Gyroscopic Precession in Helicopters
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- Опубліковано 29 вер 2024
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Today I cover Gyroscopic Precession as it pertains to helicopters.
Gyroscopic Precession is "the phenomenon of precession occurring in rotating bodies that manifests as an applied force 90 degrees after application in the direction of rotation." Simply put, any action made on a spinning body will present itself 90 degrees later in the direction of rotation. So an increase in pitch at the nose of aircraft will manifest on the left side of the rotor system. This increase in lift on the left side causes the aircraft to roll to the right. Luckily for the pilot, the engineers that built the aircraft have rigged it in a way that if you want to turn left, you simply put in left cyclic. This is because the controls are rigged with a 90 degree offset. So while you are putting in left cyclic because you want to turn left, the control input is actually being made at the aft portion of the rotor disk.
This is a fundamental concept to understand because it affects other areas of helicopter aerodynamics.
Thanks for watching and check some of my other videos!
If you're just getting started and want more information, pictures, and more explanations, I'd recommend reading the Rotorcraft Flying Handbook - amzn.to/2ifPlnZ
If you've already got a basic understanding, and want to further your professional helicopter education with advanced helicopter concepts, I'd recommend reading Cyclic and Collective, by Shawn Coyle - amzn.to/2ifQGLx
So I've been doing some research on this and am a bit confused. It seems like "Gyroscopic Precession" is only a very small portion of why the rotors operate out of phase and that "Phase Lag" is the main reason for this operation. Gyroscopic precession operating at 90 degrees out of phase (OOP) but phase lag operating anywhere up to 180 degrees OOP. Can you maybe do a video explaining Phase Lag?
I am watching all your videos as training aids to the FAA Handbook in preperation for the SIFT, your content is really appreciated.
@@shemarburke8064 I had to get permision to leave my current unit and start a new contract and my unit didnt realease me. I currently have two years left in and then depending on where Im at I may try it again.
What about now? Are you stationed somewhere where you can take the SIFT?
Loving these videos!
Due respect to your clear understanding of helicopter flight physics etc. Please don't think of me as a hater with an ax to grind against the world, my intention is to contribute. Your buffer analogy is incorrect for the following reason. When steering a floor buffer it is true that one guides the buffer with up and down inputs to the handle, the forces generated however are not the result of gyroscopic precession Gyroscopic Forces are present on this as well as any rotating body, however those forces are swamped out by the dissymmetry of traction achieved by the front and back of the brush/pad contact area. i.e. lifting the back of the machine gives more tractive force to the front while reducing tractive force at the back, causing the machine to move opposite the direction of rotation at the point of contact. To conclude, Thank you for your efforts to explain these concepts, they are for the most part well thought and executed.
A gyroscope is a rigid disc attached rigidly to the axis of rotation. A rotor system does none of this, as it is able to flex, it might have hinges to allow flapping and lead/lag, and dampers in some cases.
GP is simply a way of explaining Phase Lag to a student. Feed in a cyclic input, the pitch angle changes, the lifting FORCE is increased, and the F=MA takes over, and the blade starts to accelerate up. It takes time to get up to the desired spot, but by then the cyclic has moved the swashplate, the pitch angle has changed, the forces change, and the blade reacts by accelerating in another direction. In some helicopters, the phase lag is 90 degrees, in others, like the R-22, it is 78 degrees, mainly because it is a lighter blade and accelerates faster.
Phase lag is only approximately 90 degrees. The rotor system is not a gyroscope. Precession is only a way of helping to understand the dynamics.
THANKYOU!! I searched for this and everywhere people seem to be talking about the gyroscopic precession and it made sense to me till I learnt that some helicopters have a different phase angle between cyclic and the rotor. If gyroscopic precession was the reason, it would affect all helicopters equally.
Seriously the best explanation of gyroscopic precession and how it apllies to helicopters. Clear and concise. Great job!
Thank you so much for all of your videos. I watch at least one a day and I'm looking forward to new ones. Also, thank you and your fellow soldiers for your service from an old OH58A crew chief !
David Wallace. Glad you like them. And thanks for your service.
I'm diggin that flow fly. Nice.
What an utterly nice and helpful bloke you are Jacob. This is awesome stuff. Super helpful.
what kind of helicopter is flying at the start of the video. It looks like a huey but it seems to have a ''seeker' mounted on its nose.
Diederik de Haan It's an Apache. That's the night sight you see.
great, clear and simple. also love the AH64 (e?) intro with the lush green landscape.
So is it fair to say that a left roll input results in an increase in pitch at the rear of the disk which causes an upwards thrust at the rear of the disc which through gyroscopic procession results in a leftward rolling of the aircraft?
Watch and listen closely .
If I want the rotor disk to mo e me.to.the left my input would not be at the tear of the disk as explained but 90 degrees prior to the result in the plain of rotation.
Input would be at the nose.
Do coaxial rotors have to worrry about precession or does it cancle out?
Still applies. But the 2 separate rotors offset the torque effect and the need for a tail rotor
I'm gonna be the best damn heli pilot in VTOL Vr 😂😂 thank you
You can post your videos in Skillshare, you can be a great help
Misso Productions. Thanks for the comment. I'll take a look at it.
awesome explanation, thanks for that!
Nicely explained so almost anyone could understand
If you do a google search for Wikipedia helicopter flight controls it says that gyroscopic precession is a Misconception. It says that what is happening is called phase Lag and not gyroscopic precession. Not out to fault you, I'm just trying to learn about helicopters, since I started flying them.
Mark Kiziuk. The Gyroscopic Precession/Phase lag has been debated constantly. For years many pilots were taught Gyroscopic Precession because a rotor tended to react just like a spinning gyro in that all effects tended to manifest 90 degrees later. This was an easy way to comprehend why there was a 90 degree displacement and therefore a rigging in flight controls. But then engineers decided to step in and begin to state that it was actually "phase lag" because, unlike a gyro, rotor blades have the ability to flap. This flapping in the vertical hinge of the blades created a "phase angle" which could make inputs manifest as little as 78 degrees in some rotor systems. For most helicopters the rigging is close to 90 degrees but not exactly. In the realm of flying helicopters, Gyroscopic Precession is a commonly accepted reason for a 90 degree delay. But in the realm of engineers who design helicopters, phase angle and phase lag are the more accepted reasons. Thanks for the feedback. I hope this helps.
Helicopter Lessons In 10 Minutes or Less
Thanks for getting back to me so quickly. I guess the million dollar question is, when I take my helicopter verbal and on my written exam, what is the correct answer? Is the answer gyroscopic precession or is the answer phase Lag?
Mark
Mark. I'd say it depends on your evaluator. In my community, Gyroscopic Precession has always been the accepted answer.
It's an avocadocopter!
Excellent Job on these videos
The swash plate is a brilliant piece of engineering.
So are the control rods that are connected to it.
Thanks for the videos.
Phase lag.
New student here. When you mention control rigging, if my trainer has a built in auto-trim would that be the system that is increasing the pitch at the rear of the rotor disk for a left turn? Thanks!
i just watched LT sibanda's video, now im gonna watch some of your videos and try a little experiment. wish me luck!
That's a great explanation for someone who needs to know what it is. But I'd like to know why it is, i.e., why 90 degrees?
David Anderson. Without getting super deep into the physics of, it is 90 degrees because 90 degrees is perpendicular to the force applied. When you have a spinning body it has Angular Momentum. When a force is applied to this that is not directly at the center of mass, a new vector of Angular Momentum is introduced. The sum of these 2 momentums causes the rotating body to shift in a new direction. This is precession. I can't see ever needing to know this to fly but I hope this helps answer your question lol.
see
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or
ua-cam.com/video/XPUuF_dECVI/v-deo.html
Its actually not always 90 degrees, and in reality is rarely exactly 90 degrees offset. I believe it was Bell who did tests and found that by adding weight to the tip of the blades, they were able to bring it up to 180 degrees (I believe you could go beyond 180, but that's as far as they went, to my knowledge.) This is because it's actually something called Phase Lag. Many rotors are close to 90 degrees off, though some are significantly less than 90 degrees offset, and some are significantly more. Part of this has to do with the weight at the tip of the blade, and part of it has to do with whether the rotor system is semi-rigid or fully articulated.
Well explained concept in short.. Thanks
very helpful video! You put this information in a way that's easy to understand! thanks!
Yes, i agree with Daniel Mcphadden. . . .well explained
Perfectly explained ....in a most simplest form
Wonder how it works on coaxial helicopter?
I thought I understood this, until I sat in the Schweizer 300 with engine and rotor at rest, and applied forward cyclic and noticed the swash plate raise in the back, then when I moved the cyclic to the left the swash plate rose on the right so how does gyroscopic procession work in this situation? Thank you for sharing your great videos.
The pitch change links are connected to the horns on the blade, and they are arranged so that the input to the blade occurs around 90 degrees in advance of where it is needed. The blade then has time to fly up or down to where it is desired. Thus the swash plate can mimic where the stick is pushed, and where the disc goes to.
one big help in getting this to click in yuor brain:
Understand that the control rods from the swash plate attach to the rotor blade 90 degrees out of phase as well
For example: left cyclic -> swash plate tilts to the left -> lift on the right side created by control rod from the right side attached to blade on the aft/back position, so when the blade turns (counter clock wise) now to the right the angle of attack was already increased 90 degrees before that so the lift effect takes place on the right side of the rotor disc now generating lift on the right side and tilting the rotor disc to the left
therealTOTOfan. That's right. That's what I was pointing out towards the end of the video. Luckily pilots do not have to compensate for this 90 degree difference due to control rigging.
Very good explanation
Helicopter flight controls in Wikipedia also states that when you push the cyclic forward that the swashplate lowers in the front and raises in the aft. And that the swashplate does not go 90 degrees before the direction you want to go. Meaning if I push the cyclic forward the swashplate doesn't go to the right. Again I'm not trying to fault you, it's just that I have 2 different forms of information that seem different.
there are pitch links between the swash and the rotors which are at an approximately 90 degree angle.
This makes so much more sense now
“How does this apply to helicopters?” *draws butt plug*
deeply impressed by ur instruction. thanks....
one question about gyroscoptic precession...How about clockwise direction rotating rotor systems?
Do they behave same as CCW direction rotor systems?
I mean pitch change....
Everything is the same in concept except the precession is 90 degree prior in the other direction. So to turn right the pitch would increase over the tail to manifest on the left half of the disk.
Thank you again.
It was helpful~
Safe flight...
2nd video, loved it!
Good vídeo 👍🏾🚁
When referring to "input", is that the point in the rotation where blade pitch angle is the highest (due to the input) or is the 90 degree point where the highest blade pitch angle occurs? thanks!
T Phillips. It's the point where the change in pitch angle is made.
That's what I was thinking. Thanks!
very good 👍
Quick question:
you said when you want to make a left turn, you move the controls to the left & the swashplate increases the pitch at the rear of the rotor disc.
My thinking is, it would increase the pitch at the front of the rotor disc with desired movement occuring 90* later. Can you help me determine my error in thinking?
I intend to go through WOFT soon, thank you for these videos, I really appreciate it.
john fuller. Great question. Think of it this way though. If I want to turn left, I want to create more lift on the right side of my rotor disk than the left. This unequal lift causes the rotor system to tilt to the left and cause a left turn. Now because of how Gyroscopic Precession affects my counter clockwise spinning rotor, I need to make this input 90 degrees prior. So to increase pitch on the right side, the input needs to be made at the rear of the disk. This will manifest 90 degrees later at the right side of the disk and I will begin a left turn. Keep in mind that the correction for Gyroscopic Precession is already made for you in the control rigging and all you need to do is put in left Cyclic to have a left turn.
Helicopter Lessons In 10 Minutes or Less
Ahhhh, ok. That makes a lot more sense, thank you very much.
@@helicopterlessonsin10minut10 Hi. Could you please explain how the correction for gyroscopic precession is already done at the control rigging? Is done at the input to the swash plate, or is it done via rods and linkages between the swash plate and the spinning rotor? Also, is this correction done differently depending on the kind of helicopter. I'd really appreciate your answer!
@@helicopterlessonsin10minut10 Is this because of lag? The time for the increase in pitch to go from root of the blade to the tip? Would increasing rotor RPM make the lag greater than 90 degrees?
thanks for your job, does gyroscpoic effects the engine torque?
i hope. Gyroscopic precession in this aerodynamic sense only applies to aircraft controls/rigging and not engine torque.
@@helicopterlessonsin10minut10 is there a minimum speed that the main rotor must move to make the force precess by 90degrees.... or, even better , what is the speed dependence of the precession angle?
PREPPING FOR THE SIFT AND YOUR VIDEOS ARE AMAZING
Did you take your test yet? I recently published some prep videos
No i haven’t scheduled it yet. I feel ok in all the areas except the aviation knowledge. Every time I find a practice test it’s like everything I read isn’t questioned.
Check out some of the study guides I list in my SIFT prep videos. They have a study section and practice section that should help cover everything. The Rotorcraft flying handbook is another great reference as well
@@helicopterlessonsin10minut10 Thank you So much. I purchased some of the books you linked in the recent videos.
I did a Wikipedia search on how helicopters fly and it states that gyroscopic precession is a Misconception. It stated that what is really happening is called Phase Lag and not gyroscopic precession.