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Fuel Level
bryancobb - 5/27/2011 2:33 AM

vortexring - 5/26/2011 1:05 PM

The sight tube is always going to be the most accurate and reliable indicator you could ever think of. are you unable to turn your head for a quick glance at the tube or just trying to overly complicate things?

When flying the Mini, and later, our Tierra II, turning around was a problem. I stuck a suction cup auto mirror on the inside of the bubble, at knee level, and now, not only could I see the fuel sight tube, but I could see the Tail Rotor clearly!

Bryan I love that idea and I am absolutely going to steal it!

Rob 1
I like the rear view mirror idea too.

I have the site tube where I can see it easily, but keeping an eye on the tail rotor and area around it is a great safety benefit.

I have spent quite a bit of time thinking about how to do this (BTW my old Scorpion used a cork on a welding rod sticking up through a hole, which worked well ).

I think NASA uses ultrasonics ( zero gravity work ), but I came up with a more direct way:

Using the gas law "PV = nRT" ( Pressure (atm) * Volume (liters ) = (number of moles) * .0821 * temperature °K ),
you could measure the exact volume of liquid in a tank regardless of how it's sloshing by pumping some of vapor from the tank ( assume heptane for calculations ) into the tank 'til the pressure raises 1 PSI, then you could calculate the volume of the liquid in the tank by the volume your positive displacement pump used to do that. Alternatively, you could pump 1 liter of vapor into the tank and measure the pressure rise. You'd need to put a pressure relief valve where the vent normally is, though.

Another variation (I'm thinking about this as I type, so it's all half-baked ideas right now):
Put a one liter bladder inside the tank and inflate it with air and measure the pressure increase in the tank.

Has that been done before?

Hoyt Stearns
Scottsdale Arizona US

I do not think anyone has ever used pressurization to calculate remaining fuel volume. It would require a fuel tank to be sealed, and would need some way to vent the system for fuel consumption.

Sealing the tank alone, would be a pain in the rear.

Most systems use a floating type measuring device, or a capacitance type probe.

There are many ways to use the above two systems, along with a sight gauge.


You're undubetledy right, I just had some thoughts.

I know that commercial airliners use real mass flow meters ( pounds per second ) instruments. That's ideal, but having worked in the flow meter business from time to time, that's kind of difficult and expensive, and it doesn't tell you what's in the tanks, only how much you've used so far and your flow rate.

Here's my Brantly Low Fuel Warning System I installed in my Mini I'm almost done with.

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Bryan:  Did you incorporate your idea of a "Torque Meter" in the Mini???
Yes it will be on there. I just haven't nailed-down the detail of how I want the indicator to look on the panel. I'll have to get it flying first to be able to tell the scale of the indicator. I.E. You will never use the right half of pedal travel so that portion would be useless to indicate on the instrument.

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