Shell height

[Merlin]

Does anyone know a "simple" formula for approximating say the height of a baseball launched from a 3 inch mortar? I have looked online and the educational stuff seems to be trying to determine with precision that is unnecessary and most require known velocity.

[LambentPyro]

300 feet is a good height for a 3" baseball/shell. It takes about 9 seconds of flight time (from the lift to the ground level it was fired from) to reach 300 feet.

[rogeryermaw]

i believe the formula is 16 x time x time. http://www.skylighter.com/fireworks/how-to-make/high-powered-black-powder.asp

 

there is a formula here about half way down the page. distance in feet = 16 x time x time or 16 x time squared.

Edited November 20, 2014 by rogeryermaw

[MrB]

i believe the formula is 16 x time x time. http://www.skylighter.com/fireworks/how-to-make/high-powered-black-powder.asp

 

there is a formula here about half way down the page. distance in feet = 16 x time x time or 16 x time squared.

I wonder if a shells terminal velocity is lower then the launchspeed from the tube. If not, then you can simply start the timer at launch, and stop it when you hear the "thud" of ground impact of the dummy shell. Do the math, and cut the result in half to get the height. That removes the "trying to estimate when it's at it's highest point" factor. And your reaction-time should be the same to both the start and stop push, giving a fairly accurate result. If TV is lower then the launch speed, then it starts messing with the results...

B!

[Merlin]

Thanks. I first tried golf balls out of the appropriate tube. Lost sight and a couple are still in orbit. I will first paint the baseballs bright orange on one side.

Edited November 20, 2014 by Merlin

[rogeryermaw]

I wonder if a shells terminal velocity is lower then the launchspeed from the tube. If not, then you can simply start the timer at launch, and stop it when you hear the "thud" of ground impact of the dummy shell. Do the math, and cut the result in half to get the height. That removes the "trying to estimate when it's at it's highest point" factor. And your reaction-time should be the same to both the start and stop push, giving a fairly accurate result. If TV is lower then the launch speed, then it starts messing with the results...

B!

from further down the page:

 

Note: An interesting relationship that I've noted during past tests is the amount of time a dummy shell takes to rise to apogee after being fired from the mortar, compared to the time it takes to fall to the ground. I've noted that it takes a spherical dummy shell approximately half the time to rise to apogee that it takes the shell to fall to the ground from apogee.

 

Another way of saying this is that, of the total flight time from launch of the dummy shell from the gun to it hitting the ground, one third of the flight time is spent rising to apogee, and two thirds of the time is spent falling to the ground from the apogee.

[MrB]

Meaning it's well above TV when leaving the tube, but still has a reasonably reliable relationship between the time taken up, and down. Neat. Thanks.

B!

[rogeryermaw]

definitely do something to keep your projectiles visible. a baseball from 300 feet would really screw up your day were it to get away from you and damage you, someone else or some property you are attached to.

[LambentPyro]

Thanks. I first tried golf balls out of the appropriate tube. Lost sight and a couple are still in orbit. I will first paint the baseballs bright orange on one side.

The lift fire will most likely burn the paint up. I attach a very long burning red star on it. You can remove one from a flare or find a formula and make it yourself but Walmart sells flares and baseballs, so it's much more convenient.

[rogeryermaw]

You can remove one from a flare or find a formula and make it yourself but Walmart sells flares and baseballs, so it's much more convenient.

does it take fire easily or do you have to prime it?

[gregh]

I am sure Walmart would take fire quite easily, but I would definitely prime well anyway...

[Shadowcat1969]

Yes, the lift does burn the paint most of the way off the ball. It turns the ball mostly black, which is actually an easier to spot color when the ball is in the air. It's just harder to find on the ground after it lands.

 

As Lambent says, so sort of rising comet or smoke star mounted to the ball works fairly well to keep track of it.

 

Wear a hardhat...even though it still would hurt quite a bit to be hit by a ball falling from 300', it probably wouldn't kill you with the hardhat.

[Merlin]

Well a flare or comet is a good idea. I put a bit of a tilt on the mortar -though not perfectly vertical and hence would introduce error to the height calculation I consider it worth it to put the balls down in a safe place. Your right about the paint burned off or covered with soot. They definitely come out much faster than they land. On the first one I was looking too low and didnt see it at all. But I did here it hit the ground. Like trying to see a rifle bullet. The next one I looked higher along the what I thought would be the flight path. I did observe it about half way up and until it hit the ground. My BP was not worth trying. I pretty much use benzolift. The baseball weight 153 grams. Got a bunch of used ones from ebay cheap. I used 15 grams of benzo or about .5 ounces. The calculation came out at 700 feet which include error due to the tilt. But my 3 inch ball shells weigh only 70-80 grams. Someone said the 3" balls should approximate the weight and size of a baseball. But my shells are definitely lighter. Maybe I will waste a shell as a dummy to get the right weight. I suspect 8 to 12 grams of benzo would be in range.

Thanks for all the comments

[Mumbles]

70-80g does seem really light. Mine normally came out between probably 120-150g. I suppose there are a lot of factors at play though. Hemi material, burst, burst media, poka vs. warimono, etc.

[schroedinger]

After we had a discussion about benzolift a couple weeks ago, i tested the bezo lift with 70 % whistle and 30 % green mix.

It works quite god, but i feel it is way to agressive. On a 150 g sell with 18 g i blow the mortar. 10 g gave still gone way to high. The best lift characteristics i got with a mix of 3.5 % shellweight benzo lift of fg size mixed with 3.5 % off ok (not the fastest) ffg size riced bp.

 

I gues in your 70-80 g shells you use stars like tiger tail?

[Arthur]

There is a simple theory in the UK that a shell should break at 100ft plus 100ft per inch diameter. So a 2" shell should be 300ft and a 6" shell should be 700ft.

 

EVERYTHING actually depends on the quality of fit in the mortar and the quality and quantity of the lift powder.

 

If you can measure the muzzle velocity (around 200MPH!) then you can calculate using the equations of motion and a value for g.

 

However there is usually little to gain from complicated maths when actual mortar bore can vary along a line of matched mortars.

 

Strangely there is a debate on UKPS currently about this with two members trying to out math each other with spread sheets with double partial differential equations but using estimates of the Reynolds Number to determine losses due to air drag with assumptions of the actual smoothness of the ball

( http://www.pyrosociety.org.uk/forum/topic/6942) Not for the faint hearted and way OTT.

 

I once saw a well worked example that about 5% of the available lift was transferred to the rising ball shell, largely from gas blow by due to poor fit, and pressure lost as the shell left the tube. (Chemistry of Fireworks -Michael S Russell -RSC ISBN 0-85404-598-8 P37 et seq) see www.rsc.org Still in copyright.

[rogeryermaw]

My personal working theory is: shell go up + shell go boom + no fire hits ground + people not hurt = raging success.

[schroedinger]

There is a simple theory in the UK that a shell should break at 100ft plus 100ft per inch diameter. So a 2" shell should be 300ft and a 6" shell should be 700ft.

 

Thats quite similar to the values given by hardt on page 243 where he states a 100 ft per inch diameter

[Arthur]

I remember a test of BP where various maker's BP was tested simply by time of flight of a cricket ball from a mortar (in England!) Times from 3 seconds to 12 seconds were found. Obviously there were un checked heights achieved.

[DaMounty]

Hello Folks,

 

Extremely new to the hobby. Infact I am just in the gathering materials fase.

 

Question 1. If my can shell is to be 1" od should my mortar id be 1" or slightly larger? Is there a rule of thumb for matching can shell diameters to mortars?

 

Thanks,

Da

[schroedinger]

Best way is to get your mortar first, then build your shell after the mortar. You want your shell to fit loosely to smooth inside the mortar. On a 1" you want about 1 mm clearance around the shell.

[braddsn]

DaMounty, you will want to get HDPE pipe for your mortars. Either that or fiberglass, but HDPE is superior in my opinion. Do some research on mortars and mortar racks. And 1" seems very small, but to each their own. You might want to look into 2.5" and larger. 3" is a fun size because you have a little room to work inside the shell. A 1" shell would be challenging due to the lack of space. Just some food for thought.

Oh and you might want to start a new topic instead of hijacking Merlin's post.

[DaMounty]

Hi

 

Thank you. Sorry about the hijacking.

 

Looking forward to learning and sharing properly.

 

Da