Dipsticks

[ExSp33db1rd]

Dipsticks.

I occasionally fly an old( ish) Cessna 182, and have always assumed that the fuel dipstick is calibrated as total fuel in tanks, i.e if I dip 90 litres per tank, I have 180 litres minus 9 litres per side unusable, i.e 162 litres to not only base my endurance on, but also to enter into the weight and balance calculations, as the 18 ltrs unuseable fuel is already included in the 'empty weight' that one starts with.

But ... is this likely to be so ? I was recently questioned on this point by a pilot preparing a weight and balance loadsheet.

The original dipstick that might have had some notation that would have shown the answer is long gone, the present one is like George Washingtons' axe.

I know we can drain the tanks down and start again, but that is quite an undertaking, and can one guarantee to get down to the true unuseable figure anyway before starting to refill ?

Is there a precedent, or protocol, that is usually followed when Cessna sell a new aeroplane ? Do manufacturers even sell a dipstick with a new aeroplane, after all, it would be an indication that the fuel gauges that they provide with their product are not to be relied on - but then we all know that !

If one assumes that the fuel we measure is total fuel, then we are on the safe side so far as endurance is concerned, but 18 ltrs overweight if we load up to MUAW for take off, hardly very significant at altitudes and temperatures that we are working with, but a smart lawyer will prove that the engine failure 3 hours into the flight, that caused the crash, was due to pilot error in being overweight for take-off.

And it would be nice to know what is the true situation, too.

( OK we set to and measure it again, but any thoughts ? )

[Rod1]

All the ones I have created have just measured usable fuel. This allows me to ignore the unusable element that is already in the basic empty weight.

Rod1

[thing]

I was always led to believe that the fuel measured on the dipstick was useable fuel.The same as fuel in the tech log ie our 172 when full has 144 litres and the weight of 144 litres is what you use in your W+B. I'd be interested to hear if it's not.

[dublinpilot]

What does your dipstick show when the tank is full? Multiply this by two to get both tanks. Now does this equal the useable fuel in the poh or the total fuel in the poh?

[Whopity]

A dipstick is of no use without calibration. Unless it states on it what the calibration is, it is no better than using a garden cane or a knotted rope.

[dont overfil]

I bought a dipstick for the particular model of C182 I fly and it is calibrated with the unuseable fuel. ie 46usg.

I have doubts about how accurate the intermediate readings are due to the shape and slope of the tanks but it is adequete for flight planning unless one is exceptionally picky.

D.O.

[172driver]

In addition to the above: I'd be VERY wary of dipstick readings when checking a Cessna, especially one with long-range tanks. If the a/c is not parked perfectly level, the reading can be out by a significant margin. As a rough guide, sure, but as precise measurement, not really.

[Rod1]

I have no experience with the tanks on a 182 but in most aircraft an accurately calibrated dipstick is the only way to know what quantity of fuel is actually in the tanks. If you are not sure it is well worth the time to drain the tanks and calibrate the dipstick and if possible the gauges. I have found considerable difference between aircraft of a similar type and some dipsticks can be way out and are more of a hazard than an asset. I mentioned in another thread recently that most incidents revolve around fuel / firewall forward so knowing rather than guessing how much fuel is available is vital to fight safety.

Rod1
PS this is a general comment and not aimed at you ExSp33db1rd.

[dont overfil]

I may have sounded casual but with 8 hours endurance. a large useful load, fuel totaliser and range rings I am spoiled .

After years flying more basic aircraft knowing your machine (and your dipstick:)) is important.

Dipsticks are of limited value on most Cessnas due to the shallow tanks. Totalling the fuel used after every flight and knowing your fuel burn are the best ways to calculate endurance.

D.O.

[A and C]

I have 5 Cessna dipsticks...........................all of them rewcovered from the tanks on engineering inspections.

Please dont drop them in the tanks

[thing]

You would have to try very hard to drop them in the tanks surely? Thinking about the length of the stick and the diameter of the orifice. Mind you, human ingenuity knows no bounds..............

[ExSp33db1rd]

Thank you all for your considered inputs.

Dublinpilot - Brilliant !!! why didn't I think of that !!! Easier to fill up than drain down. Award yourself a pint of Guiness ( preferably from Dirty Nellie's near Shannon Airport, circa 1960 during 707 conversion ! )

Rod1
PS this is a general comment and not aimed at you ExSp33db1rd.

Rod1 - understood, and I totally agree, even two pilots 'dipping' in the hangar with the same dipstick will come up with two different answers. In practice the difference is not very significant under normal circumstances, but that's not the point.

[peterh337]

I always used to fill up to the top, and stick a finger in there and made sure it came out wet :E

[thing]

I'm with you there Peter, there's the 'you need x litres for that trip so you have enough in the tanks' lobby as contrasted to my 'Oh really, well I'll just fill them up until it's running down the wings thank you.' standpoint. Fuel in the bowser=useless.

[ExSp33db1rd]

...well I'll just fill them up until it's running down the wings....

Fill your average C-172 or Cherokee like that, then load you and 3 of your friendly rugby team, pls baggage - and tell me how much runway you'd need to get airborne, or where the hole would be off the end for me to start digging for you, and if you did get airborne, and had some emergency that required you to return to the airfield pronto, like one of your mates suddenly had a heart attack, could you go around with full flap when some kid ran on to the runway just as you were about to flare ? Don't tell me it will never happen, Mr. Murphy is always with us.

I'm referring to operating a Cessna on Coastguard Search and Rescue at short notice. We can't leave the aircraft topped up in case the only crew who answer the pagers are the four heaviest of our team - and I can assure you that some are HEAVY !

We have to balance the length of time we can remain airborne to Search For Those In Peril On The Sea, against the length of runway we don't have available to take-off grossly overweight - even if we were prepared to.

We upgraded to a C-182 from a C-172 to give us more flexibility in this respect but still have weight/performance restraints, sometimes.

Course, if NZ Coastguard would give us a C-130 ..... ! ( and the money to fill the tanks ... )

Nb. On of our team relates to an experience in New Guinea operating a C-182. Filled to overflowing, one tank then started to syphon out of a cap that had not been properly secured, the base of the bladder tank rose to fill the space so that it continued syphoning out of the top and the fuel gauge probe still thought that there was petrol in the tank. Engine stopped. Trees. Jungle. ( Cannibals ? ) Mountains. Mist. He survived.

Mr. Murphy is always with us.

(Sorry, not trying to be rude, but you can't just say fill 'er up )

[thing]

I must of course explain Speedbird that I refer to the usual suspects, training spamcans with two normal weight, maybe three anorexics max on board.

Cannibals, sounds interesting.

[ExSp33db1rd]

Cannibals, sounds interesting.

Wouldn't be !

Dunno, never been, only read the National Geographic about such things.