Sense of Propellor rotation
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Sense of Propellor rotation
Other than in engines with counter rotating propellors, is there a technical or historical reason for choosing an anticlockwise propellor rotation?
(when regarded from the front) I presume this is universal in western piston and turboprop designs.
(when regarded from the front) I presume this is universal in western piston and turboprop designs.
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While clockwise (viewed from rear) is predominant, there are still plenty of exceptions even today. There's no hard technical reason, but since a prop needs to be fitted, it's an advantage to make the engine turn the same direction as available props.
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With non-geared engines, subject to the engine manufacturer. Us built engines rotate clockwise where UK built engines rotate counterclockwise… even the jet engines GE and Pratts rotate clockwise whilst the RR counterclockwise.
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Not so ... Clockwise (from the rear) is only "normal" for American engines, whereas British piston engines rotate in the counter-clockwise (from the rear) direction.
That, of course, begs another question ...
JD
sorry, captjns, I inadvertently duplicated your post ...
That, of course, begs another question ...
JD
sorry, captjns, I inadvertently duplicated your post ...
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Oops... forgot about the Piper (PA-34) Senca. It has continental counter rotating engines. and the PA-31-325, the Piper Navajo CR has Lycoming counter rotating engines.
I believe that low-power British engines (gipsy major, etc) traditionally rotate anti-clockwise (when viewed from behind) to make them easier for a right-handed chap (or chapess) to swing them.
When standing in front, ones right arm naturally swings clockwise.
Eck
When standing in front, ones right arm naturally swings clockwise.
Eck
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Prop swinging.
When standing in front, ones right arm naturally swings clockwise.
Roger.
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Jet engine rotation.
With non-geared engines, subject to the engine manufacturer. Us built engines rotate clockwise where UK built engines rotate counterclockwise… even the jet engines GE and Pratts rotate clockwise whilst the RR counterclockwise.
Roger.
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US vs UK
In theory, yes, due to gyroscopic loads the rotors place on the engine structure and thus into the mountings.
But the gyro loads are quite insignificant compared to the control forces the pilot employs during normal maneuvers, and I doubt anyone ever notices.
PS - the engines available for the 757 are R-R and P&W, not GE.
But the gyro loads are quite insignificant compared to the control forces the pilot employs during normal maneuvers, and I doubt anyone ever notices.
PS - the engines available for the 757 are R-R and P&W, not GE.
Landroger,
Back in the '70s I did start Chipmunks, Stampes and Tigers a few times by prop-swinging. I found the position that the prop stopped in (2 o'clock) made it easy to use my right arm, but I see what you mean about the 'backhanded swing'. I must say I was always very careful (and a little scared). There was a horror story doing the rounds then about a poor guy who walked towards the entry door of an Aero Commander with the engines running and got minced by the prop. They found one of his hands on the hangar roof.
The trickiest part was taking a passenger for a flight and having to brief them on the operation of the cockpit controls. Always made sure we had chocks installed and brakes on for that exercise!
Back in the '70s I did start Chipmunks, Stampes and Tigers a few times by prop-swinging. I found the position that the prop stopped in (2 o'clock) made it easy to use my right arm, but I see what you mean about the 'backhanded swing'. I must say I was always very careful (and a little scared). There was a horror story doing the rounds then about a poor guy who walked towards the entry door of an Aero Commander with the engines running and got minced by the prop. They found one of his hands on the hangar roof.
The trickiest part was taking a passenger for a flight and having to brief them on the operation of the cockpit controls. Always made sure we had chocks installed and brakes on for that exercise!
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Griffon rotates the opposite way to the Merlin.
As to the man walking into the prop of the Aero Commander, on the C152 the wing strut would tend to prevent that a bit, but the new 162 sadly has the strut behind the door, which in my eyes is an accident in the making.
AS for some of the Gas Turbs, well a lot of them go both ways, as in the HP/ LP compressor rotations to counteract the rotational forces.
Damn u beat me to it as I typed !!
As to the man walking into the prop of the Aero Commander, on the C152 the wing strut would tend to prevent that a bit, but the new 162 sadly has the strut behind the door, which in my eyes is an accident in the making.
AS for some of the Gas Turbs, well a lot of them go both ways, as in the HP/ LP compressor rotations to counteract the rotational forces.
Damn u beat me to it as I typed !!
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Before all the modern c/r ships -
The fighter pilot's lament:
"Don't give me a P-38
with propellers that counter-rotate;
she loop and she'l spin
and she'll soon auger in -
Don't give me a P-38!"
The fighter pilot's lament:
"Don't give me a P-38
with propellers that counter-rotate;
she loop and she'l spin
and she'll soon auger in -
Don't give me a P-38!"
The Rolls Royce (Bristol) Pegasus engine in the Harrier uses counter rotating shafts to reduce the gyroscopic effect on the low speed handling of the aircraft.
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Thanks for the information guys - fascinating stuff. As for contra rotating spools in modern engines, you can sort of see why from the gas flow/reaction point of view, but any bearing between two spools will naturally have elements running at twice the speed of a fixed outer/moving inner arrangement and several times that of spools rotating in the same orientation. In that case I imagine one spool would be running at a percentage of the other and thus the relative speeds are quite small.
Roger.
Roger.