Disc Physics

[JHern]

Apex height could be quesstimated by an object of known height. If one were to trust the bubble scale on the tripod the camera would be level. I would not trust my system. Exit speed can be calculated from the disc diameter, because my camera has fast enough shutter speed to eliminate visible blurr from the disc. Of course a 21.2 cm disc leaves measurement inaccuracies. Could you write a program to detect the nose angle of the disc if such image recognitions software isn't available? I would think that image editing softwares would have an angle meter. Paging graphics guys help please for suggestions on software, that would do this.

Could you give specs for the grid? I can't easily haul around large objects. The larger the grid, the larger the cost. There is an accuracy throwing goal on one course around here. Too bad it's aligned so that one would have to throw across two fairways. And the ground is a bog after all the rain. The ground won't carry and will be less slippery only after it freezes. That means that indoors throwing is needed and lighting is gonna induce flicker to the pictures and force too long shutter speeds, that can easily lead to blurred disc images. Indoors halls may very well have indoor soccer goals so measuring one could help in creating the grid.

If you can calibrate distance by the disc diameter, then that would work great, no grid needed. Or just put something in the scene with known length, that is easier to measure. The nose angle just needs a level reference, and like I said, even just a quick and dirty measurement would be great.

 

[JR]

No promises, but i'll see, what is possible. My club has an indoor hour per week through the winter and it might not be possible to get the cameras far away, but i've not been there. And no idea about the lighting, so there might be a lot of flicker in the video. The flattest local soccer field is closed, because they are prepping it for ice skaters. Meaning tankers are spewing water onto the field for days in a row now :twisted: The next best field might be ok, but it's getting colder and wetter all the time and i have two days of throwing behind me and i'm not so fresh. So no promises, but if i'm up to it, i might have a quick and dirty version ready tomorrow, if i'm not dead from previous ripping. Thursday will be rainy so no go and i've got other stuff for the rest of the week.

 

[JHern]

Hey JR, sounds great. Anything would be awesome. When Avery Jenkins comes back home, I might see about getting him and a film crew out to a field to make some measurements at the more extreme end of the spectrum, just to check that everything scales properly...this is important for validating the model parameterization. This kind of exercise should allow me to fine tune the lift and drag coefficients. Once I can put them together for several different molds, then I can begin to assign physical numbers to Blake's flight chart by mapping, and begin to simulate every disc that exists, even before I get around to wind tunnel testing (the ultimate test).

 

[jubuttib]

Damnit, I have a slomo camera (210 fps, even the 420 fps could be usable), but don't have any means of making the reference grid.

 

[JR]

I think i must do this today even though i'm sore and stiff and sleep is an issue. Since Avery might help i'll use Innova only. I have to go through my stacks of discs to get discs, that are in new conditions. For limiting fade Roc and Leo are given. I have at least one lighter Champ Beast, that should be in pristine order. Unfortunately I'm outta luck with Innova putters in new condition. Leo needs to be hyzer flipped and the Beast needs a lot of power and even lower lines to avoid the onset of fade. I've just woken up and off the top of my head can't think of other common discs from Innova, that have no fade options other than on very low lines. i think my Star Dart would be ok, but throwing it low at high power is new to me, so i'll have trouble finding the correct initial hyzer angle for a flip to flat.

I think i'll buy a small water scale for level reference at the apex. I'll take a tape measure with me to the field i'll go to and will get reference height there, but i'll take a small plank with me as well. It's more accurate, than just using a disc. Lately i've had no luck at all with file sharing sites so i may need to post the results on DVD. That is if i can throw well enough. Off to rummage piles of plastic.

 

[rhatton2]

Did anything further ever happen with this?

I would love to read the full works of Jherns theories!

 

[JR]

I sent him vids of myself throwing and my form was off a little. I gave him apex height, nose angle, distance and amount of fade or lack thereof data estimations with some discs and he replied that he tries to engage local top pros for a similar shoot session. I have not heard back from him after that about this. And he has moved to Japan after that from Cali.

 

[hugh78]

Use the disc of the pro's!


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[ladysmanfelpz]

This may have been answered already, but I haven't the time to look through 10 pages of posts right now. I'll read through tomorrow as this is a very interesting thread.

So this may sound like a stupid question, but what causes a disc to fly with its flight plate parallel to the ground?

I'm serious. I've always been interested because I am a hyzer flip type of guy and love cranking on a flippy disc and letting it come to plane and turn as much as it can before fading to the ground. So is it intuitive from throwing so many discs (as obviously flat is going to maximize distance) that we develop our level of speed and snap for each disc for it to fly flat as long as possible before losing its rotation and fading to the ground? Or is there some force that when angular momentum is added to the disc that it will become parallel to the ground and fight out of the line it is placed on?

The only thing I can think of that causes it to plane even with the ground is the force of gravity. Air is in constant pressure all around the disc, well I guess lower pressure above due to the wing design, but again this would have nothing to do with it flying parallel as if it was thrown at a 90* angle it would just generate lift to the top of the disc. There is no magnetism to a disc ha so it wouldn't feel the earths magnetic field. Is there something I am missing? Is it all in my head that they truly flip to flat or is it just from our throw technique that a disc will fly flat when thrown correctly?

 

[JR]

You asked different things. Up and down is indeed a gravity vs lift batle and the disc does not truly maintain altitude. But for practical reasons it seems to for some of the way because the dropping rate of a disc thrown fast enough is under detection threshold. The hyzer issue is more complicated. Aerodynamic precession explains flipping and fade along with gyroscopics paired with nose angle. Essentially the speed of the disc varies and so does the center of lift from close to the front of the disc to close to the center. That in conjunction with the lift generated by the pressure didfference of the air paasing under vs over the disc that determines lift is multiplied with the vectors of hyzer angle and nose up, flat or down angle times spin rate of the disc. In practical terms discs often fly farther thrown mildly annied than flying flat for the most of the flight. It depends on the disc, the speed, nose angle, glide and spin rate whether a flat or annied throw goes farther per given apex height. On low lines a flat throw does go farther for many discs that do not glide enough to avoid dropping down early. If you raise the apex height of a disc that is appropriate for your arm speed and spin rate high enough to not crash down early it takes more time to fade out and drop quickly. Despite the disc dropping faster early in the flight during the anny part of the flight. The later and slower tilt toward hyzer in the fade is more than enough compensation for the anny part drop given a proper height of the throw.

 

[ladysmanfelpz]

No I think you misunderstood me. I'm just wondering if there is any force that will cause a disc to fly parallel to the ground. Like if it senses gravity below and will tend to flip to parallel with the ground due to its rotation and some other force. Like why does a tree always grow up. Say we created some disc ripping machine, could it rip an ape perpendicular to the ground with so much force that it would flip to flat and follow its flight characteristics after that with the much increased angular momentum leading to longer flight.

Or do we just get used to our discs and throw our more stable ones anny to flat for them to fly flat to slightly anny to maximize distance and release our understables with more hyzer because we simply have figured out the power and snap required for each disc to get them to fly parallel to the ground.

You can simply tell me I'm wrong if I am way off and that the disc will fly its intended path if thats what you believe/science proves.

 

[Star Shark]

Plants always grow upward to get the most sunlight. There is no force that causes a disc to remain parallel to the ground.

 

[JR]

There is no single force that does that it is a combination of forces. Aerodynamic precession expalins much of it but you need to understand those other factors as well. There are Youtube videos of disc throwing machines. With enough speed and lack of spin any disc can be flipped a lot. Flipping an Ape from vertical to horizontal needs superhuman speeds though.

 

[ladysmanfelpz]

I guess this is more what I was looking for JR. I guess I wanted a better description on the wind resistance coming from the front of the disc that causes it to flip to its proper stability level. And wouldn't lack of spin cause a disc to be less flippy?

 

[JHern]

Did anything further ever happen with this?

I would love to read the full works of Jherns theories!

Hey guys, sorry I've been quite busy, I'm now the Vice Director of a $100 million institute in Tokyo, and I have two small children...as you might imagine, I have little time for my fun hobby of modeling disc flight. I cherish the opportunity to throw, when I can, and eager to get my kids up to the age of playing full rounds.

I still have all the code and notes and everything for the disc physics, and I understand it better than ever before. I even began writing a long manuscript with all the math and gory details, and that is still sitting there. Stancil Johnson (PDGA#2) also asked me to do a write-up for his new discopedia, but that project has also seemed to falter in the past few years. I think there is a wind tunnel I could access in our host university, if I could only find the time. One day...

 

[JR]

There is an all encompassing wind tunnel over Japan each monsoon season right? :-D Enter 150 class and the fun begins.