Philip
RV-6A - 14+ years, 950+ hours
Based at 1H0 (Creve Coeur)
Paid dues yearly since 2007
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03-13-2012, 09:31 PM
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Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
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I stand corrected. Even more reason NOT to increase GW.........
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Paul
Mercy Air, White River FAWV
RV-10 ZU-IIZ - "Zeus"
Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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03-13-2012, 09:45 PM
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Join Date: Apr 2005
Location: KSLC
Posts: 4,021
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Quote:
Originally Posted by paul330
I stand corrected. Even more reason NOT to increase GW.........
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Not exactly. First you have to determine that the wing actually started
deformation just above 6 G's. Suppose that it went much higher than that, when actually tested.
L.Adamson
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03-13-2012, 11:03 PM
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Join Date: Oct 2009
Location: Victoria, BC, Canada
Posts: 3,932
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Quote:
Originally Posted by L.Adamson
Not exactly. First you have to determine that the wing actually started
deformation just above 6 G's. Suppose that it went much higher than that, when actually tested.
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I understand that was done at one point at Vans. On a factory-built wing, uniformly loaded under what one might deem "ideal conditions". I don't know, but I doubt they considered aileron deflection during that test. Still, it would be interesting to know how far the wing went before deformation occurred. And how far it went before destruction occurred.
Still, it's relevant to ask what *other* parts of the structure were tested to 6G and beyond... Engine mount? Tail surfaces? Anything? After all, the wing isn't always the first thing that fails under high G.
You didn't answer my earlier question either... You said that you still use the 1375 Aerobatic limit, so 6G, but what G-limit do you impose at your 1850 gross?
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Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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03-14-2012, 01:28 AM
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Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
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It's very simple. VANS tests the airframe to the quoted weight and g +50%. If you make no structural improvements and up the gross weight, you MUST be eating into the 50% margin. If your regulatory regime allows that and you are happy to do so, then go ahead - fill your boots. As a life-long professional pilot, it makes my skin crawl. Limits are limits and the 50% belongs to the designer, not the pilot........
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Paul
Mercy Air, White River FAWV
RV-10 ZU-IIZ - "Zeus"
Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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03-14-2012, 01:33 AM
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Join Date: Dec 2005
Posts: 976
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The "wing", and the scientific  testing assessment ' Those 6 wings, the ones that attach in the middle. Amazingly strong!' is not where I would direct my concerns... As stated much earlier, this apsect is relatively easy to mitigate:
RV-6A W&B
Aerobatic Gross Weight............................1375 lbs [6g]
leads to an equivalent at 4.4g (Utility) of 1875lbs.
It is other areas that are less certain, brakes / landing gear. Of course, RV-6 engine mount cracks have never been heard of 
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03-14-2012, 09:10 AM
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Join Date: Mar 2007
Location: McKinney, TX
Posts: 1,261
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Another thought
I had another thought which is something big jets have. It is obvious builders increasing the gross weight over what Van's has published is a fact of life. So make the increase for takeoff only, with the limitation that landing weight will be the gross weight Van's has established. There might be an emergency which would require landing above this weight, in this case a mandatory inspection of the appropriate parts of the airplane would be required (gear, spars skin etc). This seems like a way to mitigate some of the safety concerns.
You can make the same requirement for exceeding certain "G" limits, lets call it 3 Gs. If one encounters this above the Van's gross weight then down the plane until inspection in completed. In the fighter world over Gs would happen, depending on how severe it would require different levels of inspection. I will say that in the military world, G limits have more to do with the fatigue life of the airframe than what the wing can handle.
More fuel for the discussion, but I had not seen this proposed, seems to me it might settle some concerns. This is kind of along the lines of what George mentioned.
Cheers
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Mike "Nemo" Elliott
RV-8A (First Flight 12-12-12!)
KOCF
N800ME
www.mykitlog.com/rvg8tor
Dues Paid 2019
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03-14-2012, 09:30 AM
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Join Date: Apr 2005
Location: KSLC
Posts: 4,021
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Quote:
Originally Posted by RVG8tor
I had another thought which is something big jets have. It is obvious builders increasing the gross weight over what Van's has published is a fact of life. So make the increase for takeoff only, with the limitation that landing weight will be the gross weight Van's has established. There might be an emergency which would require landing above this weight, in this case a mandatory inspection of the appropriate parts of the airplane would be required (gear, spars skin etc). This seems like a way to mitigate some of the safety concerns.
You can make the same requirement for exceeding certain "G" limits, lets call it 3 Gs. If one encounters this above the Van's gross weight then down the plane until inspection in completed. In the fighter world over Gs would happen, depending on how severe it would require different levels of inspection. I will say that in the military world, G limits have more to do with the fatigue life of the airframe than what the wing can handle.
More fuel for the discussion, but I had not seen this proposed, seems to me it might settle some concerns. This is kind of along the lines of what George mentioned.
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Certainly, for a 200 lb. increase, that would be overkill, considering so many airplanes over so many years have not had a problem. As I was googleing some info yesterday, this thread popped up. Actually, it wasn't this thread. It was one from two years ago.............that looks and reads almost identical. Like I said...........about every two years... 
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03-14-2012, 03:36 PM
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Join Date: Mar 2007
Location: McKinney, TX
Posts: 1,261
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That is OK
Quote:
Originally Posted by L.Adamson
Certainly, for a 200 lb. increase, that would be overkill, considering so many airplanes over so many years have not had a problem. As I was googleing some info yesterday, this thread popped up. Actually, it wasn't this thread. It was one from two years ago.............that looks and reads almost identical. Like I said...........about every two years... 
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Every two years sounds good to me to address any good subject on this forum, after all there are new builders who don't know what they don't know and might not think to search on a subject. As it cycles through more get involved in the debate and new builders will have something to ponder or avoid, and more information might come to light.
Looking forward to the debate in two years
Cheers
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Mike "Nemo" Elliott
RV-8A (First Flight 12-12-12!)
KOCF
N800ME
www.mykitlog.com/rvg8tor
Dues Paid 2019
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03-28-2015, 09:34 AM
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Join Date: Jun 2011
Location: Nashua, NH
Posts: 536
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Its been over two years...
Time to stir the pot. I submitted my paperwork to the FAA for the certification process. In it, I set the gross weight at 1,700 pounds(a 200# increase from manual). The FAA actually called Vans to talk to them about it. Vans essentially said that "a lot of people have done it" with no problems at all, and that the airplane will easily handle it. Mention was also made that the reason they have not increased the gross weight is because they would have to reopen the testing process on a plane they don't sell many of.
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Mike
RV-4 #2750
N654ML
IO-360
WW150C Prop
1018 lbs
Flying
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