helicopter rotor control - phase delay

[@adrianlindsay3194]

One of the best descriptions and videos I've ever seen regarding controls, rotor system and aerodynamic phenomenon like gyroscopic procession (phase lag).

[@ziggy979]

My grandpa was an electrical and mechanical engineer, earned his degree at Pratt institute in 1920. When I was like 8 or 9 he started to teach me so so many things relating to the mechanical world. To witness this video and all the beautiful detail and moving parts in real time animation brings a tear to my eye… and his too, wherever he may be watching. Bless you for creating this fantastic visual treat. Ziggy

[@bzig4929]

From Zig to Ziggy... Thanks for sharing your grandpa's story. Engineers make the world what it is.

[@coreybennett564]

Great job! It’s fantastic that you’re taking more time to describe everything you considered in building the model! Would love to see you animate a tilt rotor! No one is doing anything remotely this detailed! Keep up the great work!

[@bzig4929]

thank you for the kind words! I enjoy making these videos and learning to use different modeling and animation software. A tiltrotor would be a challenge!

[@coreybennett564]

@@bzig4929 You’ve earned it! It would certainly be a challenge to say the least.

[@dennisg-ski7829]

​@bzig4929 Your channel just popped up and I subscribed after watching one! To describe all of the intricacies of the aerodynamics of rotary-wing flight would probably require a video hundreds of hours in duration. Phase-lag aka gyroscopic precession in a rotating body, as applied to an an airfoil. Centrifugal, centripetal forces, lift balance and the combination of collective lift and cyclic thrust, etc. It's a long list! I once heard an aerodynamicist remark that the aerodynamics of rocketry were simple, fixed wing intriguing, and rotary wing dynamics almost a dream come true! Thanks for your work producing this content.

[@spankyharland9845]

it is called moving the big saucer plate above your head. great video representation that took me a while to figure out. add a video on what the anti-torque pedals do and everyone will know how to "get on the choppa" and fly it.

[@tonysmith7836]

Brilliant visualisation!

[@jessysaintauret3615]

it's rare when I put a comment, but this was a very instructive and amazing explanation video thank you.

[@bzig4929]

That's a very nice comment. Thank you!

[@petehalasz7547]

Absolutely perfect explanation on your first and second vids.. love the animation.. as a heli pilot, this explanation drove me nuts, and I thought would have to prematurely input. At the end, didn't have to worry.. as you mentioned this goes out the window for 2 ,,4,,,,5,,6 blade machines.. and let's not forget fixed hubs, or lead/lag flex hubs.. Excellent work.. when I use fly i also had several RC helis,, and holy poop it was tougher to those RC then the real ones..

[@nachosanchez1798]

This is a very good explanation of phase lag but, keep in mind that lift vector is always parallel to rotation axis “the mast”, creating a torque that will tilt the whole aircraft and hence tilting the thrust vector. Otherwise, the helicopter would neither pitch nor roll.

[@andrewtsang6997]

Thank you for this excellent explanation. I have been trying to convert my flybar RC helicopter to flybarless and this describes perfectly the phase delay I was seeing that confused me at first!

[@Ben-Dixey]

Great video,! it was my understanding that the blade pitch horn sets the phase lag and the swash plate tilts in the direction of travel. You can see how the horn pitches the blade out of phase.

[@chrishard7616]

Thanks for this explanation. I was playing around with an RC helicopter and couldn’t understand why the blade pitch appeared to be out by 90 degrees. Now I know why!

[@charlieguenther5490]

It would help to describe procession in its entirety. It's a simple concept that has the greatest influence on phase delay. Thankyou for the presentation.

[@jeeberlewis7352]

Really well done. I have heard different POV's, but is it universally an 85 degree lead? I have also heard of a 90 degree lead. Does that change with respect to the type of rotor system (rigid, semi-rigid, fully articulate) or how many blades we have on the helicopter? Thanks again. Keep these coming! I am an aspiring Army Aviator and I am studying for the Army SIFT - your videos help immensely.

[@bzig4929]

Thanks! I really appreciate you letting me know this was helpful. The amount of phase lag (difference less than 90 degrees) corresponds to how much flapping hinge offset is in the rotor system. Teetering rotors, such as the bell 206, have close to zero offest so they have 90 degrees of phase lag. Mechanical flapping hinges have pysical offset and they are usually 80-85 degrees. The highest amount of offset is the virtual offset of semi-rigid rotor heads (bo-105 or lynx) and these can be 75 degrees.

[@Workerbee-zy5nx]

Great grafix, fixed wing pilots will be confused. 😉😳👍

[@bzig4929]

So right! They are always confused

[@9HighFlyer9]

I'm not confused but I'm a wanna be rotary wing pilot trapped in the budget of a fixed wing pilot.

[@Workerbee-zy5nx]

@@9HighFlyer9 Want all the free avation you can handle? Join the army for choppers, airforce for fixed wing. Its free..👈💪🇺🇸

[@MrBigShotFancyPants]

Fixed wing pilot, it's challenging at first though I'm not confused. The motor causes both types to go up. I offer as proof: lack of motor causes both to come down.

[@justinbailey2806]

I've never operated a helicopter but the learning curve for the phase delay reminds me of oversteer or understeer in a car and I imagine similarly there's a feel that is acquired for that delay in experienced piloting of a helicopter.

[@benhill31]

I always had that question! Excellent video. I knew about gyroscopic procession, but was unsure where the max pitch of the blade would be in relation to the actual desired direction of flight. Thank you for this!

[@bzig4929]

Thank you for watching and commenting!

[@spamemail124]

5:00 Specifically, it's a characteristic of a Resonance in any second order dynamic system. If you were to take mass-spring system, and give it a force input at a frequency of sqrt(k/m), (the system's natural / resonance frequency), you would observe that the position response of the mass has a 90 degree phase lag from the input force. Also another thing that's really cool: the only reason cyclic pitch is able to control the helicopter at all is because of the resonance between the blade flapping and cyclic input. Helicopter rotor blades have so much inertia that simply perturbing the blade pitch randomly will not cause them to budge at all, but the resonance causes the flap amplitude to increase significantly, allowing us to modify our thrust vector and control the aircraft! I always found it really cool how generally in engineering we avoid resonance, but here we take advantage of a resonance for the main control system of our vehicle.

[@SteveNoskowicz]

Uh. . . .__IF__ it was resonance, it wouldn't work at all rotor speeds. The amount of phase-lag would vary with rotor RPM. If you've worked extensively with resonance, you'd know that phase changes most rapidly around resonance. The pilot would be uncontrollably chasing the cyclic all over. This is not something new that needs further research. It _IS_ precession and is clearly understood as such. . If you still have trouble, try this: . Think of the rotor as just a classical gyroscope disc. .. When lift is high on that left, retreating blade, that upward force causes precession ~90⁰ later that lifts the blade as it passes above the tail. That means the rotor disc is now tilted forward, redirecting some lift to the rear - for forward speed. Got it?

[@bzig4929]

@@SteveNoskowicz It's not related to just the RPM, rather It's the ratio of the forcing function (cyclic input) to the frequency (rotor rpm). If the rotor RPM changes, so does the frequency of the forcing function. Thus the damping ratio remains constant regardless of rotor RPM and there won't be a change to the phase delay angle if the rotor speeds up or slows down. Somewhat related... Modern helicopters don't vary rotor RPM. The flight control system maintains RPM within fractions of a percent even during dynamic maneuvering. It doesn't sound like I'll convince you, but check out Gessow and Meyers, Aerodynamics of the Helicopter, Ch7, page 156 (in my edition)... "for such a system, the force displacement phase is related to the frequency of the forced system... when the exciting force is applied at the natural frequency, the phase angle is 90 degrees" The figures in the text really help the explanation. One figure is a linear spring-mass damper system, and the other is the damping ratio chart. As I said in the video, calling it a "gyroscope" or calling it "phase delay" doesn't matter so much as understanding that the input occurs about 90 degrees prior to the maximum displacement of the blade.

[@SteveNoskowicz]

@@bzig4929 Your last paragraph is the main thing. One point is that it is a precession phenomenon. The revolving mass of the rotor blades have that characteristic and that is physics. Some comments here seem to think they can speculate on other explanations because "no one knows yet"; that it's not well understood and that simply isn't true. . I highly suspect the resonant frequency of the rotor is a dominant parameter, unless you know the numbers and can state it is not. I do know that the phase shift varies most rapidly around resonance, so feel it is most likely dominant, but will not exclude other factors because the aerodynamics are always complex -- despite many folks thinking they can simplify it to some black and white story. . I can't comment on the damping ratio of rotors and won't try to guess. . I'll pass on Gessow and Meyers as my expertise is elsewhere. I came by here for a friend to provide some clarifications for him. He had problems with you referencing flapping and I was able to help him out with the fundamental concepts without the many other complexities that make aero so rough to grasp at times. Thanks.

[@SteveNoskowicz]

@@bzig4929 bzig, I should have asked you to comment on this. My friend was told by a hele pilot what he recalls as: "To start forward flight, the cyclic is first moved laterally, then moved around to being held forward, in the direction of flight." . I don't know what that pilot was flying. . Discussing this with a couple of other engineers {one who had worked on rigging a hele} we felt that this isn't part of the fundamental precession of the main rotor, but that it appears that this may be to counter the tail rotor side thrust. Can you comment.?. .

[@spamemail124]

@@SteveNoskowicz Your suspicion that the resonant frequency is the relevent paramater was correct. This phenomena is a resonance. Also touching back on your inital reply: Even if the helicopter did change rotor speeds as it flies, there would still be a resonance. This is because the resonance freqnecy of the blades' flapping motion IS (about) equal to the rotatoinal frequency of the rotor. I can't really draw out a free body diagram and write equations in a youtube comment, but you can sum the moments about a rotor blade's hinge in the flapping direction, and after making a small angle approximation you'll end up with a second order dynamic equation that has a natural frequnecy equal to the rotor rotational frequency. I can draw this out and show the equations neatly in a google doc if you would like as well. Of course, you end up making some approximations with this simple represenation of the blade flapping about its hinge, and due to damping and some higher order effects the blade flapping natural frequnecy isn't exactly the rotor speed, hence why the phase delay used in practice isn't exactly 90 degrees.

[@llwellyn1]

I subscribed after seeing this well composed technical presentation. I look forward to reviewing more from you. Keep up the good work!

[@bzig4929]

Thank you! I am planning to do more presentations on helicopter dynamics and control.

[@2whl4re]

Well done. Helicopters are the best way to fly when you don't have anywhere to go.

[@bzig4929]

or... helicopters take you anywhere slowly; airplanes take you to places you don't want to go, but 3 times faster

[@maffysdad]

You've just reinvented the Swash Plate! 😀

[@isntthatsomething8928]

Are you doing this all in blender or are you modeling in CAD? Just discovered your channel, watched several of these helicopter mechanics videos, and am floored by your work. I spent nearly two months trying to model and rig a double wishbone suspension in Blender and struggled with the kinematics but you seem to have perfected the art! Instant subscription. Don’t know if you have any behind the scenes process videos but if you do I’ll definitely be looking for them when I next have the time! Thanks for this content, inspiring.

[@bzig4929]

Fusion 360 for the CAD export to Blender as a 3MF file and then Blender for everything else. I started with IK and constraints and was about to flush the whole project... Then I discovered drivers and that made a world of difference. I should do some workflow videos... Thanks for suggesting that.

[@AlessioSangalli]

@@bzig4929master bzig, it would be great to see the workflow! I did not even know fusion could be used with blender. Doesn’t fusion 360 already have the animations?

[@markusanderson1517]

Very cool. Great animation work and explanation.

[@bzig4929]

Thanks for the kind words!

[@peterscherzer4971]

Thank you very much for this impressive presentation

[@bzig4929]

Thanks! You are much nicer than the last guy who commented 🙂

[@phobosmoon4643]

this video is so awesome!

[@dippyanddakota]

Amazingly hypnotic. As a pilot and just plain "anything that can fly" geek, you've clearly cemented how this all works. What CAD and animation are you creating these masterpieces with?

[@eiz3333]

He is using Blender. Its free and Open source. Don’t know if he made the geometry elsewhere and imported, nevertheless is an excellent job.

[@bzig4929]

Thanks for watching! Blender for the animation, but I do the CAD in Fusion 360... Fusion is better suited (IMO) for hard surface models, but Blender shines when it comes to animation.

[@nullpointer1]

my favorite video of the year! thanks for giving the gyroscope precession folks an off ramp!

[@joshm3484]

The way I think of it, the blade moving forward will naturally produce more lift than a blade moving backwards (ie the blade on the right produces more lift than the blade on the left, if counterclockwise as in this animation), proportional to the forward speed of the helicopter. You can compensate for that by increasing the angle of the blade moving backwards and decreasing the angle of the blade moving forward.

[@Tld0026]

Unfortunately retreating blade stall prevents that.

[@algroyp3r]

This is unrelated to the topic here. Phase lag occurs even if the helicopter is standing still.

[@palicgofueniczekt]

8:25 we see the yellow and green banded components bend significantly, but not the rotor blade. there seems to be another layer to this animation not mentioned (or I missed). in a static situation, you wouldn't see these components flex, right? IRL they also likely wouldn't flex that much and it would be the blades themselves that flex the most, right? The key points to your video here are the rotors flapping (much like a reciprocating piston engine) and the phase difference between maximum acceleration and maximum velocity (of the piston). Thanks.

[@bzig4929]

You're calling me out on my animation skills 😁. Rotor blades definitely bend in operation, but I haven't figured out how to make the animation software do that accurately. It's on my list of things to learn. Thanks for commenting!

[@alanwhitfield1907]

There is an omission in the graphics of this video. It omits to show the fixed scissor connected between the gearbox and the lower part of the swashplate. It is found on all helicopters that use a swashplate. Also it shows that a cyclic forward input causes al three servos to operate. This is not the case in reality. The cyclic forward/ rearward movement moves only the single servo at the forward position, and the swashplate pivots about the two stationary lateral servos. Lateral movement of the cyclic control cause the two lateral servos to operate in opposition, and the swashplate pivots about the front servo and the fixed scissor. I spent many years as a helicopter engineer in military and civil aviation so am familiar with helicopter flight controls operation and rigging.

[@SirAndi69]

excellent description !!!

[@bzig4929]

Thanks!

[@Steeyuv]

Is it just the angle of the swash plate? Surely the size of the pitch control arms on the blade roots is as much a part of the design. Stunning graphics, thank you for the video.

[@eddiexoc8430]

Great presentation.

[@edmoregonde]

WONDERFUL it's now come to sense am wondering how and how this system work

[@danielchen9841]

Thank u for the vast explenation geate greate explenation

[@bzig4929]

You are welcome. Thanks for watching!

[@hangar4851]

Excellent graphics! What I am confused about is what you are trying to tell about the 45 degrees and the 30 degrees. quote "The swashplate is centered at 30 degrees." . What do you mean by that? Gyroscopic precession - that is the term in my physics books - implies, that on a rotating mass the force orthogonal on this mass will the place exactly 90 degrees after the force has been imposed on the object. Flapping angle has to be deducted, but only if you have a rotor head allowing blade flapping. Bo 105, Blackhawks etc do not have flapping blades. The 30 degrees thing and the 45 degrees thing, ... what is that?

[@bzig4929]

I could have done better with that. Switching from 30 to 45 didn't help. The point I was trying to make is that there is a 90 degree difference from where the force is applied to where its effect is felt. But, the mechanical attachment point isn't 90 degrees away, so it appears like it's not a 90 degree difference.

[@SteveNoskowicz]

@hangar4851 Gyro precession is at 90 degrees and that applies to the main rotor blades. If you do an analysis of a gyro as a bunch of separate weights around the wheel. it is easier to understand precession. There are You Tube videos showing this. However, I've heard an explanation of why in practice it isn't precisely at 90 on a heli. There are other secondary forces, but don't recall all the detail now. . In addition, for example,, when applying collective and power going forward, the tail rotor also puts additional side thrust that must be compensated for by the main rotor counteracting to the other side or you start forward motion at an angle at an angle. . A heli pilot I talked to said some helis you start forward with the stick slightly to one side and bring it gradually forward. . It's V-E-R-Y complex. . PLUS, not all helis are rigged the same due to configuration and computer control differences. - - I talked with my AE son who did some heli rigging at Embry-Riddle Aeronautical University.

[@orchidahussuhadihcro9862]

Some say the gyroscopic precession is altogether just a lie, or a mistake. This phase lag is supposedly purely caused by the time it takes for the desired cyclic action, to apply physically on the blade due its own inertia (maybe inertia isn't the right technical word though) The maximum pitch is near 9 o'clock. The maximum flapping height is near 6 o'clock. But the angle just looks like 90°. On various helicopters models it can vary from 70° to 90°. It is said that if it was precession, it could only be perfect 90° on all helicopters. I get the feeling, only a handful of people on this planet actually understands really helicopters

[@SteveNoskowicz]

@@orchidahussuhadihcro9862 No, Inertia is indeed correct. It comes down to Newton, but gets complex here. . It really helps to understand the basic physics of precession to see the fundamental 90 degrees of classic precession. I'm sure there is a YT video on it. . Think this way: The increased lift at one point in the rotation, produces an upward force and resulting acceleration of the mass at the end of a rotating arm. This acceleration is in the direction of that force and increases the vertical speed of that tip. . That vertical speed gives the increased upward deflection {flap} that continues increasing around the rotation. In a solid body rotating, this gives the classic 90 degree precession. . The fact that the blades are not a solid gyroscope , along with factors of the craft dynamics can alter that 90 angle. . My AE son worked some on rigging helicopters and talked about the offset effect. Newton can get pretty messy at times. Cheers

[@pork_friedrice]

Next level man, fantastic!

[@larrybremer4930]

I used to own and fly an RC helicopter that was based on a Hiller Teeter rotor thus it uses a flybar mass (and in the case of the model the flybar also has paddles). It too needed the 90 degree phase differential but it was done at the linkage making the swashplate cyclic in phase with the flight axis (ie: swashplate tilt forward would move the heli forward with the linkage controlling the phase lag by connecting to a 90 degree offset). Also on the model the cyclic did not move the swashplate, rather there was an additional link that runs to a mixing arm that connects to the blade link that mechanically mixes the cyclic and collective, so the swashplate did not have to move up and down (only moves in pitch and roll axis with control inputs to the stick). My heli was only a two blade and with some high speed cameras it was interesting to see how much lead/lag imparted into the actual blades where in forward flight the two blades were not at all parallel, you could see they would at times be what I would estimate to be 15-20 degrees out of parallel from the rotational and aerodynamic forces. In fact on the model the lead lag hinge was a very loose connection, so the blades would very easily swing on that pivot with only the blades mass being what holds them out (straight) when the rotor is spinning.

[@metricdeep8856]

I design machinery for a living. There are just way too many (small and thin) moving parts for this system to carry human lives at my level of engineering! This was an awesome animation and explanation. This is a fascinating mechanism. Cheers and thanks for sharing. Edit: Is that a cir-clip at the very top of that assembly, holding those blades to the craft? There has to be more than that.

[@midynei5574]

Show de bola ⚽️ as pá gira junto com o rotor principal.. tudo de forma automática graça ao disco logo abaixo que se movimenta ... muito legal essa visualização

[@bzig4929]

Thanks for the comment!

[@robbetaverniers8563]

Thank you for the explanation. But does this count too for 2,4 or 5 bladed helicopters?

[@bzig4929]

Yes it does. The phase delay will be 90 degrees if those rotors don't have offset (from the center of rotation) flapping hinges. The amount of difference from pure 90 degree phase delay is a function of the amount of hinge offset, not the number of rotor blades. Thanks for watching!

[@f_nc]

perfect explanation.

[@EEECampus]

Nice Simulation thanks

[@chriscaprice]

7:28 felt my neck just there

[@jeffpray87]

Amazing video. I love learning about this mechanical marvel. At the beginning of the video you mentioned you had a previous video explaining the flight controls. I looked but didn't see that video. Am i blind or is it hidden? Thanks!

[@bzig4929]

kzbin.infou4SPL3XMl_E?si=ttTVpY0Z_0SKiQEc

[@bzig4929]

It's a short...maybe it's not showing up on my main channel. I put the link in another reply to your comment. Thanks for the nice words!

[@rigilchrist]

This is a brilliant job, thanks. When I did my heli pilot training, nearly 40 years ago, I was told (or I may have made this up!) that in your example, the max pitch angle was athwartships (as you say) and that this causes greater lift, causing the blade to climb (flap), reaching its maximum height over the tail. This explanation (if correct!) is more intuitive than gyroscopic precession. But is it true? Thanks again.

[@bzig4929]

thanks so much for the kind comments! I intend to do more of these helicopter aeromechanics vids but the day-job keeps getting in the way.

[@thomasbrock1882]

Great work! Very impressive. What application is this you are using for the design/animation?

[@bzig4929]

I use Fusion 360 for CAD and Blender for animation. Thanks for watching!

[@thomasbrock1882]

Thank you for the reply! Your work is something else! Engineering-minded ppl like myself found your video very informative and entertaining@@bzig4929

[@JoeJalopy]

Arthur Young would like it!!

[@maxshyperspace1622]

You mentioned the actual phase is less than 90°, in this case is 85°. Is 85° is a constant when rpm change ? If deformation (bending) of the blades is also put into consideration, does it make the phase less than 85° ？ And also the mass of the blades, do they affect this angle ?

[@bzig4929]

the phase delay is a function of the damping ratio. This is the ratio of the frequency of rotation of the blades to the natural frequency of flapping. Rotors where the flapping hinge is at the center of rotation (teetering rotors) have a phase delay of 90 degrees. Check out this lecture at the 23:20 point, he does a good job of explaining this (better than I can)... kzbin.info/www/bejne/kHm3o51olpalg7Msi=ntJwxd8--yvYsX7z&t=1400

[@ThePilot396]

I would love to see an animation depicting rotor imbalance at high G maneuvers consequently resulting in malfunction or destruction of the rotor head entirely. Or imbalance with excessive loads.

[@Jo-rz6bs]

This would make more sense if i understood why the lift vector follows max displacement and not max lift. Additional lift "flaps" the blade up to cause that displacement? But what about the displacement affects the lift?

[@bzig4929]

This is good input... You're picking up on the simplifications I used to animate this. The s/w allows python code so I thought about getting more aerodynamic with this, but in the end... As you noticed, pitch, lift and flapping all occur at the same time which is not how nature works. And, flapping up causes a reduction in lift because it changes the angle of inflow to the blade.

[@infiniteandunlimitedabundance]

Hi would you mind to explain in details again regarding lead lag, flapping? I can understand pitching but don't understand why lead lag and flapping. Thanks

[@bzig4929]

Lead lag is necessary so that angular momentum is conserved. When the blade flaps, it's center of gravity moves inward.. if the blade didn't have lead/lag, the only way to conserve angular momentum would be for the rotor to speed up. Similar to how a spinning ice skater spins faster when she brings her arms in. Because the rotor can't spin faster, that is taken up by the lead/lag hinge.

[@georgelza]

think the light came on when you showed the pitch link... we not actually controlling the blades, we controlling the pitch links, their position and direction are linked, due to the structure, the blades are offset from them, thus the procession. if i understand it... ;) still wondering though, you would think due to the max forward movement the blade would create max lift aft... i understand it's not due to position of that link, max up and then the offset of the blade from there...

[@bzig4929]

This helps me... You're walking in a straight line. Someone pushes you to the side. At the moment they push you... This is the point of maximum force, but at that point you are still on the line, but starting to deviate. It takes a step or two to get to the max deviation which happens after the original force is gone.

[@edwardhunter3647]

Thanks,I will be building a prototype soon.

[@addmix]

Why is it that we would want to achieve maximum displacement from the flapping at a certain point, rather than achieving maximum lift at a certain point of the rotation? If the goal is to move the lift vector to control the helicopter, isn't that linked to the maximum force produced by the blades, and not the maximum displacement of the flapping hinge? At the end of the day, you need the forces to balance out such that you have controlled lift on the helicopter, so I don't understand why having maximum force offset by ~90 degrees leads to this. Edit: thinking about it a little more, is it instead that on a fully articulated rotor, lift of the blades doesn't directly lift the helicopter, only giving the blades inertia, and through the centrifugal motion, that blade's inertia is then transferred to the rotor head after ~90 degrees? As a side question, what is the leaf spring-looking thing inside the lead-lag hinge in your model?

[@bzig4929]

It's not that you want the max displacement to occur at a certain point... it's that you need it to do that in order to control the aircraft. To fly forward, you need the tip-path to tilt forward, so that means each rotor blade needs to be at it's highest point of flapping at the six o'clock position (over the tail boom). To achieve this, you have to apply the lift to the blade 90 degrees prior. Maybe a way to think of it is all the blades produce (almost) equal lift. It's not the lift on each individual blade that controls the helicopter, rather it's the overall lift and the tilt of the tip-path-plane that points that lift in the correct direction. I've flown a lot of formation flight in helicopters, and it's cool to see the entire rotor disk respond to control inputs as a single entity. It really doesn't look like individual blades, but rather as a single disk that tilts in the direction the pilot wants the aircraft to go. It may also help to think that the hub isn't capable of reacting moments at the flapping hinge; lift from the individual blades can't apply a moment to the mast to maneuver the aircraft. The overall lift vector, applied through the plane of all the rotor blades, is where the control comes from. The leaf spring looking thing is a tension torsion strap that reacts CF loads. The model of the rotor head came from images of the Boeing CH-46 Sea Knight helicopter and the TT strap when through the lead-lag hinge this way. I reused that 3d model for this animation. Good eye for detail!

[@pelinelden]

I wish you take a video about Semi-Rigid rotor system too…..

[@michaeljohn8905]

Is it the same as P Factor ? Ahh ok you said it I understand now. Very interesting.

[@sjm7284]

Phase delay/gryoscopic presession can be learnt/understand from how a floor buffer or orbital sander moves.

[@bzig4929]

I love the real world example. But don't forget how no one teaches you how to use a floor buffer. Instead, they just give it to you and watch in amusement the when you slam it into a wall at high speed. Experiential learning at its finest!

[@SteveNoskowicz]

@@bzig4929 NOPE, sjm & bzig. . Having done much of that buffing, it is the friction of the buffer disc on the floor, not precession that moves it around. So that is NOT the same physics. Sorry to burst your bubble, folks. . The axis of rotation changes very little on a buffer, so precession is a Minor League player in this game. If you correctly analyze it, this makes the action completely *OPPOSITE* of the chopper.!.!.'. .. .. Max AoA and lift in front, rolls a chopper into a RIGHT bank.!. . With the same CCW rotating buffer, you lift the front {by pushing down on the handle} to you go LEFT - BECAUSE the rear has more downward force on the floor and it is moving to the right. To 'sweep' left-right lines in front of you, the handle is moved up and down. __IF__ it WAS precession, upward force on the front would BANK it right! ALSO lifting the front would make it go backward, because the lift vector would tip backward.! ! . . . It's NOWHERE near the same thing. . Physics confuses many. . . Just like all the terribly wrong videos failing at the physics of a wing's lift . . You all fail physics class for believing it's the same thing. You are in Little League. - - Physics pro here.

[@thepocketmonsterman]

Gyroscopic procession is definitely the more general term

[@falcon7350]

As a kind in the 80s 90s i loved RC airplanes and could make them by hand from my head. found a low cost used RC helicopter and had to replace some missing parts. i could never understand why i could never get it to fly right and all my inputs were about 90 off. this RC was big and not a toy for RC standers. after all most hitting my self a few times with it i gave up and used the parts for other things. for the last few years i have seen videos like this and now understand why. when you say it hard for others to understand i to was one of them on where max pitch needs to be

[@notsoancientpelican]

well done

[@ilnaz7331]

Hello everyone! Please, Where can I find and install this simulator?

[@bzig4929]

it's not really a simulator, although I may refer to it as that in some of these videos. This is done in 3d animation software called Blender. Blender is free and open source... anyone can download it and install it. Although it's animation software, I treat it like a simulation for making these videos. There are almost no animation key frames involved in making these videos. Instead, I program the equations of motion for real-world motion and aerodynamics into a feature of Blender called "drivers." Drivers allow me to interact with my 3d models using Python code and it's much better for this type of video than key framing the motion. Blender has a steep learning curve, but it's an amazing tool. Particularly since it's completely free.

[@picopilot]

is it different for a 2-blade main rotor system like a Bell 206 or Robinson R-22?

[@bzig4929]

There is a small difference. Phase delay still exists, but 2 blade systems have the flapping axis on the rotation axis so they have exactly 90 degrees of phase lag. In fully-articulated rotors, the flapping axis is offset from the center of rotation, so the phase lag is less than 90... probably 80-85 depending on how much hinge offset is present. There are other differences... such as how they conserve angular momentum when flapping. The biggest difference is that 2 blade teetering rotors are susceptible to mast bumping and, consequently, have less low-g capability than fully-articulated rotors.

[@mikemybalzich3159]

so im a little confused. is the forward tilt, the flapping, caused by the pitch of the blades, or are the links directly controlling the flapping? (edit: sorry im still learning all of this stuff)

[@bzig4929]

The pitch of the blades increases or decreases lift on the individual blades. The change in lifting force moves the rotor disk through flapping. In other words... The pitch change arms do not directly control flapping... They control blade pitch... This changes blade lift... This changes the flapping angle... This tilts the rotor disk.

[@mikemybalzich3159]

@@bzig4929 alright thank you for clearing it all up, this is the answer i was exactly looking for. that's what i was thinking but i didn't know for sure.

[@SteveNoskowicz]

@@mikemybalzich3159 It may be easier to not think about the flapping as much as just the tilting of the plane of the rotor. Try to think of the rotor as just a disc, like a DVD. I understood all this already and only came by to help a friend and I found the mentioning of flapping to be confusing until I figured out what he meant. . The rotor is a giant gyroscope. When lift is high on that left, retreating blade, that upward force causes precession ~90⁰ later that lifts the blade as it passes above the tail. That means the rotor disc is now tilted forward, redirecting some lift to the rear - for forward speed. Does this help any.?.

[@mikemybalzich3159]

@@SteveNoskowicz yeah, i understand. what i was confused was if the pitch links directly controlled flapping but i got it now

[@SteveNoskowicz]

@@mikemybalzich3159 Yea Strange that pitch links control blade pitch. (;-o) Author spends too much on flapping rather than the main phenomenon of precession.

[@PilotBlue]

I am a helicopter CFI and I was wondering if there is any way I could access this program that you are using? It would be incredibly helpful to teach new students! I loved this video!! @bzig

[@bzig4929]

The software is actually free. It's called Blender and it's used for animation and 3d modeling. The model I created has property sliders that I coded into blender... things like control positions and and the rotor DOF's. I can see how it would be useful to have a student drag the property sliders around, and see the effect on the aircraft. This would be better than just watching someone else do it on a video. But there's probably more learning, than would be worth the effort, to use the software. In this video, I did a lot of setup, behind the scenes, because the model is not a perfect simulator. I like the idea though and I wonder if I can make this a good enough simulator to take the knowledge of the animation software out of the equation... I'll work on that!

[@PilotBlue]

@@bzig4929 That would be amazing! I'd love to use it!

[@ofdlttwo]

Awesome Did Sikorsky figure out "faze delay"? (gyroscopic precession)

[@juancarloscasabuono6651]

Juan De La Cierva did the job.

[@lewismarcvs2039]

Great animation, but helo books tell that you change pitch 90º before the blade reaches the hiher point......but it looks that in the animation swashplate is perfetly directional with the disc rotor movement..... Thanks

[@bzig4929]

Yes... But the point of the video is to look at where the pitch link connects. The pitch link is about 90 degrees off... So looking at the swashplate gives the impression it's not 90 off, but it really is. The pcl connection point is what determines the phase offset.

[@lewismarcvs2039]

@@bzig4929 Impresive video, I shared in Helicopter Safety. Best explanation I heve seen in many years driving helos.

[@premo8564]

this is the most intense and detailed .blend file i've ever seen. i've used blender for a really long time now (albeit all i do is animate and model) and i wouldnt even know where to begin. fucking impressive dude. how big is the file?

[@bzig4929]

here are some stats on the blend file... 102MB file, 1640 objects, 1.2 million vertices, 1.5 million faces. I did lots and lots of "duplicate linked" to keep keep the cooling fans on my PC happy. Also, I started this effort using motion constraints for everything. This was frustrating because I needed to rebuild the constraints for every scene. I was about to give up, but then I learned drivers. Drivers made this possible at a much lower level of frustration. Drivers have heavier up-front commitment, but once they are created, this was more like a simulation that I could run for different scenarios.

[@424bowz]

more more more plz !!!!

[@orchidahussuhadihcro9862]

You seem to be very knowledgeable about these aircrafts. I've followed several courses aimed at a technician audience, and several times the explanations seemed to be overly simplistic or upsetting for various reasons. It was said that the dissymetry of lift was compensated by allowing the blades to move freely on their hinge. And then the rods would simply pull back the blades to change its angle of attack, and achieve relative balance of lift. Some others more advanced opinions on youtube seem to say that the blade going an upward motion during it's flapping, naturally changes the angle of attack thanks to this vertical motion, and it has nothing to do with mecanical links. Gyroscopic precession : I was told to think of the delay as this gyroscopic effect. But the angle isn't always 90° as it should. An other opinion online, from rc pilots, seem to say that this lag is purely mecanical, and comes from the time it takes for the blade to apply the desired force, after receiving the input, due to its inertia or something like that. I know my message is long, but all of these mysteries obsess me a bit, I would gladly read your own opinion.

[@bzig4929]

You comment on dissymmetry of lift are not contradictory. They flap on their hinge in response to the increase in lift caused on the advancing side, but then the upward flapping motion indeed reduces the angle of attack. So this is a naturally stable system... More speed causes more lift, this causes mare flapping, this reduces lift and the blades seek a stable, happy flapping angle.

[@bzig4929]

Gyroscopic prescesion vs phase delay is a hotly debated topic. Regardless of the name we call it, we know blade pitch change has to occur 90 deg prior to the motion caused by the pitch change. But 90 only applies to machines without any hinge offset. As soon as you move the hinge away from the center of rotation, the offset becomes less than 90. The lead angle is proportional to the ratio of the frequency on the rotating blades to the frequency of flapping. I personally don't think it's correct to call this gyroscopic prescesion, but it doesn't really matter what it's called as long as we understand the input and the response are separated by this angular phase shift.

[@maxshyperspace1622]

May I have the name of the software used in this demo ?

[@bzig4929]

I used Blender for the animation; however, I created the model in Autodesk Fusion. I have a playlist where I go through some of the workflow to create these videos.

[@nickthegriffin]

Iv tried lots of apps but this is the best way to get to sleep no problem out like a light every night 😂

[@jamiltv8048]

Saya dari Indonesia sering memperhatikan apa yang anda berikan,dan saya sudah anggap Anda sebagai guru saya, bagaimana acara saya ingin bertanya langsung,apakah melalui tlp atau langsung ke negara anda

[@bzig4929]

Thanks for watching and commenting. If you want to see other videos just post your questions here and I'll consider making new content.

[@sagebiddi]

Dude...absolute unbridled awesomeness that you have articulated such a complicated system in clear concise terms and I appreciate your candor and the way you spoke gratitude for us digging your content but honestly I don't know why you are as yt is SO filled with gobbledygook and just asinine stuff. I subbed the sec I realized I was about to learn without shitty music or goofball voicing. Much love from Dayton and W.P. Air Force Base

[@hansiyoutube534]

Fantastic video animation. My only suggestion is to also include the concepts of Advance angle (angle between pitch link attachment point on swash plate and blades position of max pitch) as well as Phase angle (angle between swash plate tilt and cyclic input).

[@bzig4929]

Thanks! I didn't know there was a term for the angular offset of the pitch link. I was attempting to describe "advance angle" but it certainly would have been better if I used the term.

[@helicopterovirtual-msfs6254]

Perfeito.

[@FernandoVisserCedrola]

Well done, there is not a phase delay, for the blade its vector of lift is tilted forward as a retreating motion is faster then the hub. Phase delay absence.

[@brodricj3023]

huh?

[@FernandoVisserCedrola]

@@brodricj3023 I don't believe in phase delay, we have to look at the blades, imagine 12 blades being set to the right foward AoA, there is no "delay" phase, the angles are varing from 1 degree to 9 to make the disk fly foward ...

[@brodricj3023]

@@FernandoVisserCedrola Don't complicate it. The rotor blades follow the plane of the swash plate. The helicopter just follows where the rotor disc flies to. Simple.

[@mr_moose4529]

hi, is there a way in which i can get InTouch with you?

[@bzig4929]

[e-mail]

[@cybcx404]

I’m surprised the turbine exhaust doesn’t push the helicopter forward.

[@bzig4929]

If the engineers do it correctly, there is really very little energy left in the exhaust. The power turbine is designed to extract as much useful energy as possible. I've stood near helicopter exhaust and it's out of energy within a few meters of the exit.

[@FatBikeRacer]

great explanation I wanna see more on dynamic rollover.

[@NascimentoConstantino-li2bh]

What s the software name?

[@bzig4929]

Blender... It's free and open source.

[@bzig4929]

Blender can do 3d modeling, in addition to animation, but I create the 3d models in CAD software.

[@deangwin9038]

It’s called phasing

[@janhruska4471]

en.wikipedia.org/wiki/Phase_lag_(rotorcraft)

[@stevereid7140]

This would be a lot easier to follow with a two blade rotor head.

[@bzig4929]

That's a good idea! I didn't do that because there are no (that I'm aware of) 2 bladed fully-articulated rotors, but this is a great suggestion for learning about how the blades are controlled. Or I could just use a teetering 2 blade to explain the concept.

[@stevereid7140]

@@bzig4929 Isn't the Jet Ranger a two bladed helicopter without flybar? I believe many people think the 90 deg input offset is due to gyroscopic precession. I know there is "some" procession, but the helicopter isn't forcing the disk to tilt, the tilting is done by the disk itself due to the pitch changes. The disk is tilting the helicopter, not vice versa. I tell people the 90 deg difference has very little to do with procession, and they argue with me. This is so hard to explain in a comment....

[@bzig4929]

@@stevereid7140 Yes, the jet ranger is a two bladed rotor head. The concept of phase delay would be the same as a fully-articulated rotor; with the nuance you pointed out that the entire hub tilts as opposed to individual blades. I hear you on "hard to explain with a comment." It's hard in these videos also... I think I get it right and then I read the comments and realize how I could have explained it better. Even though I could show the 2-blade teetering phase delay, I still think building a fictitious 2-blade articulated rotor would be a cool learning air for understanding of how the flapping and lead-lag hinges work. oh... even better, I can build a 4 blade, show the entire hub and hide 2 of the blades for clarity.

[@rotorway133]

No F way. Each blade is individually controlled by the swashplate tilt via the pitch horns. Cyclic does not tilt the whole rotor system. At least not on my Rotorway 2 blade

[@bzig4929]

I hear what you're saying, but the net effect on the tilt of the tip path plane is to move in the direction the cyclic is displaced. If you nove the controls on the ground you see the TPP move in the same direction as the stick... But I get what you're saying that the cyclic doesn't directly control this.

[@rotorway133]

@@bzig4929 you are correct for the ground part from the inherit static pressures or forces on the swahplate and push rods on the system but that is absolutly not how a helicopter flies or changes direction in flight. The whole purpose of the swashplate is to change the pitch of individual blades as they go around changing lift thus (in apprearance) tilting the rotor in the direction you want to go.....but not all true. Its very complex indeed

[@tedbenz8493]

👍👍👍👍👍👍

[@qwadebryson6165]

Angle of incidence

[@bzig4929]

True. But it's related to aoa by math.

[@qwadebryson6165]

@@bzig4929 I love your content, I'm a current Blackhawk instructor pilot for the Army. Keep up the good work

[@trajcepiperkoski7492]

This can be avoided with using 3 blades

[@deangwin9038]

You’re obviously not a helicopter pilot!

[@quevineuxcrougniard2985]

C'est dommage qu'il nous parle du nez avec un affreux jargon imbitable car ce devrait être intéressant !

[@MohamadRizalNauman]

Wrong ubdont understand not like that.

[@bzig4929]

Well... Thanks for watching!

[@edmoregonde]

WONDERFUL it's now come to sense am wondering how and how this system work

[@maxshyperspace1622]

You explained the tilt of the rotor disk well, but how does it cause the helicopter body(and the mast) to tilt ?

[@bzig4929]

great question! It's because of the hinge offset in the rotor system. This allows the forces on the blades to create a couple (two opposing forces offset by a moment arm) and this applies a bending moment to the mast to tilt the aircraft. Although helicopters such as Robinson and the Bell 206 fly without any hing offset in the rotor system... in the case, the fuselage just pendulums below the rotor system and the rotor disk tilt is all that allows the aircraft to fly forward.

[@constpegasus]

How do the two swash plates attach to each other. Share bearings?

[@bzig4929]

Yes, there are bearings between the two. Grease and lubrication are very important to the function of the swashplate. Many helicopters have bearing monitoring systems to give real time alerts if the bearings start to fail in flight.

[@constpegasus]

@@bzig4929 Thank you.