Lifting height

[TYRONEEZEKIEL]

Sorry if this is a repost, the search feature isnt quite precise enough to help me here. Anyway,

 

 

I am launching almost 2" shells using a commercial mortar I found at a 4th of july shoot. Cardboard, with a clay bottom. I broke all the clay out and epoxied a .5" wood block to plug the bottom. my shells dont quite fit the tube snugly, so I make a cardboard disk that is not perfectly circular, but is definitely snug in the tube which would prevent gas expansion loss. The shells I use are around 50-70g depending on the star comp. So, ive used about 8g of homemade lift (meal and granulated) which barely poof the shell out to any respectable distance, so i have been using about 7g of commercial BP to lift with, but it is only giving me 60-80 feet or so of lift.

 

My lift is ball milled.

 

I say all of that to ask what can I do to increase my lift height?

 

There variables I see are,

 

1: My lift may not be clean as I use pure lead shot instead of hardened.

2: My lift slows down?? when I granulate it with 5% DX

3: The lift disk is not adequate

4: The mortar is not adequate

5: There is just a height limit to 2" shells.

 

 

As always, I really appreciate yalls help.

[dagabu]

The rule of thumb is that you should have no more then a 5% gap around the shell to allow for escaping gas.

 

How big are the separate grains of your BP? If you are using meal or dust, there is no air space to propagate the fire and it burns slowly. If they are 1/4" grains, they are too big and the fire doesn't burn them all at once causing it to burn slowly. For a 2" ball, use 4FA, about what will not pass through window screen.

 

5% dextrin is too much, 4% is the max without affecting speed. Dissolve the dex into water and spray it on the BP until it balls together then push it through 1 4 mesh screen, wait until it starts to dry and screen it again.

 

Use hot charcoal, pine, willow, not hardwood. Ball-milling is the most important single thing you can do to make good BP, mill it until it is a fine as talcum powder and then whet it.

 

Finally, you should get a good THUMP from the shell as if leaves the mortar and disks are not necessary.

 

BTW- a 2" shell goes 300' (100" for every 1" in diameter plus 100')

Edited June 2, 2010 by dagabu

[Arthur]

Yes you may have some optimising to do but there is a limit to the height of a shell, based on the diameter and the mass.

 

For most shells 100ft per inch diameter plus a hundred feet is a very good general rule.

 

It's also a good plan to look at the inside depth of your mortar, typically the Chinese are good at mortars and use a plug about 1.5D made of clay. Now if you replace that with a long plug you are losing length. You really need 6x the diameter of tube depth.

[Mumbles]

I think the obvious answer here is that your shells just don't fit well into your mortar. This is noticeable by the fact that even commercial lift doesn't cut it. Adjust the shells, or adjust the mortar. Given what you're describing, I'd guess you're using so called 2" plastic hemispheres, that are actually about 1 5/8" OD. Even with pasting, they fit poorly into 2" mortars. There are some undersized mortars that are actually around 1.8" ID that work fairly well. If you're from North America, they're pretty cheap:

 

http://www.pyrogear....tar_tube18.html

 

If you're not pasting the shells, you might want to look for aluminum foil tube cores. The few I have are fairly thick walled (relatively) and about the dimensions of a paper towel tube. IIRC, they fit a little snugly, but should tell you if your lift is up to par.

 

The other thing you don't mention is how the lift is contained. If you're side fusing, this will hurt the performance even more. A wide thin layer of BP seems to burn slower than a more compact charge. Try to contain the lift to a plastic bag directly under the shell. You can probably still side fuse if you want, as the fuse should burn right through a plastic bag.

 

If you insist on sticking with the mortar and shell combo, you'll need a better lifting disk. What you have isn't working wither. Just one won't do much. You'll want probably 2 pieces of fairly sturdy cardboard. Put a wad of paper in between them. This will prevent the cardboard from just turning over and letting the lift gases escape.

[Arthur]

Measure the mortar inside diameter, and measure the shell outside diameter. more that 5% difference is too much.

 

My commercial 2" shells need a gentle push down a 2" mortar

[andyboy]

There are a few ways to improve your lift when the mortar isn't up to par. The easiest way is making a strong cup that you pour your lift into and attach to the shell on the bottom. I have launched 2" shells from 3" mortars without problem using this technique.

[wasd]

Sorry to steal the thread, but im having same problem... my shells are barely going anywhere however I have to force my shells in the tube to make sure they are snug. 25g shell and 10g lift and doesnt really go anywhere. Hope we can fix this problem

[Ralph]

Sorry to steal the thread, but im having same problem... my shells are barely going anywhere however I have to force my shells in the tube to make sure they are snug. 25g shell and 10g lift and doesnt really go anywhere. Hope we can fix this problem

 

sounds like your lift sucks do you ball mill it ?

[wasd]

sounds like your lift sucks do you ball mill it ?

 

Hahaha yeah for 8hours :-P

 

 

 

[TheEskimo]

I get two impressions for you post: 1). Your shells fit too tightly in you mortar. 2). Your lift is terrible.

However, point 2 should negate the effects of point 1, unless I am misreading your post. Perhaps your mortar is of incorrect size; is it at least 15 inches long? That is the minimum length for 2inch mortar tubes. Apart from making sure your shells fit the mortar, and improving your lift, I cannot see any other reasons for your shells not to work.

 

 

Edited July 9, 2010 by TheEskimo

[Bonny]

.Perhaps your mortar is of incorrect size; is it at least 15 inches long? That is the minimum length for 2inch mortar tubes. Apart from making sure your shells fit the mortar, and improving your lift, I cannot see any other reasons for your shells not to work.

 

A 15" mortar is the minumum lenght for 3" shells, not 2". The rule of thumb for mortar length is 5X the diameter of the shell (measured ABOVE the end plug). Shells will go higher from longer mortars,up until a certain length IIRC.

I shoot 2" shells from from ~12" mortars.

[TheEskimo]

O really? I Had assumed that 15 was the norm, because all I was just going with the outside height. My bad. I had never thought about that before.

[Arthur]

My mortars for commercial 2" shells are 12" long overall and there is a 1.5" plug glued in to reduce the depth to 10.5". They work fine.

 

With small shells a fine mesh cut approximating to 4FA is better than the more usual 2FA size granules used with 3 - 6" shells getting coarser as the diameter increases. Meal is too slow as it burns from the surface not throughout the pile. Well made BP really is the answer to many pyro problems.