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  #41  
Old 04-07-2013, 10:23 PM
6 Gun 6 Gun is offline
 
Join Date: Jun 2005
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Talking screws

Rob ill be waiting for numbers on 10 #8 screws so I can figure out load seven can carry I bet its seven times more than none. Im sure very few Rv's are built with no changes from plans planed or not.If one crashes its a mechanical problem (The Nut Holding the Stick) this has been a good thread hope we can all learn from it.
Bob
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  #42  
Old 04-11-2013, 12:42 AM
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Snowflake Snowflake is offline
 
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I've run a bunch of calculations on the RV-6 wing structure, which I have decided *not* to publish. As a P.Eng I do have liability to be concerned with. I will say that the limiting factor on loads on the structure is definitely not the spar or wing structure... To say that the spar on the RV-6 is overbuilt is a bit of an understatement... I'll leave it at that.

However, there may be other factors. I looked closely at the wing-fuselage interface and wing and spar construction, but didn't look further into the fuselage structure or loading to see what may be going on in the fuselage. Maybe the limiting factor is the fuselage, and the load of the pilot pushing on the seat pan... It would be interesting to mount a GoPro on the underside of the wing, looking at that overlap, and go do a loop... To see if the gap opens slightly. Or maybe some things you don't want to know.

I'm not going to pursue any further analysis right now... For many reasons. One, my -6 is 17 years old and shows no ill effects. Two, I talked to someone who had to remove the wings from his -6 for a repair, and it soudns like it really wouldn't be that hard to retrofit as per plans: pull the bolts from one wing at a time, separate the wing far enough to gain access, and then install the hardware as specified on the plans. A little more work than putting round-head screws in without removing the wings, but I hate the idea of using round-head screws... I'd rather pull the wings off than add drag.

The third reason is, regardless of any analysis I could do, even if I proved beyond any shadow of a doubt that the screws aren't needed, if I ever wanted to sell the plane, *not* having the screws would likely prove detrimental to my resale value.

So the TL;dr is, it's not that hard to retrofit, and sounds like it might be a fun experience (yeah, my definition of "fun" may be suspect... But I did just spend two nights poring over plans and running calculations for "fun" too... .
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1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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  #43  
Old 04-11-2013, 05:22 AM
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JanRV6UK JanRV6UK is offline
 
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Very interesting result... I will make sure my screws are in place when I get to that stage. Hopefully by the end of the year.
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  #44  
Old 04-17-2013, 05:16 AM
WingsOnWheels WingsOnWheels is offline
 
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For the OP: I would get in writing from Vans that the screws are required (if that is their determination) and use that letter as a negotiation point with the seller. If the rest of the aircraft passes inspection, I wouldn't let the screws turn you off completely.

On a -6 (conventional gear), it is really not that hard to unbolt the spars and pull the wing out far enough to install the screws. There is also the option of using click-bond nutplates and a screw dimpler to install the screws without removing the wing. It would be a challenge, but not impossible.

You can see the the gap between the fuselage and wing is very narrow on the -6. Not much room to work in. Probably be better to just pull the wing out a foot and support it with a sawhorse.

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  #45  
Old 04-18-2013, 12:48 PM
WingsOnWheels WingsOnWheels is offline
 
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Quote:
Originally Posted by rvmike View Post
I don't get it. They are in the plans, Vans said they have to be there. Would you buy a car with only one lug nut on each wheel. As someone else said (what else was left out?) What are you people arguing about??

Time for another beer
Mike
I think part of the confusion is that different people have received different answers from Vans. Apparently one helpline tech said they are not structual. However, if Ken says they are required, then they are 100% in my book.
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  #46  
Old 04-18-2013, 06:27 PM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by rvmike View Post
I understand the Vans conflicting answers, but they are still on the PLANS. Done with this issue
Many things are on the plans that aren't structural.

The reason this generates so much discussion is that from an engineering perspective, it just doesn't jive. You've got an .032" lower wing skin, that suddenly joins to an .025" lower fuselage skin. That's a *reduction* in cross-sectional area, when heading down the wing toward the center of the airplane. Usually, you *increase* cross sections heading inboard... Look at the spar for example. So if there is load being carried inboard by that skin, all of a sudden it's getting dumped into a smaller structure, which means a stress concentration. That's an unusual choice, from an engineering perspective.

On the other hand, this overlap looks a *lot* like a wing root fairing. The location is ideal... It's the section that's beyond an arm's reach from the leading edge from the front, and hidden behind the flap from the rear. And it aligns perfectly with a continuous piece of fuselage belly skin. With the belly skin extended a few inches, you have a fairing that only needs to be installed once... Subsequent inspections can be done by removing just the top fairing, on which you can reach all of the screws without laying on your back dropping screws all over yourself. That's an excellent design choice, from an engineering perspective.

Again: Not saying they are or are not structural. But it's not 100% clear why they're needed, when people have reported here and elsewhere that the -6 wing structure was tested to its limits at the factory without them.
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1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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  #47  
Old 04-18-2013, 07:13 PM
6 Gun 6 Gun is offline
 
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Smile Exp aircraft

Ok I have to tell the truth I thought I was building an Exp. Aircraft its not the only thing I didnt change I called Vans and ask about the brake line running across the firewall and ask why not use a little extra plastic hose inside and put bulkhead on each side I was told because thats the way its always been done I didnt want my fluid getting hot from exhaust so i have a bulkhead on each side and I think its an improvement.I wanted to build my own F.I. booster pump I posted for advice not one reply but I couldnt not do it so I have a nice booster pump for $250 .Its not in the plans but when I built windshield fairing ran two bids of carbon fiber over roll bar.Not in the plans but that 200hp angle valve looks good up front with its 74" BA.Not in the plans but I moved my stops for aileron to outboard bracket and used #3 bolts as stops. Not even going to talk about about all the speed mods but I love my Exp. RV-6.Good thing Van didnt stop at the 3!
Bob
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  #48  
Old 04-18-2013, 07:45 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Snowflake View Post
The reason this generates so much discussion is that from an engineering perspective, it just doesn't jive. You've got an .032" lower wing skin, that suddenly joins to an .025" lower fuselage skin.
I am pretty sure that the belly skins on all the 2 seat RV's is .032.
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  #49  
Old 04-19-2013, 07:55 PM
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Mel Mel is offline
 
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This thread has gone off the deep end. No ONE structural component carries all the load. Loads are distributed among many components. If you want to fly your RV-6 without these screws, that's your right.
Just don't call on me to sign off your inspection.
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<rvmel(at)icloud.com>
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  #50  
Old 04-19-2013, 09:15 PM
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Snowflake Snowflake is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
I am pretty sure that the belly skins on all the 2 seat RV's is .032.
According to my plans (I haven't measured the skins that are on the airplane), sheet 36, the fuselage belly skins F-676 and F677 are .025" 2024-T3.
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1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
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