Robinson R22 Corner [Archive copy]
Iconoclast
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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.
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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.
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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?
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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
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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
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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.
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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
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Get youself a boat. When the big one hits you will be 20 miles out in the Pacific.
To: Dave Jackson
The operative word(s) is / are (to my knowledge). The closest I ever came to a Kaman was the HOK and that was in 1949 and I am still trying to figure out how it flies.
.... the Robinson will be the only helicopter (to my knowledge) that does not have a 90-degree phase angle
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90 or 72, its 90 even in a robby
To Lu
I have read and re-read your comments on the rotor system
and I do not understand why you keep coming back to so-called rigging
offset of the R22/R44. Forgive me for trying...
A rotor is a very complex system. Most Rotorheads appear
to understand flapping and gyroscopic precession.
This is however only a first approximation and as Frank Robinson
pointed out in november 2000 there is more to it.
I assume that most Ppruners are not interested in heavy math, but
allow me to say that the mathematical equations do exist, that I think I understand them (took me a while) and that they confirm to phenomena described.
(Helicopters by Prof Dick, Von Karman institute for instance, 1991)
Allow me to rephrase Frank words (and of course I hope Frank allows me).
The first phenomenon described by Frank is a transient behaviour, that is when changing the cyclic to a new position, say from neutral to forward.
Before the rotor disk takes on its new position parallel with the requested swashplate position, the transient provokes a phase shift making a rotor tilt not fully aligned with the requested forward position, but provoking a temporary lateral effect to the right. A delta-3 coupling, that is creating a feedback system between the angle of attack and the flapping of the blades when swashplate and rotor disk are not parallel can reduce this effect. Delta-3 is achieved by tilted hinges, by elastomeric deformation or by displacing the pitch control link with respect to the flapping hinge center line. The delta-3 angle has nothing the see with the swashplate angle rigging. It provoques the upward flapping blade to reduce its angle of attack by pivoting and vice versa, so counteracting the flapping (for the mathematical inclined readers, the equation is: pitch angle change = - tg(delta-3) times flap angle change, for 18° this is -0.32, so 1 degree of extra flap changes pitch angle by -0.32 degrees). This first transient phenomenon is similar to gyroscopic precession, and happens also for instance with the B206. Try to tilt a fly-wheel forward and it will want to tilt at 90 degrees. To summarize: there can be a temporary/transient deviation between the way the cyclic is moved and the rotor disk moves. The designer may want to be compensated that as Robinson did.
The second phenomenon described by Frank happens in the case of an articulated rotor with a positive coning in steady forward flight. Important here is positive coning. The equations show that flapping is not maximal in the forward (or backward) position but is shifted by a small angle (the cone tilts again to the right as Frank stated). Simply stated this is due to the fact that the fully forward blade -because of its upward coning- still has extra lift (the wind hits it from below increasing the angle of attack, whereas the backward blade is hit from above) The aerodynamic forces on the forward blade decrease a little later (past fully forward) than would be derived from a flat disk model, creating the phase shift in the blow-back. This has nothing to see with gyroscopic precession (which again is 90°) but with coning geometry (I suggest you make a drawing of this). It is also not transient but permanent. The equations show that again a delta-3 feedback can offset the effects of this coning phase shift. Vice a versa, given a delta-3 setup, there exists a coning angle that best balances phases shift provoqued by the delta-3.
In the case of the R22 apparantly nearly full compensation of both phenomena was achieved (at +- 1°) according to Frank Robinson. In both cases this setup increases 'controllability' as you define it Lu.
I happen to own an R44 and can of course confirm that the theory works as all pilots did, forward means cyclic forward and not 18 degrees... (in the end it is as simple as that). Furthermore I checked with my own eyes and hands the following : push the cyclic forward, the swashplate goes forward (and exactly forward with no deltas). At standstill this creates a non alignment between rotor (who did not move) and swashplate : You notice a pitch change (differentially). This is because the pitch link is positioned behind the flap hinge axis (by 18°). Remark that the Delta-3 angle does not add or substract from the fixed 90° rigging, the action of this fasing is only temporary when the rotor disc is not parallel to the swashplate. Visually of course this creates an 18° angle in the rotor head, but this does not mean that the rigging is at 72°. If you don't like math go and look at the real stuff. It also may be instructive to look at the very large delta-3 angle in opposite direction of the R44 tailrotor which is not achieved by displacing rigging in the head but plainly by tilting the flap axis by I would say more then 45°. You also will remark that the R44 tail rotor has a negative coning.
I have read and re-read your comments on the rotor system
and I do not understand why you keep coming back to so-called rigging
offset of the R22/R44. Forgive me for trying...
A rotor is a very complex system. Most Rotorheads appear
to understand flapping and gyroscopic precession.
This is however only a first approximation and as Frank Robinson
pointed out in november 2000 there is more to it.
I assume that most Ppruners are not interested in heavy math, but
allow me to say that the mathematical equations do exist, that I think I understand them (took me a while) and that they confirm to phenomena described.
(Helicopters by Prof Dick, Von Karman institute for instance, 1991)
Allow me to rephrase Frank words (and of course I hope Frank allows me).
The first phenomenon described by Frank is a transient behaviour, that is when changing the cyclic to a new position, say from neutral to forward.
Before the rotor disk takes on its new position parallel with the requested swashplate position, the transient provokes a phase shift making a rotor tilt not fully aligned with the requested forward position, but provoking a temporary lateral effect to the right. A delta-3 coupling, that is creating a feedback system between the angle of attack and the flapping of the blades when swashplate and rotor disk are not parallel can reduce this effect. Delta-3 is achieved by tilted hinges, by elastomeric deformation or by displacing the pitch control link with respect to the flapping hinge center line. The delta-3 angle has nothing the see with the swashplate angle rigging. It provoques the upward flapping blade to reduce its angle of attack by pivoting and vice versa, so counteracting the flapping (for the mathematical inclined readers, the equation is: pitch angle change = - tg(delta-3) times flap angle change, for 18° this is -0.32, so 1 degree of extra flap changes pitch angle by -0.32 degrees). This first transient phenomenon is similar to gyroscopic precession, and happens also for instance with the B206. Try to tilt a fly-wheel forward and it will want to tilt at 90 degrees. To summarize: there can be a temporary/transient deviation between the way the cyclic is moved and the rotor disk moves. The designer may want to be compensated that as Robinson did.
The second phenomenon described by Frank happens in the case of an articulated rotor with a positive coning in steady forward flight. Important here is positive coning. The equations show that flapping is not maximal in the forward (or backward) position but is shifted by a small angle (the cone tilts again to the right as Frank stated). Simply stated this is due to the fact that the fully forward blade -because of its upward coning- still has extra lift (the wind hits it from below increasing the angle of attack, whereas the backward blade is hit from above) The aerodynamic forces on the forward blade decrease a little later (past fully forward) than would be derived from a flat disk model, creating the phase shift in the blow-back. This has nothing to see with gyroscopic precession (which again is 90°) but with coning geometry (I suggest you make a drawing of this). It is also not transient but permanent. The equations show that again a delta-3 feedback can offset the effects of this coning phase shift. Vice a versa, given a delta-3 setup, there exists a coning angle that best balances phases shift provoqued by the delta-3.
In the case of the R22 apparantly nearly full compensation of both phenomena was achieved (at +- 1°) according to Frank Robinson. In both cases this setup increases 'controllability' as you define it Lu.
I happen to own an R44 and can of course confirm that the theory works as all pilots did, forward means cyclic forward and not 18 degrees... (in the end it is as simple as that). Furthermore I checked with my own eyes and hands the following : push the cyclic forward, the swashplate goes forward (and exactly forward with no deltas). At standstill this creates a non alignment between rotor (who did not move) and swashplate : You notice a pitch change (differentially). This is because the pitch link is positioned behind the flap hinge axis (by 18°). Remark that the Delta-3 angle does not add or substract from the fixed 90° rigging, the action of this fasing is only temporary when the rotor disc is not parallel to the swashplate. Visually of course this creates an 18° angle in the rotor head, but this does not mean that the rigging is at 72°. If you don't like math go and look at the real stuff. It also may be instructive to look at the very large delta-3 angle in opposite direction of the R44 tailrotor which is not achieved by displacing rigging in the head but plainly by tilting the flap axis by I would say more then 45°. You also will remark that the R44 tail rotor has a negative coning.
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Correction
Sorry Lu
When rereading the previous mail I noticed a wrong sentence:
"You notice a pitch change (differentially). This is because the pitch link is positioned behind the flap hinge axis (by 18°)."
This is wrong, differential change is of course the normal cyclic way of working, and would also happen without a delta-3 angle. I should have said "you notice that the pitch links are positioned not in the extended flapping axis".
I should have suggested the following experiment : lift both blades equally (that I could not do alone..) so that they become coned maintaining the rotor head (hub) in the same position, and you will notice a pitch decrease.
Try this
____xxxx_______________xxxx
---->____xxxx________xxxx
____________xxx ! xxx
_______________!
The forward blade (I hope the rough sketch makes sense) has extra upward lift because of the wind. The rear blade loses lift. This provokes the forward blade still to rise, even when the normal cyclic way of working would make the pitch neutral in forward position (and minimal 90 degrees before that) This extra lift and associated flap/coning angle is compensated by the delta-3 rigging which will reduce the pitch in that case and so lower the blade again. Similarly the rear blade would continue to descend, but then the pitch is augmented counteracting the extra descent.
If no delta-3 were present the rotor would indeed tip later creating a right tilt of the rotor disk. So left cyclic would be necessary, meaning the system is not \'controllable\'. This is of course not noticable in flight because delta-3 removes this effect.
Good night ....
When rereading the previous mail I noticed a wrong sentence:
"You notice a pitch change (differentially). This is because the pitch link is positioned behind the flap hinge axis (by 18°)."
This is wrong, differential change is of course the normal cyclic way of working, and would also happen without a delta-3 angle. I should have said "you notice that the pitch links are positioned not in the extended flapping axis".
I should have suggested the following experiment : lift both blades equally (that I could not do alone..) so that they become coned maintaining the rotor head (hub) in the same position, and you will notice a pitch decrease.
Try this
____xxxx_______________xxxx
---->____xxxx________xxxx
____________xxx ! xxx
_______________!
The forward blade (I hope the rough sketch makes sense) has extra upward lift because of the wind. The rear blade loses lift. This provokes the forward blade still to rise, even when the normal cyclic way of working would make the pitch neutral in forward position (and minimal 90 degrees before that) This extra lift and associated flap/coning angle is compensated by the delta-3 rigging which will reduce the pitch in that case and so lower the blade again. Similarly the rear blade would continue to descend, but then the pitch is augmented counteracting the extra descent.
If no delta-3 were present the rotor would indeed tip later creating a right tilt of the rotor disk. So left cyclic would be necessary, meaning the system is not \'controllable\'. This is of course not noticable in flight because delta-3 removes this effect.
Good night ....
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To: Delta 3 and Delta 3
I just finished my post in response to your two posts and it disappeared. Now I have to start over again.
If I understand you correctly you state that the Robinson has a 90-degree phase angle. Hopefully I am correct in that assumption as my comments are based on that assumption.
Using the Bell system as a base line when the pilot moves the cyclic forward the swashplate tilts on the lateral axis and tips down over the longitudinal axis. With the blades disposed over the lateral axis the advancing blade will be at its’ lowest pitch and the retreating blade will be at the highest pitch. Since you believe in gyroscopic precession the reaction will occur 90-degrees later (discounting phase angle shift) and the advancing blade will be at its’ lowest point of flap over the nose. This is as a result of the rotor system having a 90-degree lead on the pitch horn.
If you believe in gyroscopic precession then you must also believe that the disc will tilt 90-degrees in the direction of rotation from where the perturbing force was input. In this case the perturbing force was over the right side of the disc and the disc tilts down over the nose as a result.
The Robinson control geometry is just like the Bell. If the cyclic is displaced forward from the rigged neutral position the swashplate will tilt on the lateral axis and tip down over the longitudinal axis. Unlike the Bell which is rigged for forward control with the blades disposed over the lateral axis the Robinson blade is rigged for forward control with the advancing blade 18-degrees ahead of the lateral axis. This is because the pitch horn leads the blade by 72-degrees as opposed to the 90-degree pitch horn on the Bell.
Following your statement about the Robinson having a 90-degree phase angle and your belief in gyroscopic precession the Robinson blade will have its’ maximum response 90-degrees after the maximum pitch change. If you believe that then the blade will dip down 18-degrees past the longitudinal axis.
Since you own an R-44 try this experiment. Place the blades over the longitudinal axis. Starting at the rigged neutral position move the cyclic laterally. The blades will move. Now, place the blades over the longitudinal axis and from the rigged neutral position move the cyclic forward and aft and the blades will move. If you performed this same test on a Bell the blades would not move.
Now, place the advancing blade so that the pitch horn is directly over the longitudinal axis. Move the cyclic stick laterally and the blades do not move. This is the position the blade is in when you rig for forward flight and in this position the advancing blade is at its’ lowest pitch and the retreating blade is at its’ highest pitch. If you believe in the laws of precession where should the blade be when it is in its’ lowest point on the tip path.
Forget about pitch flap coupling.
I just finished my post in response to your two posts and it disappeared. Now I have to start over again.
If I understand you correctly you state that the Robinson has a 90-degree phase angle. Hopefully I am correct in that assumption as my comments are based on that assumption.
Using the Bell system as a base line when the pilot moves the cyclic forward the swashplate tilts on the lateral axis and tips down over the longitudinal axis. With the blades disposed over the lateral axis the advancing blade will be at its’ lowest pitch and the retreating blade will be at the highest pitch. Since you believe in gyroscopic precession the reaction will occur 90-degrees later (discounting phase angle shift) and the advancing blade will be at its’ lowest point of flap over the nose. This is as a result of the rotor system having a 90-degree lead on the pitch horn.
If you believe in gyroscopic precession then you must also believe that the disc will tilt 90-degrees in the direction of rotation from where the perturbing force was input. In this case the perturbing force was over the right side of the disc and the disc tilts down over the nose as a result.
The Robinson control geometry is just like the Bell. If the cyclic is displaced forward from the rigged neutral position the swashplate will tilt on the lateral axis and tip down over the longitudinal axis. Unlike the Bell which is rigged for forward control with the blades disposed over the lateral axis the Robinson blade is rigged for forward control with the advancing blade 18-degrees ahead of the lateral axis. This is because the pitch horn leads the blade by 72-degrees as opposed to the 90-degree pitch horn on the Bell.
Following your statement about the Robinson having a 90-degree phase angle and your belief in gyroscopic precession the Robinson blade will have its’ maximum response 90-degrees after the maximum pitch change. If you believe that then the blade will dip down 18-degrees past the longitudinal axis.
Since you own an R-44 try this experiment. Place the blades over the longitudinal axis. Starting at the rigged neutral position move the cyclic laterally. The blades will move. Now, place the blades over the longitudinal axis and from the rigged neutral position move the cyclic forward and aft and the blades will move. If you performed this same test on a Bell the blades would not move.
Now, place the advancing blade so that the pitch horn is directly over the longitudinal axis. Move the cyclic stick laterally and the blades do not move. This is the position the blade is in when you rig for forward flight and in this position the advancing blade is at its’ lowest pitch and the retreating blade is at its’ highest pitch. If you believe in the laws of precession where should the blade be when it is in its’ lowest point on the tip path.
Forget about pitch flap coupling.
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To Lu,
Your remarks are correct, static neutrality occurs when the pitch horn is aligned. This is also confirmed by looking at pitch changes when the rotor is made to turn.
So applying first order reasoning this means that the rotor should tip say 20 degrees later.
But let me again try to explain why this happens.
A first fase shift occurs in the rotor because of inertia. Here a 90 degrees fase shift applies (90 degrees gyroscopic precession). This means that when keeping the helicopter on the ground, with no wind, putting to cyclic forward means that the rotor should tip at neutrality. For an R44 this is not exactly forward but slightly to the left because of the pitch horn change (I tried to film this with a simple camera but I cannot really confirm this rather small angle, the camera may be too slow to distinguish this behaviour from vibrations that occur with the associated flapping when you try this on the ground. Laterally of course the forward tilting can easily be observed by a simple camera).
For flight dynamics this has little bearing because one is supposed to first lift the helicopter, so I think its is fair to say this behaviour -if it occurs- does not affect controllability because the skids are on the ground.
Let us now consider the effect of coning and forward flight. I will not repeat the arguments but a fully articulated rotor with small excentricity displays a maximum flapping (+-) 20 degrees shifted in forward flight. So in order to compensate this effect in forward flight a negative flapping-pitch feedback is introduced, and the blades tip correctly (this is confirmed by just flying it). Allow me to quote the results from the math: For this type of rotor the flapping lags by 90 degrees the aerodynamic (conic, forward) disturbance (good old 90 degrees, which is associated with so called resonant behaviour) . But since the aerodynamic disturbance displays a fase shift (not at 90 degrees) it must be compensated by an opposite fase shift to achieve 100% controllability (by shifting the pitch horn and applying delta3 with other words, so sorry Lu here are the fase shifts again).
In contrast, from the equations also follows that the flapping fase lag is less than 90 degrees in the case of more rigid rotors (an other example that not all is 90 degrees) so that no static offset nor delta3 is needed. For typical conings the maximum aerodynamic disturbance shift is 20 degrees later in forward flight, and a more ridgid rotor only has a 70 degrees aerodynamic flapping fase lag, which adds up to a neat 90 degrees, so here compensation is obtained in a different way. Remark that ridgidity can also be obtained by increasing excentricity as large rotor systems do (so called dynamic ridgidity).
Now remains the question does this static offset create possible controllability issues: for instance picking up the helicopter, applying forward cyclic and accelerating. Here the transient behaviour comes into play : before the forward speed and coning create the aerodynamic fase shift disturbance, the transient tends to delay the static (pitch horn) offset making a normal take off enveloppe again perfectly controllable (no aerodynamic cross-coupling). Again as a R44 pilot I confirm this.
I am of course not shure that putting all of this in wording makes a lot of sense (nor that it is always formulated correctly, this is difficult..). Perhaps in a long winter night I might actually try to put all these equations in a computor a try to get some 'pictures'. I am shure designers have that. To make it more complicated the first order harmonics and fase shifts are again an approximation, still higher order harmonics are present, but again compensated by constructors. By looking closely to the R44 rotorhead I noticed for instance a positive delta3 with respect to the rotor center line and an opposite delta3 with respect to the coning centre line, so it is perhaps still more complicated. But for now I'll stick to flying.
Your remarks are correct, static neutrality occurs when the pitch horn is aligned. This is also confirmed by looking at pitch changes when the rotor is made to turn.
So applying first order reasoning this means that the rotor should tip say 20 degrees later.
But let me again try to explain why this happens.
A first fase shift occurs in the rotor because of inertia. Here a 90 degrees fase shift applies (90 degrees gyroscopic precession). This means that when keeping the helicopter on the ground, with no wind, putting to cyclic forward means that the rotor should tip at neutrality. For an R44 this is not exactly forward but slightly to the left because of the pitch horn change (I tried to film this with a simple camera but I cannot really confirm this rather small angle, the camera may be too slow to distinguish this behaviour from vibrations that occur with the associated flapping when you try this on the ground. Laterally of course the forward tilting can easily be observed by a simple camera).
For flight dynamics this has little bearing because one is supposed to first lift the helicopter, so I think its is fair to say this behaviour -if it occurs- does not affect controllability because the skids are on the ground.
Let us now consider the effect of coning and forward flight. I will not repeat the arguments but a fully articulated rotor with small excentricity displays a maximum flapping (+-) 20 degrees shifted in forward flight. So in order to compensate this effect in forward flight a negative flapping-pitch feedback is introduced, and the blades tip correctly (this is confirmed by just flying it). Allow me to quote the results from the math: For this type of rotor the flapping lags by 90 degrees the aerodynamic (conic, forward) disturbance (good old 90 degrees, which is associated with so called resonant behaviour) . But since the aerodynamic disturbance displays a fase shift (not at 90 degrees) it must be compensated by an opposite fase shift to achieve 100% controllability (by shifting the pitch horn and applying delta3 with other words, so sorry Lu here are the fase shifts again).
In contrast, from the equations also follows that the flapping fase lag is less than 90 degrees in the case of more rigid rotors (an other example that not all is 90 degrees) so that no static offset nor delta3 is needed. For typical conings the maximum aerodynamic disturbance shift is 20 degrees later in forward flight, and a more ridgid rotor only has a 70 degrees aerodynamic flapping fase lag, which adds up to a neat 90 degrees, so here compensation is obtained in a different way. Remark that ridgidity can also be obtained by increasing excentricity as large rotor systems do (so called dynamic ridgidity).
Now remains the question does this static offset create possible controllability issues: for instance picking up the helicopter, applying forward cyclic and accelerating. Here the transient behaviour comes into play : before the forward speed and coning create the aerodynamic fase shift disturbance, the transient tends to delay the static (pitch horn) offset making a normal take off enveloppe again perfectly controllable (no aerodynamic cross-coupling). Again as a R44 pilot I confirm this.
I am of course not shure that putting all of this in wording makes a lot of sense (nor that it is always formulated correctly, this is difficult..). Perhaps in a long winter night I might actually try to put all these equations in a computor a try to get some 'pictures'. I am shure designers have that. To make it more complicated the first order harmonics and fase shifts are again an approximation, still higher order harmonics are present, but again compensated by constructors. By looking closely to the R44 rotorhead I noticed for instance a positive delta3 with respect to the rotor center line and an opposite delta3 with respect to the coning centre line, so it is perhaps still more complicated. But for now I'll stick to flying.
Iconoclast
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Questions yet to be answered.
To: delta3
Aligned with what?
Later than what?
OK let's consider phase angle and phase angle shift. As I had indicated previously my explanation of phase angle is the adding of the pitch horn lead to the angle at which the swashplate tilts with forward cyclic. And phase angle shift is the number of degrees the blade actually responds to forward cyclic input and this shift is to the right of the longitudinal axis.
The examples I gave were the Sikorsky system (45-degree pitch horn and a 45-degree swashplate tilt in reference to the cyclic movement). This equals 90-degrees. On the Bell the swashplate tilts down over the nose while the advancing blade is over the lateral axis. The pitch horn leads the blade by 90-degrees. On Aerospatial helicopters the pitch horn leads the blade by 60-degrees and the swashplate tilts down 30-degrees ahead of the forward movement of the cyclic. In each case the designed rig angle or phase angle is 90-degrees. How the blades respond is a result of a lot of contributing factors. (Phase angle shift).
On most helicopters the blades respond 90-degrees after the maximum pitch input or pitch change and this is discounting phase angle shift. If the Robinson the advancing blade is 18-degrees ahead of the lateral axis (as opposed to the Bell blade which is over the lateral axis) when the pitch horn is over the maximum displacement of the swashplate.
Now without going into a lot of technical detail how will the blades respond discounting phase angle shift when the cyclic is displaced forward from the rigged neutral position? Is it 72-degrees or, is it 90-degrees?
My theory does not touch on controllability issues.
Your remarks are correct, static neutrality occurs when the pitch horn is aligned.
So applying first order reasoning this means that the rotor should tip say 20 degrees later.
OK let's consider phase angle and phase angle shift. As I had indicated previously my explanation of phase angle is the adding of the pitch horn lead to the angle at which the swashplate tilts with forward cyclic. And phase angle shift is the number of degrees the blade actually responds to forward cyclic input and this shift is to the right of the longitudinal axis.
The examples I gave were the Sikorsky system (45-degree pitch horn and a 45-degree swashplate tilt in reference to the cyclic movement). This equals 90-degrees. On the Bell the swashplate tilts down over the nose while the advancing blade is over the lateral axis. The pitch horn leads the blade by 90-degrees. On Aerospatial helicopters the pitch horn leads the blade by 60-degrees and the swashplate tilts down 30-degrees ahead of the forward movement of the cyclic. In each case the designed rig angle or phase angle is 90-degrees. How the blades respond is a result of a lot of contributing factors. (Phase angle shift).
On most helicopters the blades respond 90-degrees after the maximum pitch input or pitch change and this is discounting phase angle shift. If the Robinson the advancing blade is 18-degrees ahead of the lateral axis (as opposed to the Bell blade which is over the lateral axis) when the pitch horn is over the maximum displacement of the swashplate.
Now without going into a lot of technical detail how will the blades respond discounting phase angle shift when the cyclic is displaced forward from the rigged neutral position? Is it 72-degrees or, is it 90-degrees?
My theory does not touch on controllability issues.
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Lu Zuckerman,
You obviously fail to realize how much you discredit yourself by continuing this nonsense. You claim to be such a great engineer, yet you are performing a test via the internet with people you don't even know. How accurate and scientific is that?? How can anyone believe any conclusion of yours with such poor scientific processes. You don't have a leg to stand on, and you continue to aggrevate and annoy people. If you were really so self rightous, you would go and spend the money to conduct the tests yourself. Then you would see how wrong you are and we would all have some freaking peace and quiet from your complete babbling. I swear, I have seen these arguements on every helicopter board on the internet for more than a year.
How can you claim to have any knowledge of engineering when you don't even know how to conduct a simple test?? The only people you get to listen to you are those who haven't heard you before and have no reason not to believe you until they realize how full of crap you really are. I have seen dozens of people on boards all over the internet telling you to put up or shut up. But you are too dense to get the hint and you continue to waste the time of many people with no scientific evidence at all to support your claims!! I for one am completely sick of your baseless posts and I am sure there are others here as well that are equally or even more so sick of you!
You obviously fail to realize how much you discredit yourself by continuing this nonsense. You claim to be such a great engineer, yet you are performing a test via the internet with people you don't even know. How accurate and scientific is that?? How can anyone believe any conclusion of yours with such poor scientific processes. You don't have a leg to stand on, and you continue to aggrevate and annoy people. If you were really so self rightous, you would go and spend the money to conduct the tests yourself. Then you would see how wrong you are and we would all have some freaking peace and quiet from your complete babbling. I swear, I have seen these arguements on every helicopter board on the internet for more than a year.
How can you claim to have any knowledge of engineering when you don't even know how to conduct a simple test?? The only people you get to listen to you are those who haven't heard you before and have no reason not to believe you until they realize how full of crap you really are. I have seen dozens of people on boards all over the internet telling you to put up or shut up. But you are too dense to get the hint and you continue to waste the time of many people with no scientific evidence at all to support your claims!! I for one am completely sick of your baseless posts and I am sure there are others here as well that are equally or even more so sick of you!
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And another country is heard from.
Hey Coe long time no hear.
I would gladly have the test performed but the closest R-22 is over 200 KM away from where I live. Since you don'r believe any results that might come from tests conducted by someone on this forum I have a deal for you. How much does it cost to rent an R-22. How would you like to perform the test. If you do I will pick up the cost for 30 minutes of flight time. If you can't get a Robbie for less than one hour I will pick up the cost for one hour of flight time. The tests should take less than ten minutes and you would have 50 minutes to screw holes in the sky. This way you can build time on my dime and if you are right you can have the satisfaction of proving me wrong.
Meanwhile why not answer the questions I posed to Delta 3?
I would gladly have the test performed but the closest R-22 is over 200 KM away from where I live. Since you don'r believe any results that might come from tests conducted by someone on this forum I have a deal for you. How much does it cost to rent an R-22. How would you like to perform the test. If you do I will pick up the cost for 30 minutes of flight time. If you can't get a Robbie for less than one hour I will pick up the cost for one hour of flight time. The tests should take less than ten minutes and you would have 50 minutes to screw holes in the sky. This way you can build time on my dime and if you are right you can have the satisfaction of proving me wrong.
Meanwhile why not answer the questions I posed to Delta 3?
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Lu,
Did you even read my post? I think you are full of crap. You have no concept of how to conduct a test and if you are too lazy to drive 200KM then SHUT UP!! I drive 200KM every day going to work and back. So don't get me some story how 200KM is a long drive! If you really had any conviction that Robinsons are dangerous and you valued human life at all, 200KM is a very short drive to make to save lives isn't it? But since you are too lazy to make this drive, we all know your convictions aren't very solid. Even if you drove the 200KM now, and found a major design flaw in Robinsons, no one would believe you because you have discredited yourself as an engineer, a pilot, and a human being. All you can do is talk talk talk. If you can't get off your lazy butt and show some real proof, then SHUT UP!!!
For everyone on this board. I apologize for this but I am so fed up with Lu Zuckerman and his BS. He has been on many other boards and has many other people conduct his so called "test". They all came back with answers he did not like, so he continues to ask every Robinson driver he finds to perform the same tests. He will not be satisified until he hears what he wants. Many many people have proven him wrong, but he fails to shut up as he says he will. If he won't drive 200KM to find a deadly design flaw, how strong can his convictions be? I bet anyone on this board would drive around the world if it ment the possibility of saving someones life. Yet he complains that 200KM is too far. I have seen this on many boards and I am so freakin tired of it. He does nothing to better aviation and only hurts it by spreading a ridiculous theory he has no proof of and refuses to get proof of.
Lu Zuckerman, you are a hinderence to aviation and aviation safety. Like many other have said before me, PUT UP OR SHUT UP!
Did you even read my post? I think you are full of crap. You have no concept of how to conduct a test and if you are too lazy to drive 200KM then SHUT UP!! I drive 200KM every day going to work and back. So don't get me some story how 200KM is a long drive! If you really had any conviction that Robinsons are dangerous and you valued human life at all, 200KM is a very short drive to make to save lives isn't it? But since you are too lazy to make this drive, we all know your convictions aren't very solid. Even if you drove the 200KM now, and found a major design flaw in Robinsons, no one would believe you because you have discredited yourself as an engineer, a pilot, and a human being. All you can do is talk talk talk. If you can't get off your lazy butt and show some real proof, then SHUT UP!!!
For everyone on this board. I apologize for this but I am so fed up with Lu Zuckerman and his BS. He has been on many other boards and has many other people conduct his so called "test". They all came back with answers he did not like, so he continues to ask every Robinson driver he finds to perform the same tests. He will not be satisified until he hears what he wants. Many many people have proven him wrong, but he fails to shut up as he says he will. If he won't drive 200KM to find a deadly design flaw, how strong can his convictions be? I bet anyone on this board would drive around the world if it ment the possibility of saving someones life. Yet he complains that 200KM is too far. I have seen this on many boards and I am so freakin tired of it. He does nothing to better aviation and only hurts it by spreading a ridiculous theory he has no proof of and refuses to get proof of.
Lu Zuckerman, you are a hinderence to aviation and aviation safety. Like many other have said before me, PUT UP OR SHUT UP!