Certification of Robinson Helicopters (incl post by Frank Robinson)
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To: Try_Cyclic
Pitch coupling, and correcting for the 18-degree offset are two separate things. The rotorhead design requires the pilot to compensate for the offset and the pitch coupling results when the cyclic stick is displaced. If you read the Certification requirements for normal category rotorcraft it states that the movement of the aircraft must be in the same sense as the movement of the cyclic stick. This must be proven through the use of a stick plotting board. The question I raised in my report was, “did they use the plotting board in certification”. The regulations state that a certain amount of pitch coupling is allowed and intimates that it should not exceed a degree or two. This is normal and I’m sure that the Robinson complies with the pitch coupling aspect but it does not comply with the aircraft and cyclic stick moving in the same sense.
The delta-3 effect is normal for every helicopter and was not put in the Robinson design for any special purpose. The delta effect happens when the blade pitch horn rises above the pivotal axis of the teeter hinge on a Bell and when it rises above the “coning hinge” of the Robinson. It also happens on Sikorsky, Boeing and any other helicopter when the pitch horn/pitch link attachment point is above the actual or imagined flapping hinge. I don’t know if the effect is as pronounced on a rigid or flex beam type rotor.
Regarding Robinson putting the correction in the controls this is not true. Aside from the differences in the actual control systems the swash plate on the Robinson moves in exactly the same way as on a Bell 206.
As far as divergence is concerned ask Robinson. As I stated, there have been at least 32 accidents on R22s and R44s where the rotor diverged from the plane of rotation and struck the fuselage. If you read FAA AD 95-26-O4 you will see that the R22s and R44s have been restricted from sideslipping and out of trim flight among other restrictions. It was proved that in these two flight regimes the flapping loads are so severe as to cause mast bumping. To do this the rotor blade(s) must diverge from the controlled position selected by the pilot and where he had his controls at the time.
Regarding the blade coupling effecting the phase angle I believe that you are wrong. Blade flapping (coning) around the hinge will result in pitch coupling and have some effect in which direction the helicopter flies but it has no effect in correcting for the offset. If in altering the direction of flight pitch coupling must be restricted to 2 degrees or less (approximately).
You ask if there are any accidents that would point to blade divergence read NTSB Report PB96-917003. It completely describes 31 rotor incursion accidents on the 22 and 44. Jim Hall says that there may be more. There was another in California in August where a 20,000-hour pilot lost his rotor.
The Robinson is a semi rigid rotor with individual flapping hinges. You can call them coning hinges but the blades do not flap about the teeter hinge they flap at the coning/flapping hinge.
To: Grey Area
The so-called delta hinge effect is…..(Read above, as I don’t want to repeat myself). Naturally there is no pitch couple in a hover, as it does no occur until the pilot introduces cyclic input. If there is pitch coupling in hover the result might be a slight drift of the helicopter.
The comparison I made between the Bell and Robinson heads was the positioning of the pitch horns in relation to the tilting of the swash plate. On a Bell with forward input on the cyclic the swash plate tilts down (on most Bells). The same is true for the Robinson. On the Bell the advancing blade is at its’ lowest pitch as the pitch horn is at the forward and lowest point on the swashplate. In the same situation the Robinson pitch horn has not reached the lowest position of the swash plate because it only leads the blade by 72 degrees (approximately) and as such it must travel an additional 18 degrees (approximately) until the blade reaches the lowest pitch. Aerodynamics and the laws of physics state that a rotating body will move 90 degrees in rotation as a result of an input or perturbing force that was applied 90 degrees previously. On the Bell the perturbing force was at its’ maximum when the blades were disposed laterally over the helicopter. On the Robinson the blades are disposed 18 degrees against rotation when the maximum perturbing force was applied. That is why the helicopter will fly to the left unless cyclic position is corrected.
If you read my report I ask several question relating to what happened during the testing phase prior to certification and to what extent Frank Robinson who was the DER had in approving the tests.
To: Helo Teacher
Your first statement you stated that it doesn’t matter what you do with the cyclic in a Zero-G situation, the cyclic controls nothing but the disc. I am not a pilot but I certainly know that what you do with the cyclic in a Zero-G situation can kill you if you don’t move it correctly and at what speed you move it. I know that the right roll is caused by the tail rotor. In the Robinson POH it states that in pulling back on the cyclic you do not want to add to the right roll and you can lose control of the helicopter and you don’t want to input any left roll as it will induce high flapping loads and result in mast bumping and subsequent loss of the rotor.
Regarding rigging and its’ effects, the report lays it all out. The rigging procedures are vague, misdirecting and totally wrong. Here is an example. The cyclic is rigged in its’ neutral position. A pitch reading is taken with the blade over the nose. The mechanic must adjust his controls to get a specific pitch setting. Or, is it specific, as he is given a range. He then moves the cyclic to the forward stop and he reads the pitch setting. He then moves the cyclic to the rear stop and measures the blade angle. If it is not correct he must adjust the same controls. He is told to check if the original setting has changed (and it will) but he is not told what to do to correct it.
He then reads the pitch settings on the rear blade and goes through the same procedure. Check for changes but not told what to do if there are changes. He is then told to average the pitch setting to come up with a final figure. Here is another point. The cyclic is rigged in the center of its’ F&A travel and slightly to the right of that line. If the cyclic is in the middle of F&A travel how come the pitch readings are different from the pitch on the forward and rear blades. With a fixed amount of travel the readings have to be the same. Another point, the certification requirements state the all helicopters have adjustable control stops. In this case the stops are adjusted to the control range. On the Robinson the stops are fixed and the control range is adjusted to the stops.
Why is this design different?
In the rigging procedure there are instruction that can lead to binding of the uni-ball in the swashplate and there is a possibility of rigging in too much pitch. This is compounded by the fact that the pitch angles are measured when the blades are over the lateral and F&A axes. In this position the pitch horns have not reached the maximum displacement of the swashplate and must travel an additional 18 degrees (approximately) before they reach maximum pitch reading. In the application of cyclic the pilot under these conditions can input an excessive amount of pitch resulting in rotor stall (not retreating blade stall)
I hope this covers it all.
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
Pitch coupling, and correcting for the 18-degree offset are two separate things. The rotorhead design requires the pilot to compensate for the offset and the pitch coupling results when the cyclic stick is displaced. If you read the Certification requirements for normal category rotorcraft it states that the movement of the aircraft must be in the same sense as the movement of the cyclic stick. This must be proven through the use of a stick plotting board. The question I raised in my report was, “did they use the plotting board in certification”. The regulations state that a certain amount of pitch coupling is allowed and intimates that it should not exceed a degree or two. This is normal and I’m sure that the Robinson complies with the pitch coupling aspect but it does not comply with the aircraft and cyclic stick moving in the same sense.
The delta-3 effect is normal for every helicopter and was not put in the Robinson design for any special purpose. The delta effect happens when the blade pitch horn rises above the pivotal axis of the teeter hinge on a Bell and when it rises above the “coning hinge” of the Robinson. It also happens on Sikorsky, Boeing and any other helicopter when the pitch horn/pitch link attachment point is above the actual or imagined flapping hinge. I don’t know if the effect is as pronounced on a rigid or flex beam type rotor.
Regarding Robinson putting the correction in the controls this is not true. Aside from the differences in the actual control systems the swash plate on the Robinson moves in exactly the same way as on a Bell 206.
As far as divergence is concerned ask Robinson. As I stated, there have been at least 32 accidents on R22s and R44s where the rotor diverged from the plane of rotation and struck the fuselage. If you read FAA AD 95-26-O4 you will see that the R22s and R44s have been restricted from sideslipping and out of trim flight among other restrictions. It was proved that in these two flight regimes the flapping loads are so severe as to cause mast bumping. To do this the rotor blade(s) must diverge from the controlled position selected by the pilot and where he had his controls at the time.
Regarding the blade coupling effecting the phase angle I believe that you are wrong. Blade flapping (coning) around the hinge will result in pitch coupling and have some effect in which direction the helicopter flies but it has no effect in correcting for the offset. If in altering the direction of flight pitch coupling must be restricted to 2 degrees or less (approximately).
You ask if there are any accidents that would point to blade divergence read NTSB Report PB96-917003. It completely describes 31 rotor incursion accidents on the 22 and 44. Jim Hall says that there may be more. There was another in California in August where a 20,000-hour pilot lost his rotor.
The Robinson is a semi rigid rotor with individual flapping hinges. You can call them coning hinges but the blades do not flap about the teeter hinge they flap at the coning/flapping hinge.
To: Grey Area
The so-called delta hinge effect is…..(Read above, as I don’t want to repeat myself). Naturally there is no pitch couple in a hover, as it does no occur until the pilot introduces cyclic input. If there is pitch coupling in hover the result might be a slight drift of the helicopter.
The comparison I made between the Bell and Robinson heads was the positioning of the pitch horns in relation to the tilting of the swash plate. On a Bell with forward input on the cyclic the swash plate tilts down (on most Bells). The same is true for the Robinson. On the Bell the advancing blade is at its’ lowest pitch as the pitch horn is at the forward and lowest point on the swashplate. In the same situation the Robinson pitch horn has not reached the lowest position of the swash plate because it only leads the blade by 72 degrees (approximately) and as such it must travel an additional 18 degrees (approximately) until the blade reaches the lowest pitch. Aerodynamics and the laws of physics state that a rotating body will move 90 degrees in rotation as a result of an input or perturbing force that was applied 90 degrees previously. On the Bell the perturbing force was at its’ maximum when the blades were disposed laterally over the helicopter. On the Robinson the blades are disposed 18 degrees against rotation when the maximum perturbing force was applied. That is why the helicopter will fly to the left unless cyclic position is corrected.
If you read my report I ask several question relating to what happened during the testing phase prior to certification and to what extent Frank Robinson who was the DER had in approving the tests.
To: Helo Teacher
Your first statement you stated that it doesn’t matter what you do with the cyclic in a Zero-G situation, the cyclic controls nothing but the disc. I am not a pilot but I certainly know that what you do with the cyclic in a Zero-G situation can kill you if you don’t move it correctly and at what speed you move it. I know that the right roll is caused by the tail rotor. In the Robinson POH it states that in pulling back on the cyclic you do not want to add to the right roll and you can lose control of the helicopter and you don’t want to input any left roll as it will induce high flapping loads and result in mast bumping and subsequent loss of the rotor.
Regarding rigging and its’ effects, the report lays it all out. The rigging procedures are vague, misdirecting and totally wrong. Here is an example. The cyclic is rigged in its’ neutral position. A pitch reading is taken with the blade over the nose. The mechanic must adjust his controls to get a specific pitch setting. Or, is it specific, as he is given a range. He then moves the cyclic to the forward stop and he reads the pitch setting. He then moves the cyclic to the rear stop and measures the blade angle. If it is not correct he must adjust the same controls. He is told to check if the original setting has changed (and it will) but he is not told what to do to correct it.
He then reads the pitch settings on the rear blade and goes through the same procedure. Check for changes but not told what to do if there are changes. He is then told to average the pitch setting to come up with a final figure. Here is another point. The cyclic is rigged in the center of its’ F&A travel and slightly to the right of that line. If the cyclic is in the middle of F&A travel how come the pitch readings are different from the pitch on the forward and rear blades. With a fixed amount of travel the readings have to be the same. Another point, the certification requirements state the all helicopters have adjustable control stops. In this case the stops are adjusted to the control range. On the Robinson the stops are fixed and the control range is adjusted to the stops.
Why is this design different?
In the rigging procedure there are instruction that can lead to binding of the uni-ball in the swashplate and there is a possibility of rigging in too much pitch. This is compounded by the fact that the pitch angles are measured when the blades are over the lateral and F&A axes. In this position the pitch horns have not reached the maximum displacement of the swashplate and must travel an additional 18 degrees (approximately) before they reach maximum pitch reading. In the application of cyclic the pilot under these conditions can input an excessive amount of pitch resulting in rotor stall (not retreating blade stall)
I hope this covers it all.
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
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responding to Lu- (what is taught about rotor divergence and how to correct it)- SFAR 73 is what is taught. the premise being, at least in the case of divergence, that low rotor rpm = loss of centrifugal force. centrifugal force being the only thing keeping the blades in their proper plane. does the R22 have a predisposition to rapid rotor rpm fluctuation? you bet. the SFAR attempts to reinforce recovery procedures.
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Lu,
I don't have enormous amounts of time on my hands so I'll _try_ to be brief.
You appear to have made many points in your report, and I'm not disputing any but the one I have discussed (ie, control phase lag angle). I agree that the R-22 is very unforgiving for someone just starting to fly. I personally started in an SA-269C (Schweizer 300C) and soloed in that before I flew the R-22. I have flown R-22s since and like them much more due to their quick response, light stick and performance (better 'glide', higher cruise speed, etc). I have also practiced departure engine failures (in the R-22) in which I would drop the throttle to idle while pulling max power and a lot of collective. One must be very quick to respond, but it is possible to safely land even at max power (and I'm a relative novice).
I do however, I stick to my assertion that the rotor disc reacts in the same direction as the control stick. If you are so dead-set on your point, please go down to the local airport and sign up for a little time with an instructor in an R-22. You won't have to fly--just have him/her run it up and move the stick laterally and longitudinally while you walk around. You could also watch the tip path plane from inside. If you are correct, you will see the rotor disc move forward and slightly to the right when the stick is moved forward--it should, as you assert, be a significant angle. It's easy to watch the tip path plane move, and I am sure you'll be convinced...
As far as rotorcraft texts go, I have several, including one by Ray Prouty. In my opinion, the Johnson book is very thorough and teaches the theory behind rotorcraft dynamics (and doesn't simply go into simplified examples).
I don't have enormous amounts of time on my hands so I'll _try_ to be brief.
You appear to have made many points in your report, and I'm not disputing any but the one I have discussed (ie, control phase lag angle). I agree that the R-22 is very unforgiving for someone just starting to fly. I personally started in an SA-269C (Schweizer 300C) and soloed in that before I flew the R-22. I have flown R-22s since and like them much more due to their quick response, light stick and performance (better 'glide', higher cruise speed, etc). I have also practiced departure engine failures (in the R-22) in which I would drop the throttle to idle while pulling max power and a lot of collective. One must be very quick to respond, but it is possible to safely land even at max power (and I'm a relative novice).
I do however, I stick to my assertion that the rotor disc reacts in the same direction as the control stick. If you are so dead-set on your point, please go down to the local airport and sign up for a little time with an instructor in an R-22. You won't have to fly--just have him/her run it up and move the stick laterally and longitudinally while you walk around. You could also watch the tip path plane from inside. If you are correct, you will see the rotor disc move forward and slightly to the right when the stick is moved forward--it should, as you assert, be a significant angle. It's easy to watch the tip path plane move, and I am sure you'll be convinced...
As far as rotorcraft texts go, I have several, including one by Ray Prouty. In my opinion, the Johnson book is very thorough and teaches the theory behind rotorcraft dynamics (and doesn't simply go into simplified examples).
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To: Imlanphere
Rotor divergance as I addressed is caused by extremly high flapping loads and once it gets to that point there is very little that can be done about it. Robinsons' way of keeping you out of that situation is to restrict you from sideslipping and flying out of trim.
This is for Helo Teacher:
The certification requirements state that any new helicopter design demonstrate sideslipping by hitting the pedals to the stop while flying at .6 VNE. It must also demonstrate out of trim flight by +/- 10 degrees. If the Robinson helicopters are now restricted from flying this way because to do so will increase the flapping loads to the point of mast bumping then how did they demonstrate that capability during certification with out beating the helicopter to death. That is the main point of my report. I stated that if the helicopter were put up for certification now, and could not demonstrate these certification requirements, then the FAA would tell them to piss off.
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The Cat
Rotor divergance as I addressed is caused by extremly high flapping loads and once it gets to that point there is very little that can be done about it. Robinsons' way of keeping you out of that situation is to restrict you from sideslipping and flying out of trim.
This is for Helo Teacher:
The certification requirements state that any new helicopter design demonstrate sideslipping by hitting the pedals to the stop while flying at .6 VNE. It must also demonstrate out of trim flight by +/- 10 degrees. If the Robinson helicopters are now restricted from flying this way because to do so will increase the flapping loads to the point of mast bumping then how did they demonstrate that capability during certification with out beating the helicopter to death. That is the main point of my report. I stated that if the helicopter were put up for certification now, and could not demonstrate these certification requirements, then the FAA would tell them to piss off.
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The Cat
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To: Kyrilian
One minor correction. If I was correct the blade tip path would dip to the left not to the right as you stated.
The 18 degrees I mentioned is degrees of rotation between the pitch horn and the maximum tilt position of the swash plate. This may amount to one or two degrees of pitch change. Until I am proven wrong I will still believe in Santa Claus, The Tooth Fairy and gyroscopic precession.
Regarding my going down to the local airport and paying for a demonstration I would do that but the only R22 around here was written off due to dynamic rollover about a month ago.
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The Cat
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
One minor correction. If I was correct the blade tip path would dip to the left not to the right as you stated.
The 18 degrees I mentioned is degrees of rotation between the pitch horn and the maximum tilt position of the swash plate. This may amount to one or two degrees of pitch change. Until I am proven wrong I will still believe in Santa Claus, The Tooth Fairy and gyroscopic precession.
Regarding my going down to the local airport and paying for a demonstration I would do that but the only R22 around here was written off due to dynamic rollover about a month ago.
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The Cat
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]
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Lu,
Too bad about the rollover. One occured where I fly--nobody was hurt and the helicopter wasn't too badly damaged. I think it's back in service, but I'm not sure. One must be careful...
In my earlier post, I was saying that you would be able to see the direcion in which the disc tilted (ie, the angle from straight ahead at which the lowest point occurred when the stick was pushed forward). This point, I propose, will be dead ahead when the stick is moved forward. As the stick is moved laterally, there should be a line (running a bit to the left as you propose, or straight ahead as I propose) at which the rotor disc does not rise or fall. I realize that you disagree, but I wanted to confirm we were talking about the same angle. Maybe I'll try to take some pictures next time I go
Too bad about the rollover. One occured where I fly--nobody was hurt and the helicopter wasn't too badly damaged. I think it's back in service, but I'm not sure. One must be careful...
In my earlier post, I was saying that you would be able to see the direcion in which the disc tilted (ie, the angle from straight ahead at which the lowest point occurred when the stick was pushed forward). This point, I propose, will be dead ahead when the stick is moved forward. As the stick is moved laterally, there should be a line (running a bit to the left as you propose, or straight ahead as I propose) at which the rotor disc does not rise or fall. I realize that you disagree, but I wanted to confirm we were talking about the same angle. Maybe I'll try to take some pictures next time I go
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This forum is proving to be quite educational. To step away from the debating for a moment, perhaps someone can help with something that just popped out at me....
Assume that the phasing of the swashplate is adjusted for delta-3 effects, the rotor then will tilt in the same direction as the stick.
It seems that flapping response to dissymetry of lift should also be phase shifted since the blades react the same to any cyclic input whether it comes from the pilot or from aerodynamic forces.
The aerodynamic forces from dissymetry of lift are greatest with the blades broadside to the relative wind.
This would seem to predict a slight element of lateral tilt to the rotor disk as a result of forward flight with delta-3.
Does anyone else see it this way?
The rotor is normally canted a couple of degrees left anyway to counter translating tendency so this would reduce the required angle of cant. Thank you in advance for any comments.
Assume that the phasing of the swashplate is adjusted for delta-3 effects, the rotor then will tilt in the same direction as the stick.
It seems that flapping response to dissymetry of lift should also be phase shifted since the blades react the same to any cyclic input whether it comes from the pilot or from aerodynamic forces.
The aerodynamic forces from dissymetry of lift are greatest with the blades broadside to the relative wind.
This would seem to predict a slight element of lateral tilt to the rotor disk as a result of forward flight with delta-3.
Does anyone else see it this way?
The rotor is normally canted a couple of degrees left anyway to counter translating tendency so this would reduce the required angle of cant. Thank you in advance for any comments.
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To Try_Cyclic:
I totally agree with you. Dissymmtry of lift is the main raeson for the right cyclic input in forward flight. In relatively slow flight the teetering hinge (and to Lu NOT the flapping hinge, because there is none, there is one teetering hinge and two coning hinges!) takes care of that problem. In faster flight the pilot has to add to that by applying right cyclic to achieve forward flight.
To Lu:
I don't know, if you've ever seen an R22 from inside, but they even have a right trim knob, which will put the cyclic in a right-of-center position using a spring. Do you really think, even with Frank Robinson as the DER at the time, they could have gotten it certified with a device to correct for that right cyclic input, if it would not have been within limits. By the way, how can you just say, don't trust your textbooks?! That's what a lot of pilots tried to tell you in that forum, theory is one thing, flying the machine another one. To my aerodynamical understanding, Kyrilian showed a good point, you just overruled by saying, don't trust the books. Either trust them or don't, but don't change your mind just to hold up your point.
I'm no physicist, but i'm a pilot and that shows me that the R22 and the R44 are good helicopters, what Lu by the way admitted. They have different rotor head design, which works just fine even when the pilot violates the restrictions on a regular basis (cattle mustering, photo flights...), this is proven every day. Those 31 or 32 accidents, Lu keeps refering to never got blamed on the rotor head, guess why, because it had nothing to do with it! Same flight, same pilots, same situation in a 206, UH1... would have ended up in the same mess. That's the simple disadvantage of any two bladed semi-rigid rotor system. And i keep repeating myself, but just because there is a limitation on sideslipping, doesn't mean it can't be demonstrated. Like i said, the R22 is limited to 102kts IAS, it will go faster and don't break...
Finally i agree with Lu in one point, we are all waiting for FR response...what takes so long???
[This message has been edited by YouWillSee (edited 22 November 2000).]
I totally agree with you. Dissymmtry of lift is the main raeson for the right cyclic input in forward flight. In relatively slow flight the teetering hinge (and to Lu NOT the flapping hinge, because there is none, there is one teetering hinge and two coning hinges!) takes care of that problem. In faster flight the pilot has to add to that by applying right cyclic to achieve forward flight.
To Lu:
I don't know, if you've ever seen an R22 from inside, but they even have a right trim knob, which will put the cyclic in a right-of-center position using a spring. Do you really think, even with Frank Robinson as the DER at the time, they could have gotten it certified with a device to correct for that right cyclic input, if it would not have been within limits. By the way, how can you just say, don't trust your textbooks?! That's what a lot of pilots tried to tell you in that forum, theory is one thing, flying the machine another one. To my aerodynamical understanding, Kyrilian showed a good point, you just overruled by saying, don't trust the books. Either trust them or don't, but don't change your mind just to hold up your point.
I'm no physicist, but i'm a pilot and that shows me that the R22 and the R44 are good helicopters, what Lu by the way admitted. They have different rotor head design, which works just fine even when the pilot violates the restrictions on a regular basis (cattle mustering, photo flights...), this is proven every day. Those 31 or 32 accidents, Lu keeps refering to never got blamed on the rotor head, guess why, because it had nothing to do with it! Same flight, same pilots, same situation in a 206, UH1... would have ended up in the same mess. That's the simple disadvantage of any two bladed semi-rigid rotor system. And i keep repeating myself, but just because there is a limitation on sideslipping, doesn't mean it can't be demonstrated. Like i said, the R22 is limited to 102kts IAS, it will go faster and don't break...
Finally i agree with Lu in one point, we are all waiting for FR response...what takes so long???
[This message has been edited by YouWillSee (edited 22 November 2000).]
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To: Try Cyclic
I’m going to put the shoe on the other foot, and ask you to explain in non engineering terms, exactly how this delta hinge effect causes the disc to tilt forward when the cyclic stic is moved in a forward direction, and not to the left, as I indicated that it would. I want you to tell me in your own words and not those of the instructors at Robinson. The same goes for You Will See who in fact is an instructor on Robinson Helicopters.
You made a point saying that dissymetry of lift is greatest when the blades are disposed over the lateral axis of the helicopter. If this were true, the helicopter would roll to the left and quite fast I might add. You are totally wrong. The basic aerodynamics of a helicopter dictate that there is no dissymetry of lift. The advancing blade is at its’ lowest pitch when the blades are in the lateral position and the retreating blade is at its’ highest pitch. The decreased pitch in the advancing blade decreases the lift on that blade and the increased pitch on the retreating blade increases the lift on that blade. In effect, the lift generated on each blade is the same. In the process of this pitch change the disc is tilted providing forward thrust making the helicopter fly forward.
The only time there is a dissymetery of lift is when you start to approach retreating blade stall. In this case the dissymetry causes an imbalance of forces causing a greater amount of lift on the advancing blade and if it isn’t compensated for the force imbalance will have the effect of tilting the disc backwards. Before the tilting occurs, there is a vibratory sensation and the helicopter will roll left. If the pilot doesn’t catch it, the forces will be so great as to cause a blowback and chop the tail off. That is the only time there is a dissymetry of lift on a helicopter.
To : You Will See
You wanted to know why the rotor head or the rigging procedures might have caused the rotor loss crashes which were all labled as pilot error just like all Robinson crashes. Just remember, if you are ever involved in a crash and your family brings a law suit against Robinson helicopters Frank Robinson wiil be their worst enemy.
Conflict of interest alleged in FAA crash investigations
By MARINA MALIKOFF
Sentinel staff writer
Of the dozens of R-22 accident investigations involving main rotor loss reviewed by the Sentinel, the National Transportation Safety Board frequently listed the probable cause as "undetermined" or pilot error — findings that do not surprise Palo Alto lawyer Michael Danko.
Because pilots and victims’ families are excluded from the investigation process, fault often is placed with the pilot, he said.
"Unfortunately, when there is a crash such as this and the NTSB wants to examine whether the aircraft is defective ... they call on all the manufacturers," said Danko, who is also a pilot. "They’ll ask Robinson if it is defective. To me, that is like asking the fox to find out what happened to the chickens."
Danko, whose firm is investigating a fatal August 1999 R-22 crash in Ireland nearly identical to the Watsonville crash in August, said the NTSB will "essentially staple their report to the technical report from Robinson, which will always point to pilot error."
NTSB accident investigations are conducted by what is known as the "party system," a process where the NTSB allows interested stakeholders, such as aircraft manufacturers and the Federal Aviation Administration, to join their crash probes. Anyone in a litigation position is excluded from the investigation.
The NTSB party system was the target of a 1999 study by the RAND Corp., a nonprofit public policy think tank. A RAND panel found significant potential for conflicts of interest when manufacturers are asked to police themselves.
The study, which was commissioned by the NTSB, recommended independent analytical and engineering resources assist in investigations "if (the NTSB) is to ensure its future independence and integrity," according to a statement issued by RAND when its report was released in December 1999.
The report was recently forwarded to the NTSB, where it is under management review, said NTSB spokeswoman Lauren Peduzzi. Recommendations and changes to the system will be considered, she said.
"The board’s mission is to investigate accidents, determine relevant safety issues and issue recommendations for improvements in order to prevent similar accidents from happening again," Peduzzi said. "Although the party process allows us to tap the manufacturer’s expertise with their equipment, the board’s investigators act as impartial leaders. ... It is their job to ensure that a fair and thorough investigation is conducted and that the probable cause accurately reflects the safety issues in the case."
Benjamin F. Venti, the father of a pilot who, along with two passengers, was killed in a Robinson R-44 crash in July 1993, was so troubled by the investigation into his son’s death, he appealed to his Los Angeles County congressman, Matthew Martinez.
Martinez contacted NTSB chairman Jim Hall, who appointed Venti an official member of the investigation team, contrary to NTSB policy.
Frank Robinson, president of Robinson Helicopter Co., said he and three others from his company had been on the team.
Evidence presented by Venti led the NTSB to revise its findings to show probable cause of the crash was a fatigue failure of the control stick assembly.
The report also found that lack of FAA oversight during the R-44 certification process may have contributed to the fatal crash.
The NTSB’s initial investigation had been hampered by a post-crash fire, which obscured evidence.
The RAND study also found that the 400-member NTSB staff simply doesn’t have the resources to thoroughly investigate each accident.
Jerry Sterns, whose Oakland-based firm specializes in aviation cases, agrees.
"The board does not have the budget nor the experts to do its job properly, so it is forced to rely heavily on outside people, who of course are supplied by the very companies being investigated," he said. "The companies many times drive the investigation, and the board has consistently refused to allow any representatives of the victims to participate and treats their lawyers as subversives."
However, Robinson, founder of the helicopter company, stressed that the NTSB investigator has full control over the crash probe, and that it would be impossible to conduct a thorough investigation without the manufacturer’s expertise.
"The manufacturer is not a theorist and is not allowed to touch anything at the site unless under the direction of the (NTSB) investigator," Robinson said. "He is there to identify the parts and has absolutely no input on probable cause."
In 1994, though, the NTSB learned that Robinson was serving as the quality assurance liaison to the FAA, raising concern of a conflict of interest during safety reviews.
Robinson confirmed he had served in that capacity — called the designated engineering representative — at various times over the years, and said it was "standard practice" in the industry for company officers to do so.
Robinson said he voluntarily resigned from that role four or five years ago. He now has three employees assigned to the job, one of whom is a company officer.
But accident investigations are still tainted by the cozy relationships that develop between FAA representatives and the manufacturers, according to several aviation law attorneys, who note that juries frequently reach conclusions about accident causes that are different than what the official investigators determine.
"In more than 50 percent of our cases, we have a cause that is different than the NTSB," said Richard Schaden, an attorney and aeronautical engineer. "The NTSB’s probable cause is heavily loaded on the pilot-error side."
When it comes to Robinson helicopters, that’s an appropriate finding, Robinson said.
"The fact remains that the vast majority of accidents do result from pilot error," Robinson said. "When they are used in training and by low (flying) time private pilots, it’s very high."
Those statistics don’t comfort families who have lost loved ones in Robinson crashes, said Danko, who maintains that a design flaw in the sensitive R-22 controls prevents flight instructors from responding quickly enough to prevent the crashes.
"History has shown the R-22 is not safe, and the fact is you have many high time pilots who have suffered the same scenario," Danko said. "You can’t blame all these accidents on pilots."
Aptos pilot Kent Reinhard and his student Gary Sefton died Aug. 18 when the rotor blades tore through the cockpit of Reinhard’s copter in midair during an instructional flight near Watsonville.
Reinhard, 57, had flown airplanes and helicopters for decades. He earned his first pilot’s license in 1961, and had logged thousands of flight hours — including 1,000 hours in the R-22 — at the time of his death.
In May 1996, Reinhard completed the Robinson Helicopter safety course and received an "average" rating — the most common rating, according to Robinson, who considers Reinhard a "high time" pilot.
Reinhard, a corporate pilot for Dole Food Co., operated a flight school out of the Watsonville Airport and was an R-22 stunt pilot with Showcopters, a Salinas-based air show team.
Sefton, 46, of Hollister, was studying for his airplane pilot’s license when he changed his focus to helicopters a year ago. The fatal flight with Reinhard was his first lesson.
Investigators from the NTSB, FAA and Robinson Helicopter Co. were at the crash scene the following day, along with local Sheriff’s Office inspectors.
The cause of the accident is still under investigation. The preliminary findings indicate loss of main rotor control is a factor, along with mast bumping, which is typically caused by abrupt input into the controls.
Reinhard’s sister, Jean Grace of Carmel, said Robinson’s position that pilot error likely caused the crash is predictable, but added that she is reserving judgment until the NTSB finalizes its report.
"From a liability standpoint, what else can (Robinson) say," Grace said. "At this point, we consider this a tragic accident."
Contact Marina Malikoff at [email protected].
------------------
The Cat
I’m going to put the shoe on the other foot, and ask you to explain in non engineering terms, exactly how this delta hinge effect causes the disc to tilt forward when the cyclic stic is moved in a forward direction, and not to the left, as I indicated that it would. I want you to tell me in your own words and not those of the instructors at Robinson. The same goes for You Will See who in fact is an instructor on Robinson Helicopters.
You made a point saying that dissymetry of lift is greatest when the blades are disposed over the lateral axis of the helicopter. If this were true, the helicopter would roll to the left and quite fast I might add. You are totally wrong. The basic aerodynamics of a helicopter dictate that there is no dissymetry of lift. The advancing blade is at its’ lowest pitch when the blades are in the lateral position and the retreating blade is at its’ highest pitch. The decreased pitch in the advancing blade decreases the lift on that blade and the increased pitch on the retreating blade increases the lift on that blade. In effect, the lift generated on each blade is the same. In the process of this pitch change the disc is tilted providing forward thrust making the helicopter fly forward.
The only time there is a dissymetery of lift is when you start to approach retreating blade stall. In this case the dissymetry causes an imbalance of forces causing a greater amount of lift on the advancing blade and if it isn’t compensated for the force imbalance will have the effect of tilting the disc backwards. Before the tilting occurs, there is a vibratory sensation and the helicopter will roll left. If the pilot doesn’t catch it, the forces will be so great as to cause a blowback and chop the tail off. That is the only time there is a dissymetry of lift on a helicopter.
To : You Will See
You wanted to know why the rotor head or the rigging procedures might have caused the rotor loss crashes which were all labled as pilot error just like all Robinson crashes. Just remember, if you are ever involved in a crash and your family brings a law suit against Robinson helicopters Frank Robinson wiil be their worst enemy.
Conflict of interest alleged in FAA crash investigations
By MARINA MALIKOFF
Sentinel staff writer
Of the dozens of R-22 accident investigations involving main rotor loss reviewed by the Sentinel, the National Transportation Safety Board frequently listed the probable cause as "undetermined" or pilot error — findings that do not surprise Palo Alto lawyer Michael Danko.
Because pilots and victims’ families are excluded from the investigation process, fault often is placed with the pilot, he said.
"Unfortunately, when there is a crash such as this and the NTSB wants to examine whether the aircraft is defective ... they call on all the manufacturers," said Danko, who is also a pilot. "They’ll ask Robinson if it is defective. To me, that is like asking the fox to find out what happened to the chickens."
Danko, whose firm is investigating a fatal August 1999 R-22 crash in Ireland nearly identical to the Watsonville crash in August, said the NTSB will "essentially staple their report to the technical report from Robinson, which will always point to pilot error."
NTSB accident investigations are conducted by what is known as the "party system," a process where the NTSB allows interested stakeholders, such as aircraft manufacturers and the Federal Aviation Administration, to join their crash probes. Anyone in a litigation position is excluded from the investigation.
The NTSB party system was the target of a 1999 study by the RAND Corp., a nonprofit public policy think tank. A RAND panel found significant potential for conflicts of interest when manufacturers are asked to police themselves.
The study, which was commissioned by the NTSB, recommended independent analytical and engineering resources assist in investigations "if (the NTSB) is to ensure its future independence and integrity," according to a statement issued by RAND when its report was released in December 1999.
The report was recently forwarded to the NTSB, where it is under management review, said NTSB spokeswoman Lauren Peduzzi. Recommendations and changes to the system will be considered, she said.
"The board’s mission is to investigate accidents, determine relevant safety issues and issue recommendations for improvements in order to prevent similar accidents from happening again," Peduzzi said. "Although the party process allows us to tap the manufacturer’s expertise with their equipment, the board’s investigators act as impartial leaders. ... It is their job to ensure that a fair and thorough investigation is conducted and that the probable cause accurately reflects the safety issues in the case."
Benjamin F. Venti, the father of a pilot who, along with two passengers, was killed in a Robinson R-44 crash in July 1993, was so troubled by the investigation into his son’s death, he appealed to his Los Angeles County congressman, Matthew Martinez.
Martinez contacted NTSB chairman Jim Hall, who appointed Venti an official member of the investigation team, contrary to NTSB policy.
Frank Robinson, president of Robinson Helicopter Co., said he and three others from his company had been on the team.
Evidence presented by Venti led the NTSB to revise its findings to show probable cause of the crash was a fatigue failure of the control stick assembly.
The report also found that lack of FAA oversight during the R-44 certification process may have contributed to the fatal crash.
The NTSB’s initial investigation had been hampered by a post-crash fire, which obscured evidence.
The RAND study also found that the 400-member NTSB staff simply doesn’t have the resources to thoroughly investigate each accident.
Jerry Sterns, whose Oakland-based firm specializes in aviation cases, agrees.
"The board does not have the budget nor the experts to do its job properly, so it is forced to rely heavily on outside people, who of course are supplied by the very companies being investigated," he said. "The companies many times drive the investigation, and the board has consistently refused to allow any representatives of the victims to participate and treats their lawyers as subversives."
However, Robinson, founder of the helicopter company, stressed that the NTSB investigator has full control over the crash probe, and that it would be impossible to conduct a thorough investigation without the manufacturer’s expertise.
"The manufacturer is not a theorist and is not allowed to touch anything at the site unless under the direction of the (NTSB) investigator," Robinson said. "He is there to identify the parts and has absolutely no input on probable cause."
In 1994, though, the NTSB learned that Robinson was serving as the quality assurance liaison to the FAA, raising concern of a conflict of interest during safety reviews.
Robinson confirmed he had served in that capacity — called the designated engineering representative — at various times over the years, and said it was "standard practice" in the industry for company officers to do so.
Robinson said he voluntarily resigned from that role four or five years ago. He now has three employees assigned to the job, one of whom is a company officer.
But accident investigations are still tainted by the cozy relationships that develop between FAA representatives and the manufacturers, according to several aviation law attorneys, who note that juries frequently reach conclusions about accident causes that are different than what the official investigators determine.
"In more than 50 percent of our cases, we have a cause that is different than the NTSB," said Richard Schaden, an attorney and aeronautical engineer. "The NTSB’s probable cause is heavily loaded on the pilot-error side."
When it comes to Robinson helicopters, that’s an appropriate finding, Robinson said.
"The fact remains that the vast majority of accidents do result from pilot error," Robinson said. "When they are used in training and by low (flying) time private pilots, it’s very high."
Those statistics don’t comfort families who have lost loved ones in Robinson crashes, said Danko, who maintains that a design flaw in the sensitive R-22 controls prevents flight instructors from responding quickly enough to prevent the crashes.
"History has shown the R-22 is not safe, and the fact is you have many high time pilots who have suffered the same scenario," Danko said. "You can’t blame all these accidents on pilots."
Aptos pilot Kent Reinhard and his student Gary Sefton died Aug. 18 when the rotor blades tore through the cockpit of Reinhard’s copter in midair during an instructional flight near Watsonville.
Reinhard, 57, had flown airplanes and helicopters for decades. He earned his first pilot’s license in 1961, and had logged thousands of flight hours — including 1,000 hours in the R-22 — at the time of his death.
In May 1996, Reinhard completed the Robinson Helicopter safety course and received an "average" rating — the most common rating, according to Robinson, who considers Reinhard a "high time" pilot.
Reinhard, a corporate pilot for Dole Food Co., operated a flight school out of the Watsonville Airport and was an R-22 stunt pilot with Showcopters, a Salinas-based air show team.
Sefton, 46, of Hollister, was studying for his airplane pilot’s license when he changed his focus to helicopters a year ago. The fatal flight with Reinhard was his first lesson.
Investigators from the NTSB, FAA and Robinson Helicopter Co. were at the crash scene the following day, along with local Sheriff’s Office inspectors.
The cause of the accident is still under investigation. The preliminary findings indicate loss of main rotor control is a factor, along with mast bumping, which is typically caused by abrupt input into the controls.
Reinhard’s sister, Jean Grace of Carmel, said Robinson’s position that pilot error likely caused the crash is predictable, but added that she is reserving judgment until the NTSB finalizes its report.
"From a liability standpoint, what else can (Robinson) say," Grace said. "At this point, we consider this a tragic accident."
Contact Marina Malikoff at [email protected].
------------------
The Cat
Guest
Posts: n/a
Lu, you asked for an explanation in my own words and I will attempt it, in non engineering terms.
If I lift up on a rotor blade that has a delta hinge, the pitch changes, correct?
Take a helicopter and let's use a Bell 206
with conventional rotorhead...
Place the rotors in the lateral position.
Move the stick back and , naturally, the advancing blade has positive pitch of 5 deg. approx.
Now go and walk the advancing blade around over the nose. Precession tells us that the blade will be highest here and pitch =zero.
Lift the blade UP because thats where it would be with back stick.
The rotor is tilted back , the blades have zero pitch and the stick is back. All is well.
Now, lets leave it in that position, but REPLACE the teeter hinge with a delta hinge.
Now look at the blade in front. It is raised up, so the delta hinge will pull pitch out and the pitch will be less than zero.
Can you see that that delta hinge is up to no good?
It is pulling pitch out of the blade when the swashplate wants the pitch to be zero.
The pitch actually was zero at some point before the blades got to the fore and aft position.
The only way to get the pitch to be zero in the front is to phase the pitch links like a R-22.
That's it. That's the best I can do.
Forget the dissymetry of lift, that is a minor point compared to this
If I lift up on a rotor blade that has a delta hinge, the pitch changes, correct?
Take a helicopter and let's use a Bell 206
with conventional rotorhead...
Place the rotors in the lateral position.
Move the stick back and , naturally, the advancing blade has positive pitch of 5 deg. approx.
Now go and walk the advancing blade around over the nose. Precession tells us that the blade will be highest here and pitch =zero.
Lift the blade UP because thats where it would be with back stick.
The rotor is tilted back , the blades have zero pitch and the stick is back. All is well.
Now, lets leave it in that position, but REPLACE the teeter hinge with a delta hinge.
Now look at the blade in front. It is raised up, so the delta hinge will pull pitch out and the pitch will be less than zero.
Can you see that that delta hinge is up to no good?
It is pulling pitch out of the blade when the swashplate wants the pitch to be zero.
The pitch actually was zero at some point before the blades got to the fore and aft position.
The only way to get the pitch to be zero in the front is to phase the pitch links like a R-22.
That's it. That's the best I can do.
Forget the dissymetry of lift, that is a minor point compared to this
Guest
Posts: n/a
To: Try Cyclic
On the Robinson rotor system the only way you could get the delta effect is if you move the blade in relation to the rotorhead.
If you do it the way you described and you displaced the rotor in the same manner as the Bell then there would be no pitch change.
On the Bell however, if you do the same thing and the pitch horn is not coincident with the teeter hinge then you will get some change. If you were to raise the collective on the Bell and the differential between the pitch horn and the teeter hinge is less then the pitch change is less. The design of any rotor head is to get the pitch horn/pitch link attach point as close to the center of teeter or flap or, cone in order to minimize pitch coupling when the helicopter is flying.
On the Robinson, the blade must cone (flap)
in relation to the head to get a delta hinge effect and the greater the displacement of the pitch horn and the cone hinge the greater the coupling.
------------------
The Cat
On the Robinson rotor system the only way you could get the delta effect is if you move the blade in relation to the rotorhead.
If you do it the way you described and you displaced the rotor in the same manner as the Bell then there would be no pitch change.
On the Bell however, if you do the same thing and the pitch horn is not coincident with the teeter hinge then you will get some change. If you were to raise the collective on the Bell and the differential between the pitch horn and the teeter hinge is less then the pitch change is less. The design of any rotor head is to get the pitch horn/pitch link attach point as close to the center of teeter or flap or, cone in order to minimize pitch coupling when the helicopter is flying.
On the Robinson, the blade must cone (flap)
in relation to the head to get a delta hinge effect and the greater the displacement of the pitch horn and the cone hinge the greater the coupling.
------------------
The Cat
Guest
Posts: n/a
My reply had a text diagram that I messed up; I'll just do without it for now.
Lu,
The blades flap as a unit, about the teeter bolt.
The blades do not flap at the coning hinges.
Coning will not affect the pitch links, because they are coincident with the coning hinge centerline.
Flapping happens just like on a Bell; the rotor teeters as a unit . The pitch links will then change pitch on the blades since they are not coincident with the teeter bolt.
That is why there is a delta effect.
Take a good look at this, because I think you are thinking erroneously about the role of the coning hinges: they are not flapping hinges.
Congatulations, We set a record!
Its because a certain Dog won't drop his bone.
GRRRRRR!!!! Bad Doggy
Lu,
The blades flap as a unit, about the teeter bolt.
The blades do not flap at the coning hinges.
Coning will not affect the pitch links, because they are coincident with the coning hinge centerline.
Flapping happens just like on a Bell; the rotor teeters as a unit . The pitch links will then change pitch on the blades since they are not coincident with the teeter bolt.
That is why there is a delta effect.
Take a good look at this, because I think you are thinking erroneously about the role of the coning hinges: they are not flapping hinges.
Congatulations, We set a record!
Its because a certain Dog won't drop his bone.
GRRRRRR!!!! Bad Doggy
Guest
Posts: n/a
To: Try Cyclic
The reason for the coning hinges as they are called is to reduce the flapping and bending loads on the blades. If there are flapping loads then there is flapping and, if the hinges are there to reduce bending loads then the blade must be free to FLAP!!!
And once again if there is no flapping then there is no delta hinge effect. The same is true for the tail rotor. If you are running up and there is no wind the blades will stay on a single track. If under the same conditions the pilot applies some pitch to the blades the track will remain the same.
If however there is a gusting wind the blade will flap to compensate for that wind. When the helicopter is flying forward there is an advancing an retreating blade. The advancing blade sees more relative wind than the retreating blade and as a result flaps to decrease pitch. Since the tail rotor is one unit the retreating blade will flap in the opposite direction and increase pitch thus equalizing the load across the tail rotor disc.
The same is true for the main rotor. If the blade flaps up on the coning hinge due to the increased air flow it will decrease pitch and return the blade to the in track position. But,in order to do this, the pitch link/pitch horn cannot be coincident with the coning hinge However due to the tip speed of over 600 feet per second I doubt if the aerodynamic restoring effect even takes place. If the wind continues on the ground during runup then the wind can be a perturbing force and cause the disc to tilt due to precession.
Here is what you said in your post above:
The blades flap as a unit, about the teeter bolt.
The blades do not flap at the coning hinges.
Coning will not affect the pitch links, because they are coincident with the coning hinge centerline.
If the pitch links are coincident with the coning hinges, then there is no delta hinge effect. This can only take place if they are not coincident with the coning hinge AND ONLY THEN IF THE BLADE MOVES ABOUT THE CONING HINGE. THIS ON ANY OTHER HELICOPTER IS CALLED FLAPPING.
I have to give you credit for your diagram as it must have taken a lot of time and effort to create it.
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
The reason for the coning hinges as they are called is to reduce the flapping and bending loads on the blades. If there are flapping loads then there is flapping and, if the hinges are there to reduce bending loads then the blade must be free to FLAP!!!
And once again if there is no flapping then there is no delta hinge effect. The same is true for the tail rotor. If you are running up and there is no wind the blades will stay on a single track. If under the same conditions the pilot applies some pitch to the blades the track will remain the same.
If however there is a gusting wind the blade will flap to compensate for that wind. When the helicopter is flying forward there is an advancing an retreating blade. The advancing blade sees more relative wind than the retreating blade and as a result flaps to decrease pitch. Since the tail rotor is one unit the retreating blade will flap in the opposite direction and increase pitch thus equalizing the load across the tail rotor disc.
The same is true for the main rotor. If the blade flaps up on the coning hinge due to the increased air flow it will decrease pitch and return the blade to the in track position. But,in order to do this, the pitch link/pitch horn cannot be coincident with the coning hinge However due to the tip speed of over 600 feet per second I doubt if the aerodynamic restoring effect even takes place. If the wind continues on the ground during runup then the wind can be a perturbing force and cause the disc to tilt due to precession.
Here is what you said in your post above:
The blades flap as a unit, about the teeter bolt.
The blades do not flap at the coning hinges.
Coning will not affect the pitch links, because they are coincident with the coning hinge centerline.
If the pitch links are coincident with the coning hinges, then there is no delta hinge effect. This can only take place if they are not coincident with the coning hinge AND ONLY THEN IF THE BLADE MOVES ABOUT THE CONING HINGE. THIS ON ANY OTHER HELICOPTER IS CALLED FLAPPING.
I have to give you credit for your diagram as it must have taken a lot of time and effort to create it.
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
Guest
Posts: n/a
To: You will See
The function of the Cyclic Lateral (Right)Trim spring is to remove the left stick forces in cruise conditions. My question to you as a pilot/instructor is what causes the tendency for the cyclic to move to the left?
It appears that by pulling up on the stem that the cyclic right bias spring is distorted thus increasing the right bias thus providing more resistive force. If the cyclic is moved to the right the bias is decreased. If the cyclic is moved left the bias increases providing some kind of feedback to the pilot.
Is this correct?
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
The function of the Cyclic Lateral (Right)Trim spring is to remove the left stick forces in cruise conditions. My question to you as a pilot/instructor is what causes the tendency for the cyclic to move to the left?
It appears that by pulling up on the stem that the cyclic right bias spring is distorted thus increasing the right bias thus providing more resistive force. If the cyclic is moved to the right the bias is decreased. If the cyclic is moved left the bias increases providing some kind of feedback to the pilot.
Is this correct?
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
Guest
Posts: n/a
Lu, the R22 and many helicopters rig the disk
or mast slightly left to compensate for translating tendency caused by tail rotor thrust- in a hover this works well but at speed, the vertical stabilizer and helicopter fuselage are providing heading control and the pilot can reduce tail rotor thrust, which
reduces translating tendency- but the mast or disk is still rigged slightly left- so the trim knob helps alleviate some of that
force felt at the cyclic.
Above there was some argument about disymmetry of lift and what caused the need for slight lateral cyclic during acceleration- this is caused by transverse flow effect (inflow roll) and not disymmetry of lift. Indeed the flapping caused by disymmetry of lift (which by the way IS present anytime the helicopter is moving in relation to the air around it) is subject to the 90 degree phase shift- this is called blow-back (the disk reaching its high point over the nose of the helicopter and low point
over the tail). The pilot simply moves the stick farther forward to compensate for this effect. Lateral cyclic during acceleration is necessary to compensate for transverse flow effect.
or mast slightly left to compensate for translating tendency caused by tail rotor thrust- in a hover this works well but at speed, the vertical stabilizer and helicopter fuselage are providing heading control and the pilot can reduce tail rotor thrust, which
reduces translating tendency- but the mast or disk is still rigged slightly left- so the trim knob helps alleviate some of that
force felt at the cyclic.
Above there was some argument about disymmetry of lift and what caused the need for slight lateral cyclic during acceleration- this is caused by transverse flow effect (inflow roll) and not disymmetry of lift. Indeed the flapping caused by disymmetry of lift (which by the way IS present anytime the helicopter is moving in relation to the air around it) is subject to the 90 degree phase shift- this is called blow-back (the disk reaching its high point over the nose of the helicopter and low point
over the tail). The pilot simply moves the stick farther forward to compensate for this effect. Lateral cyclic during acceleration is necessary to compensate for transverse flow effect.
Guest
Posts: n/a
To: Imlanphere
I totally agree with what you said. Now I'm awaiting Try-Cyclics' answer to the above post regarding Flapping vs Coning.
I got the same answer somewhere in this thread and I gave a smart ass answer to the effect if inflow causes the pilot to push the cyclic forward to reposition the disc and, he goes faster with a greater velocity of inflow air at what point does this result in retreating blade stall?
I'm not being a smart ass in stating this but if you please, can you provide an answer.
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
I totally agree with what you said. Now I'm awaiting Try-Cyclics' answer to the above post regarding Flapping vs Coning.
I got the same answer somewhere in this thread and I gave a smart ass answer to the effect if inflow causes the pilot to push the cyclic forward to reposition the disc and, he goes faster with a greater velocity of inflow air at what point does this result in retreating blade stall?
I'm not being a smart ass in stating this but if you please, can you provide an answer.
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 22 November 2000).]
Guest
Posts: n/a
To: Try_Cyclic
Your pictures are very nice but there is a flaw.. The first picture depicts a rotor system in a hover condition. The second picture is wrong as it shows the rotorhead teetered but the swashplate is still in the hover condition. On this type of rotorhead just like on most Bell rotorheads the tip path and the swash plate are parallel to each other. In order for the tip path to tilt, there must be an input by the swashplate. The number two picture would apply to a tail rotor not, a main rotor.
In the case of the second drawing this condition can't exist. In order to get coupling the blades must deviate from a fixed tip path and flap up which will reduce the pitch or, down which will increase the pitch. But only if the pitch link/pitch horn is not concentric with, in the case of the Robinson, the coning hinge.
It is difficult to continually compare the Robinson to a Bell rotorhead as it is a mixture of a Bell system and an articulated rotor system with flapping capability.
Here is another gem. Since the blades are free to flap then they also will lead and lag. Since there is no lead/lag hinge the tendency to lead/lag is resisted by the cone hinge and transmitted to the drive shaft via the rotor head. This sounds crazy but I saw two R22 rotor heads at Geneva Aviation in Everett, Washington where the A106 Journals on the rotorhead were worn into an egg shape.
The teeter bolt passes through the two journals and any tendency to wear was reacted by the shaft. I cant say that the flapping induced lead lag was continuous throughout the life of the rotorhead but the lead lag that did occur was sufficient to cause the out-of-round of the two journals. It was true on both rotorheads.
When the lead lag takes place I would guess that it is four times the rotational speed of the shaft which means that the shaft is winding and unwinding to the point that it might fatigue. The lead lag forces applied to the journals are generated by the blades which are bent spanwise four times the speed of the rotor.
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 23 November 2000).]
Your pictures are very nice but there is a flaw.. The first picture depicts a rotor system in a hover condition. The second picture is wrong as it shows the rotorhead teetered but the swashplate is still in the hover condition. On this type of rotorhead just like on most Bell rotorheads the tip path and the swash plate are parallel to each other. In order for the tip path to tilt, there must be an input by the swashplate. The number two picture would apply to a tail rotor not, a main rotor.
In the case of the second drawing this condition can't exist. In order to get coupling the blades must deviate from a fixed tip path and flap up which will reduce the pitch or, down which will increase the pitch. But only if the pitch link/pitch horn is not concentric with, in the case of the Robinson, the coning hinge.
It is difficult to continually compare the Robinson to a Bell rotorhead as it is a mixture of a Bell system and an articulated rotor system with flapping capability.
Here is another gem. Since the blades are free to flap then they also will lead and lag. Since there is no lead/lag hinge the tendency to lead/lag is resisted by the cone hinge and transmitted to the drive shaft via the rotor head. This sounds crazy but I saw two R22 rotor heads at Geneva Aviation in Everett, Washington where the A106 Journals on the rotorhead were worn into an egg shape.
The teeter bolt passes through the two journals and any tendency to wear was reacted by the shaft. I cant say that the flapping induced lead lag was continuous throughout the life of the rotorhead but the lead lag that did occur was sufficient to cause the out-of-round of the two journals. It was true on both rotorheads.
When the lead lag takes place I would guess that it is four times the rotational speed of the shaft which means that the shaft is winding and unwinding to the point that it might fatigue. The lead lag forces applied to the journals are generated by the blades which are bent spanwise four times the speed of the rotor.
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 23 November 2000).]
Guest
Posts: n/a
Lu, What flaw is in my 2nd picture?The swashplate is level, but there is forward airspeed. The pilot may have just levelled the ship after a manuever.
The point is that the tip path plane does not always follow the incline of the swashplate. That's what flapping does- it allows the blades to tilt off of the plane of the swashplate to compensate for dissymetry of lift.
It has been said that lead-lag forces in a teetering rotor can be reduced with the proper undersling. That's another topic
[This message has been edited by Try_Cyclic (edited 23 November 2000).]