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Calculating projectile range

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Calculating projectile range

Unread postAuthor: Matt_NZ » Sat Apr 24, 2010 11:14 pm

Does anyone know what the inputs for this calculator mean?

http://www.ajdesigner.com/phpprojectile ... uation.php


Does anyone know how to calculate initial velocity and acceleration of gravity (9.82? earth gravity?).

I have got velocity from GGDT.
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Unread postAuthor: MrCrowley » Sat Apr 24, 2010 11:32 pm

You can calculate range with GGDT also.

GGDT>Tools>External Ballistics Calculator.
You will need to know the drag coefficient of your projectile though, the Cd value. I usually use between .2 to .25 for a golfball to get the most accurate results (in my experience). I've never calculated the range for any other projectile so hopefully someone else can help you with more Cd values.
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Re: Calculating projectile range

Unread postAuthor: Ragnarok » Sun Apr 25, 2010 8:16 am

Matt_NZ wrote:Does anyone know what the inputs for this calculator mean?

Yes, but more important is what this means: "Note: Valid only for equal initial and final elevation."

And what that means is that it's next to useless for almost any real-world projectile, because it doesn't account for drag.
If you're trying to calculate the range of a fast moving projectile over a long distance, not including drag in the equation makes the result utterly useless.
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Unread postAuthor: saefroch » Sun Apr 25, 2010 8:34 am

I'm confused by your post, Ragnarok. You mention a quote regarding elevation change, then relate this to drag? A formula for calculating range over different elevations can be derived using basic projectile motion equations, and it is possible to account for drag if you know the numbers... personally I take some issue with online calculators, and would rather crunch what numbers I can by hand.
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Unread postAuthor: spudtyrrant » Sun Apr 25, 2010 9:02 am

saefroch wrote:I'm confused by your post, Ragnarok. You mention a quote regarding elevation change, then relate this to drag? A formula for calculating range over different elevations can be derived using basic projectile motion equations, and it is possible to account for drag if you know the numbers... personally I take some issue with online calculators, and would rather crunch what numbers I can by hand.
what he means is according to this calculator a projectile landsat the same angle it leaves the launcher, but this is only true in an absolute vacuum, in real world examples the path is changed because of the drag and other variables. It takes a little more than basic knowledge once you bring drag and other variables into the equation, if you want it to be very accurate that is.
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Unread postAuthor: Ragnarok » Sun Apr 25, 2010 4:44 pm

saefroch wrote:You mention a quote regarding elevation change, then relate this to drag?

Depends on whether you take elevation to mean "angle of elevation" or "altitude" - both are reasonable interpretations of the word elevation.

And as far as angles, any projectile suffering drag will land at a greater angle than it was launched at*.

*Well, it's a little more complex than that. The earth's curvature means it's possible for a very fast and very low drag projectile to land at a lesser angle than it was launched at, but I don't believe there are many things capable of that task. Lift can also result in that, but again, rare that it will happen.

and it is possible to account for drag if you know the numbers

Sure. But possible does NOT mean simple or easy.

Even I'd head for a pre-written program if I wanted to calculate trajectories. Admittedly, I wrote said program, but I think that demonstrates the situation all the better - it's hugely less effort to write the program than it is to actually try and crunch the numbers yourself.

And there's no shame in that. Computers are designed to do mathematical calculations en masse.
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Unread postAuthor: saefroch » Sun Apr 25, 2010 6:27 pm

Ah, I thought you were referring to altitude, not angle of launch and landing. Yup, numbers are for number crunching, so if you can produce a program in a reasonable amount of time that will be used often, all the better. I've personally never found it easier to write a program than crunch the numbers for that specific scenario, but that's awesome if you're that good at programming.

And so far as drag is concerned, you'd need a wind tunnel or some sort like that to actually find the number for a homemade projectile, so I'd just use a chrono at a safe shooting range and forget about this whole discussion about calculating muzzle velocity.
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Unread postAuthor: SpudBlaster15 » Sun Apr 25, 2010 6:54 pm

saefroch wrote:I've personally never found it easier to write a program than crunch the numbers for that specific scenario


In that case, it's clear you have never accounted for a fluid atmosphere in any of your drag calculations.

A few years back, I wrote a relatively simple iteration based projectile range calculator in Excel, which could fairly effectively account for the force of drag. It took a fair amount of time to set the program up; but once it was done, one could obtain a range figure in a matter of seconds. If a person were to do the same calculations by hand, it would take hours to obtain just a handful of results.

As Ragnarok said, computers are designed for this very purpose.
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Unread postAuthor: saefroch » Sun Apr 25, 2010 7:24 pm

Again, sorry for context issue. What I meant was: "I've personally never found it easier to write a program for ONE INSTANCE than crunch the numbers for that specific scenario." I do know that creating a program to solve a problem like that multiple times is much worth it.
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Unread postAuthor: Ragnarok » Sun Apr 25, 2010 7:59 pm

saefroch wrote:What I meant was: "I've personally never found it easier to write a program for ONE INSTANCE than crunch the numbers for that specific scenario."

Hitting the "Calculate" button on my range calculator sets off a cycle of many tens of thousands of calculations.

If you think it'd be easier to do the number crunching manually, rather than writing a program that will do it for you, then be my guest. Personally, given that writing the program would be less work than the manual number crunching, even if I were only doing it once - and given that I plan on using the program thousands of times - I'm writing the program.
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