To: Helo Teacher Re 72-degree Vs 90-degree pitch horn
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Er...well the answer to that (is it really a serious question?) would be the pilot would close the throttle (or pull the ICO, but that's a bit drastic).
Now I know why some others have become so exasperated, I've managed to avoid it thus far. I cannot believe that the above is being proferred as serious, technically sound theory.
I don't think I'll bother with any more of these R22 threads.
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Another day in paradise
Now I know why some others have become so exasperated, I've managed to avoid it thus far. I cannot believe that the above is being proferred as serious, technically sound theory.
I don't think I'll bother with any more of these R22 threads.
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Another day in paradise
Guest
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To: 212man
The bit about how the pilot gets the helicopter on the ground was said in jest. The other parts were in answer to your previous posts.
In each of your posts you concentrated on autorotation and collective settings. I still don't know if you fully understand what I was driving at relative to a 90-degree pitch horn Vs a 72-degree pitch horn.. Please don't go away.
I will sit at my computer and answer to the best of my ability any question you might raise about the thread subject..
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The Cat
The bit about how the pilot gets the helicopter on the ground was said in jest. The other parts were in answer to your previous posts.
In each of your posts you concentrated on autorotation and collective settings. I still don't know if you fully understand what I was driving at relative to a 90-degree pitch horn Vs a 72-degree pitch horn.. Please don't go away.
I will sit at my computer and answer to the best of my ability any question you might raise about the thread subject..
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The Cat
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Lu, explanations like that KILL my respect for your knowledge. Again you have ignored what I said, design does not consist of the process you are describing, I'll go point at a time.
1. Minimum (better than flat) pitch
I would expect that the minimum pitch setting would be rerigged a lower value such that the pitch realized at hover coning angles would approximate those experienced prior to the change.
2. Correlator
Simply put, if pitch is being added at a rate of say 135% to previous, the correlator gets rerigged to open the throttle at 135% the revious rate.
3. Jump T/O
Adjust the collectice rigging. If I need to explain how...
If you want to declare something impossible, try to use a reaalistic example of its implementation.
Sorry about the tone of the post, but I really expected better.
1. Minimum (better than flat) pitch
I would expect that the minimum pitch setting would be rerigged a lower value such that the pitch realized at hover coning angles would approximate those experienced prior to the change.
2. Correlator
Simply put, if pitch is being added at a rate of say 135% to previous, the correlator gets rerigged to open the throttle at 135% the revious rate.
3. Jump T/O
Adjust the collectice rigging. If I need to explain how...
If you want to declare something impossible, try to use a reaalistic example of its implementation.
Sorry about the tone of the post, but I really expected better.
Guest
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Lu,
I mentioned earlier on a different thread that it is perhaps possible that the rotor head was designed around the 72' pitch horn concept (for the reasons explained by FR, transverse flow etc.)and that perhaps this very concept allowed the coning hinges and hence light weight blades to be employed.
You dismissed this possibility by claiming that the coning hinges were designed into the system first.
Do you have any hard evidence of this? Did FR tell you so or does it merely support your arguement to make such a claim?
It matters little which came first,the chicken or the egg, so long as there are chickens. The same can be said for the R22 rotor head. I does not matter which part was designed first.IT WORKS !
The fact that it works is indisputable.Every pilot who has ever flown one will tell you that the machine travels in the intended direction of flight.If you do not believe this then you must get your butt into one before you are eligible for further comment.
Assuming that you do believe it, then by continueing to attack the integrety of FR's explaination you set out only to prove/disprove FR's honour.This is of little consequence to anybody except maybe his friends and family and since it has nothing to do with the safety of the R22 is of very little interest in this forum.
I mentioned earlier on a different thread that it is perhaps possible that the rotor head was designed around the 72' pitch horn concept (for the reasons explained by FR, transverse flow etc.)and that perhaps this very concept allowed the coning hinges and hence light weight blades to be employed.
You dismissed this possibility by claiming that the coning hinges were designed into the system first.
Do you have any hard evidence of this? Did FR tell you so or does it merely support your arguement to make such a claim?
It matters little which came first,the chicken or the egg, so long as there are chickens. The same can be said for the R22 rotor head. I does not matter which part was designed first.IT WORKS !
The fact that it works is indisputable.Every pilot who has ever flown one will tell you that the machine travels in the intended direction of flight.If you do not believe this then you must get your butt into one before you are eligible for further comment.
Assuming that you do believe it, then by continueing to attack the integrety of FR's explaination you set out only to prove/disprove FR's honour.This is of little consequence to anybody except maybe his friends and family and since it has nothing to do with the safety of the R22 is of very little interest in this forum.
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To: Helo Teacher and Outside Loop
From the very beginning I referenced the FAA advisory circular 27-1 that addressed the Robinson rotorhead as a new and unusual design and, in order to get it certified Robinson had to perform testing over and above the normal tests to prove rotorhead structural integrity, reliability and safety. If Robinson had submitted the R22 with a teetering head similar to the Bell he would not have to perform the extra testing. What constitutes new and unusual was the fact that the R22 rotorhead was the first and only rotorhead that had both teetering capability and it also was comprised of two coning hinges. If you had read my report or, the questions I posed to the FAA and Robinson you would know that I inquired as to whether this extra testing had been performed. What prompted me to ask that particular question was the fact that both Robinson helicopters had been restricted from sideslipping and out of trim flight. The reason for the restriction was that in performing these maneuvers the helicopter could suffer a mast-bumping incident due to excessive flapping.
Why does a Bell not have these restrictions? Because, it is not subject to these excessive flapping loads. If the Robinson rotorhead was comprised of one teeter hinge and two coning hinges it could never incorporate a 90-degree pitch horn that Frank Robinson said he had considered. His entire explanation about delta 3 had absolutely nothing to do with compensating for the 18-degree offset. Absolutely nothing! Yet because he said it no matter his reason everyone thinks I am wrong and he is right simply because of whom he is. Do you remember in his explanation he stated that it would require a lot of highly technical descriptions to explain this phenomenon and that he also said that many helicopter engineers don’t even understand it. That might be true for a guy that designs landing gear or transmissions but not the guys that design the helicopter dynamic systems.
I think the reason that different individuals don’t understand what I am saying is because of several reasons. 1) They are blinded from the facts because they conflict with what Frank Robinson said in his response. Or, 2) they can’t conceptualize or they don’t have the capability of using imagery to visualize in their mind how mechanical things work or, 3) chose your own reason.
It all boils down to this.
1) The Robinson rotorhead was designed with the coning hinges
2) A rotorhead with flapping capability or coning can not incorporate a pitch horn that extends beyond the flapping or coning axis due to the generation of massive pitch coupling.
3) The FAA or any other certification authority would never certify a rotorhead that fell under (2) above.
4) Because of 1,2.3 above, what Frank Robinson stated about having considered a 90-degree pitch horn was totally untrue. In other words he lied and I state here and now that I strongly feel that he lied about the delta 3 effect compensating for the 18-degree offset. He then covered it up by stating that to properly explain how it works would involve highly technical descriptions. In other words he was saying that the participants on these threads were too ignorant to understand. He further buried the subject by inferring that many helicopter engineers don’t even understand the subject. This man is your god but he has feet of clay.
Now, how difficult is it to understand what I have been saying?
None of this is meant to be offensive or cutting any of you down, but I keep trying to explain by sending my message to you as if I were shooting a bow and arrow, but the target, seems to move around a lot and I can never hit the bulls eye. (Another sports analogy).
To: Outside loop
If you had read one of my previous posts I stated that the position of the coning hinges on the rotorhead may have been determined by design analysis and ended up as requiring a 72-degree pitch horn. True Frank Robinson referenced the location of the coning hinges in reference to transverse flow but the coning hinges have nothing to do with transverse flow, The pilot compensates for it by applying left cyclic. The coning hinges allow blade flapping to minimize flapping loads and they minimize blade bending. Because of the delta 3 effect the blades when they flap up and out of the tip path the delta 3 effect reduces the blade pitch and causes the blade to drop back in track. The opposite is true if the blade flaps down. This is common to all helicopters including a single rotor bell and especially those helicopters with flapping hinges.
It must be obvious to a lot of you that since I first entered into this forum my opinions have changed and that is due to these back and forth discussions. It is true that my opinions have changed but only to sharpen the technical aspects of those opinions. When I first discussed the 18-degree offset everyone jumped on me and said I was wrong. After a lot of bashing I started to look at this factor in a different light. That is when I considered transverse flow effect. I stated that the helicopter would fly left when the cyclic was pushed forward from the rigged neutral position. I still feel that way. But when you consider transverse flow effect and the left cyclic compensation it became clear that when the pilot moved his stick back to the right until he was flying in the direction intended he had compensated for the offset. In other words the transverse flow and the left cyclic masked the 18-degree offset. Does this seem plausible?
One other thing which I had mentioned previously is that I had asked why if the blade is offset by 18-degrees and it has a phase angle of 90-degrees (this was stated in two Robinson websites) why doesn’t it flap down to the left? Don't tell me because Frank Robinson said so.. The two websites that are supported by Robinson dealers stated that the Robinson blade had a 90-degree phase angle.
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The Cat
[This message has been edited by Lu Zuckerman (edited 07 January 2001).]
From the very beginning I referenced the FAA advisory circular 27-1 that addressed the Robinson rotorhead as a new and unusual design and, in order to get it certified Robinson had to perform testing over and above the normal tests to prove rotorhead structural integrity, reliability and safety. If Robinson had submitted the R22 with a teetering head similar to the Bell he would not have to perform the extra testing. What constitutes new and unusual was the fact that the R22 rotorhead was the first and only rotorhead that had both teetering capability and it also was comprised of two coning hinges. If you had read my report or, the questions I posed to the FAA and Robinson you would know that I inquired as to whether this extra testing had been performed. What prompted me to ask that particular question was the fact that both Robinson helicopters had been restricted from sideslipping and out of trim flight. The reason for the restriction was that in performing these maneuvers the helicopter could suffer a mast-bumping incident due to excessive flapping.
Why does a Bell not have these restrictions? Because, it is not subject to these excessive flapping loads. If the Robinson rotorhead was comprised of one teeter hinge and two coning hinges it could never incorporate a 90-degree pitch horn that Frank Robinson said he had considered. His entire explanation about delta 3 had absolutely nothing to do with compensating for the 18-degree offset. Absolutely nothing! Yet because he said it no matter his reason everyone thinks I am wrong and he is right simply because of whom he is. Do you remember in his explanation he stated that it would require a lot of highly technical descriptions to explain this phenomenon and that he also said that many helicopter engineers don’t even understand it. That might be true for a guy that designs landing gear or transmissions but not the guys that design the helicopter dynamic systems.
I think the reason that different individuals don’t understand what I am saying is because of several reasons. 1) They are blinded from the facts because they conflict with what Frank Robinson said in his response. Or, 2) they can’t conceptualize or they don’t have the capability of using imagery to visualize in their mind how mechanical things work or, 3) chose your own reason.
It all boils down to this.
1) The Robinson rotorhead was designed with the coning hinges
2) A rotorhead with flapping capability or coning can not incorporate a pitch horn that extends beyond the flapping or coning axis due to the generation of massive pitch coupling.
3) The FAA or any other certification authority would never certify a rotorhead that fell under (2) above.
4) Because of 1,2.3 above, what Frank Robinson stated about having considered a 90-degree pitch horn was totally untrue. In other words he lied and I state here and now that I strongly feel that he lied about the delta 3 effect compensating for the 18-degree offset. He then covered it up by stating that to properly explain how it works would involve highly technical descriptions. In other words he was saying that the participants on these threads were too ignorant to understand. He further buried the subject by inferring that many helicopter engineers don’t even understand the subject. This man is your god but he has feet of clay.
Now, how difficult is it to understand what I have been saying?
None of this is meant to be offensive or cutting any of you down, but I keep trying to explain by sending my message to you as if I were shooting a bow and arrow, but the target, seems to move around a lot and I can never hit the bulls eye. (Another sports analogy).
To: Outside loop
If you had read one of my previous posts I stated that the position of the coning hinges on the rotorhead may have been determined by design analysis and ended up as requiring a 72-degree pitch horn. True Frank Robinson referenced the location of the coning hinges in reference to transverse flow but the coning hinges have nothing to do with transverse flow, The pilot compensates for it by applying left cyclic. The coning hinges allow blade flapping to minimize flapping loads and they minimize blade bending. Because of the delta 3 effect the blades when they flap up and out of the tip path the delta 3 effect reduces the blade pitch and causes the blade to drop back in track. The opposite is true if the blade flaps down. This is common to all helicopters including a single rotor bell and especially those helicopters with flapping hinges.
It must be obvious to a lot of you that since I first entered into this forum my opinions have changed and that is due to these back and forth discussions. It is true that my opinions have changed but only to sharpen the technical aspects of those opinions. When I first discussed the 18-degree offset everyone jumped on me and said I was wrong. After a lot of bashing I started to look at this factor in a different light. That is when I considered transverse flow effect. I stated that the helicopter would fly left when the cyclic was pushed forward from the rigged neutral position. I still feel that way. But when you consider transverse flow effect and the left cyclic compensation it became clear that when the pilot moved his stick back to the right until he was flying in the direction intended he had compensated for the offset. In other words the transverse flow and the left cyclic masked the 18-degree offset. Does this seem plausible?
One other thing which I had mentioned previously is that I had asked why if the blade is offset by 18-degrees and it has a phase angle of 90-degrees (this was stated in two Robinson websites) why doesn’t it flap down to the left? Don't tell me because Frank Robinson said so.. The two websites that are supported by Robinson dealers stated that the Robinson blade had a 90-degree phase angle.
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The Cat
[This message has been edited by Lu Zuckerman (edited 07 January 2001).]
Guest
Posts: n/a
Well, I've finally found a diagram (from maintenance manual) of the head, and it doesn't seem to tally with Lu's (funny old thing). For one thing, the pitch horn is exactly in line both vertically and laterally with the coning hinge (one side, hence singular). So any blade movement about this hinge will not result in any pitch change. However, as the main flapping takes place about an underslung teetering bearing there will be some delta 3 effect ( as Lu has stated before). From what I have hand written in my notes, the reason given was that it reduced the flapping forces that were being fed back to the stick. This is entirely logical, in that that flaping taking place about the coning hinges would not be felt, where as that about the teetering head would be.
Secondly, if you draw a line through the centre of the pitch horn bearing (where the pitch change link connects) to the centre of the axis of rotation, you get an angle of about 25 degrees, giving an advance angle of 65 degrees. So where does the 18 degrees come from? Is it from the direction the swashplate moves?
The reason for going on about auto rev settings was that the subject of different power settings required to hover had crept in. I had not realised that you were trying to relate this to pitch change due to coning. However, that is still a flawed argument because even if the pitch did increase with coning, the pilot would then have to lower the collective to reinstate the required net pitch angle for those conditions. If he did not, the a/c would rise. At the end of the day, power required is only a measure of blade drag which in turn reflects the blade angle of attack. For any given weight this will depend on the density altitude and will vary. However, within normal ranges, the drag will be much the same for any given weight and so will the power required. All that changes is the collective setting.
In the absence of more diagrams and not being able to locate FR's comments that's about all I can say for now.
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Another day in paradise
[This message has been edited by 212man (edited 07 January 2001).]
Secondly, if you draw a line through the centre of the pitch horn bearing (where the pitch change link connects) to the centre of the axis of rotation, you get an angle of about 25 degrees, giving an advance angle of 65 degrees. So where does the 18 degrees come from? Is it from the direction the swashplate moves?
The reason for going on about auto rev settings was that the subject of different power settings required to hover had crept in. I had not realised that you were trying to relate this to pitch change due to coning. However, that is still a flawed argument because even if the pitch did increase with coning, the pilot would then have to lower the collective to reinstate the required net pitch angle for those conditions. If he did not, the a/c would rise. At the end of the day, power required is only a measure of blade drag which in turn reflects the blade angle of attack. For any given weight this will depend on the density altitude and will vary. However, within normal ranges, the drag will be much the same for any given weight and so will the power required. All that changes is the collective setting.
In the absence of more diagrams and not being able to locate FR's comments that's about all I can say for now.
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Another day in paradise
[This message has been edited by 212man (edited 07 January 2001).]
Guest
Posts: n/a
To: 212man
What you discovered in your drawing is what we have been talking about all along.
First you have proven that the pitch horn is almost coincident with the cone hinge. Which is what I had stated in other threads. When the pitch horn / pitch link connection is coincident with the cone hinge there is no pitch coupling when the blade flaps about the cone hinge. However as I had previously stated in other threads if the pitch horn / pitch link connection is above or below the cone hinge then there would be a delta 3 connection and when the blade flaps up the pitch will be removed. If the blade flaps down the pitch will be added thus in both cases restoring the blade to the in track position. If the blades (rotorhead) tilts in relation to a fixed swashplate the same thing will happen. The high blade has pitch removed and the low blade gets pitch added thus restoring the disc to the originally commanded position. It makes no difference if the pitch horn / pitch Inc connection is coincident with the cone hinge or not.
I’m confused by what you said about the underslung rotor head reducing the flapping loads. If you are talking about the Robinson rotorhead the reason for the underslung rotor design is to reduce lead and lag caused by the flapping of the blades. This obviously hasn’t happened because the cone bushings and the teeter bushings are high replacement items due to the leading an lagging of the blades. The purpose of the cone hinges is to reduce the flapping loads and the resultant feedback and also, to relieve blade bending caused by coning. Please note, a Bell blade also cones but it is allowed by bending of the blade and on some Bell rotor heads the head itself is preconed to relieve some of the bending loads on the blade and the rotorhead.
Regarding your angular measurement it probably is correct but the 18-degree offset is measured in circular degrees or, degrees of rotation. Log onto this website and download the diagram.
http://pprune.homestead.com/files/rigging.jpg
This shows the rigging position for setting fore and aft pitch setting on both the bell and the Robinson. You will note the position of the Bell blade. This is because it has a 90-degree pitch horn. Now, look at the Robinson blades. In order to set the fore and aft settings the blade is rotated in the direction of normal rotation until the pitch horn /pitch link are directly over the longitudinal axis of the helicopter just like the Bell. Please note the Bell and the Robinson swashplates move exactly the same when the cyclic stick is moved. The rotation of the blades to place the pitch horn / pitch link over the longitudinal centerline is about 18-degrees. This is because the Robinson has a 72-degree pitch horn. The reason the Robinson can’t have a 90-degree pitch horn like on the Bell is because the pitch horn can not cross the cone hinge. It would be bad design and the FAA would not allow it. Besides, you wouldn’t want to fly an R22 or an R44 if it had a 90-degree pitch horn.
Regarding your comment about auto rev I totally agree. I was only trying to construct a scenario about auto rotation if you had a 90-degree pitch horn.
Now, if and that’s a big if, you understand and believe what I wrote above then, is it possible the Frank Robinson told a falsehood.
Here is Frank Robinsons' response
I have read some of the comments about the R22 helicopter printed in this forum. Most were favorable and I appreciated that. However, some were obviously misinformed, and I will comment on several of those.
SIDESLIP WITH THE R22
Concerning the caution against excessive sideslips in the R22 flight manual, this was in part due to a misunderstanding by the FAA. In the Army training film on mast bumping, it showed excessive side slipping as one cause of mast bumping. This was true for the Army Bell Cobras and Hueys, because both aircraft have high centers-of-gravity and relatively low side silhouettes due to their high-mounted powerplants and low-mounted tailcones. During a severe sideslip, the resultant fuselage drag could be below the center-of-gravity and cause the helicopter to roll out of a turn, instead of into the turn, i.e. a negative dihedral or adverse roll characteristic. Airplanes prevent this by having wings with positive dihedral.
The basic R22s and R44s have low-mounted engines, high tailcones, and aerodynamic mast fairings. Consequently, neither the basic R22 or R44 had any tendency toward adverse roll during FAA certification. However, all helicopters (including the R22 and R44) tend to have an adverse roll characteristic when they are equipped with inflated floats, because the floats move the side silhouette area down considerably. For that reason, I did not object to the caution in the R22 flight manual against extreme sideslips during forward flight.
R22 FAA TYPE CERTIFICATION
During the R22 certification, both the FAA test pilots and our own company test pilots flew the R22 through all required maneuvers and flight regimes, and it met all of the FAA regulations. No exemptions were issued for the R22 by the FAA during its certification. Also, I was not a DER (designated engineering representative) during the FAA certification of the R22. No DERs were used during its original certification. After it was certified, the FAA appointed me as a DER with limited authority, so I could approve some minor design changes which commonly occur during production of a new aircraft.
R22 ROTOR SYSTEM
I have read various explanations in this forum attempting to explain the dynamic and aerodynamic characteristics of the R22 rotor system, especially the 18-degree delta-three angle designed into the R22 swashplate and rotor hub. This is a highly technical subject which can only be fully explained using very technical engineering terms. However, since there appear to be a number of misconceptions and a great deal of interest by some pilots and mechanics, the following is a physical explanation of the reasons for the 18 degree delta-three phase angle.
First, keep in mind that the 18 degrees is only in the upper rotating half of the swashplate. The lower non-rotating swashplate is aligned with the aircraft centerline and always tilts in the same direction as the cyclic stick.
Many helicopter engineers have difficulty understanding how delta-three (pitch-flap coupling) affects the phase relationship between the rotor disc and the swashplate. Delta-three only affects the phasing when the rotor disc is not parallel to the swashplate and there is one-per-rev aerodynamic feathering of the blades. For instance, feathering occurs while the rotor disc is being tilted, because an aerodynamic moment on the rotor disc is required to overcome the gyroscopic inertia of the rotor. But once the rotor disc stops tilting, the rotor disc and swashplate again become parallel and the delta-three has no effect on the phasing. Aerodynamic feathering also occurs in forward flight, because it is necessary to compensate for the difference in airspeed between the advancing and retreating blades. Otherwise the advancing blade would climb, the retreating blade would dive, and the rotor disc would tilt aft.
The R22 rotor system was designed with 18 degrees of delta-three to eliminate two minor undesirable characteristics of rotor systems having 90-degree pitch links. In a steady no-wind hover, when forward cyclic pitch is applied, the 90-degree rotor disc will end up tilted in the forward direction, but if no lateral cyclic is applied, the rotor disc will have some lateral tilt while the rotor disc is tilting forward, sometimes referred to as “wee-wa.” This occurs because while the rotor disc is tilting, the forward blade has a downward velocity and the aft blade has an upward velocity. This increases the angle-of-attack of the forward blade causing it to climb, and reduces the angle-of-attack of the aft blade causing it to dive. If no lateral cyclic was applied, this would result in a rotor disc tilt to the right while the rotor plane was tilting forward. Pilots subconsciously learn to compensate for this by applying some lateral cyclic as the cyclic is being moved forward. The amount of delta-three required to eliminate “wee-wa” in the R22 rotor system was calculated to be 19 degrees.
The other undesirable characteristic in rotor systems having 90-degree pitch links is the lateral stick travel required with airspeed changes during forward flight at higher airspeeds. The ideal rotor control system would require only longitudinal stick travel to increase or decrease the airspeed. This is not possible with a 90-degree pitch link system, because the rotor coning angle causes the rotor disc to roll right as the airspeed increases. This occurs because the up-coning angle of the forward blade increases that blade’s angle-of-attack with increased airspeed, while the up-coning angle of the aft blade reduces its angle-of-attack. Consequently, the forward blade then climbs while the aft blade dives, thus causing the rotor disc to roll right with increased airspeed. To compensate for this with a 90-degree pitch link rotor, the pilot must apply some left lateral cyclic as the airspeed increases. The amount of delta-three required to compensate for this effect in the R22 rotor system was calculated to be 17 degrees.
A delta three angle of 18 degrees was selected as the best compromise angle to reduce or eliminate the two undesirable characteristics described above, which would have been present in the R22 had a 90-degree pitch link design been used. Subsequent instrumented flight test data confirmed the choice of the 18-degree delta-three angle.
Hopefully, this will help clarify a few of the misconceptions concerning the design of the R22.
Frank Robinson
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The Cat
What you discovered in your drawing is what we have been talking about all along.
First you have proven that the pitch horn is almost coincident with the cone hinge. Which is what I had stated in other threads. When the pitch horn / pitch link connection is coincident with the cone hinge there is no pitch coupling when the blade flaps about the cone hinge. However as I had previously stated in other threads if the pitch horn / pitch link connection is above or below the cone hinge then there would be a delta 3 connection and when the blade flaps up the pitch will be removed. If the blade flaps down the pitch will be added thus in both cases restoring the blade to the in track position. If the blades (rotorhead) tilts in relation to a fixed swashplate the same thing will happen. The high blade has pitch removed and the low blade gets pitch added thus restoring the disc to the originally commanded position. It makes no difference if the pitch horn / pitch Inc connection is coincident with the cone hinge or not.
I’m confused by what you said about the underslung rotor head reducing the flapping loads. If you are talking about the Robinson rotorhead the reason for the underslung rotor design is to reduce lead and lag caused by the flapping of the blades. This obviously hasn’t happened because the cone bushings and the teeter bushings are high replacement items due to the leading an lagging of the blades. The purpose of the cone hinges is to reduce the flapping loads and the resultant feedback and also, to relieve blade bending caused by coning. Please note, a Bell blade also cones but it is allowed by bending of the blade and on some Bell rotor heads the head itself is preconed to relieve some of the bending loads on the blade and the rotorhead.
Regarding your angular measurement it probably is correct but the 18-degree offset is measured in circular degrees or, degrees of rotation. Log onto this website and download the diagram.
http://pprune.homestead.com/files/rigging.jpg
This shows the rigging position for setting fore and aft pitch setting on both the bell and the Robinson. You will note the position of the Bell blade. This is because it has a 90-degree pitch horn. Now, look at the Robinson blades. In order to set the fore and aft settings the blade is rotated in the direction of normal rotation until the pitch horn /pitch link are directly over the longitudinal axis of the helicopter just like the Bell. Please note the Bell and the Robinson swashplates move exactly the same when the cyclic stick is moved. The rotation of the blades to place the pitch horn / pitch link over the longitudinal centerline is about 18-degrees. This is because the Robinson has a 72-degree pitch horn. The reason the Robinson can’t have a 90-degree pitch horn like on the Bell is because the pitch horn can not cross the cone hinge. It would be bad design and the FAA would not allow it. Besides, you wouldn’t want to fly an R22 or an R44 if it had a 90-degree pitch horn.
Regarding your comment about auto rev I totally agree. I was only trying to construct a scenario about auto rotation if you had a 90-degree pitch horn.
Now, if and that’s a big if, you understand and believe what I wrote above then, is it possible the Frank Robinson told a falsehood.
Here is Frank Robinsons' response
I have read some of the comments about the R22 helicopter printed in this forum. Most were favorable and I appreciated that. However, some were obviously misinformed, and I will comment on several of those.
SIDESLIP WITH THE R22
Concerning the caution against excessive sideslips in the R22 flight manual, this was in part due to a misunderstanding by the FAA. In the Army training film on mast bumping, it showed excessive side slipping as one cause of mast bumping. This was true for the Army Bell Cobras and Hueys, because both aircraft have high centers-of-gravity and relatively low side silhouettes due to their high-mounted powerplants and low-mounted tailcones. During a severe sideslip, the resultant fuselage drag could be below the center-of-gravity and cause the helicopter to roll out of a turn, instead of into the turn, i.e. a negative dihedral or adverse roll characteristic. Airplanes prevent this by having wings with positive dihedral.
The basic R22s and R44s have low-mounted engines, high tailcones, and aerodynamic mast fairings. Consequently, neither the basic R22 or R44 had any tendency toward adverse roll during FAA certification. However, all helicopters (including the R22 and R44) tend to have an adverse roll characteristic when they are equipped with inflated floats, because the floats move the side silhouette area down considerably. For that reason, I did not object to the caution in the R22 flight manual against extreme sideslips during forward flight.
R22 FAA TYPE CERTIFICATION
During the R22 certification, both the FAA test pilots and our own company test pilots flew the R22 through all required maneuvers and flight regimes, and it met all of the FAA regulations. No exemptions were issued for the R22 by the FAA during its certification. Also, I was not a DER (designated engineering representative) during the FAA certification of the R22. No DERs were used during its original certification. After it was certified, the FAA appointed me as a DER with limited authority, so I could approve some minor design changes which commonly occur during production of a new aircraft.
R22 ROTOR SYSTEM
I have read various explanations in this forum attempting to explain the dynamic and aerodynamic characteristics of the R22 rotor system, especially the 18-degree delta-three angle designed into the R22 swashplate and rotor hub. This is a highly technical subject which can only be fully explained using very technical engineering terms. However, since there appear to be a number of misconceptions and a great deal of interest by some pilots and mechanics, the following is a physical explanation of the reasons for the 18 degree delta-three phase angle.
First, keep in mind that the 18 degrees is only in the upper rotating half of the swashplate. The lower non-rotating swashplate is aligned with the aircraft centerline and always tilts in the same direction as the cyclic stick.
Many helicopter engineers have difficulty understanding how delta-three (pitch-flap coupling) affects the phase relationship between the rotor disc and the swashplate. Delta-three only affects the phasing when the rotor disc is not parallel to the swashplate and there is one-per-rev aerodynamic feathering of the blades. For instance, feathering occurs while the rotor disc is being tilted, because an aerodynamic moment on the rotor disc is required to overcome the gyroscopic inertia of the rotor. But once the rotor disc stops tilting, the rotor disc and swashplate again become parallel and the delta-three has no effect on the phasing. Aerodynamic feathering also occurs in forward flight, because it is necessary to compensate for the difference in airspeed between the advancing and retreating blades. Otherwise the advancing blade would climb, the retreating blade would dive, and the rotor disc would tilt aft.
The R22 rotor system was designed with 18 degrees of delta-three to eliminate two minor undesirable characteristics of rotor systems having 90-degree pitch links. In a steady no-wind hover, when forward cyclic pitch is applied, the 90-degree rotor disc will end up tilted in the forward direction, but if no lateral cyclic is applied, the rotor disc will have some lateral tilt while the rotor disc is tilting forward, sometimes referred to as “wee-wa.” This occurs because while the rotor disc is tilting, the forward blade has a downward velocity and the aft blade has an upward velocity. This increases the angle-of-attack of the forward blade causing it to climb, and reduces the angle-of-attack of the aft blade causing it to dive. If no lateral cyclic was applied, this would result in a rotor disc tilt to the right while the rotor plane was tilting forward. Pilots subconsciously learn to compensate for this by applying some lateral cyclic as the cyclic is being moved forward. The amount of delta-three required to eliminate “wee-wa” in the R22 rotor system was calculated to be 19 degrees.
The other undesirable characteristic in rotor systems having 90-degree pitch links is the lateral stick travel required with airspeed changes during forward flight at higher airspeeds. The ideal rotor control system would require only longitudinal stick travel to increase or decrease the airspeed. This is not possible with a 90-degree pitch link system, because the rotor coning angle causes the rotor disc to roll right as the airspeed increases. This occurs because the up-coning angle of the forward blade increases that blade’s angle-of-attack with increased airspeed, while the up-coning angle of the aft blade reduces its angle-of-attack. Consequently, the forward blade then climbs while the aft blade dives, thus causing the rotor disc to roll right with increased airspeed. To compensate for this with a 90-degree pitch link rotor, the pilot must apply some left lateral cyclic as the airspeed increases. The amount of delta-three required to compensate for this effect in the R22 rotor system was calculated to be 17 degrees.
A delta three angle of 18 degrees was selected as the best compromise angle to reduce or eliminate the two undesirable characteristics described above, which would have been present in the R22 had a 90-degree pitch link design been used. Subsequent instrumented flight test data confirmed the choice of the 18-degree delta-three angle.
Hopefully, this will help clarify a few of the misconceptions concerning the design of the R22.
Frank Robinson
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The Cat
Guest
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What I said (meant to say?) was that the pitch horn is ON THE CONING HINGE AXIS ie, as you say, there is no pitch coupling. That is what my diagram shows.
The bit about loads was that with the above accepted, some of the loads caused by flapping (ie those about the coning hinges) are not transmitted to the pilot, whereas some (those caused by flapping about the head) are.
I haven't had time to read FR's bit, I'll do that later.
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Another day in paradise
The bit about loads was that with the above accepted, some of the loads caused by flapping (ie those about the coning hinges) are not transmitted to the pilot, whereas some (those caused by flapping about the head) are.
I haven't had time to read FR's bit, I'll do that later.
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Another day in paradise
Guest
Posts: n/a
Lu,
I understand your explanations on why a 90' pitch horn is not possible on this particular rotor system and I totally agree. You seem however to have missed my point completely.
FR stated that he had considered a 90'pitch horn for the R22. This does not imply that the design of the rotor head would have otherwise been identical.
The design as it stands is a package. You can't radically change one component of it and expect it to function as a unit.
It is quite possible that FR could have designed a more conventional system employing 90' pitch horns. Obviously the whole head would be different and it wouldn't have coning hinges.
It would also tend to fly to the right in forward flight and it would be necessary to apply a little left cyclic.
BTW I do not consider FR to be any sort of Diety.I have never met the man.I do not know whether he is a liar or not, much less care.I merely do not believe he has presented enough evidence in his response on this forum to be branded such.
I understand your explanations on why a 90' pitch horn is not possible on this particular rotor system and I totally agree. You seem however to have missed my point completely.
FR stated that he had considered a 90'pitch horn for the R22. This does not imply that the design of the rotor head would have otherwise been identical.
The design as it stands is a package. You can't radically change one component of it and expect it to function as a unit.
It is quite possible that FR could have designed a more conventional system employing 90' pitch horns. Obviously the whole head would be different and it wouldn't have coning hinges.
It would also tend to fly to the right in forward flight and it would be necessary to apply a little left cyclic.
BTW I do not consider FR to be any sort of Diety.I have never met the man.I do not know whether he is a liar or not, much less care.I merely do not believe he has presented enough evidence in his response on this forum to be branded such.
Guest
Posts: n/a
To: 212man
What I said (meant to say?) was that the pitch horn is ON THE CONING HINGE AXIS i.e., as you say, there is no pitch coupling. That is what my diagram shows.
MOST LIKELY YOUR DIAGRAM LIKE MY DIAGRAM SHOWS THE SYSTEM AT REST IN A NEUTRAL POSITION. ON BOTH DIAGRAMS YOU HAVE TO VISUALIZE WHAT HAPPENS WHEN THERE IS RELATIVE MOVEMENT OF THE COMPONENTS WITHIN THE NEUTRAL OR, AT REST CONDITION. MY DIAGRAM SHOWS THE BLADE IN THE PURE RADIAL POSITION WITH FULL DOWN COLLECTIVE. ANY MOVEMENT OF THE COLLECTIVE WILL CAUSE THE BLADE TO CONE UP. WITH THE 72-DEGREE PITCH HORN AND NEUTRAL CYCLIC THERE SHOULD BE NO PITCH COUPLING. WITH THE 90-DEGREE PITCH HORN THE PITCH COUPLING IS MASSIVE. GETTING BACK TO YOUR DIAGRAM IF THE TWO ELEMENTS WERE NOT COINCIDENT AND YOU PULLED COLLECTIVE THERE WOULD BE SOME COUPLING.
The bit about loads was that with the above accepted, some of the loads caused by flapping (i.e. those about the coning hinges) are not transmitted to the pilot, whereas some (those caused by flapping about the head) are.
PITCH COUPLING IS PITCH COUPLING NO MATTER IF IT COMES WHEN THE BLADES TEETER IN RELATION TO A FIXED SWASH PLATE OR, WHEN THE BLADES CONE ABOUT THE CONE HINGES WHEN THE TWO POINTS ARE NOT COINCIDENT.
THERE WILL BE SOME FEEDBACK REFLECTED IN THE CYCLIC. SOME OF THAT FEED BACK IS GENERATED BY PROPELLER TWISTING MOMENT AND SOME FROM DYNAMIC FLEXING OF THE BLADE IN FLIGHT. THAT IS THE REASON FOR THE HYDRAULIC BOOST ON THE R44 RAVEN. THE PILOT DOES NOT NEED EXTRA POWER TO INPUT CYCLIC, HE NEEDS THE BOOST TO CANCEL THE FEEDBACK. IF THE ROBINSON IS PLACED IN A SITUATION WHERE THE FLAPPING LOADS INCREASE TO THE POINT WHERE MAST BUMPING WOULD OCCUR THE PILOT WOULD FEEL IT IN THE CONTROLS AND IN HIS BUTT BECAUSE OF ALL THE SHAKING.
I haven't had time to read FR's bit; I'll do that later.
To: Outside Loop
I understand your explanations on why a 90' pitch horn is not possible on this particular rotor system and I totally agree. You seem however to have missed my point completely.
FR stated that he had considered a 90'pitch horn for the R22. This does not imply that the design of the rotor head would have otherwise been identical.
IF FRANK ROBINSON CHOSE A 90-DEGREE PITCH HORN HIS ROTOR SYSTEM WOULD LOOK VERY MUCH LIKE A BELL 206. THE BELL BLADES AND ROTORHEAD HAVE SUFFICIENT STRUCTURAL INTEGRITY TO RESIST THE CONING AND BENDING MOMENTS PLACED ON THEM. IF WE CAN ASSUME THAT THE ROBINSON DESIGNED BLADES WERE USED ON THAT 90-DEGREE ROTORHEAD THE APPLIED MOMENTS AND BENDING LOADS WOULD LEAD TO FAILURE VERY SHORTLY AFTER THE HELICOPTER LIFTED OFF ON THE FIRST FLIGHT. IF THE BLADES WERE DESIGNED TO ACCEPT THOSE LOADS WITH A MARGINE OF SAFETY YOU WOULD HAVE TO PUT A SECOND ENGINE IN THE AIRFRAME.
The design as it stands is a package. You can't radically change one component of it and expect it to function as a unit.
I ACCEPT THAT. MY ONLY ARGUMENT IN THIS THREAD IS THAT IF FRANK ROBINSON DESIGNED THE ROTORHEAD TO HAVE A 90-DEGREE PITCH HORN HE WOULD HAVE A MINIATURE BELL ROTORHEAD. THEN HE WOULD HAVE TO REDESIGN HIS BLADES TO ACCEPT THE BENDING, TWISTING AND VIBRATORY LOADS WITH A SUFFICIENT MARGINE OF SAFETY. THE ARGUMENT CONTINUES STATING THAT IF THE ROTORHEAD DESIGN WAS FIXED FROM THE BEGINNING (WHICH IT WAS) HE COULD NEVER HAVE CONSIDERED USING A 90-DEGREE PITCH HORN, WHICH IS WHAT HE CLAIMED IN HIS RESPONSE.
It is quite possible that FR could have designed a more conventional system employing 90' pitch horns. Obviously the whole head would be different and it wouldn't have coning hinges.
I AGREE WITH THE CONCEPT OF YOUR STATEMENT. HE MAY EVEN HAVE CONSIDERED USING A MULTI BLADE SYSTEM BUT THAT WAS IN THE CONCEPTUAL DESIGN PHASE. NOW THESE ARE MY WORDS AND THEY ARE BASED ON WHAT I HAVE READ ABOUT MR. ROBINSON. HE HAD WORKED FOR SEVERAL LARGE HELICOPTER COMPANIES AND HAD EXPERIENCE WITH A LOT OF DIFFERENT ROTORHEAD DESIGNS. MR. ROBINSON WANTED TO CREATE A HELICOPTER FOR THE MASSES AND HIS BOSSES AT THOSE COMPANIES WOULDN’T LISTEN TO HIM. HE PROBALLY GAVE CONSIDERATION TO ALL TYPES OF DESIGNS BUT WHAT HE DECIDED UPON WHEN HE INITIATED DESIGN ON THE R22 IS WHAT YOU HAVE ON THE R22 AND THE R44. HE NEVER INTENDED TO PUT A BELL TYPE ROTORHEAD INTO PRODUCTION OR, TO USE A 90-DEGREE PITCH HORN ON THE EXISTING DESIGN..
It would also tend to fly to the right in forward flight and it would be necessary to apply a little left cyclic.
ANY HELICOPTER WOULD FLY TO THE RIGHT AND WOULD REQUIRE THE APPLICATION OF LEFT CYCLIC TO COUNTER THE RIGHT ROLL. THAT IS CALLED TRANSVERSE FLOW EFFECT. HIS STATEMENT HAD NOTHING TO DO WITH THE 18-DEGREE OFFSET OF THE BLADES
BTW I do not consider FR to be any sort of deity have never met the Man. do not know whether he is a liar or not, much less care. I merely do not believe he has presented enough evidence in his response on this forum to be branded such.
LOOK AT IT THIS WAY, IF HE HAD ADMITTED TO ANYTHING RESEMBLING THE HELICOPTER FLYING LEFT WHEN THE CYCLIC WAS MOVED FORWARD HE WOULD HAVE IMMEDIATELY INCURRED THE WRATH OF THE FAA AND OTHER CERTIFICATION AUTHORITIES AND MUCH WORSE, OPEN HIMSELF UP TO A LOT OF LAW SUITS. WHY DIDN’T HE EXPLAIN IT EVEN THOUGH THE MAJORITY OF THE FORUM PARTICIPANTS INCLUDING MYSELF WOULDN’T UNDERSTAND HIS EXPLANATION AND WHY DID HE STATE THAT HELICOPTER ENGINEERS DON’T FULLY UNDERSTAND HOW A HELICOPTER FLIES?
IP: Logged
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The Cat
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
What I said (meant to say?) was that the pitch horn is ON THE CONING HINGE AXIS i.e., as you say, there is no pitch coupling. That is what my diagram shows.
MOST LIKELY YOUR DIAGRAM LIKE MY DIAGRAM SHOWS THE SYSTEM AT REST IN A NEUTRAL POSITION. ON BOTH DIAGRAMS YOU HAVE TO VISUALIZE WHAT HAPPENS WHEN THERE IS RELATIVE MOVEMENT OF THE COMPONENTS WITHIN THE NEUTRAL OR, AT REST CONDITION. MY DIAGRAM SHOWS THE BLADE IN THE PURE RADIAL POSITION WITH FULL DOWN COLLECTIVE. ANY MOVEMENT OF THE COLLECTIVE WILL CAUSE THE BLADE TO CONE UP. WITH THE 72-DEGREE PITCH HORN AND NEUTRAL CYCLIC THERE SHOULD BE NO PITCH COUPLING. WITH THE 90-DEGREE PITCH HORN THE PITCH COUPLING IS MASSIVE. GETTING BACK TO YOUR DIAGRAM IF THE TWO ELEMENTS WERE NOT COINCIDENT AND YOU PULLED COLLECTIVE THERE WOULD BE SOME COUPLING.
The bit about loads was that with the above accepted, some of the loads caused by flapping (i.e. those about the coning hinges) are not transmitted to the pilot, whereas some (those caused by flapping about the head) are.
PITCH COUPLING IS PITCH COUPLING NO MATTER IF IT COMES WHEN THE BLADES TEETER IN RELATION TO A FIXED SWASH PLATE OR, WHEN THE BLADES CONE ABOUT THE CONE HINGES WHEN THE TWO POINTS ARE NOT COINCIDENT.
THERE WILL BE SOME FEEDBACK REFLECTED IN THE CYCLIC. SOME OF THAT FEED BACK IS GENERATED BY PROPELLER TWISTING MOMENT AND SOME FROM DYNAMIC FLEXING OF THE BLADE IN FLIGHT. THAT IS THE REASON FOR THE HYDRAULIC BOOST ON THE R44 RAVEN. THE PILOT DOES NOT NEED EXTRA POWER TO INPUT CYCLIC, HE NEEDS THE BOOST TO CANCEL THE FEEDBACK. IF THE ROBINSON IS PLACED IN A SITUATION WHERE THE FLAPPING LOADS INCREASE TO THE POINT WHERE MAST BUMPING WOULD OCCUR THE PILOT WOULD FEEL IT IN THE CONTROLS AND IN HIS BUTT BECAUSE OF ALL THE SHAKING.
I haven't had time to read FR's bit; I'll do that later.
To: Outside Loop
I understand your explanations on why a 90' pitch horn is not possible on this particular rotor system and I totally agree. You seem however to have missed my point completely.
FR stated that he had considered a 90'pitch horn for the R22. This does not imply that the design of the rotor head would have otherwise been identical.
IF FRANK ROBINSON CHOSE A 90-DEGREE PITCH HORN HIS ROTOR SYSTEM WOULD LOOK VERY MUCH LIKE A BELL 206. THE BELL BLADES AND ROTORHEAD HAVE SUFFICIENT STRUCTURAL INTEGRITY TO RESIST THE CONING AND BENDING MOMENTS PLACED ON THEM. IF WE CAN ASSUME THAT THE ROBINSON DESIGNED BLADES WERE USED ON THAT 90-DEGREE ROTORHEAD THE APPLIED MOMENTS AND BENDING LOADS WOULD LEAD TO FAILURE VERY SHORTLY AFTER THE HELICOPTER LIFTED OFF ON THE FIRST FLIGHT. IF THE BLADES WERE DESIGNED TO ACCEPT THOSE LOADS WITH A MARGINE OF SAFETY YOU WOULD HAVE TO PUT A SECOND ENGINE IN THE AIRFRAME.
The design as it stands is a package. You can't radically change one component of it and expect it to function as a unit.
I ACCEPT THAT. MY ONLY ARGUMENT IN THIS THREAD IS THAT IF FRANK ROBINSON DESIGNED THE ROTORHEAD TO HAVE A 90-DEGREE PITCH HORN HE WOULD HAVE A MINIATURE BELL ROTORHEAD. THEN HE WOULD HAVE TO REDESIGN HIS BLADES TO ACCEPT THE BENDING, TWISTING AND VIBRATORY LOADS WITH A SUFFICIENT MARGINE OF SAFETY. THE ARGUMENT CONTINUES STATING THAT IF THE ROTORHEAD DESIGN WAS FIXED FROM THE BEGINNING (WHICH IT WAS) HE COULD NEVER HAVE CONSIDERED USING A 90-DEGREE PITCH HORN, WHICH IS WHAT HE CLAIMED IN HIS RESPONSE.
It is quite possible that FR could have designed a more conventional system employing 90' pitch horns. Obviously the whole head would be different and it wouldn't have coning hinges.
I AGREE WITH THE CONCEPT OF YOUR STATEMENT. HE MAY EVEN HAVE CONSIDERED USING A MULTI BLADE SYSTEM BUT THAT WAS IN THE CONCEPTUAL DESIGN PHASE. NOW THESE ARE MY WORDS AND THEY ARE BASED ON WHAT I HAVE READ ABOUT MR. ROBINSON. HE HAD WORKED FOR SEVERAL LARGE HELICOPTER COMPANIES AND HAD EXPERIENCE WITH A LOT OF DIFFERENT ROTORHEAD DESIGNS. MR. ROBINSON WANTED TO CREATE A HELICOPTER FOR THE MASSES AND HIS BOSSES AT THOSE COMPANIES WOULDN’T LISTEN TO HIM. HE PROBALLY GAVE CONSIDERATION TO ALL TYPES OF DESIGNS BUT WHAT HE DECIDED UPON WHEN HE INITIATED DESIGN ON THE R22 IS WHAT YOU HAVE ON THE R22 AND THE R44. HE NEVER INTENDED TO PUT A BELL TYPE ROTORHEAD INTO PRODUCTION OR, TO USE A 90-DEGREE PITCH HORN ON THE EXISTING DESIGN..
It would also tend to fly to the right in forward flight and it would be necessary to apply a little left cyclic.
ANY HELICOPTER WOULD FLY TO THE RIGHT AND WOULD REQUIRE THE APPLICATION OF LEFT CYCLIC TO COUNTER THE RIGHT ROLL. THAT IS CALLED TRANSVERSE FLOW EFFECT. HIS STATEMENT HAD NOTHING TO DO WITH THE 18-DEGREE OFFSET OF THE BLADES
BTW I do not consider FR to be any sort of deity have never met the Man. do not know whether he is a liar or not, much less care. I merely do not believe he has presented enough evidence in his response on this forum to be branded such.
LOOK AT IT THIS WAY, IF HE HAD ADMITTED TO ANYTHING RESEMBLING THE HELICOPTER FLYING LEFT WHEN THE CYCLIC WAS MOVED FORWARD HE WOULD HAVE IMMEDIATELY INCURRED THE WRATH OF THE FAA AND OTHER CERTIFICATION AUTHORITIES AND MUCH WORSE, OPEN HIMSELF UP TO A LOT OF LAW SUITS. WHY DIDN’T HE EXPLAIN IT EVEN THOUGH THE MAJORITY OF THE FORUM PARTICIPANTS INCLUDING MYSELF WOULDN’T UNDERSTAND HIS EXPLANATION AND WHY DID HE STATE THAT HELICOPTER ENGINEERS DON’T FULLY UNDERSTAND HOW A HELICOPTER FLIES?
IP: Logged
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The Cat
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
[This message has been edited by Lu Zuckerman (edited 08 January 2001).]
