Prop AoA
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Prop AoA
Can anybody tell me if it is in fact possible to stall a propeller by attempting a go around or take off with a CSU set to an extremely low RPM?
At the moment I imagine that at a very low TAS a prop in the full fine position would have a relatively high AoA as full fine still gives forward thrust up to moderate airspeeds.
If the CSU was to increase blade angle in an attempt to reduce RPM to a low figure, assuming sufficient engine torque, could it not end up going beyond 16 degrees and therefore lose the forward thrust component?
I am assuming that this is one of the many reasons full fine is always set for take off or a go around. Am I incorrect? Is there any protection against this from happening?
At the moment I imagine that at a very low TAS a prop in the full fine position would have a relatively high AoA as full fine still gives forward thrust up to moderate airspeeds.
If the CSU was to increase blade angle in an attempt to reduce RPM to a low figure, assuming sufficient engine torque, could it not end up going beyond 16 degrees and therefore lose the forward thrust component?
I am assuming that this is one of the many reasons full fine is always set for take off or a go around. Am I incorrect? Is there any protection against this from happening?
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I'm not sure if the airfoil would actually stall in the situation you describe, but you certainly wouldn't get full performance. If you have a boosted engine you might overboost and damage it. 
There is another angle to this - on approach, the prop in fine pitch has a bit more drag, and if you don't have it in fine pitch you can expect more "float" (less aerodynamic braking).
GUMPF!
There is another angle to this - on approach, the prop in fine pitch has a bit more drag, and if you don't have it in fine pitch you can expect more "float" (less aerodynamic braking).
GUMPF!
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Propellors for both turboprop and piston engines are specified to allow for full BHP (or ESHP for the turboprop) at the fine (low pitch) position.
Therefore, the props are set to this on short finals to allow the max BHP (ESHP) to be available in the event of a go-around.
Sometimes.
On large radial piston engines, the props are normally not moved to the fine pitch position, unless a go-around is desired.
This is to minimise, as much as possible undue master connecting rod bearing wear.
In addition, with some larger GA type opposed engines (TCM GTSIO and Lycoming IGSO series especially) the props are generally not set to the flight fine position on final either, as this minimises undue bifler pendulum damper (counterweight) bushing wear.
Therefore, the props are set to this on short finals to allow the max BHP (ESHP) to be available in the event of a go-around.
Sometimes.
On large radial piston engines, the props are normally not moved to the fine pitch position, unless a go-around is desired.
This is to minimise, as much as possible undue master connecting rod bearing wear.
In addition, with some larger GA type opposed engines (TCM GTSIO and Lycoming IGSO series especially) the props are generally not set to the flight fine position on final either, as this minimises undue bifler pendulum damper (counterweight) bushing wear.
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Not sure if this is of interest but...
Some model aircraft competition classes are prone to prop stalling. An example would be the F5B class that uses 2000W motors running at 30-50,000rpm.
It's quite an "interesting" experience to hand launch one of these and find that instead of climbing away at 7000 feet per min (yes really) it performs a series of torque rolls at head height and the carbon fiber prop tries to give you a new hair cut.
This is how it should go..
http://ewc2004.users.btopenworld.com...tos/F5B-10.jpg
Some model aircraft competition classes are prone to prop stalling. An example would be the F5B class that uses 2000W motors running at 30-50,000rpm.
It's quite an "interesting" experience to hand launch one of these and find that instead of climbing away at 7000 feet per min (yes really) it performs a series of torque rolls at head height and the carbon fiber prop tries to give you a new hair cut.
This is how it should go..
http://ewc2004.users.btopenworld.com...tos/F5B-10.jpg
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This is generally done at 50% power or less. The objective is simply to fully exercise the pitch change system, and it needn't be at high power.
If a multiengine, the feathering check certainly stalls the airfoil - but you don't stay there long. (In fact the inboard section of the blade airfoil will be at a negative AOA stall...)
If a multiengine, the feathering check certainly stalls the airfoil - but you don't stay there long. (In fact the inboard section of the blade airfoil will be at a negative AOA stall...)
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Indeed, barit1 is quite correct.
On large radial engines, the magneto checks are done at the ambient pressure (29 inches at sea level, approximately, less at higher altitudes) and the propellor feathering checks done at a lower power setting.
No harm done whatsoever.
I have always thought that the best propellor/power arrangement was on the first successful turbine engine in commercial service, the RR Dart series.
One lever (and an electric fuel trimmer) to set the power and RPM.
Good idea, then, even better now, even after all these years.
So what if it was a screamer during ground ops...airports are supposed to be noisey places...
On large radial engines, the magneto checks are done at the ambient pressure (29 inches at sea level, approximately, less at higher altitudes) and the propellor feathering checks done at a lower power setting.
No harm done whatsoever.
I have always thought that the best propellor/power arrangement was on the first successful turbine engine in commercial service, the RR Dart series.
One lever (and an electric fuel trimmer) to set the power and RPM.
Good idea, then, even better now, even after all these years.
So what if it was a screamer during ground ops...airports are supposed to be noisey places...
