Fuel Gauge & Sender

[skippydiesel]

Attention Brain Trust - would very much appreciate your recommendations  (Make & type) for a fuel gauge & sender kit. The gauge just seems to be a question of choosing the style & matching (Ohms) it to the correct sender. My difficulty is selecting an appropriate type of sender  - ALAS Lever Arm Adjustable  -  Reed Switch (come in variose lengths to suit tank depth) and Tube (others??)

[skippydiesel]

Has no one fitted/replaced a fuel gauge/sender in their aircraft ?

[spacesailor]

Sight tube, seems reliable !.

The old K I S 

Spacesailor

[Blueadventures]

2 hours ago, skippydiesel said:

Has no one fitted/replaced a fuel gauge/sender in their aircraft ?

I am not a fan for these for my flying, plus in the marine game of many years; found the sensor parts wear and readings loose accuracy.  For my aircraft I could fit sight tubes and also to increase the fuel available monitoring I placed a clear (Savannah collector container) surge tank behind the right seat so I can look behind and see the amount of fuel that's in it.  Allows checking to see its full; has an air bubble in the top so easy to see contents level at 6 litres.

 

Had a flow meter in the Skyfox and it failed eventually.

 

Fuel flow meters are nice but when getting low you need exact quantity left and available information.  I do notice in mine that when wing tanks are low the collector tank does not fill at the rate of engine fuel usage at high rpm.  To do' I expect' with the low amount of fuel in the above head height wing tanks and the air that is displaced from the collector tank not getting back up the feed tube.  I slow rpm a little and all good again.   

 

If I could not see the contents level in the collector / surge tank I would not be aware of this fact before the low fuel light came on.

[skippydiesel]

Personally I like to use several systems for fuel remaining -  total -L/H x time elapsed, dipping the tank, fuel computer and fuel gauge.  I never feel comfortable even getting close to my fixed reserve (45 minutes). There is no gauge in the aircraft I am considering, so would like some advise on gauge/sender types that others have experience with.

[IBob]

Hi Skippy, I can't comment on senders and gauges. But I would say that a receiver or collector tank, as described by Blueadventures above, is a very simple and worthwhile fix for various known gotchas, including momentary unporting of main tanks, and exhausting available fuel for various reasons on takeoff or climbout.

The one he is using is 6L capacity, and fitted with a level switch at the top, giving approx 20minutes of low fuel warning, which is 20 minutes to sort out whatever your problem is and/or decide where to land.

I can't see the one in my aircraft, so am unable to visually check for air, but I do routinely check both the dashboard indicators (LED, flashing) and the switch.

FWIW they are more usually piped up now with one incoming at the top, and one outgoing breather (also at the top) to avoid captive air pockets in the tank. And in my aircraft the bottom of this tank is the low point in the system and has an external bleed valve. Outgoing fuel is taken from a point just above the bottom of the tank.

[Blueadventures]

45 minutes ago, IBob said:

Hi Skippy, I can't comment on senders and gauges. But I would say that a receiver or collector tank, as described by Blueadventures above, is a very simple and worthwhile fix for various known gotchas, including momentary unporting of main tanks, and exhausting available fuel for various reasons on takeoff or climbout.

The one he is using is 6L capacity, and fitted with a level switch at the top, giving approx 20minutes of low fuel warning, which is 20 minutes to sort out whatever your problem is and/or decide where to land.

I can't see the one in my aircraft, so am unable to visually check for air, but I do routinely check both the dashboard indicators (LED, flashing) and the switch.

FWIW they are more usually piped up now with one incoming at the top, and one outgoing breather (also at the top) to avoid captive air pockets in the tank. And in my aircraft the bottom of this tank is the low point in the system and has an external bleed valve. Outgoing fuel is taken from a point just above the bottom of the tank.

Agree IBob, I did revise my original fit up described before by plumbing both fuel feeds from the wing tanks (2 at 52 litres each) into one of the collectors top fittings and the other top fitting is plumbed to the top starboard wing tank contents sight tube fitting ( idea from Mark Kyles info some time back). This sorted the delivery rate when tank in the lower 25% left range.

[skippydiesel]

In short I dont know if a header/collector tank would be appropriate to the aircraft I am considering - it has a single large fuselage tank, located behind the sets (similar to a small Jab) in the shape of a rectangular inverted U. Primary fuel supply drawn of the bottom of one leg of the U, while the other acts as a reserve (KISS).

 

My very provisional concept is to mount a fuel level sender through the top surface, on the reserve side.

 

Without the benefit of others experience,  I am favoring the Tube first and the Reed Switch type second, as they have the "look" of  systems less impacted by fuel movement/slop

[Thruster88]

18 hours ago, skippydiesel said:

In short I dont know if a header/collector tank would be appropriate to the aircraft I am considering - it has a single large fuselage tank, located behind the sets (similar to a small Jab) in the shape of a rectangular inverted U. Primary fuel supply drawn of the bottom of one leg of the U, while the other acts as a reserve (KISS).

 

My very provisional concept is to mount a fuel level sender through the top surface, on the reserve side.

 

Without the benefit of others experience,  I am favoring the Tube first and the Reed Switch type second, as they have the "look" of  systems less impacted by fuel movement/slop

The fuel tank description caused me to recall this accident. https://www.atsb.gov.au/publications/investigation_reports/2016/aair/ao-2016-077/

We can all learn a lot from this report.

[skippydiesel]

Thanks T88 - you reminder of this incident, as with all completely avoidable fuel exhaustion incidents, is welcome but what of my fuel level monitoring system ?? I would like to learn a lot about this.

[skippydiesel]

Just heard about a fuel sender that operates on head pressure - anyone know anything about this?

[IBob]

Skippy, did you look at Appendix A, Fuel System Additional Information?

It goes into the fuel system in detail, and sounds to be using a tank similar to what you describe. And it seems to me it gives a good view of the possible shortcomings of such a system, at least as configured in that particular aircraft, where they had quite different readings on the ground and in flight, plus confusion as to whether fuel figures included the reserve side quantity. Add to that the possibility of unporting on low fuel in a hard climb, and uncertainty around actual quantities due to the possibility of fuel sloshing from one side to the other in flight.

I would add that I was surprised to see the fuel tank and level tube have separate vents to atmosphere. With that arrangement, even a very minor difference in airflow round the two vents will result in an incorrect level reading in flight.

[IBob]

Hi again, Skippy. We used to use pressure sensors to gauge level in industrial hot and cold water systems, but these were big tanks, and even then the transducers (senders) had to be quite sensitive.

In very round imperial numbers, 1 atmosphere pressure of petrol would be 40ft deep = 14.5 PSI

So if your tank was, say, 32" tall, your pressure gauges would have to detect a range of 0 to 0.96PSI, from empty to full.
This can certainly be done, but in practical terms those are quite fine pressure measurements, and keeping such a sender calibrated and free of temperature drift would be quite challenging.
 

[skippydiesel]

Thanks IBob - the one that I had heard about is the Belite Fuel Probe, being sold by Aircraft Spruce  https://www.aircraftspruce.com/pages/ep/fuelsender/belitefuel10-05866.php

 

I agree with all the points you have made - cant see how it would work reliably in a small fuel tank

[IBob]

9 hours ago, skippydiesel said:

Thanks IBob - the one that I had heard about is the Belite Fuel Probe, being sold by Aircraft Spruce  https://www.aircraftspruce.com/pages/ep/fuelsender/belitefuel10-05866.php

 

I agree with all the points you have made - cant see how it would work reliably in a small fuel tank

They certainly claim a pretty impressive spec. for that device, Skippy: and to be fair, it does sound as though it would do the job. I see it also incorporates filtering, which will be some digital or analog system for averaging readings over a period, providing a steady reading if the fuel is sloshing around.

 

About all I can add is that we learnt to select transducers of an appropriate material for the liquid being measured. We generally overspecced them in terms of range for improved durability (eg if expecting to measure 0 to 10PSI, we would install a 0 to 20PSI transducer). We learnt to provide a warm dry environment where possible (the body of the instrument will 'breathe' with varying atmospheric pressure, and is likely to fail earlier if 'breathing' moisture or contaminants). And our experience was a significant initial failure rate (maybe 10%?) but with surviving units usually providing good long service (which would seem to indicate some critical potential flaw in manufacturing).

This was in very large hot and cold water tanks and also in industrial refrigeration plants with 4 to 6 compressors, where each compressor would have 5 or 6 transducers, and the whole engineroom would then have a further 3 'master' transducers.

I hope and expect the technology has moved on greatly since then: industrial transducers is a huge and constantly evolving industry

 

[Blueadventures]

The Europa method of a forward placed sight tube that is influenced by pitch errors is a crap system, especially in the low contents range; say under 25% remaining. Need the sight tubes on the tank and visible from seat via Mk1 eyeball, and if not possible perhaps fit an auto reversing camera to view it.

Edited March 20, 2021 by Blueadventures

[kgwilson]

Fuel gauges are notoriously inaccurate whether they are in a motor vehicle or anything else. Depending on damping you get variable readings with changes in pitch, bank and yaw. Wing tanks are terrible to try and gauge as they are long and shallow.

 

A gauge will give you an indication, that's all. When I built my aircraft I put in an automotive VDO gauge with an adjustable float on an arm similar to a ballcock arrangement and set it to show empty when empty, full when full at 1/2 when actually half full. Then I just added fuel on level ground 5 litres at a time and recorded the position of the indicator against the quantity till full at 100 litres & stuck the chart on the panel next to the gauge. So that gives me a pretty good guess of how much fuel I have when flying straight and level. The indicator did not even start to move till I got 15 litres in (there is a 4 litre sump before any fuel gets to the bottom of the tank) and due to tank shape the gauge marks were completely inaccurate.

 

I also have 2 wing tanks which I use on long trips to transfer fuel to the main fuselage tank & know how long it takes to transfer the 35 litres in each to the main. As it transfers I see the gauge indicator go up. When a wing tank is empty the Facet electric transfer pump starts to clatter & I can actually hear it.

 

My calibrated dip stick is the only real accurate indicator and then just knowing the fuel burn is probably the most accurate measure when flying.

 

A good fuel flow gauge will tell you how much you have used but my setup & method is good enough for me. My legal reserve is 12 litres but I have never got anywhere near that as I always want a minimum of 20 litres left, and almost always more.

[skippydiesel]

9 hours ago, kgwilson said:

Fuel gauges are notoriously inaccurate whether they are in a motor vehicle or anything else. Depending on damping you get variable readings with changes in pitch, bank and yaw. Wing tanks are terrible to try and gauge as they are long and shallow.

 

A gauge will give you an indication, that's all. When I built my aircraft I put in an automotive VDO gauge with an adjustable float on an arm similar to a ballcock arrangement and set it to show empty when empty, full when full at 1/2 when actually half full. Then I just added fuel on level ground 5 litres at a time and recorded the position of the indicator against the quantity till full at 100 litres & stuck the chart on the panel next to the gauge. So that gives me a pretty good guess of how much fuel I have when flying straight and level. The indicator did not even start to move till I got 15 litres in (there is a 4 litre sump before any fuel gets to the bottom of the tank) and due to tank shape the gauge marks were completely inaccurate.

 

I also have 2 wing tanks which I use on long trips to transfer fuel to the main fuselage tank & know how long it takes to transfer the 35 litres in each to the main. As it transfers I see the gauge indicator go up. When a wing tank is empty the Facet electric transfer pump starts to clatter & I can actually hear it.

 

My calibrated dip stick is the only real accurate indicator and then just knowing the fuel burn is probably the most accurate measure when flying.

 

A good fuel flow gauge will tell you how much you have used but my setup & method is good enough for me. My legal reserve is 12 litres but I have never got anywhere near that as I always want a minimum of 20 litres left, and almost always more.

Ditto - except that I calibrated my gauge, by sticking an arc of paper to the face and marking the 10 L increments as indicated, as I filled the tank, using an accurate measuring jug.

 

As luck would have it, my gauge turned out to be remarkably accurate & consistent  (checked regularly over time) - I still only used it as an indication of fuel level and to facilitate in flight fuel transfers.

[Yenn]

I found that when I built the RV4 that the sender which is the same as KGWilsons could not be accurate at empty. before it reached that stage the float was on the bottom and there was still about an inch of fuel there and also because of the dihedral, there was even more inboard of the float. I calibrated the gauge for in flight  level and on ground level, then hardly ever used it. Not having a good fuel gauge forces you to keep tabs on fuel use with the dipstick and you get a quick indication if anything changes.

[skippydiesel]

7 hours ago, Yenn said:

I found that when I built the RV4 that the sender which is the same as KGWilsons could not be accurate at empty. before it reached that stage the float was on the bottom and there was still about an inch of fuel there and also because of the dihedral, there was even more inboard of the float. I calibrated the gauge for in flight  level and on ground level, then hardly ever used it. Not having a good fuel gauge forces you to keep tabs on fuel use with the dipstick and you get a quick indication if anything changes.

Sooooo! Is the moral of the story that the lever type sender, is not the best for this application ?/

 

This lends weight to my ill informed observation that the "Tube"  and "Reed Switch" type of senders have the "look" of  systems less impacted by fuel movement/slop and may in fact, when suitably specified (length) be able to indicate true levels from empty to full.

[Bruce Tuncks]

On my old Jabiru, the fuel gauge consists of a scale stuck to the outside of the translucent fuel tank. Accurate and reliable...  BUT at low fuel, it is very hard to read.

I have been thinking of arranging for a raised U tube ...  one side connected to a tube which went from the top of the tank to the bottom. the other side to the top of the tank.  To read it, you would use a squeeze bulb which pumped air into the long tank tube, until the U tube stabilized on account of blowing bubbles from the tank bottom. The stable reading would show exactly the level of fuel above the bottom of the long tube.

This U tube could be anywhere you liked.

I would love to hear any comments/criticisms. it is not often that I want to know the fuel left in the tank, but gosh sometimes you REALLY want to know.

The other possibility is a sender stuck onto the outside of the tank which reads the prescence of liguid on the other side. You could have one at say 10 liters and another at 5 for example.

[skippydiesel]

22 hours ago, Bruce Tuncks said:

On my old Jabiru, the fuel gauge consists of a scale stuck to the outside of the translucent fuel tank. Accurate and reliable...  BUT at low fuel, it is very hard to read.

I have been thinking of arranging for a raised U tube ...  one side connected to a tube which went from the top of the tank to the bottom. the other side to the top of the tank.  To read it, you would use a squeeze bulb which pumped air into the long tank tube, until the U tube stabilized on account of blowing bubbles from the tank bottom. The stable reading would show exactly the level of fuel above the bottom of the long tube.

This U tube could be anywhere you liked.

I would love to hear any comments/criticisms. it is not often that I want to know the fuel left in the tank, but gosh sometimes you REALLY want to know.

The other possibility is a sender stuck onto the outside of the tank which reads the prescence of liguid on the other side. You could have one at say 10 liters and another at 5 for example.

Yep! Ye old sight /level tube is about as KISS as you can get. They can work very well in high wing aircraft (as long as the tube remains clear and there is a background that will highlight the fuel.

Low wings and or tank in fuselage systems dont seem to be compatible - the sight tube is sometimes in the foot well - dark & hard to see. Possibly worse, behind the pilot, necessitating a high degree of flexibility to obtain a view - usually accompanied by the aircraft making a steep dive/climb turn - tad unnerving.