OK Guys... educate me... C172 Fuel Problem

[witwiw]

is it possible that there is a leak in the tank/associated system which has allowed fuel to drain back down the inside of the wing, coming out somewhere to leave that 6" wide stain on the underside of the flap?

maybe due to possible fatigue that has caused something to rupture after refuelling for the 2nd leg?

[Tee Emm]

Sunfish.

You might like to suggest that the school do a couple of short flights with a known fuel load and dipstick

Call me a cynic but do you really think the flying school will actually go to the trouble to actually fly a non revenue test flight in order to improve the flight safety aspect of an aircraft that may have a fuel problem? I think not..

[Oldlearner]

Should be

2400 / 2450 rpm lean at any cruising alt.due engine not needing all that lead with a standard 0 320. Book says "lean to smooth" . at altitude go to allowable full throttle still lean to smooth. better than six hour and good speeds still. Use the cyl,egt and oil temps for monitoring temps. check the POH for limits . Pilots that are disappointed in a stock 172 are those that have not read that novel sized POH. Easy to average 32 litres per hour for 160 hp 0 320. Not leaning is dumb

[Ratshit]

speed2height

A couple of golden rules for operating in the GA world of us low lifes!

1) Always know how much fuel you're starting out with - ie full tanks, known fuel burn, or calibrated dip stick.

2) Know how to operate the aircraft to achieve a particular fuel burn - and do so.

3) Always keep a fuel log.

4) Monitor the fuel guages with a moderated measure of scepticism.

5) If in doubt LAND THE BLOODY THING - before the fan stops.

This has kept me safe for 35 yrs - although there have been two incidents - both involving Cessnas.

1) Took off in a Hawk XP that I had never flown before with full tanks and adequate fuel for the journey. By about 3/4 distance along the route, the fuel guages were both on about 1/4. Decided to divert for fuel. Lowered the nose to decend from A100 - and the guages headed for empty. Started thinking about all the stories I have read in "Crash Comics" about people who ignored empty guages and flew on until the donk stopped and they crashed in tiger country just short of their destination. So I landed on a road, dipped the tanks and determined that I did actually have sufficient fuel, then took off and continued to my destination uneventfully, with the guages sitting well below 1/4. On refuelling the tanks took the expected amount of fuel.

2) Took over a C402 from the CP for a charter - out and back without refuelling . The CP told me the fuel on board - which was sufficient for the flight, with comfortable reserves (I had enough time in the aircraft to know that I could consistently achieve the required fuel burn) - no calibrated dip stick was available to confirm the fuel on board - but the guages looked about right. By TOD I was concerned that there was insufficient fuel on board to complete the return flight. Rang the CP on landing to discuss the issue - he was adament that there was sufficient fuel on board. So I took off and climbed out on the mains then in cruise changed one side on to the aux tank which the CP was confident I could get 30 min from. After 10 min, the engine surged - and scared the crap out of my pax. I changed back to the main and diverted and topped up the tanks. Probably would have made my destination but I would have been into my fixed reserves. CP and I argued for along time about what actually happened here. CP - "You dopey prick - you can't have leaned it properly!". RAT - "The bloody thing never had the fuel on board you stupid bastard!"

R

[Westaussielame]

Another thing to watch out for with cessna high wing singles is that the fuel vent which hangs down behind the strut where it enters the wings must have its opening immediately behind the trailng edge of the strut ,if it is not fuel will not draw evenly from both tanks when system selected to both.

[speed2height]

Originally Posted by kiwiblue

The comments/reasons as to the possible excessive fuel burn have been excellent! Many many possible causes there. I would like to present another possibility:

The Lycoming engine as fitted to many C172's does have one interesting little feature that once very nearly claimed me... if the aircraft is being operated at or very near to full-throttle, as in an extended climb, the mixture is put into an 'auto-full-rich' setting, regardless of the pilots manipulation of the mixture control.

In an extended full-throttle climb, this alone can almost double the flight-planned fuel burn.

Hope this is of some benefit.

Regards

RS

kiwiblue I think you may have hit the nail on the head! I conducted an extended climb out on departure, and then another climb and descent to get over and then under some SC, these climbs took around 10-15min at 200-300fpm each. If what you say about the mixture being put auto full rich is true then this accounts for up to 45 minutes of extra flight fuel burned!!!!

So event though I leaned in the climb above 5000' the mixture may not have leaned at all?

Guys thanks for all your comments and suggestions, and thanks for not being too crtitical with 20/20 hindsight

[scroogee]

Two points of interest to add,

1. In a vintage aircraft the gauge read TOTAL or could be toggled to indicate L or R. Following reassembly the TOTAL was correct but L and R were not, to the extent that another pilot made noises about replacing the floats etc and not flying the aircraft until it was done. As we made a dipstick we noticed that the L tank indicated full when it was empty and the right was full- the wires to the gauge had been swapped.

2. Another aircraft I had spent some time in had a forced landing due to fuel exhaustion, at a previous landing the tanks had been dipped and indicated minimum but sufficent fuel for the flight plus legal reserve. Subsequent investigation found the dipstick miscalibrated in the mid range- it was ok for low (less than 25%) and high (above 75%) fuel levels. The aircraft owner had miscopied the markings when re-doing the dipstick.

In summary, know your product and tools, and check anything suspicious.

scroogee

[speed2height]

Just to finish off this thread, I have now been informed that the engineer inspected the right fuel tank on the aircraft and found a previous repair that had separated causing a significant leak.

This leak coupled with my low time on the aircraft and lack of knowledge of GA fuel system gotchas and techniques resulted in the aircraft being landed at a diversion airfield with only 3ltrs in it.

I guess any incident/accident is the result of a chain of events, and that any incident/accident can be avoided by intervening at ANY link in that chain. The fuel leak was simply a single link in a chain of events that was ultimately broken by a diversion at the last possible moment.

Now I have the feedback from this forum I can see at least six opportunities that I missed to sever the chain of events earlier.

Thanks for your feedback guys.

[kiwiblue]

Originally Posted by kiwiblue

This is easily verifiable by an 172 drivers out there... simply climb to an appropriate level, set your cruise RPM and lean to peak, rich of peak or lean of peak, wherever it may be you operate your aircraft. Note the reading of your EGT gauge. Then simply slide full throttle in and watch what happens to your EGT.

It is possible to operate the engine at or close to full RPM without reaching the auto-full-rich, but you need first to know about it, before you know how to avoid it.

Speed2Height: it's a sucker-punch this one. Probably something mandated by Yank lawyers after a lawsuit, built in by Lycoming to minimise the risk of pilot mishandling. Solve one problem, create another. Make something idiot-proof, watch some bastard make a better idiot. Familiar tune? Knots my knickers something fierce that this is not more common knowledge. Is probably a factor on other similarly equipped GA types also, but it's been a while since I was last regularly flying fixed-pitch aircraft.

Best of luck bro. Drop us a PM sometime if about the Hunter NSW. Bevvie would be a fine thing.

[RENURPP]

Interesting stuff.
Its been over 15yrs so a bit fuzzy.....
One thing I didn't see mentioned, was alternating tanks.
I used to teach the student to operate on either left or right tank just like you would do in a larger cessna or piper.
Carried out correctly and you will always have some fuel left in the other tank, even if yoiu stuff up the consumption, leaning, power settings, fuel onboard at start, leaking tanks etc.

BOTH for take off and landing.
Gauges are poor quality but they generally give you an idea.
You landed before the fuel ran out so they did save you.