Thorp Air Command - T18.net

So, my new-to-me T-18 has fuel tanks in the outer wings. Those are plumbed to refill the header via a Facet pump and a left-right toggle switch.

But there's no fuel gauge for those wing tanks, and I'd really like to know, with some confidence, how much fuel is in them through a long flight. I've thought about adding a totalizer for each tank, but that won't really tell me how much fuel is in the tanks if there's a leak, etc.

I'm contemplating adding a fuel capacitance sending unit to each side, and wonder if anyone has done this- especially to a flying airplane. It would involve drilling a hole through the ribs- but maybe that's workable.

Anyone have any thoughts on the subject?

Thanks,

Peter

I just use a float switch in the wing tanks. It turns on a light on the panel when the tank goes dry. When wing tanks are dry, I have two hours plus reserves left in the main. I feed the wing tanks into the main from the top so there is no back flow. I also have a float switch in the main that cuts power to the transfer pumps so it will not overfill. I gage my fuel in hours, not gallons. I burn ten gallons per hour, so 5 in each side gives me an extra hour.

_________________
Bob Highley
N711SH
SN 835
KLAL

10 years ago, I too bought my T18 with wing tanks but no wing tank fuel gauges. Like yours, my tanks pump fuel to the main header tank. When I first bought my plane I had the same desire as you. In the end, I decided use a timer on my panel to tell me how much fuel has been pumped into my header tank.

By testing over many iterations, I know my facet fuel pump sends .67 gallons per minute to the header. So I run mine pump in 3 gallon increments for 4 minutes and 30 seconds at a time. I then verify fuel has been added to the main tank by verifying that the digital fuel gauge in my header tank has increased. If I see no fuel is being added to my header tank (via the digital fuel gauge reading), I know I have a fuel transfer problem.

Thanks Bob and Ryan.

I have read through lots of the posts, and see that some builders have installed float sending units in their wings. Others know the transfer rate of their pump, and use a clock.

My wing tanks run from the inboard to the outboard rib on the front of each outer wing. Because of the dihedral, I don't know that a float gauge would measure the full capacity.

If nothing else, I may install a liquid (fuel) detector in the fuel line for each wing tank- that will show when a tank is empty, at least. Many of the Glasair guys (I also have a Glasair) have installed the long capacitance probes in their wings and are very happy with the accuracy. Just not sure if a retrofit is feasible.

The reality is that I won't be filling these tanks often so, like you, Ryan, I may just use the instruments I have now- a clock and a header fuel gauge.

Hi fellas,

I have the same setup like you and Bob for wing tanks. A Facet pump feeds he header; I simply open the valve from one wing or the other. I also bought a Dual LM394 Module, a small circuit board for about $8 online, and connected both channels to a wire from the main sender. One turns off the Facet pump when full, the other turns on a warning light when about only 6 gallons remain, before the engine goes quiet.

For wings, I simply wanted to know when each one is empty so not to needlessly run the pump when dry. I plan on alternating each wing and timing each draw, as others mentioned. The sensor is simply a small Neodymium magnet in a float, captured in a vertical track on the most inboard rib (bottom end) of the tank. Outside the rib is a magnetic reed switch, which likewise can turn on the light. No holes to drill or feed-through wiring to worry about. Magnets conveniently work right through aluminum. If anyone would like to try the same thing I have a few extra reed switches. They’re really small and free for the asking.

Les

Thought pictures would help.
Besides, I like pictures and figure others may too. The Facet pump is in forward tunnel, pushing through a tube going up center of the firewall to top of main tank. Floor panel is removable, also with access cover at center. Float can be seen in other photo, and pickup tube with screen.
Les

thats cool Les. Nice idea!