Rotation side of jet engine? / critical engine?
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The Pegasus in the Harrier has LP and HP spools rotating in the opposite direction (to minimise gyroscopic precession in the hover
To add a fly to the ointment, Coriolis meant reversing everything in the Southern Hemisphere (remember it was already contra-rotating, so there's no ability to swap the direction of rotation). Embarked on a ship, this involved a LOT of concentration having crossed 'The Line' and having to do it all over again on the way home wasn't too much fun either.
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Pontius,
do you mean that my Piper Cub in Australia will yaw right during take-off when I’ll push forward to lift its tail , due to Coriolis effect, ??
I do not believe that ! ! Be serious ! !
do you mean that my Piper Cub in Australia will yaw right during take-off when I’ll push forward to lift its tail , due to Coriolis effect, ??
I do not believe that ! ! Be serious ! !
Rotation side of jet engine? / critical engine?
I do not believe that ! ! Be serious ! !
But if you are, you might want to re-read the thread title.
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DaveReid
DaveReid
I suspect that you misunderstand the fact that rotational mass (i.e.: rotors, like spools, propellers,fans) dynamics is completely independent from the type of engine behind it ! !
D
I suspect that you misunderstand the fact that rotational mass (i.e.: rotors, like spools, propellers,fans) dynamics is completely independent from the type of engine behind it ! !
D
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Daniel, what Pointus is talking about is an effect induced by the propeller. Since because the propeller is also a "wing" when you nose up, the the angle of attacks change between (or among) the blades. so the down going blade and the up going blade produce a net force that make a yaw - Asymmetric propeller effect
Heavy 4 engined turbo props have their vertical stabilizer offset the butt line of the fuselage to compensate this, and not sure about the Cub but small single engined piston props have their engine little angled against the butt line. I have also heard (not seen yet!) there are small props with wash-in in one wing and wash-out in the other.
the maximum effect of these forces induce at the cruising speed, so they design the plane to be stable for the cruise.
stand to be corrected!
Heavy 4 engined turbo props have their vertical stabilizer offset the butt line of the fuselage to compensate this, and not sure about the Cub but small single engined piston props have their engine little angled against the butt line. I have also heard (not seen yet!) there are small props with wash-in in one wing and wash-out in the other.
the maximum effect of these forces induce at the cruising speed, so they design the plane to be stable for the cruise.
stand to be corrected!
Last edited by code0; 8th Nov 2012 at 15:16.
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Code0
Code0
thank you for clarification, but..
the effect you are referring to is sometime called P-Factor (I do not know why), and is purely, as correctly you are saying, an aerodynamic effect ; when the propeller axis is not parallel with the wind (but only and strictly in this case) , the downgoing blade has an higher AoA of the upgoing blade, and this creates an asymmetry, which results in moving the center of lift (thrust, in the propeller case) toward the downgoing blade – and not in the center of the propellerazis. This happens an a bycicle a/c, even if it rests in its three-point attitude ; even if the axis is not moved, the asymmetry gives a yawing torque.
But when the tail is lifted in ‘my’ Cub (or in the Harrier !), the rotor axis (propeller, or jet engine spool in the Harrier case) is subject to a disturbing torque, and reacts with a 90° torque, which becomes greater if the disturbing action is quicker (gyroscopic effect)
D
thank you for clarification, but..
the effect you are referring to is sometime called P-Factor (I do not know why), and is purely, as correctly you are saying, an aerodynamic effect ; when the propeller axis is not parallel with the wind (but only and strictly in this case) , the downgoing blade has an higher AoA of the upgoing blade, and this creates an asymmetry, which results in moving the center of lift (thrust, in the propeller case) toward the downgoing blade – and not in the center of the propellerazis. This happens an a bycicle a/c, even if it rests in its three-point attitude ; even if the axis is not moved, the asymmetry gives a yawing torque.
But when the tail is lifted in ‘my’ Cub (or in the Harrier !), the rotor axis (propeller, or jet engine spool in the Harrier case) is subject to a disturbing torque, and reacts with a 90° torque, which becomes greater if the disturbing action is quicker (gyroscopic effect)
D
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you are welcome!
Add to that...
The effects acting on a propeller aircraft are as follows - NOT the Harrier and I have no idea about how Harrier behaves!
Torque Reaction - your engines turn one way and fuselage try to turn the other way - makes a yaw effect
Gyroscopic Effect - when you yaw, it tries to make a nose down and when you pitch up, it tries to make a yaw, its just because the 90` effect of the point a force is applied from.
Spiral Effect - single engine prop wash make a "air wrap-around" the fuselage and attack the fin, making a yaw!
Asymmetric Blade Effect - what you have precisely mentioned
Finally and importantly
Atmospheric conditions - whatever the weather report contains!
I am not sure how these effects are applied on a turbofan, but mostly applied on turbo props and piston props! the explanation is quite lengthy! if you can do a search on above mentioned you will sure find the answer what you are looking for.
Code0
Add to that...
The effects acting on a propeller aircraft are as follows - NOT the Harrier and I have no idea about how Harrier behaves!
Torque Reaction - your engines turn one way and fuselage try to turn the other way - makes a yaw effect
Gyroscopic Effect - when you yaw, it tries to make a nose down and when you pitch up, it tries to make a yaw, its just because the 90` effect of the point a force is applied from.
Spiral Effect - single engine prop wash make a "air wrap-around" the fuselage and attack the fin, making a yaw!
Asymmetric Blade Effect - what you have precisely mentioned
Finally and importantly
Atmospheric conditions - whatever the weather report contains!
I am not sure how these effects are applied on a turbofan, but mostly applied on turbo props and piston props! the explanation is quite lengthy! if you can do a search on above mentioned you will sure find the answer what you are looking for.
Code0
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Code0
“NOT the Harrier” ? Not really indeed ! Gyroscopic effect act on every (every) rotational mass, even on rotor spool and fans (and if I remember correctly, Harrier has a proportionately biiig fan! ).
….and after having ‘my search’ done during many years of my professional life, I can confirm you that, as I have correctly stated in my post #27, only the gyroscopic effect - among those you listed -is the only one that applies also to jet engines – including the Harrier’s one , though me too I have no idea how this aircraft behaves .But I am sure engine and bearing designers did a lot of homework to take it into consideration in their design ! !
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“NOT the Harrier” ? Not really indeed !
But I will leave one clue with you, as the Harrier could "hover" or take off and land vertically, during this maneuver, if the engine is rotated in one direction, how to cancel out the force? wouldn't the fuselage and the whole body try to yaw (rather rotate) as it takes off? Helicopters have a tail rotor, does the Pegasus has some sort of mechanism? I have no idea, just for the learning!
Code
But I will leave one clue with you, as the Harrier could "hover" or take off and land vertically, during this maneuver, if the engine is rotated in one direction, how to cancel out the force?
GEnx has contra rotating shafts as do some variants of the RR Trent.
I think it's to reduce the need for a row of stators between the IP/LP shafts in the case of the Trent and the LP/HP shafts for the GEnx.
Shortens the engine, saves weight etc.
Although I could be wrong.
Shortens the engine, saves weight etc.
Although I could be wrong.
I think it's to reduce the need for a row of stators between the IP/LP shafts in the case of the Trent and the LP/HP shafts for the GEnx.
Shortens the engine, saves weight etc.
Shortens the engine, saves weight etc.
Agree with that, I must have missed another ewe turn again. I thought we were in a critical engine on a side thread
