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Disc Flight Ratings Chart
- Thread starter Blake_T1
- Start date
smarkquart
* Ace Member *
Blake_T said:
Just a couple of comments about the Striker and Riot. Based upon what I throw, which I believe is close to what you have described, I have seen the Striker as -0.5, 2.0, 5. Not a huge deviation but I find the Riot far more stable than the Striker, more like 0.0, 3.0, 5. For the almost everything else I agree with your chart and it has been incredibly handy trying to compare discs across different manufacturers.
A few weeks ago I was in and bought the Core, Vision, Riot, XXX, and Striker and Charlie said he would like to hear what I thought of them, so I have been out throwing them quite a bit (at least everything but the Vision because I lost that the second day I had it).
Scott
Blake_T1
* Ace Member *
because the OLS is supposed to be used as a (fairly) straight driver. it requires a 325'+ power throw to get it to fly with its -1.5/+3 characteristics.
the OLF is a moderately overstable driver. it only requires 275' of power to get its intended flight path, thus it is power level 4.
the flight path of an OLF doesn't change much from 275' to 325', but an OLS will have a very different flight path when thrown with 275' of power vs. 325' of power.
e.g.
OLF @275' = HSS 0 LSS +3
OLF @325' = HSS 0 LSS +3
OLF @350' = HSS -0.5 LSS +3
OLS @275' = HSS 0 LSS +3
OLS @325' = HSS -1 LSS +3
OLS @350' = HSS -1.5 LSS +3
make sense?
GGGT is working on getting discmania. if/when that happens, yes.
interesting feedback. the riots we threw required more speed to get the turn but turned way more than the striker. the strikers we threw only turned over into the wind and only when dan threw them with 430'+ power into the wind. in calm conditions they were pretty much hss 0. the +3 LSS rating for the striker i got was based upon relativity more than anything and averaging out different flight paths.
we only threw riots and strikers from a single run that were fairly close together in weight.
smarkquart
* Ace Member *
Blake_T said:
I played three more rounds today at Bassett with both the Striker and Riot as my main drivers. I can most definitely chalk up these differing results to the way that I play (I drive about 350') but here is what I saw:
The Striker, for good or bad, held whatever line it was launched on and was easy to turn over if I did not add a touch of hyzer to it. Its best shot is a slow right turn where it does not fight back into a fade and then slowly settles onto the ground with no roll or skip. I am taking my Monarch out of my bag because of what I can do with this disc. My Riot needed a little more help into a turnover but it was not much of a struggle. However, unlike the Striker where it stayed on that line, the Riot always fought back with a soft fade at the end. Several drives off of Hole #8 at Bassett, with the big tree to the right, had some of the most beautiful S-Curves I have ever seen, several times parking under the basket.
Most definitely I could have fluky discs as they are the only ones of these names I have and do not have others to compare them against. I just thought I would pass along a little more data because I am suddenly hooked on these discs. I will be throwing them a lot so I can have them dialed in for the Majestic.
Scott
Jesse B 707
* Ace Member *
im guessing you guys tested domey (172+ yellow or clear) strikers cuz to me the #s sound about right on for those. my flat 170ish merlots and purples definitely have a good deal less HSS than my domey ones. at 380 or so of power i can flip em up from 15+ degrees of hyzer or from flattish to a nice anny angle without putting too hard of a pull on em, but maybe my form isnt quite as clean as i think it is :?
Donkeypuncher1
Double Eagle Member
Why are no discmania discs listed on the chart? I know a few of them have been out longer than a lot of the newer discs listed.
JimW
Double Eagle Member
GGGT doesn't carry Discmania (I think DGV is the only place that you can order them from) so Blake and Dan don't have them around to test out.
Blake_T1
* Ace Member *
i've never owned a discmania disc, nor had any at my disposal to throw for the chart.
Blake_T1
* Ace Member *
yep.
I think the Boss should have a higher LSS due to its greater speed. It has a much more dramatic LSS than the Destroyer (both rated 4). Also, the Orc and Boss are my 2 main D drivers and the difference between their respective LSSs is definitely greater than .5. IMO the Boss should be 4.5 or perhaps even 5 (especially the Champs). I also think the XS is given too much range for a fairway type driver. This would really confuse me if I had never thrown one before and bought one (especially considering the Z has got to be the most popular version).
I've spent a lot of time thinking about the flight ratings charts, and how complicated a topic it really is to rate the flight characteristics of a disc. Here is my take on it presently, from a physical point-of-view. It is interesting to think about how this can be made more quantitative. By quantitative, I mean the potential for taking numbers from a ratings chart and doing a physical simulation of the disc's flight to predict its behavior under a number of conditions. This is the future Blake, and I think we might be able to collaborate on this, and perhaps be the first one's to do it well.
It seems to me that there are three separate physical phenomena that occur in a disc's flight:
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1. Disc Drag: This is the aerodynamic drag on the disc due to its displacement of the surrounding air, and tends to decrease the speed of the disc in flight. Disc flight is typically in the turbulent flow regime, so that the drag is proportional to the square of the disc speed. The rule of thumb is: if you throw the disc with twice the speed, you get four times the aerodynamic drag.
Drag force is a function of the shape of the disc, nose angle, and speed alone. Drag force is completely independent of the disc mass. The drag typically increases in proportion to its cross-sectional area projected along its flight trajectory. If the disc's nose angle changes, then so too will the cross-sectional area of the disc.
Off-axis torque, OAT, is induced when the disc has a component of spin about an axis that isn't exactly parallel to its axis of symmetry. This causes the disc to wobble, and creates a pocket of turbulent air around the edge of the disc that tends to cling to it instead of flowing smoothly past the disc. This causes the effective cross-sectional area of the disc to increase.
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2. Disc Lift: This is the "wing" effect of the disc in flight, an aerodynamic force that causes the disc to lift upward and fight against gravity to remain in the air.
The lift force is approximately directed along the axis of symmetry of the disc (if the disc is laying on a flat surface, the axis of symmetry will point directly upward at right angles to that surface). It increases in proportion to the square of the disc speed, the planform area of the disc (which differs little from pi times the disc radius squared), and a lift coefficient. The lift coefficient is a function of the nose angle (or "angle of attack"). The lift force on the disc in flight is not, however, always directed through the center of the disc. Rather, the center of lift, or center of pressure, can either be in front, or in back, of the disc center (front/back relative to the disc's line of motion). This leads to precession, as discussed next.
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3. Disc Precession: This is what causes the disc to change its hyzer angle leftward or rightward while in flight. This is important, because the disc tends to travel in the direction of its in-flight hyzer angle. Given a clean release (no OAT), for a given nose angle and speed, the disc orientation does one of three things...
A. It fades. Fade is defined here as the disc's natural tendency to increase its hyzer angle while in flight through precession (left for RHBH). b]Fade[/b] is caused by a center-of-pressure/lift that is in front of the center of the disc. I.e., lifting the leading edge of the disc more than the trailing edge causes the disc to precess in a manner that makes it fade.
B. It holds the hyzer angle it is currently on. A disc can hold the line/angle it is on when the center-of-pressure/lift is at the very center of the disc.
C. It turns. Turn is defined here as the disc's natural tendency to decrease its hyzer angle while in flight through precession (right for RHBH). Turn is caused by a center-of-pressure/lift that is behind the center of the disc. I.e., lifting the trailing edge of the disc more than the leading edge causes the disc to precess in a manner that makes it turn.
The disc will typically fade or turn over a range of flight speeds, always fading at low speed and only turning at sufficiently high speeds. At some magic speed the disc is neither turning or fading, but holding the line. It is useful to define a number to the turn, and take fade as negative turn (i.e., in the opposite direction as turn). Then the holding speed is the speed of the disc in flight (for a given nose angle) at which the disc has zero turn (and by extension, zero fade).
The rate of turn, how fast the disc turns or fades for a given nose angle, is inversely proportional to the angular momentum, which is itself proportional to both the disc's mass and shape (moment of inertia) and the rate of spin on the disc. If you increase the spin rate, the disc will turn more slowly. The golden rule is: spin it twice as fast, and it will turn half as quickly in flight.
As mentioned above, the tendency to turn has to do with the center-of-pressure relative to the center of the disc. The center of pressure is the center of the lift force projected onto the disc. It tends to fall along a line parallel to the trajectory of the disc that goes through the center of the disc.
Also as mentioned previously, off-axis torque causes the disc to wobble, and creates a pocket of turbulent air around the edge of the disc that tends to cling to it instead of flowing smoothly past the disc. This interferes with the flow of air around the disc in a way that pushes the center of pressure back and therefore increases the turn.
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So, that's the basic outline. I have written down a set of equations that can be used to simulate the motion of the disc, given the above assumptions and a few more. I'll probably try some simulations soon to see what it looks like.
I think there are some important numbers here. In the chart is the strength of the turn at low and high speed (LSS and HSS), and the power (speed) requirement. To me, one measure of the power requirement could be something like the power (in terms of distance is fine) needed to get a disc to hold a straight line. Speed at zero turn would be even better, but I don't think most players are cognizant of their speeds. Anyways, with some modeling, we could indeed begin to tabulate this kind of information for various discs, but there are many variables that need to be better constrained first...I'll have to think about how to do that in the best way without too much special equipment being required.
It seems to me that there are three separate physical phenomena that occur in a disc's flight:
-----------------------------------------------------------------
1. Disc Drag: This is the aerodynamic drag on the disc due to its displacement of the surrounding air, and tends to decrease the speed of the disc in flight. Disc flight is typically in the turbulent flow regime, so that the drag is proportional to the square of the disc speed. The rule of thumb is: if you throw the disc with twice the speed, you get four times the aerodynamic drag.
Drag force is a function of the shape of the disc, nose angle, and speed alone. Drag force is completely independent of the disc mass. The drag typically increases in proportion to its cross-sectional area projected along its flight trajectory. If the disc's nose angle changes, then so too will the cross-sectional area of the disc.
Off-axis torque, OAT, is induced when the disc has a component of spin about an axis that isn't exactly parallel to its axis of symmetry. This causes the disc to wobble, and creates a pocket of turbulent air around the edge of the disc that tends to cling to it instead of flowing smoothly past the disc. This causes the effective cross-sectional area of the disc to increase.
-----------------------------------------------------------------
2. Disc Lift: This is the "wing" effect of the disc in flight, an aerodynamic force that causes the disc to lift upward and fight against gravity to remain in the air.
The lift force is approximately directed along the axis of symmetry of the disc (if the disc is laying on a flat surface, the axis of symmetry will point directly upward at right angles to that surface). It increases in proportion to the square of the disc speed, the planform area of the disc (which differs little from pi times the disc radius squared), and a lift coefficient. The lift coefficient is a function of the nose angle (or "angle of attack"). The lift force on the disc in flight is not, however, always directed through the center of the disc. Rather, the center of lift, or center of pressure, can either be in front, or in back, of the disc center (front/back relative to the disc's line of motion). This leads to precession, as discussed next.
-----------------------------------------------------------------
3. Disc Precession: This is what causes the disc to change its hyzer angle leftward or rightward while in flight. This is important, because the disc tends to travel in the direction of its in-flight hyzer angle. Given a clean release (no OAT), for a given nose angle and speed, the disc orientation does one of three things...
A. It fades. Fade is defined here as the disc's natural tendency to increase its hyzer angle while in flight through precession (left for RHBH). b]Fade[/b] is caused by a center-of-pressure/lift that is in front of the center of the disc. I.e., lifting the leading edge of the disc more than the trailing edge causes the disc to precess in a manner that makes it fade.
B. It holds the hyzer angle it is currently on. A disc can hold the line/angle it is on when the center-of-pressure/lift is at the very center of the disc.
C. It turns. Turn is defined here as the disc's natural tendency to decrease its hyzer angle while in flight through precession (right for RHBH). Turn is caused by a center-of-pressure/lift that is behind the center of the disc. I.e., lifting the trailing edge of the disc more than the leading edge causes the disc to precess in a manner that makes it turn.
The disc will typically fade or turn over a range of flight speeds, always fading at low speed and only turning at sufficiently high speeds. At some magic speed the disc is neither turning or fading, but holding the line. It is useful to define a number to the turn, and take fade as negative turn (i.e., in the opposite direction as turn). Then the holding speed is the speed of the disc in flight (for a given nose angle) at which the disc has zero turn (and by extension, zero fade).
The rate of turn, how fast the disc turns or fades for a given nose angle, is inversely proportional to the angular momentum, which is itself proportional to both the disc's mass and shape (moment of inertia) and the rate of spin on the disc. If you increase the spin rate, the disc will turn more slowly. The golden rule is: spin it twice as fast, and it will turn half as quickly in flight.
As mentioned above, the tendency to turn has to do with the center-of-pressure relative to the center of the disc. The center of pressure is the center of the lift force projected onto the disc. It tends to fall along a line parallel to the trajectory of the disc that goes through the center of the disc.
Also as mentioned previously, off-axis torque causes the disc to wobble, and creates a pocket of turbulent air around the edge of the disc that tends to cling to it instead of flowing smoothly past the disc. This interferes with the flow of air around the disc in a way that pushes the center of pressure back and therefore increases the turn.
-----------------------------------------------------------------
So, that's the basic outline. I have written down a set of equations that can be used to simulate the motion of the disc, given the above assumptions and a few more. I'll probably try some simulations soon to see what it looks like.
I think there are some important numbers here. In the chart is the strength of the turn at low and high speed (LSS and HSS), and the power (speed) requirement. To me, one measure of the power requirement could be something like the power (in terms of distance is fine) needed to get a disc to hold a straight line. Speed at zero turn would be even better, but I don't think most players are cognizant of their speeds. Anyways, with some modeling, we could indeed begin to tabulate this kind of information for various discs, but there are many variables that need to be better constrained first...I'll have to think about how to do that in the best way without too much special equipment being required.
Here is a figure I whipped up to help explain how the offset between the center-of-pressure and the center of the disc causes it to turn while in flight. I hope it makes sense.
George1
Newbie
JHern,
Your figure is excellent, thanks for posting that!
I would add to your explanation that the weight of the disc affects the disc flight in (at least) two different ways. One is the moment of inertia (which you explain)—a lighter disc of the same shape will have a smaller moment of inertia, and, if the angular velocity is the same, will have a smaller angular momentum and therefore be subject to greater precession.
The second manner in which the weight enters is in the angle of attack. If two discs, identical except for mass, are thrown level with the same speed and the same angular velocity, the lift on the two discs will be the same, but the force of gravity will be smaller on the lighter disc. The net upward force will therefore be greater on the lighter disc, and it will rise faster. A level disc that is rising has a negative angle of attack. (I'm considering angle of attack to be slightly different from nose angle in that angle of attack is with respect to the air whereas nose angle is with respect to the horizontal ground.) Because of its faster rise, the angle of attack of the lighter disc will be more negative (than that of the heavier disc), causing the center of pressure to move farther behind the center of the disc, and thereby creating a greater torque and more precession. When a level disc is falling, the reverse is true: the center of pressure moves forward. In airfoils, I believe this effect is largely characterized by the pitching moment coefficient, which also changes with angle of attack, but I could be wrong.
Jonny Potts (who founded Discwing) measured the pitching moment of a disc (I don't think it was a golf disc) in a wind tunnel and measured the change of pitching moment with angle of attack and described it in this paper:
http://www.discwing.com/research/flowOverRotate.html
Although the initial turn and the final fade are generally thought of solely in terms of speed by disc golfers, I think the changing angle of attack (negative in the first part of the flight, and positive in the final part) plays a major role in causing the typical S-curve flight. Of course since lift increases with increasing speed, the angle of attack and the speed are closely related.
Disclaimer: I am not an aerodynamicist but I am a physicist (and a mediocre rec masters disc golfer).
George
Your figure is excellent, thanks for posting that!
I would add to your explanation that the weight of the disc affects the disc flight in (at least) two different ways. One is the moment of inertia (which you explain)—a lighter disc of the same shape will have a smaller moment of inertia, and, if the angular velocity is the same, will have a smaller angular momentum and therefore be subject to greater precession.
The second manner in which the weight enters is in the angle of attack. If two discs, identical except for mass, are thrown level with the same speed and the same angular velocity, the lift on the two discs will be the same, but the force of gravity will be smaller on the lighter disc. The net upward force will therefore be greater on the lighter disc, and it will rise faster. A level disc that is rising has a negative angle of attack. (I'm considering angle of attack to be slightly different from nose angle in that angle of attack is with respect to the air whereas nose angle is with respect to the horizontal ground.) Because of its faster rise, the angle of attack of the lighter disc will be more negative (than that of the heavier disc), causing the center of pressure to move farther behind the center of the disc, and thereby creating a greater torque and more precession. When a level disc is falling, the reverse is true: the center of pressure moves forward. In airfoils, I believe this effect is largely characterized by the pitching moment coefficient, which also changes with angle of attack, but I could be wrong.
Jonny Potts (who founded Discwing) measured the pitching moment of a disc (I don't think it was a golf disc) in a wind tunnel and measured the change of pitching moment with angle of attack and described it in this paper:
http://www.discwing.com/research/flowOverRotate.html
Although the initial turn and the final fade are generally thought of solely in terms of speed by disc golfers, I think the changing angle of attack (negative in the first part of the flight, and positive in the final part) plays a major role in causing the typical S-curve flight. Of course since lift increases with increasing speed, the angle of attack and the speed are closely related.
Disclaimer: I am not an aerodynamicist but I am a physicist (and a mediocre rec masters disc golfer).
George
No problem. It is part of a more complete write-up I've been doing on my free time, to summarize and teach the knowledge I've gained about disc flight, which I'll post publicly when I finish (or maybe before, for comments). I'm also going to begin simulating disc flights, and sharing that info as well. This is relative straightforward to do, I only need to code up a basic time integration (Runge-Kutta should be more than adequate).George said:
I've been inspired by some work done at UC Davis, described here...
http://mae.ucdavis.edu/~biosport/frisbee/frisbee.html
They basically have all sorts of parameters for their flight model, which they can fine tune in order to simulate the flight of almost any disc. They do a flight test with a real disc, high speed camera and calibration markers. Then they compare a simulation run with an initially guessed set of parameters to the flight measurements, and change the parameters in a manner that improves the fit, wet hair, lather, rinse, and repeat several times until the fit is very good.
Right. Moment of inertia is typically proportional to mass, and to radius-squared. A change in mass from m_i to m_f (so long it isn't also accompanied by radial shrinkage/expansion) will cause the rate of increase in turn to be slower for a given throw by the ratio m_f/m_i.George said:
Yes, the inertia and gravity are both proportional to mass, while the aerodynamic forces depend solely on shape. So the lift will go inversely with mass.George said:
However, there is another phenomenon which seems very important, and points to many of the sensitive trade-offs in optimal disc design and flight. For every disc, at a given angle of attack (almost always negative, and around -4 degrees according to Potts' experiments) the lift force (defined here as the aerodynamic force component normal to velocity) completely vanishes, in which case the mass cancels in the force balance along the lift direction. (Also, according to Potts, this angle of attack corresponds to the same angle that minimizes drag.)
One might think that the disc begins a parabolic trajectory if the lift force vanishes, but in reality the disc never gets to that point. Instead, there is a dynamically stable balance achieved between lift and rise rate as follows: Your hypothetical flat disc rises up and the angle of attack becomes negative. If the disc rose so quickly that the angle of attack reduces to -4 degrees or so, then the disc would stop lifting and commence leveling out . This causes the angle of attack to increase again, hence providing positive lift once again. A flat disc (ignoring any changes in nose angle during flight) can steadily rise at an angle (=angle of attack, in this instance) where a balance is achieved between lift and gravity.
(It is physical reasoning and thought experiments like this that convince me we can refine disc flight simulation models for each mold by careful comparison to disc flight.)
His experiments were quite fun. This is recommended reading for all disc golf nerds.George said:
The lift force function (call it "F_l") is fairly well constrained. If you look at the figure I drafted, there is an offset "x_p" of the lift force from the center of the disc. The pitching moment is easily calculated as x_p*F_l, that is, if one knows x_p. This x_p is, however, initially a poorly constrained function of speed ("v") and angle of attack ("alpha"), i.e., x_p=x_p(v,alpha).George said:
But here is the gold mine in the rough: the function x_p(v,alpha) contains the most essential information about how a given disc flies.
Heh, but the physics is pretty straightforward, at least at the descriptive level we are discussing. If you read the Potts flow visualization papers, you'll see that the aerodynamics part of the picture is not at all simple. I love the schematic flow planforms they artfully whipped up. Of course, these studies were also mostly descriptive, and I didn't see any attempt to derive particular flow structures or their characteristics using math.George said:
George1
Newbie
JHern,
Thanks for the post--I agree entirely. I have a physics student looking for a disc related project and was contemplating a simple simulation, but probably quite a bit simpler than what you're thinking of. I've seen the UC Davis work.
I see your point about the lift force vanishing and the stabilizing feedback--I hadn't thought of that and that explains a lot about the flight. I was naively assuming that drag would slow the disc and cause the lift to diminish before that negative critical attack angle was reached. (Probably because I don't throw very far--300 feet is a good distance throw for me :wink: )
The aerodynamics is indeed much tougher than the basic mechanics. Have you seen this work?
http://www.microcfd.com/download/pdf/dissertation.pdf
I was lost through much of it but it might have some of the more numerical, less descriptive aerodynamics you're looking for.
I would like to see your simulation when you get farther along. I'd also be interested in seeing what you come up with for x_p(v, alpha).
Finally, perhaps there should be a disc physics thread. I think this thread is more for Blake's/Joe's flight chart. I'd start one but I'm still getting use to the board. I've been lurking a long time but only registered recently.
George
Thanks for the post--I agree entirely. I have a physics student looking for a disc related project and was contemplating a simple simulation, but probably quite a bit simpler than what you're thinking of. I've seen the UC Davis work.
I see your point about the lift force vanishing and the stabilizing feedback--I hadn't thought of that and that explains a lot about the flight. I was naively assuming that drag would slow the disc and cause the lift to diminish before that negative critical attack angle was reached. (Probably because I don't throw very far--300 feet is a good distance throw for me :wink: )
The aerodynamics is indeed much tougher than the basic mechanics. Have you seen this work?
http://www.microcfd.com/download/pdf/dissertation.pdf
I was lost through much of it but it might have some of the more numerical, less descriptive aerodynamics you're looking for.
I would like to see your simulation when you get farther along. I'd also be interested in seeing what you come up with for x_p(v, alpha).
Finally, perhaps there should be a disc physics thread. I think this thread is more for Blake's/Joe's flight chart. I'd start one but I'm still getting use to the board. I've been lurking a long time but only registered recently.
George
George,
Sure thing, I'll get a thread going ("Disc Physics" seems like a good name), where we can all follow this particular discussion (and maybe spawn other off-shoots). No need for you to be shy about starting threads though...there are a ton of of threads that are started and never go anywhere.
I'll bump my present posts over there...maybe you can also copy some of your's over?
Sure thing, I'll get a thread going ("Disc Physics" seems like a good name), where we can all follow this particular discussion (and maybe spawn other off-shoots). No need for you to be shy about starting threads though...there are a ton of of threads that are started and never go anywhere.
I'll bump my present posts over there...maybe you can also copy some of your's over?
