22 replies to this topic

[maxman]

I use your delay mix on my coreburners and it makes a lovely tail. I must be lucky I don't get many catos, its surprising how well 1lb core burners fly's on quite poor fuel. I even use 63/27/10 kn03 /icing sugar/ sulphur very successfully. The main problem with that mix is that after you have rammed above the core it may be best to ram something more energetic as the sugar mix burns with no thrust and the rocket can get very low before its finished burning.

I use meal and pine charcoal 80/20 for my 4oz core burners

[BrightStar]

Karl's formula looks interesting with its high sulfur content. Most RP / RPH type mixes seem to have 8 - 10% sulfur, rather than Karl's 13.3%. Maybe the sulfur burns more predictably than the Charcoal (with all its variables), hence fewer catos?

It's also interesting that Estes also use approx. 13% S in their BP motors...

Edited by BrightStar, 26 January 2007 - 06:10 PM.

[al93535]

I had a few cato's when moving on from ramming to using a press. Too weak of a press It did not consolidate the propellant well enough. But when I ram I get quite well performing rockets. I can lift 220 gram headers to a good height. But I prefer to keep them less them 200 to get them up a bit higher.

Here is the formula I use now:

kno3 62%
sulfur 10%
------- all hardwood charcoal ----
30-40 mesh 4%
40-60 mesh 5%
60-100 mesh 4%
airfloat 15%

[BrightStar]

Hmm, I have urgent work to complete this weekend. Do I work on that or get some fresh air and test Karl's formula...

So, KNO3 - 63.5, Sulphur - 13.3, Willow charcoal - 23.2, milled for 60 mins and rammed HARD. The tube was ordinary - 3.5mm wall 3/4" id parallel wound. The nozzle mix 10 parts rough ground cheap kitty litter (quite sandy), 10 parts premium milled bentonite, 1 part candle wax dissolved in excess Coleman fuel (purified gasoline), 2 parts fine graphite. The tooling was from pyrotooling.com, ignition via 1/16 visco bent over at the end to hold it in place and placed 1" into the grain.

The business end:



Ready to fly (no header):



Vanishing into the sky:

1lb launch video (divx, 933 KB)

This was actually the second attempt, first time round I cracked the grain while ramming. Powder would fall out of the open end every time it was tapped. I fused it with visquick right up into the core for quick ignition (pictured above) and sure enough there was a VERY loud cato. At least I recovered the stick...

1lb cato video (divx, 747 KB)

This fuel is certainly very powerful and easy to make. I still like the idea of high-sulphur fuel for consistency between batches. The hardwood mixes are cheaper for me though... On with the experiments

Edited by BrightStar, 30 January 2007 - 08:08 PM.

[Wyvern]

Thanks to everyone who gave me advise me on this, i finaly got round to doing a test with a slower mix and 4mm tube walls. here was the outcome.

http://video.google....323031660403032

Edited by Wyvern, 07 February 2007 - 03:41 PM.

[BrightStar]

I have just spent a happy evening testing 1lb 18mm id core-burner motors lofting various sand ballasts...

I used cheap and simple fuel - 63:27:10 with garden hardwood charcoal chips, milled for 2 hours, dampened and granulated with water/IPA mix (no binder) then dried to avoid dust. The tubes were ordinary quality 3.5mm wall, not up to NEPT quality but good enough. Tooling was from pyrotooling.com.

A few lessons on reliability learnt (most of which we already knew):

1) Nozzle length: Just use about 1.3 level tsp (teaspoon) of clay nozzle mix. This gives a nozzle length of ~1cm at it shortest point, ~2cm at the outer radius. 2 tsp or more is too much and invites failure of the tube.

2) Ram hard in increments of 1 tsp with 5 blows with a big mallet. 2 tsp is often too much. Note that this is much less than the recommended limit of 1 * id in length. Interestingly, this seems much more important than the actual fuel mix used.

3) Tap your drifts on a hard surface between increments to clear any lodged composition - you might be surprised at how much falls out...

With this, you are one step closer to a really reliable motor

Now I just have to find some cheaper sticks...

[digger]

Now I just have to find some cheaper sticks...

can't you Just cut up some old wood on a table saw?

[BrightStar]

can't you Just cut up some old wood on a table saw?

LOL Ummm... yes.

The process would be: 1) Spend less time on pyro, 2) Earn more money as a result, 3) Buy bigger house, 4) Build bigger workshop, 5) Buy table saw, 6) Make cheap rocket sticks.

Easily done, but I'm having great difficulty with Step 1)