Visual determination of fuel on board

[edasmus]

Hi Dave....

My model is a 1973 337G (no turbo and no pressure). Fuel determination can be a bit of a challenge for these planes. My plane has 4 tanks in each wing and one place to fuel all four way out towards the end of the wing and then the fuel SLOWLY feeds down to the inboard tanks. A calibrated dipstick would not work on my plane because I would only be dipping the outermost tank. I don't know if you have been reading about all my fuel gauge troubles lately but up until a few weeks ago I had very good luck with my gauges being very accurate and dependable. I do however never rely on them.

My methodology for determining fuel quantity is quite rudimentary but very dependable. When I top the tanks, making sure to take my time so the fuel has time to feed down to the inner tanks, I simply subtract 20 gallons for every hour I fly. Realistically the fuel burn is more like 16-18 gallons per hour but 20 makes a nice conservative round number guesstimate. You will most likely need to take the time to "get to know" your airplane and see precisely what it takes at the pump when you top it off. I find that I can usually be within 2 gallons when I fill her up. Just make sure your first few flights are with full tanks and learn what she uses and then add a little extra per hour for your flight planning and you will be fine. As I said, rudimentary but accurate enough.

I will reiterate once again, top her off SLOWLY and give the fuel time to feed down the line. The fuel pumps are ALWAYS faster than the plane can take the fuel. I personally will go back and fourth between each wing at least twice and occasionally 3 times if I was too impatient while SLOWLY feeding the tank the last several gallons.

My gauges always made a nice X-check with my math and I hope to have those back on line within a few days!

Hope this helps!

Ed Asmus

[edasmus]

Oh yeah...

One more thing. Nobody fuels my airplane without my direct supervision. I prefer to do it myself but if the FBO must do it, then I am there period. Nobody secures my fuel caps except me!

Ed

[Ernie Martin]

I beg to differ with Ed, but I have exactly the same aircraft and you can indeed use a calibrated dipstick as long as you recognize the limitation, specifically that it won't measure below 30 gal per side. Above that, it's very accurate. Most of my flights are over water, adequate fuel is more critical to me than for most other Skymaster pilots, and I spent considerable time researching the system and making the information available in the Fuel Supply Management page at www.SKymasterUS.com

Other techniques, like supervising fueling and keeping close tabs on time, are critical, but for me the most important is climbing on the wings and using my dip tube.

Ernie

[edasmus]

Ernie is correct. I was thinking in terms of the entire wing. One other thing I would like to add for Dave is to make certain you understand YOUR fuel system on YOUR particular model of Skymaster. These fuel systems vary greatly depending on the model!

Thanks for keeping me on my toes Ernie. I appreciate attention to detail!

Ed

[aldoradave]

Dear Ernie,

Just so I fully understand (given the model year differences) my 73 P337 with 128 gal capacity, should be the same as your 73 in fuel tankage. That is, if I can see fuel below the fuel tube, then I have at least 30 gallons. I will of course confirm this myself, but correct me if I am wrong.

Thanks,

Dave Dillehay

[Ernie Martin]

Yes, if the wing/tank arrangements are the same between your P model and my normally aspirated model, then if you see a thin film of fuel under the filler hole you have 30 gallons, and the tube (after you calibrate it) is used to determine quantity when you have more than just a film (1/4", 3/4", 1.5", etc.). The airplane must be on a level surface for accuracy, and, as mentioned by others, you need to wait until fuel has settled because the fuel SLOWLY feeds down to the inboard part of the tank system.

Filling is important, also. If you're starting from a very low fuel situation, use of the visual-and-tube technique on the first tank/side you fill will give you an inaccurately high reading, because the weight of the fuel on that side (unbalanced by the emptiness of the other side) will make the aircraft tilt in the direction of the tank you are filling, bringing more fuel under the fill port than there would be if the aircraft was level. So, when you just barely see fuel under the port (after waiting for fuel to settle, of course) you won't have 30 gallons, but 28 or 26 or perhaps less. Same with the tube. After calibration, if it shows you have 50 gal, you might have 45. The solution is to go fill the tank on the other wing and then return to the first tank to re-measure and refill as necessary. Generally, this iteration is not needed on the second tank/side, just the first.

Ernie

[rick bell]

shadden, shadden digflo !!! unbelievably accurate all it takes is for the dumbass to reset the computer every time you get gas. on long fligths i would switch to mph. best mpg was 9+ gallons per mile

[tkirklindale]

is there any stc engine gages out there for the 337 ??