Light Aircraft Association

I am getting around to that stage in my project when i have to start thinking about fuel gauges amongst other things. I have a single scuttle tank with gravity feed. I would welcome any thoughts, experiences people have had with the various options for the dreaded fuel gauge question
Dave

David,

The plans for my Boredom Fighter project show a float system using a “simple” swinging arm arrangement. This is made from two short lengths of stainless 1/8”OD wire. The shaft exits the tank through a flanged hole in the upper tank wall and is sealed by means of flexible tubing. The outer end of the shaft is then connected to an indicator in the cockpit with a light flexible drive. This operates smoothly and looks pretty damn neat, but it remains to be seen whether or not it will be entirely fuel proof.

Although I have used this system, it is really too involved and I notice that the majority of other builders in the U.S. have (perhaps very wisely) used the more conventional and simpler “float on a piece of wire”!

Ian

Although I am not a builder, I do wonder if anyone has ever tried using the fuel guage and sender out of a motor car.
Aircraft fuel guages seem to be extraordinarily innacurrate in my experience.
Car fuel guages are reasonably accurate, and require a sender fitted to the fuel tank and guage fitted to panel. The voltage is about the same.

Plenty do! The old Citroen ones were popular in Jodels for a start.
________
Sportivo Coupe

How about rigging an ultrasonic tape measure to give the distance to the top of the fuel, easily convertible into volume? No moving parts! I believe you can buy the ultrasonic sensors as separate standalone items (so even smaller and lighter), but you'd need the electronic wherewithal to set this up. (Such a sensor could fit on the bottom side of the filler cap. That would be neat!)

The easiest thing to build into an aircraft is complexity. What do you need to know - how much fuel is left. What is the cheapest and least complex method to achieve that - either a sight guage (tube with a coloured ball), or a float and wire sticking out the cap. No electrics or electronics, minimum weight, and virtually nothing to go wrong.

Brian, I agree about complexity, but (a) a sight gauge only tells you there's fuel in that tube; and (b) floats occasionally don't live up to their name and wires can get stuck in sleeves.

A dipstick and watch. The dipstick tells you how much you have to start with and the watch tells you roughly how much you have used. Simple, leak free, cheap, reliable and no less accurate than most light aircraft fuel gauges.

Brian, where do you get the Balls

I shudder to think how long yer made in PRC plastic ultrasonic tape measure will work.

The only problem I have with sight tubes is that they do add complexity to the tank plumbing - 2 more joints to weep smelly stuff.

I share the view that on a simple, non aero plane the cork and knitting needle is the most failsafe ( and accurate ) solution

Ultrasonic measurement of tank contents is notoriously UNRELIABLE. The MOD abandoned it over twenty years ago.

The MOD abandoned it over twenty years ago.

...And of course there have been no advances in electronics at all in the last two decades...

Nick,
Ultrasonic measurement is OK when the tank contents are rock steady. When fuel is sloshing about in a tank, the "rebounding" signal from the sender to the receiver is "all over the place". There are other variables which affect the signal. I would agree that the absolute solution is the good old gauge glass tube. For those that have the "fuel in tube" sight glass, another method of increasing the visibility of the fuel is to stick a thin (3mm) wide piece of tape, say red, behind the "glass". The fuel in the tube magnifies the tape and appears red.

Thanks for the replies
A cork and knitting needle or sight glass wouldn't really work in this application (T18) so as far as I can tell I am left with the following options:
1.dipstick (Don't know what engineering thinks of no fuel gauge at all)

2.conventional float type gauge (car style may not be particularly reliable)

3.capacitance style probe gauge (apparently confused if you switch Av to Mogas

4.probe style involving a floating magnet and reed switches (nothing known)

5.flowmeter and computation (need to ensure failsafe such that it will not block off fuel flow but apparently very accurate)

Does anyone have any experience or comments to add to these options.
Ta Muchly
Dave

I share the view that on a simple, non aero plane the cork and knitting needle is the most failsafe ( and accurate ) solution

Until the cork breaks off and your failsafe fuel gauge then indicates no fuel when you took off with a full tank 20 mins previously. Has happened to me and it took 2 hours with a grabber thingy to get the cork and other bits from the drained tank

Dave

David.

Re 'no gauge, just using a dipstick before flight'.

FRED has no gauge system at all and, since it has the tank in the front of the wing centre section, there is no way of viewing it other than an electric gauge or Stearman-type sight gauge.

There is currently (and has always been like this) nothing on it but I've bought a capactiance type system.