Helicopter Physics Series – #4 They’re Gyroscopes – Smarter Every Day 48
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Helicopter Physics Series – #4 They’re Gyroscopes – Smarter Every Day 48

September 8, 2019


Hey it’s me Destin. Welcome to Smarter Every Day. So you know you’re in trouble when you have to break out the tinker toys to explain
a concept. What are you gonna build? (son) Tinker toy ducks, scrod and rolls over your ham. [??] Good idea. What are you gonna do?
(Daughter) The sunset.
The sunset. OK. So we’re gonna start building.
Go. Alright here at Smarter Every Day we’re right in the
middle of a series on how helicopters work, and if you recall, I told you at the beginning that
helicopters are very very complicated. So here’s the tinker toy helicopter that I just made,
and if you recall from the other videos, I told you that as the blades on the
helicopter spin around they have the ability to change pitch as they go around in the rotor disc. Now this is called
cyclic pitch, and if you don’t understand this concept you need to go watch this
remedial video so you can remind yourself about what I’m talking about. So let’s assume that
we fully understand how that works. Here’s the question.
If I have a helicopter and I simply want to make a manouver and I want to tilt
the helicopter up and forward just like this, how do we change the pitch in the rotor disc. So to me it’s logical that I would want to increase
the lift on the back of the rotor disc, so what that would do is that
would cause more lift here which would cause it to tilt forward. This makes sense to me.
Does it make sense to you? Well here’s the deal. You’re absolutely
wrong if it does. This is why. You actually provide more lift on the side of the helicopter and that will
tilt the helicopter forward. When I first figured this out, it blew my mind
because it just did not make intuitive sense, but it has something to do
with this little gadget right here. You may have seen one before.
It’s called a gyroscope. So what does this have to do with helicopters.
If you think about it, it’s a big mass spinning very fast. Look at a helicopter. What do we have on top?
It’s a big mass, spinning very fast.
So when the rotors are aligned with the helicopter body, if I wanted to pitch the helicopter body forward like so, I would expect us to be in phase right here, and I would expect to take less of a bite with this rotor and and more of a bite with this rotor to rock it over is that what?..
(Carl) That’s not the case. It does seem like that would be, but due to gyroscopic precession, any force on a spinning disc, which these blades do act as a disc, takes effect over a 90 degree phase. So if we give it a force here, to push down or up to roll the helicopter forward, it’ll actually take effect 90 degrees later, and roll the helicoper sideways. So in order to roll it forward we give the pitch when it’s 90 degrees away from ..
(Destin) Oh, so it’s like.. It’s almost like predicting the future or something like that.
(Carl) Something like that.
(Destin) So, if I wanted to rock the helicopter forward, I would take less of a bite when I’m 90 degrees out of phase and more of a bite over there, and that would do it?
(Carl) Yep, so the blade here pulls up. This one pushes down, and it takes effect 90 degrees later when it’s parallel with the machine, and the machine will rock, like so. Yeah. I’m not getting it either. In fact, I got a one-on-one explanation from an ex-pilot at the Smithsonian and I still didn’t get it.
To control to 90 degrees in front, on the swashplate.
(Destin) Like everything on Smarter Every Day, I finally understood this when I made an experiment for myself. Alright so Carl and I have setup a really super high tech experiment involving bicycle wheels. Hey the Wright brothers did it. It’s good enough for me if it’s good enough for them. And we have a camera aligned along a force application device, which is a metal strip, and do you want to explain what we’ve got going on here?
(Carl) Alright, we’re going to
(Destin) Wait! I’m better, go ahead.
(Carl) We’re going to apply a force, straight up, and as you can see here the tyre rotates in the same plane as we’re moving this bar. But, when it’s spinning, it’s going to be different.
(Destin) Let’s..Let’s just check it out. Here we go. I used to play with my mom’s exercise machine when I was like 5, so I’m highly qualified to apply angular momentum here. Angular momentum applied! Hit the brakes. (Carl) Trying to control this thing.
(Destin)Alright.
(Carl) So now we’re gonna do the same test again. We’re gonna apply force straight up, here. And.. it rotates, 90 degrees from where we apply the force. (Destin) Alright this principle is called gyros.. [cough] gyroscopic precession, and that’s basically the forces applied orthogonal to the plane of rotation, it acts 90 degrees out of phase to that applied force. I think it’s pretty interesting. So, I have a plane of rotation here of the force, but it actually acts in this plane. And so if you look at the horizon that the camera is looking at as he pushes up, it rotates opposite of that. It’s pretty cool! Anyway that’s it. That’s why helicopter blades operate 90 degrees out of phase. Anything you want to add? Besides the fact that I was kneeling in a horse biscuit the entire time?
Hey horse. What do you know about gyroscopic precession? [silence]
It’s what I thought. [laugh] So I realise this was one of the more complicated videos and I hope you got it. If you would, leave me some comments and let me know, so I can figure out how to best explain things in the future. Also, if you’re interested, subscribe because next week we’re gonna talk about the helicopter speed limit, and it’s not because of the FAA. It’s physics. I’m Destin.
You’re getting Smarter Every Day. [ Captions by Andrew Jackson ] Captioning in different languages welcome.
Please contact Destin if you can help.

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  1. Great, studied mechanical engineering at tech university Vienna, guess nobody from their would know this, besides that we did a bunch of brainaas calculation with something called precission

  2. i love your videos so much. i felt this one didn't really explain WHY though. i get that it will be 90 degrees out of phase, but why is this? are there any diagrams or reference material? i used to work on bikes for a living so this demonstration to people is always a fun one. it would be cool to be able to scientifically explain it though. why 90 degrees? why not 76.3? i don't know, maybe i didn't pay attention to the video enough, but i don't feel i have a grasp of the physics behind it, just an understanding and expectation of what will happen when i apply a force

  3. ok but WHY IS IT 90 degrees ????? why not 99 or 87 or any other number near 90??? explain that and people would go ohhhhhhh

  4. Hi, I enjoyed your video but sorry to say you have misunderstood what is happening. All helicopters have flapping hinges or either flexible blades or blade roots that allow the blades to flap up and down. Without, as speed increased there would be uncontrollable rolling moments. Since there is a hinge there can be little or no gyroscopic forces. The 90 degree phase lag is purely aerodynamic. Please check out any helicopter text book and read up on “flapping to equality” and all will become clear. However, nice presentation. Good luck. (Helicopter pilot and test pilot for 45 years).

  5. 1. It’s not cyclic pitch, it’s collective pitch.
    2. The blades also flap up and down, they also cone upward.

    Helo pilot.

  6. Gday Destin just a quick question does gyroscopic prosession affect the thrust produced by a propeller on an outboard?

  7. Destin,
    your videos are always great man, and such kewl topics – of course I could suggest a few as well……..

    where's the helicopter speed limit vid? I remember that from army training but can't recall the specifics
    five star mate, your vids are five star great stuff sir.

  8. I think Vsauce explained it well in his video "Spinning" with the analogy of a satellite orbiting.

    https://youtu.be/XHGKIzCcVa0?t=6m4s

  9. Destin, I made it to "orthogonal" 4:52 and developed a migraine. Thank you for that. Sorry, but I cannot continue. I still think you're awesome, tho.

  10. Hey Dustin you could talk about the torque applied to change the angular momentum, according to Right hand thumb rule! 😅

  11. Hi, to some degree I understand the issue with gyroscopic effect on a spinning mass. A fixed wing A/C has some issues during take-off which can cause the A/C to yaw due the gyroscopic effect. therefore you have to counter-attack with the rudder to keep where you want it to be. However I don't understand when you want to pitch forward the helicopter that the force is effective 90 degrees in the plane of rotation. When you apply the control input to controls to pitch forward how does it work to the force is applied at the right time so that it does indeed pitch forward rather then sideways movement.

  12. Hi Destin, I love the videos you make. This one here is 6 years old now, but I'm only seeing it just now and I still think I should write this comment. The other day I was scrubbing the floor with a rotating scrub machine. You know, a big rotating disc you push to the floor. You really have to tame it, otherwise you'd be running around chasing it through your room. Anyway, say it runs clockwise. If you want it to go forward (away from you), you'd have to tilt the device to the right so the right part of the disc (that's spinning towards you) gets more grip and pushes the scrubber away from you. And vice versa, tilt to the left to make it want to go towards you. I think you got the picture. My question here is: does this effect have anything to do with helicopters?

  13. Destin – How cool is it that after learning from this video that gyroscopic procession is a thing and understanding it, I saw videos about orbital dynamics that also reference gyroscopic procession as part of how orbit works. When you want to change your orbit, you do a burn 90 degrees ahead. 🙂

  14. How does the control work? In independence day, Will Smith pushes forward and crashes the UFO backwards and just turns the paper around and says, 'ooops, lets try that again'. Is it a matter of pushing the stick forward, but actually it is a pitch on the rotor to the left.

  15. 0:20 If you go frame-by-frame in the time-lapsed tinker toy build intro, there are several frames where the kids are more interested in what dad's doing than what they're doing themselves.

    I like that. The kiddos are curious. Great set up for learning cool stuff.

  16. Does the reaction force, felt 90 degrees out of phase, have the same magnitude as the initial force applied?

  17. I understand why this happen. because when you apply a force at 0 degree, acceleration will take time to increase speed. It reach max "+" speed when it turn to 90 degree. After 90 degree, the speed would decrease because neg acceleration, at 180 degree speed will be 0, After 180 degree, "-" speed will increase, then so as 270 degree, "-" speed will be max , and speed will return to 0 at 360 degree.this is why it progression at 90 degree in the rotation direction.

  18. I bookmarked this video back in 11th grade, my English wasn't good so I didn't understand it at all. Now I'm in 3th year of college, finally understand it.

  19. I believe the exact same thing happens when you ride a bicycle- if you want to lean left into a curve, you would push your right hand forward and pull your left hand back. These diametrically opposed forces causes the bike to tilt off the vertical plane to the left.
    It’s very intuitive for anyone riding a bike, which by the way is a gyroscope machine. Why it’s not obvious when thinking of a helicopter? Beats me.

  20. Old video, but just thought I'd comment to see if my intuition could be right.

    The fact that to pitch the helicopter forwards or backwards, the blades most pitch 90 degrees out of phase makes a lot of sense to me. Just imagine the air passing over the pitched blades, when they are aligned with the tail they are pitched such that when the air hits the blades it will produce a force to roll the helicopter. When the blades are perpendicular to the tail of the aircraft then the blades are pitched such that the air hitting them will produce forwards/backwards pitch.

    Hard to explain without a drawing but hope you get what I mean.

    @smartereveryday did you figure this one out in the end?

  21. Destin. Please make a video on the physics behind countersteering a motorcycle. This involves gyroscopic forces as well as the angle of the front forks creating a gimble, and several other factors in play as well. Turning the handlebars left to go right is a concept that most riders never fully grasp and form dangerous bad habits because of it. A video (or series) from you would dramatically improve the motorcycle community's knowledge and understanding of their bike and be greatly appreciated. California Superbike School would be a great company to collaborate with on a video.

  22. Hey Dustin,

    Believe it or not, steering a motorcycle at speed uses the exact same principle.

    At near walking speeds, it is as simple as turning the handlebars in the direction you want to turn.

    But, at speed, you have to push on the handlebars in the direction you want to turn.

    Push left to lean left to turn left.

    Push right to lean right to turn right.

    It sounds rather cerebral, but even bicycling at faster speeds, you use the same technique. The result is that it becomes second nature and you do it without thinking about it.

  23. but what about use of gyroscope in mobiles phones and navigation system,do they work on same phenomenon or differently as they did ?

  24. This is very late for when the video was uploaded, but this makes sense. A car tire is spinning at 0 miles an hour regardless of speed when in contact of the road. If your going 50 mph the bottom of the tire is 0 mph. Top of the tire 100 mph. The front and back are going 50 mph. I know this is more centrifugal force rather that the gyro explained. For my mind it makes sense that there is a quarter of delay in moving a helicopter forward as to a car tire rotating to make the car go forward. What do you think of this dustin?

  25. i emailed you on this topic before because your explanation is partially correct however your missing 2 key points (you never replied to me). I teach this topic to engineering students and have come quite fond of the discussion this inevitability creates.
    the term 'Gyroscopic Precession' when in the Helicopter world has 2 functions to it
    A) the 90 deg out of phase force effect due to the normal meaning of the word Gyroscopic Precession', and,
    B) a 90 deg aerodynamic out of phase effect to provide true directional control via the cyclic.
    Lets discuss deeper but do it B) first then A). also naming convention used here in 12 o'clock =forward, 6 o'clock rear, 3 o'clock pilots right hand side and therefore 9 o'clock is the pilots left hand side.
    B) to move the helicopter in the forward 12 o'clock direction we DO NOT have a higher lift production at the rear (6 o'clock) of the disc but rather wee have the blade at the 6 o'clock position flying higher (relative to the POR, plane of rotation of the disk). that way the total reaction of all the blades is forward of the mast axis. meaning the 12 o'clock blade lift force if vertical and the 6 o'clock blade's lift force is not vertical any more it is forward of vertical.. the question is HOW do we get the rear blade to fly higher than the rest or cone up more than the rest when the pilot pushes forward on the cyclic…. see A)
    A) the nature of the out of phase control linkage between the cyclic, scissor levers, control rods, pitch horns on the blade grips and the location of the pitch horns are not this way by accident (obviously) rather are there because of the two factors discussed here in.
    A1) the aerodynamic part of the gyroscopic precession feature (not correctly used term but non the less a important factor). i need the blade to fly high at the rear of the disk if i want to fly forward however it takes some time to alter the path of the rotating blade so i need to tell it to fly high when the blade is at the 3 o'clock position. Thus the blade at the 3 o'clock position has the highest blade pitch input because we need the blade to be lifted up to a higher tip path to generate the forward facing life force when it becomes at the 6 o'clock position.
    A2) knowing that i need to provide a mechanical input force to the blade pitch change point/axis and knowing that true gyroscopic precession exists with this large rotating mass i need to apply that 'up force' to the pitch change control rod (swash-plate to pitch horn on the blade grip) when the blade is 90 deg before the required up force. thus i push up on the control rod at the 3 o'clock position.

    NETT RESULT
    to fly forward i use an aerodynamic 'gyroscopic' effect coupled with the try gyroscopic effect of the rotating mass of the blades and the disk.

    NOTE; the term aerodynamic gyroscopic effect has nothing to do with the mass of the object rather a out of phase delay that happens.

  26. Five years later, I presume you clarified in your mind the difference between cyclic pitch and gyroscopic precession.

  27. I got lucky I guess. I wanted to know how a helicopter works and found this. No for dummies, but, you don't need a degree in physics either. Thanks.

  28. when i was a kid i loved RC airplanes . 1 day some 1 gave me a RC gas power helicopter . it was givin to me as a gift as they could not get it to fly right . i to as a kid looked at it the same way you did and never got it to fly right . after months i just pulling the motor and put it in a rc plane . it was not tell i was 38 years old that i fould out why . this is only the 2ed video i have seen to show why

  29. How do we know exactly when to apply the Cyclic pitch to make the craft bend forwards, while the rotor is in motion at 500 RPM? how do we know that we are changing pitch exactly 90-degree angle in advance?

  30. I know this vis is old, and thanks Dustin, you helped me get the what, but not the why. Not really. Why 90 degrees phase? Why not say, 78? or 123 degrees out of phase?

  31. Thanks Destin I'm working on testing an invention a gyroscope that counters the force applied to it so this was very helpful.

  32. Destin, helicopters don't really fly. they simply beat the wind into submission. That's another reason there is so much more maintenance required on them as opposed to conventional aircraft. 🙂

  33. So I have a question about speed of rotation and amount out of phase of Motion and Applied Force. Does the amount OUT of phase Increase as the Speed of Rotation Increases and visa versa if you slow down rotation does it get closer to being IN phase… becaaaaaause if it is at rest the motion is completely IN Phase with the Force Applied. Now, if that were crazy enough to happen could you increase the speed to a point where the motion would move all the way around 360 degrees BACK to the beginning and then be IN PHASE with the motion applied?

  34. If we continue the experiment as the wheel slows down, would we find that the 90 degrees thing becomes 89 degrees, 88 degrees and so on?

  35. I presume this is related to electrical current and the resulting magnetic field at 90° from its direction,, sort of, or voltage and current being 90° out.

  36. Just watched this old vid now and wanted to comment. Mind blown but makes sense to a novice rc heli pilot :-O

  37. Not that I've read every comment, but I see a lot of "rules" but no "why". Here's my best guess: The force applied to one end of a spinning disk imparts inertia to a point on the disk. As that point spins to the opposite side of the disk, it counteracts itself exactly 180 degrees out. IE: The "same" amount of force is applied to both sides of the axle/fulcrum causing zero angular force. However, assuming the initial force was downward, at 90 degrees from the initial force there would be residual downward inertia, while ate 270 degrees the residual inertia from the opposite side would be upward because the original force, applied against the disc and against the fulcrum/axle caused upward inertia on the opposite side. In other words, the inertia at 0 and 180 degrees cancel each other out while the inertia at 90 and 270 degrees is complimentary. Does this make any sense to anybody? 🙂

  38. Finally someone explained this to me… I was looking for ages!

    Perhaps you could do a video explaining the elements of lift as these are air being pushed down through tilting the rotor and the normal lift due to the shape of the wing.

  39. i like how in the beginning when you are all building you can see you take all the tinker toy parts to finish your 'copter

  40. You're wrong,. Try putting a rotor in a vacuum jar with a motor osillating remove the air and it will stop the rotor turning period even though the head still turns. The flapping teeter hinge compensates for the change of angle of attack of each Blade due to the precession. This is part of the reason cierva put the flapping blades on , retreating blade dissimetry lift and controlling for gyroscopic precession.

  41. The thing I don’t understand yet, why we hear the engine on but the blades don’t move yet, does it has a clash or gear box? Nobody explain that

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