Fuel Tank Readings

[Releew]

All....

 

I have 92 M20-J MSE version.  Aircraft has typical fuel gauges on the instrument cluster panel and has dial indicating gauges on the wing tanks.  Really nice setup for verification.  Just recently I've starting flying the aircraft for longer duration's.  I am noticing below 8 gallons on the Instrument Cluster I am seeing 10 to 12 gallons on the wing dials.  I am also seeing a very erratic moment on the instrument gauge cluster.  Reading will bounce from 0 to ~8........

 

I do not see an erratic instrument cluster movement when the tanks are in 15 to full range.....  I have also seen the instrument gauge cluster needle stick at 0.  A slight bounce of the rudder seems to bring it back to a reading but still always lower than the dial gauges on the wings.

 

Having said the above........when the tanks have more than ~15 gallons the accuracy between the wing gauges and the instruments gauges are very close.  Does anyone know what creates an erratic instrument reading and inaccurate differences at lower tank volumes?

 

Thanks in advance!   Other than this.....This baby is flying GREAT!

 

Rick

[StinkBug]

I'm not positive on the mechanism used in our planes, but I suspect it's not much different than an automotive fuel sender. Essentially a potentiometer that gives a varying resistance to the gauge. In the case of my C I don't even bother to look at the gauges because they are nowhere near accurate. They almost always show close to full even when they are under half. I did discover today that they will show empty when you run a tank dry (well the left one anyways). I just measure before flying, plan carefully, and also have a fuel flow meter that is quite accurate as long as you tell it how much is in the tank to start with. 

[gsxrpilot]

Yeah, I wouldn't rely on my factory fuel gauges at all. I use the fuel flow and totalizer in my G2 engine monitor and check it against every fill up. 

[Releew]

Thanks......

 

The engineer side of me says there is an explanation for the erratic behavior below 8 gallons and the differential readings between devices.  I believe the instrument cluster is resistance and the tanks are mechanical but there has to be a calibration point/procedure to bring them somewhat in line.............

 

Rick

[Houman]

I'm wondering if one can install gages on the wing tank, any supplier and pricing idea ?

I have problems with my right tank instrument panel gauge, even when it is compltely full, it still only reads 27 g, where it should be reading 32 and my left tank reads properly... I always cut my tripps to less than 3 hours because of my lack of confidence in the gauges and my personal blater

[StinkBug]

Thanks......

 

The engineer side of me says there is an explanation for the erratic behavior below 8 gallons and the differential readings between devices.  I believe the instrument cluster is resistance and the tanks are mechanical but there has to be a calibration point/procedure to bring them somewhat in line.............

 

Rick

 

Well after 40 years of wet and dry conditions I'm not all that surprised that the senders are kinda flakey. I've replaced plenty of senders in cars a quarter of that age. I've never seen a way to calibrate any of those either. Those of you with the little gauges in the wings, can you see those gauges from inside the plane? Those I believe are straight mechanical, where the ones in the panel are electrical. If you can see the wing gauges out the window I'd consider adding them to my plane just to make me feel better.

[DonMuncy]

Yes, you can see one and the co-pilot can see the other. If no co-pilot, with some contortions you can see it too.

[Hank]

I just take off rich, climb to altitude, set power and lean. I fly by my watch, only been really nervous once, flying into the wind and circumventing icing; switched with ~3 gal in the left tank, shut down with almost 9 in the right, after 4:40 in the air.

This is why I won't put a tablet / GPS on the yoke, I need to see the clock. The red settable hands that don't move are key, set them after winding the clock, and it's my reminder to switch every hour and a constant check against total time since start. It's also what I use to figure out flight time for my logbook.

Knowing the plane helps, it's pretty reliable a 9 gph, proven on short breakfast runs and long vacation trips.

Find something that works for you, and verify it every fill up. This is what I don't like about now being hangared at a full service only field, I almost never get fuel receipts, just a charge in dollars on my card. But it's nice to come home late, put her away, then call back later to have her filled up and waiting the next time I want to go fly.

[Releew]

Interesting.....  This must be a difficult question that has had little discussion.  There is generally much more technical input.

 

Thanks for comments!  I'll start with looking for null-point in the sensor (sending unit.)  I'm certain something is worn out and creating this condition.  Will post my findings......  This has to be occurring on more than my aircraft...

 

Thanks!

 

Rick

[joepilot]

Ive only had my MSE a few months, but after detailed fuel logs, I have an idea what the guages are telling me. ie, the wing guages read X gallons high, the left cockpit guage reads X gallons low, etc. They are consistent. But I have my Shadin fuel computer tweaked to within 1/10th gallon.

I personally wouldn't waste $ on fixing guages, unless they're inop, or you don't have a fuel computer. GA fuel guages are not volume sensing specific gravity electrical current sensors (like an airliner). I just don't think they are going to be +/- 1 gal precise.

-joe

[Deb]

This thread discusses fuel senders made by a company called CIES. Theysupply senders for Cirrus. The senders are TSO'd. They are not yet STC'd for Mooneys. I spoke with the president of the company, Scott Philiben; he knows Tom Bowen at Mooney and he hopes to get them STC'd for Mooney.

Engineering types might give him a call to determine whether his senders are in fact more accurate and robust.

http://www.beechtalk.com/forums/viewtopic.php?f=7&t=103920

[FloridaMan]

I don't trust panel mounted fuel gauges at all. Even my newly installed EDM-900 I believe will confidently read a precise, but inaccurate gallon value. The wing-mounted dials seem to be much more trustworthy, even in flight. In level cruise, they seem to read a couple gallons lower than when on the ground and stop reading at just under around 10 gallons. I periodically check them in cruise to validate against my totalizer and to verify there's fuel in the tank. 

[Richard Allen]

has anyone experience in adjusting the gain and null pots on rochester fuel guages used on 19190 m20j?

[A64Pilot]

EI also supplies a decent fuel sending unit, if you don’t use theirs and keep the stock resistance ones when you install say an MVP-50 you will need another box to convert your resistance signal.

Only aircraft fuel systems that I've seen that had gauges I’d trust work off of the fuels capacitance and I don’t know of any of those systems available for small aircraft.

A lot of the problem stems from the shape and depth of aircraft fuel tanks, they are relatively shallow and one inch often means a lot of gallons and due to the dihedral, one inch is a variable amount of fuel too.

‘When setting up an MVP-50 for example there are several calibration points to account for this, I picked every 5 gls on another aircraft, but I don’t believe you can do that with a standard fuel measuring system.

‘If you rely at all on you fuel quantity system, I promise that it will lead to a bad outcome one day.

‘It’s not a difficult problem to solve, but to my knowledge no one has.

A problem with using the fuel used to compute fuel remaining is if you ever fly with partial fuel loads to carry more weight, it’s not really possible to be certain how much you started with. For that reason I always start with topped off tanks and build in several conservative measures. 

In short the factory fuel quantity measuring system is for entertainment only. I believe the FAA only requires it to be accurate when the tanks are empty

 

In other words, I wouldn’t waste my money

Edited May 29, 2021 by A64Pilot

[moosebreath]

I just adjusted my panel gauges on Thursday, my right gauge was reading about 28 gallons when full and it was driving me crazy.

It is just a simple span and zero adjustment.  The best way to set zero is with the tank empty.  How you do that is an “exercise for the maintainer”.  Do it first.

Set the span on a level surface with the tank full.  You will have to exercise the span screw a bit and then make several adjustment trials to get it to read properly.  Mine did not have a simple linear change as you might expect.  The adjustment seems to persist once it is made however.

Be VERY VERY careful not to overtighten the gauge locking screw.  Use two fingers and stop when it is only a bit snug.  If you go further you will break the corner of the plastic gauge face.  Rochester will be glad to make you one to order for around $175 plus shipment.  Ask me how I know …

Once the above is done use the fuel totalizer and ignore the gauges.   I have my totalizer calibrated to within a few tenths of a gallon out of 50.  That is better than 1%.  It is easy to do and the procedure can be found searching here. The panel gauges are reliable within 5 gallons or so, maybe.

 

 

[Yetti]

On 5/29/2021 at 8:15 AM, Richard Allen said:

has anyone experience in adjusting the gain and null pots on rochester fuel guages used on 19190 m20j?

I would guess you could add resistors to the circuit.  More than likely the sender units 2 per side need some cleaning.   Adding wing gauges from Rochchester will help you know.   I prefer the stick.  The good paint stick.   Keep it and a sharpie in the baggage area.   Draw a line.  Fill up subtract from what the pump says and write it on the stick.  It's kind of not linear. using the stick placed the same place each time.   I like to get out and stretch ever 2 hours anyways.

[A64Pilot]

If you use a stick and they are good, be darn sure to use a stick long enough so that it can’t be dropped into the tank.

‘I had a heck of a time fishing one out of a C-210’s wing.

‘Oh, and back the totalizer up with a clock, only time you can have too much gas is if your on fire.

Edited June 1, 2021 by A64Pilot

[laytonl]

On 3/8/2015 at 8:07 PM, Releew said:

All....

 

I have 92 M20-J MSE version.  Aircraft has typical fuel gauges on the instrument cluster panel and has dial indicating gauges on the wing tanks.  Really nice setup for verification.  Just recently I've starting flying the aircraft for longer duration's.  I am noticing below 8 gallons on the Instrument Cluster I am seeing 10 to 12 gallons on the wing dials.  I am also seeing a very erratic moment on the instrument gauge cluster.  Reading will bounce from 0 to ~8........

 

I do not see an erratic instrument cluster movement when the tanks are in 15 to full range.....  I have also seen the instrument gauge cluster needle stick at 0.  A slight bounce of the rudder seems to bring it back to a reading but still always lower than the dial gauges on the wings.

 

Having said the above........when the tanks have more than ~15 gallons the accuracy between the wing gauges and the instruments gauges are very close.  Does anyone know what creates an erratic instrument reading and inaccurate differences at lower tank volumes?

 

Thanks in advance!   Other than this.....This baby is flying GREAT!

 

Rick

Rick, I have also have a ‘92 J.  There are two 30 ohms resistive senders in each tank that are wired in series.  You might have an issue with the senders at the lower end of the pot.  You may want to remove the fuel gauge and check the resistance from the tank senders.  You could have someone move the float arm up and down and see if the resistance is linear.
 

if you believe it is a gauge issue, air parts of Lock Haven Pa does a good job repairing them.

this link shows how it is set up.

https://1drv.ms/u/s!ApFurD_oU_HRgf0rkFbyTru6GyiWvQ

 Lee

[larrynimmo]

I don’t need to stretch...I use my iphone11 and take a picture of the gage with a zoom setting

[Ulysse]

My plane is supposed to have 75 gal usable fuel. I also have unreliable gauges, with the right one showing 27 when full and the left one always showing full. I have a flap on top of the tank and I wonder when I should consider the tank to have reached 37.5 gal: when fuel is just level with the flap or until it almost overflows ?

[Warren]

I have a 231 and I have to be very patient and fill to the limit of overflowing to get close to the rated capacity -- mine is a little more confusing with the extended range tanks.  However, I believe that you need to squeeze in every ounce to get to rated volume on the K models.

[McMooney]

PPL CFI beat it into my head, panel fuel gauges are NEVER accurate, never use.  20+ years never have.

time and fuel flows are all i use, verified after every flight.

  I think someone said something about a cies fuels sender that's super accurate

[carusoam]

On 6/4/2021 at 10:51 AM, McMooney said:

PPL CFI beat it into my head, panel fuel gauges are NEVER accurate, never use.  20+ years never have.

time and fuel flows are all i use, verified after every flight.

  I think someone said something about a cies fuels sender that's super accurate

modern updates make it possible to have accurate instruments...

Nice to have when your time and FF miss a beat...  

 

I think your CFI may have meant in their school planes....

He probably also included that the FAA thinks the gauge only needs to be accurate on E....   and that isn’t quite true either...

PP thoughts only, not an instrument guru...  but there is a guy here that sells those digital fuel floats for maximum accuracy...

Best regards,

-a-

[M20F-1968]

On 4/5/2015 at 1:42 PM, FloridaMan said:

I don't trust panel mounted fuel gauges at all. Even my newly installed EDM-900 I believe will confidently read a precise, but inaccurate gallon value. The wing-mounted dials seem to be much more trustworthy, even in flight. In level cruise, they seem to read a couple gallons lower than when on the ground and stop reading at just under around 10 gallons. I periodically check them in cruise to validate against my totalizer and to verify there's fuel in the tank. 

The wing mounted gauges are meant to be accurate as to volume only on the ground.  

A fuel totalizer (assuming the K factor is adjusted correctly) is a great help.  Keeping track of how much fuel actually used each 1/2 hour is very helpful.  The fuel flow is measured constantly with a small water-wheel type device in the fuel line.  A note pad and timer is all the extra equipment needed.  

The Cies senders are much improved and consistent.  Completely Digital set-up is best.

John Breda

[hoot777]

One problem with using fuel flow instruments is it will not show you a fuel leak. It happened to my dad in a V35 BO. The fuel drain came off in flight and he made a precautionary landing in Chattanooga . The gauge did show empty and it was. I have a M20 G and only one gauge is trustworthy to a point. Time your fuel burns and always be conservative. Fly safely.