VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > Model Specific > RV-12/RV-12iS
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 06-30-2014, 08:35 PM
Bill_H's Avatar
Bill_H Bill_H is offline
 
Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,793
Default RV-12 alternate fuel system

Well, in my mail today I found something interesting. And if you search on the net you can find information, including video and pics, of a full replacement tank system for the 12. Two tubular tanks are placed in each wing (9 feet long) and plumbed together as one single tank. They seem to be supported by the lightening holes with a polymer shield and tab mechanism to prevent lateral movement. Two more gallons capacity. Unusable fuel on the ground (not banked) is about a pint. Existing tank totally removed. Fill points in each wing, near the outboard ends. Quick disconnect fittings in the wing roots - pull the wing out about a foot to do the disconnect. Single low point drain. The claim is that retrofit is easy.

The existing single fuel shutoff valve is retained.

Some unanswered questions:
Difference in weight? Are they baffled? Unusable fuel seems quite low in an unbanked condition. Description of the modification process, i.e. wing skin removal? Hole cutting? Baggage floor removal? ("One day" might be optimistic!) I don't immediately understand the fuel level indication mechanism. Appears to be supported by the rib lightening holes? Structural analysis? If being installed in a plane with the ROTAX, is the existing redundant electrical pump retained, relocated, or replaced? I assume wing removal involves draining the system from the single low point? Is that also a sump point? Not sure I care for the Tygon tubing simply pressed onto barb fittings in fuel vent service. Are the filling caps vented? A schematic diagram would be really helpful.

Last edited by Bill_H : 06-30-2014 at 09:16 PM.
Reply With Quote
  #2  
Old 06-30-2014, 10:14 PM
Bill_H's Avatar
Bill_H Bill_H is offline
 
Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,793
Default

Some answers from the vendor: "Very little difference in weight. Each of the 4 fuel tanks weigh in at 2.5lb.
Each tank does not need any baffling since they are only 5.5 gal each. There is always an opposing tank, no matter what. No wing skin removal. Just pull the wing off, install plastic liner and fuel tanks. No baggage floor removal needed. Just drill as indicated in installation instructions and install stand pipe. It is a one day factory installation procedure. Be sure to use whatever time you need for your installation. Solidworks structural analysis showed worst case scenario having the combined fuel in the existing fuselage location and a superior distribution using the Viking fuel tanks. The tanks work equally in a Rotax or Viking powered aircraft. Fuel pumps and return fuel stay the same. Fueling is much better with the wing tanks. Yes, the drain is at the lowest point and all fuel can be drained there. Fuel does not have to be drained for wing removal. Just use quick disconnect fuel fittings. The tygon tubing is just your vent. No pressure and no problem. Caps should not be vented and are not. Venting is done through float bowls for a safe and secure vent system, without spillage. The system is identical to the existing system. 4 cells making up one tank."
Reply With Quote
  #3  
Old 06-30-2014, 10:57 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 3,161
Default

I look forward to seeing the posts from owners that do this.
Reply With Quote
  #4  
Old 07-01-2014, 12:39 AM
rgmwa rgmwa is offline
 
Join Date: Feb 2010
Location: Perth, Western Australia
Posts: 1,675
Default

Quote:
Originally Posted by Bill_H View Post
They seem to be supported by the lightening holes with a polymer shield and tab mechanism to prevent lateral movement.
That would concern me a bit. Those ribs are designed for flight loads, not to support the up/down, front/back and sideways concentrated loads of full fuel tanks bearing on the edges of the holes in the web when flying in turbulence, maneouvering or in a hard landing for example. Not saying it wouldn't work, but just wondering what design checks they've done.
__________________
rgmwa
RV-12LR 912ULS
120346
Reply With Quote
  #5  
Old 07-02-2014, 09:52 AM
WingedFrog's Avatar
WingedFrog WingedFrog is offline
 
Join Date: Mar 2010
Location: Raleigh, NC
Posts: 864
Default

The main reason for putting the tank inside the fuselage was the issue of connecting/disconnecting fuel lines because VANs wanted a no-brainer wing removal feature (which is distinguishing the RV-12 from the rest of the LSA low wings crowd IMHO). This Viking initiative shows, as well as the comments in this thread, that with the proper fittings, this fuel line connection is a non issue. However, the solution offered by Viking looks to me as a kludge (as the successive fuel tank mods by VANs do btw), no offense to Viking as it's the best they can do not owning the design. Actually I hope Viking is successful because that would give VANs a pause and incline them to have a look at a factory option for fuel tanks in the wings, "a l? RV", i.e. the way they did it in all other models than the RV-12.
Enough of mods on the current fuel tank!
__________________

Builder's name: Jean-Pierre Bernoux
Sport Pilot
Kit # 120395 N124BX
Flying as of 9/11/2013

Builder's Blog:http://vieilleburette.blogspot.com/
EAA 1114
Reply With Quote
  #6  
Old 07-02-2014, 12:15 PM
rvbuilder2002's Avatar
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,654
Default

A few comments regarding some of the details I have read....

Mass distributed outboard in the wings -
This negates all factory spin testing results. Has a new spin test program been completed? If not, consider spin recovery ability to be a total unknown.

"Solidworks structural analysis showed worst case scenario having the combined fuel in the existing fuselage location and a superior distribution using the Viking fuel tanks." -
Solid works does not do load analysis. It is a design tool. You don't push a button and have it give you a green "good to go" or Red "needs more design work" indication.

Low wing airplane using fuel pumps to draw fuel from the tanks, but both tanks "T"ed together to the single (standard) shut-off valve is a major design problem.

4 cells making up one tank. No it doesn't when they are interconnected with small lines, particularly between the two wings.

Increased baggage capacity -
To 175 lbs? Really?
Moving the fuel to a different location on the airplane doesn't change the maximum gross weight of the airplane.
If the airplane occupants were light enough to allow for 175 lbs of baggage, the baggage area floor wasn't designed for it (the current fuel tank loads are not carried by the baggage area floor), and the CG would probably be extremely aft of the limit with full fuel.

Very little difference in weight -
The current tank installation weighs 9 lbs ( I measured it).
Based on the quoted tank weights, my guess is this system would weight (at a minimum) about 15 lbs installed... net increase in empty weight of at least 6 lbs

Fuel does not have to be drained for wing removal. I guess it depends on how much fuel is in the wing... full tanks would add another 66 lbs to wing weight... more than 1/2 again what a wing weighs.

Influence on wing structure at high G loads is a big question...
The wings bend/flex at 4 G's. How is that influenced by the tanks? Does it cause rib crushing, etc.?

Just some of the many questions anyone considering the mod should think about...
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #7  
Old 07-02-2014, 01:09 PM
Bill_H's Avatar
Bill_H Bill_H is offline
 
Join Date: Aug 2010
Location: Marshall TX (KASL)
Posts: 1,793
Default

Scott - have you ever seen ANYONE support something like this in rib wing holes?
__________________
Bill H, RV12, N412BR "Sweetie", Skyview-equipped, KASL Marshall TX
Reply With Quote
  #8  
Old 07-02-2014, 01:35 PM
rvbuilder2002's Avatar
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,654
Default

I think some of the add on aux tanks for other models are installed that way. Not sure what level of engineering anal. was done.
Ribs in the RV-12 wing are .020 material. Doesn't. Look good to me, but I haven't done any anal. so I don't know for sure.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
Reply With Quote
  #9  
Old 07-02-2014, 04:58 PM
yankee-flyer yankee-flyer is offline
 
Join Date: Jun 2009
Location: Dayton, OH
Posts: 838
Default Thoughts from an aero engineer

After spending 30+ years as a design specialist at WPAFB I can offer a few thoughts-- THOUGHTS only, no analysis done.

Fuel in the wings is a good thing-- IN FLIGHT. Lift bends the wings up, weight of fuel reduces that.
Fuel in the wings, and especially outboard in the wings is a bad thing-- DURING HARD LANDINGS. Puts a negative G loading on the wing. Having admired the spars in our wings while building, I don't think that would affect the spars. Effect on those .020" ribs is another thing indeed, not to mention all those reinforcing doublers and bolts we had so much fun installing. Don't know how much negative G load the tanks can take either.

Not exactly what the effect would be on the fuel system during a prolonged slip. Less sure what the effect would be during a climbing turn (aborted landing). We already have a 4-gallon minimum for takeoff due to the fuselage angle. Add a steep bank to that at minimum fuel and...."

I DEFINITELY want someone else to be the test pilot during spin tests!!

My first though on getting the postcard was-- yeah, I'll go for that! Following thoughts are listed above.

If you always make nice gentle landings, never stall/spin, never do a steep climb at minimum fuel, and avoid slips, you're good to go. I'd like to see those concerns addressed before spending I pony up for the conversion.

Wayne 120241/143WM
Reply With Quote
  #10  
Old 07-02-2014, 07:18 PM
dick seiders dick seiders is offline
 
Join Date: Jan 2006
Posts: 905
Default

Well dang Bill, your thread is apparently more interesting than mine, but I don't mind as I am enjoying the dialogue about this Viking proposed fuel alternative. What I still don't understand tho is if it's so hot why did it take four years after you first saw it to be be offered to us RV12 flyers? That is really curious. Anyway the topic is interesting and the comments thought provoking.
Dick Seiders
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 10:40 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.