angle and height calculations

[wrtiii]

Because the shell is moving rapidly? Because it is at its peak only for a very brief time?

[stuntborg]

Besides drag and initial velocity you must also account for the friction loss of the tube. Length of the tube will also change your results.

Density must also be accounted for in your calc's (density=mass/volume). Mass, regardless of where it is (vacuum or atmosphhere) always remains constant.

IMO you also need to account for human interaction. Calculations of amount of material proportions (lift charge etc.) that go into the production of these "projectiles" will skew your results.

Can someone explain why the angle from the ground to the shell can't be accurately measured?

Getting way to complicated here. Last question first. Follow these simple directions.
1. Stand up.
2. Put your left arn in.
3. Put your left arm out.
4. Put your left arm in. Do the hokey pokey and turn yourself about.

Hmm...doesn't seem right, lets try again.

1. Stand up.
2. Put your left arm out.
3. Put your right arm out but point it at the ceiling light in the next room over.
The angle between your left and right arm is the angle of interest. Now, pretend you are shooting a shell. Your right arm points to the shell as it goes up. You some how need to acurately measure that angle. thats one way to calculate the maximum height of a shell.

Another way would be to use a high speed camera and calculate the muzzle velocity. Friction in the tube, lift charge, height of the tube, all that stuff doesn't factor in since it happens before you measure. You still get the argument about air resistance and all that fun stuff. Probably a valid argument.

Best way to measure the height of a shell? Get a really long and big tape measure. Mount it to something two hundred feet tall. Shoot 20 shells and record the height of each shell based on the tape measure.

[lamrith]

I haven't gone thru my training manuals in a while, but I recall from my training class years ago you don't want that much angle (15*) on your mortars anyway? If I recall I think the max my instructor recommended as Std practice was like 3* with 1.3, as the hieghts involved would do the work to separate the shells, plus the issue of duds falling to earth and wanting them to do that INSIDE the safety zone. Maybe there isn't a code, that was his rule for safety (His shoot, his rules), but it is one I have always followed even on my own private 1.4 shows.

[nepyro]

The link below is to a wonderful piece of work by Developed by John Harradine, Manly, Queensland, Australia with additions by Tom Smith, Davas Ltd, UK. It is called ShellCalc. I use it when I am worried about where a shell will go or where a dud might come down.

ShellCalc - via Journal of Pyrotechnics Archive

Their brains have more wrinkles than mine

Enjoy!

[unipyro]

http://www.ehobbies.com/qus7812.html...mpaign=froogle

so simple..

[Pyro Nut]

Your way is definitely easier dude. I'm with you on this one.
....my head hurts...

It's like having a slurpee on a hot summer day and getting that brain freeze feeling.........ow, ow, Ow, OW

lol

[stuntborg]

http://www.ehobbies.com/qus7812.html...mpaign=froogle

so simple..

I remember using those back in high school. They work about as well as you would expect a six dollar altitude measuring tool to work.

[unipyro]

I remember using those back in high school. They work about as well as you would expect a six dollar altitude measuring tool to work.

yes, but if you don't want to do any calculations, its very simple.

[Hfireworks]

This chart may help, I use it to vary shell size and distance.

[fourqtwo808]

niceee

[hi-revr]

These type threads are always entertaining. They make me realize there are a lot of people much smarter than me. The topic is a good one and it makes me think. I too have wondered how much angle I should give racks. The problem is no two shots are ever identicle. Having a shell canted to one side will affect it's height. Variations in shell OD will affect the pressure generated by the lift charge.

I wonder if cylinder shells are more consistent? I don't have enough experience to answer that.

[infinite1der]

I wonder if cylinder shells are more consistent?

I'd say that the increased volume of a cylinder shell would allow for a greater variance in mass between shell1, shell2,...shelln, and would be less consistent. But, them more data points you have, the smoother the curve, eh?

--JamesT

[John Ross]

Just found this thread.

First, initial velocity of a mortar round is MUCH higher than the calculations based on lift time in a vacuum would indicate.

With appropriate lab gear I measure the velocities of bullets regularly, and can do the same with shells if you want, but the initial velocity of a shell doesn't do much to tell us how high the shell will go. Drag is huge compared to a bullet and will vary a lot depending on shell construction.

Standing off a large distance (1000 feet or so) and using a protractor type device to measure the angle to the burst is going to be the most reliably accurate method.

JR

[Marty]

Neils chart is a good rule of thumb for standard star shells but,

Size, weight and wind are major factors in specialty shells. In a mild wind a 6" parachute shell breaks much lower. They are very light with a lot of area the wind will hit, add that to the long burn time of the lance or water fall effects and you have a fire recipe. Willow/brocade shells are another high wind problem.

Another problem with mortar angles, ball shells leave the tube spinning and react like a pitchers curve ball sometimes.

I don't know about other choreography software, but I like the "Priority" assignments you can use in FireOne to shut down certain shells during the display without interrupting the display if weather problems arise.

[yeagerb]

I have often wondered if the ball shells were "curve balling".....I've noticed that on many occassions while spotting shells...thought it was an optical illusion or time to get my eyes checked!

And that is a KEWL feature of Fire One - prioritizing shells and the ability to drop priority while shooting....

[hi-revr]

I have often wondered if the ball shells were "curve balling".....I've noticed that on many occassions while spotting shells...thought it was an optical illusion or time to get my eyes checked!

Good thought. Actually they are "knuckle-balling". The "curve-ball" effect is similar to a wing shape causing differences in air pressure/flow on one side verses the other. If we had rifled mortars they would be much more predictable and would rise higher.I have given some thought on how to accomplish this.

Problem one(of many)....necessity of consistent shell O.D.
Problem two....damage to shell ....King-sized Sabot?
Problem three.... increased pressures.......Old cannon barrels, 105mm is 4 1/8" approx. HHMMMMM

Just found this thread.

First, initial velocity of a mortar round is MUCH higher than the calculations based on lift time in a vacuum would indicate.

With appropriate lab gear I measure the velocities of bullets regularly, and can do the same with shells if you want, but the initial velocity of a shell doesn't do much to tell us how high the shell will go. Drag is huge compared to a bullet and will vary a lot depending on shell construction.

Standing off a large distance (1000 feet or so) and using a protractor type device to measure the angle to the burst is going to be the most reliably accurate method.

JR

Sounds like between us we could do some killer research. I have the diagnostic equipt to measure pressures very accurately and a shoot site. Maybe we could get a grant from Wash U?

I think the protractor refered to a few times is called a clinometer, used for things such as measuring tree height for logging. I have always wanted one. It would be easy to rig an inclinometer to a large stick on a stand and have a simple aiming device. Since you would be at a known distance(within reason) height of a group of the same shells could be averaged. Where's a statistician when you need one?