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  #11  
Old 11-17-2014, 07:06 PM
moll780 moll780 is offline
 
Join Date: Aug 2011
Location: Austin TX
Posts: 347
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those sure are cool looking!
but yeah.. my range is not determined by the plane... but by my bladder.

Quote:
Originally Posted by LifeofReiley View Post
Do the tanks act as Lavatory Storage too? Or you'll need a case of Little Johnnys. Doing the basic math, 4 hours @ 3.5 GPH= 14 Gallons. Pretty good fuel burn.
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  #12  
Old 11-17-2014, 07:16 PM
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rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
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Quote:
Originally Posted by anandaleon View Post
\

- The tanks actually give 4 more hours of flight at 145 Kts.
Unless you've reduced the drag by some huge amount, going 145 knots on 3.5 GPH in an RV9A doesn't compute...
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  #13  
Old 11-17-2014, 07:53 PM
anandaleon anandaleon is offline
 
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Location: Oviedo, FL
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my bad! its 14 gallons per tank... total is 28 gallons...
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  #14  
Old 11-17-2014, 08:45 PM
PCHunt PCHunt is offline
 
Join Date: Feb 2007
Location: San Diego, CA
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I'm not an engineer, and I didn't sleep at any motel chain last night. But I would be concerned about that much weight at the tip of the wing. 84 lbs on each wing, plus the weight of the mod wing tip. Is the Van's spar and wing assembly strong enough for that, say in turbulence? Will there be a twisting load in turbulence? And what about a firm landing with full or nearly full wing tip tanks?

Gee, that all sounds so negative, and I actually like the idea of the experiment!!
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  #15  
Old 11-17-2014, 09:17 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,791
Default This is experimental aviation after all...

Quote:
Originally Posted by PCHunt View Post
I'm not an engineer, and I didn't sleep at any motel chain last night. But I would be concerned about that much weight at the tip of the wing. 84 lbs on each wing, plus the weight of the mod wing tip. Is the Van's spar and wing assembly strong enough for that, say in turbulence? Will there be a twisting load in turbulence? And what about a firm landing with full or nearly full wing tip tanks?

Gee, that all sounds so negative, and I actually like the idea of the experiment!!
But there are even more potential issues that where hopefully considered and now need to be tested.

The polar moment of inertia of the fuel weight and heavier tanks at the wing tips, and its effect on yaw stability, spin recovery, etc.
The RV-9 was extensively spin tested. This type of mod. effectively throws all of that test data out the window.
I know tip tanks have been installed on RV's in the past, but with the longer wing span of the RV-9, it makes the inertia factor that much bigger.
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  #16  
Old 11-17-2014, 10:22 PM
rockwoodrv9 rockwoodrv9 is offline
 
Join Date: Dec 2011
Location: Meridian ID, Aspen CO, Okemos MI
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Quote:
Originally Posted by rvbuilder2002 View Post

The RV-9 was extensively spin tested. This type of mod. effectively throws all of that test data out the window.
I know tip tanks have been installed on RV's in the past, but with the longer wing span of the RV-9, it makes the inertia factor that much bigger.

I would love to know more info on the spin testing for the 9. If the spin testing info is available, is there a link to the info?

Thanks
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  #17  
Old 11-17-2014, 10:25 PM
Jrskygod Jrskygod is offline
 
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Location: Edinburg, TX
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RVbuilder if the 9 was extensively spin tested why are we plackarding them for no spins
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  #18  
Old 11-18-2014, 05:11 AM
g zero g zero is offline
 
Join Date: Jun 2007
Location: palm coast fl.
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Quote:
Originally Posted by Jrskygod View Post
RVbuilder if the 9 was extensively spin tested why are we plackarding them for no spins
They were spin tested , maybe the test did not end well .
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  #19  
Old 11-18-2014, 05:22 AM
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pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,922
Default Have them engineered.

Nice work guys, buuuut.....

I fly Air Tractors in my spraying business and our wings have a 5,000hr. spar life, then the lower spar cap (steel) has to be replaced by the factory.

There is a winglet manufacturer that makes and advertises them in our trade publications, to create less vortices and so on.

Air Tractor sent out fliers and in magazine articles, that the winglets reduce our spar life by 40% !! ...and we only fly at 140 MPH. Granted, these winglets are quite a bit taller than yours and would then create a stronger twisting force.

At near 200 MPH, the twisting force at the wingtip, where the spar is thinnest, concerns me, sans aeronautical engineering consultants.

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  #20  
Old 11-18-2014, 07:18 AM
gtmule gtmule is offline
 
Join Date: Oct 2007
Location: Macon, GA
Posts: 507
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The wing structural load would be highest with EMPTY tip tanks and FULL seats in a high G maneuver.

Any positive effect on lift happens at the outboard end of the wing, so ignoring all the twisting, you have to realize that at the same G-load as before, the bending moment on the root of the spar might be quite a bit higher.

The only time the added fuel weight is a bad thing is on landing, but my guess is that that won't be as much of an issue as the added moment with empty tips and high G's.

Did you do a fatigue analysis of your spar mod to make sure it doesn't cause more problems than it solves?

Of course the twisting (there isn't much to an RV rear spar, afterall) and dynamics (polar moment, etc) are different issues entirely that deserve to be addressed as well.
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