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Bruce Tuncks

Fuel Gauge for Jab SK

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When the fuel is low, I find it hard to see the level in the tank behind me. Has anybody done something here? Maybe a fuel gauge, maybe an optical thing so you can see the fuel better.

 

 

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maybe an optical thing so you can see the fuel better

Isn't that "optical thing" normally called a mirror? :cheezy grin:It's what I use, to see what's behind me.

 

 

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How does a mirror help? I can imagine a setup of mirrors. An optical thing would also be a fiber-optic plus a light source I think.

 

There was a story about a Jab running out of fuel in a CASA booklet lately, and the pilot had not been easily able to see the last 10 liters or so. If he had, the engine would not have surprised him when it went quiet.

 

( I especially was impressed how the fuel consumption in that story was 17 liters per hour, while he flight planned on his usual 15. Murphy in action huh.)

 

One method would be to put in a low fuel warning by drilling a hole down low into the fuel tank and putting a small float-switch in there.

 

I was just wondering if others have done something here.

 

 

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Bruce, maybe get your Arduino mate to set up an IR sensor to read the lower level through the tank or an ultrasonic to read from the top as a contents gauge. ............just thinking

 

 

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I'm sorry, but I'm not familiar with the Jab tank setup and you didn't explain how far back the tank is, and whether the fuel level could be seen from the seat position with a single mirror.

 

Is it not possible to adapt a fuel gauge system from a road vehicle to fit? You can buy off-the-shelf simple fuel gauge kits for automotive fuel tanks. Is the tank a weird shape that makes fuel gauging a PIA?

 

 

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The tank is a rectangular box right behind the seats. It is made of FRP and is transparent enough to see the fuel inside. There is a scale glued to the front of the tank. You need to turn to see the fuel level, and the fuel shows up better if you shine a light

 

It works fine except for the last 20 liters when it is low and hard to see.

 

Yes you could use an auto gauge , I have never seen such a thing installed though and I don't think they are very accurate.

 

I tried using a camera ( hold the camera down there and take a pic) but it didn't work as I hoped.

 

I liked cherk's comment about ultrasonics but don't want to do any development work. After all, the thing is nice and simple as it is.

 

 

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O.K. I do agree with your opinion as regards the accuracy of automotive fuel gauges - but most light aircraft use simple float gauges too, and they also suffer from accuracy problems. Thus the reason for dipsticks, and fuel flow calculations.

 

SMD Fluid Controls supply multi-point fuel level sensors that can advise on various levels remaining in the tank - but I have no idea of their cost, the company needs to be contacted to determine your precise needs and the calculated cost.

 

Custom Multi-Level Float Switches & Multi-Point Level Sensors

 

Airplane Fuel Gauges: How they Work, Challenges, & Solutions | SMD Fluid Controls

 

Perhaps a good quality electronic fuel-flow meter which provides accurate LPH fuel consumption is also a worthy addition to your Jab?

 

Fuel Flow from Aircraft Spruce

 

 

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I recall someone had a system with a bright light attached to fuel tank somehow, when turned on level could be seen more clearly

 

 

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Not at all very ingenious I know, but I just shine a torch from the top and the 'ol AVGAS lights up pretty well...

 

I have actually got an MGL fuel flow instrument which also has a gauge in it. If you're after a panel mounted gauge, it could be the go?

 

 

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If it's accurate at 20 won't that give you enough warning? You have say 70 minutes till it stops.. No one should rely on the last few drops so say 50 and be ready to LAND with the engine still running. It's easier than hoping it won't stop and far better to get an accurate approach into a tricky place. Nev

 

 

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Bruce, we are trialing a strip of LED lights similar to:

 

Cool White 5050 Led Strip Lights 300 LEDs Waterproof Flexible DC 12V + DIMMER | eBay

 

The lights have an adhesive strip on their back, we glued them into a length of very light gauge polished stainless which is then fixed to the back surface of the tank with some super strong double sided scotch tape. A Press button on the central spine between the seats lights the strip and shows the tank level very well. Haven't tried it in flight yet but dummy runs in even bright sun seem to suggest that it will be a go-er.

 

If I recall correctly Belite also has a neat little in- tank capacitive sender that can be hooked to one of their bar graph style displays LED Instruments - Fuel Gauges - Belite Aircraft

 

 

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Bruce, You can cut the strip to pretty much any length you want. On ours the strip was cut just slightly shorter than the depth of the tank.

 

 

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Getting more technical, I have a Princeton capacitive fuel level sensor coupled with an MGL Stratomaster Ultra Horizon. It is very reliable but was a real pain to fit and calibrate. It is fitted from the bottom of the tank but I'm guessing it could be calibrated for fitting from the top. I think they are also sensitive to fuel type. If you use a mogas you will get different readings from using avgas and I have heard that ethanol kills them.

 

 

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A "U" tube on the panel with one side running to a vertical pipe down into the fuel would give the fuel level accurately. To get a reading, you would need to push a bit of air in until the tank pipe blew a bubble or two.

 

If there was water in the U tube and avgas in the tank, the head as seen in the U tube would be smaller by the density difference between avgas and water.

 

This is not a very tidy idea and pumping air into the tank pipe could be seen as a fire hazard, but an earthing wire could be incorporated to prevent a static build-up.

 

Has this ever been done?

 

 

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Bruce, I used ultra-sonic sensor and Arduino to measure the level of water in a bucket with a view to developing a fuel gauge. It works well, let me know if you want to develop the thing further. I still have your Arduino stuff here, keep forgetting to bring it to the club.

 

 

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Sure do thanks. I reckon an arduino ultrasonic would be the answer to having a cheap and non-invasive fuel gauge. I'm finding it harder to twist and bend to see that last bit of the fuel tank, but it is exactly when you have less than 20 litres that you really want to know how much there is. Lately I've again tried a camera to hold down there and click but this didn't work any better than before.

 

If the ultrasonic system could work on those shallow wing tanks then late model planes would benefit too. A hard ask though.

 

 

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I used a mechanical lever type float, just as used in cars, with a sender unit and a gauge up front. Relatively easy to fit. Works very well, but you need to double-check fuel level on tank, before taking off.

 

 

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Something like this: Fuel Level Gauge Car/Boat/Marine Fuel Tank Level Gauge With Fuel Sensor E-1/2-F 7642316249679 | eBay

 

This gauge beats the reading on the Jabiru tank, which is not really visible below 40l, when in flight. You can tune it yourself with the mechanical arm, on mine I can read down to some 3-5 litres. I calibrated it myself by filling the tank litre by litre. Very good to do your in-flight fuelcheck on route. But still, plan your fuel before you leave. Don’t rely just on this gauge!

 

Good luck.

 

 

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hi all

 

for those pondering fuel sensors /warning lights etc here is a couple of links that you might find interesting the site has all sorts of instrument s& plane related things also their own kit plane

 

Fuel Sender | Belite Aircraft

 

Bingo 3 Liquid Detector - Radiant Technology

 

happy reading

 

 

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Here's an idea. Have a tube with a sliding rod in it fixed to the top of the tank so that a float attached to the rod is just above the bottom of the tank. When the fuel gets low the float (and hence the rod) slide down allowing a micro switch connected to the top of the rod to activate a light on the dash. No electrics required in the tank and if the plane lands upside down, the fuel can't drain out of the tube because the end will then be above the fuel level. The rod assembly would not need be any wider than a pencil. Then again, it might be a nuisance having this assembly poking up out the top of the tank...

Edited by Jabiru7252

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If you take the cap off a Cherokee and look in you will see a steel tab gauge protruding up from the bottom of the tank.  It gives you a very good method of judging approximately how many litres you have in the tank. If you take a look inside the tank, you'll see that the wing is a deep section, so the length and width of the tank is relatively small.

 

If you then go to a J170, get some steps and take a look in the top:

1. There's no tab, so you can only look at the fuel level in relation to the top of bottom.

2. Notice the much thinner wing section and much shallower tank.

This means that for long distance cruising the tank has to be much longer and wider compared to its depth.

We have a very shallow but very long and wide tank for our visual checks, stick check, and our fuel height gauge sender, whatever meothod is used.

The 170 fuel gauge is rather vague, not because it is of low quality, but because to the difficult job measuring fuel level while the aircraft is in flaight and the fuel is moving backwards and forwards to the extremities.

I also managed to drain a fair amount of fuel from the aircraft when it was standing, by not noticing that one wheel was sitting higher than the other.

For the same reason my stick levels were erratic.

There's nothing with your sliding tube concept, but for the same reasons it would be inaccurate.

And for the same reason a warning light isn't going to be any help.

 

What you can do, is before a long trip, fill with a known amount of fuel and then, if the Jab fuel burn rate is accurate, calculate your endurance on the known quantity by calculating the fuel burn. 

 

Jabiru are getting plent of lift now out of the J170 wing profile, and the slim profile has other advantages, so I thing the long term solution is to design three digital senders with a digital gauge/computer to dynamically calculate average fuel level.

That way you can manually check with a level stick and cross check that with the gauge which will show the same.

 

 

 

 

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I think the original problem was: Can we have a solution such that during flight, and with some accuracy determine how much fuel is remaining in the tank of a Jabiru SK. The level is hard to see when it's low and swiveling around to view it isn't that easy. The Jabiru SK tank is not long and flat, it's a box shape. I think my idea would work. I also built a prototype level indicator on the bench using ultrasonic sensors and an Arduino micro purchased from Jaycar. That worked quite well, just more work getting it setup properly.

 

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1 hour ago, Jabiru7252 said:

I think the original problem was: Can we have a solution such that during flight, and with some accuracy determine how much fuel is remaining in the tank of a Jabiru SK. The level is hard to see when it's low and swiveling around to view it isn't that easy. The Jabiru SK tank is not long and flat, it's a box shape. I think my idea would work. I also built a prototype level indicator on the bench using ultrasonic sensors and an Arduino micro purchased from Jaycar. That worked quite well, just more work getting it setup properly.

 

In that case you should be able to get an accurate measurement of fuel prior to take off.

The normal procedure taught in the Performance and Operations segment is to calculate your remining endurance during flight from your fuel burn calculation.

So, calculate startup, taxi/hold fuel burn, climb fuel burn, then track fuel burn, descent fuel burn, taxy fuel burn and ensure you have your legal reserve after that.

If you enter your flight data every 10 minutes, you will be able to call back ATC with your endurance at any time should you have an incident en route.

Fuel burn rates for GA aircraft are accurate.

To cover an en route fuel leak/hose failure/tank crack etc. you check your gauges against your calculated fuel burn.

There's no problem in having an extra indicator for when the tank is low (still bearing in mind what Facthunter said)

 

 

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