1569 replies to this topic

[BurlHorse]

I remember reading somewhere that having a gap under the shell (caused, for example, by a tall lift cup) does not actually cause much reduction in power, but does reduce the shock from the lift quite a bit. I have not personally tried this in practice, but it sounds like it should be correct: As I see it, reducing the available length for a shell to accelerate along a 60cm long mortar by 5cm will not cause a great loss in power. If that 5cm is placed under to shell (perhaps doubling the volume beneath it) then the initial pressure will be halved. This will obviously significantly reduce the kick the shell gets as the lift ignites, but that initial kick probably doesn't do all that much to move the shell, but does pyut quite a lot of stress on it. It is the less violent push along the length of the mortar that sends it skyward, and having a taller lift cup will not really affect that. Therefore you make the initial short, high shock stage gentler, at the loss of a little acceleration, but the bulk of the push along the mortar remains unaffected. That's how it seems to me anyway...

You are indeed on the Money Phoenix, Lifting the Shell A Bit from the bottom Mortar DOES signifigantly reduce the Stress on the shell, For Aerial Salutes Bigger than 6"s or bigger we always Use a 16OZ Paper Drink Cup after the Lift to Pick up the shell off the Bottom of the Mortar, 6"salutes are great in the Air, Flowerpots will reduce your Mortar Inventory by one every time.....

Regards,

Stay Green,

Bear

[Phoenix]

OK, good. I'm going to give it a try ASAP now. One with a normal lift bag, and one with a drink cup or cardboard tube to lift it off the bottom of the mortar. I'll see for myself how it affects the height reached.

[skipjack]

time for some videos again!

i built 2 shells about 2,5" diameter. same payload (tigertail). only difference in the burstcharge.

the shell in VIDEO#1 contains BP on ricecrispies as a burst.
the shell in VIDEO#2 contains Flash on ricecrispies as a burst.

finished the evening with my 1,5"-white-strobe-ballshell mounted onto a commercial rocketmotor.
VIDEO#3

[Kembang Api]

Skipjack: Great shell. Was the noise loud enough, comparing with KP bursting charge, because in video is very hard to tell. What was the ratio you used between BP and ricecrispies. I had been play with my 3 inches shell for months now. I still can't produce a lighted stars, mostly are blinded. Even I had change from KP to BP coated on rice hulls for the bursting charges.
My stars had been tested using star tester and they all shoot out very well, but when I put in the shell they just went blind.

Daniel Scott: I use about 25 grams of lift charges for all my 3 inches shell and with 3 second fuse. I had about 5 to 7 mm gap in between the tube and the shell. I make sure that all my shell sit nicely on the bottom of my tube.

[skipjack]

@ Kempang Api: i used 10g BP. i didnt weigh the crispies though.
it was exactly the amount to fill up the starloaded hemispheres with it.

thats strange that your stars dont light properly - especially with the BP.
are they all blown blind or are there a few that do light?
what kinda hemis do you use? plastic or selfmade?

[Kembang Api]

In my 3 inches shell, I fill it with 8 mm stars and the rest is bursting charge with the ratio of 6 to 1. it is a home made hemispheres paper shell and pasted with 150 grams kraft paper about 4 layers. Attach a picture of the shell I made
Out of all the stars fill in, at the most only 4 to 6 lighted.

Edited by Kembang Api, 11 November 2004 - 09:40 PM.

[Jerronimo]

Those shells look nice Kembang Api.

Did u use kp in these shells?
They should all ignite when primed with a layer of BP, it's also common when rolling to let the stars ''spike'' when almost the desired diameter, this creates a irregular surface aiding in ignition.

[Kembang Api]

I had been using KP bursting charge mostly and last week I change to BP. but the result still the same. The sound of the break is much lowwer with BP which is not interesting.
I did prime the stars with meal powder, maybe not thick enough. Still blinded stars produce.
Red stars compopsition was taken from Alany website. I am planning to replace some of the KCLO4 to KCLO3 (about 25%) and prime with KP (Non sulfur) and hope it works. will see the result.

[skipjack]

truly dignified shells there, Kembang Api!
like Jerronimo said, you could try to make the starsurface al lil more fuzzy by mixing a little bit of sawdust into the prime.

[alany]

I blow that composition blind all the time too. Put some aluminium in the prime, and just screen it so it burns longer and hotter.

Bleser KP #2 swaps 1 part of the red gum for an extra 1 part charcoal, that may make it more ignitable.

Try Keystone KP:

69 Potassium Perchlorate
12 Red Gum
8 Strontium Carbonate
6 Charcoal (airfloat)
5 Dextrin

Or Shimizu KP:

66 Potassium Perchlorate
13 Red Gum
12 Strontium Carbonate
5 Dextrin
2 PVC
2 Lampblack

Conkling Blue KP #1 stars are easier to ignite. As are Chrysanthemum #6 which are also quite cheap, easy to make and are excellent for testing things without wasting more expensive and difficult to obtain chemicals.

[paul]

Kembang Api, these shells look so neat! But as I can see from this small picture you use another procedure for pasting them!

Could you post a close up of one of these shells? I used the Shimizu method, but your shells look different. More like you pasted only in one direction "from up to down". Sry, its hard to explain for me, because we only learn this school english here. Colloquial english is hard to learn for german people :)

Edited by paul, 12 November 2004 - 12:32 PM.

[sasman]

er

Edited by sasman, 25 October 2010 - 09:17 PM.

[paul]

Wohow! This simply looks amazing! I?m very impressed. The break was nice and the stars changed their color/effect almost at the same time!

My favourite shell in this topic so far!

[alany]

Wow, that was amazing, love it!

What composition were those two star layers? And the priming system?