Thread: Site tubes and accurate fuel readings

Hey all,

I was wondering how accurate everyone has found the site tubes to be vis a vis the actual amount of fuel in the tanks. With the Pipers, and most of the Cessnas, if you are lucky the gauges will tell you that you indeed do have some amount of fuel somewhere in one of the tanks or the other or maybe not...

I am wondering this as an extension to the MTOW discussion. Obviously the more accurately you can measure the fuel, the better you can calculate the load. Unlike the Pipers, at least with the Cessnas you can measure the fuel with a stick from on top of the wing and get a pretty good idea. Does anyone use external measurement?

Lastly, I would imagine the pitch, speed, attitude, etc of the plane effects the tubes - centrifugal force being what it is. But in level cruise do you all find the tubes to be pretty accurate? On the 6XT we use an EDM-800, but that seems like overkill here. I ask in my never ending quest to extract as much information from this board as humanly, or maybe humanely possible.

Thanks

the site tubes are great, they don't lie, ever!

you do have to know how to read them. if you slip or skid you will slosh fuel outboard on one side and inboard on the other.

if you fly uncoordinated for a period of time you will drain one tank faster then the other or even transfer fuel and loose it from the vent.

in turbulence and when somewhat low on fuel the readings will fluxuate.

you can (and should) dip the tanks for accurate readings between flights.

the site tubes when low on fuel will tell you that fuel is available to the engine, if you can see fuel there is fuel available. it is possble to exhaust one tank and unport (slosh outboard) the other but in this case no fuel will be visible.

the 1st 2 hours of fuel are not readable on the site tubes, after 2 hours of coordinated flying you will begin to see fuel levels. after 4-5 hours the levels become important.

The sight tubes work well, and the nice thing is there are no moving parts to break. Just replace the tubes now and then when they get discolored. When they get replaced you have to put the marks back on for the various fuel levels. Its always best to get a good fuel dip like Charlie Tango mentioned and time your flight. Those equipped with the Dynon 120/180 engine system have the fuel flow indicator and a calculated fuel level based on a input starting fuel level.

Eric Swisher
Copper City Aviation Services

Good-day all!

My fuel dip stick has come up missing. Anyone know what the fuel cap slot dimensions are so I can fabricate one while I order a new one. Specifically, the blade to unscrew the cap. What is the blade's size? I'm going to modify a 1 inch steel carpenters square, or will it fit without altering it, any guess? \ BB

I can't seem to remember the rule that Russ taught me a couple of years ago at Page and I was hoping that somebody here could remind me. It has to do with uneven tanks on long X-C's and when they are low. You have to fly it uncoordinated for a period of time to get the tanks back into even fills. Something like you put the ball towards the lesser tank or reverse of that. Could somebody help me out? Thanks, John

the fuel follows the ball. left side low, ball to the left.

Say your right tank is low: " Push to flush (empty) " is how I remember what to do. So then I push the left pedal, ball goes over to the right, left tank contents flow towards the right tank, all the time still flying in a straight line. Because having pushed left pedal, I now need right aileron to remain straight; this raises the left wing and so empties the left tank. You may see nada in the right tube in this configuration, but it will come back when you straighten up and fly right..

And dont sideslip the wrong way on low fuel, or you run dry with usable fuel away from the outlet.

My old DPE told me a C152 on low fuel will suck out the very last drop by alternate side forward slipping, so will a CT.

As long as you can see fuel over either outlet you stay going.

Could someone could take their fuel stick and trace the outline for size then lay a piece of paper on it and transfer both sides of the stick onto the paper by running a pencil back and forth on it? They could then scan that and upload here allowing us to make our own. Remember the the left and right sides are different I believe.

I had mine for a long time until I left it at fuel stop a month back.

Roger H

Roger H. Instead of trying to trace the dipstick on paper, how about me taking a picture of my dipstick with a 12 inch ruler alongside it? I'll take a shot of both sides of the stick and you will be able to see where each graduation lines up with the ruler. You're right, the dipstick has unique calibration marks for the left and right tanks. I can give you the thickness of the stick too.

Dick, Roger H and all,
I bought the small 8x12 steel carpenters square at Home Depot for $3.XX. Small end fits SW fuel cap slot like it was made for it and either end goes in the filler neck. Both sides are in inches, just need to figure a way to calibrate them and maybe hagsaw 4-5 inches off the small end and file edges round.