Certification of Robinson Helicopters (incl post by Frank Robinson)
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Lu :
You said "the blade dropping down over the tail when the tip speed is around 600 feet per second and then rising back over the nose and then dropping over the tail once again."
Personally speaking , I feel that once the retreating blade has gone through the tailboom once, the rest is academic.
It's comments of this nature which lead me to believe that you have a absolutely wonderful grasp of the engineering and theory concepts, but not the real world application.
As regards the offer about you starting a new thread about how a rotor blade doesn't stall like a fixed wing, I'll pass this time thanks.
You said "the blade dropping down over the tail when the tip speed is around 600 feet per second and then rising back over the nose and then dropping over the tail once again."
Personally speaking , I feel that once the retreating blade has gone through the tailboom once, the rest is academic.
It's comments of this nature which lead me to believe that you have a absolutely wonderful grasp of the engineering and theory concepts, but not the real world application.
As regards the offer about you starting a new thread about how a rotor blade doesn't stall like a fixed wing, I'll pass this time thanks.
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Dear Who Needs Runways,
Wow, it seems that I have set off a reaction regarding blade stall. Most of the helicopter pilots that I know are really decent people and I would think that all of you stick pushers out there are the same. When most of you were kids, you wanted to know how things worked. Most of you had cars and many or you tore into the engines and suspension systems to modify them and make them even better. When you finished the job, you felt proud and that you knew every thing that there was to know about wheeled vehicles. Now, you are driving vehicles that are worth millions and the majority of you have to depend on mechanics that hopefully know what they are doing. First, to fly and or work on a helicopter, you must know how it works, so I am going to try and explain the basic aerodynamic and aeromechanical aspects of retreating blade stall.
Try to visualize this, or better still, pick up a pencil and paper and draw a picture of a circle. Cut the circle into four equal parts. On the circumference of the circle where one line meets, write the letter N for North. Now, label the other lines East, West and South. North is the direction the helicopter is flying. The existing way of teaching blade stall aerodynamics is to say that the blade is stalled over West and because the blades have a precession angle of 90 degrees the effect will take place 90 degrees later or, over South. That sounds reasonable, but can you picture a blade that has a tip speed near the speed of sound flying from an in track position at West to a stalled position over the tail cone at South. Now, try and picture that same blade flying from that low position over South to an in track position over the right side at East. Then, because the pilot has the cyclic in a forward position, that same blade, because of precession, will be flying low over the nose or, North and back up to an in track position over West and then, it starts all over again at the rate of say 250 or more times a minute. Most pilots will complain about a minor vibration caused by blades being out of track. Can you visualize the vibratory forces involved in the above described scenario?
I would suggest that you stop thinking of individual blades flying in a circle. Instead, think of the blades as a solid disc just like the rotor on a gyroscope. If you apply a force to a gyro that is on gimbals, the gyro because of precession will react 90 degrees later in the direction of rotation. The same is true on a helicopter. Cyclic input will change the pitch relationship across the disc and will result in an imbalance of forces. If the pilot pushes the stick forward, the greater force is over the West side of the disc. This upward force (due to precession) will cause the disc to raise over South and drop over North. Aerodynamics plays a minimal part in this action. The change in disc position was caused
by the change in lift forces but the actual movement was caused by the gyroscopic characteristics of the spinning disc. In the case of blade stall the retreating blade is generating less lift than the advancing blade. (If you want to say it is stalling that's OK with me.) This lift imbalance will react 90 degrees in the direction of rotation and the disc will rise over the nose and down over the tail boom. This action is not instantaneous. You do get some warning in that the rotor is a bit unstable and then you roll to the left (or right if you are flying a French helicopter) and if you haven't countered the instability and roll by this time the rotor blows back and most likely hits the tail boom.
Individual blades do not fly to a position, the are collectively moved by gyroscopic forces and,"Individual blade do not stall. They simply change the balance of forces across the disc and physics does the rest".
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The Cat
Wow, it seems that I have set off a reaction regarding blade stall. Most of the helicopter pilots that I know are really decent people and I would think that all of you stick pushers out there are the same. When most of you were kids, you wanted to know how things worked. Most of you had cars and many or you tore into the engines and suspension systems to modify them and make them even better. When you finished the job, you felt proud and that you knew every thing that there was to know about wheeled vehicles. Now, you are driving vehicles that are worth millions and the majority of you have to depend on mechanics that hopefully know what they are doing. First, to fly and or work on a helicopter, you must know how it works, so I am going to try and explain the basic aerodynamic and aeromechanical aspects of retreating blade stall.
Try to visualize this, or better still, pick up a pencil and paper and draw a picture of a circle. Cut the circle into four equal parts. On the circumference of the circle where one line meets, write the letter N for North. Now, label the other lines East, West and South. North is the direction the helicopter is flying. The existing way of teaching blade stall aerodynamics is to say that the blade is stalled over West and because the blades have a precession angle of 90 degrees the effect will take place 90 degrees later or, over South. That sounds reasonable, but can you picture a blade that has a tip speed near the speed of sound flying from an in track position at West to a stalled position over the tail cone at South. Now, try and picture that same blade flying from that low position over South to an in track position over the right side at East. Then, because the pilot has the cyclic in a forward position, that same blade, because of precession, will be flying low over the nose or, North and back up to an in track position over West and then, it starts all over again at the rate of say 250 or more times a minute. Most pilots will complain about a minor vibration caused by blades being out of track. Can you visualize the vibratory forces involved in the above described scenario?
I would suggest that you stop thinking of individual blades flying in a circle. Instead, think of the blades as a solid disc just like the rotor on a gyroscope. If you apply a force to a gyro that is on gimbals, the gyro because of precession will react 90 degrees later in the direction of rotation. The same is true on a helicopter. Cyclic input will change the pitch relationship across the disc and will result in an imbalance of forces. If the pilot pushes the stick forward, the greater force is over the West side of the disc. This upward force (due to precession) will cause the disc to raise over South and drop over North. Aerodynamics plays a minimal part in this action. The change in disc position was caused
by the change in lift forces but the actual movement was caused by the gyroscopic characteristics of the spinning disc. In the case of blade stall the retreating blade is generating less lift than the advancing blade. (If you want to say it is stalling that's OK with me.) This lift imbalance will react 90 degrees in the direction of rotation and the disc will rise over the nose and down over the tail boom. This action is not instantaneous. You do get some warning in that the rotor is a bit unstable and then you roll to the left (or right if you are flying a French helicopter) and if you haven't countered the instability and roll by this time the rotor blows back and most likely hits the tail boom.
Individual blades do not fly to a position, the are collectively moved by gyroscopic forces and,"Individual blade do not stall. They simply change the balance of forces across the disc and physics does the rest".
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The Cat
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Well I'll be buggered,
A good story if nothing else.
If you want to talk statistically - how does the V22 measure up as far as accident/fatalities go? It is a new design that is sure to throw up some interesting problems (single rotor vortex ring for one) but does this mean it should not be certified? Or do you think they will put a flight manual restriction on the thing. Most people feel that it is a good concept worthy of the effort to keep it flying.
The R22 was a new design (the rotor head especially), it too showed some interesting problems. But as with the ossprey, people thought it was worthy of the effort to keep it flying. They opted to put a flight manual restriction in place to do this.
If you put the R22 in a known dangerous position it will be the same result as putting a V22 in a known dangerous position, regardless of the design.
No doubt in 20 years time someone will look back on the V22 design and wonder how the hell they ever let a thing like that be certified. They, in 20 years time, will be glad that we did.
A good story if nothing else.
If you want to talk statistically - how does the V22 measure up as far as accident/fatalities go? It is a new design that is sure to throw up some interesting problems (single rotor vortex ring for one) but does this mean it should not be certified? Or do you think they will put a flight manual restriction on the thing. Most people feel that it is a good concept worthy of the effort to keep it flying.
The R22 was a new design (the rotor head especially), it too showed some interesting problems. But as with the ossprey, people thought it was worthy of the effort to keep it flying. They opted to put a flight manual restriction in place to do this.
If you put the R22 in a known dangerous position it will be the same result as putting a V22 in a known dangerous position, regardless of the design.
No doubt in 20 years time someone will look back on the V22 design and wonder how the hell they ever let a thing like that be certified. They, in 20 years time, will be glad that we did.
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Dear Rotorque,
This thread is about the R22 and R44 not the V-22. However in my opinion the V-22 will never gain civil certification as it has an autorotational speed of 4-6000 feet per minute. The FAAs way of getting around this little problem is to certify it as a powered lift aircraft and not apply helicopter restrictions to it. There are also problems in the prop rotor system that will cause rotor thrust divergence when the V-22 is in the Airplane mode and is maneuvered from the straight-ahead position. How do I know you might ask? I worked on the V-22 as an engineering consultant and I continuously brought these problems to the attention of my Boeing superiors. They dismissed it saying that these were Bell problems. Soon, these will be US Marine and USAF problems.
Now, back to the R22 and the R44. Somewhere in the postings in this thread I stated the problems about the R22 and the R44 which are:
The rotor system was not adequately tested because if it were it would have shown that extremely high flapping loads would result in certain maneuvers. These flapping loads would be generated if you placed the helicopter in a sideslip or if you flew it out of trim (balance).
The FAA design regs for Normal Category Rotorcraft require that it be demonstrated that the helicopter can sideslip by flying at around .6 VNE and the pilot apply hard left pedal to the stops and then return the helicopter to neutral and then hard application of right pedal. It is also required to demonstrate out of trim (balance) + - 10 degrees.
All helicopters have to meet these criteria. Since the R22 and R44 rotor heads are the same now as they were when the helicopter was certified did the test take place? If it did, was it noted that high flapping loads were generated when the tests were performed? Were the test results made known to the FAA? Did Frank Robinson as the FAA DER report his findings or did he cover it up?
Why, (IF) the R22 (and R44) met the test requirements then, why are they being restricted from sideslip and out of trim flight now? In doing this, they have in a sense stated that the helicopter does not meet the requirements of certification
A copy of the report and a diagram are on the way. Read the report and then come back on the forum with your comments.
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The Cat
This thread is about the R22 and R44 not the V-22. However in my opinion the V-22 will never gain civil certification as it has an autorotational speed of 4-6000 feet per minute. The FAAs way of getting around this little problem is to certify it as a powered lift aircraft and not apply helicopter restrictions to it. There are also problems in the prop rotor system that will cause rotor thrust divergence when the V-22 is in the Airplane mode and is maneuvered from the straight-ahead position. How do I know you might ask? I worked on the V-22 as an engineering consultant and I continuously brought these problems to the attention of my Boeing superiors. They dismissed it saying that these were Bell problems. Soon, these will be US Marine and USAF problems.
Now, back to the R22 and the R44. Somewhere in the postings in this thread I stated the problems about the R22 and the R44 which are:
The rotor system was not adequately tested because if it were it would have shown that extremely high flapping loads would result in certain maneuvers. These flapping loads would be generated if you placed the helicopter in a sideslip or if you flew it out of trim (balance).
The FAA design regs for Normal Category Rotorcraft require that it be demonstrated that the helicopter can sideslip by flying at around .6 VNE and the pilot apply hard left pedal to the stops and then return the helicopter to neutral and then hard application of right pedal. It is also required to demonstrate out of trim (balance) + - 10 degrees.
All helicopters have to meet these criteria. Since the R22 and R44 rotor heads are the same now as they were when the helicopter was certified did the test take place? If it did, was it noted that high flapping loads were generated when the tests were performed? Were the test results made known to the FAA? Did Frank Robinson as the FAA DER report his findings or did he cover it up?
Why, (IF) the R22 (and R44) met the test requirements then, why are they being restricted from sideslip and out of trim flight now? In doing this, they have in a sense stated that the helicopter does not meet the requirements of certification
A copy of the report and a diagram are on the way. Read the report and then come back on the forum with your comments.
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The Cat
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Helidrvr! Thanks for the edit. Just back.
I don't really want to continue this debate. It is low quality - Lu concedes nothing.
1.There is no LIMITATION. (agree? do you actually know what the word means in this context?)
2.Robbies can physically demonstrate the certification requirements (and do all over the world regularly) (agree?)
3.It does not fail in the way he predicts - there would be evidence and there is NOT.(agree?)
4.The rigging proceedure likewise.(agree?)
5.I predicted what Lu's arguement would be re blade stall. (he then said it was somthing else)
None of these points - which totally undermine Lu's premis have been adressed.
Lu invited WNR to a thread on RBStall and was declined (correctly) by WNR, and Lu waded straight into one regardless...?
NO you haven't set off "a reaction regarding blade stall" I just desparately don't want to get oblidged to waste my time debating a subject with you which you don't understand - and so I am not going to! (exept for the fact that your RBS argument 'has become' what I said it would be - funny that!).
Helidrvr: sure I'm frustrated... moderation must be difficult sometimes. The low grade of this debate means that the very real and balanced factors which should be discussed by pilots (for pilots) are getting lost - this is counter productive and leaves a confused and not particularly 'enriched audience'
Lu might be well intentioned (I actually don't think he is). I am nevertheless impressed that he is able to scratch a living consulting for the companies he claims to. He does a good impression of sounding like he knows what he is talking about - but he doesn't.
Hold him to account fairly - or this is pointless. No RBS debate ..... p.l.e.a.s.e...
(he just doesn't move: Lu:"I’ll say it one more time, flying out of trim (balance) or in a side slip will result in extremely high flapping loads that can lead to eventual failure of the rotor and blades or it can result in mast fracture." Well THAT would be FATIGUE ... but THAT just does NOT happen. (bangs head against wall AGAIN .... )
Enough..
I don't really want to continue this debate. It is low quality - Lu concedes nothing.
1.There is no LIMITATION. (agree? do you actually know what the word means in this context?)
2.Robbies can physically demonstrate the certification requirements (and do all over the world regularly) (agree?)
3.It does not fail in the way he predicts - there would be evidence and there is NOT.(agree?)
4.The rigging proceedure likewise.(agree?)
5.I predicted what Lu's arguement would be re blade stall. (he then said it was somthing else)
None of these points - which totally undermine Lu's premis have been adressed.
Lu invited WNR to a thread on RBStall and was declined (correctly) by WNR, and Lu waded straight into one regardless...?
NO you haven't set off "a reaction regarding blade stall" I just desparately don't want to get oblidged to waste my time debating a subject with you which you don't understand - and so I am not going to! (exept for the fact that your RBS argument 'has become' what I said it would be - funny that!).
Helidrvr: sure I'm frustrated... moderation must be difficult sometimes. The low grade of this debate means that the very real and balanced factors which should be discussed by pilots (for pilots) are getting lost - this is counter productive and leaves a confused and not particularly 'enriched audience'
Lu might be well intentioned (I actually don't think he is). I am nevertheless impressed that he is able to scratch a living consulting for the companies he claims to. He does a good impression of sounding like he knows what he is talking about - but he doesn't.
Hold him to account fairly - or this is pointless. No RBS debate ..... p.l.e.a.s.e...
(he just doesn't move: Lu:"I’ll say it one more time, flying out of trim (balance) or in a side slip will result in extremely high flapping loads that can lead to eventual failure of the rotor and blades or it can result in mast fracture." Well THAT would be FATIGUE ... but THAT just does NOT happen. (bangs head against wall AGAIN .... )
Enough..
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Good to see you back JoePilot. For a moment I thought that you had finally thrown in the towel.
Since I don't have access to a Robbie RFM or have much time in them (too old...), there is little I can do but observe the two of you fight it out in the ring. I will say this though: when I finally got around to getting the full SFAR checkout a few years ago, I was very impressed that Mr.Robinson had managed to build so much for so little.
It appears that neither Lu nor you can let the other have the last word, so maybe you'll both bow out gracefully and leave that honor to me.
After everything is said and done, this has been one of the most educating threads I have come across since the Osprey accident. Regardless of who is right and who is wrong, I have been provoked into reading up on a lot of stuff which I no longer remembered but should have. For that alone, you both deserve my heartfelt gratitude.
In the end, the whole thing strikes me as a little bit of a bumble bee argument. You know the one: For many years aerodynamic theory had all the eggheads convinced that a bumble bee's C of G is all wrong and that the little critter should therefore not be able to fly. There was only one problem, nobody ever told the bumble bees, so they kept on flying anyway.
Good night all.
[This message has been edited by helidrvr (edited 03 October 2000).]
Since I don't have access to a Robbie RFM or have much time in them (too old...), there is little I can do but observe the two of you fight it out in the ring. I will say this though: when I finally got around to getting the full SFAR checkout a few years ago, I was very impressed that Mr.Robinson had managed to build so much for so little.
It appears that neither Lu nor you can let the other have the last word, so maybe you'll both bow out gracefully and leave that honor to me.
After everything is said and done, this has been one of the most educating threads I have come across since the Osprey accident. Regardless of who is right and who is wrong, I have been provoked into reading up on a lot of stuff which I no longer remembered but should have. For that alone, you both deserve my heartfelt gratitude.
In the end, the whole thing strikes me as a little bit of a bumble bee argument. You know the one: For many years aerodynamic theory had all the eggheads convinced that a bumble bee's C of G is all wrong and that the little critter should therefore not be able to fly. There was only one problem, nobody ever told the bumble bees, so they kept on flying anyway.
Good night all.
[This message has been edited by helidrvr (edited 03 October 2000).]
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The posts by RHC Employee have been removed by me. This indvidual went way beyond the standards which we publish as acceptable.
We have managed to keep this debate civil so please let's keep it that way.
P.S.: I know that managers the Robinson Company have been monitoring these threads and deserve to be commended for their remarkable restraint. On the other hand, isn't it about time that they give us their view on the rotorhead story?
[This message has been edited by helidrvr (edited 25 October 2000).]
We have managed to keep this debate civil so please let's keep it that way.
P.S.: I know that managers the Robinson Company have been monitoring these threads and deserve to be commended for their remarkable restraint. On the other hand, isn't it about time that they give us their view on the rotorhead story?
[This message has been edited by helidrvr (edited 25 October 2000).]
Guest
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Helidrvr,
Nicely put.
The arguments/discussions about Robbo's CAN be decided/answered by those who know more than us. ie, employees of Robinson Helicopter Inc.
Eagerly awaiting your reply Mr Employee!
[This message has been edited by helidrvr (edited 27 October 2000).]
Nicely put.
The arguments/discussions about Robbo's CAN be decided/answered by those who know more than us. ie, employees of Robinson Helicopter Inc.
Eagerly awaiting your reply Mr Employee!
[This message has been edited by helidrvr (edited 27 October 2000).]
Guest
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Nice to see you on the thread Frank.
Not sure I like your use of the term 'allegations' though. I do hope you are not going to spoil a grown up discussion by throwing your toys in the corner and get all legal. Just defend your nasty little helicopter with some reasoned debate.
Not sure I like your use of the term 'allegations' though. I do hope you are not going to spoil a grown up discussion by throwing your toys in the corner and get all legal. Just defend your nasty little helicopter with some reasoned debate.
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ArkRoyal :
"Defend your nasty little helicopter with reasoned debate."
So you want reasoned debate, but like starting it with a slagging ? Please make your mind up.
[This message has been edited by WhoNeedsRunways (edited 29 October 2000).]
"Defend your nasty little helicopter with reasoned debate."
So you want reasoned debate, but like starting it with a slagging ? Please make your mind up.
[This message has been edited by WhoNeedsRunways (edited 29 October 2000).]
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In several of my posts I alluded to the fact that Frank Robinson at one time during the certification of the R22 acted as the Designated Engineering Representative. I stated that it was a conflict of interest and that part is true but according to FAA regulations it is allowed. So when I stated that he should not have been allowed I was in error. However by the FAAs own regulations they had recognized the fact that it was a conflict of interest but they allowed it anyway.
Here is the wording in FAA document 8130.37C Page 33 dated 9/30/98. This particular document may have been originally published long before the R22 certification but I don't know if this particular reg was in force at that time.
CONFLICT OF INTEREST: THE RISK OF CONFLICT OF INTEREST INCREASES AS A COMPANY DER TAKES ON ADDITIONAL RESPONSIBILITIES AND RISES TO AN "EXECUTIVE" LEVEL WITHIN THE COMPANY, WHERE THE PRIMARY JOB DUTIES ARE SCHEDULE-DRIVEN AND DEVOTED TO OUTPUT OF THE COMPANIES'WHOLE SALEABLE PRODUCTS
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The Cat
[This message has been edited by Lu Zuckerman (edited 01 November 2000).]
[This message has been edited by Lu Zuckerman (edited 01 November 2000).]
Here is the wording in FAA document 8130.37C Page 33 dated 9/30/98. This particular document may have been originally published long before the R22 certification but I don't know if this particular reg was in force at that time.
CONFLICT OF INTEREST: THE RISK OF CONFLICT OF INTEREST INCREASES AS A COMPANY DER TAKES ON ADDITIONAL RESPONSIBILITIES AND RISES TO AN "EXECUTIVE" LEVEL WITHIN THE COMPANY, WHERE THE PRIMARY JOB DUTIES ARE SCHEDULE-DRIVEN AND DEVOTED TO OUTPUT OF THE COMPANIES'WHOLE SALEABLE PRODUCTS
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The Cat
[This message has been edited by Lu Zuckerman (edited 01 November 2000).]
[This message has been edited by Lu Zuckerman (edited 01 November 2000).]
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I am surprised at the number of replies to this thread - is it really worth it ??
Its only got one engine (of sorts) and not much more - Pilots who want to be "Old and Bold" would be wise to avoid these strange little meccano sets.
SARcastic
Its only got one engine (of sorts) and not much more - Pilots who want to be "Old and Bold" would be wise to avoid these strange little meccano sets.
SARcastic