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  #1  
Old 12-10-2019, 07:58 PM
swjohnsey swjohnsey is offline
 
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Default Engine out best glide CS prop

High rpm or low rpm? What is the default in the event of no oil pressure?
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Old 12-10-2019, 08:17 PM
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N941WR N941WR is offline
 
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Which prop?
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Old 12-10-2019, 08:20 PM
swjohnsey swjohnsey is offline
 
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Quote:
Originally Posted by N941WR View Post
Which prop?
Hartzell HC-C29R-1BF on Lycoming IO-360.
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Old 12-10-2019, 09:08 PM
Canadian_JOY Canadian_JOY is offline
 
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Some interesting testing has been done to answer this question.

The summary statement would be pull prop to full COARSE pitch for maximum reduction in prop-induced drag and engine pumping losses.

For most hydraulically-controlled constant speed props, loss of oil pressure results in the props being spring-loaded to the fine position. Should the engine failure be accompanied by a loss of oil pressure most props will default to fine pitch, becoming very nice aerodynamic brakes.

Aerobatic props generally are the opposite, being spring-loaded to full coarse pitch in the event of oil pressure loss. This is done to prevent a major overspeed condition which could result in severe mechanical damage (think prop or engine coming off the airplane - the engine is already toast so we're now only concerned about saving the souls on board). Keep in mind that a loss of oil pressure could occur when the aircraft is on a down-line, rapidly converting altitude into speed, speed which would cause a full-fine pitch prop to turn at crazy-high RPM.
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Old 12-11-2019, 05:37 AM
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Steve Melton Steve Melton is online now
 
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I chopped power to IDLE turning base with a headwind. I barely made it in.
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Old 12-11-2019, 06:36 AM
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Set to low RPM/course in a real emergency but practice with it set for fine/max RPM when training as this is probably what you will get if you have a normal CS installation...
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Last edited by control : 12-11-2019 at 06:36 AM. Reason: spelling
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  #7  
Old 12-11-2019, 08:39 AM
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FasGlas FasGlas is offline
 
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Well, if you have no oil pressure you won't be able to change a CS prop. If the engine is free wheeling in the wind you should have some oil pressure, pull the blue knob for course pitch. If your engine is seized don't bother pulling the blue knob. Fine pitch had more drag.
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Old 12-11-2019, 10:18 AM
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Educate me. I know my CS will go to fine pitch with loss of oil pressure. I'm not sure about the drag penalty of a fine pitch prop being worse IF the choices are:

a windmilling prop in coarse pitch or a stopped prop in fine pitch.

So my side-question is will the prop stop if the engine has lost oil pressure and the prop goes as flat as it can, or will it keep turning - because if so the coarse pitch is clearly the better option, but if not the fine pitch may well be less drag.

I know a seized engine won't windmill but I am speculating about situations where pressure is very low but not zero. Are there any such, that could last more than a few seconds?
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Old 12-11-2019, 10:31 AM
swjohnsey swjohnsey is offline
 
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Did some testing this morning in the RV-4, IO360, Hartzell CS. Downwind at 100 mph, about a wingtip (1 /1/4 mi) from runway. Pulled power, prop high rpm/fine abreast of numbers and immediately turned base, trimmed for 90 mph/best glide, no flaps. Didn't make the runway by quite a bit. Same scenario but full low rpm/coarse, was about 100 feet over the numbers, dumped full flaps and made a nice 3 pt.

Prop setting makes a big difference!

I'm thinking the default with no oil pressure is fine/high rpm, not sure. I'm pretty sure the prop will windmill unless efforts are made to stop it like nosing up to stall. Not sure if a windmilling prop will produce enough oil pressure to operate prop.

Last edited by swjohnsey : 12-11-2019 at 10:35 AM.
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  #10  
Old 12-11-2019, 10:31 AM
Bavafa Bavafa is offline
 
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Quote:
Originally Posted by FasGlas View Post
Well, if you have no oil pressure you won't be able to change a CS prop. If the engine is free wheeling in the wind you should have some oil pressure, pull the blue knob for course pitch. If your engine is seized don't bother pulling the blue knob. Fine pitch had more drag.
Plus one, in case of an engine related emergency one of my first task is to pull the blue knob all the way and drag reduction, if wind milling is very noticeable


Quote:
Originally Posted by Bill Boyd View Post
Educate me. I know my CS will go to fine pitch with loss of oil pressure. I'm not sure about the drag penalty of a fine pitch prop being worse IF the choices are:

a windmilling prop in coarse pitch or a stopped prop in fine pitch.

So my side-question is will the prop stop if the engine has lost oil pressure and the prop goes as flat as it can, or will it keep turning - because if so the coarse pitch is clearly the better option, but if not the fine pitch may well be less drag.

I know a seized engine won't windmill but I am speculating about situations where pressure is very low but not zero. Are there any such, that could last more than a few seconds?
Good point and my test has shown the wind milling a prop, even at full coarse, is more drag than a not turning prop. However, it does take a bit to get the prop to stop wind milling and that is the time that is spent during an emergency. It does take some practice, at least for me, to do that with the calm head. I have shut down my engine, even though high and above an airport, the rush and nervousness is still there.
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