Lift for BP Lampare

[Nessalco]

I've been working on a project to make a lampare broken by BP rather than flash. My small scale shells were successful, and I now have a full size model to test. It contains 32 ounces of fuel and 18 ounces of -4/+12 willow BP for the break, in two charges separated by ~1/4 second.

 

The shell weighs five pounds, and is 4" in nominal diameter. Excellent fit in the mortar.

 

 

My smaller shells weighed about 3 pounds, and I used 3 ounces of the same -4/+12 powder for lift. It lifted significantly higher than necessary, so for the small shell I'd dial back to 2.5 ounces.

 

I'm thinking of using a lift of 4 ounces for the five pound shell, in HDPE mortars, double plugged. Am I still within a reasonable range for the mortar?

 

Thanks!

 

Kevin

[AlexPyro66]

I believe it is better to use 5 ounces of lift and experiment with the timefuse for the timing.

[Wiley]

Very interesting concept! I look foreward to seeing how it turns out. Be sure to post video and construction pics !

[Hoppy]

4oz might be a bit interesting...but then you may want to cut back a bit on timefuse. Wish I was with you to do testing...low lifted shells are also fun if not enough lift/timefuse.

 

How high is "significantly higher?"

[Nessalco]

Hoppy, I didn't measure it directly, but perhaps 20% higher than my standard lifted ball shells the same size. It went up there...

 

I don't have a problem with overlifting it during testing - easy to dial back if necessary. I was more wondering if four (or five) ounces of BP in a 4" gun was still a safe load. I've never worked with shells this heavy before.

 

Kevin

[AlexPyro66]

Can you please post the lampare composition?

[WonderBoy]

Mumbles or someone else might be able to give you a better answer, I don't have enough experience with HDPE, but it would make me a little nervous. For perspective, my last 3 break 4" shell weighed about 5lbs. I've had it set in my mind that I shouldn't shoot larger than 2 breaks from HDPE, but I don't know that that is a rule of thumb or anything.

 

That sounds like an interesting concept. How do you have the charges separated? Is it built like a traditional lampare, just with BP instead of flash, or nested in the BP somehow?

 

WB

Edited November 15, 2012 by WonderBoy

[Nessalco]

I've made two types. Both are made in 3" ID spiral wound tubes I salvaged, with 6 layers of 90# filament reinforced paper, 12 of 50# virgin kraft, and spiked at 16 points/every 1/2". All are top-fused.

 

The first type uses 6:1 willow BP on rice hulls, with a slow flash booster of 50g/pound of hulls. The fuel is enclosed in a fairly rigid PETE bottle, and embedded in the hulls. Here's a video of a very small one I tried in a daylight test, with only 12 ounces of fuel (straight unleaded gas).

 

http://www.youtube.com/watch?v=Ig1ssg0byv8&feature=g-upl

 

I made a 20 ounce version that performed similarly though with a more impressive fireball (missed it with the camera). The 12 ounce version had 13 ounce break charge. The 20 ounce had 18 ounces of break.

 

The PETE bottles I'm using are off the shelf soda and water bottles. I've found the 12 ounce and 20 ounce bottles with fancy sculpting are the most rigid (sprite bottles are good).

 

The large version I made offered different problems. In the smaller versions the PETE bottles were fairly rigid and deformed very little as the fuel expanded and contracted from temperature changes. To find a bottle that would fit in the tube and contain 32 ounces of fuel, I found only one option. Unfortunately it is a simple cylinder, and deforms significantly as the temperature fluctuates. The smaller bottles are also of a diameter that hulls can be packed completely around them, with the larger one this is not the case it's a bit of a squeeze to get it in the tube.

 

((Note: I'm in Vermont. The temp range I'm dealing with this time of year is 65 one day, 15 the next. In the future I'm probably going to stick to making these in the summer, when temps are a bit more consistent.)

 

To make the larger bottle work I set it up more like a traditional lampare, with a collar retaining the powder above (though in intimate contact with) the bottle. The main charge is 16 ounces. Beneath the bottle is a 3 ounce charge lightly contained and physically attached to the bottle, ignited by a quickmatch leader from the upper charge. I have one constriction in the leader that has pretty consistently given me about 1/4 second delay in testing.

 

I also changed the fuel mix to 90% unleaded, 10% bar & chain oil.

 

I'll let you know how it goes, and try to get video.

 

Kevin

[Hoppy]

Kevin,

Good stuff...I'm curious about a few more things:

 

1) Are you using caulk to seal the PETE bottle to the tube?

2) Ever try a solid fuel (Naphthalene) instead of Kerosene/unleaded/bar & chain oil?

3) How do you confine/contain your charge? (as we all know changes in confinment can change the reaction/output/result)

[Nessalco]

Hoppy,

 

1) I use an epoxy putty made by JB Weld, called WaterWeld. It is easy to work with, fast, and fuel resistant. I made up one bottle about a month ago that I haven't built into a device - just to check for leaks and durability. It's sitting outside, temperature cycling like mad, and is positioned cap-down. So far no problem.

 

2) Nope. I've only made a few of these so far, and all have been liquid fuels.

 

3) If you mean generally, the details are in the first paragraph of my previous post. More specifically, the main charge is in a compartment above the bottle. An insert made from a piece of cut-down tube is glued in place just above and in contact with the bottle. The charge then fills the existing cavity (pretty much like a traditional lampare). The secondary charge is built into the 'dimple' in the bottom of the bottle, and contained in a single wrap of 50# kraft.

 

Kevin

[Nessalco]

Just re-read your first question, Hoppy, and realized I didn't respond to what you asked.

 

The bottles are not physically connected to the tube, though as I mentioned I use a cardboard ring glued into place to keep things from shifting around during storage, handling, and firing.

 

It looks like tonight will be an OK night to give this a try.

 

Kevin

[Nessalco]

Here's a cutaway of the shell in the picture.

 

The support collar is taped to the bottle, filled with BP, then covered with kraft.

 

The retaining collar is glued to the tube, but not the bottle.

 

Kevin

 

 

Edited November 16, 2012 by Nessalco

[Hoppy]

Thanks for answering my questions quickly. Nice design, clean and straight to the point. Looks great.