Calculating Lift

[Guest PyroManiac1]

I have heard lift is 8% of shell weight, 10%, 12%, and even 15%. I am trying to calculate the lift of 2 and 3 inch ball shells, could anyone point me towards the right percentage that will launch my shells a safe height. Thank You.

[Richtee]

Well, kinda depends on the lift powder being used. Let me re-phrase that... it almost ALL depends on the powder being used

 

I’d reliably lift 3” shells with 12-15 grams of my corned BP ( around 6% shell weight) but it was a really good powder. You can use a baseball (or a dummy shell) to gauge your lift amounts. Height in feet= (t^2 x 32.2Ft/sec^2)/2 where t= time aloft

 

Also consider my 3” tubes were 22” long..this affects lift amounts as well..shorter tubes, more lift powder needed.

 

(on edit: fit of the shell in the tube as well. I always took reasonable care to have no more than about .125” clearance... so your taping matters as well.)

 

There’s a chart somewhere on safe lift heights,,, I think you want at least 300 feet for 3”? And it’s always best to err on the side of too much lift as you can imagine.

Edited June 5, 2020 by Richtee

[Mumbles]

Have you made any star mines, comets, or anything else that had been lifted yet? It might give you an idea of how good your lift is. Personally, I'd start on the higher end, and back it off if you need to. Maybe 15% to start. Less is more common. I personally settled in around 10% using 4FA for ball shells. A little over 6% (1oz per pound) is more common with cylinder shells and heavier shells. You'd want to get up towards a pound or two at least for that though.

[MadMat]

A 3" tube is a real good fit for a baseball! If you weigh your baseball and then, starting at about 10% do a few trial launches with different percentages of lift powder, you will get a good idea of how much to use. I personally do base ball tests on every new batch of BP I make. These tests let me know how good of a job I did making it and, if any, adjustments need to be made using the batch. I have found, with my usual quality of BP, that 10% is good for smaller shells. As the shell size increases that percentage goes down. Remember, this may be a little different for you. Oh yeah, I exclusively make cylinder shells.

Edited June 5, 2020 by MadMat

[Arthur]

Lifting small shells may need proportionally more powder than lifting large shells

 

2" shells same lift and shell weight

6" shell 1oz per pound shell weight

16" shell 3 pounds of lift to about 50 pounds of shell.

 

Do tests, test high then reduce the lift til the shall breaks safely. the shell should break high enough to keep the stars well off the ground.

[Guest PyroManiac1]

I will be using an 18" tube as that seems to be the average for 3" and a 12" tube for 2". The powder is pretty fast, it doesn't burn through paper and makes a pretty nice poof. Thanks for the advice everyone, I'll get to some testing Edited June 7, 2020 by PyroManiac1

[Arthur]

The lift is part of your design! too little lift and the shell breaks dangerously low, too much lift and it breaks high and looks lost in a big sky.

 

Note also that small shells need a finer lift than large shells, a 2" shell may use 4FA while a 16" shell will use a cannon grade or 0FA (grains you can pick with fingers).

[kingkama]

I use 15 to 18 of 2 hours milled willow bp, dextrine bonded 2% and granulated by water. The idea is to lift a shell until the explosion go off at apogee or when shell starts to fall

[dynomike1]

1oz per lb works pretty good up to i think 10lbs. I dont have my notes right now.