R22 Corner
Iconoclast
Joined: Sep 2000
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
18-degree offset. Accident or, intentional?
To: Gaseous
To my understanding Frank Robinson designed his rotorhead and then designed the helicopter around it. The 18-degree offset is the result of incorporating cone hinges on the rotorhead. With the design of the rotorhead being the driving force Frank had to settle on a 72-degree pitch horn as he could not even consider a 90-degree pitch horn as he had stated in his posted response.
However the control system is very much like a Bell in that the swashplate tilts down over the nose with input of forward cyclic. This resulted in the Robinson rigging procedure that places the pitch horn over the forward edge of the swashplate and in order to accomplish this the blade must be 18-degrees forward of the lateral centerline.
If the blade in fact has a 72-degree phase angle with no phase angle shift then I am totally wrong. However if it is like the Lynx then I am right.
Has anyone considered the human physiology aspect of this, and as such did FR come to the 18 degrees offset based on what felt "right" rather than any other design criteria. It cannot be contested that the offset is not a problem to pilots under normal circumstances.
However the control system is very much like a Bell in that the swashplate tilts down over the nose with input of forward cyclic. This resulted in the Robinson rigging procedure that places the pitch horn over the forward edge of the swashplate and in order to accomplish this the blade must be 18-degrees forward of the lateral centerline.
If the blade in fact has a 72-degree phase angle with no phase angle shift then I am totally wrong. However if it is like the Lynx then I am right.
Joined: Nov 2001
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From: Alderney or Lancashire UK
Lu,
I love your conviction and belief that all you hear is true.
"To my understanding Frank Robinson designed his rotorhead and then designed the helicopter around it."
As a pilot, which you reportedly are not, I cannot believe that, if the 18 degree offset was a cock up, that the R22 ended up such a good machine to fly. Make no mistake, Frank Robinson is no idiot. 18 degrees was planned. The story that got out is the one he wanted to prevail. It may not be true but the result is as desired. His design prevailed. If, as you suggest, the rotorhead was designed first then it is a tribute to engineering genius that it flies as well as it does. I suggest this is not the scenario as I do not consider Frank Robinson a genius either. His ramblings on this very matter confirm this. For a start, if he was so good, why muck up the head in the first place.? Why not do the conventional, easy thing and go for 90 degrees phase lag. Cone hinges could be designed with 90 degree pitch horns. We are not privileged to access the true development of the R22, nor the failures along the way, nor the reasoning behind the unusual features. The R22 is not an accident. It may not be the result of conventional engineering but maybe that is it's success. I suspect without the 18 degree offset, however Frank arrived at that figure, the R22 would have been less good than it is.
72 degrees phase ange is crap. 90 degrees is not negotiable. Why on earth should the incorporation of cone hinges and 72 degree pitch horns determine the phase lag. This could be allowed for in the design of the rest of the control system, notably the effect the controls have on the swashplate. Frank could have selected any phase offset he liked without altering the rotor head.
I am not saying you are wrong, in fact I think you may be right(!) -and the phenomenon you have described is to the benefit rather than the detriment of the R22.
I'd still rather have my Enstrom!
I love your conviction and belief that all you hear is true.
"To my understanding Frank Robinson designed his rotorhead and then designed the helicopter around it."
As a pilot, which you reportedly are not, I cannot believe that, if the 18 degree offset was a cock up, that the R22 ended up such a good machine to fly. Make no mistake, Frank Robinson is no idiot. 18 degrees was planned. The story that got out is the one he wanted to prevail. It may not be true but the result is as desired. His design prevailed. If, as you suggest, the rotorhead was designed first then it is a tribute to engineering genius that it flies as well as it does. I suggest this is not the scenario as I do not consider Frank Robinson a genius either. His ramblings on this very matter confirm this. For a start, if he was so good, why muck up the head in the first place.? Why not do the conventional, easy thing and go for 90 degrees phase lag. Cone hinges could be designed with 90 degree pitch horns. We are not privileged to access the true development of the R22, nor the failures along the way, nor the reasoning behind the unusual features. The R22 is not an accident. It may not be the result of conventional engineering but maybe that is it's success. I suspect without the 18 degree offset, however Frank arrived at that figure, the R22 would have been less good than it is.
72 degrees phase ange is crap. 90 degrees is not negotiable. Why on earth should the incorporation of cone hinges and 72 degree pitch horns determine the phase lag. This could be allowed for in the design of the rest of the control system, notably the effect the controls have on the swashplate. Frank could have selected any phase offset he liked without altering the rotor head.
I am not saying you are wrong, in fact I think you may be right(!) -and the phenomenon you have described is to the benefit rather than the detriment of the R22.
I'd still rather have my Enstrom!
Joined: Jan 2003
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From: TI
Seems a lot of people don't really understand this........
In days gone by I remember having to carry out this one:
05 MAY 1998
SB 600N-011
CYCLIC CONTROL MIXER LINKS REPLACEMENT
(EIGHT DEGREE PHASE SHIFT RECOVERY)
Reason:
To recover the cyclic phase shift caused by adding the sixth blade to the main rotor system.
Complying with the requirements of this Bulletin will result in reduced pilot workload. (Read - meet FAA certification requirements)
The fix was to fit a drive link to the stationary swashplate with an 8 degree offset. The control links all ended up kind of leaned over.
Flying it before and after produced little change to the total "workload" however.
The most significant change from the 4 and 5 bladed head was the shortening of the pitch horn so you could fit all six blades on. This resulted in the total phase adding up to approximately 82 degrees by all accounts as the pitch horn is not in line with the feathering and flapping hinge point.
This aircraft, which has not been the most successful, has some very interesting engineering anomalies. Most of it was driven by trying to stay away from having to develop a new main rotor blade. The rotor produces the required thrust but unfortunately not at the ideal A of A for best L/D.
As to the Robinson comments. It works - kind of!!
05 MAY 1998
SB 600N-011
CYCLIC CONTROL MIXER LINKS REPLACEMENT
(EIGHT DEGREE PHASE SHIFT RECOVERY)
Reason:
To recover the cyclic phase shift caused by adding the sixth blade to the main rotor system.
Complying with the requirements of this Bulletin will result in reduced pilot workload. (Read - meet FAA certification requirements)
The fix was to fit a drive link to the stationary swashplate with an 8 degree offset. The control links all ended up kind of leaned over.
Flying it before and after produced little change to the total "workload" however.
The most significant change from the 4 and 5 bladed head was the shortening of the pitch horn so you could fit all six blades on. This resulted in the total phase adding up to approximately 82 degrees by all accounts as the pitch horn is not in line with the feathering and flapping hinge point.
This aircraft, which has not been the most successful, has some very interesting engineering anomalies. Most of it was driven by trying to stay away from having to develop a new main rotor blade. The rotor produces the required thrust but unfortunately not at the ideal A of A for best L/D.
As to the Robinson comments. It works - kind of!!
Iconoclast
Joined: Sep 2000
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
It can't be done
To: Gaseous
In response to quote 1): If you have a cone hinge upon which the blade flaps or cones the 90-degree pitch horn would have to reach across the cone hinge. The cone hinge in this case acts as a fulcrum. If the blade cones or flaps up the pitch horn would move down (first class lever). If the pitch horn moves down its' movement is restrained by the fixed pitch link. Since the pitch link is rigid the downward movement of the pitch horn would result in the increasing of the pitch in the blade. In order for pitch flap coupling to exist upward flapping should cause the extraction of pitch in order to return the blade to the tip path plane. The opposite would be true for the retreating blade. With a 90-degree pitch horn when the blade flaps up pitch would be added and when either blade flapped down pitch would be extracted. This would render the helicopter uncontrollable.
If the pilot pulled enough pitch to hover the upward coning blades would increase pitch over and above what the pilot pulled collective wise. And when the pilot pushed the cyclic the pitch input into the blades may be increased or decreased over or below what was input by the cyclic movement depending on the movement of the blades.
Regarding Quote 2): It was my contention all along that the phase angle of the R-22 was 90-degrees just like any other helicopter. Unlike other helicopters that had a built in rig phase angle of 90-degrees the R-22 did not. It was their contention that the phase angle was 72-degrees and the maximum pitch deflection took place 18-degrees ahead of the lateral axis and all downward flap took place in the following 72-degrees.
Cone hinges could be designed with 90 degree pitch horns.
72 degrees phase angle is crap. 90 degrees is not negotiable. Why on earth should the incorporation of cone hinges and 72 degree pitch horns determine the phase lag.
If the pilot pulled enough pitch to hover the upward coning blades would increase pitch over and above what the pilot pulled collective wise. And when the pilot pushed the cyclic the pitch input into the blades may be increased or decreased over or below what was input by the cyclic movement depending on the movement of the blades.
Regarding Quote 2): It was my contention all along that the phase angle of the R-22 was 90-degrees just like any other helicopter. Unlike other helicopters that had a built in rig phase angle of 90-degrees the R-22 did not. It was their contention that the phase angle was 72-degrees and the maximum pitch deflection took place 18-degrees ahead of the lateral axis and all downward flap took place in the following 72-degrees.
Joined: Apr 2003
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From: Vancouver, BC, Canada
Simplistic explanation of delta3 and phase lag.
The phase lag in a conventional teetering rotor is 90º. This means that the teetering (flap) angle will match the pitch angle, but this match will be 90º further on. The first three columns in the following table show this relationship.
Delta3 is a flap-pitch coupling. As the flap angle gets greater, the delta3 will remove more and more pitch. In other words, the increasing blade flap removes some of the pitch instruction that is telling the blade to flap, in the first place.
The last 2 columns show the results of delta3. The difference between the 'Pitch' column and the 'Modified pitch' column is due to the delta3. The 'Modified flap' column shows the flap of the blade due to its receiving the 'Modified pitch' instruction.
Lu. The 'Modified pitch' column shows that at approximately 72º azimuth there is no more pitch instruction going to the blade. Therefor the blade will stop flapping at 72º azimuth. To point the helicopter in the desired direction the rotor must be rigged to start the pitch instruction 18º later.
[To put it another way; if delta3 causes 7º of flap to give -2º of pitch, then at 70º azimuth, in the following table, the -2º will cancel the +2º. In other words at 70º azimuth, there is no more pitch instruction to make the blade flap anymore.]
Addition rotations of the rotor will be required to eventually work the maximum flap up the cycle's 9º
Azimuth . Pitch . . . Flap . Modified pitch . Modified flap
00` . ` . `.9` . ` . ` 0` . ` . ` 9.0` . ` . ` 0.0
10` . ` . ` 8` . ` . ` 1` . ` . ` 7.9` . ` . ` 1.0
20` . ` . ` 7` . ` . ` 2` . ` . ` 6.7` . ` . ` 1.9
30` . ` . ` 6` . ` . ` 3` . ` . ` 5.4` . ` . ` 2.8
40` . ` . ` 5` . ` . ` 4` . ` . ` 4.0` . ` . ` 3.7
50` . ` . ` 4` . ` . ` 5` . ` . ` 3.5` . ` . ` 4.6
60` . ` . ` 3` . ` . ` 6` . ` . ` 1.9` . ` . ` 5.5
70` . ` . ` 2` . ` . ` 7` . ` . ` 0.2` . ` . ` 6.4
80` . ` . ` 1` . ` . ` 8` . ` . ` 0.0` . ` . ` 6.3` . ` . `
90` . ` . ` 0` . ` . ` 9
The incorporation of delta3 in a main rotor plus the inclusion of the flapping hinges does move Robinson's rotor head away from the purity of a basic teetering rotor, but IMHO, it will take much more than an interesting discussion to determine the degree of safety, if any, that is lost due to the configuration of the Robinson hub.
Delta3 is a flap-pitch coupling. As the flap angle gets greater, the delta3 will remove more and more pitch. In other words, the increasing blade flap removes some of the pitch instruction that is telling the blade to flap, in the first place.
The last 2 columns show the results of delta3. The difference between the 'Pitch' column and the 'Modified pitch' column is due to the delta3. The 'Modified flap' column shows the flap of the blade due to its receiving the 'Modified pitch' instruction.
Lu. The 'Modified pitch' column shows that at approximately 72º azimuth there is no more pitch instruction going to the blade. Therefor the blade will stop flapping at 72º azimuth. To point the helicopter in the desired direction the rotor must be rigged to start the pitch instruction 18º later.
[To put it another way; if delta3 causes 7º of flap to give -2º of pitch, then at 70º azimuth, in the following table, the -2º will cancel the +2º. In other words at 70º azimuth, there is no more pitch instruction to make the blade flap anymore.]
Addition rotations of the rotor will be required to eventually work the maximum flap up the cycle's 9º
Azimuth . Pitch . . . Flap . Modified pitch . Modified flap
00` . ` . `.9` . ` . ` 0` . ` . ` 9.0` . ` . ` 0.0
10` . ` . ` 8` . ` . ` 1` . ` . ` 7.9` . ` . ` 1.0
20` . ` . ` 7` . ` . ` 2` . ` . ` 6.7` . ` . ` 1.9
30` . ` . ` 6` . ` . ` 3` . ` . ` 5.4` . ` . ` 2.8
40` . ` . ` 5` . ` . ` 4` . ` . ` 4.0` . ` . ` 3.7
50` . ` . ` 4` . ` . ` 5` . ` . ` 3.5` . ` . ` 4.6
60` . ` . ` 3` . ` . ` 6` . ` . ` 1.9` . ` . ` 5.5
70` . ` . ` 2` . ` . ` 7` . ` . ` 0.2` . ` . ` 6.4
80` . ` . ` 1` . ` . ` 8` . ` . ` 0.0` . ` . ` 6.3` . ` . `
90` . ` . ` 0` . ` . ` 9
The incorporation of delta3 in a main rotor plus the inclusion of the flapping hinges does move Robinson's rotor head away from the purity of a basic teetering rotor, but IMHO, it will take much more than an interesting discussion to determine the degree of safety, if any, that is lost due to the configuration of the Robinson hub.
Joined: Apr 2004
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From: US
Lu,
As you have posted your resume numerous times across the World Wide Web, and I may have missed it, but from what University did you receive your engineering degree ? I've noticed a few factory schools and being a mechanic for the USCG. Have I missed something somewhere ?
3RM
As you have posted your resume numerous times across the World Wide Web, and I may have missed it, but from what University did you receive your engineering degree ? I've noticed a few factory schools and being a mechanic for the USCG. Have I missed something somewhere ?
3RM
Joined: Nov 2001
Posts: 571
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From: Alderney or Lancashire UK
Lu
90 degree pitch horns plus coning hinges.
Correct. The situation you describe would occur with the pitch horn crossing the coning hinge. What I had in mind was to move the coning hinge to the same point as the teeter hinge so the pitch horn would not cross the fulcrum. Please tell me if this would correct the situation.
Bear in mind I am not an engineer or designer. Just a thick pilot.
I have a horrible feeling we agree over the phase angle thing.
I suspect that delta3, if I have understood DJs explanation, means that the blade only flaps over 78 degrees of the 90 degree phase lag so the EFFECTIVE phase angle is 78 degrees.
Perhaps an issue of semantics.
Has anyone else tried flying an R22 left handed and found it harder than expected?
90 degree pitch horns plus coning hinges.
Correct. The situation you describe would occur with the pitch horn crossing the coning hinge. What I had in mind was to move the coning hinge to the same point as the teeter hinge so the pitch horn would not cross the fulcrum. Please tell me if this would correct the situation.
Bear in mind I am not an engineer or designer. Just a thick pilot.
I have a horrible feeling we agree over the phase angle thing.
I suspect that delta3, if I have understood DJs explanation, means that the blade only flaps over 78 degrees of the 90 degree phase lag so the EFFECTIVE phase angle is 78 degrees.
Perhaps an issue of semantics.
Has anyone else tried flying an R22 left handed and found it harder than expected?
Iconoclast
Joined: Sep 2000
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
I can hear it now.
To: 3 ROMEO MIKE
This will probably generate a lot of laughs, guffaws and a lot of who is he trying to fool and a few I knew its'.
First of all I do not have an engineering degree. I majored in Industrial Design at North West Michigan College when I was in the military and upon discharge transferred to Michigan State College (now Michigan State University). I was married and had two kids and it was difficult to make ends meet on the GI Bill even with a part time job with the college. After a while I knew I had to go to work and luckily, Sikorsky was interviewing for design engineers. I talked to the HR rep from Silkorsky and told him of my military background and within one hour I had a job offer to attend a fourteen-month training program for field service engineers. That was my first “engineering job”.
Since that time I have worked for Philco Corporation, Lockheed, Douglas, General Dynamics, Boeing, Hughes Helicopters, Bell Helicopters, TRW, Agusta and the European Space Consortia (ESTEC). I have been a private consultant on Commercial transports, Regional Jets and Air cargo systems. I also managed a training program for the US Army on helicopters. I even worked for Eli Lilly doing analysis on capital equipment. During that time (1955 to the present) I have had an engineering classification with titles like Member of Technical Staff (TRW). Senior Member of the Technical Staff (Systems Evaluation). Engineering Scientist Specialist (Douglas). And I have had several engineering management positions but I never tried to pass myself off as a design engineer and to top all of this off I never graduated from college nor did I ever officially graduate from high school. I got a GED in service. During that time my salary ranged from $368.00 per month to $127,000 a year plus expenses. I think that’s pretty damned good for a fat kid from Cleveland.
I also have teaching credentials in four subject areas from the State of California and I have an FAA A&P ticket.
This will probably generate a lot of laughs, guffaws and a lot of who is he trying to fool and a few I knew its'.
First of all I do not have an engineering degree. I majored in Industrial Design at North West Michigan College when I was in the military and upon discharge transferred to Michigan State College (now Michigan State University). I was married and had two kids and it was difficult to make ends meet on the GI Bill even with a part time job with the college. After a while I knew I had to go to work and luckily, Sikorsky was interviewing for design engineers. I talked to the HR rep from Silkorsky and told him of my military background and within one hour I had a job offer to attend a fourteen-month training program for field service engineers. That was my first “engineering job”.
Since that time I have worked for Philco Corporation, Lockheed, Douglas, General Dynamics, Boeing, Hughes Helicopters, Bell Helicopters, TRW, Agusta and the European Space Consortia (ESTEC). I have been a private consultant on Commercial transports, Regional Jets and Air cargo systems. I also managed a training program for the US Army on helicopters. I even worked for Eli Lilly doing analysis on capital equipment. During that time (1955 to the present) I have had an engineering classification with titles like Member of Technical Staff (TRW). Senior Member of the Technical Staff (Systems Evaluation). Engineering Scientist Specialist (Douglas). And I have had several engineering management positions but I never tried to pass myself off as a design engineer and to top all of this off I never graduated from college nor did I ever officially graduate from high school. I got a GED in service. During that time my salary ranged from $368.00 per month to $127,000 a year plus expenses. I think that’s pretty damned good for a fat kid from Cleveland.
I also have teaching credentials in four subject areas from the State of California and I have an FAA A&P ticket.
Last edited by Lu Zuckerman; 20th April 2004 at 23:29.
Joined: Nov 2001
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From: Alderney or Lancashire UK
Lu
Oops. I can see a rather gaping hole in my above suggestion.
Plan B. Mount pitch horn inboard of coning hinge and add secondary lever system to feed coning information back into pitch change mechanism. Slightly messy but possible?
Oops. I can see a rather gaping hole in my above suggestion.
Plan B. Mount pitch horn inboard of coning hinge and add secondary lever system to feed coning information back into pitch change mechanism. Slightly messy but possible?
Iconoclast
Joined: Sep 2000
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Sound like an idea.
To: Gaseous
I can’t honestly say if it would solve the problem or not. What you describer is a Bell rotorhead with flapping hinges. You are correct in your assumption that it would solve the problem of a 90-degree pitch horn on a Robinson head but I do not know if the rotor system would perform as an aerodynamic entity. However the CH-47 has a similar situation as it has a flapping hinge as does the conventional Sikorsky designs. The blade flapping hinges and the pitch horns are almost coincident with each other when there is no pitch in the blade. When pitch is input into the blade the pitch horn rises above the hinge line and when the blade flaps due to gusting you get delta three with the attendant pitch flap coupling. There is however a problem that results from flapping and that is you get lead and lag. On the Robinson and Bell heads they are underslung to minimize if not eliminate lead and lag. On the Robbie what little lead and lag you get it is absorbed in the inplane bending of the blade and is reacted by the cone hinges, the main mast at the teeter point and eventually the fuselage.
It would be difficult to design a rotorhead that is both underslung and has flapping hinges. That is not to say it can’t be done but not on an R-22 or R-44.
Regarding your messy comment: If you want to see messy look at the rotorhead on an S-51. The pitch input crosses both the flapping hinge and the lead lag hinge.
I can’t honestly say if it would solve the problem or not. What you describer is a Bell rotorhead with flapping hinges. You are correct in your assumption that it would solve the problem of a 90-degree pitch horn on a Robinson head but I do not know if the rotor system would perform as an aerodynamic entity. However the CH-47 has a similar situation as it has a flapping hinge as does the conventional Sikorsky designs. The blade flapping hinges and the pitch horns are almost coincident with each other when there is no pitch in the blade. When pitch is input into the blade the pitch horn rises above the hinge line and when the blade flaps due to gusting you get delta three with the attendant pitch flap coupling. There is however a problem that results from flapping and that is you get lead and lag. On the Robinson and Bell heads they are underslung to minimize if not eliminate lead and lag. On the Robbie what little lead and lag you get it is absorbed in the inplane bending of the blade and is reacted by the cone hinges, the main mast at the teeter point and eventually the fuselage.
It would be difficult to design a rotorhead that is both underslung and has flapping hinges. That is not to say it can’t be done but not on an R-22 or R-44.
Regarding your messy comment: If you want to see messy look at the rotorhead on an S-51. The pitch input crosses both the flapping hinge and the lead lag hinge.
Iconoclast
Joined: Sep 2000
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Yes and know or is it Guess and Know.
To: Dave Jackson
First I have to say that I am amazed by your technical knowledge. However each time you make one of your pronouncements I get more confused. I agree with the first part of the above quote relative to the higher the flap the more pitch is removed. I do not believe the second part is correct. It is not a pitch instruction that is telling the blade to flap. It is an outside force (gusting) that the blade is responding to and not pitch input from the pilot. When the blade flaps you get pitch flap coupling and it is this action that results in pitch being extracted from the blade. It is the removal of the pitch that causes the blade to return to its' track position and in doing so (flapping down) that the blade pitch returns to the pitch that the pilot commanded.
Regarding your use of number to illustrate your point my eyes begin to cloud up. I understand what pitch flap coupling is and what causes it but when you add numbers I am technically lost.
To: Gaseous
If it is not too overcast check the moon. You will note that is blue.
Delta3 is a flap-pitch coupling. As the flap angle gets greater, the delta3 will remove more and more pitch. In other words, the increasing blade flap removes some of the pitch instruction that is telling the blade to flap, in the first place.
Regarding your use of number to illustrate your point my eyes begin to cloud up. I understand what pitch flap coupling is and what causes it but when you add numbers I am technically lost.
To: Gaseous
You changed your mind!
If it is not too overcast check the moon. You will note that is blue.
Joined: Nov 2001
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From: Alderney or Lancashire UK
Lu
For once, you made me smile.
It is indeed an aerodyamic force rather than pilot induced force that causes flap. Forward air speed and associated dissymmetry of thrust is the usual reason although gusting certainly induces flap.
For once, you made me smile.
It is indeed an aerodyamic force rather than pilot induced force that causes flap. Forward air speed and associated dissymmetry of thrust is the usual reason although gusting certainly induces flap.
Joined: Apr 2003
Posts: 1,635
Likes: 1
From: Vancouver, BC, Canada
Lu,
Who cares whether a gust moved the tip-path plane off the control plane, or the pilot moved the control plane off the tip-path plane?
In both cases, the end result is that the blade (tip-path plane) will teeter toward the position dictated by the cyclic (control plane). All that delta3 does is effect how this realignment of the two planes takes place.
How come I'm getting a sense of déjà vu?
It is not a pitch instruction that is telling the blade to flap. It is an outside force (gusting) that the blade is responding to and not pitch input from the pilot.
In both cases, the end result is that the blade (tip-path plane) will teeter toward the position dictated by the cyclic (control plane). All that delta3 does is effect how this realignment of the two planes takes place.
How come I'm getting a sense of déjà vu?
Iconoclast
Joined: Sep 2000
Posts: 2,132
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
The test and the results.
To: Mr. Selfish
I can accept the results but only if you made all of the movements starting at the rigged neutral position.
Now for the airborne test and possibly more ground tests.
If it is proven that even from the rigged neutral position the disc moves as you have indicated both on the ground and in the air the Robinson will be the only helicopter (to my knowledge) that does not have a 90-degree phase angle
R22 fwd & aft cyclic (on the gnd) = fwd & aft disc tilt (no lateral, with witnesses)
Now for the airborne test and possibly more ground tests.
If it is proven that even from the rigged neutral position the disc moves as you have indicated both on the ground and in the air the Robinson will be the only helicopter (to my knowledge) that does not have a 90-degree phase angle
Joined: Mar 2002
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From: Queensland Australia
Lu said ,
"Try this: …snip…. In forward flight keep the cyclic in the forward-displaced position and move the cyclic laterally to the rigged neutral position. If I am right the helicopter will fly to the left. If it doesn't deviate from the flight direction I am wrong and I will shut up. It is a simple test and could take all of 15 seconds."
R.R.
Hang on. If you are in steady flight and you deviate the cyclic laterally of course the helicopter will deviate in the direction of the movement. Your assumption is that forward cyclic will cause the disc to tilt to the left and will thus need right cyclic to maintain the forward direction.
In solo flight the cyclic is across to the LEFT and forward (as previously stated it hangs tail low and has tail rotor drift thus needs forward & left cyclic . No surprise there. This applies to forward flight as well as hover. Returning it to the neutral position is rearward and right.
What I did:
At the hover to return it to the neutral position causes lift in the front of the disc. I was not prepared to sustain that rearward drift for more than an instant while trying to visually fixate on the disc. Easy to get a sort of disorientation and a reactive driving the tail into the ground. I suspect there was some right tilt of the disc because the helicopter went that way but I didn’t see it so I can’t say I proved it. So from hover to neutral cyclic position caused rearward and rightward movement of the helicopter.
From the hover position (cyclic slight forward and to the left) to translation and climb needed forward cyclic only with definitely no further lateral deviation.
To return it to the rigged neutral position (in flight) caused a sudden climb and deviation to the RIGHT. Again no surprise because those effects are fully explainable by the CofG movements when solo.
So in short it did the opposite lateral to what you expected but it was explainable. What it would need is to load the helicopter to a C of G that allowed the machine and rotor disc to both hang horizontally at the hover to at least counter those effects.
Lu:
"Or, try this:
At your next start up place the cyclic in the rigged neutral position.
With the blades turning at 100% pull a slight amount of collective to get the blades to cone slightly. Move the cyclic forward from the rigged neutral position. Note what the blade disc does. Does it tip down over the nose or does it tip to the left. Another fifteen second test neither of which will place you or the helicopter in danger. "
RR
Result:
This was easy and absolutely unequivocal. I even moved my body across so I was looking from the centre of the aircraft.
From the rigged neutral position on the ground at 100% RRPM with slight up collective.
Forward cyclic = downward tilt on disc directly over the nose.
Rearward cyclic = upward lift in front of disc
Right cyclic = right tilt
Left cyclic = left tilt
"Try this: …snip…. In forward flight keep the cyclic in the forward-displaced position and move the cyclic laterally to the rigged neutral position. If I am right the helicopter will fly to the left. If it doesn't deviate from the flight direction I am wrong and I will shut up. It is a simple test and could take all of 15 seconds."
R.R.
Hang on. If you are in steady flight and you deviate the cyclic laterally of course the helicopter will deviate in the direction of the movement. Your assumption is that forward cyclic will cause the disc to tilt to the left and will thus need right cyclic to maintain the forward direction.
In solo flight the cyclic is across to the LEFT and forward (as previously stated it hangs tail low and has tail rotor drift thus needs forward & left cyclic . No surprise there. This applies to forward flight as well as hover. Returning it to the neutral position is rearward and right.
What I did:
At the hover to return it to the neutral position causes lift in the front of the disc. I was not prepared to sustain that rearward drift for more than an instant while trying to visually fixate on the disc. Easy to get a sort of disorientation and a reactive driving the tail into the ground. I suspect there was some right tilt of the disc because the helicopter went that way but I didn’t see it so I can’t say I proved it. So from hover to neutral cyclic position caused rearward and rightward movement of the helicopter.
From the hover position (cyclic slight forward and to the left) to translation and climb needed forward cyclic only with definitely no further lateral deviation.
To return it to the rigged neutral position (in flight) caused a sudden climb and deviation to the RIGHT. Again no surprise because those effects are fully explainable by the CofG movements when solo.
So in short it did the opposite lateral to what you expected but it was explainable. What it would need is to load the helicopter to a C of G that allowed the machine and rotor disc to both hang horizontally at the hover to at least counter those effects.
Lu:
"Or, try this:
At your next start up place the cyclic in the rigged neutral position.
With the blades turning at 100% pull a slight amount of collective to get the blades to cone slightly. Move the cyclic forward from the rigged neutral position. Note what the blade disc does. Does it tip down over the nose or does it tip to the left. Another fifteen second test neither of which will place you or the helicopter in danger. "
RR
Result:
This was easy and absolutely unequivocal. I even moved my body across so I was looking from the centre of the aircraft.
From the rigged neutral position on the ground at 100% RRPM with slight up collective.
Forward cyclic = downward tilt on disc directly over the nose.
Rearward cyclic = upward lift in front of disc
Right cyclic = right tilt
Left cyclic = left tilt
Iconoclast
Joined: Sep 2000
Posts: 2,132
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From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Possible misunderstanding.
To: RobboRider
If you are in forward flight you have already compensated for lateral displacement, CG position and blowback. The cyclic is out of the rigged neutral position. If in forward flight the swashplate is tilted down and most likely to the right. If you move the cyclic laterally to the left the swashplate will be in the neutral position laterally and tipped down over the nose. At this point there is no lateral cyclic input. If I am wrong the disc will not tilt to the left.
What you say about the movement of the helicopter as the cyclic is moved to the rigged neutral position is correct. The disc will follow the cyclic movement. When the cyclic reaches the rigged neutral position the movement will stop. My question is where is the disc at this point? Some of you have run the test on the ground and your findings say I am not correct in my beliefs and that's OK.
Take it one step further and perform the test in forward flight and If I am wrong I will shut up and this thread will die a natural death.
Hang on. If you are in steady flight and you deviate the cyclic laterally of course the helicopter will deviate in the direction of the movement. Your assumption is that forward cyclic will cause the disc to tilt to the left and will thus need right cyclic to maintain the forward direction.
What you say about the movement of the helicopter as the cyclic is moved to the rigged neutral position is correct. The disc will follow the cyclic movement. When the cyclic reaches the rigged neutral position the movement will stop. My question is where is the disc at this point? Some of you have run the test on the ground and your findings say I am not correct in my beliefs and that's OK.
Take it one step further and perform the test in forward flight and If I am wrong I will shut up and this thread will die a natural death.
Joined: Apr 2003
Posts: 1,635
Likes: 1
From: Vancouver, BC, Canada
Lu
The Kaman helicopters have delta3. I believe that they use a phase lag of less than 90º with their delta3.
Reference; Kaman rotorheads
Dave
.... the Robinson will be the only helicopter (to my knowledge) that does not have a 90-degree phase angle
Reference; Kaman rotorheads
Dave