Understability Really Two Things?

[DG_player]

The wheel is not freely spinning, unless it's spinning out.

Imagine I jump off a ramp into space and the wheel detaches from my bike, is it suddenly going to stop?

 

[sidewinder22]

Imagine I jump off a ramp into space and the wheel detaches from my bike, is it suddenly going to stop?

The torques stop, but the rubber wheel will spin and have some rebounding after un-compressing from the ground. A bike wheel is also spun more intrinsically while a disc is initially spun orbit-ally which will have a larger rebound from warping.

 

[DG_player]

The torques stop, but the rubber wheel will spin and have some rebounding after un-compressing from the ground. A bike wheel is also spun more intrinsically while a disc is initially spun orbit-ally which will have a larger rebound from warping.

Well at any rate you're wrong. A rigid body's motion can always be described as a linear motion of the center of mass and a rotation around the center of mass. It's an important concept for doing a lot physics.

For instance you can simply calculate the trajectory of a disc. Say you have a 20 cm disc that you are throwing very simply, by rotating around a single axis of your body, like a discus thrower. Let's assume your arm is 1m long and your rotating at 20 radians per second. How fast is the disc going after you throw it and how fast is it spinning. The COM would be at 1.1M, so it's a real simple calculation, 1.1M (radius) * 20rad/s (spin) = 22 m/s (linear velocity). How fast is it spinning. The outside edge of the disc would be going at 1.2 * 20rad/s = 24 m/s and the inside edge at 1.0M * 20 rad/s = 20 m/s. That works out to a the rim moving around the center at +2 on the outside edge and -2 on the inside edge. If we work the velocity equation backwards, 2m/s / 0.1m gives us 20 radians/s.

You'll notice the spin rate of the thrown object is the exact same as the spin of your body. This will always hold true, regardless of the size of the object or the distance you hold it from your body. This has important implications when it comes to throwing a disc. Let's say for instance you decided to throw the disc the same speed, but instead held it closer to your body and rotated faster. You could still get the 22 m/s release velocity by bending your arm and having the COM at 0.55 m and spinning at 40 rad/s. However the disc would be spinning twice as fast, 40 rad/s.

 

[sidewinder22]

That's all great in theory if the disc was a rigid body. Your calculation is going to be wrong if you don't account for warping. Do you disagree with R D Lorenz?

 

[Doofenshmirtz]

http://www.innovadiscs.com/discs/fairway-drivers/speed-7/teebird.htmlYou will notice the rotating gyroscope precesses and wobbles around in a cone shape like the disc images in the Innova site. When the force is applied downward the gyro nutates/wobbles in the direction of the spin downward into the cone. When the force is applied upward the gyro nutates/wobbles in the direction opposite of the spin upward into a cone. This is the same effect as the retrograde precession we consider turn vs fade when the COP is on the front or back end of the disc flipping the direction of precession mid during flight, and the wobble can flip direction as well during flight.

This is wrong. You know that a flying disc doesn't have its spin axis tied to the ground by gravity don't you? Disc wobble isn't the product of nutation, it is a product of having it's axis knocked off a right angle to it's flight plate. Like so:

 

[sidewinder22]

This is wrong. You know that a flying disc doesn't have its spin axis tied to the ground by gravity don't you? Disc wobble isn't the product of nutation, it is a product of having it's axis knocked off a right angle to it's flight plate. Like so:

That's why I linked the Innova wobbler. I only used the gryo image to show direction of wobble.

 

[Doofenshmirtz]

That's why I linked the Innova wobbler. I only used the gryo image to show direction of wobble.

Okay. I couldn't get the youtube video at work.

 

[sidewinder22]

Okay. I couldn't get the youtube video at work.

Youtube? I think it's java.

 

[DG_player]

That's all great in theory if the disc was a rigid body. Your calculation is going to be wrong if you don't account for warping. Do you disagree with R D Lorenz?

For all intents and purposes it's a rigid body. Sure it's not a purely rigid body in the ideal physics sense, but it's close enough for analytical purposes.

I'm not sure what you think Lorenz is saying. In the section where's he's talking about nutation in the first few seconds of flight he's referring to torque free precession. This is caused by the initial spin axis being off of the symmetrical max inertia axis (spinning flat). It is still spinning around the COM even though it's wobbling. The angular momentum is still pointing in the same direction. The only thing special is that the rotation axis precesses around the spin axis. It's a necessary condition in order to satisfy the conservation of momentum when spinning around an asymmetric axis.

Here is a video that will help illustrate it (I couldn't find one of a disc or plate):

https://www.youtube.com/watch?v=PDLXVSkDFVk

 

[sidewinder22]

The wobble causes the disc to move left or right as the airspeed torques it.

 

[HyzerUniBomber]

https://www.youtube.com/watch?v=N92FYHHT1qM&feature=youtu.be&t=2749

45:51 if it doesn't jump you in.

Fantastic visual to help with understanding the gyroscopic physics of spin angular momentum when torque is added (which is what air does to the disc when thrown).

The more torque he adds, the faster the spin agular momentum chases the torque. Makes me think that the more wobbley a disc is, the more the wind affects it (creating more torque to make more disc turn).

 

[sidewinder22]

Wobble is changing the effective AoA causing gyro precessional rolling moments.
Wobble is also aerodynamically sailing the disc more left or right depending on the direction of the wobble into it's airspeed.

 

[sidewinder22]

Hmmm....

The three physical factors that affect a disc's performance are a combination of aerodynamics, linear momentum, and angular momentum. These three physical properties occur simultaneously to allow a disc to stay in flight.

Linear momentum is a disc's ability to maintain a forward traveling energy as a result of its mass and traveling velocity. This linear momentum is coupled with aerodynamics to allow the disc to stay in flight by means of Bernoulli's principle. Angular momentum, also known as the gyroscopic effect, is the third aspect of disc flight that is the result of a disc's rotating mass which keeps it spinning on its axis of rotation so that the disc will be aerodynamically supported in flight.

The amount of angular momentum is determined by a disc's moment of inertia. Increasing a disc's moment of inertia will increase its angular momentum and allow it to be maintained longer throughout its flight. The process of transferring mass away from the axis of rotation increases the disc's moment of inertia at parabolic proportions.

Since linear and angular momentum and aerodynamics act upon each other simultaneously, an enhanced gyroscopic effect will improve all aspects of disc flight. Increased angular momentum of a disc in flight will allow the disc to stay on its rotational axis for a longer period of time, which means that its aerodynamic properties will be better exhibited for a longer period of time.

Phases of Flight
Gyro Fade - Forward fade at spin down.
Aerodynamic Fade - Disc pulls of out turn as spin decreases.
Aerodynamic Turn - Aerodynamic profile turns the disc during the late high-speed phase
Gryo Push - Inertia carries the disc forward during the initial high speed phase

 

[TheBeardedFatGuy]

The wobble causes the disc to move left or right as the airspeed torques it.

Airspeed is a measurement of air speed. It doesn't torque anything. That's like saying cheetah speed eats gazelles. Also, torque promotes rotation, it doesn't inhibit it, and I don't see how air anything promotes rotation, unless you're talking pinwheels. Air 'resistance', for example, can act against the torque already present, but I don't see how it can promote it.

My two cents on wobble is that it causes diametrically opposite points on a disc's rim (highest and lowest) to alternately turn into and then away from the onrushing air as the disc moves through it. The result is air brake up, air brake down, air brake up, air brake down. And that's not even taking into account the disastrous airfoil this makes during all degrees of wobbled rotation. All told, the effect is to slow or stall the forward progression. It can't help but slow rotation, too, I suppose - friction is friction. If there's any validity at all to wobble contributing to left or right movement it would be because the resistance caused by the high and low points is greater on the left (RHBH) because they're rotating into the wind, than on the right because they're rotating away from the wind. Unless you can make a case for deflection in addition to drag, the effect must be to turn the disc to the left (again, RHBH) because, like a tank with a bad tread, resistance pulls a moving object in the direction towards the side with greater drag. Same thing if you try to walk a straight line dragging a cinder block tied to your left ankle - it'll turn you to the left.

 

[vdWcontact]

Airspeed is a measurement of air speed. It doesn't torque anything. That's like saying cheetah speed eats gazelles. Also, torque promotes rotation, it doesn't inhibit it, and I don't see how air anything promotes rotation, unless you're talking pinwheels. Air 'resistance', for example, can act against the torque already present, but I don't see how it can promote it.

My two cents on wobble is that it causes diametrically opposite points on a disc's rim (highest and lowest) to alternately turn into and then away from the onrushing air as the disc moves through it. The result is air brake up, air brake down, air brake up, air brake down. And that's not even taking into account the disastrous airfoil this makes during all degrees of wobbled rotation. All told, the effect is to slow or stall the forward progression. It can't help but slow rotation, too, I suppose - friction is friction. If there's any validity at all to wobble contributing to left or right movement it would be because the resistance caused by the high and low points is greater on the left (RHBH) because they're rotating into the wind, than on the right because they're rotating away from the wind. Unless you can make a case for deflection in addition to drag, the effect must be to turn the disc to the left (again, RHBH) because, like a tank with a bad tread, resistance pulls a moving object in the direction towards the side with greater drag. Same thing if you try to walk a straight line dragging a cinder block tied to your left ankle - it'll turn you to the left.

I have always thought "high speed turn" is a result of high angular velocity. When spinning at high speeds the relative velocity of the left side of the disc and the right side of the disc are drastically different, with the left side being faster and the right side being slower. I always thought the higher velocity relative to the air was, the more lift you would generate, which is why discs turn to the right when initially thrown (this is all for RHBH). I have noticed my own OAT makes things turn to the right way more than they should, and always assumed it's because wobble enhances the effects of high angular velocity.

Is this totally asinine?

 

[Aim For The Chains]

Hmmm....

come on brah... you know that's all made up and just a marketing ploy :hfive:

 

[sidewinder22]

Airspeed is a measurement of air speed. It doesn't torque anything. That's like saying cheetah speed eats gazelles. Also, torque promotes rotation, it doesn't inhibit it, and I don't see how air anything promotes rotation, unless you're talking pinwheels. Air 'resistance', for example, can act against the torque already present, but I don't see how it can promote it.

My two cents on wobble is that it causes diametrically opposite points on a disc's rim (highest and lowest) to alternately turn into and then away from the onrushing air as the disc moves through it. The result is air brake up, air brake down, air brake up, air brake down. And that's not even taking into account the disastrous airfoil this makes during all degrees of wobbled rotation. All told, the effect is to slow or stall the forward progression. It can't help but slow rotation, too, I suppose - friction is friction. If there's any validity at all to wobble contributing to left or right movement it would be because the resistance caused by the high and low points is greater on the left (RHBH) because they're rotating into the wind, than on the right because they're rotating away from the wind. Unless you can make a case for deflection in addition to drag, the effect must be to turn the disc to the left (again, RHBH) because, like a tank with a bad tread, resistance pulls a moving object in the direction towards the side with greater drag. Same thing if you try to walk a straight line dragging a cinder block tied to your left ankle - it'll turn you to the left.

What are you talking about... cheetah eat gazelle speed? And disc can wobble in two different directions.

Friction or resistance is anti-torque. To walk a straight line with a cinder block on one leg, you have to apply the torque to overcome the friction/resistance. The cinder block is not creating torque, it's creating friction/resistance.

The onrushing air into the disc as it wobbles around nose up torques the disc into a roll or rotation, it's lift in another direction or sailing. Wobble does also create air braking friction/drag and slows the disc's momentum, but that is different from the torque created.

 

[Atvizory2000]

What are you talking about... cheetah eat gazelle speed? And disc can wobble in two different directions.

Friction or resistance is anti-torque. To walk a straight line with a cinder block on one leg, you have to apply the torque to overcome the friction/resistance. The cinder block is not creating torque, it's creating friction/resistance.

The onrushing air into the disc as it wobbles around nose up torques the disc into a roll or rotation, it's lift in another direction or sailing. Wobble does also create air braking friction/drag and slows the disc's momentum, but that is different from the torque created.

:clap:

 

[TheBeardedFatGuy]

What are you talking about... cheetah eat gazelle speed? And disc can wobble in two different directions.

Friction or resistance is anti-torque. To walk a straight line with a cinder block on one leg, you have to apply the torque to overcome the friction/resistance. The cinder block is not creating torque, it's creating friction/resistance.

The onrushing air into the disc as it wobbles around nose up torques the disc into a roll or rotation, it's lift in another direction or sailing. Wobble does also create air braking friction/drag and slows the disc's momentum, but that is different from the torque created.

Dude, you need to look 'torque' up in the dictionary 'cause you're using it wrong. It doesn't mean what you think it does. I'd also recommend working on your reading comprehension as you respond to things that weren't actually said.

 

[TheBeardedFatGuy]

I have always thought "high speed turn" is a result of high angular velocity. When spinning at high speeds the relative velocity of the left side of the disc and the right side of the disc are drastically different, with the left side being faster and the right side being slower. I always thought the higher velocity relative to the air was, the more lift you would generate, which is why discs turn to the right when initially thrown (this is all for RHBH). I have noticed my own OAT makes things turn to the right way more than they should, and always assumed it's because wobble enhances the effects of high angular velocity.

Is this totally asinine?

I used to think this, too, but it's incorrect. Lift comes from the shape the air passing over the entire disk is forced to take, creating lower air pressure above than below. The airfoil shape of the disc is not affected by the fact the disc is spinning. If there us any difference between the left and right sides of the disc it's wind resistance - greater on the side moving into the wind, lesser on the side retreating. How much tesistance/drag difference there is is up for debate. It's probably minimal because discs tend to be smooth, and probably more pronounced at lower spin velocity as gyroscopic effects at high spin can counter any drag on the left side of a clockwise spinning disc. I do still wonder if this drag on the left side isn't at least partly the reason the disc fades, but Sidewinder will just insist a disc spins at the same velocity from start of flight to end. He's wrong, but he will insist.