Fuel at Filler Port for Long Range 150 gallon 337G Models

[Ernie Martin]

Those of you with 337G models with Long Range 150 gallon tanks (S/N 1607 and higher), have you ever determined how much fuel is in the 75 gal tanks per side when fuel is just visible under the filler port?

In my old '73 337G with 64 gal tanks per side, there was 30 gal when the fuel just reached the area under the filler port. Wondering if anyone knows what it is for newer models with 75 gal per side and a filler port much further outboard.

Ernie Martin

[Mich3773]

We just bought an H model with 75 gallons per side. The previous owners left us a graph of gallons usable verses the reading on a Universal XL Fuelhawk. We've been verifying the graph against the fuel gauges and the fuel added and so far, it appears correct. There are 50 gallons remaining in each long range tank, when the fuel is just visible.

[hharney]

Looks legit but I think I will stick with my fuel gauges and JPI. Each tank could be set a little different from the factory in the wing.


https://www.aircraftspruce.com/catal...9calibrate.pdf


http://www.mypilotstore.com/mypilots...tion-Guide.pdf

[Ernie Martin]

I bought the Universal Fuelhawk (not the XL) and on my 1977 337G there are 43 gal remaining in each long range tank when the fuel is just visible. Here are the gallons remaining for each marking of the Universal Fuelhawk tube:

Marking Fuel Remaining
1 48
2 53.5
3 58.1
4 63
5 66.5
6 69.5
7 72

Ernie

[SteveG]

Calibrating a fuel tube is an interesting exercise but expressing the results to the nearest one-tenth of a gallon has me wondering about the methodology used which would permit such a level of precision much less such a level of accuracy. Do these values represent absolute fuel remaining or usable fuel remaining? Depending on whether the tanks were manually drained and from what point or whether the engines were allowed to stop from fuel starvation. And depending on the aircraft's lateral & longitudinal position at the time. Whether leveled on jacks or whether level flight at some arbitrary center of gravity was approximated. Seven gallons per side difference between Mich3773's results and Ernie's results would seem to suggest, assuming similar methodology, that values to the nearest gallon would be optimistic and only applicable to that particular craft. Notoriously inaccurate panel gauges probably provide similarly usable data. That is to say "yes, there is some fuel in the tanks but I'm not going to bet on the quantity plus or minus ten gallons." As for me, I think that I will continue to rely on self-fueling to the top of the filler for quantity and rely on a fuel flow totalizer cross-checked with running time and panel gauges for consumption.

[Ernie Martin]

You're right, no one is suggesting that this is accurate to a gallon, let alone a tenth of a gallon. My only objective in providing the above table is to give the points on the curve for those who have a 337G with extended tanks and buy a Universal Fuelhawk, so they don't have to go through the process of generating the curve.

But the point of this tube -- and to know how much fuel there is when fuel is just visible under the filler port -- is to be able to load the fuel you need for a flight.

For those who've never calibrated such a tube, the methodology is straight forward and accurate. Take the point at which fuel is just visible under the filler port. That, of course, represents 0 on the tube. If you now add fuel and it takes 30 gallons to fill the 75 gallon tank, then you know that the "just visible" marker (0 on the tube) means you have 45 gallons. You follow the instructions and you end up with fuel quantities for the markings on the tube (0, 1, 2, 3, etc.).

I trust the readings for initial fuel load, and believe that the differences between the Mitch3773 readings and mine are real, because his is an H and mine is a G.

Ernie