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#11
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Feathering an engine
"Tim" wrote in message m... "vaughn" wrote in message ... "Tim" wrote in message m... So you are saying if I loose power at high altitude in a fixed pitch prop aircraft, like a Skyhawk, I will have less drag if I stop the prop, as opposed to letting it windmill? Yes, but with a fixed pitch prop you may or may not be able to stop the prop by slowing down to a near stall. Once stopped, it may or may not stay stopped at best glide speed. It would depend on the pitch of your prop, the compression of your engine, your plane's best glide speed, the quality of the pilot's speed control, and the phase of the moon. Vaughn Are you high? Have you actually done it? I can assure you, all aspects of it are much easier than you imply. Vaughn is absolutely correct in stating that many aircraft with fixed-pitch props will windmill all the way in, as you would have to be near or below its rated stall speed for it to stop. Depends on the particular aircraft in question :-) |
#12
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Feathering an engine
Orval Fairbairn wrote:
wrote: Scott Skylane wrote: As an aside, the drag created by a windmilling propeller, i.e. one not feathered and attached to a dead engine, creates as much drag as a flat plate the same size as the area of the prop arc. Nope. The blades cannot be everywhere at once, and so the area affected is no larger than the blade area. YES! In aeronautical engineering analysis, a windmilling prop is considered to be a flat disk, with drag numbers to match. Feathering the prop greatly reduces drag. Three answers not entirely correct, none entirely wrong - how can this be? Because as shown by simple empirical measurements, "it depends" as indicated in this thesis: http://www.goshen.edu/physics/PropellerDrag/thesis.htm (Scroll down to review figures 11 through 14 if you are in a hurry. Figure 13 label provides a summary relevant to this thread.) As the author of that thesis noted: "The available publications and information in the area of propeller drag are almost non-existent, not because of any difficulties of the research sophistication, but because of the simplicity of it. To investigate propeller drag one does not need electronics and a large grant, one only needs a wind tunnel and a spring for a quick measurement. Therefore, most of the research in this field was done before articles were indexed as they are now. It was not until I found some journals from the 1930's that I could actually piece together trails of research." |
#13
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Feathering an engine
"John E. Carty" wrote in message ... "Tim" wrote in message m... "vaughn" wrote in message ... "Tim" wrote in message m... So you are saying if I loose power at high altitude in a fixed pitch prop aircraft, like a Skyhawk, I will have less drag if I stop the prop, as opposed to letting it windmill? Yes, but with a fixed pitch prop you may or may not be able to stop the prop by slowing down to a near stall. Once stopped, it may or may not stay stopped at best glide speed. It would depend on the pitch of your prop, the compression of your engine, your plane's best glide speed, the quality of the pilot's speed control, and the phase of the moon. Vaughn Are you high? Have you actually done it? I can assure you, all aspects of it are much easier than you imply. Vaughn is absolutely correct in stating that many aircraft with fixed-pitch props will windmill all the way in, as you would have to be near or below its rated stall speed for it to stop. Depends on the particular aircraft in question :-) Perhaps, but that wasn't the question, and what does the phase of the moon have to do with anything but starting a ****ing contest? There is no doubt in my mind that all the singles I have flown will windmill all the way in. I'm not aware of any direct drive, piston singles that won't. You in fact have to be very, very slow to stop the prop, but it's not difficult do to do. But even at airspeeds well above max glide, I have never had a stopped prop restart against compression without at least bumping the starter. The point was how much do you gain by stopping a fixed pitch prop, as opposed to letting it wind mill. I was taught many years ago, that if you experience a power failure at high altitude, stopping the prop could mean the difference in reaching a distant landing area. Some of the posts in this thread suggests it makes no difference. I thought it might be to everyone's benefit to clarify. |
#14
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Feathering an engine
In article ,
"Tim" wrote: "Orval Fairbairn" wrote in message news In article , wrote: On May 5, 1:06 pm, Scott Skylane wrote: As an aside, the drag created by a windmilling propeller, i.e. one not feathered and attached to a dead engine, creates as much drag as a flat plate the same size as the area of the prop arc. Nope. The blades cannot be everywhere at once, and so the area affected is no larger than the blade area. Dan YES! In aeronautical engineering analysis, a windmilling prop is considered to be a flat disk, with drag numbers to match. Feathering the prop greatly reduces drag. So you are saying if I loose power at high altitude in a fixed pitch prop aircraft, like a Skyhawk, I will have less drag if I stop the prop, as opposed to letting it windmill? That is correct! -- Remove _'s from email address to talk to me. |
#15
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Feathering an engine
Jim Logajan wrote:
Orval Fairbairn wrote: wrote: Scott Skylane wrote: As an aside, the drag created by a windmilling propeller, i.e. one not feathered and attached to a dead engine, creates as much drag as a flat plate the same size as the area of the prop arc. Nope. The blades cannot be everywhere at once, and so the area affected is no larger than the blade area. YES! In aeronautical engineering analysis, a windmilling prop is considered to be a flat disk, with drag numbers to match. Feathering the prop greatly reduces drag. Three answers not entirely correct, none entirely wrong - how can this be? Because as shown by simple empirical measurements, "it depends" as indicated in this thesis: http://www.goshen.edu/physics/PropellerDrag/thesis.htm (Scroll down to review figures 11 through 14 if you are in a hurry. Figure 13 label provides a summary relevant to this thread.) As the author of that thesis noted: "The available publications and information in the area of propeller drag are almost non-existent, not because of any difficulties of the research sophistication, but because of the simplicity of it. To investigate propeller drag one does not need electronics and a large grant, one only needs a wind tunnel and a spring for a quick measurement. Therefore, most of the research in this field was done before articles were indexed as they are now. It was not until I found some journals from the 1930's that I could actually piece together trails of research." True that propeller research went away around WWII, but wind turbine research is currently a hot topic and that's what the propeller becomes when the engine stops. -- Jim Pennino Remove .spam.sux to reply. |
#16
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Feathering an engine
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#17
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Feathering an engine
Jim Logajan wrote:
wrote: True that propeller research went away around WWII, but wind turbine research is currently a hot topic and that's what the propeller becomes when the engine stops. True, but if the propeller airfoil has asymmetrical camber then when the engine stops, the relative wind is inverted (coming from the wrong side - similar to inverted flight.) So it wouldn't be terribly efficient and attributes like prop stall angle differ from engine on versus engine off. When the engine stops producing power, it becomes a frictional load to the prop, which becomes a wind turbine. There is nothing about the prop being attached to an airplane that invalidates analysis as a wind turbine under that condition. Whether it is an efficient wind turbine or not is irrelevant, it is still a wind turbine when the engine is not producing power and air is flowing past it. -- Jim Pennino Remove .spam.sux to reply. |
#18
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Feathering an engine
On May 6, 2:00*pm, wrote:
Jim Logajan wrote: wrote: True that propeller research went away around WWII, but wind turbine research is currently a hot topic and that's what the propeller becomes when the engine stops. True, but if the propeller airfoil has asymmetrical camber then when the engine stops, the relative wind is inverted (coming from the wrong side - similar to inverted flight.) So it wouldn't be terribly efficient and attributes like prop stall angle differ from engine on versus engine off. When the engine stops producing power, it becomes a frictional load to the prop, which becomes a wind turbine. There is nothing about the prop being attached to an airplane that invalidates analysis as a wind turbine under that condition. Whether it is an efficient wind turbine or not is irrelevant, it is still a wind turbine when the engine is not producing power and air is flowing past it. -- Jim Pennino Remove .spam.sux to reply. Yeah,, but. If the prop is not efficient enough to even rotate with the wind passing over it it never really becomes a wind turbine.... Those need to spin to be called that. A non rotating prop is called .. DRAG . A rotating prop not under power is called more DRAG.. IMHO Ben. |
#19
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Feathering an engine
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