windmilling prop RPM and water in float bowls

[RFguy]

Does anyone know what the windmilling prop RPM will be for a Cherokee in best glide at WOT setting. (IE minimum intake restriction likely results in higher windmilling speed).

 

Reason for question. In the case of water in the lines, how long does it take after changing tanks to ingest all the water through the engine, and given the low vapour pressure of water, will it even be effectively pulled into the intake system  at all ?  or will it just fill the float bowl and stop moving ?

 

The 1/4 ID lines is only 31.7mL per meter. say a 1.3m worth from the fuel switch = 41mL, or at 7000mL/hour =  21 seconds. 

 

[facthunter]

If you've got water in the fuel lines and into the carburetter WOT won't suck it through and best you concentrate on flying it. Nev

[RFguy]

yeah I was wondering as what rate it would pull the water out of the float bowl . maybe reduce throttle opening is better because it creates lower pressure and might assist vapourizing the water.  dunno . 
water VP is only 2.5 kPa. fuel is ~ 30-60.... . 20 " of Hg pressure below atm .. 67kPa below ATM so no..... 

Does anyone know what happens in the real world witht his question ?

 

[facthunter]

Yes Starting a motor with the throttle wide open will not pull any fuel through the system of a carburetted motor. No Venturi effect as the velocity is miniscule. Anyhow the dampness on the plugs would probably kill them too.  Nev

[pluessy]

you will find that the surface tension of water will stop it from going through the main jet without significant differential pressure (more than the venturi can provide). Water in a carby is usually a dead-stop until removed by draining/cleaning.

[facthunter]

Total strip and clean and even use of alcohol or compressed air.  Nev

[RFguy]

hmm Non invasively, the only way to figure if there is fuel in the lines is to tap the line and watch the pipe vibration frequency. 

but if the lines post the selector are full of water, you are dead in the water. so.... it needs to be detected between the tank and the fuel selector cock. 

and at a velocity of about 27cm/second in 1/4" line at cruise (8 gph) , that aint long o do something about it

fuel injected system will behave differently. 

 

Primer comes from elsewhere. Might keep engine alive with primer if primer has access to the fuel ?  WHat's the primer pumped quantity per push in the cherokee ? something like a 2" travel in a 1/4" bore  every 3 seconds... no, that's not going to keep it USEFULLY  alive. you are better to fly it. 

Edited July 4, 2023 by RFguy

[RossK]

Not sure about water, but I've been told it takes 13 seconds to get fuel from the useable tank after running the other tank dry in a PA-28.

I reckon that would feel like a very long time.

[facthunter]

You're blinding yourself with Science. Most primers don't go to all cylinders. It would work in a supercharged radial but only to about 1/8th throttle position due to the priming rate.. Aviate Just fly the plane well.. There's limited time for distractions.  Here's another I didn't post straight away . Sorry Folks.  Nev

[Area-51]

🤔

[facthunter]

Ross K, that seems excessive. If it only had air in it the fuel should move quite quickly.  Nev

[Thruster88]

9 hours ago, RFguy said:

Does anyone know what the windmilling prop RPM will be for a Cherokee in best glide at WOT setting. (IE minimum intake restriction likely results in higher windmilling speed).

 

Reason for question. In the case of water in the lines, how long does it take after changing tanks to ingest all the water through the engine, and given the low vapour pressure of water, will it even be effectively pulled into the intake system  at all ?  or will it just fill the float bowl and stop moving ?

 

The 1/4 ID lines is only 31.7mL per meter. say a 1.3m worth from the fuel switch = 41mL, or at 7000mL/hour =  21 seconds. 

 

Great minds think alike. After listening to the Archer pod cast I wondered would water in the carb bowl be able to be sucked thru the carb jets to clear after changing to a good tank.

 

I have my doubts water was the problem in this case, on the PA-28 the drains are correctly located at the lowest point and there is x? amount of unusable fuel. Why did the engine not fail when that tank was initially selected if water of a very significant amount was present? 

 

One possible solution to clear water from the carb of a lycoming would be to pump the throttle. The accelerator pump should?  pump fluid of any viscosity.

 

Prop will continue to windmill around 1000-1200 at best glide, my guess 

[RossK]

14 hours ago, facthunter said:

Ross K, that seems excessive. If it only had air in it the fuel should move quite quickly.  Nev

The information comes from testing, following the forced landing of a PA32, that had plenty of fuel onboard, but the pilot cycled through the tanks too quickly.

Forced landing was spectacular effort though, so well done to the pilot on that point.

Edited July 5, 2023 by RossK

[RFguy]

It would depend on how fast the air could be pushed out  the float bowl (breather/equalization passages).

[pluessy]

some 1st hand experience from today!

My mower had some water in the fuel and stopped. I drained the fuel tank and the float bowl, flushed the line and added some metho and clean fuel. The engine wouldn't start unless I covered the carb intake with my hand, then it would run for a few seconds. I had to repeat that for a couple of minutes before the engine would run normally.

 

Bottom line: water in a carb means dead-stick landing, no matter what!

[facthunter]

Having the throttle wide open at say 1000 rpm is likely to cause more engine shaking than doing it closed. With the throttle closed it's hardly getting any air into the cylinders at  all. You never kick a large bore bike engine over with the throttle open and you can start a 13:1 CR Speedway bike pulling the rear wheel with the throttle closed and the bike laid over to let the wheel spin.  Nev

Edited July 9, 2023 by facthunter
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