# Are discs frisbees: No?

We recently got foam discs for spin up. After some testing, it became apparent that these are not frisbees. They are symmetrical discs, which seem to generate zero lift when tossed through the air. We came to this conclusion through a few tests as well as some research.

We compared different throwing methods, and different objects to figure it out. We threw the discs in three different orientations: like a frisbee, vertically, and like a catapult. We compared these throwing methods to a tennis ball and frisbee. When comparing different objects we tried our best to throw them in the same way and took some notes on the movement of the objects.

The same person at approximately the same power for each throw.

• We threw a disc and a tennis ball in the way you would throw a frisbee, and they approximately traveled the same distance. The disc was stable while it was spinning, but did arc, while the tennis ball traveled in a straight path.
• Throwing a frisbee and a disc with a frisbee throw resulted in the frisbee going MUCH farther than the disc.
• Comparing the disc to a ball in an overhand throw(see fig 2) resulted in the disc being slow and not traveling very far while the ball moved in a parabolic trajectory.
• Throwing a disc in a vertical orientation(see fig 3) in an overhand throw results in the ball going further than the disc. I think that the way we through this one compared to the ball is a bit different because it’s weird to try to flick a ball.
• Throwing the disc underhand while flicking the wrist(fig 4) made the disc go further than the ball, but this might just be the fact that the flick of the wrist is easier for the disc than the ball.
• Throwing a disc and a ring like a frisbee resulted in them going approximately the same distance.
Pictures

Figure 1: All thrown objects.

Figure 2: overhand throw orientation disc horizontal.

Figure 3: overhand throw orientation disc vertical.

Figure 4: underhand throw with flick of the wrist.

An airplane wing (and a frisbee / Nerf gun disc) generate lift through the air by forcing the air to travel a longer distance over the top than the bottom, as the frisbee is traveling through the air. These are symmetrical, thus they cannot generate lift while traveling through the air and do not “fly” like a frisbee.

One might bring up the question of stunt planes, and ask “how do the stunt planes fly upside down?” These planes have symmetrical wings and instead rely on the engine to pull them up when they are flying upside down. In this case, the angle of the wing is facing upwards and the air is being pulled underneath the wing, by the power of the engine. Without the engine pulling the plane forward, there would be no lift and the plane would fall. An extreme example of this is when the airplane is flying straight up into the air, just on the power of the engines.

The rotation of the discs does have a gyroscopic effect in “conserving” angular momentum. I.E. a disc tossed parallel to the ground, will tend to stay parallel to the ground while it is spinning – much like someone at the circus spinning plates on the ends of sticks.

Bottom line, the dynamics of these discs will more closely resemble those of a tennis ball than they do a frisbee, but key aspects of the discs, gyroscopic stability, resemble the movement of a frisbee.

I would like to learn more about the dynamics of these discs and how they fly, so I might do more tests with less human error at some point.

This started with us looking at the kinematics graphing tool topic that @TheRichDarth. @LastMinuteFix brought up a paper on the physics of frisbee which brought about our debate if discs are frisbees.

Sources
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(They’re also not rings!)

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Well said, the discs do behave similar to a ball being thrown. However, it is important to note (and this is something that was brought up in the other thread) that an angle of attack (which causes lift) does develop as the disc is thrown because the heading of the disc’s velocity vector changes.

However, with light, small foam discs like the ones we are using for this years game, this effect is barely noticiable over short distances, especially to the human eye. If you look at the final graph I posted you will see that it varies slightly from a parabola. However, I suspect that if discs are not being launched quickly, and are not being launched very long distances, this affect will remain largely un-noticed.

In Summary: The aerodynamic affects of a frisbee do affect the disc, they are just hard to notice,

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You guys are all wrong they are pancakes.

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My team here are calling them pizzas.

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There are 4 replies to my topic three of which are about the naming of discs

When thrown the rings and the discs act similarly.

The next test might involve throwing pancakes to establish if discs resemble their motion.

I could also test the dynamics of pizza.

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how bout plates
(20 char)

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Well I did actually mention plates in the post so you got some leeway there and it could be entreating to do an experiment on the dynamics of a plate.

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I would avoid syrup on pancakes you are going to throw…

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This is fascinating! I have a few questions about your methods and results below.

Firstly, I’m assuming that you picked the tennis ball because it was approximately the same weight. Is this the case?

Correct me if I’m wrong here but based on these pictures, it doesn’t seem like you threw the discs horizontally like you would a frisbee. If that is the case, would it be possible to test them in that manner? Also do you have (even qualatative) data on the flight path of the discs as compared to the tennis ball? With minimal drag, the ball should travel in a parabolic path. (As the kinematic analysis I did modelled) Was the disc at all similar to this? Was the disc flight path similar to the frisbee fight graphs (below) shown in the MIT Paper originally shared by @LastMinuteFix ?

Did they fly in a similar manner?

Also,

Based on this, do you expect kinematic parabolic motion to be the best practical method of modelling flight?

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I don’t have my computer in front of me right now, so I cannot run anymore tests with my code. However, when using @46X’s simulation made in Khan Academy, it does not look like the aerodynamics have a large affect even at greater angles and possibly distances. The MIT papers only show the graphs like the way they did because they only varied the angle of attack of the disc. The launch of the disc was actually assumed to have 0 initial velocity in the y-direction.

With that being said, I think that because of the possibility of 10g variation in the disc’s mass, and the possibility that flywheels might not always be spinning at full speed when launching the disc, the actual aerodynamic affects on the disc will have little to no visual affect on the disc because of other inconsistencies. As a result a kinematic graph will probably be ‘good-enough’ when it comes to determining the angle of a shooter. At least this is my instinct on this. If anyone else has any other thoughts I would be happy to hear them

Also I think that it is important to note, because I have not seen anyone else mention it on the forum, but the flight of the discs when modeled with the simulation assumes perfect gyroscopic stability. This is something that could also vary from flywheel to flywheel, which is yet another potential source of error.

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The tennis ball was picked for a few reasons similarity in size as well as weight. I just looked up the weight of a tennis ball and Google says it’s about 56 grams which are comparable to the ± 10 grams for the 65-gram discs.

I did throw the discs horizontally like a frisbee. The pictures were there to the other methods of throwing that I tried were more difficult to explain or visualize.

The qualitative data is what I observed when throwing the discs. My perspective was as the thrower, but I was able to compare where different objects landed. The disc flight path did not seem to mimic any of the graphs that you showed, I will likely do more tests with more ppl to help take down better data.

As far as I can tell the discs and the ring flew in the most similar way from my viewpoint, and both landed at approximately the same distance. I will likely do more tests with more ppl to help take down better data.

From my testing, I do think that for now, kinematics is likely the best way to model the flights of the discs, but the accuracy could be iffy.

This all this.

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So I got to playing with the discs as a frisbee during lunch today. You can throw the discs like a frisbee and they can fly very far. Now the discs don’t seem to mimic the graphs of the frisbee(go up with lift) but they seem to fly further than what would be expected with a parabolic trajectory.

My hypophysis is that because the disc was spinning it there was air resistance on the bottom of the disc making it fall slower and fly for a longer time.

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The reason the disc is falling slower, and therefore flying further, would be because of the angle of attack that develops as the heading of the velocity vector changes, and causes lift.

It is important to note that spinning the frisbee provides it gyroscopic stability, it is not what is directly inducing lift.

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Are discs frisbees pt.2 Comming soon

Are these questions going to be answered who know?!?

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[off topic] Happy cake day @seenSeal !

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Isn’t it his birthday, not cake day?

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Are discs frisbees pt.2

Useing Ansys Discovery fluid simulation I have simulated both discs and frisbees to better understand the dynamics and to really answer the question of how much lift does a disc have. Now for the purpose of this simulation the primary independent variables are angle of attack and spin of the disc.

For a disc with a angle of attack of 0 and no spin flying though the air at 20 m/s we get something like this.

This x axis of the graphs are changes that i have made to the simulation. Thoses changes are increasing the velocity of the air. Starting at 0.05 m/s, then 5 m/s, 10 m/s, 15 m/s and finally 20 m/s.

We can see that the lift decrease as velocity increases and the inverse for drag. The graphs here really highlight the expontional nature of air resistance.

This picture shows the pressure around the disc with an angle of attack 20 degrees. This simulation doesn’t take gravity in to account, so the lift force that we see here is counted acted by gravity.
Fg = 9.8 m/s^2* 0.065 kg = 0.637N down. If the disc was traveling at 20 m/s (very unrelastic)

Now lets compare this to a CAD model of a frisbee that I found.

I don’t know anything about this actually firsbee its just a model i found. But we can clearly see the pressure differences on the top vs the bottom. The light blue low pressure and the orange red high pressures clearly indicate that there should be lift. This frisbee has 41.4N of lift force at a 20 degree angle of attack with 20 m/s flow. That is significantly more than the disc.

The fact that one can clearly see the pressure differences on the frisbee simulation compared to the disc simulation where there are small pockets of different pressures indicates that discs are not comparable to frisbees.

Now what hasn’t been taken into account yet is the spin of the disc and frisbee. Searching up how fast a frisbee’s rotation is we get a number between 3.9 and 6.14 rps, which 234 rpm - 368.4 rpm. As for the disc speed I chose a high value of 3000 rpm.

Adding the rotational comptantes to the simulation seems to change the rate at which the lift increases for the velocity, and not being as much lift. The caviat to this is the rpm is really high. The drag numbers for spin and no spin at 20 m/s are roughly the same.

With the frisbee simulated in the same conditions as before but with 300 rpm of spin the lift decreased to 26.5 N, but there is 4.5N less dragn on the frisbee.

More Discs

More Frisbee

Ring

Plates

What are the dynamics of a random CAD model of a plate?

Spinning Flexwheels?

FlexWheel

d

Wheel is simulated spinning at 3000 rpm in very slow moving stagnant air.

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I have no clue what I read but it looked cool.

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Disc not a Frisbee

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