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  #21  
Old 09-20-2019, 06:25 AM
Gyrodoug Gyrodoug is offline
 
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Default 1650 vs 1800

My naive question is: As the 2nd owner of the RV6A, can we adjust the builders gross weight of 1650lbs up to 1800 lbs? One response above was, "Phase 1 Flight test". Is that sound accurate to the rest of you?
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  #22  
Old 09-20-2019, 09:38 AM
SPX SPX is offline
 
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Quote:
Originally Posted by Gyrodoug View Post
My naive question is: As the 2nd owner of the RV6A, can we adjust the builders gross weight of 1650lbs up to 1800 lbs? One response above was, "Phase 1 Flight test". Is that sound accurate to the rest of you?
If we agree that a gross weight change is a major modification, your operating limitations will dictate how to proceed. Most likely, yes, you will need to enter Phase I for some period of time; Generally five hours.

Keep in mind, Vans does make the gross weight of the airplane as high as possible, given their engineering data (or regulations, if we are talking about a LSA). Therefore, I view a gross weight change as more than just paperwork and flying the airplane around in Phase I again.. there would be some engineering involved.
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  #23  
Old 09-20-2019, 10:19 AM
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DeeCee 57 DeeCee 57 is offline
 
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Quote:
Vans does make the gross weight of the airplane as high as possible, given their engineering data
Yes, but at the times the -6 was designed, Vans was basically a one man show and the -3/-4/-6 were calculated with larger margins than the -7 and following models are.
Considering the number of sixes flying (and those still getting finalized), Vans could consider reverse engineering the aircraft and hopefully get a higher MTOM...
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  #24  
Old 09-20-2019, 06:37 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DeeCee 57 View Post
Yes, but at the times the -6 was designed, Vans was basically a one man show and the -3/-4/-6 were calculated with larger margins than the -7 and following models are.
This is not true.
The same engineering was used for each.

If you have some specific info or documentation you can point to that indicates otherwise, I would appreciate knowing wher to look for it.
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  #25  
Old 09-20-2019, 07:08 PM
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titanhank titanhank is offline
 
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Directly from vans. The -6 wing is the strongest of the bunch and failed well over 9 G’s during testing. The rumor i have heard from reliable folks it was approximately 11 G’s. Another 100lbs of gross weight is not going to cause a failure.

The -8 wing failed at 9 G’s.

I raised my gross weight to 1750lbs. Called the local fsdo and they said to enter phase 1, test at that weight and make a logbook entry.

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Last edited by titanhank : 09-20-2019 at 07:15 PM.
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  #26  
Old 09-20-2019, 08:03 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by titanhank View Post
Directly from vans. The -6 wing is the strongest of the bunch and failed well over 9 G’s during testing. The rumor i have heard from reliable folks it was approximately 11 G’s. Another 100lbs of gross weight is not going to cause a failure.

The -8 wing failed at 9 G’s.

I raised my gross weight to 1750lbs. Called the local fsdo and they said to enter phase 1, test at that weight and make a logbook entry.

The wing is not the only structural element of the airplane that is effected by all up load.
If the statement you quoted was meant to imply that because of the overall wing strength the RV-6 gross weight could be increased, the official published gross weight would have been updated long ago.

Additionally, if you re read the document you attached, you might notice that the RV-8 wing did not fail at 9 G's


BTW I was present for the RV-6 (and the RV-8) wing tests..... I don't agree with the rumors.
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Last edited by rvbuilder2002 : 09-20-2019 at 08:18 PM.
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  #27  
Old 09-21-2019, 04:24 AM
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plehrke plehrke is offline
 
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Default Exceeding Vans design max gross weight

I am amazed at the number of people who appear to question the engineers that have much more data. Lots of rationalizing why they can and antidotes of good performance at higher weight. Is there a cliff, no. Is there higher risk, absolutely. As an aeronautical structural design engineer, I know all the unknowns that go into aircraft strength analysis. The safety factors and margins are there for a reason.
Just one thing to ponder, to exceed Vans published designed to gross weights maximums you most likely need to be carrying a passenger. You may be willing to take the risk. Are they?
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Last edited by plehrke : 09-21-2019 at 05:02 AM.
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  #28  
Old 09-21-2019, 09:16 AM
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titanhank titanhank is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
The wing is not the only structural element of the airplane that is effected by all up load.
If the statement you quoted was meant to imply that because of the overall wing strength the RV-6 gross weight could be increased, the official published gross weight would have been updated long ago.

Additionally, if you re read the document you attached, you might notice that the RV-8 wing did not fail at 9 G's


BTW I was present for the RV-6 (and the RV-8) wing tests..... I don't agree with the rumors.
The -6 wing failed at well above -9g and the -8 wing failed at 9g according to the released document until it was redesigned.

Vans upped the gross weight by 50lbs when they installed the nose wheel. Do you think they were concerned about the all up gross weight increase effects on anything else? I doubt they did a complete structural analysis for a 50lb increase. History has proven the -a model gear is weaker than the tailwheel airplanes, yet they get the gross weight increase.

The wing area is less on the -6, 110 sqft and at 1750lbs, the wing loading is 15.9lbs/ft. The -7 is 14.8 and the -8 is 15.5. The wing loading is virtually identical until you over gross the -6 and then it falls in line with other vans designs using the exact same airfoil and design techniques.

Vans designed the -7 as a -6 replacement, per their website, why would they go to any trouble to better the capabilities of the -6 and take sales away from the new models.

To my understanding, the -6 and -7 share the same gear legs, same engine mount design, same longeron design, same skin thickness and virtually every part is the same materials and design but optimized for the newer construction techniques. My airplane has .020” tail feathers.

The -6 was designed from the start to be a 150-160hp, 0320, fixed pitch, lightweight airplane and the -7 was designed to be a 180-200hp, 0360, constant speed prop airplane. The power loading, wing loading and performance charts suggest the gross weight was limited to give the desired performance as the limiting factor with the smaller engines and was never revisited after the -7 was introduced. Why would they?

Scott, i know you were there the day the test were conducted. The literature has your name on it. I respectfully ask from someone who was in the room, that flies an rv6 and has more vans knowledge than any of us could hope for, where is the weak link for a 100lb gross weight increase? Thousands of rv6 doing two up aerobatics and exceeding vne with engines that vans could never have dreamed of has proven the airframe as strong as any of the others in all respects.

Help us understand the dangers and stop repeating the same line over and over. Thousands of flying airplanes have proved this line of thinking wrong. Show us were the -6 is deficient and i was yell in from the mountain tops. My -6 has a 320 putting out 180+hp and constant speed prop. It flies, at 1750lbs, very similar to an -7 or -8 at the same weight except with a slightly higher sink rate power off.

The one caution i will make, DO NOT under any circumstances exceed the published aft cg limit of a vans airplane. This is one area, from testing, that i have found should have probably been a little more conservative. The airplane becomes very difficult as you pass the aft cg limit. Just because you can haul it with your new higher gross weight, does not make it safe if you can not keep the cg within range.

I am ready to learn.
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Last edited by titanhank : 09-21-2019 at 09:29 AM.
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  #29  
Old 09-21-2019, 03:39 PM
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DeeCee 57 DeeCee 57 is offline
 
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titanhawk +1

Scott, no disrespect here...
Quote:
specific info or documentation you can point to that indicates otherwise
... and no hard facts, but a couple of comments:
Flew a demo flight outta Fond-du-Lac with Dick (Van's) himself in 1987 or 88 in Old Blue. Next year with the -4 proto outta KOSH. Then went to visit Old Plains barn en route to AK in May 96, still of last century. Also avidly read all the RVator (good all times, before face to book bs times), and what I saw was slipstick calculations done for the early RVs. Later in history Van hired additional engineers in, CAD and pre-punching came along and got the ball of to easy build and increased business rolling. And computerised calculations as well.
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  #30  
Old 09-22-2019, 12:43 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Threads like this never go anywhere good, regardless of what I say so I’m choosing to say very little.

The info that should be considered would require much more than a few lines of text in a forum post.

Rather than it turning in to a long running debate, I re-raise the question that I already posted.

If everyone is right, and the RV-6(A) is rated extremely conservative regarding gross weight, why do you think Van’s hasn’t raised the official published gross weight after doing the tests that have been quoted?
This is a question anyone considering a higher gross weight should ask them self.

I actually know why.
All of the info regarding wing testing and the ultimate strength was published by someone working in a marketing / publicist capacity, with the purpose of it being to promote positive aspects of the RV-6.
All of the official performance #’s and specifications are owned and controlled by the engineering dept. It is there, that the decision to raise the gross weight after doing the wing test would have had to happen.
Obviously the decision was not to do so.

Something that people should keep in mind....
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