Operational definition of "glide"

[Alexplz]

I hear the word "glide" tossed around a lot. Innova's definition is: "Glide describes the discs ability to maintain loft during flight."

I recently started a thread on NWDG news asking for suggestions for good drivers in the woods. I have had trouble with glidey discs rising up and hitting branches. I got contradictory answers - some thought more glide was better, some thought glide was the enemy when it came to tight low ceiling shots.

I did an advanced search and it seems like when pressured nobody really knows what they're talking about when they refer to "glide."

Here's the question I posed to get closer to the answer:

Just when I felt like I had a good handle on the physics of disc golf, this talk about glide comes along! Thanks for giving me the breakdown, still not sure I completely understand. Imagine two hypothetically identical discs - two cobras for example - 4/5/-2/2. Say you could make some change to one of the discs that altered only its glide rating, holding all else equal and resulting in a 4/2/-2/2 disc. Then say I have a robotic disc throwing rig that I set to throw the un-altered cobra out to 300 feet. If I load the altered, less glidey disc in and throw it with the same settings, how will the flight characteristics differ?

:wall:

 

[sidewinder22]

I agree with Innova's definition, but talking about glide is barking up the wrong tree and could go either way depending on the nose angle. A disc rising is due mostly to nose angle, not so much glide. Faster discs with wide rims are harder to keep the nose down and tend to lift/rise as they have a sharper nose/edge which carves more air. Slower discs tend to glide further as they have maintain more air under the flight plate and blunter nose carves less air. So the answer to your disc quest is either fix the nose angle on drivers or throw slower discs, but really do both.

 

[RyanisCorriganis]

And I agree with sidewinder22 but have always tried to simplify it even more. Discs that have a high glide rating are more sensitive to air speeds than those with low ratings.

 

[Alexplz]

I agree with Innova's definition, but talking about glide is barking up the wrong tree and could go either way depending on the nose angle. A disc rising is due mostly to nose angle, not so much glide. Faster discs with wide rims are harder to keep the nose down and tend to lift/rise as they have a sharper nose/edge which carves more air. Slower discs tend to glide further as they have maintain more air under the flight plate and blunter nose carves less air. So the answer to your disc quest is either fix the nose angle on drivers or throw slower discs, but really do both.

OK well I don't know much about physics but imagine this: any disc is thrown slow with some arbitrary amount of spin, perfectly flat. It stays in the air for a short period and falls to the ground after a few seconds.

Then, the same disc is thrown faster, we'll say as fast as a pro drives. Say we maintain the same flat angle and amount of spin. It stays in the air longer - maybe double the amount of seconds.

The only thing we changed was how fast the disc was travelling and it kept the disc off the ground for longer.

Finally, imagine we use a disc throwing robot to throw the disc with the same angle and spin, only twice or three times as fast as a pro. Last time we increased the speed it increased the airtime we achieved; I would expect the robot would keep it in the air the longest.

The quality of the disc that converts speed to hangtime must be "glide." If it's the case that glide is not causing my disc to rise, then what exactly would you expect to happen when we threw the two hypothetical cobras I talked about previously? It's not necessarily the case that glide means more distance - most of the time we wouldn't care much about hangtime for the sake of hangtime if the disc goes up high, stalls and fades.

This is confusing as hell! :doh:

 

[Kenny53691]

I agree with Innova's definition, but talking about glide is barking up the wrong tree and could go either way depending on the nose angle. A disc rising is due mostly to nose angle, not so much glide. Faster discs with wide rims are harder to keep the nose down and tend to lift/rise as they have a sharper nose/edge which carves more air. Slower discs tend to glide further as they have maintain more air under the flight plate and blunter nose carves less air. So the answer to your disc quest is either fix the nose angle on drivers or throw slower discs, but really do both.

And I agree with sidewinder22 but have always tried to simplify it even more. Discs that have a high glide rating are more sensitive to air speeds than those with low ratings.

^^^ I agree

 

[tylerc]

I always thought glide was the amount of lift that a disc could produce

 

[bradharris]

Glide is probably the most useless "stat" in flight descriptions. It is an intangible, immeasurable concept that people seem to lean on heavily.

The disc is kept aloft by a number of factors, lift being the primary one. In addition to lift you have kinetic forces (ie, throwing on an upward trajectory). A disc also exhibits a sort of parachute effect on the flight plate where air resistance slightly reduces the force of gravity.

All of these factors work together to keep the disc aloft and gliding.

Stability also has an effect on the perceived glide. Overstable discs are considered less glidey (yes I'm making up words) because they tend to crash to the ground hard at low speeds, whereas an understable disc can extend its flight longer by maintaining a more level flight.

 

[zjones9]

Nose angle definitely seems to be your issue. In most cases, a disc thrown on a flat line with the nose flat (not up) even the most glidey discs will not rise much at all, they will just fall more slowly.

EDIT: this is assuming there is not some strange/intense wind conditions...wind can also do some funny things with a disc!

 

[BogeyNoMore]

Not sure I can accurately describe glide, but I know it when I see it... some discs just stay up better and longer than others.

Pretty sure "glide" is a function of the lift force that develops as the disc moves through the air behaving like a wing. If you threw two identical discs with two identical shots (say flat) and the only difference was the initial velocity, lift or glide is the reason the disc that's thrown faster will stay aloft longer than the disc that's thrown slower. By the time one disc has slowed down to the point where (gravity > lift), it begins to drop, while the faster disc still has enough velocity to provide lift and glide.

Otherwise, they'd hit the ground at the same time.

Also not positive what disc characteristics contribute to glide, but I'd think dominess is one - because of the whole wing-like air moving faster across the top provinding lift thing... you'd think the greater the dominess, the greater the difference in air pressure, the greater the lift and glide.


Your thoughts?

 

[Jukeshoe]

OK well I don't know much about physics but imagine this: any disc is thrown slow with some arbitrary amount of spin, perfectly flat. It stays in the air for a short period and falls to the ground after a few seconds.

Then, the same disc is thrown faster, we'll say as fast as a pro drives. Say we maintain the same flat angle and amount of spin. It stays in the air longer - maybe double the amount of seconds.

The only thing we changed was how fast the disc was travelling and it kept the disc off the ground for longer.

Finally, imagine we use a disc throwing robot to throw the disc with the same angle and spin, only twice or three times as fast as a pro. Last time we increased the speed it increased the airtime we achieved; I would expect the robot would keep it in the air the longest.

The quality of the disc that converts speed to hangtime must be "glide." If it's the case that glide is not causing my disc to rise, then what exactly would you expect to happen when we threw the two hypothetical cobras I talked about previously? It's not necessarily the case that glide means more distance - most of the time we wouldn't care much about hangtime for the sake of hangtime if the disc goes up high, stalls and fades.

This is confusing as hell! :doh:

I don't believe you can throw a disc "faster" without imparting more on-axis spin, but I'm far from an expert in these matters.

 

[garublador]

I did an advanced search and it seems like when pressured nobody really knows what they're talking about when they refer to "glide."

That's about it. It's either the same as lift; a disc's ability to fly farther without fading; or some combination of those two.

 

[disc qualified]

i like to use a paper airplane vs. a brick analogy

airplane has a lot of glide and will fly with less effort
a brick needs a lot of power to fly

what was the question again?

 

[RyanisCorriganis]

Glide is probably the most useless "stat" in flight descriptions. It is an intangible, immeasurable concept that people seem to lean on heavily.

I've wondered where the spec came from and how it's measured?

 

[Alexplz]

I've wondered where the spec came from and how it's measured?

My biggest problem with flight ratings is that they are apparently measured subjectively. That is, some guys go out and huck some discs then write down how they flew. This of course does not isolate variables like human error and individual differences.

One big thing I've noticed is that for the most part glide is very correlated with fade - the more fade, the less glide. It seems that overstable discs may be essentially dumping the energy that glidier discs maintain.

 

[BogeyNoMore]

i like to use a paper airplane vs. a brick analogy

airplane has a lot of glide and will fly with less effort
a brick needs a lot of power to fly

what was the question again?

Simplistic as it is, this works for me. Never heard anyone explain it any better.

 

[Dan Ensor]

Glide is the portion of a flight between the turn and the fade. It's not getting lift from speed anymore, but it's not dropping. It's just maintaining forward penetration. This isn't a definition or anything, just what I see when I say glide.

If I were going to give it a definition it'd be: a discs ability to maintain characteristics that gain distance.

If I were anyone else, though, I'd ask "which characteristics" ... to which I would reply "i dunno"

:doh:

 

[BogeyNoMore]

Glide is the portion of a flight between the turn and the fade. It's not getting lift from speed anymore, but it's not dropping. It's just maintaining forward penetration. This isn't a definition or anything, just what I see when I say glide.

Gravity never stops acting on the disc... ever.
If not for lift, every disc falls at 9.8m/sec/sec... anywhere on this planet.
As long as the disc has velocity, it has some amount of lift. When it slows to the point where gravity > lift, it begins to fall. If gravity is only a bit greater than lift, the more gentle the descent. If gravity is significantly greater than lift, it drops faster. That's why spike hyzers penetrate the ground: the flight plate is essentially in line with the ground, so the disc's lift isn't really counteracting gravity, it's actually pushing the disc on toward whatever direction the top is facing.

 

[BogeyNoMore]

Hmmm, last post got me thinking...
Lift is generated as the disc moves through the air. The faster the disc goes, the greater the lift force. As the disc slows enough, eventually gravity > lift, disc begins to descend.

Maybe glide is a meant to express how fast the disc needs to travel to generate enough lift to keep it aloft?
Or how well does the disc stay aloft when the flight slows?
All discs seem to glide pretty well shortly after release, but discs most of us describe as "glidey" tend to milk good distance toward the end of the flight... as they begin to slow before the fade (as Mr Ensor indicated :thmbup.

Discs with a lot of glide don't need much speed to generate that lift. Discs with less glide need more velocity to generate that lift. When lower glide discs "run out of steam" they drop faster than discs with more glide.

Just thinking out loud... please comment, bash, elaborate. opcorn:

 

[teemkey]

I answered the OP's question on NW discgolf the same as Dan Ensor. But reading these I think Bogey No More's answer is best: you know it when you see it.

Think of it this way: try writing down the criteria that distinguishes a cat from a dog. It's difficult, lengthy, and probably will have to be revised. Yet, we can correctly distinguish the two 99.9999% of the time just by looking. Are we all being subjective? Probably not.

Throw a River, Saint, and Mamba. Then throw a Gator, Trident, and Stiletto. You'll see.

 

[BogeyNoMore]

^ Great analogy! I can't argue with your logic - you know it when you see it. Throw those discs, and you'll see what glide is. I'm just science dweeb, so I like to understand how stuff works.