8 replies to this topic

[cplmac]

I built my first lampare yesterday and sent it up last night. Well not so much up as out. No idea what went wrong here, but whatever it was it was the loudest boom I've ever caused intentionally or otherwise.

3" Lampare flowerpot


On the left is the shell wrap, on the right is the only piece of the mortar I could find. It was buried several inches in the ground.
I'll give it another go next weekend, hopefully without losing a mortar.

[Mortartube]

Perhaps we can help if you give us a little insight into how you constructed it.

[cplmac]

I had 1/8" wall tubing that fit the fuel bottle snugly. I took a length of that tube about two inches longer than the bottle, capped one end, inserted the full bottle (70/30 gasoline/30 wt. oil), hot glued the circumference of the bottle on top where it met the tube, filled the rest with standard 70/30 flash (about 75 grams), top fused the shell with flash being the top, spiked it, wrapped it with 3 wraps of 80lb paper, ran quickmatch down the side, pulled the piping off about four inches of of the quickmatch leader at the top of the shell, tied off the exposed match to the inside area with the time fuse, added a teaspoon of BP meal to help ensure time fuse ignition, closed off the top of the shell covering the time fuse and exposed match, attached lift cup to bottom of the shell with 1.5oz of elephant 2FA, inserted safety fuse in quickmatch at top of shell, tied on a twine leader to lower the shell, lit shell and scooted to a safe distance (this is entirely relative). The shell was a tight fit initially, not super tight, but I had to nudge the bottom through the top of the mortar, once the bottom cleared the top of the mortar it slid easily to the bottom. Initially I though this might be the problem but I've definitely had shells that were a tighter fit. Now I'm leaning towards burn through at the time fuse. The fuel bottle had 1 pint of fuel in it.

[Arthur Brown]

So did the fire reach the flash before the tube left the mortar? 75g of flash is a LOT and would do that much damage, especially if assisted by a pint of aerosolled fuel. Check that the fire reaches the lift before the burst.

[Mortartube]

Crikey, that is a heck of a lot of flash. I would suggest it's over the top by between 65 and 70 Grammes. You are only trying to break the bottle and ignite the fuel. With that much flash, it may not have lit even if it did get up there. Too much causes the fuel to be projected away from the flame front at such a speed that the fuel droplets disperse before the flame front can spread throughout the fuel effectively.

Use a strong bottomed bottle such as a Coke bottle with the bulbous nodules on the base to help withstand the shock of lift as well.

[cooperman435]

I would suggest it's over the top by between 65 and 70 Grammes.

Id say it was over the top but you are still gonna need 25 to maybe even 40 for a large shell to get good breaks? also depends on the quality of your flash.

[Caramanos2000]

Lmao omg dude. Does your backyard look like the moon now?

[Arthur Brown]

Flash can be sensitive to the impact of a heavy launch too, so do a trial with water and lots less flash. then do a trial with fuel and the minimum amount of flash that you find necessary. Make very sure that the lift happens 1 - 3 seconds before the burst so that the container is well out of the way upwards before the burst.

Time the rise of a water filled test shot to the top of it's trajectory and set the burst fuse to that time. you dont want it to burst too close to the ground! You may want to also account for the difference in density between water and fuel! water is denser so the fuel cell will possibly rise more.

[cplmac]

Okay, in no particular order here. I use about the same amount of flash as I would use on a decent 3" salute, for the same reasons, I want a concussive report with the fireball. Someone with a keen eye pointed out the cause of the failure to me. The lift charge never went off. Actually it did, but not until after the shell. There was a failure in the quickmatch leader or some such so the shell operated properly the lift just failed to ignite. If you watch the video again you will see the lift charge go off with a whoosh at the end of the video. Also I'd like to clear up that flash will NOT blow so hard as to prevent the fuel from lighting if you are using gasoline. The flash in this shell was standard 70/30, not the most powerful flash in the world but plenty strong enough. Arthur I actually fired this exact same shell off the previous weekend, only that time it was the time fuse that failed to light. I know it was constructed satisfactorily because it survived that substantial fall and still did not leak any fuel or flash. Next weekend I will post another video, with any luck a success. Thanks for the input everyone!