Gyroscopic precession engineering question
A lot of our understanding of things like this are based on simplifications, but we then tend to run into the limitations of those simplifications when something doesn't fit into this mould anymore. That doesn't mean that the principle is wrong. We can get into a lovely discussion on how Bernoulli does not fully explain how a wing produces lift and drag. It does not mean that Bernoulli got it wrong. It means that we've got an opportunity to learn.
Avoid imitations
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Also note that if the rotor system was truly a gyroscope, it would have to follow the first property of a gyroscope - RIGIDITY IN SPACE, i.e. it would be very difficult to disturb it from its axis.
A puff of wind will knock it off, causing flapping and diversion.
Ergo, it is not a gyroscope. But sometimes it behaves LIKE a gyroscope.
A puff of wind will knock it off, causing flapping and diversion.
Ergo, it is not a gyroscope. But sometimes it behaves LIKE a gyroscope.
Hey Robbie, well yes, it says "like a gyro", but with all the explanation following that statement, it is still wrong.
Directly from the Rotorcraft Flying Handbook:
Gyroscopic Precession
The spinning main rotor of a helicopter acts like a gyroscope.
As such, it has the properties of gyroscopic action, one of
which is precession. Gyroscopic precession is the resultant
action or deflection of a spinning object when a force is
applied to this object. This action occurs approximately 90°
in the direction of rotation from the point where the force
is applied (or 90° later in the rotation cycle). (And so on ...)
I am pretty sure it is 72°.
Directly from the Rotorcraft Flying Handbook:
Gyroscopic Precession
The spinning main rotor of a helicopter acts like a gyroscope.
As such, it has the properties of gyroscopic action, one of
which is precession. Gyroscopic precession is the resultant
action or deflection of a spinning object when a force is
applied to this object. This action occurs approximately 90°
in the direction of rotation from the point where the force
is applied (or 90° later in the rotation cycle). (And so on ...)
I am pretty sure it is 72°.
Oh, Robbie, my excuses, it wasn't my intention to patronise you, not at all. We have met on this forum quite often and I sometimes get the impression, that you try to be at bit too modest. You have crossed swords with quite a few of our most experienced egos lurking here and I must say, your opinion is much appreciated. You do bring sometimes another perspective and that is needed in a discussion. Discussions are made for changing opinions. If we don't think about what others say and even sometimes get things wrong, we don't learn. Exchanging opinions and not thinking about them, is utterly useless.
Common, admit it, you are interested in all things helicopter related. Even if you think it does not make you a better pilot, I think it does. Every little piece of knowledge changes how you look at it. Even if it is a stupid bolt on an airframe that isn't secured properly. It makes you think and you like that. Otherwise you would not hang out here.
Common, admit it, you are interested in all things helicopter related. Even if you think it does not make you a better pilot, I think it does. Every little piece of knowledge changes how you look at it. Even if it is a stupid bolt on an airframe that isn't secured properly. It makes you think and you like that. Otherwise you would not hang out here.
Robbiee, you'll like this one.
A while back when this subject was running a physicist got involved, and challenged even the most experienced members on here to justify their reasoning why a rotor is not a gyroscope, or even like a gyroscope. After endless debate, some crusty old naval pilot chipped in with:
That was the last post on that thread if I remember. A man after your own heart I guess !
A while back when this subject was running a physicist got involved, and challenged even the most experienced members on here to justify their reasoning why a rotor is not a gyroscope, or even like a gyroscope. After endless debate, some crusty old naval pilot chipped in with:
Sitting in my helicopter on a wild day with rotors running, my AI showed every heave and toss of the ship. My rotor stayed locked in its plane parallel to the deck. The AI is a gyro, the rotor is not.
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Robbiee, you'll like this one.
A while back when this subject was running a physicist got involved, and challenged even the most experienced members on here to justify their reasoning why a rotor is not a gyroscope, or even like a gyroscope. After endless debate, some crusty old naval pilot chipped in with: That was the last post on that thread if I remember. A man after your own heart I guess !
A while back when this subject was running a physicist got involved, and challenged even the most experienced members on here to justify their reasoning why a rotor is not a gyroscope, or even like a gyroscope. After endless debate, some crusty old naval pilot chipped in with: That was the last post on that thread if I remember. A man after your own heart I guess !
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this is basic stuff out of a rotor dynamics textbook.
Anyway, I'm just a bored troll stirring the pot from time to time for his own amusement. I feed on conflict, not compliments.
So glad I missed this rehash of an old topic - is there a way of getting PPrune to react to the combination of words 'rotor' plus 'gyroscope' so it automatically leads the poster to all the previous discussions we have had on this topic?
I know there is a search function but nowadays people just like to ask the question and wait.
I know there is a search function but nowadays people just like to ask the question and wait.
Sitting in my helicopter on a wild day with rotors running, my AI showed every heave and toss of the ship. My rotor stayed locked in its plane parallel to the deck. The AI is a gyro, the rotor is not.
Remember that the stick would have been held central, with the swash plate level with the deck, so the rotor couldn't have done much different.
Originally Posted by [email protected]
But if the rotor was a gyro it would have maintained position in space - it could have flapped around the hinges quite markedly regardless of the swashplate position. But it didn't because it's not a gyro - as I know you know
If the pitch horns weren't offset, then when you push the cyclic forward, you wouldn't go forward, you'd go left (i.e. in the direction of the rotor's rotation),...maybe not a full 90° left, but some degree anyway. What other device does something like that? Oh yeah,...a gyro!
I thought very carefully about whether to add to this post, but on balance I think there's an important point to be made.
What I think good teachers are trying to do is to give you enough information to do the job, and although it may not be the whole truth, they make sure that nothing they offer is wrong. That way anyone coming in later isn't trying to correct mistakes, they're trying to extend and enrich what you know already. If you teach that rotors are 'like' gyros, you're picking on a single common feature that can't support any extension, and is easily proved to be wrong from the example of the helicopter on the ship.
Robbiee, you've already said that your interest is purely flying, and that these aerodynamic curiosities are just hurdles you have to cross to get to do that. I'd say that's completely fine and I wish you luck and success in your flying career. If you ever have to teach though, I think there's a responsibility to dig a little deeper, and acknowledge the simplifications you might choose to make, and to make those simplifications act as foundations not detours.
What I think good teachers are trying to do is to give you enough information to do the job, and although it may not be the whole truth, they make sure that nothing they offer is wrong. That way anyone coming in later isn't trying to correct mistakes, they're trying to extend and enrich what you know already. If you teach that rotors are 'like' gyros, you're picking on a single common feature that can't support any extension, and is easily proved to be wrong from the example of the helicopter on the ship.
Robbiee, you've already said that your interest is purely flying, and that these aerodynamic curiosities are just hurdles you have to cross to get to do that. I'd say that's completely fine and I wish you luck and success in your flying career. If you ever have to teach though, I think there's a responsibility to dig a little deeper, and acknowledge the simplifications you might choose to make, and to make those simplifications act as foundations not detours.