Fuel Tank Baffling Question

[WingedFrog]

While building the fuel tank, my attention was focused by the warning on page 37-03 about the fuel passages between the main compartment and the area where the fuel lines connect. These passages are clearly intended to allow the rest of the fuel in the main compartment to feed the fuel lines once the level of the fuel in the tank is below the top of the baffles. As the passages are very tiny, a friend of mine deemed it unlikely that they would be able to produce a fuel flow of up to 5 Gal./hour. Concerned, I called VANs and was told that the role of the baffles is to prevent the fuel to go in the back of the tank during the nose up of a go around with low fuel. This makes perfect sense to me, but... how will I ever get in this situation if the engine dies as soon as the level of fuel gets under the level of the baffles?

 

[DonFromTX]

I have sat and studied that myself. Still wonder just how it will work in all circumstances. I am assuming that in level flight the flow into the baffle area will be enough to feed the engine.

 

[Jetguy]

There you go over thinking again!

Here we go again. The bottom line is it works great. But Ill join the Hanger talk on the subject. While you have the top off the tank add water and see how many gallons are added to get the level above those baffles. My guess is 3 gallons or so. Maybe Scott M can weigh in on the subject and tell us. So here is another question. What do you think on average will be the lowest amount of fuel most people will land with? Me personally would be around 3 gallons. So if my logic is correct then almost all your flying will be done above those baffles. If landing below the baffles then in the pattern you will need to dampen the fuel some while making those last few turns as well as if the ride is choppy. That's my story and Im sticking to it.

 

[rvbuilder2002]

About all I will say is that there is a specific portion of the ASTM requirements for S-LSA certification, that deals with fuel delivery.
The RV-12 fuel tank was designed to meet all of the requirements, and tests were done to prove that it does.... if built per the plans.

 

[Geico266]

Minimum fuel for take off is 4 gallons I think. Minimum fuel to land is 1/2 hour or 3 gallon. In any event, the holes are certainly big enough to flow 5 gallons in an hour.

My minimum is 5 gallons. It's the only tank you got. Don't push it.

 

[Mich48041]

A hypothetical flight.

A pilot goes on a long cross country trip and encounters a head wind. Upon arrival at the destination there are only two or three gallons of fuel left. Just before touching down, some deer run across the runway in single file. The pilot elects to go around. The RV-12 is in a steep climbing attitude. The fuel tank baffles keep the fuel from rushing to the aft of the tank. The engine keeps running long enough for the plane to reach pattern altitude. The engine sputters just as the plane levels off. The pilot lowers the nose to maintain flying speed. The fuel now flows forward and seeps through the baffle holes fast enough to keep the engine running. The pilot makes an uneventful landing and still has enough fuel left to taxi up to the fuel pumps. The line boy does not question the amount of fuel purchased: 20.03 gallons.
Joe Gores

 

[Ausflyer]

I have some numbers

About 10 months ago I removed my tank to fit a Moeller fuel guage, and find out why my fuel flow PAP tests had been marginal. I did a range of bench tests with water, after finding that drainage of water from the open tank was within 2% of the times recorded with mogas.
I collected a lot of data, gradually gaining a better understanding of how the tank works with varying quantities and tank attitudes .
The figures relevant to the discussion above were:
1 litre dumped into the rear compartment of a level tank (front face vertical) takes 2 min 11 sec to drain out through the fuel supply fitting. Average flow rate is 25 l/hr or 7.26 US gal/hr
1 litre dumped into the rear compartment of a tank sloped forward 3 ½ degrees takes 1 min 53 sec to drain out through the fuel supply fitting. Average flow rate is 31 l/hr or 8.4 US gal/hr.
These tests were repeated several times and I am confident of the results
However to meet the 3 minute PAP test I had to enlarge the internal drain holes. I did get it working ok. The dump test was down to 1 min 34 seconds before I was happy with the flow from the tank. This gave me a 2 min 56 second result on the PAP test (2 repetitions with mogas, tank installed)
My general impression of the tank is that it works OK as intended. But there must be a lot of builders out there wondering whether their tanks really passed the PAP test.
Rod

 

[dick seiders]

I am one of those who feels confident Van's designers made certain a low fuel issue such as that described would have been taken into consideration. My question is barring a catastrophic leak from an unfortunate event why would anyone fly to a fuel level below 5 to 6 gal.? I start planning/looking for a fuel stop at ten. I don't like off field landings.
Dick Seiders