Aerodynamics ~ Coriolis
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Aerodynamics ~ Coriolis
To keep separate subjects in separate threads - Oh sure 
___________
A change in the coning angle is an example of the Coriolis effect.
Is teetering an example of a 'temporary' Coriolis effect; or is it an example of the Knuckle Joint effect?
[ 27 November 2001: Message edited by: Dave Jackson ]
___________
A change in the coning angle is an example of the Coriolis effect.
Is teetering an example of a 'temporary' Coriolis effect; or is it an example of the Knuckle Joint effect?
[ 27 November 2001: Message edited by: Dave Jackson ]
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To: Dave Jackson
“A change in the coning angle is an example of the Coriolis effect”.
I believe that you have placed the cart ahead of the horse. Speaking about multi blade helicopters that have lead lag as well as flapping capability any change in cyclic position will effect the cone angle. Cyclic input causes the blades to flap up from the pure hover cone and it causes the blades to flap down relative to the pure hover cone angle. Aft cyclic will cause the cone angle to deflect rearward and the opposite is true for forward cyclic. In the process of coning deflection from the pure hover cone angle the blades flap as previously stated. It is the flapping that causes the rotating axis of the disc to deviate from the driven axis. When blades flap they are made to lead and lag due to conservation of angular momentum or, Coriolis effect. All of this assumes that there is no compensation for tail rotor propeller effect and that the tip path is parallel to the local horizon. If these conditions are taken into consideration the cone angle will be deflected leftward to compensate for propeller effect and this would result in flapping with resultant lead lag.
You can look at the change in cone angle as the result of either aerodynamic precession or, gyroscopic precession.
“A change in the coning angle is an example of the Coriolis effect”.
I believe that you have placed the cart ahead of the horse. Speaking about multi blade helicopters that have lead lag as well as flapping capability any change in cyclic position will effect the cone angle. Cyclic input causes the blades to flap up from the pure hover cone and it causes the blades to flap down relative to the pure hover cone angle. Aft cyclic will cause the cone angle to deflect rearward and the opposite is true for forward cyclic. In the process of coning deflection from the pure hover cone angle the blades flap as previously stated. It is the flapping that causes the rotating axis of the disc to deviate from the driven axis. When blades flap they are made to lead and lag due to conservation of angular momentum or, Coriolis effect. All of this assumes that there is no compensation for tail rotor propeller effect and that the tip path is parallel to the local horizon. If these conditions are taken into consideration the cone angle will be deflected leftward to compensate for propeller effect and this would result in flapping with resultant lead lag.
You can look at the change in cone angle as the result of either aerodynamic precession or, gyroscopic precession.
Lu, Lu, Lu,
1. Flapping has nothing to do with cone angle.
2. Precession has nothing to do with cone angle.
3. While the tip path plane changes with the introduction of cyclic, and the disc is tilted left (American heicopter) due to tail rotor roll, neither of these have anything to do with cone angle.
I suggest you look up the definition of cone angle, and then mix in all the other complications. Again, we are stuck on basics.
Dave:
Changes in cone angle do affect the RRPM due to the conservation of angular momentum. Coning angle is a function of G (or to be more accurate: the lift being produced by the blades) Vs RRPM where and increase in lift or a decrease in RRPM will increase cone angle.
Thus, when you flare the aircraft, you are (apart from aerodynamic flare effects) increasing the G and therefore the apparent weight of the aircraft. The cone angle thus increases. As the cone angle increases, the CofG of the blade moves closer to the center of rotation, and the RRPM increases (conservation of angular momentum). The RPM increase is limited by the fact that an RRPM increase will cause more centripetal (or centrifugal if you prefer) force thereby trying to reduce the cone angle. The engine spools down to get the RRPM back to 100% (governed turbine here) and a new equilibrium is found. As you relax the flare or bunt, the reverse happens: G is reduced, thus coning angle, thus CofG moves out again, and according to conservation of angular momentum, the RRPM droops until the engine can catch up and restore equilibrium.
The old analagy is the ice skating bint. She enters a spin and then draws her arms into her body. She goes much faster, her dress lifts higher and we can enjoy seeing her knickers (why else would you watch ice skating?) . She then puts her arms out and slows down, her skirt falls and there is no point watching any further. Conservation of viewer intrest...I mean angular momentum!!
As for teetering heads, you have bought Lu's line on Bell teetering systems. Despite Lu's theories, the Bell blades do flap individually without an equal flap down on the other side. Accordingly, they react the same with regard to cone angle and conservation of angular momentum. And all those whom have flown the Huey can tell you, there is a LOT of coning angle visible after a touch down auto if you are anything like me!!
What is the knuckle joint effect? Is that what I experience when I get drunk and gob off in the bar, or is it another term for Hookes Joint Effect?
1. Flapping has nothing to do with cone angle.
2. Precession has nothing to do with cone angle.
3. While the tip path plane changes with the introduction of cyclic, and the disc is tilted left (American heicopter) due to tail rotor roll, neither of these have anything to do with cone angle.
I suggest you look up the definition of cone angle, and then mix in all the other complications. Again, we are stuck on basics.
Dave:
Changes in cone angle do affect the RRPM due to the conservation of angular momentum. Coning angle is a function of G (or to be more accurate: the lift being produced by the blades) Vs RRPM where and increase in lift or a decrease in RRPM will increase cone angle.
Thus, when you flare the aircraft, you are (apart from aerodynamic flare effects) increasing the G and therefore the apparent weight of the aircraft. The cone angle thus increases. As the cone angle increases, the CofG of the blade moves closer to the center of rotation, and the RRPM increases (conservation of angular momentum). The RPM increase is limited by the fact that an RRPM increase will cause more centripetal (or centrifugal if you prefer) force thereby trying to reduce the cone angle. The engine spools down to get the RRPM back to 100% (governed turbine here) and a new equilibrium is found. As you relax the flare or bunt, the reverse happens: G is reduced, thus coning angle, thus CofG moves out again, and according to conservation of angular momentum, the RRPM droops until the engine can catch up and restore equilibrium.
The old analagy is the ice skating bint. She enters a spin and then draws her arms into her body. She goes much faster, her dress lifts higher and we can enjoy seeing her knickers (why else would you watch ice skating?) . She then puts her arms out and slows down, her skirt falls and there is no point watching any further. Conservation of viewer intrest...I mean angular momentum!!
As for teetering heads, you have bought Lu's line on Bell teetering systems. Despite Lu's theories, the Bell blades do flap individually without an equal flap down on the other side. Accordingly, they react the same with regard to cone angle and conservation of angular momentum. And all those whom have flown the Huey can tell you, there is a LOT of coning angle visible after a touch down auto if you are anything like me!!
What is the knuckle joint effect? Is that what I experience when I get drunk and gob off in the bar, or is it another term for Hookes Joint Effect?
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To: helmet fire
I don’t know what your definition of cone angle is but here is mine. First of all we have to remove one thing from the equation and that is some helicopters have a left bias built into the mixing unit and when the pilot pulls collective tail rotor propeller effect is automatically compensated for. We will not consider this as it has an effect on cone angle nor, will we consider pilot input to compensate for translation as this too effects the cone angle.
With the helicopter on the ground and the rotor turning at speed the cyclic is in the rigged neutral position the blades are in the pure radial position as the only force acting on them is centrifugal.
At this point there is zero cone angle. If you have a Bell with a pre-coned head and it is in the same condition as described above that is the zero cone angle for that aircraft. It is most apparent on an articulated rotor system so we will deal with that type of rotor as any change in the cone angle effects lead and lag.
This can be best described by viewing the helicopter from the left-hand side. When the blades are in a pure radial position the blades are in line with the rotor head so there is a straight line from tip to tip passing through the rotorhead. At this point in time the driving axis (mast) and the driven axis (a line perpendicular to the rotor disc and coincident with the mast) are in alignment and, there is no cone angle.
When the pilot pulls collective in order to hover the blades will cone up to the point where lift is balanced out by the centrifugal forces and now the disc forms a flat ‘V” with the flat portion being the rotorhead. At this time the driven and driving axes are still coincident with each other. The flat “V” is the basic cone angle and all other movement of the blade disc will be about this point.
When the pilot pushes forward cyclic the blade over the tail will raise and the blade over the nose will fall. If you draw a line from the higher rear blade to the lower forward blade you have described the tip path plane for this condition. Now, draw a line that is normal to the tip path plane and intersect the center of the rotorhead. This line represents the driven axis. Draw a line coincident with the mast. The difference in angular displacement between the two lines can be also construed as the coning angle. It is this difference that results in lead and lag due to Coriolis forces or conservation of angular momentum. The greater the angular difference the greater the lead lag. If the pilot brings the two lines to a point where they are coincident with each other there is no leading or lagging.
Confused?
1. Flapping has nothing to do with cone angle.
Response:
The way I learned it flapping of the blades above the radial position is what prescribes the cone angle. The higher the flap the greater the angle.
2. Precession has nothing to do with cone angle.
Response:
Precession has everything to do with the cone angle. Whether you believe in aerodynamic or gyroscopic precession precession is what causes the tilting of the disc and as a result it creates an angular difference between the driving axis and the driven axis.
3. While the tip path plane changes with the introduction of cyclic, and the disc is tilted left (American helicopter) due to tail rotor roll, neither of these have anything to do with cone angle.
Response:
As I indicated above compensation for tail rotor propeller effect will cause a change in cone angle. That is why I removed it from the equation and referenced the viewing angle for the rotor system.
[ 28 November 2001: Message edited by: Lu Zuckerman ]
[ 28 November 2001: Message edited by: Lu Zuckerman ]
I don’t know what your definition of cone angle is but here is mine. First of all we have to remove one thing from the equation and that is some helicopters have a left bias built into the mixing unit and when the pilot pulls collective tail rotor propeller effect is automatically compensated for. We will not consider this as it has an effect on cone angle nor, will we consider pilot input to compensate for translation as this too effects the cone angle.
With the helicopter on the ground and the rotor turning at speed the cyclic is in the rigged neutral position the blades are in the pure radial position as the only force acting on them is centrifugal.
At this point there is zero cone angle. If you have a Bell with a pre-coned head and it is in the same condition as described above that is the zero cone angle for that aircraft. It is most apparent on an articulated rotor system so we will deal with that type of rotor as any change in the cone angle effects lead and lag.
This can be best described by viewing the helicopter from the left-hand side. When the blades are in a pure radial position the blades are in line with the rotor head so there is a straight line from tip to tip passing through the rotorhead. At this point in time the driving axis (mast) and the driven axis (a line perpendicular to the rotor disc and coincident with the mast) are in alignment and, there is no cone angle.
When the pilot pulls collective in order to hover the blades will cone up to the point where lift is balanced out by the centrifugal forces and now the disc forms a flat ‘V” with the flat portion being the rotorhead. At this time the driven and driving axes are still coincident with each other. The flat “V” is the basic cone angle and all other movement of the blade disc will be about this point.
When the pilot pushes forward cyclic the blade over the tail will raise and the blade over the nose will fall. If you draw a line from the higher rear blade to the lower forward blade you have described the tip path plane for this condition. Now, draw a line that is normal to the tip path plane and intersect the center of the rotorhead. This line represents the driven axis. Draw a line coincident with the mast. The difference in angular displacement between the two lines can be also construed as the coning angle. It is this difference that results in lead and lag due to Coriolis forces or conservation of angular momentum. The greater the angular difference the greater the lead lag. If the pilot brings the two lines to a point where they are coincident with each other there is no leading or lagging.
Confused?
1. Flapping has nothing to do with cone angle.
Response:
The way I learned it flapping of the blades above the radial position is what prescribes the cone angle. The higher the flap the greater the angle.
2. Precession has nothing to do with cone angle.
Response:
Precession has everything to do with the cone angle. Whether you believe in aerodynamic or gyroscopic precession precession is what causes the tilting of the disc and as a result it creates an angular difference between the driving axis and the driven axis.
3. While the tip path plane changes with the introduction of cyclic, and the disc is tilted left (American helicopter) due to tail rotor roll, neither of these have anything to do with cone angle.
Response:
As I indicated above compensation for tail rotor propeller effect will cause a change in cone angle. That is why I removed it from the equation and referenced the viewing angle for the rotor system.
[ 28 November 2001: Message edited by: Lu Zuckerman ]
[ 28 November 2001: Message edited by: Lu Zuckerman ]
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Lu,
It's a language thing. Helicopter pilots, aerodynamicists and engineers call the COLLECTIVE angular displacement of the blades coning and CYCLIC changes are called flapping. Why not join us on earth and speak our language instead of inventing your own designed to contradict everything anyone says?
It's a language thing. Helicopter pilots, aerodynamicists and engineers call the COLLECTIVE angular displacement of the blades coning and CYCLIC changes are called flapping. Why not join us on earth and speak our language instead of inventing your own designed to contradict everything anyone says?
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To: Grey Area
“It's a language thing. Helicopter pilots, aerodynamicists and engineers call the COLLECTIVE angular displacement of the blades coning and CYCLIC changes are called flapping. Why not join us on earth and speak our language instead of inventing your own designed to contradict everything anyone says”?
Response:
In order for the blade to cone they must flap up on the horizontal hinge or if they are of the elastomeric persuasion they flap upward on the theoretical flapping point. So in this case, coning = flapping.
With cyclic input flapping takes place and the disc for whatever reason tips in the direction of cyclic movement. This produces cyclic flapping (up and down) and the cyclic flapping alters the coning angle. So in this case, flapping = change in cone angle.
They are all interrelated and one could not exist without the other.
“It's a language thing. Helicopter pilots, aerodynamicists and engineers call the COLLECTIVE angular displacement of the blades coning and CYCLIC changes are called flapping. Why not join us on earth and speak our language instead of inventing your own designed to contradict everything anyone says”?
Response:
In order for the blade to cone they must flap up on the horizontal hinge or if they are of the elastomeric persuasion they flap upward on the theoretical flapping point. So in this case, coning = flapping.
With cyclic input flapping takes place and the disc for whatever reason tips in the direction of cyclic movement. This produces cyclic flapping (up and down) and the cyclic flapping alters the coning angle. So in this case, flapping = change in cone angle.
They are all interrelated and one could not exist without the other.
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Lu,
It's a language thing. Helicopter pilots, aerodynamicists and engineers call the COLLECTIVE angular displacement of the blades coning and CYCLIC changes are called flapping. Why not join us on earth and speak our language instead of inventing your own designed to contradict everything anyone says?
QED
It's a language thing. Helicopter pilots, aerodynamicists and engineers call the COLLECTIVE angular displacement of the blades coning and CYCLIC changes are called flapping. Why not join us on earth and speak our language instead of inventing your own designed to contradict everything anyone says?
QED
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helmet fire:
Please excuse my fellow countryman, Lu. He live in Quebec and it is quite obvious that he writes in English but only reads in French.
A very clear description of Coriolis.
Your analogy with the coning skirt makes it worthwhile to prod deeper into this subject.
Please, Please, Please, don't say that "you have bought Lu's line"
I believe that rotorcraft's reference to the Hook's Joint effect (universal joint, Cardan joint) is similar to rotorcraft's reference to centrifugal force. They both come from the early days of gyrocopters, and helicopters with teetering rotors. Hooke's joint appears to be a reference to gimbaled rotorheads, such as the Bell-47. Today's teetering rotor heads only have one joint, hence knuckle joint.
The reference to 'temporary' Coriolis effect v.s. knuckle joint effect is a mind teaser. It is easier to equated with a teetering rotor. It is related to the application of, and the temporary maintaining of, a cyclic input. In this situation, a sinusoidal rotational velocity is taking place.
Assume a person is capable of putting one of his eyeballs on the mast's axis (hub plane) and look up at the blade tips. He will see their path as being elliptical and will assume that the rotor blades are therefor accelerating and decelerating twice per revolution; hence 'temporary' Coriolis effect.
If he puts one of his eyeballs in the center of the rotor disk (tip path plane) and looks down, he will see a sinusoidal discrepancy in the relationship between the rotor disk's rpm and the mast's rpm; hence knuckle joint effect.
If he has both eyeballs open at the same time he going to develop a split personality.
[ 28 November 2001: Message edited by: Dave Jackson ]
Please excuse my fellow countryman, Lu. He live in Quebec and it is quite obvious that he writes in English but only reads in French.
A very clear description of Coriolis.
Your analogy with the coning skirt makes it worthwhile to prod deeper into this subject.
Please, Please, Please, don't say that "you have bought Lu's line"
I believe that rotorcraft's reference to the Hook's Joint effect (universal joint, Cardan joint) is similar to rotorcraft's reference to centrifugal force. They both come from the early days of gyrocopters, and helicopters with teetering rotors. Hooke's joint appears to be a reference to gimbaled rotorheads, such as the Bell-47. Today's teetering rotor heads only have one joint, hence knuckle joint.
The reference to 'temporary' Coriolis effect v.s. knuckle joint effect is a mind teaser. It is easier to equated with a teetering rotor. It is related to the application of, and the temporary maintaining of, a cyclic input. In this situation, a sinusoidal rotational velocity is taking place.
Assume a person is capable of putting one of his eyeballs on the mast's axis (hub plane) and look up at the blade tips. He will see their path as being elliptical and will assume that the rotor blades are therefor accelerating and decelerating twice per revolution; hence 'temporary' Coriolis effect.
If he puts one of his eyeballs in the center of the rotor disk (tip path plane) and looks down, he will see a sinusoidal discrepancy in the relationship between the rotor disk's rpm and the mast's rpm; hence knuckle joint effect.
If he has both eyeballs open at the same time he going to develop a split personality.
[ 28 November 2001: Message edited by: Dave Jackson ]
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To: Grey Area
I totally agree with you. Collective causes coning and cyclic causes flapping. All I was doing is to explain what is happening when the pilot pulls collective. In order to cone the blades must flap upward. That is what happens. This forms the collective cone angle. When the pilot pushes cyclic the blades will flap and the disc will tilt. On the advancing side the blades are flapping downward and on the retreating side the blades are flapping upward. Do we agree on that?
In establishing this tilt to the rotor disc there is a difference between the driving axis and the driven axis. It is this difference that causes the leading and lagging. Do we agree on that?
If we don’t agree on these two points then it is you that have the problem not me.
This last statement is not meant to be offensive.
To: Dave Jackson:
I am not a countryman although I live in Quebec and I don’t speak or read a word of French.
I totally agree with you. Collective causes coning and cyclic causes flapping. All I was doing is to explain what is happening when the pilot pulls collective. In order to cone the blades must flap upward. That is what happens. This forms the collective cone angle. When the pilot pushes cyclic the blades will flap and the disc will tilt. On the advancing side the blades are flapping downward and on the retreating side the blades are flapping upward. Do we agree on that?
In establishing this tilt to the rotor disc there is a difference between the driving axis and the driven axis. It is this difference that causes the leading and lagging. Do we agree on that?
If we don’t agree on these two points then it is you that have the problem not me.
This last statement is not meant to be offensive.
To: Dave Jackson:
I am not a countryman although I live in Quebec and I don’t speak or read a word of French.
Lu,
Grey Area tried to explain something to you the first time. You merely repeated your lines. So he merely repeated his, but only this time you agreed with him! How did that work?
You said: >>To: Grey Area
I totally agree with you. Collective causes coning and cyclic causes flapping. All I was doing is to explain what is happening when the pilot pulls collective.<<
But Lu, you are wrong. That is NOT what Grey Area said. Collective DOES NOT cause conning (although it can). What he said was – Conning is the term applied to COLLECTIVE change of angular displacement…NOT a change DUE to collective. Do you have any idea of the distinction? It goes back to your misapplication of the term conning angle. I say again: You need to read the definition of this prior to continuing any meaningful discussion on this point. Simply stating your definition IS NOT a substitute for the actual definition. While you are at it, I think you provided an “explanation” not a “definition”, so look up the word definition too!
Perhaps then you will be able to respond to my points with some form of coherence, as I have shown below in sticking to the original points
1. Flapping has nothing to do with cone angle.
Lu Response:
The way I learned it flapping of the blades above the radial position is what prescribes the cone angle. The higher the flap the greater the angle.
My Response:
The way you learned it IS the problem, go and get a definition out of all those books you quote about gyroscopics, etc. “Radial position” is not a term applicable in this discussion. If you get the definition of cone angle you will find no reference to flapping (or radial position). What Grey Area was saying is pertinent here. Blades can flap independently – ie CYCLICALLY, ie flap to different positions dependant upon where they are in the rotational CYCLE. That is why it is called CYCLIC flap. Again, you STILL need to learn the basics of flapping to equality to grasp this. Flap is not the term we apply to a collective (all together) change in angular displacement. Therefore, your statement that >>the higher the flap the greater the cone angle<< CANNOT be correct. I
If it WAS correct, lets look at how you proposition holds up. Aircraft bunts. Blades flap down at front and up at rear. Therefore, has the cone angle increased (viewed from rear) or decreased (viewed from front)? Aircraft now pitches nose up, blades flap up at front, down at rear, what has happened to the cone angle Lu? NOW do you see the flaw Lu?
2. Precession has nothing to do with cone angle.
Lu’s Response:
Precession has everything to do with the cone angle. Whether you believe in aerodynamic or gyroscopic precession precession is what causes the tilting of the disc and as a result it creates an angular difference between the driving axis and the driven axis.
My Response:
Tilting of the disc IS NOT changing the cone angle. See the argument under (1). Precession is applicable to flapping (and understanding of flapping to equality will again be required to grasp this), therefore precession (like flapping) has nothing to do with cone angle. Now you have introduced more terms: driven axis and driving axis. If you stick to the common language suggested by Grey Area, then I might be able to examine your statement, because (and remember – I am no aerodynamicist) I have no idea what you are saying with these terms. Suffice to say, cone angle definition does not include these terms.
3. While the tip path plane changes with the introduction of cyclic, and the disc is tilted left (American helicopter) due to tail rotor roll, neither of these have anything to do with cone angle.
Lu’s Response:
As I indicated above compensation for tail rotor propeller effect will cause a change in cone angle. That is why I removed it from the equation and referenced the viewing angle for the rotor system.
My response:
No Lu. Tilting the disc has nothing to do with cone angle because this is achieved cyclically as per the arguments above in (1). Doesn’t matter why you are tilting the disc (tail rotor propeller effect or what) it is not cone angle.
I believe you are mixed up with the terminology. A “DISC” does not actually exist, it is merely the term applied to the circle scribed by the tip path plane. The disc does not tilt as a solid, in fact the tip path plane changes due to the different flap position of the blades as they go around, creating the “illusion” of disc tilt. Grasping this may also help you understand why countering the pitch up and roll during retreating blade stall with cyclic can severely exacerbate the problem – it is not a disc to be changed, but individual blades that need consideration.
Dave,
I only have eyes for the ice skater. I cannot get my head around your suggestions - sorry – I have a brain only for ice skaters too! Je ne comprendez pas. (or something like that).
Grey Area tried to explain something to you the first time. You merely repeated your lines. So he merely repeated his, but only this time you agreed with him! How did that work?
You said: >>To: Grey Area
I totally agree with you. Collective causes coning and cyclic causes flapping. All I was doing is to explain what is happening when the pilot pulls collective.<<
But Lu, you are wrong. That is NOT what Grey Area said. Collective DOES NOT cause conning (although it can). What he said was – Conning is the term applied to COLLECTIVE change of angular displacement…NOT a change DUE to collective. Do you have any idea of the distinction? It goes back to your misapplication of the term conning angle. I say again: You need to read the definition of this prior to continuing any meaningful discussion on this point. Simply stating your definition IS NOT a substitute for the actual definition. While you are at it, I think you provided an “explanation” not a “definition”, so look up the word definition too!
Perhaps then you will be able to respond to my points with some form of coherence, as I have shown below in sticking to the original points
1. Flapping has nothing to do with cone angle.
Lu Response:
The way I learned it flapping of the blades above the radial position is what prescribes the cone angle. The higher the flap the greater the angle.
My Response:
The way you learned it IS the problem, go and get a definition out of all those books you quote about gyroscopics, etc. “Radial position” is not a term applicable in this discussion. If you get the definition of cone angle you will find no reference to flapping (or radial position). What Grey Area was saying is pertinent here. Blades can flap independently – ie CYCLICALLY, ie flap to different positions dependant upon where they are in the rotational CYCLE. That is why it is called CYCLIC flap. Again, you STILL need to learn the basics of flapping to equality to grasp this. Flap is not the term we apply to a collective (all together) change in angular displacement. Therefore, your statement that >>the higher the flap the greater the cone angle<< CANNOT be correct. I
If it WAS correct, lets look at how you proposition holds up. Aircraft bunts. Blades flap down at front and up at rear. Therefore, has the cone angle increased (viewed from rear) or decreased (viewed from front)? Aircraft now pitches nose up, blades flap up at front, down at rear, what has happened to the cone angle Lu? NOW do you see the flaw Lu?
2. Precession has nothing to do with cone angle.
Lu’s Response:
Precession has everything to do with the cone angle. Whether you believe in aerodynamic or gyroscopic precession precession is what causes the tilting of the disc and as a result it creates an angular difference between the driving axis and the driven axis.
My Response:
Tilting of the disc IS NOT changing the cone angle. See the argument under (1). Precession is applicable to flapping (and understanding of flapping to equality will again be required to grasp this), therefore precession (like flapping) has nothing to do with cone angle. Now you have introduced more terms: driven axis and driving axis. If you stick to the common language suggested by Grey Area, then I might be able to examine your statement, because (and remember – I am no aerodynamicist) I have no idea what you are saying with these terms. Suffice to say, cone angle definition does not include these terms.
3. While the tip path plane changes with the introduction of cyclic, and the disc is tilted left (American helicopter) due to tail rotor roll, neither of these have anything to do with cone angle.
Lu’s Response:
As I indicated above compensation for tail rotor propeller effect will cause a change in cone angle. That is why I removed it from the equation and referenced the viewing angle for the rotor system.
My response:
No Lu. Tilting the disc has nothing to do with cone angle because this is achieved cyclically as per the arguments above in (1). Doesn’t matter why you are tilting the disc (tail rotor propeller effect or what) it is not cone angle.
I believe you are mixed up with the terminology. A “DISC” does not actually exist, it is merely the term applied to the circle scribed by the tip path plane. The disc does not tilt as a solid, in fact the tip path plane changes due to the different flap position of the blades as they go around, creating the “illusion” of disc tilt. Grasping this may also help you understand why countering the pitch up and roll during retreating blade stall with cyclic can severely exacerbate the problem – it is not a disc to be changed, but individual blades that need consideration.
Dave,
I only have eyes for the ice skater. I cannot get my head around your suggestions - sorry – I have a brain only for ice skaters too! Je ne comprendez pas. (or something like that).
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To: Helmet Fire
Let’s first discuss comparative religion. Each religion (Judeo Christian) has it’s own bible and they have their own liturgy yet when it comes down to it they worship the same god. In the helicopter religion there are different liturgies and there are different bibles yet when you get down to basics the bibles and the liturgies describe the same thing but they employ different words. Precession is one point. One religion teaches aerodynamic precession and the other teaches gyroscopic precession. It seems that the definition of coning angle fits into this category. Whether we are talking religion relating to god or the helicopter religion it is difficult to proselytize one individual and bring him into your religion especially if you are trying to convince that person that your religious concepts are better and more pure than his concepts.
Here are a few excerpts from the bible used in my religious worship of helicopters. These words are drawn from the famous blue bible and apply to the worship of Sikorsky helicopters. This bible also addresses helicopters of other faiths. The Bible is the Sikorsky Helicopter Flight Theory for Pilots and Mechanics. This bible unlike other bibles contains illustrations as well as text.
I will speak from the illustrations and then quote from the text.
In the first illustration it describes a blade that has 50,000 pounds of centrifugal force. With no collective added the blade would be in the RADIAL position. With the addition of collective the blade will be generating 3,600 pounds of lift. The blade will rise until the lift forces are balanced out by the centrifugal force. This creates a resultant or ANGLE. It is easy to see if collective were not applied there would be no resultant (ANGLE). In order to raise at the tip to produce the resultant the blade must move on its’ hinge or elastomeric bearing. This upward movement is called FLAPPING. Unlike cyclic flapping the blade flaps up and will stay there until rotor speed increases or decreases or weight is added to the helicopter or weight is dropped from the helicopter.
With reference to the above description the text reads: With reference to figure 18, it may be seen that the rotor blades in rotating form an inverted cone with its’ apex centered at the main rotor shaft. This situation gives rise to the expression “CONING ANGLE”. The coning angle will be less with a low gross weight and greater with a higher gross weight.
The application of cyclic pitch will cause the disc to tilt (oh yes, disc is referenced in the text as well) and this tilting will alter the resultant relative to the radial plane and cause a change in the cone angle. This is what my bible tell me please tell me what description of coning angle is preached in your bible.
Incidentally, flapping to equality is not referenced in my bible. However, gyroscopic precession is.
If you do not understand what is being described as driven axis and driving axis you do not understand what causes leading and lagging. If there is no difference between these two elements there is no leading and lagging. If the difference is minor then lead and lag are minor. The greater the difference the greater the magnitude of leading and lagging. Now, in order to get this difference you must have precession whether it be aerodynamic or gyroscopic. In order to obtain the difference you must have cyclic input. With cyclic input the blades will flap cyclically and all of the other stuff follows. If you did not displace the cyclic there would be; no change in the cone angle, the disc would not precess, there would be no difference between the driven and driving axes and there would be no lead and lag. Every thing that happens in the rotor system is completely interrelated. I’m sure that your bible covers these subjects and based on the arguments on this thread (and others) I’m sure the words used to describe these phenomena are different.
[ 29 November 2001: Message edited by: Lu Zuckerman ]
Let’s first discuss comparative religion. Each religion (Judeo Christian) has it’s own bible and they have their own liturgy yet when it comes down to it they worship the same god. In the helicopter religion there are different liturgies and there are different bibles yet when you get down to basics the bibles and the liturgies describe the same thing but they employ different words. Precession is one point. One religion teaches aerodynamic precession and the other teaches gyroscopic precession. It seems that the definition of coning angle fits into this category. Whether we are talking religion relating to god or the helicopter religion it is difficult to proselytize one individual and bring him into your religion especially if you are trying to convince that person that your religious concepts are better and more pure than his concepts.
Here are a few excerpts from the bible used in my religious worship of helicopters. These words are drawn from the famous blue bible and apply to the worship of Sikorsky helicopters. This bible also addresses helicopters of other faiths. The Bible is the Sikorsky Helicopter Flight Theory for Pilots and Mechanics. This bible unlike other bibles contains illustrations as well as text.
I will speak from the illustrations and then quote from the text.
In the first illustration it describes a blade that has 50,000 pounds of centrifugal force. With no collective added the blade would be in the RADIAL position. With the addition of collective the blade will be generating 3,600 pounds of lift. The blade will rise until the lift forces are balanced out by the centrifugal force. This creates a resultant or ANGLE. It is easy to see if collective were not applied there would be no resultant (ANGLE). In order to raise at the tip to produce the resultant the blade must move on its’ hinge or elastomeric bearing. This upward movement is called FLAPPING. Unlike cyclic flapping the blade flaps up and will stay there until rotor speed increases or decreases or weight is added to the helicopter or weight is dropped from the helicopter.
With reference to the above description the text reads: With reference to figure 18, it may be seen that the rotor blades in rotating form an inverted cone with its’ apex centered at the main rotor shaft. This situation gives rise to the expression “CONING ANGLE”. The coning angle will be less with a low gross weight and greater with a higher gross weight.
The application of cyclic pitch will cause the disc to tilt (oh yes, disc is referenced in the text as well) and this tilting will alter the resultant relative to the radial plane and cause a change in the cone angle. This is what my bible tell me please tell me what description of coning angle is preached in your bible.
Incidentally, flapping to equality is not referenced in my bible. However, gyroscopic precession is.
If you do not understand what is being described as driven axis and driving axis you do not understand what causes leading and lagging. If there is no difference between these two elements there is no leading and lagging. If the difference is minor then lead and lag are minor. The greater the difference the greater the magnitude of leading and lagging. Now, in order to get this difference you must have precession whether it be aerodynamic or gyroscopic. In order to obtain the difference you must have cyclic input. With cyclic input the blades will flap cyclically and all of the other stuff follows. If you did not displace the cyclic there would be; no change in the cone angle, the disc would not precess, there would be no difference between the driven and driving axes and there would be no lead and lag. Every thing that happens in the rotor system is completely interrelated. I’m sure that your bible covers these subjects and based on the arguments on this thread (and others) I’m sure the words used to describe these phenomena are different.
[ 29 November 2001: Message edited by: Lu Zuckerman ]
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Iconoclast
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To: Grey Area
The original issue of the Blue bible was some time in the late 1940s. When I went to work for Sikorsky in 1955 I was issued an updated version. Nothing was revised but a lot of information was added. The copy I have was published in 1964 and I am sure that it has been updated since that time. John R. Montgomery and aerodynamicist at Sikorsky originally wrote it. I don’t believe he is still alive but the 1964 edition still carries his name as the author. In any case I requested the copy I have from the service school at Sikorsky two years ago so it is still being used to teach helicopter aerodynamics.
[ 29 November 2001: Message edited by: Lu Zuckerman ]
The original issue of the Blue bible was some time in the late 1940s. When I went to work for Sikorsky in 1955 I was issued an updated version. Nothing was revised but a lot of information was added. The copy I have was published in 1964 and I am sure that it has been updated since that time. John R. Montgomery and aerodynamicist at Sikorsky originally wrote it. I don’t believe he is still alive but the 1964 edition still carries his name as the author. In any case I requested the copy I have from the service school at Sikorsky two years ago so it is still being used to teach helicopter aerodynamics.
[ 29 November 2001: Message edited by: Lu Zuckerman ]
Bibles Schmibles. Blah blah blah.
Again.
The point has AGAIN been raised. The blue book is to teach helicopter aerodynamics in a simple easy to understand manner. It is NOT an authoratative text book on the subject, but then if you had been formally qualified as an aero engineer, or as an aerodynamacist you would know that.
Around we go. Perhaps we could ask a formally qualified expert from Sikorsky about the level of authoratativeness (not really a word!) of this particular section. If only we knew such a person......
I think this is an excellent example of "a little bit of knowledge is a bad thing"
Again.
The point has AGAIN been raised. The blue book is to teach helicopter aerodynamics in a simple easy to understand manner. It is NOT an authoratative text book on the subject, but then if you had been formally qualified as an aero engineer, or as an aerodynamacist you would know that.
Around we go. Perhaps we could ask a formally qualified expert from Sikorsky about the level of authoratativeness (not really a word!) of this particular section. If only we knew such a person......
I think this is an excellent example of "a little bit of knowledge is a bad thing"
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helmetfire,
The Blue Book was written by "Monty" Montgomery, a friend and co-worker for decades. He retired a few years back, and he would eat Lu for a light lunch. The Blue Book was written to convey a simplified sense of what goes on for mechanics and pilots under training at our Service School. It was never intended to be an engineering text, it is more like a "Classics Illustrated" comic book. The descriptions and illustrations are not of the level or authority of such texts as Ray Prouty, Gareth Padfield, George Saunders or Stepnewski and Keys.
To quote the Blue Book is a sign of technical unsophistication.
The Blue Book was written by "Monty" Montgomery, a friend and co-worker for decades. He retired a few years back, and he would eat Lu for a light lunch. The Blue Book was written to convey a simplified sense of what goes on for mechanics and pilots under training at our Service School. It was never intended to be an engineering text, it is more like a "Classics Illustrated" comic book. The descriptions and illustrations are not of the level or authority of such texts as Ray Prouty, Gareth Padfield, George Saunders or Stepnewski and Keys.
To quote the Blue Book is a sign of technical unsophistication.
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Nick, I'm assuming that list of authors are some who you would recommend. I'm shopping for a book in helicopter aerodynamics and would like recommendations.
Leishman has a big expensive book. Is it any good?
Matthew.
Leishman has a big expensive book. Is it any good?
Matthew.
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My favorite basic engineering reference is:
Stepniewski, W.Z. & Keys, C.N. Rotary - Wing Aerodynamics
NY, Dover, Trade PB EditionIncludes Vol. 1: Basic Theories of Rotor Aerodynamics and Vol. 2: Performance Prediction of Helicopters.
I have not seen Leishman's book, he is very bright, U of Maryland.
Try www.abe.com for used book searches, about 2000 bookstores world wide.
Stepniewski, W.Z. & Keys, C.N. Rotary - Wing Aerodynamics
NY, Dover, Trade PB EditionIncludes Vol. 1: Basic Theories of Rotor Aerodynamics and Vol. 2: Performance Prediction of Helicopters.
I have not seen Leishman's book, he is very bright, U of Maryland.
Try www.abe.com for used book searches, about 2000 bookstores world wide.
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To: Nick Lappos
” To quote the Blue Book is a sign of technical unsophistication”.
I just read your condescending statement above and as a result I put in a call to your friend Ray Prouty. I asked him if there was such a thing as centrifugal force and he replied, “Well yes, it is the force that the rotorblades create and it is reacted by the rotorhead”. I told him of the argument about centripetal force and centrifugal force and that you as much had quoted engineering text stating that centrifugal force was a non-force.
His reply was,” If that is what he is stating then he is splitting hairs”.
Do you have a response to his comments or would you like to ask him personally?
” To quote the Blue Book is a sign of technical unsophistication”.
I just read your condescending statement above and as a result I put in a call to your friend Ray Prouty. I asked him if there was such a thing as centrifugal force and he replied, “Well yes, it is the force that the rotorblades create and it is reacted by the rotorhead”. I told him of the argument about centripetal force and centrifugal force and that you as much had quoted engineering text stating that centrifugal force was a non-force.
His reply was,” If that is what he is stating then he is splitting hairs”.
Do you have a response to his comments or would you like to ask him personally?
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I hope Ray Prouty reads the posts you drivel on with Lu, the Chinook posts, the Autorotation post, the Gyroscopic precession obsession, write a Helicopter Aerodynamics book and get it published, otherwise you would be wise to listen to the experts (which I am not) on aerodynamics, flight test and physics.