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I've come down to 3 possible ways to "see " the last 20 litres or so in my Jabiru behind the pilot tank.

On account of getting old, I don't twist so good that I can see it anymore.

So... here are the 3 ways ...

1. A "u" tube above the tank, fed by a squeeze-bulb air pump. To see the tank fuel, you would pressurise one side of the u tube until an inlet pipe blew bubbles from the bottom of the tank, at which point the level in the u tube would stop rising and you would get a fuel-remaining level.

2. A lever-arm float within the tank as a sender plus the fuel gauge. You can get these for about $30, and the lever arm can be tweaked till you get at least the last 20 litres fairly correct

3. Buy an endoscope ( 25 dollars or so ) and route it to the tablet display which also runs ozrunways. The inlet to the endoscope would be at the tank of course.

 

I am currently leaning towards option 3 on account of this being the lightest way. Any comments welcome.

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Mobile phone endoscopes are pretty cheap. Under $10.00 the last time I looked (Ebay from China).

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  • 1 month later...

four ideas for you Bruce :

capacitance sensor (external), ultrasonic sensor (external, self calibrates), tank audio resonance sensor, light transmission sensor.

------

 

a capacitance dielectric sensor . This is old school and works well. The tank is non metal, right ? (in fact, what is it, precisely ?)

The presence of a quantity fuel in the tank can be readily measured in that fuel displaces air, and the dielectric of air is different to that of fuel

- could be done as a capacitance sensor from the outside of the non metal tank.

- you could use a multimeter to do this with a pair of plates on the outside of the tank.

 

the tank could have a ultrasonic transducer attached to it underneath

The ultrasonic transducer can directly measure the depth of the fuel because the ultrasonic pulse bounces off the boundary layer of the fuel and the air above the fuel.The speed of sound in AVGAS is probably about 1000 m/s and fairly constant with a comfortable range of temperatures.

-these are off the shelf.

 

 

if the tank is a hard fuel cell, you could rap/tap on it and it will have a specific audio frequency, you could read that frequency with a guitar tuner, cellphone app, or just use your ear with a mic taped to the tank and plumbed into the intercom.

 

is the tank translucent ? , a LED on top of the tank and a light sensor underneath, the transmission of light will vary with fuel level.

 

-GLEN

 

glen

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Just to be unhelpful -

 

The best fuel gauge for flying is:

 

Sight (dip stick or level tube) and a stop watch, combined with knowing your fuel consumption/hr for the operation type envisaged.

 

Unlike the host of elctro/mechanical systems - very unlikely to give a false reading

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Some of those fuel tanks that sit behind you made of semi transparent plastic of some kind are CALIBRATED in the most simple way. Have a bit in and run it dry so you still have the unusable fuel. Then add increments off 20 L or so measured carefully and mark each level with a dark line Go all the way to the top and write total fuel XY litres. THAT has got to be fool proof. Thin and long wing tanks are not so easy. but you know when they are FULL and when they are EMPTY. IF you add a measured amount to an empty tank you KNOW how much is in it . You can also drain a measured amount from a full tank. These are accepted ways to accurately determine what fuel is on board. Even the best engines in the world need fuel. or they stop. Dip sticks are OK if the plane's level and the stick is correct for your plane and you KNOW that it is. Absolutely full tanks can vent fuel parked on slopes or taxying fast on bends. Fuel can disappear from your plane overnight. Nev

Edited by facthunter
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Some of those fuel tanks that sit behind you made of semi transparent plastic of some kind are CALIBRATED in the most simple way. Have a bit in and run it dry so you still have the unusable fuel. Then add increments off 20 L or so measured carefully and mark each level with a dark line Go all the way to the top and write total fuel XY litres. THAT has got to be fool proof. Thin and long wing tanks are not so easy. but you know when they are FULL and when they are EMPTY. IF you add a measured amount to an empty tank you KNOW how much is in it . You can also drain a measured amount from a full tank. These are accepted ways to accurately determine what fuel is on board. Even the best engines in the world need fuel. or they stop. Dip sticks are OK if the plane's level and the stick is correct for your plane and you KNOW that it is. Absolutely full tanks can vent fuel parked on slopes or taxying fast on bends. Fuel can disappear from your plane overnight. Nev

You cannot see the fuel level in the Wing tanks on my J170.

Since I am the only Pilot, and am hangared, I always know my fuel state, but still have 3 ways of checking.

Analogue float gauges at the Wing Roots

Electrical sender gauges on the Panel in front of me

and

A JPI Fuel Scanner instrument which is very accurate within a couple of Litres at each refuelling.

The first 2 items were standard equipment when the Aircraft was built at the Factory.

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Automotive reversing camera? I set one up in stepdaughters horse float so she can monitor the GeeGee enroute. Actually was a two channel setup, one for reversing the car to the float, one in the float.

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You cannot see the fuel level in the Wing tanks on my J170.

Since I am the only Pilot, and am hangared, I always know my fuel state, but still have 3 ways of checking.

Analogue float gauges at the Wing Roots

Electrical sender gauges on the Panel in front of me

and

A JPI Fuel Scanner instrument which is very accurate within a couple of Litres at each refuelling.

The first 2 items were standard equipment when the Aircraft was built at the Factory.

I didn't do any trips in the J170, but found the panel gauges would move into a position and sit there, and you'd look back later and they would show something else, sometimes less, sometimes more, but not always related to fuel burn. Three Jabs were the same. We had a dipstick, but on one occasion the aircaft wasn't quite level and I dipped the high tank then realised my mistake when it was on the level. the 170s drained themselves partly when they were parked on a slope overnight, and I found the small flat tanks difficult to judge with the dipstick because of the slopes.

 

Dies the JPI Fuel Scanner make up for this?

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Trying to be helpful - You could go for a fuel flow /monitor eg Gauges & Sensors. Just meter the quantity in the tank and it will tell you not only what you are using but how much is left

Yes my JPI FS450 instrument does all that plus gives me rate of usage, fuel remaining etc.

Easy to set up and interpret.

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Its when there is about 20 litres left that I really want to know the amount. Unfortunately, at this time, the view of the tank is difficult for me to see as as I get older and not so inclined to bend and twist. And yes RF, the tank is translucent FRP and it has a stuck-on tape with the numbers on it.

One way that I reckon would work is to make a "U " tube remote from the tank. ( but where i could see it good) One arm goes to the bottom of the tank and between this and the u tube you have a squeeze bulb to inject air. The pressure required to blow bubbles then shows the amount of fuel left.

But this is a bit downmarket and I would prefer a gauge on the panel.

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How much fluid is that above the tank floor / bottom ? (height) ?

can you get under the tank, for a transducer (affixed, say 5mm thick ) ?

two options come to mind - 1) ultrasonic fluid height sensor (external).

2) reflectance sensor on side of tank, can tell where fluid is above that level, or not. Am doing work with SPO2 sensors right now, perfect. I will order an extra one for you.

 

Here you go Bruce

 

http://www.naylampmechatronics.com/img/cms/Datasheets/XKC%20Y25%20T12V.pdf

 

https://www.ebay.com.au/itm/XKC-Y25-V-Y25PNP-Non-Contact-Liquid-Water-Level-Sensor-Induction-Switch-Detector/192913253604?

 

I will get a few different types .... use a pair of them each side in a AND style and drive a single bright LED etc.

Edited by RFguy
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Thanks RF. Those switches look like they go on/off when the liquid level passes the point at which the thing is mounted... is this so? If it is, i reckon you would need 3, at 20,15 and 10litres respectively. This would be a lot better than what i have now.

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Hi Bruce

yeah there are a family these sort of devices, many variations, this is just one of them. Need to get one to see if they play OK with gasoline - IE sense it reliably. In numbers they cost about $4 each...

I might be able to find one with continuous sensors. There might be one with say variable output 0 to 10 V etc, or multiple outputs...

 

What is the height of the fuel in the tank at 20 litres , approx ?

 

Glen.

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Hi Bruce

yeah there are a family these sort of devices, many variations, this is just one of them. Need to get one to see if they play OK with gasoline - IE sense it reliably. In numbers they cost about $4 each...

I might be able to find one with continuous sensors. There might be one with say variable output 0 to 10 V etc, or multiple outputs...

 

What is the height of the fuel in the tank at 20 litres , approx ?

 

Glen.

Hi Glen,

In my J-120 the tank is also behind the seat and very difficult to see the last 20 litres of fuel quantity.

Each 5 litres measures 17mm on the quantity scale, so 20 litre mark is 68mm from the bottom of the fibreglass tank in my plane.

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How thick is the tank wall ? what is the material (precisely) - FRP or made out of the same stuff as the airframe is ?

 

Need to get one of those level sensors and see how it goes with detecting AVGAS behind the thick tank wall.

It's an easy yes/no solution. (two of them AND logic to deal with sloshing) .

 

There are many options.

If you can get under the tank, a few mm thick, an ultrasonic level sensor could go there. (bounced off the air/fuel interface). accurate to a few mm.

 

I would have a level yes/no sensor at 1 hour and the ultrasonic level sensor. A bit like the low fuel light and the fuel gauge in your car.

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Thhe gauges on my RV4 were unreliable when full or near empty, due to the shape of the wing tanks. I fitted a red cube flow meter which gave very reliable flow measurements plus it gave fuel used. Could be reset to full at any top up, or the actual figure could be put in. No use of course if you get a leak before the actual meter, but better than the gauges.

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Any tank with a near flat bottom can let air in and may not fully empty reliably. The gascolator system makes it much more likely to empty better and is a known volume which means time of assured operation of the engine. Nev.

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I will "second" the usefulness of a flow meter.

Not an absolute solution in itself, but combined with gauges and known initial amount, you can compare readings in flight....

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