C152 Fuel gauges...

[Vee One...Rotate]

Very quick question.

Why are the fuel gauges in a 152 of no use whatsoever? Is it just me who thinks they tell you absolutely nothing. I was practicing some solo departures/rejoins yesterday and all the fuel gauge needles did all flight was crazily jump from empty to full in a mocking fashion.

Of course, the visual check during the walkaround was enough to tell me I had plenty of fuel - I just found myself wondering who's bright idea it was to design a completely useless instrument like this...!

Is the C152 notorious for this? Or was my particular a/c a bit rubbish? Do most a/c in this class have similar issues with fuel gauges?

Just curious...I know my car gauge is pretty good (point taken that it's not buffeting around at 2000 ft though!) and I know that most airliners have pretty snazzy systems.

Thanks folks,

V1R :ok:

[Kolibear]

ALL light a/c gauges are notoriously, infamously and reliably, unreliable.

In our group aircraft, when the gauges read 1/4 full, we know we have half tanks.

[distaff_beancounter]

I have often wondered why light aircraft manufacturers cannot fit fuel guages that are at least somewhere near accurate. :*

When I was learning to fly, a very aged instructor gave me the following advice, which I have always followed:-

"Always assume that the faul gauges are inaccurate -
Always check visually or use a dipstick before flight -
And the only time that you should believe the guages -
IS WHEN THEY ARE ALL HEADING RAPIDLY TOWARDS EMPTY!" :{

[Genghis the Engineer]

It is actually in the regulations against which most light aircraft are certified that the fuel gauge must be accurate when reading empty. There's no requirement for them to be accurate at any other time.

Technically, you could therefore just fit a sticker that reads "TANKS EMPTY", and be quite legal (as well as very nearly as useful as the standard Cessna fuel gauges).

Piper gauges are a little better, but only a very little.

For reliability, you want a float (a la Aeronca) or a sight tube (a la Piper Cub).

G

[dublinpilot]

Is there something inherently wrong in their design, or are they simply badly calibrated, or just old and worn out?:confused:

dp

[LowNSlow]

Swiftly dons anorak:

Genghis, the Super Cub has a sight level, the Cub has a float and wire with an ickle flag on top.

Anorak off, door opening, departure imminent

PS The Auster has an accurate rotary fuel guage that looks like a compass. Mine reads accurately as long as you remember it UNDERreads by 3 Imperial gallons on the ground and 2 in the air.

[deice]

In my experience, the more expensive the aircraft the better the fuel gauges.
The gauges in the Commander 114B I fly seem to be spot on all the time. In fact, when I dial in 12gph on the FF indicator that is exactly what I get and the gauges both agree.

But then, it doesn't cost like a C150...

Mind you, all Cessnas I've flown, 150, 172, 177, 182 all have windshield wiper gauges... I think it's part of the design, it keeps the mist off the back of the glass so that you can see the wipers darting back-n-forth ... :E

[ShyTorque]

Perhaps the gauges don't have effective voltage regulators? Fuel slopping about in the tank causes the float sensor to bob up and down with the varying fuel height, and the gauge needle will follow suit if there is no electrical damping.

Even Reliant Robins have voltage regulators to damp the readings....

[Genghis the Engineer]

Genghis, the Super Cub has a sight level, the Cub has a float and wire with an ickle flag on top.
Ah, you've found me out now - I've only ever flown a PA18, and not a J3.

G

[MLS-12D]

I know that most airliners have pretty snazzy systems.I guess. But that doesn't make them especially reliable. Hence, the infamous Gimli Glider (http://en.wikipedia.org/wiki/Gimli_Glider) incident.

[Wide-Body]

You can make accurate fuel gauges.

Our YAK 52 has very accurate gauges. Mind you they need to be with only 120 litres and 360HP. The gauges will show you the minimum fuel onboard within a few litres.

Silly questions to ask a YAK pilot on landing "Do you need any fuel!!!!"

(I know there is a mod option)

All the best

Wide

[Windy Militant]

For reliability, you want a float (a la Aeronca)

As long as you don't stick a ping pong ball onto the end of it to make it easier to see! A cautionary tale I was told by a well known Aircamper owner. He was cheerfully flying along thinking how well the old girl was doing on fuel. That is until he throttled back to land and the ball shot from view like a lead balloon. The extra drag on the ball caused the rod to bind in the hole and not fall along with the fuel level. Luckily for him his fuel calcs were bang on so he had sufficent to reach his destination. Even Luckier for him he decided to stop for lunch and not to press on a little further as his fuel state was so good! :\


PS The Auster has an accurate rotary fuel guage that looks like a compass.

It's accurate if the indicator dial is properly riveted to the float mechanism and not free to rotate randomly as ours was. We very often found it indicating empty when we'd just filled the tank or Full when we'd dipped the tank and knew it was empty. Very confusing :confused:.
I don't know if all Austers have, it but ours has two scales. There's one on the top face for Level Flight and a smaller one round the circumference for ground attitude. ;)

[FlyingForFun]

The Europa I used to own a share of had a very reliable capacitance-type guage - the same type, as far as I know, as airliners use. It had to be accurate, though - there was absolutely no way of visually checking the fuel. We did debate fitting some kind of sight tube, but the guage proved to be reliable enough that we decided it wasn't necessary.

Likewise, I've just done a couple of hours flying in a Seneca 5, which is a very nice aeroplane with just a small problem regarding its load-carrying capacity. With more than 1 person on board, it's practically impossible to put in enough fuel to be able to see the fuel from the fuel-filler cap, so again the only way of knowing how much fuel is in it is to check the guages. Not sure what type of sensor they use (I'm sure I could find out if I had the manual to hand, or maybe someone knows?), but they did seem to be pretty reliable.

So I guess it comes down to necessity - where it's not possible to see the fuel, the manufacturer puts in a decent guage. In a C152, they decided to go for the cheaper option because you can clearly see how much fuel you've got left, especially with the aid of a dipstick?

FFF
-------------

[MikeJ]

This is a subject close to my heart. I just cannot accept that the authorities should allow certified aircraft to only be required to have accuracy in its guages when empty. Presumably, with one gallon of usable fuel, its legal if it shows half full. No one would buy a car without an accurate fuel guage, and they are excellent. And cars slosh fuel around in cornering, braking etc just as much as aircraft do!

Remember the Seneca at Shoreham crashing with no fuel. None of the prosecution or defence rested on any consideration of the fuel guages.

In my permit aircraft, getting VERY erratic readings, I replaced the senders with capacitance type (see comment previously by a Europa owner). I could not believe the gimcrack, Heath Robinson, devices which serve as aircraft fuel level senders, which I removed. The cap. type has no moving parts, physically prevents sloshing affecting the reading, without any electrical damping. For me, they have been perfect for many years. Like many aircraft, including the Seneca, I cannot visually inspect, or dip, contents of main tank when less than nearly full.

Why not mount a campaign to require all aircraft to have reasonably accurate guages? After all, Number One reason for engine failures is fuel exhaustion or mismanagement!

Perhaps more comment from Genghis?

Mike.

[justinmg]

Out of interest, is there a preferred method for checking fuel on a Robin 2160?

[Genghis the Engineer]

MikeJ I couldn't agree with you more. It's an area where I regularly exceed my CAA delegated authority by insisting upon accurately and reliably calibrated fuel gauges - it is not difficult to do, and for little cost and complexity adds enormously to the safety of the aeroplane.

One point by the way, capacitance type fuel gauges can be a bit erratic as the fuel companies modify the mix through the year, giving significantly different readings. Personally, for little AVGAS or MOGAS drinking aeroplanes, I much prefer floats or sight tubes.

Incidentally, this (http://www.avnet.co.uk/lts/pages/fuelgauge.htm) is what you'll find fitted to many microlights these days - cheap, reliable, and accurate enough for any reasonable purpose. Hard to see why something like that can be fitted to a microlight, but a C172 costing several times as much as the highest spec microlight can't manage the same degree of accuracy.

G

[IO540]

The only plane I ever saw with usable fuel gauges was a current model TB20. On that, they are accurate to the thickness of the needle (which is very thin). They are probably accurate to 3% or so.

So it can be done. But it costs more - they are capacitive gauges. The standard gauges are of a useless design which isn't any good even when brand new.

Presumably, the reason why fuel gauges are crap is because they can be; a "pilot showing proper airmanship" should not be using them; he should plan the flight properly. One can't just pop into a petrol station when the gauge reads a bit low.

I think one should still have working gauges, to cover the possibility of a gross error elsewhere, and to enable reasonably accurate tank switching.

But it won't happen. People operating C152s and similar old metal have, for the most part, no money (well not after they paid for their £5000 suprise annual) so there is almost no market for an upgrade kit. Same goes for most things which could improve GA ops.

Somebody wishing to know how much fuel they have can buy a totalising flowmeter (e.g. Shadin). They come with certification for a lot of planes and once set up they can be accurate to < 1%. Link it to a decent GPS and you get a projected FOB (fuel on board) at the programmed destination. (Actually the system assumes the current GS for the remainder of the flight, but it's still pretty good).

You just have to enter the FOB when you fill up, and assume that nobody plays with the FOB setting thereafter (a great incentive to do that when renting the plane "dry" and I even know of one instructor who used to do that - I caught him through the EDM700 engine log).

[Windy Militant]

The main problem is that to install different fuel gauges onto a C of A aircraft would require the submission of a mod to the CAA. Now fuel gauge senders that were out of date when they were fitted to Austin A40s and Morris Minors have a a bit of paper saying that they're approved for use on aircraft. The high tech ones mentioned here probably don't which is why PFA types and Microlights have decent gauges and GA types don't.

I agree that fuel burn should be calculated for each trip however fuel gauges can warn of other problems, a lost fuel cap, a leaking drain cock or a leaking tank. Faults like these may not be visible from the cockpit in flight, so the gauges may be the first indication of a problem.

[IO540]

In principle, anything can be approved if somebody pays for it. These old planes (Cessnas, PA28s, etc) have been around for decades and have had useless fuel gauges all along, from brand new.

For some reason, certified replacements that are any better are not available fr most of these types.

If there were a lot of desperate buyers, the volumes would be very substantial. With an STC, one could sell all over the USA (which is perhaps 90% of the world market) and the STC holder could then apply to EASA and flog the stuff all over EASA land.

I would guess this has not happened because the market is not perceived as being there. The CAA is not the issue - they preside over a fleet which is barely relevant, commercially. This would be done under FAA, if anywhere.

[Onan the Clumsy]

It is actually in the regulations against which most light aircraft are certified that the fuel gauge must be accurate when reading empty.

[:8]

I thought the requirement was to be acurate when the tanks were empty. In your example, you could have empty tanks, with a full gauge and be legal.

...and to become overbearingly pedantic, here's a truth table

Guage Tank Requirement Instead of
----- ---- ----------- ----------
E E pass pass
E NE pass fail
NE E fail pass
NE NE pass pass

where E = empty, NE = Not Empty


Therefore placarding the guages to read "tanks empty" would work with my scenario and not yours.

[/:8]


:} :ugh:

[Genghis the Engineer]

From FAR-23, the code most often used for light aeroplanes...



Sec. 23.1337 Powerplant instruments installations

(a) Instruments and instrument lines.
(1) Each powerplant and auxiliary power unit instrument line must meet the
requirements of Sec. 23.993.
(2) Each line carrying flammable fluids under pressure must--
(i) Have restricting orifices or other safety devices at the source of
pressure to prevent the escape of excessive fluid if the line fails; and
(ii) Be installed and located so that the escape of fluids would not create
a hazard.
(3) Each powerplant and auxiliary power unit instrument that utilizes
flammable fluids must be installed and located so that the escape of fluid
would not create a hazard.
(b) Fuel quantity indication. There must be a means to indicate to the
flightcrew members the quantity of usable fuel in each tank during flight. An
indicator calibrated in appropriate units and clearly marked to indicate
those units must be used. In addition:
(1) Each fuel quantity indicator must be calibrated to read "zero" during
level flight when the quantity of fuel remaining in the tank is equal to the
unusable fuel supply determined under Sec. 23.959(a);
(2) Each exposed sight gauge used as a fuel quantity indicator must be
protected against damage;
(3) Each sight gauge that forms a trap in which water can collect and
freeze must have means to allow drainage on the ground;
(4) There must be a means to indicate the amount of usable fuel in each
tank when the airplane is on the ground (such as by a stick gauge);
(5) Tanks with interconnected outlets and airspaces may be considered as
one tank and need not have separate indicators; and
(6) No fuel quantity indicator is required for an auxiliary tank that is
used only to transfer fuel to other tanks if the relative size of the tank,
the rate of fuel transfer, and operating instructions are adequate to--
(i) Guard against overflow; and
(ii) Give the flight crewmembers prompt warning if transfer is not
proceeding as planned.
(c) Fuel flowmeter system. If a fuel flowmeter system is installed, each
metering component must have a means to by-pass the fuel supply if
malfunctioning of that component severely restricts fuel flow.

(d) Oil quantity indicator. There must be a means to indicate the quantity
of oil in each tank--
(1) On the ground (such as by a stick gauge); and
(2) In flight, to the flight crew members, if there is an oil transfer
system or a reserve oil supply system.

Sec. 23.1553 Fuel quantity indicator.

A red radial line must be marked on each indicator at the calibrated zero
reading, as specified in Sec. 23.1337(b)(1).

Sec. 23.1555 Control markings.

(a) Each cockpit control, other than primary flight controls and simple
push button type starter switches, must be plainly marked as to its function
and method of operation.
(b) Each secondary control must be suitably marked.
(c) For powerplant fuel controls--
(1) Each fuel tank selector control must be marked to indicate the position
corresponding to each tank and to each existing cross feed position;
(2) If safe operation requires the use of any tanks in a specific sequence,
that sequence must be marked on or near the selector for those tanks;
(3) The conditions under which the full amount of usable fuel in any
restricted usage fuel tank can safely be used must be stated on a placard
adjacent to the selector valve for that tank; and
(4) Each valve control for any engine of a multiengine airplane must be
marked to indicate the position corresponding to each engine controlled.
(d) Usable fuel capacity must be marked as follows:
(1) For fuel systems having no selector controls, the usable fuel capacity
of the system must be indicated at the fuel quantity indicator.
(2) For fuel systems having selector controls, the usable fuel capacity
available at each selector control position must be indicated near the
selector control.
(e) For accessory, auxiliary, and emergency controls--
(1) If retractable landing gear is used, the indicator required by Sec.
23.729 must be marked so that the pilot can, at any time, ascertain that the
wheels are secured in the extreme positions; and
(2) Each emergency control must be red and must be marked as to method of
operation. No control other than an emergency control, or a control that
serves an emergency function in addition to its other functions, shall be
this color.

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964; 30 FR 258, Jan. 9, 1965, as
amended by Amdt. 23-21, 43 FR 2319, Jan. 16, 1978; Amdt. 23-50, 61 FR 5193,
Feb. 9, 1996]



Simplified English translation
- There must be a fuel gauge
- It must have units marked on it
- It must read zero correctly when down to unuseable fuel.
- There must be a red line at zero.
- There must also be a dipstick.


G

[IO540]

Doesn't anyone wonder why somebody spent so much time writing a spec for something that is in the end completely useless.......

What use is a fuel gauge which is useless, except when the tank is empty?

The only explanation I can think of for this farce is that, many years ago, the Great American Aeroplane Manufacturers made a forceful representation to the FAA along the lines that if they had to fit better fuel gauges, it would result in the loss of 7,343 AMERICAN jobs. And some complete mug in the FAA bought it.

It doesn't suprise me the CAA bought it too because a) they couldn't just walk away from all the CofA fees and b) pilots aren't supposed to need working fuel gauges (a proper pilot, remaining clear of cloud and in sight of the surface, reaches out of the cockpit and dips the tank with the middle bit of his slide rule).

The one positive result of massive cockups like the Lycoming defective crankshaft disaster (currently going through phase 2; phase 1 happened in 2002) is that practically everybody now realises that the Great American Aeroplane Manufacturers quite often make a load of crap.

[Onan the Clumsy]

That must be why they sold...how many thousand Skyhawks?


:confused:

[Penguina]

Dr Ghengis...

capacitance type fuel gauges can be a bit erratic as the fuel companies modify the mix through the year, giving significantly different readings

:{ Waaa. Thought I was getting somewhere with this techy stuff, until you said that.

I thought the point of capacitance-type gauges was that as long as the permittivity of the dielectric at the bottom of the tank (ie - the 'unusable' fuel), measured by the reference capacitor there, is the same as that of the fuel in the rest of the tank, then a comparison can be made (because the dielectric constant of air is known) and the mass of fuel determined?

Or are they calibrated to such an extent that only minor variations in permittivity due to changes in density with temperature can be accounted for?

Or am I just talking rubbish? :confused: :) :rolleyes:

Bl00dy ATPLs. My brain feels like it's had too much Christmas dinner and needs an intellectual alka seltzer before it regurtitates some of it's unwanted information at a socially unacceptable moment. :ugh:

[dublinpilot]

as long as the permittivity of the dielectric at the bottom of the tank (ie - the 'unusable' fuel), measured by the reference capacitor there, is the same as that of the fuel in the rest of the tank, then a comparison can be made (because the dielectric constant of air is known) and the mass of fuel determined?

Or are they calibrated to such an extent that only minor variations in permittivity due to changes in density with temperature can be accounted for?


I can see that conversation next weekend is going to be fun ;) ;) :O

dp

[Penguina]

Take heart, mate, I'll have had a beer or two by then... :O

[Vee One...Rotate]

Crikey. Thanks for all the input.

Obviously a topic close to some people's hearts...!

It's always (he says, with about 15 hours in the logbook) been something that confuddled me...

V1R :O

[S-Works]

I own a 152. Put new gauges and senders in last year and they are accurate to within a gnats cock. I have a fuel scan 450 fuel computer to test them against and they are very accurate.

I think they just wear out overtime and no body bothers to fix them rather than being innacurate.

V1 PM and I will shopw you as I am Leicester based.

[Big Pistons Forever]

It's an unwritten law of aviation. All light aircraft must have useless fuel guages, allong with a clock which can't keep time and uncomfortable seats ;)