Sensor for Fuel Tank Level

[skippydiesel]

Aside from the simplest & best, the ever reliable sight tube, I am intersted in your experience and recommendations (with rational) for a fuel tank level sensor.

[skippydiesel]

A good number of "viewers" but no comment - nobody fitted a fuel tank level sensor?

[Thruster88]

I did not install the old school float and variable resistance senders in my RV. They work very well. Due to the shape of wing tanks they only show 45L per side of the 70l tank when full, once 25l is burned off they show litres remaining very accurately. They are connected to one of these gauges.  

 

[skippydiesel]

Thanks Thruster,

 

I am a little confused; "I did not install the old school float and variable resistance senders " -  do you mean you installed the variable resistance type senders?

 

I have been researching Capacative senders (sometimes known as Princeton Capacitive Fuel Level Probes) but have yet to hear from anyone who has experience of this system (reliability/accuracy/tolerance of fuel type variation).

 

As a back up I have also looked at the latest column float style - mainly marine.

 

I have a three tank system, 30L x 2  wing tanks and a 40lL in fuselage tank. I am particularly keen to have the fuselage tank fitted with a reliable level system, as this will be the primary tank for flying, the wings acting as reserve supply to the centre .

Edited July 19, 2023 by skippydiesel

[Thruster88]

I meant the original builder installed them in 1998, they work very well after all that time. The vertical marine types look good, quality of manufacturer may be a bit unknown.

 

A vid from our local CFI why aircraft have fuel gauges. 

 

 

[facthunter]

Everyone likes to have a fuel gauge but if it's not dependable, it's not a lot of use. Backed up by a fuel flow and total use indication  you're getting somewhere..  Nev

[skippydiesel]

1 hour ago, facthunter said:

Everyone likes to have a fuel gauge but if it's not dependable, it's not a lot of use. Backed up by a fuel flow and total use indication  you're getting somewhere..  Nev

Nev,  no offence mate but your comment does not address my desire to fit a suitable level sensor into my main fuel tank.

 

PS My mistake I wrote 40lL -  its a 40L main tank not a 401L tank 

[facthunter]

My suggestion is it's not suitable IF it's not dependable and simple mechanical ones are the most dependable. A long thin wing is the worst of all to  cater for.. Anyhow Legally NO gauge can be used on it's own to determine fuel quantity. Rocking your wings and being able to see a result helps confidence..   Nev

[skippydiesel]

I would realy like to hear from any home builders, who have sourced & installed a fuel tank level sensor?

 

• Brand?
• Type?
• Gauge type (mine is a Dynon Skyview)?
• Reasons for selection?
• Is it meeting expectations ?

[gareth lacey]

here is the type i am using in my baffled D box f/glass 75 litre wing tanks sensor.htmsensor.htmsensor.htm

[skippydiesel]

Hi Gareth,

 

I have seen these KUS sensors advertised as marine units - not that that that disqualifies them from aviation - may be a plus, as have to contend with more fuel movement than  a car.

 

Why:

• Did you chose this probe/sensor?
• Have you flown with it - how does in perform?
• What instrument/gauge do you have it feeding into?

 

Utilising a magnetic field to control the reed on-off switch, the sender features a long service life and protection against vibration.

Compatible with Fuel Gauges with a 240-33 Ohms resistance.

• 5 SAE standard holes.
• 316G stainless steel main body.
• Rubber gasket provides a liquid tight seal.
• IP67 rated.
• Operating temperature: -40°C - +85°C.
• 300mm tinned wire with a PVC material cover.
• Stainless steel screws included.
• 33mm float cut out.
• Metal Cap Diameter: 70mm
• Internal Diameter inside screw holes: 38mm

Note:

• Length is measured from the underside of the flange to the base of the shaft.
• Be sure to select a matching gauge marked 240-33 Ohms to work with this fuel sender.
• Tank sender should be slightly shorter than the depth of the tank.

PART N

[gareth lacey]

Used these in another build worked fine , Sensotec dual switchable gauge, not flown still building wings, and i only have 160mm depth in tanks and the mechanical ones are not that good in bigger tanks,only from my experience and also easier to get at in top of tank side mounted not very accessible in my build( d box ends areflush to tank

Cheers Gareth

[Markdun]

I have constructed or modified several fuel tanks: all have fuel level gauges.  First one was in a Minimax low wing aircraft with a 20 litre tank (fibreglass) above one’s knees.  Fuel level sensor was a stainless wire (from an old Teleflex cable) with a cork glued onto the lower end. The wire passed through a copper tube brazed on the fuel cap.  The amount of wire seen in front of the windshield indicated the fuel level. It failed once when the cork fell off…fixed with some safety wire.  Very accurate; very reliable.  Slight drag (but whose to say in a 65kt Aircraft).

 Second was a 67 litre tank in my Cygnet SF2A. This tank was composite construction: plywood with epoxy coating and joints filleted and reinforced with fibreglass. The tank is mounted behind your head. It has two fuel level sensors. The primary one is a clear fibreglass ‘window’ facing forward with calibrated markings going vertically up.  Absolutely the best.  The second is a translucent fuel hose (& vapour return line) which is good but not as good as the ‘window’ sensor. Over 1000 hours & 23 years there’s been no failures or problems with the ‘window’. Like I said it’s the best. The translucent hose one requires frequent replacement of hoses and it’s difficult to see the fuel level sometimes.  It also has a good fuel flow and calibrated fuel remaining which you can cross check with your visual and manual calculations as I do (I’m a nervous flyer).

 Third is in a Corby Starlet with a 40 litre aluminium tank which is also ‘above the knees’ like the Minimax.  In this aircraft I installed a high tech resistive float sensor designed for a motor scooter.  I calibrated it (tail down and tail up) and programmed the EFIS accordingly, including fligging around with dampening to reduce wild fluctuations from fuel waves in the tank. It works, but I ignore it & rely on an old Navman fuel flow transducer connected to the EFIS which gives ‘calculated’ fuel level. I’m thinking the knitting needle with a cork would be better.
Fourth, is a J200 I recently restored. It came with the wing root ‘window’ gauge, the wing root mechanical gauge (little round unreadable display) and resistive outputs to the EFIS. None of these work reliably, despite careful calibration and dampening.  One minute I’ve got 70 litres remaining, the next it’s 15 litres.  A piece of paper noting the estimated fuel burn and flight time is a thousand times better. In addition I have calculated fuel level from the fuel flow sensor (expensive ‘Aircraft’ one); but this too is total crap as the fuel flow reads 60lph until the bus voltage reaches 13.9V and then reads as it should…so I trust it as much as I do a politician’s promise.  In the 100 hours in this aircraft I rely on the window sensor, although whenever you climb the fuel sloshes to the rear and you see no fuel in the window…. and I’m thinking a fuel leak and where’s that big paddock?
In summary, first preference is the window in the fuel tank so you can actually see what’s sloshing around. Second preference is the knitting needle with a cork. Third is a piece of paper recording estimated fuel burn and flight time.

 

And by the way, the plywood fuel tank in the Cygnet has NEVER EVER produced any water in the fuel…. Unlike the aluminium tank in the Corby. Just saying.

 

 Cheers, Mark

[skippydiesel]

Thanks Mark.

 

In my aircraft a fuel level tube is a real possibility - not sure where I would locate it on my very small & crowded panel and have no idea what sort of clear hose would allow me to see 95-98 RON (with contrasting backing)& last a good few years before going opaque.

 

My last aircraft (10 years+ and 900+ hrs) had an extraordinarily accurate & reliable gauge but a very diffrent tank & fuel system to what I have now. 

 

I have a fuel flow, remaining gauge but have not yet calibrated it - I have no doubt it will become  my main (after time elapsed/fuel flow) fuel management devise.

 

[lyle janke]

hi 

 i have used a low level warning sensor from these guys . they have good customer focus & can not do enough to help 

see the range of gauges / sensors it take s fuel management to a new level/ thinking 

i have a dual fuel guage /sender set ( previous model ) which i was going to fit to my jabiru but won`t currently with the dynon but maybe if i feel an up-grade /replacement is needed 

https://www.radiantinstruments.com/#top

this may help in your quest for knowledge

[Area-51]

I've heard of a novel fuel quantity device that monitors the mass pressure of the fuel in the tank via a pressure transducer. The sensor is calibrated after installation. As the fuel gets used the pressure weight is less so gauge reads lower. The AC also has a seperate flow rate monitor.

 

Another aircraft I made a 7L custom header tank with a magnetic low level sensor that activates a light on the instrument panel when the header tank drops 250ml, providing 20min flight time at max cruise. The warning lamp also has a test button for preflight checks. A seperate flow rate monitor is fitted as well.

 

 

[Marty_d]

6 hours ago, Area-51 said:

 

 

Another aircraft I made a 7L custom header tank with a magnetic low level sensor that activates a light on the instrument panel when the header tank drops 250ml, providing 20min flight time at max cruise. The warning lamp also has a test button for preflight checks. A seperate flow rate monitor is fitted as well.

 

 

Savannah have that setup, I'm using it in my CH701 too. Basically the header should always be full (gravity fed from wings) so if the sensor at the top goes dry it sets off the warning light on the panel. 

[skippydiesel]

8 hours ago, lyle janke said:

hi 

 i have used a low level warning sensor from these guys . they have good customer focus & can not do enough to help 

see the range of gauges / sensors it take s fuel management to a new level/ thinking 

i have a dual fuel guage /sender set ( previous model ) which i was going to fit to my jabiru but won`t currently with the dynon but maybe if i feel an up-grade /replacement is needed 

https://www.radiantinstruments.com/#top

this may help in your quest for knowledge

 

40 minutes ago, Marty_d said:

Savannah have that setup, I'm using it in my CH701 too. Basically the header should always be full (gravity fed from wings) so if the sensor at the top goes dry it sets off the warning light on the panel. 

Hi Guys,

 

I have the Belite  pressure system(as in weight of fuel above) is what I have and have found it to be completely impractical - works well in stationary aircraft/tank but unable to cope with in tank pressure changes and fuel slop.

[Markdun]

I’m not a great fan of the low level warning light, because if the light comes on, it’s just confirmation and proof you’ve already fucked up;  a bit like the mirror found on many magnetic compasses—-its there so you can see the fool that’s lost.

 

 The problem is that wing tanks being shallow produce a lot of surge and waves and a small vertical distance means a lot of fuel…as opposed to say a cube.  That said, I’ve had experience with a Tecnam that has wing tank  resistive float sensors which were very good, although I didn’t rely on them using fuel flow ‘calculated’ and the bit of paper & Flight time times estimated fuel burn from the POH every 20 minutes to cross check when we flew it across from Kal to Forrest.  We also checked the fuel in the tanks with a graduated stick before taking off as well.

 

I am pretty much sold on the calculated fuel from fuel flow using the EFIS with cross check to a window to see the fuel sloshing around.  Once the fuel flow transducer is calibrated AND you have sorted the Jabiru voltage regulator pulses problems, they are very accurate and the computer happily calculates nifty things like ‘fuel remaining at next waypoint’ and fuel burned per nautical mile (enabling you to adjust throttle for best efficiency.

 

Skippy, the problem with seeing the fuel level in the hose is an issue. Most fuel hose has reinforcing and that makes it even more difficult…but it does work. And if you play around with the size of the holes you can get some damping if it’s subject to surges.

 

 

[facthunter]

Fuel tanks should have BAFFLES to prevent surges that can actually damage fuel tanks.   If you have a "you're out of fuel in five minutes" warning you get a chance to do a quick POWERED "off aerodrome" landing which beats having NO power.  Nev

[Marty_d]

With a 7 litre header tank it's more like 20 minutes. If you're more than 20 minutes away from ANY suitable landing site then planning was probably lacking in the first place.

[skippydiesel]

No offence intended  guys (just venting my frustration)-

 

I appreciate this is an open Forum and submitters are free/will go off on tangent (occasionally guilty),

• That have little/no relevance to the question posed  (eg"fuel tank baffles"???) 
• Self affirming statements about their adherence to basic training techniques (fuel consumed against time and known quantity????) 

It would be nice, helpful even,  if those with the knowledge actually addressed question, before having all the tangential fun.

[Markdun]

Yeh yeh…you can never have too much back up. How many of us fly with a parachute?
 I haven’t removed the 3.5 l header tank low fuel warning light (might save a 100 grams) in the J200, but I wouldn’t have made the effort to install it.  Really a 20 minutes warning because you didnt plan the fuel reserve properly?  The risk is that with that system you don’t plan your fuel because your know you have the 20 minute warning .. its  like ignoring the risk of dingo attack on Fraser Is because you know the bad ones have been killed. As it goes if I’m flying at 2500agl I’ve got 3 minutes at 700fpm sink rate to do an outlandiing…. So to the chagrin of my snobbish GA mates whose Lycosaurs never fail, I fly with an outlanding paddock already picked out & I might actually diverge from the straight line course to ensure it is within gliding distance. Perhaps it’s that NZ gliding hours experience with instructors pulling the tow release at 150’agl, or deploying the spoilers to drop one below the ridge between you and the airfield and calmly saying, ‘it’s your aircraft’.

[Markdun]

Sorry Skip. I think my main point is that if you’ve got wing tanks the fuel level sensor issue is not easy…. hence go for calculated fuel remaining with a good fuel flow sensor & EFIS and beer prepared for the effort to get it setup/calibrated. The low level warning  in my book is a distraction.  All builders know about the free fluid effect and the need for baffles…. Still shallow flat tanks are much harder to ‘gauge’ even with baffles than say a cube.

[skippydiesel]

 

11 hours ago, Markdun said:

Sorry Skip. I think my main point is that if you’ve got wing tanks the fuel level sensor issue is not easy…. hence go for calculated fuel remaining with a good fuel flow sensor & EFIS and beer prepared for the effort to get it setup/calibrated. The low level warning  in my book is a distraction.  All builders know about the free fluid effect and the need for baffles…. Still shallow flat tanks are much harder to ‘gauge’ even with baffles than say a cube.

I am not so concerned with my wing tanks - they have been relegated to reserve supply, feeding my large (whopping 40L) the centre header tank.

I intend flying off the header, so this is the one that I want a fairly reliable level sensor in. Its quite a bit deeper than the wing tanks being 230mm deep at on end and 188mm at the other.

It would have been great having internal baffles -  to  not fit, was the decision of the first builder.

 

I am becoming intersted in the VDO "Dip Pipe Senders". This is a well proven design (used in older Mercedes) using a float on a column, moving up/down two resistor wires, all contained within an aluminium tube, with small in/out holes. The tube "smooths out" the sloshing effect. I have repaired a couple of thes e in MB cars that were 40 years old.

 

https://www.merlinmotorsport.co.uk/files/transfer/technical/doc/vdodiptubespec.pdf

 

The VDO is a bit more expensive than the KUS senders - the KUS have a good reputation (used in marine , as well as automotive applications) but I don't like the look of the exposed float

 

https://kus-usa.com/products/liquid-level-sender/