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Calculating Gun Performance

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Calculating Gun Performance

Unread postAuthor: dapaintballer331 » Tue Jan 01, 2008 2:47 am

I made a quick physics calculator in PHP.
All numbers given will never be reached because of air drag, but they can give you a rough estimate. This is all for fun.

Part 1: (shooting gun straight up for simple calculations)

Code: Select all

Part 2: (using part 1's info to find max distance traveled for angled shots):

Code: Select all

(I can probably re-work my equations to not need so much information, but for now it isn't *that* hard to find distance (just more info needed&I could probably add more possibilities (new landing height, etc)))

I DO NOT have ads, it's all here for fun.

I will probably post the source code once I get it all cleaned up, for those interested in how it's calculated.

I'm sure there are better calculators out there, maybe even in this forum. Just thought I'd post what I made. Most of you make replicas, better or worse of other's guns, why not another calculator?

Edit 2:
If you want accuracy, use this. If you are't going to use calculations to try and hit (or not hit) something, then my calculator is fine.
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Unread postAuthor: jimmy101 » Tue Jan 01, 2008 12:50 pm

Hmm. For the first calculation;
If a projectile's path is perfectly parabolic, air resistance has little affect.

That isn't true. The only time air resistance "has little affect" is when either the projectile has very low drag or very low velocity (or both). In general, air drag has a large affect on the trajectory of a projectile the size of a spud moving at typical spud gun velocities.

For hang times, there is a huge difference between the calculations with and without air drag.

Baseballs and golfballs both have terminal velocities of about 130 FPS. Figure a spud has a similar terminal velocity. When fired straight up the velocity that these shells will hit the ground will never be more than their terminal velocities (~130FPS). But, their muzzle velocities are usually much greater. For a spud from a typical combustion spud gun the muzzle velocity would be in the range of 300~600 FPS. This totally hoses the results from any hang time calculation that ignores air resistance.

Still, it is a nice javascript app.
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Unread postAuthor: WOW!! » Tue Jan 01, 2008 1:18 pm

Its a good start but there are others that are more accurate. Also as Jimmy said air drag as a super big affect on the different projectiles, and also the wind factor, if its blow off course it will mess with the time in turn with you results.

Its a good start.
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Unread postAuthor: Ragnarok » Tue Jan 01, 2008 1:31 pm

jimmy101 wrote:Hmm. For the first calculation;
If a projectile's path is perfectly parabolic, air resistance has little affect.

That isn't true.

I hate to correct you, but what he has said isn't that inaccurate.
If there is no air resistance, a projectile will follow a parabolic arc (assuming constant gravity), so - if something is following something close to a parabolic arc, air resistance must be very low.

However, you are of course completely correct when you say that things do not follow parabolic arcs in reality, and won't come close to it unless they are low drag co-efficent, low velocity or both. For low velocity calculations, the results shouldn't be too far out, but for our purposes, when almost all projectiles are over 100 m/s, the results are going to be come pretty inaccurate.
As an example, I know that one of my cannons fires a spud slug in the region of just under 300 metres (measured and confirmed), with a MV of 180 m/s, 30 degree angle, hang time of about 8 seconds. The calculator tells me my spud will hit over 1.2 km out, which would be enough for me to put a spud well into the next county. That's an error of over 300%, which could even be in to the realm of dangerous if someone places too much faith on the numbers.

It's good Javascript writing, but the maths behind it misses a seriously important element.
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