[Music] [Music] welcome back the humblest ten minutes some Jacob and the subject of this video is 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're aggressive of aggressively maneuvering a helicopter so not your typical traffic pattern stuff now the law of conservation of angular momentum states that angular momentum of a rotating body will remain constant unless external forces are applied now in essence it's a variation of Newton's law of motion that states that an object in motion will remain in motion unless acted upon by an outside force only here it's applied to a rotating body simply put the rotor blades want to maintain their momentum they want to conserve their angular momentum now conservation of angular momentum is sometimes used synonymously not honestly with Coriolis force or the Coriolis effect which deals with a tendency of a rotating body to increase in velocity as the center of gravity gets closer to the axis of rotation now in a nutshell your conservation of angular momentum is used to explain the Coriolis effect but for the purposes of the helicopter and this lesson they'll just be used interchangeably so how does all this physics stuff apply to me flying a helicopter well I'm glad you asked imagine you imagine you're conducting flight maneuvers that increase and decrease the G loading on your rotor system you know you're really yanking and banking putting some aggressive maneuvers on a helicopter well your rotor system is going to start off looking like this so if you have your your mass attached to your hub and then your red or blade coming off typical maneuvering flight you really don't have much of a coning angle but as you increase the G loading your rotor system is going to start to cone so what does that mean that means the coning angle is going to start to form and it's going to look something like this obviously it's on this side as well but for simplicity just drawing it on one side so the steps for this very first thing you're going to experience for conservation of angular momentum is G loading is going to start increasing your coning and that's just this motion right here as it starts to cone up now the rotor begins to cone when the g-forces increase and vice-versa so as you get are you shed some of those g-forces it wants to reduce them that coding angle now as this is going on the blade diameter is going to shrink like this total area is starting to shrink as the blades cone and while it's doing that the center of gravity or the the center of mass is going to shift closer to the axis of rotation so if you have center of gravity say right here on the blade as it starts to cone up now you're looking somewhere about right here and if we were to just draw these lines straight down you can see that as the blade starts to cone up this distance between a and B is starting to decrease so the area is reducing the center of gravity shifting closer to the axis of rotation now because of this your rotor rpm is going to decrease so back to my steps right here the center of gravity slept slash your center of mass shifts inwards and now this causes your rotor rpm to increase all right now the easiest analogy here to see this is imagine a figure skater spinning in circles now as the skaters arms come closer to her body she tends to speed up her rpms increase and as she tends to extend her arms that rpm or her rotational velocity being begins to slow down now both the figure skater and your rotor blades have angular momentum while spinning they have that momentum in a rotational direction that they're trying to maintain and now when the center of gravity or the location of mass changes that rotational velocity changes also another way to think about this is imagine a racecar going around a track so if we have a track right here we have a racecar and he's going this way around the track it's say 60 miles per hour let's say this track is one mile so it's 60 miles an hour he can make one revolution or one rpm and 60-seconds now if we were to have this racecar driver cut inside to an inner loop in the track say he transitions to here and pardon the drawing here now he transitions to this inner loop he's still maintaining the same 60 miles per hour but now his diameter or his his distance around the track is going to be shorter but the momentum is remaining the same so instead of one revolution in 60 seconds maybe his revolution has now cut down to 50 seconds so he's maintaining the same momentum the same conservation of angular momentum going around the track but now he has a shorter distance and so it's increasing his rounds per minute from 60 seconds down to 50 seconds so he can make more rpms than when he maintained on the outside of the track but the engine control system of our helicopter is doing pretty much the same thing it's constantly trying to maintain rotor rpm so when they see the rotor rpm tend to increase due to the coning what does the engine control unit do what sees the rotor climbing without it needing to increase or without it needing to continue fuel at the same amount of fuel flowing to the engine so it backs off some of the fuel flow because it says Oh aerodynamically these rotors are just you know they're able to maintain their rpm without me needing dump all this fuel so it kind of steps back it's fuel to the engine but when the rotor starts to unload now it's slowing down rpm and the engine says oh crap my rotor is slowing down what'd I do dump a bunch of fuel into the engine to speed this rpm back up so the engine control unit is constantly chasing this rotor rpm to try to manage it keeping in mind that as it has changes in its G loading and shifting of the center of gravity inward that rotor rpm is constantly accelerating decelerating now just because it's trying to maintain its momentum now because of lit of this if you aren't aware of these rapid rotor fluctuations resulting from the Coriolis force you can have some negative effects on the helicopter and by that I mean things like over speeding a rotor so if this happens too quickly you're potentially over speeding a rotor outside of your aircraft limitations you could potentially under speed of rotor if this slows down and the engines aren't able to keep up in time or if this happens fast enough and your engines are right there with it your engine could be dumping a lot of fuel to maintain or your engine control unit could be dumping a lot of fuel into the engine to maintain the RPM and potentially exceeding an aircraft torque limit in essence over torquing the aircraft trying to maintain this this rotor now the over torquing can occur rapidly during rapid unloading of the G's and the rotor system so typically when you're flying around the quicker and more aggressive than maneuver the greater the torque fluctuations are going to be but that wraps up conservation of angular momentum / Coriolis force the biggest takeaway so that the rotor always wants to maintain its momentum and that as the rotor cones do to G loading it has a tendency to speed up and vice-versa now this can cause limitations in the aircraft whether that be over speed under speed or exceeding a torque lemon now this can cause a lot of issues with some newer pilots because they're not really sure how to predict these so biggest thing out there is to understand where these shifts and angular momentum these shifts and rotor rpm can come from so that you can better be ready for it with collective application prior to exceeding some kind of limit such as these but once again this concludes the video thanks for watching be sure to hit like and subscribe below once again I'm Jacob and this has been helicopter lessons in ten minutes [Music] you