Water in Fuel question

[pelmet]

According to the Cherokee Cruiser POH which I am reviewing now(really the checklist), if there is an engine failure due to water.......

"Try other fuel tanks. (Water in the fuel could take some time to be used up, and allowing the engine to windmill may restore power. If power loss is due to water, fuel pressure indications will be normal.)"

I never really thought of this before. If the pprop is windmilling, is the liquid from the fuel tank continuing to go through the engine and at some point(assuming only a limited amount of water), the contamination will have finished going throiugh the engine and it will re-start because fuel is available again?

Thanks

[PilotDAR]

because fuel is available again?

I would think so. Water can be pumped through an engine, but is not fuel - it displaces fuel. If the water runs out, and fuel is allowed to be pumped through the engine, you've got fuel! Add fire and oxygen, and it should run. A windmilling engine can be expected to pump water though about as well as fuel.

That having been said, a carb float bowl will hold a minute or so of fuel anyway, and a minute can seem like a really long time with a windmilling engine. I'd be looking forward to a restart, though still planning the forced landing! Once you have initiated the definitive steps toward a forced landing which seems to have a hope of success, be very wary if the engine sparks back to life. Wouldn't it be great if it ran again, and you could fly on. Wouldn't it be worse if you thought it would run again, you abandoned what my be a good forced landing, to now find yourself with a second engine failure, and much less choice as to when to go, completely rethinking what had been a good plan. You might use the "it ran a bit more" power to perfect the forced approach you'd already set up - don't let it carry you beyond the safe landing place you chose, to be forced to crash further on.

[lownslow]

How could a tank gather enough water in flight to quit?

[PilotDAR]

How could a tank gather enough water in flight to quit?

I doubt it would gather the water in flight, though a pilot could have taken off with enough water in a tank that when that water shifted in flight, it was ingested. This has been known to happen with bladder tanks, which may have wrinkles which prevent completely draining the sumps. This is a reason it's particularly important to assure venting of bladder tanks, so they don't suck down with fuel burn in flight, and collapse, changing their attachment, and shape in the wing.

[pelmet]

because fuel is available again?

I would think so. Water can be pumped through an engine, but is not fuel - it displaces fuel. If the water runs out, and fuel is allowed to be pumped through the engine, you've got fuel! Add fire and oxygen, and it should run. A windmilling engine can be expected to pump water though about as well as fuel.

That having been said, a carb float bowl will hold a minute or so of fuel anyway, and a minute can seem like a really long time with a windmilling engine. I'd be looking forward to a restart, though still planning the forced landing! Once you have initiated the definitive steps toward a forced landing which seems to have a hope of success, be very wary if the engine sparks back to life. Wouldn't it be great if it ran again, and you could fly on. Wouldn't it be worse if you thought it would run again, you abandoned what my be a good forced landing, to now find yourself with a second engine failure, and much less choice as to when to go, completely rethinking what had been a good plan. You might use the "it ran a bit more" power to perfect the forced approach you'd already set up - don't let it carry you beyond the safe landing place you chose, to be forced to crash further on.

Thanks,

I have read accident reports of situations where one had an engine failure and on final approach, the engine roared back to life temporarily at the last second destabilizing the forced approach leading to an incident as the aircraft did not land where the pilot intended to land. That is why once committed to the forced approach, you should....close the throttle. Perhaps some but not all of the water had been piumped through the engine.

[Posthumane]

A relevant video that discusses the topic of engine sporadically restarting after a failure:
https://www.youtube.com/watch?v=BBpqvPujZgM
P51 Mustang had an engine failure during an air demonstration, and the pilot would plan a forced approach, the engine would restart, and he would abandon the approach trying to make it back. Rinse, repeat.

I think water in a fuel injection system would probably clear up faster than in a carburetor, especially with an electric boost pump, but I could be wrong about that.

[lownslow]

I think water in a fuel injection system would probably clear up faster than in a carburetor, especially with an electric boost pump

I would think all else being equal a set of injectors should push as much fuel per minute as a carburetor pulls.

[waterdog]

This summer I saved what I believe would have been a forced approach, simply by being thorough. My plane is stored outside and mud daubers can plug a drain that goes from the fuel scupper ( area around the fuel neck) to a harmless area on the side. I check this drain often as it is a known problem. Well on this occasion the "holes on the swiss cheese started to align" . Just so happens that on the same night that a little mud dauber clogs my drain we get a torrential downpour. Luckily the next day, the day before my planned flight I went to the airport to check over the plane, thoroughly, without the family anxiously watching....... Now, I don't sample my fuel with the little shot glass like I used to because I learned that its not nearly good enough. I use a large sample container and if there is any question I use a 1L glass mason jar. So, I check my fuel and there is a ton of water. I dump the sample and check again...water. I get the mason jar and check repeatedly for 45 minutes.....water in every sample. I drive home, get my fuel jugs and a water filter and start to filter out the entire tank ( 40 gallons). I had water in every gallon of fuel until I was through 35 gallons of fuel. This took me into the late hours of the night. In flight school I was taught that water sinks to the bottom and can easily be screened out......In the real world it can hide in all kinds of nooks and crannies and takes real effort to ensure you have clean fuel after contamination. Bottom line is, take a large sample of fuel when you check and don't settle for any contamination at all, 100' off the ground at the end of a runway is no time to be wishing you had got the water out!

[photofly]

How did the water get in?

[C.W.E.]

If the airplane has been parked for an extended period of time and you are going to drain the tanks for water it is best to taxi it in a few left and right circles and wait for a few minutes then drain it, that often will get water that may be trapped in the fuel tanks moved to the drain sumps.

[aeroncasuperchief]

not so , fuel through a carburetor is a function of throttle position AND vacuum. With an engine around idle, regardless of throttle position, there will be low fuel usage, since an idling engine does not have the mass flow to produce higher vacuum at open throttle setting. With an injected engine, the fuel flow is basically a function of throttle position ( primarily ) and engine speed. More fuel will be pumped through the injectors as the throttle is advanced even if engine speed is low. Another way to evacuate the water in the system is to put the fuel pump on "hi" and the throttle to full. Using the primer in carburetted engines may get you some fresh fuel to get over the hump !

[PilotDAR]

fuel through a carburetor is a function of throttle position AND vacuum

Isn't the vacuum regulated by the throttle position? If the engine is turning over (including windmilling), it's creating some vacuum. The throttle setting will regulate that vacuum. Vacuum will suck air, and if available, liquid in the carburetor. For some simple engines, priming is possible by obstructing the carb inlet, and turning the engine over, the vacuum pulls fuel in, 'cause it can't pull in air. (then you've flooded it, and spend a half hour yelling at it, 'cause it won't start!).

[photofly]

The fuel unit in an injected engine tries to meter the same amount of fuel as a carburetor, which is both cases is the right amount to give a combustible mixture based on air flow. So for the same RPM, mixture and throttle position they should both pass the same amount of water, allowing for some differences in the method of dispersal and different viscosities of fuel vs water.

in other words, 65% power is going to be (say) 11gph of gasoline whether it’s a carburettor or fuel nozzles, and that’s going to lead to something like 11gph of water in both cases, if you keep the RPM the same in your power-off glide!

[aeroncasuperchief]

Isn't the vacuum regulated by the throttle position?

The throttle is downstream ( towards the cylinders ) of the venturi (where is main fuel jet is.) There are tiny orifices at the throttle valve for idle and low power and with a closed or nearly closed throttle, high vacuum pulls a small amount of fuel through these orifices.

[aeroncasuperchief]

So for the same RPM, mixture and throttle position they should both pass the same amount of water,

Correct, however , with a wind-milling engine due to water, the rpm will be low. If you move the throttle to full, you will introduce more fuel than the engine will accept. Not so on a carburetted engine, you just introduce accelerator forced fuel for acceleration purposes

[photofly]

You’re not convincing me that the water flow for a given rpm will be less through a carb than through an injection system. Given that if the fluid was 100LL the flow would be the same, why would it be significantly different for water?

[Posthumane]

I suppose if there is enough air flow to be on the main jet in the carb then there would be close to the same fuel flow as an injected engine. But I suspect that with a windmilling prop, the airflow through the carb will be quite low (unless you're diving fast enough to Windmill to prop at cruising rpm). A carb might be on the idle jet or if the throttle is open, it might be be able to pull through any jet.
The Bendix fuel injection system with have some flow through the injectors even with zero air flow, which is why you can prime it by setting the mixture rich with the boost pump on.

Anyway, I was speculating as I've never actually tried it.

[Heliian]

you just introduce accelerator forced fuel for acceleration purposes

Everytime you pump the throttle. Just keep pumping the throttle. Also the manual type primer will pump the water faster.

However, if you have that much water, you probably don't have enough time.