Operational definition of "glide"

[Dan Ensor]

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.

9.8m/s^2 to a point; terminal velocity ... wind resistance decreases that number (not sure that's the same as lift, necessarily) ... e.g. a parachute doesn't accelerate at 9.8m/s^2 ... is that lift? mmmm ... my head hurts:\

 

[BogeyNoMore]

9.8m/s^2 to a point; terminal velocity ... wind resistance decreases that number (not sure that's the same as lift, necessarily) ... e.g. a parachute doesn't accelerate at 9.8m/s^2 ... is that lift? mmmm ... my head hurts:\

Parachutes provide wind resistance, not sure I'd refer to it as lift. Nonetheless, that force opposes gravity and the larger the parachute, the sooner it will reach terminal velocity.

Technically speaking, lift is well defined in aerodynamics and is completely applicable to a moving disc as air passes over the curved top faster than the air moving under the disc.* The difference in speed of the air passing above/below the disc creates a difference in air pressure above/below the disc, generating lift.

Next time your buddy tees off, drop a driver flat from the height he tees off at. Bet your disc hits the ground before his does (unless his shot sucks).

*Enough air remains trapped under the flight plate to allow it to behave as if it were flat on the bottom.

I doubt terminal velocity comes into play with the heights discs are thrown at and the amount of wind resistance the flight plate encounters "falling."

And a moving disc really isn't in free fall - it's aerodynamic qualities are different from an object dropped from the top of a tall building.

 

[bikinjack]

The parachute thing I do believe is considered lift. If you think of it in engineering terms, like drawing a force vector diagram, what else would you call the force acting in the opposite direction of gravity?

 

[BogeyNoMore]

The parachute thing I do believe is considered lift. If you think of it in engineering terms, like drawing a force vector diagram, what else would you call the force acting in the opposite direction of gravity?

You are correct in that if you draw a free body diagram of a parachute falling, there's certainly a force vector pointing up due to the resistance of the air on the parachute. If you want to call that lift go ahead.

I was referring to lift in the sense that a disc, like a wing, discs get lift from the differential in pressure caused by air passing over it the upper and lower surfaces at different speeds as it travels forward.

Going back to the OP's question:
I would define glide as: How well a disc stays aloft as it loses speed.

All other factors being equal, discs with more glide go further because they stay aloft longer as they slow down. Discs with less glide don't go as far because they lose altitude (faster than discs with more glide) as they slow down.*

Beyond that, I was just explaining what force keeps them aloft - lift, caused by a difference in air pressure above and below the disc... which is strictly a function of its shape and it's motion through the air.


* i.e. all discs will lose altitude as they slow, but discs with more glide lose altitude slower than discs with less glide.

 

[BogeyNoMore]

^ Should have said :

...lift, caused by a difference in air pressure above and below the disc... which is strictly a function of its s̶h̶a̶p̶e̶ physical properties and it's motion through the air.

since as plastic types seem to have an effect as well.

 

[bradharris]

I think a better way to define glide would be to say it's a disc's ability to stay level at low speeds.

Overstable discs don't get good glide ratings simply because precession takes over at low speeds causing the disc to tip, changing the direction of the lift vector such that it's no longer counteracting the force of gravity as directly.

A disc like the River which is often regarded as one of the best gliders is understable at high speeds and stays stable at low speeds. This means it will tend to stay level towards the end of it's flight, allowing it to continue to produce upward lift.

 

[BogeyNoMore]

^ excellent point!

 

[DG_player]

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:

That's what I always assumed glide referred to, the ability of the disc to generate more lift at lower speeds, and thus maintain a more stable, less drastic descent at the end of it's flight.

 

[DiscChainBasket18]

Glider!

Broken down further it looks like Glide = movement
Some quick definitions may help here:
Move with a smooth continuous motion
Make an unpowered flight, either in a glider or in an aircraft with engine failure
A smooth continuous movement
To move in a smooth, effortless manner: a submarine gliding through the water.

 

[bradharris]

Make an unpowered flight

Every disc does this.

The question is how do you quantify the unpowered flight a disc makes?

It's like assigning a "roll" rating to a wheel.

 

[Dan Ensor]

I don't think we're answering the question. Op wants an "operational" definition: Glide is the flight rating Lat64 uses to trick people into buying a River over a Leopard.

 

[ohtobediscing]

^^^You know, you could just say "I don't like Rivers!" instead of hiding behind the definition of glide.

 

[elmexdela]

glide=hangtime to me

 

[chevis]

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?

can i get a flight rating for these 2?

 

[3j0hn]

I don't think we're answering the question. Op wants an "operational" definition: Glide is the flight rating Lat64 uses to trick people into buying a River over a Leopard.

:thmbup:

I think of glide as a 1 to 6 scale of Rock to Frisbee.

 

[knettles]

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.

Here's the issue I have with glide. People often talk about how slower discs have more glide, but Innova's flight ratings don't reflect that. More importantly, however, the discs' flights don't reflect that either. If you throw a driver and a putter on the same angle, flat, the putter will start to drop sooner. To get the putter to glide far, you have to throw it nose up/at a slight upward angle. So, I basically am no closer to being able to accurately describe glide now than I was before this thread.

 

[teemkey]

Innova's flight ratings are not meant to describe the exact flight of any disc model. They are to be used to compare between models. For instance, a Wraith at 11, 5, -1, 3 is a faster type than the 10 speed models and slower than the 12 and 13 speed models. The Glide, Turn, and Fade cannot be compared to other speeds, but can be compared to other discs at the same speed. This way the Wraith can be compared to a TeeRex and Max on the same line.

my emphasis

 

[Dan Ensor]

^^^You know, you could just say "I don't like Rivers!" instead of hiding behind the definition of glide.

I don't like rivers or leopards, and I was going to just say "glide is the rating lat can put a big number under to sell discs", but river being a 6 (highest I've ever seen) and leo being ... one of the best discs ever ... and the fact that people actually throw the river ...

I was really just saying that, operationally, don't pay attention to the definition of glide.

 

[chain_ape7]

I don't know how disc manufacturer's study and test "glide" but in skydiving all parachutes (square and some rounds) have a glide ratio of forward momentum vs. loss of altitude( ex. 2.5:1 or 3:1 glide ratios).

The PDGA or some governing body, or even the manufacturing companies themselves might want to implement some guidelines for published glide numbers so we have some bench line standards for consumers.

 

[sidewinder22]

Here's the issue I have with glide. People often talk about how slower discs have more glide, but Innova's flight ratings don't reflect that. More importantly, however, the discs' flights don't reflect that either. If you throw a driver and a putter on the same angle, flat, the putter will start to drop sooner. To get the putter to glide far, you have to throw it nose up/at a slight upward angle. So, I basically am no closer to being able to accurately describe glide now than I was before this thread.

The flight ratings are relative to disc speed so they are indeed reflected. It's like saying a Boss is an overstable disc. Also you shouldn't throw a putter nose up for it to glide far, that's actually counter productive. A putter nose up will glide further than a driver nose up, but that's because a putter has a less sharp nose. If you throw a putter and driver with the same amount of power, say 25% power, the putter will glide out further than a driver.