YellowJacketsRC
70cc twin V2
Yes I understand P-Factor...
Also, that wheel is turning around the string because the weight of the wheel is in essence placing a force onto the axle. If you were to put two strings hanging down so that each end of the axle were supported with the wheel in the middle, then the wheel would spin around its axle but would not precess. That is my point here. The precession only occurs when a force pushes on the axle in an attempt to change the plane that the wheel is spinning in. In the video that force is gravity.
On an aeroplane, the propellor is held up by the axle which is connected to the motor. So there is no weight to act upon the axle and thereby cause precession. Only when a rudder or elevator puts a force onto the spinning prop does precession occur.
Let's look at it another way. If the axle of that bicycle wheel were a bit longer, it could be attached to a piece of wood. Then you could take that piece of wood and stick in onto another axle which is standing vertical from the ground. So now you have a piece of wood that is sitting no this vertical axis, and the wood can actually spin around the vertical axle. When you spin the bike wheel up in this case, no precession will occur, because there is no affect of gravity on the axle going into the bike wheel because it is completely supported by the block of wood. You could cause the wheel to turn around the vertical axle by pushing it, but it will not do it on its own.
Please explain how this is wrong if it is, cause I no get it.
Also, that wheel is turning around the string because the weight of the wheel is in essence placing a force onto the axle. If you were to put two strings hanging down so that each end of the axle were supported with the wheel in the middle, then the wheel would spin around its axle but would not precess. That is my point here. The precession only occurs when a force pushes on the axle in an attempt to change the plane that the wheel is spinning in. In the video that force is gravity.
On an aeroplane, the propellor is held up by the axle which is connected to the motor. So there is no weight to act upon the axle and thereby cause precession. Only when a rudder or elevator puts a force onto the spinning prop does precession occur.
Let's look at it another way. If the axle of that bicycle wheel were a bit longer, it could be attached to a piece of wood. Then you could take that piece of wood and stick in onto another axle which is standing vertical from the ground. So now you have a piece of wood that is sitting no this vertical axis, and the wood can actually spin around the vertical axle. When you spin the bike wheel up in this case, no precession will occur, because there is no affect of gravity on the axle going into the bike wheel because it is completely supported by the block of wood. You could cause the wheel to turn around the vertical axle by pushing it, but it will not do it on its own.
Please explain how this is wrong if it is, cause I no get it.
Aeroplayin
70cc twin V2
Your missing the point. Forget about the weight, and forget about the rotation around the string once the wheel is perpendicular to the floor because I'm not talking about the "torque chasing the angular momentum" here (gyroscopic propulsion).... the wheel would spin flat and horizontal to the floor if there were no angular momentum.
So when the wheel hangs from the string and is horizontal to the floor, consider the wheel the propeller on a plane facing straight down to the ground. As the wheel rotation speed increases, the difference between torque and angular momentum applies force to the wheel axle that is 90 degrees from the string. So if the plane is still facing down to the ground, the precession wants to move the rotating disk of the prop 90 degrees, which translates to left yaw.
The thing you are missing is the first frames of the video where the wheel is hanging from the sting and not rotating. The difference between that position, and perpendicular position of the rotating wheel, is supported by angular momentum. In an airplane, this force yaws the plane to the left more and more as the speed of the rotating propeller increases. This is one of the other reasons why, in a hover, and with no increases AoA, when you goose the throttle, the plane jerks to the left.
I'll find another video to explain this further.
So when the wheel hangs from the string and is horizontal to the floor, consider the wheel the propeller on a plane facing straight down to the ground. As the wheel rotation speed increases, the difference between torque and angular momentum applies force to the wheel axle that is 90 degrees from the string. So if the plane is still facing down to the ground, the precession wants to move the rotating disk of the prop 90 degrees, which translates to left yaw.
The thing you are missing is the first frames of the video where the wheel is hanging from the sting and not rotating. The difference between that position, and perpendicular position of the rotating wheel, is supported by angular momentum. In an airplane, this force yaws the plane to the left more and more as the speed of the rotating propeller increases. This is one of the other reasons why, in a hover, and with no increases AoA, when you goose the throttle, the plane jerks to the left.
I'll find another video to explain this further.
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alawson999
70cc twin V2
I have become completely confused.
Guess I should keep using rudder to hold the nose up in a slow roll.
I don't mind
Guess I should keep using rudder to hold the nose up in a slow roll.
I don't mind
Aeroplayin
70cc twin V2
Consider the shaft in this video as the motor/engine shaft and the weight as the propeller. Consider the shaft is pointing striaght down to the ground, so that the attitude of the plane would be 180 degrees from straight up.
The angular momentum is applying a supporting force vector perpendicular to the shaft which enables this nancy-boy to support the 40 pound weight perpendicular to the ground holding the other end of the shaft with no weight. The gyroscopic precession rotates the shaft around the guy and is not the vector I'm talking about, and neither is the torque vector.
https://www.youtube.com/watch?v=GeyDf4ooPdo
The angular momentum is applying a supporting force vector perpendicular to the shaft which enables this nancy-boy to support the 40 pound weight perpendicular to the ground holding the other end of the shaft with no weight. The gyroscopic precession rotates the shaft around the guy and is not the vector I'm talking about, and neither is the torque vector.
https://www.youtube.com/watch?v=GeyDf4ooPdo
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Aeroplayin
70cc twin V2
Actually, it's getting physical in here... this is all pure and simple physics 101.
I’m not sure I can explain this further in a thread like this because there are too many force vectors influencing the “Change in Angular Momentum”, but here’s the last stab:
We have gravity torque, which has its own precession
We have torque due to the weight of the system, which has its own precession
We have the Angular Momentum, which is in the direction along the rotating axis
We have the direction the axis will precess as a result of the angular momentum vector and the torque vector.
With a propeller rotating in a normal direction, this difference (Delta L) is perpendicular to the rotating shaft, and to the left.
For this to happen, we don’t need to change AoA or have a rotating body that has a camber or a pitch.
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Enterprise
150cc
When you look at a few General Aviation airplanes like a Cessna 172, you will see the vertical stab offset as well to compensate for the prop forces. The forces acting on the airplane become even more critical when you deal with two prop on a twin. You can ellimate some of this with a counter rotating dual props like they are doing in F3P, but that does not get away from the gyro effect of having two spinning masses being deflected out of their rotatational plane.
YellowJacketsRC
70cc twin V2
Ok, let me ask another way. What happens when Funny Cars drag race? At the beginning of the race, the wheel accelerate at incredible speeds. If precession were acting upon them, then why doesn't the car veer way off course as the wheels spin and slip over the asphalt? SHouldn't the back end of the car slide to the left or right? Or does the fact that you have two wheels at either end of the axle cancel out the precession?
If so, then what about a motorcycle? When you pop the clutch on a Bike, should the spinning wheel slip over the ground and cause the tail to swing to the right?
If so, then what about a motorcycle? When you pop the clutch on a Bike, should the spinning wheel slip over the ground and cause the tail to swing to the right?
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Aeroplayin
70cc twin V2
There are actually a few things going on here again, so let’s see if I can explain in a few sentences what it took me an entire 4 credit college course to understand, because there are different vectors involved here. I'm thinking that maybe the better way to illustrate this is by looking at the system in full rotation, then trying to change the direction, instead of trying to illustrate the relationship of forces going into creating the rotating system.
The reason why it is so easy to balance on a bicycle when the wheels are rotating as opposed to trying to balance on it while sitting still, is a result of a few of these rotational vectors and inertia. This is similar to why a gyro on a satellite keeps it from wobbling, but it also has to do with the fact that trying to make a rotating object move in a completely different direction from how it is initially rotating, takes force. So once the wheels are spinning at a high velocity, changing the rotational direction or angle means you must add more energy to the system. So once the Funny Car wheels are turning and facing in one direction, they will tend to stay in that direction. The same reason is why you lean on a motorcycle to turn, instead of steering with the handlebars -- which would change the direction of one of the spinning wheels which is something the wheel will resist. But according to Delta L above (change in angular momentum) a monocycle (one wheel only) will try to precess around the seat in accordance with the right hand rule – where you wrap your fingers of your right hand around the shaft in the direction of rotation and your thumb points in the direction of Angular Momentum L. The difference between the direction and force of angular momentum and the direction and force of the torque vector is the force that precesses the shaft to the left.
In an airplane, the angular momentum and torque are acting together to create a resulting force vector. If you try to turn the plane in any direction, the prop still wants to maintain the same rotation and attitude. So in a KE spin, where you are forcing the plane to rotate in a way that is counter to inertia and the forces being applied by torque and angular momentum, you are forcing the prop and motor shaft to go in a direction it does not want to, and it will resist. Forcing the prop and shaft to change directional attitude in an electrical motor setup can cause magnets to collide without support and bearings that can handle the input force, etc.
Some planes can only KE spin under full throttle because of the force needed to do this. Some effort also is needed to do rolling harriers in different directions because the force is different in one direction than in another.
The reason why it is so easy to balance on a bicycle when the wheels are rotating as opposed to trying to balance on it while sitting still, is a result of a few of these rotational vectors and inertia. This is similar to why a gyro on a satellite keeps it from wobbling, but it also has to do with the fact that trying to make a rotating object move in a completely different direction from how it is initially rotating, takes force. So once the wheels are spinning at a high velocity, changing the rotational direction or angle means you must add more energy to the system. So once the Funny Car wheels are turning and facing in one direction, they will tend to stay in that direction. The same reason is why you lean on a motorcycle to turn, instead of steering with the handlebars -- which would change the direction of one of the spinning wheels which is something the wheel will resist. But according to Delta L above (change in angular momentum) a monocycle (one wheel only) will try to precess around the seat in accordance with the right hand rule – where you wrap your fingers of your right hand around the shaft in the direction of rotation and your thumb points in the direction of Angular Momentum L. The difference between the direction and force of angular momentum and the direction and force of the torque vector is the force that precesses the shaft to the left.
In an airplane, the angular momentum and torque are acting together to create a resulting force vector. If you try to turn the plane in any direction, the prop still wants to maintain the same rotation and attitude. So in a KE spin, where you are forcing the plane to rotate in a way that is counter to inertia and the forces being applied by torque and angular momentum, you are forcing the prop and motor shaft to go in a direction it does not want to, and it will resist. Forcing the prop and shaft to change directional attitude in an electrical motor setup can cause magnets to collide without support and bearings that can handle the input force, etc.
Some planes can only KE spin under full throttle because of the force needed to do this. Some effort also is needed to do rolling harriers in different directions because the force is different in one direction than in another.
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