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  #71  
Old 01-04-2014, 05:17 AM
Tony Spicer Tony Spicer is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
It is not possible to mold a poly tank with flow control baffling inside to keep fuel at the outlet in all attitudes (kind of important).
Even if it could be done, it would be very expensive at the production volume that would be needed for the RV-12.
The Sonex has been flying since 1998 with a 16 gal rotationally molded poly tank.
No internal baffles, and no issues with the pickup unporting. The tank has been thru some really nasty crashes without breaching. Get a quote on tooling and I think you'll be surprised. Downside is it's not as light as an aluminum tank.

Tony
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  #72  
Old 01-04-2014, 08:00 AM
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DonFromTX DonFromTX is offline
 
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I have no knowledge of how poly tanks are made, but one must ask just how Sonex does it? They seem to have had no problems with their tanks or baffling (or lack of baffling), and the cost for one is only $325.

Quote:
Originally Posted by rvbuilder2002 View Post
It is not possible to mold a poly tank with flow control baffling inside to keep fuel at the outlet in all attitudes (kind of important).
Even if it could be done, it would be very expensive at the production volume that would be needed for the RV-12.

BTW, those prosealed corners you are concerned about having been flying on every model of RV since the RV-4 was introduced over 30 years ago.
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Last edited by DonFromTX : 01-04-2014 at 08:05 AM.
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  #73  
Old 01-04-2014, 08:16 AM
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Bill_H Bill_H is offline
 
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Can't plastic like that be ultrasonically welded? Spin or blow a tank with no internals, cut it in half (probably with the cut parallel to the floor), put in baffles, and weld it back together? (Hmmm... That might add something expensive to the tool list...)

Or, this sounds like an ideal app for 3D printing. Besides the baffles, you could even print the inside fuel return line.

I am happy with the RV12 Useful load. I can load 2 big guys, full fuel, and baggage, no problem. But an extra 5 gallons would be nice. But it would be important to not cover the baggage compartment floor plates any more than they currently are covered. And the tank is pretty "tight" getting it in and out as it is...
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  #74  
Old 01-04-2014, 09:16 AM
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TomVal TomVal is offline
 
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What would you recommend?

1) Purchase a new tank with all of the mods installed.

2) Install the current SB plus the Moeller gage and the fuel tank vent mod and do this all through the fuel sender opening.

3) Do #2 above but remove the tank top to perform the mods.

My preference is #1 but I am not sure if this option is available. When I talked to Van's technical support last week, they said that over the years, not many builders opted to purchase the completed tank option and was not sure if that option was still available.
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Last edited by TomVal : 01-04-2014 at 10:32 PM.
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  #75  
Old 01-04-2014, 09:48 AM
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bhassel bhassel is offline
 
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I just bought a prebuilt tank this year (before the SB's)...

Bob
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  #76  
Old 01-04-2014, 10:34 AM
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TomVal TomVal is offline
 
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Originally Posted by bhassel View Post
I just bought a prebuilt tank this year (before the SB's)...

Bob
Thanks Bob. The person I spoke with in technical support was going to check if Van's was going to re-introduce the pre-built tank option. It sounds like they may have recently discontinued that option due to low demand. I was asked to check back with them in about a week for an update.
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Last edited by TomVal : 01-04-2014 at 10:39 AM.
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  #77  
Old 01-04-2014, 11:01 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Tony Spicer View Post
The Sonex has been flying since 1998 with a 16 gal rotationally molded poly tank.
No internal baffles, and no issues with the pickup unporting. The tank has been thru some really nasty crashes without breaching. Get a quote on tooling and I think you'll be surprised. Downside is it's not as light as an aluminum tank.

Tony
This looks like a tank intended to mount up high?...... fwd of the instrument panel?
Regardless of the material it is made of, a more fwd mounting location would not be a better choice than the current location. But, if a high mounting location is used, it does allow for a bottom shape that will keep fuel present at the outlet regardless of aircraft attitude (does away with the need for internal baffling). In the RV-12, doing that would eat up even more of the baggage space and some of the vocal owners say that is already not large enough.

BTW, a rotary molded tank is not the holy grail some think it is. If you do a little research you will find that some kit manufacturers that have used them have suffered through problems.
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  #78  
Old 01-04-2014, 08:11 PM
RFSchaller RFSchaller is offline
 
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Seems like Vans is married to the current design. I guess if they keep telling us how great it is we will eventually believe it. Obviously us telling them it has shortcomings is not having that effect on them.
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  #79  
Old 01-04-2014, 09:38 PM
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Bill_H Bill_H is offline
 
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~800 kits sold is powerful that they got it "pretty right." It is just some clever engineering and a few parts that make the wings easily removable - it is not adding much weight and it is a feature that you don't have to use if you don't want to. But is really convenient in certain conditions - like painting in pieces.

Regarding the tank connection via the frangible bolt. OK, the bolt is really loaded in shear for vertical forces. Has to support a full tank when pulling +/-Gs. And the design and rotation issue is that we really want the bolt to fail early in a tension load. Well - wouldn't it have been better to have that support "sit on top" of the member it is currently bolted through? Like your hand when you are doing a pull-up? (Properly constrained for negative Gs.) Engineered in such a way as to not tear the tank open if the member rotates? Or what if the currently-frangible bolt did not go into a nutplate on the tank but just into a bushing? With some spacers to prevent the tank from moving forward (it is also bolted at the rear) the bolt would not even need to be frangible. It becomes a Pin. Or it could be an aluminum rod rather than a bolt, one that could bend but would still have the needed shear strength.

Oh well, too late now.
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  #80  
Old 01-04-2014, 10:26 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Bill_H View Post

Regarding the tank connection via the frangible bolt. OK, the bolt is really loaded in shear for vertical forces. Has to support a full tank when pulling +/-Gs. And the design and rotation issue is that we really want the bolt to fail early in a tension load. Well - wouldn't it have been better to have that support "sit on top" of the member it is currently bolted through? Like your hand when you are doing a pull-up? (Properly constrained for negative Gs.) Engineered in such a way as to not tear the tank open if the member rotates? Or what if the currently-frangible bolt did not go into a nutplate on the tank but just into a bushing? With some spacers to prevent the tank from moving forward (it is also bolted at the rear) the bolt would not even need to be frangible. It becomes a Pin. Or it could be an aluminum rod rather than a bolt, one that could bend but would still have the needed shear strength.
All valid ideas Bill, and every single one of them was considered and kicked around, with the current design being the end result after considering all of the different design requirements... many of which are spelled out in the portion of the ASTM's that specify the design requirements for the fuel tank(s)
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