Aerodynamics ~ Coriolis
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IS there a problem with the oft-quoted 45deg+45deg system (and so all the other permutation of that principle) that when the heli is perturbed in attitude the disc will not follow since the swash plate has not moved in the direction required for it to cause a deisc attitude change?
(the ? denotes this is a question)
(the ? denotes this is a question)
heedm said:
>>I, for one, enjoy being challenged to explain something clearly. The questions he posed did challenge me and did inspire a lot of postings on these threads.<<
I totally agree. And I do get a kick out of some of the big calls.
>>I, for one, enjoy being challenged to explain something clearly. The questions he posed did challenge me and did inspire a lot of postings on these threads.<<
I totally agree. And I do get a kick out of some of the big calls.
Iconoclast
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To: Grey Area
This is not intended to start another argument but to determine if we are talking about the same thing. Please provide a definition of what you understand as phase lag. There is no mention of it in the FAA Rotorcraft Handbook but then it might be called something else.
This is not intended to start another argument but to determine if we are talking about the same thing. Please provide a definition of what you understand as phase lag. There is no mention of it in the FAA Rotorcraft Handbook but then it might be called something else.
Iconoclast
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To: Joe Pilot
Hopefully this does not open me up for chastisement or ridicule but I will respond to your ??
Assume that heavy gusting perturbs the disc. When the blades flap up or down in relation to the commanded disc attitude there will be pitch flap coupling and the blades should return to the original tip path.
Now we stretch that point a bit further. If it is possible to perturb or move the fuselage in relation to the blades with out disturbing the disc, the blades, due to GYROSCOPIC RIGIDITY, will maintain their position. However the swash plate, which is fixed by the servos will move in relation to the rigid blade disc forcing the pitch links upward or downward depending upon the relative movement between the blades and the fixed pitch links and some pitch change will be input.
I am now open to criticism.
Hopefully this does not open me up for chastisement or ridicule but I will respond to your ??
Assume that heavy gusting perturbs the disc. When the blades flap up or down in relation to the commanded disc attitude there will be pitch flap coupling and the blades should return to the original tip path.
Now we stretch that point a bit further. If it is possible to perturb or move the fuselage in relation to the blades with out disturbing the disc, the blades, due to GYROSCOPIC RIGIDITY, will maintain their position. However the swash plate, which is fixed by the servos will move in relation to the rigid blade disc forcing the pitch links upward or downward depending upon the relative movement between the blades and the fixed pitch links and some pitch change will be input.
I am now open to criticism.
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Dave
>The camera is rigidly attached to the fuselage and is located directly below the mast. It is therefor on the mast axis (i.e. 'rotor hub plane').
the only way the mast axis is the same as the hub plane when cyclic input is put in, is a ridgid rotor head.
the coning is increased only when collective is applied after original dissplacment of the cone with cyclic.
to see the circle of light the camera MUST be directly under the blade tip path. not the mast.
>The camera is rigidly attached to the fuselage and is located directly below the mast. It is therefor on the mast axis (i.e. 'rotor hub plane').
the only way the mast axis is the same as the hub plane when cyclic input is put in, is a ridgid rotor head.
the coning is increased only when collective is applied after original dissplacment of the cone with cyclic.
to see the circle of light the camera MUST be directly under the blade tip path. not the mast.
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Heedm,
Answers:
WHAT ARE THE HINGE OFFSETS:
(Source Prouty)
........ Rotor. Hinge. Offset
........ Radius Offset Ratio
AS332 . 7.79m 0.288m 0.037
SA365 . 5.96m 0.227m 0.038
UH60 ... 8.17m 0.384m 0.047
S76 ..... 6.70m 0.255m 0.038
WG30 .. 6.65m 0.818m 0.123
BO105 . 4.92m 0.689m 0.140
WHERE DO THEY COME FROM?
Hinge offset is calculated in 1 of 3 ways.
1 - For articulated heads - Devide hinge offset distance by rotor radius. (Easy)
2 - For non articulated heads - Determine rotor stability and control characteristics, describe system in terms of "effective hinge offset" being the hinge offset of an articulated head with the same characteristics.
3 - For non articulated heads - Displace tip, point at which straight line through blade passes through rotor head plane is your flapping hinge. Not very useful as blade and root stiffness change the blades' performance. Not used much, tells you nothing useful.
Unfortunately I don't have the ISA Lock numbers or moments of inertia of the systems so the calculations were a bit approximate.
ARE THEY SPECIFIC TO A CERTAIN FLIGHT REGIME:
Yes. Lock number describes the relationship between aerodynamic and inertial forces in a rotor. The Lock number is proportional to air density so it will reduce with altitude, which in turn means the angle of phase lag will reduce, so the control cross couple will change with altitude.
Note: On top of this an acceleration cross couple often exists which creates a different control cross couple as a function of the rate of control appplication.
HOW MUCH DO THEY CHANGE:
That depends on the offset ratio. Take an extreme, 18000' (with Oxygen of course), S76 changes -1.5 deg, BO105 changes -5 deg (roughly).
Now that's why we lie to pilots and tell them 90 deg, because the truth is complex, confusing and hardly gets noticed. It perhaps serves a purpose for the likes of BO105, Lynx etc as the effects can be found in normal regimes but I've yet to meet a student who has so little to worry about flying the thing that he spots a 5 deg cross couple.
GA
(For Lu: Phase Lag IS defined as the angle between the applied control input and the rotor response. It varies with air density EXCEPT for 2 Bladed teetering heads, where it sticks at 90 degrees).
(Edited to make it look prettier! Didn't work!)
[ 04 December 2001: Message edited by: Grey Area ]
Answers:
WHAT ARE THE HINGE OFFSETS:
(Source Prouty)
........ Rotor. Hinge. Offset
........ Radius Offset Ratio
AS332 . 7.79m 0.288m 0.037
SA365 . 5.96m 0.227m 0.038
UH60 ... 8.17m 0.384m 0.047
S76 ..... 6.70m 0.255m 0.038
WG30 .. 6.65m 0.818m 0.123
BO105 . 4.92m 0.689m 0.140
WHERE DO THEY COME FROM?
Hinge offset is calculated in 1 of 3 ways.
1 - For articulated heads - Devide hinge offset distance by rotor radius. (Easy)
2 - For non articulated heads - Determine rotor stability and control characteristics, describe system in terms of "effective hinge offset" being the hinge offset of an articulated head with the same characteristics.
3 - For non articulated heads - Displace tip, point at which straight line through blade passes through rotor head plane is your flapping hinge. Not very useful as blade and root stiffness change the blades' performance. Not used much, tells you nothing useful.
Unfortunately I don't have the ISA Lock numbers or moments of inertia of the systems so the calculations were a bit approximate.
ARE THEY SPECIFIC TO A CERTAIN FLIGHT REGIME:
Yes. Lock number describes the relationship between aerodynamic and inertial forces in a rotor. The Lock number is proportional to air density so it will reduce with altitude, which in turn means the angle of phase lag will reduce, so the control cross couple will change with altitude.
Note: On top of this an acceleration cross couple often exists which creates a different control cross couple as a function of the rate of control appplication.
HOW MUCH DO THEY CHANGE:
That depends on the offset ratio. Take an extreme, 18000' (with Oxygen of course), S76 changes -1.5 deg, BO105 changes -5 deg (roughly).
Now that's why we lie to pilots and tell them 90 deg, because the truth is complex, confusing and hardly gets noticed. It perhaps serves a purpose for the likes of BO105, Lynx etc as the effects can be found in normal regimes but I've yet to meet a student who has so little to worry about flying the thing that he spots a 5 deg cross couple.
GA
(For Lu: Phase Lag IS defined as the angle between the applied control input and the rotor response. It varies with air density EXCEPT for 2 Bladed teetering heads, where it sticks at 90 degrees).
(Edited to make it look prettier! Didn't work!)
[ 04 December 2001: Message edited by: Grey Area ]
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vorticey
>"the only way the mast axis is the same as the hub plane when cyclic input is put in, is a rigid rotor head. "<
Not quite. When considering a teetering rotor the 'U' shaped saddle that holds the teetering axle is considered the hub.
"The rotor hub plane is perpendicular to the rotor shaft." ~ Leishman
>"the coning is increased only when collective is applied after original displacement of the cone with cyclic. "<
Agreed. You are envisioning a smaller circle caused by the coning. I am referring to an oval caused by a tilting of the original circle.
>" to see the circle of light the camera MUST be directly under the blade tip path. not the mast."<
If the camera were to be way below the helicopter, it will still see the circle of light plus the bottom of the helicopter in the middle of this circle.
___________
Lu
There is no intent to detract from Grey Area's very informative posting, nor from his brief and concise statement about the teetering head. But before you jump on him, please remember that the Robinson's head has delta-3 and is therefor one of the few teetering rotors that is not 90-degrees.
[ 04 December 2001: Message edited by: Dave Jackson ]
>"the only way the mast axis is the same as the hub plane when cyclic input is put in, is a rigid rotor head. "<
Not quite. When considering a teetering rotor the 'U' shaped saddle that holds the teetering axle is considered the hub.
"The rotor hub plane is perpendicular to the rotor shaft." ~ Leishman
>"the coning is increased only when collective is applied after original displacement of the cone with cyclic. "<
Agreed. You are envisioning a smaller circle caused by the coning. I am referring to an oval caused by a tilting of the original circle.
>" to see the circle of light the camera MUST be directly under the blade tip path. not the mast."<
If the camera were to be way below the helicopter, it will still see the circle of light plus the bottom of the helicopter in the middle of this circle.
___________
Lu
There is no intent to detract from Grey Area's very informative posting, nor from his brief and concise statement about the teetering head. But before you jump on him, please remember that the Robinson's head has delta-3 and is therefor one of the few teetering rotors that is not 90-degrees.
[ 04 December 2001: Message edited by: Dave Jackson ]
Iconoclast
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To: Grey Area
Thanks for the explanation. Dave Jackson also provided a similar definition via email. Perhaps I should have used the term lead angle as opposed to phase angle as it caused a bit of confusion. What I was describing was the relationship between the direction of movement of the swash plate relative to the longitudinal and lateral axes of the helicopter and the angular lead of the pitch horn relative to the blades. On all helicopters that I am familiar with the swashplate angular deflection and the pitch horn lead add up to 90-degrees. All except the Robinson. I also understand that aerodynamics can play a part relative to actual disc deflection as well as the effect of coupling will have an effect. The certification documents allow for this difference in movement relative to command and they limit it to several degrees all of which can be compensated for by cyclic input.
To: Dave Jackson
What you say about the Robinson head is true but I must add that all helicopters have a delta (hinge) effect as this is the way they compensate for flapping by neutralizing (my word) the flapping through pitch flap coupling. If a blade flaps up the pitch is reduced. If a blade flaps down the pitch is increased. This increase or decrease is caused when the blade flaps up or down and the pitch link / pitch horn connect point is above the coning or flapping axis. I had made this same statement on several occasions and likened it to the tail rotor which has a delta relationship between the flapping axis and the location of the pitch input to the tail rotor blades.
[ 04 December 2001: Message edited by: Lu Zuckerman ]
[ 04 December 2001: Message edited by: Lu Zuckerman ]
Thanks for the explanation. Dave Jackson also provided a similar definition via email. Perhaps I should have used the term lead angle as opposed to phase angle as it caused a bit of confusion. What I was describing was the relationship between the direction of movement of the swash plate relative to the longitudinal and lateral axes of the helicopter and the angular lead of the pitch horn relative to the blades. On all helicopters that I am familiar with the swashplate angular deflection and the pitch horn lead add up to 90-degrees. All except the Robinson. I also understand that aerodynamics can play a part relative to actual disc deflection as well as the effect of coupling will have an effect. The certification documents allow for this difference in movement relative to command and they limit it to several degrees all of which can be compensated for by cyclic input.
To: Dave Jackson
What you say about the Robinson head is true but I must add that all helicopters have a delta (hinge) effect as this is the way they compensate for flapping by neutralizing (my word) the flapping through pitch flap coupling. If a blade flaps up the pitch is reduced. If a blade flaps down the pitch is increased. This increase or decrease is caused when the blade flaps up or down and the pitch link / pitch horn connect point is above the coning or flapping axis. I had made this same statement on several occasions and likened it to the tail rotor which has a delta relationship between the flapping axis and the location of the pitch input to the tail rotor blades.
[ 04 December 2001: Message edited by: Lu Zuckerman ]
[ 04 December 2001: Message edited by: Lu Zuckerman ]
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Lu,
The Advance Angle (Pitch Change Rod) and the Rigging Angle (Offset of Jacks) are set to match a mean Phase Lag chosen by the manufacturer through flight test (or variable as in Comanche) not 90 deg.
Really.
Honest.
Well at least in the last 20 years.
GA
The Advance Angle (Pitch Change Rod) and the Rigging Angle (Offset of Jacks) are set to match a mean Phase Lag chosen by the manufacturer through flight test (or variable as in Comanche) not 90 deg.
Really.
Honest.
Well at least in the last 20 years.
GA
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Lu
In different words, is this what you are saying?[list=a][*]The Robinson has intentionally offset its pitch horn/link horizontally from the teetering hinge. [*]All conventional teetering hubs will unintentionally find that their pitch horn/link is offset vertically from the teetering hinge, when they are subjected to a large amount of collective.
[*]In both cases, when the blades teeters up some of the pitch will automatically be pulled out.[/list=a]
If the above is a correct interpretation of what you are saying, then I agree with you.
What you might want to do is sketch out the two situations. The amount of flap or teeter is relatively small and the blade is close to the horizontal, of course. Therefor you will find that a horizontal offset of 1/2" will change the pitch far far more that a vertical offset of 1/2" will.
Hope this make sense.
[ 04 December 2001: Message edited by: Dave Jackson ]
In different words, is this what you are saying?[list=a][*]The Robinson has intentionally offset its pitch horn/link horizontally from the teetering hinge. [*]All conventional teetering hubs will unintentionally find that their pitch horn/link is offset vertically from the teetering hinge, when they are subjected to a large amount of collective.
[*]In both cases, when the blades teeters up some of the pitch will automatically be pulled out.[/list=a]
If the above is a correct interpretation of what you are saying, then I agree with you.
What you might want to do is sketch out the two situations. The amount of flap or teeter is relatively small and the blade is close to the horizontal, of course. Therefor you will find that a horizontal offset of 1/2" will change the pitch far far more that a vertical offset of 1/2" will.
Hope this make sense.
[ 04 December 2001: Message edited by: Dave Jackson ]
Iconoclast
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To: Dave Jackson
A. The Robinson has intentionally offset its pitch horn/link horizontally from the teetering hinge.
Answer to A)
Yes and no. The position of the pitch link / pitch horn connection point was dictated by the position of the cone (flapping) hinge. If you want to say intentionally that’s OK but the location was not arbitrary.
B. All conventional teetering hubs will unintentionally find that their pitch horn/link is offset vertically from the teetering hinge, when they are subjected to a large amount of collective.
Answer to B) Yes, but again I don’t like the word unintentionally because the design of the helicopter and the input of control dictate it.
C. In both cases, when the blade teeters up some of the pitch will automatically be pulled out.
Answer to C) Yes but it is true for all helicopters that have flapping hinges or an apparent flapping point
If the above is a correct interpretation of what you are saying, then I agree with you.
What you might want to do is sketch out the two situations. The amount of flap or teeter is relatively small and the blade is close to the horizontal, of course. Therefor you will find that a horizontal offset of 1/2" will change the pitch far far more that a vertical offset of 1/2" will.
If I understand your point above you refer to the horizontal displacement of the pitch link /pitch horn connection in relation to the hinge line. If that is what you mean the point of reference can be several feet outboard of the hinge and still not make any pitch change if the two points are coincident with each other. However if you move the point above (Vertical) the hinge line, when the blade flaps up, pitch will be removed.
A. The Robinson has intentionally offset its pitch horn/link horizontally from the teetering hinge.
Answer to A)
Yes and no. The position of the pitch link / pitch horn connection point was dictated by the position of the cone (flapping) hinge. If you want to say intentionally that’s OK but the location was not arbitrary.
B. All conventional teetering hubs will unintentionally find that their pitch horn/link is offset vertically from the teetering hinge, when they are subjected to a large amount of collective.
Answer to B) Yes, but again I don’t like the word unintentionally because the design of the helicopter and the input of control dictate it.
C. In both cases, when the blade teeters up some of the pitch will automatically be pulled out.
Answer to C) Yes but it is true for all helicopters that have flapping hinges or an apparent flapping point
If the above is a correct interpretation of what you are saying, then I agree with you.
What you might want to do is sketch out the two situations. The amount of flap or teeter is relatively small and the blade is close to the horizontal, of course. Therefor you will find that a horizontal offset of 1/2" will change the pitch far far more that a vertical offset of 1/2" will.
If I understand your point above you refer to the horizontal displacement of the pitch link /pitch horn connection in relation to the hinge line. If that is what you mean the point of reference can be several feet outboard of the hinge and still not make any pitch change if the two points are coincident with each other. However if you move the point above (Vertical) the hinge line, when the blade flaps up, pitch will be removed.
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Grey Area,
Don't forget that d-3 also affects phase lag...
"It varies with air density EXCEPT for 2 Bladed teetering heads, where it sticks at 90 degrees)."
The Robinson is an example where the fact that it's a 2-bladed teetering head does not limit it to 90°--it has delta-3.
I'm not sure how you got your numbers for phase lag, as I tried them using just the hinge offset and got different numbers. Do you have delta-3 numbers for those helicopters or do none of them have it?
Don't forget that d-3 also affects phase lag...
"It varies with air density EXCEPT for 2 Bladed teetering heads, where it sticks at 90 degrees)."
The Robinson is an example where the fact that it's a 2-bladed teetering head does not limit it to 90°--it has delta-3.
I'm not sure how you got your numbers for phase lag, as I tried them using just the hinge offset and got different numbers. Do you have delta-3 numbers for those helicopters or do none of them have it?
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Lu
>"If I understand your point above you refer to the horizontal displacement of the pitch link /pitch horn connection in relation to the hinge line. "<
Yes.
>" If that is what you mean the point of reference can be several feet outboard of the hinge and still not make any pitch change if the two points are coincident with each other."<
I don't fully understand the above sentence. Perhaps you could elaborate.
Using the Robinson R-22 as an example; only because it has two types of hinges. If the blade 'teeters up' then pitch will be removed. If the blade 'flaps or cones up' there will be no change to the pitch.
>"If I understand your point above you refer to the horizontal displacement of the pitch link /pitch horn connection in relation to the hinge line. "<
Yes.
>" If that is what you mean the point of reference can be several feet outboard of the hinge and still not make any pitch change if the two points are coincident with each other."<
I don't fully understand the above sentence. Perhaps you could elaborate.
Using the Robinson R-22 as an example; only because it has two types of hinges. If the blade 'teeters up' then pitch will be removed. If the blade 'flaps or cones up' there will be no change to the pitch.
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To: Dave Jackson
“>" If that is what you mean the point of reference can be several feet outboard of the hinge and still not make any pitch change if the two points are coincident with each other."<
I don't fully understand the above sentence. Perhaps you could elaborate.
Response: I meant that if you were to scribe a virtual line from the centerline of the cone hinge for two feet and at that point attach the pitch link to the pitch horn. As long as the attach point remains coincident with the centerline of the cone hinge and the blade flaps there will be no pitch change. However if the connection point is raised and is no longer coincident with the cone hinge there will be a pitch change and in this case pitch will be extracted. If the blade flaps downward the pitch will be increased. On the actual head the two points are several inches apart.
“Using the Robinson R-22 as an example; only because it has two types of hinges. If the blade 'teeters up' then pitch will be removed. If the blade 'flaps or cones up' there will be no change to the pitch”.
If this were true then it would blow the hell out of Nick Lappos's and Frank Robinson's story about pitch flap coupling causing the blade to respond to cyclic input and flying down over the nose in 72-degrees. With teetering alone the pitch flap coupling is just like a Bell. If the two points are not coincident there is pitch change. With flapping on the cone hinge it is just like a Sikorsky or any other articulated head and there will be a pitch change. The greater the difference in the two points the greater the pitch change.
There is pitch flap coupling when the blades flap individually. This may be part of the problem in rotor incursion or mast bumping. I don’t know what 100% Nr is on the Robinson but let’s say 400 RPM. It is specifically stated that certain maneuvers and an improper recovery from zero G can cause severe flapping loads. At that rotational velocity with the blades flapping up and down at a high rate and extreme excursions there will be high frequency pitch changes from positive to negative (not negative pitch) and imagine the aerodynamic changes that occur during this time and the vibratory forces that would be generated.
“>" If that is what you mean the point of reference can be several feet outboard of the hinge and still not make any pitch change if the two points are coincident with each other."<
I don't fully understand the above sentence. Perhaps you could elaborate.
Response: I meant that if you were to scribe a virtual line from the centerline of the cone hinge for two feet and at that point attach the pitch link to the pitch horn. As long as the attach point remains coincident with the centerline of the cone hinge and the blade flaps there will be no pitch change. However if the connection point is raised and is no longer coincident with the cone hinge there will be a pitch change and in this case pitch will be extracted. If the blade flaps downward the pitch will be increased. On the actual head the two points are several inches apart.
“Using the Robinson R-22 as an example; only because it has two types of hinges. If the blade 'teeters up' then pitch will be removed. If the blade 'flaps or cones up' there will be no change to the pitch”.
If this were true then it would blow the hell out of Nick Lappos's and Frank Robinson's story about pitch flap coupling causing the blade to respond to cyclic input and flying down over the nose in 72-degrees. With teetering alone the pitch flap coupling is just like a Bell. If the two points are not coincident there is pitch change. With flapping on the cone hinge it is just like a Sikorsky or any other articulated head and there will be a pitch change. The greater the difference in the two points the greater the pitch change.
There is pitch flap coupling when the blades flap individually. This may be part of the problem in rotor incursion or mast bumping. I don’t know what 100% Nr is on the Robinson but let’s say 400 RPM. It is specifically stated that certain maneuvers and an improper recovery from zero G can cause severe flapping loads. At that rotational velocity with the blades flapping up and down at a high rate and extreme excursions there will be high frequency pitch changes from positive to negative (not negative pitch) and imagine the aerodynamic changes that occur during this time and the vibratory forces that would be generated.
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Lu
>"Response: I meant that if you were to scribe a virtual line from the centerline of the cone hinge for two feet and at that point attach the pitch link to the pitch horn. As long as the attach point remains coincident with the centerline of the cone hinge and the blade flaps there will be no pitch change. "<
I agree.
>"However if the connection point is raised and is no longer coincident with the cone hinge there will be a pitch change and in this case pitch will be extracted. "<
I agree.
I agreed with this in my post 04 December 2001 20:54. It does not mater if the flapping hinge offset is 2" or 2'. Please note; I also suggested that you sketch out the action that you are talking about. You will find that the amount of pitch, which is removed by flapping, is very very minimal. In fact the word 'inconsequential' might be more appropriate.
Hold on Lu. There is no desire or ability to go into anything else until this one point is established.
_______________
The Edit:
Having reread your last two paragraphs, I agree that the cyclic change we are talking about will be similar to your analogy with the Bell.
I agree to nothing more
A question; how big a problem is this with the Bell?
A second question; What is going to make the Robinson's amount of flap/cone be anywhere near as great as the Bell's amount of teeter?
[ 05 December 2001: Message edited by: Dave Jackson ]
[ 05 December 2001: Message edited by: Dave Jackson ]
>"Response: I meant that if you were to scribe a virtual line from the centerline of the cone hinge for two feet and at that point attach the pitch link to the pitch horn. As long as the attach point remains coincident with the centerline of the cone hinge and the blade flaps there will be no pitch change. "<
I agree.
>"However if the connection point is raised and is no longer coincident with the cone hinge there will be a pitch change and in this case pitch will be extracted. "<
I agree.
I agreed with this in my post 04 December 2001 20:54. It does not mater if the flapping hinge offset is 2" or 2'. Please note; I also suggested that you sketch out the action that you are talking about. You will find that the amount of pitch, which is removed by flapping, is very very minimal. In fact the word 'inconsequential' might be more appropriate.
Hold on Lu. There is no desire or ability to go into anything else until this one point is established.
_______________
The Edit:
Having reread your last two paragraphs, I agree that the cyclic change we are talking about will be similar to your analogy with the Bell.
I agree to nothing more
A question; how big a problem is this with the Bell?
A second question; What is going to make the Robinson's amount of flap/cone be anywhere near as great as the Bell's amount of teeter?
[ 05 December 2001: Message edited by: Dave Jackson ]
[ 05 December 2001: Message edited by: Dave Jackson ]
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To: Dave Jackson
I honestly can’t say how much the blades flap but they flap sufficiently to induce leading and lagging. If you remember in another thread an individual indicated that they used a training aid in one of his classes in a Robinson school. He indicated strange wear patterns on the cone hinges. His instructor told him the wear pattern was caused by excessive power application. In actuality the elliptical wear pattern was caused by a tendency to lead and lag with this lead and lag being reacted by the cone bushings. The rotorhead was removed from an Australian R-22 that was used in cattle mustering where they are constantly maneuvering the helicopter. I saw the same pattern on a rotorhead that came off of an R-22 used to train Japanese pilots at a flight school in Everett, Washington.
Because of the wear pattern I would venture to say that there is a lot of flapping going on.
Regarding the amount of pitch change Vs flap angle I am looking at a very detailed drawing of an R-22 rotorhead. In the picture the pitch change rod is coincident with the cone hinge. Looking at the drawing and visualizing the upward movement of the pitch link and then trying to visualize the flapping angle it appears that there is some degree of pitch change with flapping but I can’t say how much.
[ 05 December 2001: Message edited by: Lu Zuckerman ]
I honestly can’t say how much the blades flap but they flap sufficiently to induce leading and lagging. If you remember in another thread an individual indicated that they used a training aid in one of his classes in a Robinson school. He indicated strange wear patterns on the cone hinges. His instructor told him the wear pattern was caused by excessive power application. In actuality the elliptical wear pattern was caused by a tendency to lead and lag with this lead and lag being reacted by the cone bushings. The rotorhead was removed from an Australian R-22 that was used in cattle mustering where they are constantly maneuvering the helicopter. I saw the same pattern on a rotorhead that came off of an R-22 used to train Japanese pilots at a flight school in Everett, Washington.
Because of the wear pattern I would venture to say that there is a lot of flapping going on.
Regarding the amount of pitch change Vs flap angle I am looking at a very detailed drawing of an R-22 rotorhead. In the picture the pitch change rod is coincident with the cone hinge. Looking at the drawing and visualizing the upward movement of the pitch link and then trying to visualize the flapping angle it appears that there is some degree of pitch change with flapping but I can’t say how much.
[ 05 December 2001: Message edited by: Lu Zuckerman ]
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dave
i said :>" to see the circle of light the camera MUST be directly under the blade tip path. not the mast."<and what i ment was the camera must be perpendicular to the blade tip path (not under the tip)and you will always see the circle not an oval
i said :>" to see the circle of light the camera MUST be directly under the blade tip path. not the mast."<and what i ment was the camera must be perpendicular to the blade tip path (not under the tip)and you will always see the circle not an oval
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Hi vorticey
OK, I understand.
The original question was for the fun of it. It was based on a mast rotating with a constant angular velocity, a teetering hub, and a tip path axis that is not aligned with the mast's axis. The tip path axis must be experiencing acceleration and deceleration twice per revolution. The question was if it was best to explain the acceleration/deceleration by the mathematics of a knuckle joint or by the mathematics of cyclical Coriolis (i.e. flapping).
Someone should start a thread on delta-3 v.s. flapping hinge offset; when the current stuff slows down.
OK, I understand.
The original question was for the fun of it. It was based on a mast rotating with a constant angular velocity, a teetering hub, and a tip path axis that is not aligned with the mast's axis. The tip path axis must be experiencing acceleration and deceleration twice per revolution. The question was if it was best to explain the acceleration/deceleration by the mathematics of a knuckle joint or by the mathematics of cyclical Coriolis (i.e. flapping).
Someone should start a thread on delta-3 v.s. flapping hinge offset; when the current stuff slows down.
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To: Dave Jackson
“A question; how big a problem is this with the Bell”?
Response:
Which problem (not being smart it is just that I did not understand the question).
“A second question; What is going to make the Robinson's amount of flap/cone be anywhere near as great as the Bell's amount of teeter”?
Response:
First of all we must address the fact that both heads teeter. Just a wild guess but I would think that there would be a similar but scaled down teeter on the Robinson with the gross weight and comparative profiles being the difference that caused this. Now we can address the flapping. On the Bell you get pitch flap coupling when the blade teeters and on the Robinson you get pitch flap coupling when the blade teeters and when the blades flap. You would have to do a comparative engineering analysis to determine which helicopter has the greater amount of pitch flap coupling for their respective sizes.
“A question; how big a problem is this with the Bell”?
Response:
Which problem (not being smart it is just that I did not understand the question).
“A second question; What is going to make the Robinson's amount of flap/cone be anywhere near as great as the Bell's amount of teeter”?
Response:
First of all we must address the fact that both heads teeter. Just a wild guess but I would think that there would be a similar but scaled down teeter on the Robinson with the gross weight and comparative profiles being the difference that caused this. Now we can address the flapping. On the Bell you get pitch flap coupling when the blade teeters and on the Robinson you get pitch flap coupling when the blade teeters and when the blades flap. You would have to do a comparative engineering analysis to determine which helicopter has the greater amount of pitch flap coupling for their respective sizes.