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Old 06-17-2017, 04:30 PM
bobnoffs bobnoffs is offline
Join Date: Jul 2012
Location: n. wi
Posts: 487
Default fuel tank specs

hi all,
i am looking for some general rules to follow.
for simplicity say the fuel tank is 36'' wide, 12'' high and 12'' fore to aft. 2 baffles make 3 compartments, each about a foot square. floor of tank slopes down forward about 8 deg. when longerons are level. max. fuel burn at w.o.t for 110 hp about 10 gph.criuse burn 5.5 gph.
to allow fuel to fuel to flow to engine i am thinking 3- 3/8'' holes at the bottom of each full forward, another an inch aft of that and the 3rd at the aft edge.
for venting the same set up but the holes would be at the top edge of the baffles.
for fuel flow thru tank while refueling i really don't know. maybe 2 in each baffle, 8'' above the floor of the tank? i won't even guess at their size. i close, right on, or way out in left field? i would like some advice from someone who has been there.
thanks for any input.
Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying
RV-12 kit as of 9/13
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Old 06-18-2017, 10:48 PM
Bevan Bevan is offline
Join Date: Sep 2007
Location: BC
Posts: 1,523

Need more info. Is this an aux fuel tank? Is it gravity feed or pumped? Is it pumped to engine or to another tank?

RV7A Flying
O-360-A1F6 (parallel valve) 180HP
Dual P-mags
Precision F.I. with AP purge valve
Vinyl Wrapped Exterior
Grand Rapids EFIS
Located in western Canada
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Old 06-19-2017, 08:17 AM
rv7charlie rv7charlie is online now
Join Date: May 2006
Location: Pocahontas MS
Posts: 2,761

The tanks in the single digit RV's have a ~1" dia hole in the bottom aft corner (low point) of each rib. They also have ~1" dia holes near the center of the ribs (I'm guessing those are for ease of filling the tank quickly). Much smaller holes at the top of the ribs for venting between cells.

If I were building the tank, I'd go to at least 1/2" or 3/4" for the holes along the bottom, consider the 3/8" top 'vent' holes more than adequate, and add one at least 3/4" dia in the middle for filling.

But I'm no fluids engineer; I just copy what works....

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Old 06-20-2017, 11:55 AM
n82rb's Avatar
n82rb n82rb is offline
Join Date: Jan 2007
Location: fort myers fl
Posts: 707

General disclaimer:I'm an EE, never had to take fluids, thank god. But it depends on purpose of tank. Aerobatic? Aux cruise? Primary? The holes not only have to allow transfers from bay to bay, reduce sloshing, reduce unporting, but they also have to allow for filling of the tank. If you use small holes you risk not transferring enough for normal fuel flow, to big and you could get sloshing and unporting. I would use at least 3/4 inches at the low point of the baffle for normal flow, 1 to 1 1/2 in the middle for filling and 3/8 or so in top to vent.

Those are just guesstimates but should work.

Bob burns
Rv-4 n82rb
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Old 06-20-2017, 12:33 PM
bobnoffs bobnoffs is offline
Join Date: Jul 2012
Location: n. wi
Posts: 487

this will be the main tank. fuel is pumped to the engine at 30-35 gph and most is returned to the tank to the sump mounted in the floor of the tank. no aerobatics.
sounds like 3 1/2'' holes along the bottom and a couple 1'' holes in the baffle for refueling would work. yea, 3/8 on top for venting.
thanks guys
Bob Noffs
n. wi.
dakota hawk/jab 3300 built and flying
RV-12 kit as of 9/13
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