Helicopter Urban Myths
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phase angle
Nick,
I have a mini electric RC helo. It works great for learning rotor physics because you can hold it in your hand and power it up, then tilt the rotor to feel the reaction.
I could not figure why the phase angle did not seem to be 90 degrees.
Then I noticed that it seemed to change at higher rrpm.
Your explanation confirms the real behavior I could feel and see in the model.
Thanks for that.
P.S. RC helo from Hobby Lobby called Aerohawk is about $200 complete with radio. Works well for hover. Electronic control died twice, so far they have sent parts. www.hobby-lobby.com
I have a mini electric RC helo. It works great for learning rotor physics because you can hold it in your hand and power it up, then tilt the rotor to feel the reaction.
I could not figure why the phase angle did not seem to be 90 degrees.
Then I noticed that it seemed to change at higher rrpm.
Your explanation confirms the real behavior I could feel and see in the model.
Thanks for that.
P.S. RC helo from Hobby Lobby called Aerohawk is about $200 complete with radio. Works well for hover. Electronic control died twice, so far they have sent parts. www.hobby-lobby.com
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Lu,
If it is not an apple, is it an orange? Pear?
It is how the rotor behaves as it flaps, it is approximated in some pretty hairy equations, and it is not generally 90 degrees.
Just because our helos are rigged that way does not make their gama exactly 90 degrees, but they are close enough so that it works. I would bet that a sizable percentage of production helos have gammas that are 10 degrees different than their controls are rigged, but it is so hard to notice, nobody cares.
When we build helos, we actually look to see what it s. I personally did it on the S-76 and Comanche. It is also not a constant for an aircraft, as slowrotor has observed, it changes with rpm (because it is a factor of the blade flapping inertia, centripital field, aerodynamic damping, hinge offset and several other things that escape me (phase of the moon?) Gamma even changes short term vs long term. If the rotor is rapidly flexed with cyclic, it dips in a different place than where it ends up long term. Boelkow drivers know this, and automatically compensate.
If it is not an apple, is it an orange? Pear?
It is how the rotor behaves as it flaps, it is approximated in some pretty hairy equations, and it is not generally 90 degrees.
Just because our helos are rigged that way does not make their gama exactly 90 degrees, but they are close enough so that it works. I would bet that a sizable percentage of production helos have gammas that are 10 degrees different than their controls are rigged, but it is so hard to notice, nobody cares.
When we build helos, we actually look to see what it s. I personally did it on the S-76 and Comanche. It is also not a constant for an aircraft, as slowrotor has observed, it changes with rpm (because it is a factor of the blade flapping inertia, centripital field, aerodynamic damping, hinge offset and several other things that escape me (phase of the moon?) Gamma even changes short term vs long term. If the rotor is rapidly flexed with cyclic, it dips in a different place than where it ends up long term. Boelkow drivers know this, and automatically compensate.
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Differing points of view.
To: NickLappos
The reason I asked is that in past postings I referenced gyroscopic precession and got jumped by guys from the UK and OZ with them telling me there is no such thing as gyroscopic precession. They insisted it was aerodynamic precession. Now settle the argument. (Which witch is which?). In reference to your posting above you reference the dynamics involved. Are these functions related to gyroscopic or aerodynamic precession or is precession even involved?
So, which is it?
If it is not gyroscopic precession is it aerodynamic precession?
If it is not an apple, is it an orange? Pear?
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Evasive maneuver.
To: Posters from the UK and OZ
Now is the time to chime in. Nick states that there are differing philosophies which is what I have stated time and again. I stated that it depends on where you got you education.
Nick leaves the question open. Don't you want to know which witch is which?
Now is the time to chime in. Nick states that there are differing philosophies which is what I have stated time and again. I stated that it depends on where you got you education.
Nick leaves the question open. Don't you want to know which witch is which?
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I am not sure what the argument is that I am about to enter, but here goes. I never liked the gyroscopic progression explaination, mainly because it is like gravitational acceleration. I don't know why or how massive bodies are attracted to one anouther, but I will accept it. I don't know why or how gyroscopic progression works, but it does and you can feel it. What I can understand is that when you change the pitch angle of a blade, you change its flight path. If you start to reduce the pitch over the tail maximise the input over the pilots right shoulder and slowly re attain "neutral" pitch over the nose, I can see the rotor disc tilts forward. Simple.
The real story though seems to be one of those engineering compromises. My betting is that there is a little bit (questionable if it is significant) of gyroscopic procession, alot of aerodynamics and a healthy dose of mechanics that go into this, hence the variety of phase angles.
Maybe I should enroll in an aeronautics engineering degree - this is fascinating!
The real story though seems to be one of those engineering compromises. My betting is that there is a little bit (questionable if it is significant) of gyroscopic procession, alot of aerodynamics and a healthy dose of mechanics that go into this, hence the variety of phase angles.
Maybe I should enroll in an aeronautics engineering degree - this is fascinating!
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Lu,
"...which one it is"???
Nick is correct--it is not either/or. Gyroscopic infers only inertial effects, while aerodynamic infers only aerodynamic effects. The rotor is affected by both the dynamic (mass/inertia) and aerodynamic (external force) characteristics. A helicopter is a complex bit of machinery, not a fruit!
What Nick was getting at earlier is that even the relative importance of each (aerodynamic and 'gyroscopic'/inertial) characteristic changes as rotor speed is changed, ambient air conditions (density) change, etc, etc, etc. Those who teach that gyroscopic precession causes a 90 degree phase lag on all rotors are oversimplying, and are quite frankly, wrong. Sure, there are some rotors that are physically set up such that the blades respond 90 degrees past their input, but those just make up a sample, rather than define the general rule.
Rotor dynamics cannot be defined in simplistic ways like you want to believe, Lu. Frankly, the complexity is what drives some texts to incorrectly define the physics the way they have. And for its purposes, at least in the past when most(?) rotors did essentially behave the way you think they all behave, this explanation served its purpose. To me, the point of teaching this to pilots is for them to realize that the blades don't respond instantaneously, but instead change position some azimuthal distance past the input. Whether it's 90, 85 or 72 degrees, I don't think really matters to many. If it's rigged so that forward cyclic gets you going forward, then exactly how it got there doesn't really matter. Giving it delta-3 or larger hinge offset will shrink that phase lag, but the pilots will care more about how this effects the handling qualities than the intricacies of the head and phase lag.
However, when we have a technical (engineering) discussion about what is actually going on, you need to forget about the lessons you've learned again and again in all your technical training lessons. Just let go of your simple version of reality and open a book (I'd suggest Leishman)!!!! Asking others, many of whom have simply been taught what we were all taught at first, doesn't make what they say more correct. This is not meant as a slight to all the folks out there who were taught gyroscopic precession or the blades flying to position--I was too. It takes a good deal of engineering education to thoroughly understand this stuff, or at least a great deal of insight to understand it a little!
"...which one it is"???
Nick is correct--it is not either/or. Gyroscopic infers only inertial effects, while aerodynamic infers only aerodynamic effects. The rotor is affected by both the dynamic (mass/inertia) and aerodynamic (external force) characteristics. A helicopter is a complex bit of machinery, not a fruit!
What Nick was getting at earlier is that even the relative importance of each (aerodynamic and 'gyroscopic'/inertial) characteristic changes as rotor speed is changed, ambient air conditions (density) change, etc, etc, etc. Those who teach that gyroscopic precession causes a 90 degree phase lag on all rotors are oversimplying, and are quite frankly, wrong. Sure, there are some rotors that are physically set up such that the blades respond 90 degrees past their input, but those just make up a sample, rather than define the general rule.
Rotor dynamics cannot be defined in simplistic ways like you want to believe, Lu. Frankly, the complexity is what drives some texts to incorrectly define the physics the way they have. And for its purposes, at least in the past when most(?) rotors did essentially behave the way you think they all behave, this explanation served its purpose. To me, the point of teaching this to pilots is for them to realize that the blades don't respond instantaneously, but instead change position some azimuthal distance past the input. Whether it's 90, 85 or 72 degrees, I don't think really matters to many. If it's rigged so that forward cyclic gets you going forward, then exactly how it got there doesn't really matter. Giving it delta-3 or larger hinge offset will shrink that phase lag, but the pilots will care more about how this effects the handling qualities than the intricacies of the head and phase lag.
However, when we have a technical (engineering) discussion about what is actually going on, you need to forget about the lessons you've learned again and again in all your technical training lessons. Just let go of your simple version of reality and open a book (I'd suggest Leishman)!!!! Asking others, many of whom have simply been taught what we were all taught at first, doesn't make what they say more correct. This is not meant as a slight to all the folks out there who were taught gyroscopic precession or the blades flying to position--I was too. It takes a good deal of engineering education to thoroughly understand this stuff, or at least a great deal of insight to understand it a little!
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Thanks, Doopystop and Kyrilian, for your help in explaining it.
Lu, when you ask someone a question of one thing or the other, and the true answer is neither, do not expect them to pick up your music and dance to it. You are so far from understanding this, it is not really close.
The answer I gave you was from Hamlet, who described the ghost to Horatio, who could not understand, and so Hamlet said, "There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy."
Lu, when you ask someone a question of one thing or the other, and the true answer is neither, do not expect them to pick up your music and dance to it. You are so far from understanding this, it is not really close.
The answer I gave you was from Hamlet, who described the ghost to Horatio, who could not understand, and so Hamlet said, "There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy."
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Gyrosnapic precision
To: Droopystop
You send your kids to school and buy them books but their understanding of the different subjects is based on the schools you send them to and the books you buy them and how well they assimilate the information presented.
If you attended engineering university 20 to 30 or more years ago you would have been taught gyroscopic precession and how it applied to differing rotational objects from a spinning rotor in an aircraft instrument, an aircraft propeller or even the rotor of a helicopter. It seems that universities are now teaching that gyroscopic precession does not apply to helicopter rotors. Instead they substitute all types of calculations and formulae to explain how the rotor system responds to input.
Even though it doesn’t apply to helicopters (any more) it still applies to gyro instruments on an aircraft, the propellers on aircraft, the wheels on a motorbike or bicycle. A propeller you ask? When an aircraft maneuvers the gyroscopic turning moment on the propeller causes the propeller to bend to the point that the blade tips depart the rotational plane. When the maneuver stops the “centrifugal” moment will restore the blade position.
I managed a training program for the US Army teaching maintenance on helicopters. We taught gyroscopic precession and the mechs. and maintenance officers would ask, “if the blades are independent from each other then how could they respond as a disc”?
We had the model shop construct a gyro that had twelve arms each weighing several ounces. These weights were attached to a disc, which in turn was driven by an electric motor. We constructed a rudimentary swashplate, which allowed perturbation of the independent weights on the disc. The disc was brought up to speed and when we input a perturbing force the independent weights would respond 90-degrees later until the rotating weights (rotor disc) were all tilted 90-degrees after the control input.
It is easier to use gyroscopic precession because it is easily understood and, it can be demonstrated. Is it right or wrong? It depends on where you went to school and of course, when.
You send your kids to school and buy them books but their understanding of the different subjects is based on the schools you send them to and the books you buy them and how well they assimilate the information presented.
If you attended engineering university 20 to 30 or more years ago you would have been taught gyroscopic precession and how it applied to differing rotational objects from a spinning rotor in an aircraft instrument, an aircraft propeller or even the rotor of a helicopter. It seems that universities are now teaching that gyroscopic precession does not apply to helicopter rotors. Instead they substitute all types of calculations and formulae to explain how the rotor system responds to input.
Even though it doesn’t apply to helicopters (any more) it still applies to gyro instruments on an aircraft, the propellers on aircraft, the wheels on a motorbike or bicycle. A propeller you ask? When an aircraft maneuvers the gyroscopic turning moment on the propeller causes the propeller to bend to the point that the blade tips depart the rotational plane. When the maneuver stops the “centrifugal” moment will restore the blade position.
I managed a training program for the US Army teaching maintenance on helicopters. We taught gyroscopic precession and the mechs. and maintenance officers would ask, “if the blades are independent from each other then how could they respond as a disc”?
We had the model shop construct a gyro that had twelve arms each weighing several ounces. These weights were attached to a disc, which in turn was driven by an electric motor. We constructed a rudimentary swashplate, which allowed perturbation of the independent weights on the disc. The disc was brought up to speed and when we input a perturbing force the independent weights would respond 90-degrees later until the rotating weights (rotor disc) were all tilted 90-degrees after the control input.
It is easier to use gyroscopic precession because it is easily understood and, it can be demonstrated. Is it right or wrong? It depends on where you went to school and of course, when.
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Lu,
A small device like you describe is impacted mostly by its dynamic characteristics, so it really isn't acting like a larger rotor. A propeller is also more affected by inertia and less by aero forces than a rotor. So sure, a bike wheel and propeller and even helicopter rotors have some characteristics of a gyroscope--and it may be easier to teach gyroscopic precession--but that does NOT mean that gyroscopic precession is the correct description for it. Thus in answer to your question, this teaching IS WRONG, but suffices in some circles to get certain partial ideas across.
Now please let this be! Just be content that this is the way lots of people have been and continue to be taught--not just you. But don't let yourself believe that it is real.
If anyone else would like to understand this and are willing to let go of the dogma that they may have first been taught, check the other threads (search under "phase lag" for many of them or start a new thread) and continue to ask questions. I'm sure there are some of us who wouldn't mind responding.
A small device like you describe is impacted mostly by its dynamic characteristics, so it really isn't acting like a larger rotor. A propeller is also more affected by inertia and less by aero forces than a rotor. So sure, a bike wheel and propeller and even helicopter rotors have some characteristics of a gyroscope--and it may be easier to teach gyroscopic precession--but that does NOT mean that gyroscopic precession is the correct description for it. Thus in answer to your question, this teaching IS WRONG, but suffices in some circles to get certain partial ideas across.
Now please let this be! Just be content that this is the way lots of people have been and continue to be taught--not just you. But don't let yourself believe that it is real.
If anyone else would like to understand this and are willing to let go of the dogma that they may have first been taught, check the other threads (search under "phase lag" for many of them or start a new thread) and continue to ask questions. I'm sure there are some of us who wouldn't mind responding.
Peturbing thoughts there Lu!
Diethelm....
Like a discussion of "limits" in math....analogy was similar...if you are allowed to step half the remaining distance to that fair lady...and then again step half the remaining distance...and again....one would never get to her...but you would get close enough....that the remaining distance would not matter.
Like a discussion of "limits" in math....analogy was similar...if you are allowed to step half the remaining distance to that fair lady...and then again step half the remaining distance...and again....one would never get to her...but you would get close enough....that the remaining distance would not matter.
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If Lu tried to take that "rotor" he had built and fly it back then, we wouldn't have to go through this now! That was not a rotor, and the demo he gave was not illustrating rotor blade flapping.
As this thread has tried to spark, the old myths die hard, but Lu, they are dead.
It is not a "different way of saying it." It is not an "old school" vs a "new school". The experts then knew it was wrong, but it was close enough, so they let it slide, and a few generatons of plots and mechanics "knew" it was gyroscopic precession. The designers and engineers knew the real story, the old school had some very bright people in it.
As this thread has tried to spark, the old myths die hard, but Lu, they are dead.
It is not a "different way of saying it." It is not an "old school" vs a "new school". The experts then knew it was wrong, but it was close enough, so they let it slide, and a few generatons of plots and mechanics "knew" it was gyroscopic precession. The designers and engineers knew the real story, the old school had some very bright people in it.
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Why I say "gyroscopic precession"
Nick,
I totally agree with you about the phase angle, no gyro precession and all. Actually, I would add a reference to this discussion: p.93 (the section on "Blade flapping equation of motion") in Simon Newman's "The foundations of helicopter flight". It's all there.
HOWEVER: just try and discuss that while you take an FAA (PPL, CPL...) practical test! In the US, I dont think you would pass if you do not pronounce the phrase "gyroscopic precession". So, while it is good to understand what is really going on, it is also good not to forget the lingua franca.
LG
I totally agree with you about the phase angle, no gyro precession and all. Actually, I would add a reference to this discussion: p.93 (the section on "Blade flapping equation of motion") in Simon Newman's "The foundations of helicopter flight". It's all there.
HOWEVER: just try and discuss that while you take an FAA (PPL, CPL...) practical test! In the US, I dont think you would pass if you do not pronounce the phrase "gyroscopic precession". So, while it is good to understand what is really going on, it is also good not to forget the lingua franca.
LG
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Go to the source of the problem.
To: NickLappos
Nick if you really believe this then I would strongly suggest that you go to your own service school and set them straight instead of making fun of their "Blue Book" written by John Montgomery and vetted by Ralph Lightfoot.
The preface of the Blue Book says in part: “It is not intended for the engineer or aerodynamicist. Explanations given are simplified and are not in any sense offered as Sikorsky criteria, design or otherwise”.
The blue book, which you have classified as a comic book, has illustrations in it that can be found in most aerodynamic texts.
The Blue Book is intended for pilots and mechanics and suffices to educate them to a level where they understand how a helicopter works. (Or, according to you, they think they know how a helicopter works). If they and I guess myself still believe in Gyroscopic precession then I guess ignorance is bliss. I and I assume many of the posters on these forums do not understand the full engineering descriptions offered by you graduate engineers but they still fly the helicopters and if the opportunity would arise I would continue teaching gyroscopic precession. And, in the back of my mind I would know that I was lying to them.
The purpose of the device was to illustrate that a segmented gyro rotor could react in the same way a solid gyro rotor would react to a perturbing input. This was in response to the questions from the students as to how a fully articulated rotor system could act as a gyro rotor. Whether you disagree with the demonstration or not the students came away from the class with a better understanding of gyroscopic precession as applied to a helicopter rotor system.
Remember Nick this was in 1956 and everyone including the helicopter gods believed in gyroscopic precession. By the way, what were you taught in the Army flight school? And did you believe in Gyroscopic precession up until you walked through the front door of Georgia Tech?
It is not a "different way of saying it." It is not an "old school" vs a "new school". The experts then knew it was wrong, but it was close enough, so they let it slide, and a few generatons of plots and mechanics "knew" it was gyroscopic precession. The designers and engineers knew the real story, the old school had some very bright people in it.
The preface of the Blue Book says in part: “It is not intended for the engineer or aerodynamicist. Explanations given are simplified and are not in any sense offered as Sikorsky criteria, design or otherwise”.
The blue book, which you have classified as a comic book, has illustrations in it that can be found in most aerodynamic texts.
The Blue Book is intended for pilots and mechanics and suffices to educate them to a level where they understand how a helicopter works. (Or, according to you, they think they know how a helicopter works). If they and I guess myself still believe in Gyroscopic precession then I guess ignorance is bliss. I and I assume many of the posters on these forums do not understand the full engineering descriptions offered by you graduate engineers but they still fly the helicopters and if the opportunity would arise I would continue teaching gyroscopic precession. And, in the back of my mind I would know that I was lying to them.
If Lu tried to take that "rotor" he had built and fly it back then, we wouldn't have to go through this now! That was not a rotor, and the demo he gave was not illustrating rotor blade flapping.
Remember Nick this was in 1956 and everyone including the helicopter gods believed in gyroscopic precession. By the way, what were you taught in the Army flight school? And did you believe in Gyroscopic precession up until you walked through the front door of Georgia Tech?
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Lu, I don't ever recall anyone here denying the existence of gyroscopic precession, simply that helicopters don't use gyroscopic precession, per se, as the primary control.
Similar to the model you mentioned, there is a child's "helicopter" toy that consists of a one-piece moulded plastic "rotor", with usually three or four fixed-pitch blades set at a positive pitch angle. The blades are moulded together with the hub and have a perimeter rim also moulded in, so the blades cannot move independently. Effectively, therefore, this little "helicopter" is a lightweight GYRO. The "Helicopter" is made to fly by using a launcher, a handle with a vertical spindle. The spindle can be rapidly rotated by pulling a string wound round it. These toys usually fly over the hedge into the next door neighbour's garden or onto the roof because they exhibit the qualities of a gyro and cannot be controlled....because a precessional force cannot be applied once the rotor leaves the launcher.
However, a helicopter as we know it has separate blades that can and do move independently from each other. The blades do exhibit rigidity but they ARE independent. NOT the same as that toy rotor/gyro wheel where the perimeter is joined.
Archimedes reputedly said "Give me a lever long enough and a place to stand and I will move the world". However, there has to be a place to stand to apply a force! The force has to be large enough to produce the required motion at the required rate.
IF gyroscopic precession was to be used to control the path of the rotor as the pilot wished, where would the place to stand be and how long the lever? The rigidity of the blades due to the gyroscopic properties would strongly resist him. Would the pilot be able to overcome the huge rigidity of the system? Come to think of it though, there would be no need to use cyclic pitch changes, just a push / pull rod directly connected to the underside of the blade hub for the pilot to heave on... Hate to think how long the cyclic "lever" would have to be..
Instead, the blades have a pitch change sleeve and a pitch angle control horn connected to the pilot's controls. Now, a relatively small force can be used to alter the pitch angle, via the cyclic. This causes a change in the angle of attack of the blades, which fly to a new position. The aerodynamic forces overcoming their rigidity / inertia, call it what you will. They cannot do this immediately, so the blades follow a path similar to that taken had they been gyroscopically precessed.
Kaman's servo-tab rotor control system illustrates the point quite well. Where is the gyrocopic precession there? The blades are quite clearly flown to their new positions.
So, in UK, Oz and in quite a few other places the blades are flown to the desired position, not gyroscopically precessed. That is where your opinion and that of most others here seems to differ.
Similar to the model you mentioned, there is a child's "helicopter" toy that consists of a one-piece moulded plastic "rotor", with usually three or four fixed-pitch blades set at a positive pitch angle. The blades are moulded together with the hub and have a perimeter rim also moulded in, so the blades cannot move independently. Effectively, therefore, this little "helicopter" is a lightweight GYRO. The "Helicopter" is made to fly by using a launcher, a handle with a vertical spindle. The spindle can be rapidly rotated by pulling a string wound round it. These toys usually fly over the hedge into the next door neighbour's garden or onto the roof because they exhibit the qualities of a gyro and cannot be controlled....because a precessional force cannot be applied once the rotor leaves the launcher.
However, a helicopter as we know it has separate blades that can and do move independently from each other. The blades do exhibit rigidity but they ARE independent. NOT the same as that toy rotor/gyro wheel where the perimeter is joined.
Archimedes reputedly said "Give me a lever long enough and a place to stand and I will move the world". However, there has to be a place to stand to apply a force! The force has to be large enough to produce the required motion at the required rate.
IF gyroscopic precession was to be used to control the path of the rotor as the pilot wished, where would the place to stand be and how long the lever? The rigidity of the blades due to the gyroscopic properties would strongly resist him. Would the pilot be able to overcome the huge rigidity of the system? Come to think of it though, there would be no need to use cyclic pitch changes, just a push / pull rod directly connected to the underside of the blade hub for the pilot to heave on... Hate to think how long the cyclic "lever" would have to be..
Instead, the blades have a pitch change sleeve and a pitch angle control horn connected to the pilot's controls. Now, a relatively small force can be used to alter the pitch angle, via the cyclic. This causes a change in the angle of attack of the blades, which fly to a new position. The aerodynamic forces overcoming their rigidity / inertia, call it what you will. They cannot do this immediately, so the blades follow a path similar to that taken had they been gyroscopically precessed.
Kaman's servo-tab rotor control system illustrates the point quite well. Where is the gyrocopic precession there? The blades are quite clearly flown to their new positions.
So, in UK, Oz and in quite a few other places the blades are flown to the desired position, not gyroscopically precessed. That is where your opinion and that of most others here seems to differ.
D'oh!
I knew I shouldn't have mentioned gyroscopic precession. But I just couldn't help myself. Lu, the intro to the Blue Book, as you quoted, is the best explanation you will get for this, and even for centrifugal: Use an easily understood "explanation" for an observed phenomenon so that you can concentrate on imparting the important info, not the labourious detail of a means to an end. but we have explained that so many times...
oops...Sorry Nick, I'll leave it alone.
Re the Centrifugal and cone angles, you spotted the myth part - centrifugal force is not real (despite Lu and Flight Safety!)
Other myths, mmmm....... do we even go near
"rotor blades emit a visible light when flying through mountain/desert air at night"?
how about:
"helicopter technical texts are not limited by the understanding of their authors, rather they become factual and unquestionable explanations merely by being checked for spelling by an editor, and achieving print"
I knew I shouldn't have mentioned gyroscopic precession. But I just couldn't help myself. Lu, the intro to the Blue Book, as you quoted, is the best explanation you will get for this, and even for centrifugal: Use an easily understood "explanation" for an observed phenomenon so that you can concentrate on imparting the important info, not the labourious detail of a means to an end. but we have explained that so many times...
oops...Sorry Nick, I'll leave it alone.
Re the Centrifugal and cone angles, you spotted the myth part - centrifugal force is not real (despite Lu and Flight Safety!)
Other myths, mmmm....... do we even go near
"rotor blades emit a visible light when flying through mountain/desert air at night"?
how about:
"helicopter technical texts are not limited by the understanding of their authors, rather they become factual and unquestionable explanations merely by being checked for spelling by an editor, and achieving print"
Last edited by helmet fire; 18th Jan 2005 at 03:15.