My guess is that your forces are a factor of 9.8 too high - when those units are used, it'll come out in newtons. What's the formula that you are using for lift coefficient as a function of angular velocity by the way?

Oh, and another note - those drag coefficients sound high. I'm pretty sure that the flow should be occuring at a supercritical reynolds number in this case, and the drag coefficient should be in the ~0.2-0.3 range (based on information in my aero textbook [Foundations of Aerodynamics, Arnolde Kuethe and Chuen-Yen Chow])

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If we're re-running the numbers, let's use a 10" diameter pumpkin weighing 9.0 lb -- that's typical for competition.

I've been going to fire up the ATreb trebuchet simulator and see what it suggests for launch angles but haven't gotten to it yet. Perhaps this evening.

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I wish I had some solid numbers for you folks to work with, but I don't. I can say that launch velocities can easily exceed 100 mph. This is from research done with a radar gun and from rough calculations based on empirical data of field tests. That would be at the low end of the speeds, for small machines, hurling small projectiles (oranges, golf balls, etc.) When you get into the bigger machines, well the speeds get high enough that even 'hard shelled' Lumina's (a preferred type of pumpkin for hurling) will either get crushed during the acceleration phase or rip themselves apart in the air, due to SPIN. I and many others have seen this happen too many times to count. This usually occurs fairly close to the time after the payload has left the Sling/Pouch, yet far enough away (most of the time) to eliminate the Sling itself as a possible instrument in the payloads destruction.

I should point out that under the right circumstances, the Sling can and has been able to 'reach out' and 'spank' the payload. In the case of softer payloads, this can result in two or more chunks of payload going 'that-a-way' rather than a single load. On very rare occasions, the payload may be under enough stress already, due to a high spin rate, that a light touch by the sling will cause the stress to overcome the structural integrity of the payload. *splat*

I concur with others here that the vast majority (90% +) of hurled projectiles have a back-spin to them. This assumes that the machine in use has a typical Sling and is not a 'spoon-a-pult' or other style.

Having seen my kids safely grown up, I've abandoned certain precautions in my life and have stood 'on target' while a variety of projectiles have come in for a landing. I do NOT suggest anybody try this! (I'm stupid, okay?) The closest anything has come to me is about 1 foot. It was a 16 pound bowling ball at the completion of approximately 130 yards of ballistic travel. (I did say I was stupid, yes?)

Point being, the Trebuchet in use was considered to be a fairly low-power machine and the spin on the bowling ball was slow enough to see very clearly with the naked eye. Back-spin, no doubt.

When you switch over to the more powerful machines though, trying to determine what, if any, spin the projectile has becomes very difficult, for two reasons.

1. That sucker gets out of sight too quickly!
2. The spin is so great that is becomes almost impossible to see which direction it is spinning in.

Spin in other directions? Yes, although usually oriented close to the same horizontal axle of rotation of the more typical hurls. In some cases, not too rare, the Sling (for whatever reason) will twist such that instead of back-spin, either side-spin or even top-spin will occur.

I've hurled many types of projectiles, from little 1/4" wooden balls, golf and tennis balls, bowling balls, gallon jugs of liquid, chain maille shirts, computer units, etc. I've used many types of Pouches with different designs and made of different materials.

My own experience and observations, for whatever they're worth, indicates to me that Payload Spin is derived from several sources.

1. Rotation of Sling and Throwing Arm.
Oddly, this would put top-spin on the payload, something seldom seen. The force producing the rotation rate by this action though is considerably less then that produced by other angular momentum forces, so is not seen. It does have an effect though, reducing whatever spin rate the other forces generate.

2. As indicated by Ron, the two Sling anchor points and the separation between them can produce what we call Pouch Roll. This will, with a typical Sling set up, produce back spin and can be tuned. This is an area of tuning not often used though, as it can produce other, undesired effects, such as less range or too high a spin rate. *splat again*

3. Friction between the Payload and the Pouch.
Now this is something that I cannot quantify, even by empirical methods. I simply have no way to measure it, I have observed it though. If there is a low coefficient of friction between the Pouch and Payload, the spin rate is reduced. Vise-versa can be observed also. I should point out that this is an area of research that, to the best of my knowledge after 10+ years in this hobby, has not been done heavily. I do know that there is controversy about it and that some Hurlers say it matters a great deal and others say not. There are simply too many differing variables between the hobbyists, in regards to observations, pouch materials, pouch designs, type of payloads, etc., to make even a good theory on empirical evidence.

I believe that Payload/Pouch friction is a large contributor to spin though.

By the way, spinning bowling balls make a wonderful noise! The fingers holes make a whistling like sound but it 'warbles' as the ball spins.

Just remembered: During a 1 shot test experiment, using a bungee cord powered catapult, with a sling, I shot a ping-pong ball. Yea, over-kill big time! Point being, the ball released at a very low angle, close to horizontal, then climbed up sharply and I ran after it, thinking I could catch it, which I did. The 'oddest' thing about this was that I was under the ball at or near the time of apogee and did NOT have to move forward any more to catch it. The forward flight of the ball had dropped to zero. No proof, no pictures and you don't have to believe me. I take that experience though and include it in my thinking when considering flights of pumpkins.

Request:
You folks seem to have a good grasp of aerodynamics and the mathematics behind it all. My math has rotted away over the years and although I can research equations, I've never come across a Reynolds number for pumpkins, of any species. From what I've learned though, without a Reynolds numbers, any computations will be pretty lean on accuracy. So is there are good number available and where could I find it?

Maybe I need to set up my own wind tunnel for gourds?

Reynolds number is fairly easy to come by, actually. It is simply the product of the density of the air, the velocity of the air, and a characteristic length (usually diameter for a sphere-like object), all divided by the dynamic viscosity of the fluid. I'll assume 100mph, standard sea level air, and 10" diameter for a quick calculation here:

V=44.7 m/s
rho=1.225 kg/m^3
L=0.254 m
Dynamic viscosity=1.983*10^-5 Pa*s

This gives a reynolds number Re=7*10^5. Typically, for a sphere, reynolds numbers of over around 3 or 4 *10^5 imply turbulent flow, and a Cd of around 0.2. Since pumpkins are somewhat lumpy and irregular, this would if anything increase turbulence (similar to the dimples on a golf ball), which means that it is likely that the critical reynolds number is even lower (and that the pumpkin is even more solidly in the region of turbulent flow).

The main factor that I am unsure of now is a plausible lift coefficient.

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Lift coefficient isn't a function of angular velocity. Lift, however, is: F = 1/2 * p * w * r * V * A * l

Where:

p 1.2 kg/m^3 density of the fluid
w 221 RPM angular velocity
r 0.1524 m radius of the ball
V 44.7 m/s velocity of the ball
A 0.072965877 m^2 cross-sectional area of the ball
l 0.225347651 lift coefficient


Sorry!

For smooth ball with spin ratio of 0.5 to 4.5, typical lift coefficients range from 0.2 to 0.6

0.5 0.2
4.5 0.6
4 0.4
slope (m) 0.1
y-intercept (b) 0.15
y=mx+b

And:

Drag coefficients (standard)
sphere 0.47
half-sphere 0.42
cone 0.5
Angled cube 0.8
rough sphere 0.4

So no way you're going to get a .20 Cd.
.3 is way low, too.

That's excellent, as the drag coefficients are for 10^2 Reynolds numbers, so we're very close.

Here are some numbers and a trajectory for a 200mph shot with a lift coefficient of 0.2, released 10 feet off the ground, and pumpkin dimensions as given by Trebuchet above (10", 9lb):

Range: 360 meters
Optimum angle: 28.65 degrees
Flight time: 10.32 sec
Max altitude: 109 meters

(In feet, that's 1181 feet range, and 358 feet max alt)

The trajectory is attached - the axes are scaled equally, so this is what the trajectory would actually look like. It's interesting how linear the initial climb is.

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PumpkinTrajectory.png (9.1 KB, 12 views)

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Here's the page I'm going off of from my Aero textbook - as you can see, those look like values for a subcritical (laminar) flow, while the pumpkin is supercritical (turbulent). Take a look at the sharp dropoff in drag at around Re=10^5.


(Hopefully, reproducing a single page is OK)

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Sphere drag.jpg (139.2 KB, 13 views)

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My bet is that those drag coefficients are for laminar flow at Re=10^3-10^4 or so. Take a look at my scan from my aerodynamics textbook - for Re~10^6 (as it is for the pumpkin), the drag should be quite a bit lower.

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Where are you getting that equation? I'd be curious to see the source, since it is vastly simpler than anything I've found so far.

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This is a great discussion. I won't pretend to be trying to understand the math at this point. Even though I work in aerospace, I'm not an aerodynamicist. (I do know a few of them, however.)

CJL, I'm surprised how low that trajectory is. 200mph for a starting velocity seems a bit high for most trebs. Would a lower speed have a higher optimum angle? What you've modeled looks about like what I'd expect for an onager (torsion catapult) however.

Oh, and hi Rip! Nice to see you here. Too bad the original poster has not seen fit to return.

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A lower speed would have a higher optimum angle, yes (for the same lift and drag coefficients). What kind of distance are the higher end pumpkin trebuchets throwing though? 200mph may sound high, but I wouldn't be that surprised if it were fairly close to that (and knowing a typical distance would help narrow down some of the other parameters).

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As an interesting experiment, I just plugged in some values for a ping-pong ball with lots of spin (Cd~0.5, Cl=0.3) at 100mph launch speed into my program, and here's the optimum trajectory:

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The big guy at our event in Snohomish threw about 1800 feet. They've done 1866.9 in the past, which was a world record at the time. There are a couple of folks pushing for 2000 feet at the world championships in Delaware next weekend.

By the way, the launch height for that big guy is on the order of 90 feet -- 58.5 feet to the arm tip plus around 30 feet of sling!

The best of the torsion catapults did over 3000 feet in Delaware last year. I can well believe over 200mph for them.

I did play around with the simulator software last night, varying sling lengths to get different launch angles. But it also affects the speed and I couldn't find where to get it to tell me the angle. I'll take a look at modeling a large treb and see what sort of launch speed it tells me.

If you go to this page and type Burlington in the search box, you'll get some videos that include the big guy and assorted others. If you see people in lab coats and funny wigs, that's my team!

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And if I account (admittedly quite roughly) for the fact that something as low mass as a ping pong ball at high speed will significantly slow down its rotation in flight (thus dropping the coefficient of lift as it flies), the optimum trajectory becomes this (quite close to your description, actually):

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If anything, 200mph is too slow then. Even with unrealistically high lift coefficients and quite low drag, I can't get a pumpkin thrown at only 200mph to reach anywhere near 550m (~1800 feet). I can get 400m, but the lift to drag ratio needs to be something like 3:1 in order to do that (which I sincerely doubt a pumpkin can pull off).

Now, 270mph is sufficient to pull off that kind of throw, especially with a bit of backspin. The trajectory is quite low initially to do it though...

Details of this shot: Cl=0.2, Cd=0.25, V0=120m/s (~268mph), h0=30m.

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I'm playing with the simulator and just ran an old model of my 2008 machine. Release velocity was 30.9 m/s, around 69 mph, for a throw of 95.3m or 312 ft. That's a modest machine so 200mph is sounding much more realistic to me now. Flight time for that comes out as 5.56 sec. The sim lists a "release angle" of 41 degrees but based on last night that doesn't correspond with the angle we're looking for. I don't know what it is.

By the way, actual distance that year was around 280 feet. I don't think we had as much counterweight as I had put on the sim.

It'll take me a little while to put together a reasonable model of the big guy so I probably won't have that until this evening.

Edit to add:
Found a model of a more powerful version.
Range 332m ~ 1090 ft
Flight Time 10.29 sec
Missile velocity 63.2m/sec ~ 141 mph

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Hmm...
332 meters with 63m/s? That corresponds quite well to my model if I use a Cl of 0.2 and a Cd of 0.25. I get 333 meters and an optimum angle of 32 degrees using those values. My flight time is a bit short though - only 9 seconds.

I also just reran my simulation for the above case, and it turns out that the above values are wrong. I accidentally used radius instead of diameter, so the values there are for a much smaller pumpkin. Using the correct value for diameter, I can get to 1800 feet with 90m/s launch velocity at 30m initial height (201 mph).

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You're right in that the Re~10^6, so according to your graph, Cd=0.1.

Now when I spin the numbers using the Excel spreadsheet I created, the Magnus effect remains equal to the pumpkin's mass:

12" pumpkin
221 RPM
100 mph

But the initial drag falls to 8.75 kg, or 0.6 g, which is a lot more reasonable.

Thanks, cjl!

I still think you're doing the units wrong - I get 8.9 newtons of drag for the scenario that you are describing.

EDIT: I also found that formula for lift that you are describing. I'll look into it a bit more and see if I can't make some sense of a good way to simulate it.

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Well, after significant expansions to my code, and the addition of velocity and spin dependent Cl and Cd values (I found a couple of useful papers and research documents), I have what I believe to be the most accurate code yet. Here's the plot for 200mph, 10" 9lb pumpkin, 95 ft initial height, 2000rpm spin rate (somewhat of a guess based on the fact that at 90m/s, a 10" pumpkin would spin at 3400rpm if it were on a stationary surface and not slipping) - the optimum angle is now 30.1 degrees.

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Oh, and here's the new code (sorry, some sections are kind of ugly)


%% Pumpkin throwing calculation

%This program calculates the distance and ideal angle for a pumpkin of some
%size and density thrown at a user-inputted velocity and rotation.

clear all
close all
clc


%% User inputs
v=input('What is the release velocity of the pumpkin (m/s)?');
h0=input('How high off the ground is the pumpkin at release (m)?');
d=input('What is the diameter of the pumpkin (m)?');
rho=input('What is the density of the pumpkin (g/cm^3)?');
Omega=input('What is the spin speed of the pumpkin (rpm)');

%% Initial values
% Setting up an array of angles
alpha=linspace(0,pi/2,1000); %rad


%Calculating needed values
mass=4/3*pi*(d/2)^3*rho*1000; %kg
Area=pi*(d/2)^2; %m^2
Omega=Omega/60*2*pi; %rad/s
v_spin=Omega*d/2; %m/s
%Setting constants
rho_air=1.225; %kg/m^3
DeltaT=0.01;
n=1;
G=-9.81;
mu_air=1.983*10^-5; %Pa*s
Re_Crit=2*10^5; %Critical reynolds number for transition to turbulent flow



%Initializing arrays
x=zeros(1,length(alpha));
y=zeros(1,length(alpha));
y(1,:)=h0;
vx=zeros(1,length(alpha));
vy=zeros(1,length(alpha));
v_tot=zeros(1,length(alpha));
Spin_ratio=zeros(1,length(alpha));
vx(1,:)=v*cos(alpha);
vy(1,:)=v*sin(alpha);
v_tot(1,:)=v;
Reynolds(1,:)=rho_air.*v_tot(1,:).*d./mu_air;
Cd=zeros(1,length(alpha));
Cl=zeros(1,length(alpha));


%% Calculating trajectories
while(max(y(n,:)>-.1))
Spin_ratio(n,:)=abs(v_spin./v_tot(n,:));
%Defining piecewise functions for Cl and Cd as a function of spin ratio
%for supercritical reynolds numbers
Cl(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<0.3)=-Spin_ratio(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<0.3)/5;
Cl(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<0.6 & Spin_ratio(n,:)>=0.3)=-0.27+0.733*Spin_ratio(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<0.6 & Spin_ratio(n,:)>=0.3);
Cl(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<1.5 & Spin_ratio(n,:)>=0.6)=.03+.233*Spin_ratio(n,Reynol ds(n,:)>Re_Crit & Spin_ratio(n,:)<1.5 & Spin_ratio(n,:)>=0.6);
Cl(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)>=1.5)=0.44-0.04*Spin_ratio(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)>=1.5);
Cd(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<0.1)=0.3+2*Spin_ratio(n,Reynolds(n ,:)>Re_Crit & Spin_ratio(n,:)<0.1)/5;
Cd(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<0.6 & Spin_ratio(n,:)>=0.1)=0.36-.13*Spin_ratio(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<0.6 & Spin_ratio(n,:)>=0.1)/0.6;
Cd(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)<1.5 & Spin_ratio(n,:)>=0.6)=0.1+.2*Spin_ratio(n,Reynolds (n,:)>Re_Crit & Spin_ratio(n,:)<1.5 & Spin_ratio(n,:)>=0.6)/0.9;
Cd(n,Reynolds(n,:)>Re_Crit & Spin_ratio(n,:)>=1.5)=0.38+.05*Spin_ratio(n,Reynol ds(n,:)>Re_Crit & Spin_ratio(n,:)>=1.5)/1.5;

%Defining piecewise functions for Cl and Cd as a function of spin ratio
%for subcritical Reynolds(n,:) numbers
Cl(n,Reynolds(n,:)<Re_Crit & Spin_ratio(n,:)<2)=Spin_ratio(n,Reynolds(n,:)<Re_C rit & Spin_ratio(n,:)<2)*0.225;
Cl(n,Reynolds(n,:)<Re_Crit & Spin_ratio(n,:)<10 & Spin_ratio(n,:)>=2)=0.45-(0.25/4)+Spin_ratio(n,Reynolds(n,:)<Re_Crit & Spin_ratio(n,:)<10 & Spin_ratio(n,:)>=2)*0.25/8;
Cl(n,Reynolds(n,:)<Re_Crit & Spin_ratio(n,:)>=10)=.065*Spin_ratio(n,Reynolds(n, :)<Re_Crit & Spin_ratio(n,:)>=10);
Cd(n,Reynolds(n,:)<Re_Crit & Spin_ratio(n,:)<5)=0.5;
Cd(n,Reynolds(n,:)<Re_Crit & Spin_ratio(n,:)>=5)=0.6-.02*Spin_ratio(n,Reynolds(n,:)<Re_Crit & Spin_ratio(n,:)>=5)/1.5;

if Omega<0
Cl(n,:)=-Cl(n,:);
end

%Calculation of lift, drag, and the actual trajectories
n=n+1;
x(n,:)=x(n-1,:)+vx(n-1,:)*DeltaT;
y(n,:)=y(n-1,:)+vy(n-1,:)*DeltaT;
xDrag=-vx(n-1,:).^2*rho_air/2.*Cd(n-1,:)*Area.*sign(vx(n-1,:));
yDrag=-vy(n-1,:).^2*rho_air/2.*Cd(n-1,:)*Area.*sign(vy(n-1,:));
xlift=-vy(n-1,:).^2*rho_air/2.*Cl(n-1,:)*Area.*sign(vy(n-1,:));
ylift=vx(n-1,:).^2*rho_air/2.*Cl(n-1,:)*Area.*sign(vx(n-1,:));
xaccel=xDrag/mass+xlift/mass;
yaccel=yDrag/mass+G+ylift/mass;
vx(n,:)=vx(n-1,:)+xaccel*DeltaT;
vy(n,:)=vy(n-1,:)+yaccel*DeltaT;
v_tot(n,:)=(vx(n,:).^2+vy(n,:).^2).^0.5;
Reynolds(n,:)=rho_air.*v_tot(n,:).*d./mu_air;
clc
simulation_elapsed_time=(n-1)*DeltaT %#ok<NOPTS>
end

clc
%Eliminating data points that are underground
x(y<0)=NaN;
y(y<0)=NaN;

%Finding optimum angle
range=max(x);
alpha_optimum=alpha(range==max(range));

%% Displaying and plotting optimum results

Optimum_Angle=alpha_optimum*180/pi %#ok<NOPTS>
Range=max(range) %#ok<NOPTS>

plot(alpha*180/pi,range)
xlabel('launch angle (degrees)')
ylabel('range (meters)')
title('Range vs launch angle','Fontsize',16);

figure

plot(x(:,alpha==alpha_optimum),y(:,alpha==alpha_op timum));
xlabel('range (m)');
ylabel('altitude (m)');
title('Optimum trajectory','Fontsize',16);
axis equal

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Wow! cjl, you are doing some very interesting work. Of course the next step is to build yourself a pumpkin hurler and verify your theoretical work with experimental results!

For what it's worth, Trebarbaric, the big machine I've referred to, throws MUCH higher than what you've calculated. Probably more like 60 degrees to the horizontal than 30. High enough that I've actually felt a bit of concern about the TV news helicopter hovering over the park. Probably it's not optimum and they would do better if they could lower their trajectory.

However, I do think your spin rate is too high. Just as a guess, let's say the pumpkin makes 1/4 turn in 1/10 of a second coming out of the pouch. That would be 150 RPM. Also, pumpkins are not spherical. If launched end-over-end, it's more of a tumble than a spin. So we may be giving Magnus too much credit.

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I did actually bump the drag up a bit and the lift down to try to account for the non-spherical nature of the pumpkin (though it's hard to get a really good result this way). As for the spin rate, what would be really nice would be some good high-speed video of a pumpkin throw. Anyone have any? As for angle, the trajectory there is already pretty darn high - it's already exceeding 500 feet in altitude for that calculation, which is nothing to sneeze at. I looked up some video of TreBarbaric, and it's hard to tell what kind of angle it's launching at. The sling appears to release significantly lower than 60 degrees to me, but given the video quality, it is extremely difficult to be sure.

(Honestly, while you're almost definitely right that 2000rpm is too high, I think 150rpm sounds low. I'll run some more numbers though)

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Here's a picture of Barbaric releasing one in 2007, the year they did 1866.9 ft at Burlington. Looks high to me. I've felt it was probably going over 1000 feet up but it's purely a guess. I suppose next year I should take along a stopwatch and see how long it's up there.

I don't know of any good video, likely there's some out there.

Edit to add: Since you've seen video of Barbaric, you've presumably heard the sound it makes. You should hear it for real. I will NEVER get tired of that!

One more edit: I just realized the motion blur in that picture gives a good impression of the launch angle. Looks higher than 45 degrees but not as much as 60 -- perhaps 50 degrees? If the video is at 30fps, does this show how far the pumpkin is moving in 1/30 of a second?

Yet another edit: Aaargh! That's not a video capture - I took it with a DSLR. Lots less than 1/30 second!

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Kind of a silly question, but has anyone ever tried to design a pumpkin catcher? I imagine there would be tremendous difficulties since you don't know where it will go, but maybe a big net dragged by a truck or something.

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Most folks kind of like to avoid being too near the landing site! And the pumpkins are rather fragile. I suspect the net would act as a sort of sieve. During the hurling events, however, there are guys out in the field in ATV's chasing down the landings to get measurements. I've seen them get a little too close on occasion and get splattered with pumpkin.

The little pumpkins I was hurling this year are a bit stouter, and some can be re-used a couple of times. You could catch them with a baseball mitt.

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Such joy!

As a fond former right-fielder, I'm with you! I think I'd be more fun to tackle them with a bat, though...

After watching some more video, it seems even more difficult to be sure of what the actual spin rate is. You're right that Barbaric seems to be releasing higher than the optimum, but there are other machines throwing quite far that look like they are going for a fairly low trajectory (here's one example I found: http://www.youtube.com/watch?v=vsSwOb9PtaA ).

Overall, I can keep guessing, but without having some better information, it's hard to refine anything more. Was that shot taken in a sequence by any chance?

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Nope, no sequence, just the one shot. And yes, certainly most of the other reasonably high performance machines, such as J-Buchet in your linked video, throw lower. It's just as well Barbaric wasn't optimized -- the event was in a public park and the pumpkin landed 10 feet from the park fence, splattering pumpkin on someone's house. They actually took some weight off for their next throw and probably went farther, but it couldn't be measured because it went over a dairy warehouse, over a couple of houses, and landed next to someone's horse trailer. That was the end of hurling for distance at Burlington, it's accuracy now.

J-Buchet, by the way, is extremely impressive in person. Darn near silent, just smooth and powerful. And beat me out (just) for the efficiency award, range divided by counterweight. It was professionally built by a company that designs and manufactures tooling for composites, including for Boeing. It was the first large hurler using a new design concept. If you looked at the Burlington videos, you may have seen a traction trebuchet operated by two skinny teenagers pulling on ropes. One of those kids invented J-buchet. A very smart young fellow.

For spin rate, how does this sound:
Let's say pumpkin leaves the pouch in 1/20 second, turning 1/2 revolution as it does so. That's 10 rev per second or 600 rpm. I think that may be reasonable.

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