| Turns out we build pressure sensors that are used for measuring fluid level (the most fun one is for the sewage holding tank on the Airbus 320). Unfortunately, there are lots of problems with using this method for fuel level. One is that the pressure is relatively low - if the full fuel level is 1 foot above the sensor the pressure is only about 0.4 psi, so you need a fairly low pressure sensor, but that's not too bad. The sensor needs to be vented and it should be vented to the vapor in the tank just in case the tank vent system isn't perfect, and most Lancair system aren't because the vent is pointed forward, slightly pressurizing the tank. However, if any liquid fuel gets in the vent the accuracy is destroyed - and maybe the sensor as well. Also, the pressure sensor would presumably be located at the wing root, so there would be substantial errors induced caused by out-of-level conditions (slips). And, of course, the sensor has to be compatible with liquid gasoline.
I have been playing around with just such a device that can be used for checking fuel level during a preflight, especially useful on a low-wing plane where the dipstick doesn't always reach the fuel. I rigged up a pressure sensor with a fitting that can be pushed against the quick-drain and it will read fuel level, either by displaying a pressure number, or actual fuel quantity by calibrating it for the specific airplane. A few details need to be sorted out, but it can be made to be fairly accurate; within about 1 percent. If the plane is parked where it isn't level there would be an error, but that condition isn't the norm. And there is no problem with venting the sensor to atmosphere as the tank shouldn't be pressurized while standing still. What I don't know is whether anyone would be willing to buy such a thing (probably about $100). Might be a good stocking stuffer for the pilot who has everything else. Any potential interest?
Gary Casey N224SG
Date: April 5, 2007 6:38:53 AM PDT Subject: Re: [LML] Re: Testing for fuel leaks and fuel probes to use
Bryan, I heard of one builder that used pressure sensors as fuel level sensors. I think they were rated at 0-5psi. Sounds like this may be a solution for you too. Mark S.
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