ballistic equations

[jim_w]

Hi all.

Does anyone know the maths behind things like chairgun? I got a bargin on a chrono at the gun shop, (I was the only > 14yo in the shop, so he was nice to me! ) so I've been thinking about ballistics. Given my pellet weight, can I just use newtonian mechanics and conservation of energy to work out the trajectory? Or are there special ballistic equations? Presumably I've got to take account of air resistance and things...

[GaraGun]

Don't you come on here with your fancy mathematics young man

'senough to give an old git heart palputations

Good luck in your quest for knowledge

[jim_w]

Bwahahahh. I can't find a smiley for 'waving A-level physics at you', so I'll just give you this one:

[Rich]

Seeing as air resistance has something like 50 times as much influence as gravity on the pellet's flight it would be a mistake to neglect it that's for sure.

Rich

[jim_w]

Yup. Is this what the 'ballistic coefficient' I've seen is for?

[Numb Nut]

Download and install chairgun 2. The equations used to calculate trajectories are in it's help pages if I remember correctly.

[AndyBlissett]

newtonian mathematics will get you most of the way there, Its only for really high velocities that newtonian methematics begins to break down (einstein et al). Air guns dont have velocities anywhere near in this range (you are looking at velocities above 0.5c really)

However, last time i checked i dont think that air resistance is in this field, and and far as i understand it, the rate of slowdown is a function of the balistic coef (but I dont know the function,altough it will probably be eithe linear or quadratic, with 0 constant, as obviously you wont have air resitance at 0 fps!)

Andy

[jim_w]

Andy: yeah, I seem to remember that air resistance goes with the square of velocity... And that's about all I remember from A-levels! ;-P

numbnut: yeah, I'll slide over to the gf's windows box and see what I can do.

[scottywong]

....errr weathers nice today init!!!

[Brian.Samson]

I made up a spreadsheet a little while ago which uses Steve_In_NC's equations (I believe the latest version of Chairgun uses these equations as well)

It's an Excel spreadsheet and there are two sheets in the workbook - should give you enough information to do whatever calcs you require.

The equations are taken as is from another application, so I'm not able to explain how they work or what the 'magic' number is all about, although I have a rough idea.

Have a look and see what you think. If you want to finish off the spreadsheet into a more polished solution, I'd be interested to see what you come up with.

You'll also notice on sheet 2 that for each range there's the option of entering a different BC value. The idea behind this was to investigate the suggestion that BC values will vary along the trajectory.

Personally - and I'm no expert by a long way! - I believe that BC is at best a rough estimate when applied to the sort of velocities involved in calculating airgun trajectories. It will vary from one barrel to the next and will also vary with differing MV's ( This was also Cardew's opinion as well, so maybe it's not such a silly theory afterall ).

The Excel spreadsheet can be downloaded from here : Ballistics Excel Spreadsheet Link

If you don't have a copy of Excel - you're out of luck

Hope that helps
All the best
Bri

[Gibbon]

If you don't have a copy of Excel - you're out of luck

No you're not !
If you don't have Microscrote Excel then you can download Open Office which is compatible with Excel files .... and Word ... and PowerPoint ... etc etc etc

Best of all ... it's FREE, which is more than can be said for the 'Office' Suite by Bill's bandits

[Brian.Samson]

Does 'Open Office' open my Excel spreadsheet Gibbon?

I seem to remember getting my copy of MS Orifice nice and cheap

[Gibbon]

As above ... Open Office is compatible with all the MS Office file formats

ATB