Most efficient firing system (shell w/ lift cup or mortar with cardboard disks (like cake mortars))?

[Pirotecnia]

Hi,

 

What of those firing systems you consider the most efficient?

 

1 - Shell with lift cup inside normal tube (mortar)

 

or

 

2 - Mortar with cardboard disk between the shell and the lifting charge (like cake mortars)

 

Using the same quantity of lifting powder and the same mortar lenght, which of them will reach the best altitude?

You can see the image attached to understand better what i´m saying.

 

 

Thanks!

[dan999ification]

most efficient is not always best,

for mines i prefer to use pistons to get the stars and inserts higher, for shells i see no benefit, if they dont go high enough use more bp or slightly tighter fitting shells, having a piston under a shell may cause overpressure in the mortar if its heavy same with tight fits, shells are meant to be a loose ish fit not like shooting cannonballs and with reasonable bp they should go high enough with 8-12% else the bp is not right in some way.

you also have more fallout with this method.

 

 

dan.

 

 

[Arthur]

I see two issues.

1/ whatever piston you use the pressures that BP should make will bend it or tip it so releasing the gas. Remember that the gas from the BP passing round the shell acts as lubricant to centre the shell in the mortar and to smooth it's exit. Odd loose bits may well leave extra debris that you have to clear up.

 

2/ transporting a firework to it's firing site is usually easily done within the law. transporting a shell in tube which is in UN category 1.1 may have problems for you, and in some places loose BP is more tightly regulated than the BP inside a shell/lift.

[dan999ification]

there could also be ignition problems, a pressed delay is almost essential,cake bombettes use pistons for a few reasons, good height on minimal bp sometimes as little as 5% and im sure it helps stop the bp getting trapped around the walls of the tube and insert or above it where its useless for lift.

transporting them without damage is easier if evrything stays where its supposed to be, shells are meant to be loaded on site so come complete ready to load, carrying a loaded cannon or many is not wise nor is loading this way on site.

and as arthur said [and i forgot] the lift gasses help centre the shell in the mortar giving it a smoother ride up and a straighter flight out.

taping a lift bag to the time fuse and pasting/taping it in is easier/quicker imho than making lift cups and safer than loading loose bp, some manafacturers and hobbyists do this to test items rather than making perfect shells that are just not needed for the purpose of testing.

 

dan.

[Seymour]

While both methods are perfectly good, the answer to your question depends on many factors... How tight does the disk? What is the construction of the lift cup like?

 

Overall though I think that the lift cup method is going to be "best". While you'll almost always be able to add more wadding (As Arthur pointed out, not always a good thing when you consider fallout), being a disk or otherwise to the side fused version to increase efficiency, the compact shape of the lift cupped lift charge reduces the distance the fire must travel to get full ignition. Furthermore you can just increase confinement by way of pasting layers of Kraft over the lift charge to easily further increase the efficiency.

 

A few years ago my black powder was of ok, but quite frankly below average. I was not terribly motivated to do anything about this, because with just two layer of pasted paper I was lifting shells with less black powder than most rules of thumb for commercial powder.

 

Anyone who has watched Black powder do it's thing at very high pressure (gun, cannon, anvil throwing...) will understand how much energy there is if efficiently harnessed, and really how inefficiently we use the stuff. This is not for no reason, and even if you were going to come up with some ideal efficiency of Black powder, taking in to account all the factors; Ignition, Safety, Cost... both methods will be able to be tweaked to get there and beyond. Given that they are able to be the same in efficiency, it will be the other factors you will be wanting to consider.