Conservation of Angular Momentum / Coriolis Force in Helicopters

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Once again, I'm Jacob and this video's topic covers the Law of Conservation of Angular Momentum and how it applies to helicopters, more specifically maneuvering flight. I say maneuvering flight because you typically will not experience the effects of this unless you are aggressively maneuvering a helicopter. This isn't your typical traffic pattern stuff.
The Law of Conservation of Angular Momentum states that Angular Momentum of a rotating body will remain constant unless external forces are applied. In essence it's a variation of one of Newton's law that states that an object in motion will remain in motion unless acted upon by an outside force. Only here it is applied to a rotating body. Simply put, the rotor blades want tot maintain their momentum. Conservation of Angular Momentum is sometimes used synonymously with Coriolis Force/Effect which deals with the tendency of rotating bodies to increase in velocity as the center of mass (COM) or Center of Gravity (CG) shifts closer to the axis of rotation. In a nutshell, Conservation of Angular Momentum is used to explain the Coriolis Effect. But for the purposes of helicopter flying and this lesson, they are used interchangeably.
So how does all the physics stuff apply to flying a helicopter? I'm glad you asked. Imagine you're conducting flight maneuvers that increase and decrease the G-loading on your rotor system. As the helicopter G- loads, the rotor begins to cone. Because of this the blade diameter shrinks and the CG/COM shifts closer to the axis of rotation. Because of this the rotor RPM increases.
The easiest analogy to use to explain this is a figure skater spinning in a circle. As the skater's arms come closer to her body she speeds up. Her rotations per minute increases. Both the figure skater and your rotor blades have Angular Momentum while spinning. They want to maintain this momentum and when the center of gravity / center of mass changes, rotational velocity changes. Another way to think about it is a race car going around a track. If the car is traveling 60 mph and the trac is 1 mile, it takes 60 seconds to complete a lap. Now let's say the driver takes an inner loop while still maintaining 60 mph. The driver's momentum remains the same but now travels a shorter distance. So the momentum has maintained or been "conserved." But the RPM has increased. Now instead of 1 revolution in 60 seconds it may be something like 50 seconds. The time it takes to make 1 full revolutions has decreased.
But the engine control units of our helicopter want to maintain a specific rotor RPM. So when they see the rotor RPM increase, they reduce fuel flow to maintain the desired RPM. but when the rotor unloads the G forces and coning reduces, the rotor RPM decreases. So what do the engine control units do? They increase fuel flow to the engines to arrest this decreasing rotor RPM and speed the rotor back up. The engine control system that is supposed to maintain rotor RPM is always reacting to changes in rotor speed from aerodynamic forces.
Because of this, if you aren't aware if rapid rotor fluctuations resulting from Coriolis forces, you could have some negative effects while flying. These include:
1. Rotor overspeed: as the rotor cones the RPM can increase drastically
2. Rotor underspeed: as the rotor coning subsides the RPM can reduce drastically
3. Exceed Aircraft Torque Limit: in an effort to stop a rotor from underspeeding your engine control unit could cause your engines to produce more power than your drive system can handle and result in an overtorque.
Typically the quicker and more aggressive the maneuver, the greater the fluctuations in rotor RPM and torque.
That wraps up The Law of Conservation of Angular Momentum/ Coriolis Forces! The biggest takeaways are that the rotor always wants to maintain its momentum and that as the rotor canes due to G loading, it has a tendency if speed up and vice versa. These fluctuations can result in aircraft limitations being exceeded fairly rapidly. Thanks for watching! Don't forget to hit like and subscribe below. Be sure to like us on Facebook as well. As always, safe flying!
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

[@shockerthreeone]

At 3:55 you said "decrease" where i think you meant "Increase". Love your videos though!

[@helicopterlessonsin10minut10]

shockerthreeone. You're right. I didn't catch that when editing. Looks like I say it correctly when writing out point #4. Sorry for any confusion.

[@shockerthreeone]

No worries brother. I'm a National Guard UH-60 SP/IE and I use your videos for my own personal study. Gotta keep the sword sharp! Thanks for your time and effort with these.

[@harrylee591]

Video suggestion: why does torque spike when turning right on a counter clockwise rotor system? Really liking the videos!!

[@gensyed]

@@harrylee591 May I? A counter clockwise rotor system in situation as suggested will cause a precession resulting in a force that torques the rotor forward and down. The reverse will happen on clockwise rotor system. I don;t know how this affects the lift or engine performance. Hope this gave some insights.

[@VitorMoura]

You're quite good at drawing, I doubt I'd be able to draw those diagrams and straight lines like you, thanks!

[@cmtedan]

Superclass mate! Greetings from Brazil!

[@leathelhit]

fist of all thanks for taking time recording the video and making the people understand. I have few questions; 1. Coriolis effect, as it is described almost every where else, is related to water/air movement towards east in northern and towards west in southern hemisphere due to earth rotation. How this is applied/related to rotatory aerodynamics, particularly in helicopters? for which I'm here to seek the application of Coriolis effect. 2. conservation of angular momentum, spinning speed remains constant unless acted upon by some external force (torque). What is link between conservation of angular momentum and Coriolis effect? How do they relate? In your video, the main point I got is rotational speed changes as the CM of rotating body comes closer or goes far from its rotational axis, that's perfectly fine and understandable. Now, is that what you are calling Coriolis effect? shifting of CM towards or outwards from axis of rotation? As the rotor rotates, with positive blade angle, it produces lift, heli goes up in the air. Moving against the centrifugal force (trying to extend blades straight in the direction of rotation) the blades tilt upward instead staying parallel to the ground because lift force taking them up and at the same time centrifugal force pulling them outwards which results conning in the rotor. This conning causes to move CM of blades towards their axis of rotation and as a result rotor speeds up more with same power being delivered from the engine. Am I getting this correct? So, now at which point where the Coriolis effect coming in here? Or to what you call Coriolis effect? I am very thankful if you take time and help me understand the topic. I have read at many places, all they talk about theory stuff but no where I got the opportunity to understand how angular momentum/coriolis effects actually at play in the rotors. Looking forward to your kind response.

[@Ty-vk5do]

Coriolis is an important factor for heli blade flapping or coning as your blade mass is getting closer to the center of rotation and will want to speed up causing stresses on the system if its not fully articulated If you let the blades hunt it will take some of the force off the rotor head.

[@leathelhit]

@jim thanks for comments. My query still there. Waiting video maker to address my question.

[@donramown2495]

@@leathelhit +1

[@antoinecamus51]

Thanks Jacob, another​ good one

[@ahmadbems]

Great video again. Thank you jacob👍🏻

[@chrisbutler4413]

Great videos and easy to understand. I was wondering if you had time to discuss transient torque?

[@ONCEuponAtime999]

could u make a video on climbing and descending rate and angle please? and endurance and range too ;)

[@memofrf]

So much to learn. Thank you.

[@ahmadtheaviationlover1937]

Awesome explanation

[@jeremygardner1968]

Do you mean Coriolis Effect? Coriolis Force is applicable when talking about what happens to global wind patterns as the earth rotates.

[@ISMERETTENGER]

Jake, again, do not use equivalently the Conservation of Angular Momentum and the Coriolis Force. They are two totally different things. The Conservation of Angular Momentum is a law in Physics. It is NOT a physical quantity, it does not have a unit of measure. The Angular Momentum is a physical quantity and it has a unit of measure . The Coriolis Force IS also a physical quantity and it has a different unit of measure from the unit of measure of the Angular Momentum. Both the Angular Momentum and the Coriolis Force are vectors, that is they have a direction addition to their size. The direction of the Angular momentum of the blade in a counter-rotating helicopter is determined by the right-hand rule and it is pointing upwards parallel with the mast and its size is proportional to the blade rotational velocity. The Coriolis Force acting on the blade is vertical to the mast and has the opposite direction to the velocity of the blade. In a articulated system the Coriolis Force pushes back the advancing blade - legging - and the size of this force is proportional to the up-and-down flapping velocity of the blade. Thanks for the video.

[@kamalprajapat5015]

Thank you 👍

[@bajakitesurfer]

Excellent Excellent Brief 👍🏼👍🏼👍🏼

[@governmentisslavery]

Misspoke at 3:54, said RPM would decrease, but actually will increase as you state later.

[@davidwallace5738]

Thanks again sir.

[@n00bslayherttv92]

Amazing

[@davidwallace5738]

Sir, can you please explain what the results of over torquing the rotor system and what yo look for if the situation occurs. Thanks.

[@theeatonskbunk]

Over torquing subjects the drive train to stress/strain which exceeds the design limits. This can quickly or eventually result in component failure depending on the severity. In a helicopter with a torque gauge it will indicate excess torque is being produced. An engine monitor will log the event and the mechanic will charge for the inspection/repair/ replacement parts. Potentially several hundred thousand dollars in a turbine powered machine. In a piston powered machine the manifold pressure gauge will indicate excess power being produced as a result of the governor or you twisting the throttle.

[@tex2952]

The analogy I was always given for this was an ice skater extending or retracting their arms and legs. Not criticizing at all just commenting. Great video thanx!

[@mariojorgepiresdasilva9956]

Good vídeo 👍🏾🚁

[@jaafarmahmood6430]

amazingly useful videos sir. .. i would like to ask you if you can explain in detail (aerodynamically) the effect on torque when applying aft cyclic .

[@Ryman180]

Awesome videos, just waiting for the merch that says "Yanking and banking" now.

[@cassioalves7561]

Great Video ! I saw all your videos and I am looking for more ! I am looking to see more related videos if you can tell me some interesting channels would be great !

[@helicopterlessonsin10minut10]

Cássio Alves. Thanks! I'd recommend also checking out the channel Helicopter Online Ground School. They've got a lot of really great stuff on that channel as well.

[@axelram5510]

I love when you talk physics lol lol lol.😂

[@astelraimedia4149]

So is it always the Coriolis effect that causes blade flap then?

[@Bendigo1]

Blade flap??? As in the changing aoa of the blade?

[@kyneticking6647]

What is g loading

[@bryanblaze4085]

Up

[@eulinpetit-woodyear6816]

This video needs to be taken down as it is filled with inaccuracies.