5 replies to this topic

[Xrayelite1]

Hello everyone.

 

I'm new to model rocketry but ever since I bought a kit the other weekend and flew my first rocket I'm hooked! I started to build my next rocket from scratch (no kit) and doing the same for the motor. Regarding black powder as a propellant, what type of motor is best and why?

 

- End burner

       or

- Core burner?

 

Thanks team.

 

 

"Knowledge is the true currency and prize in life"

Edited by Xrayelite1, 20 June 2021 - 02:00 AM.

[Arthur]

In my opinion and only that!

 

Milled and corned dust (about 160 mesh) is best for end burning rockets and very small core burners (less than half inch tube bore).

 

If you look in Ron Lancaster's book ( Fireworks Principles and Practice ) (available on Abe books) he has a scheme using BP and added BP ingredients to slow powder down for larger tube sizes.

[mabuse00]

It depends on what your aims are and what efforts you are ready to take.

 

Do you want to invest in a ball mill, do you have a place to operate it safely?

Do you have access to good charcoal or can you make it yourself?

Or as an alternative: Is whistlemix an option for you? Do have access to perchlorate?

 

 

If not, stick to long spindled coreburners. Everything else needs high quality fuels to operate properly.

 

 

If it's no problem for you, endburners become an option. Not for lifting high loads, but for a more suitable scalespeed and the looks, long burntimes... personally I love EBs

[LiamPyro]

Estes model rocket motors are all end burners. Back in the day before I could make my own black powder, I would dissect Estes motors and break up the fuel grain into my own "corned" BP. Now, using an arbor press and 1/2" I.D. tubes, I've been making motors that closely resemble the common mid-size Estes engines and lift payloads as well as model rockets quite well. I use hot willow BP for the fuel grain, and something slow burning like Tiger Tail for the delay. To eject the parachute, all that's needed is a small scoop of granulated BP on top of the delay with a paper disc over it. Using the press, I've been compacting each increment at 6,000 psi (probably excessive) which creates a ceramic-like grain just like the commercial motors. The motors look and burn just like Estes' and are extremely consistent since they are all pressed at the same force with the same sized powder increments. 

[SharkWhisperer]

I fly a lot of Estes type low/mid-power models, kits and scratch-build. Generally up to about G impulse. I also hand-ram BP motors for these, with good success. Without a press, you'll never get the grain densities that a press will give you, and your motors will generally be larger than an equivalent Estes, but cost about 5-10% as much once you dial things in. And you can make them as big as you want!!!

 

For finned rockets, BP motors such as Estes are endburners or else have a short core. For example, the same-dimension 24mm-diameter Fat C11 motors and D12 motors are packed in the exact same tube but the D12 has a little deeper coring and more initial "oomph" (would have to get out calipers to see if there's nozzle differences, too). With APCP composite motors, they are fully cored and need ignition at the very top end of the core to function properly.

 

Regular fireworking coreburners will rip the fins of of most low/mid power kit model rockets unless they''re majorly reinforced (aircraft plywood fins instead of balsa; TTW construction; thick fillets; reinforced motor mount; body tube reinforcement on longer ones). It's definitely doable. Endburners typically use a hot 75% BP whereas fireworking coreburners often use a cooler 60-65% BP (% is KNO₃, btw). I regularly make 1lb (3/4" inner diameter) motors for finned models and they work great. You can also make smaller ones with 1/2" tubes--18 mm outer diameter like Estes A-C motors.

 

Two good resources for this kind of project are Gorski's article over at Skylighter, where he tried to recreate I think D motors:  https://www.skylight...-rocket-engines . Good advice is not to repeat his wasted time using crappy commercial hardwood airfloat charcoal at all and go straight to a hot BP made with a hot charcoal (ERC is simple to make or to purchase). I think he only used screenmixed BP, but I get better results with damp granulating (no binder!) before ramming. Less of a mess and the ingredients get better incorporated. If your powder/granules are dry, then moisten with 2% water before ramming or pressing for better compaction. Another good reference is to look up the threads on this site started by member "hcb". He also has some Youtube videos of an Estes Patriot missile flying (and popping it's parachute for safe recovery) on a homemade C+ equivalent motor. I can fill in any details.

[dagabu]

Hello everyone.

 

I'm new to model rocketry but ever since I bought a kit the other weekend and flew my first rocket I'm hooked! I started to build my next rocket from scratch (no kit) and doing the same for the motor. Regarding black powder as a propellant, what type of motor is best and why?

 

- End burner

       or

- Core burner?

 

Thanks team.

 

 

"Knowledge is the true currency and prize in life"

 

You will have to use an endburner for 'kit' rockets, core burners provide too much thrust all at once (miliseconds) while the impulse of an endburner lasts for a long while, about 2 seconds per inch of Black Powder fuel.

 

Using an energetic charcoal will yield better results from an endburner and a ball mill (cheap harbor freight rock tumbler) will help wring all the energy out of your fuel. You certainly can get BP too hot for an endburner so light a few to test them out (upside-down so you dont have to worry about fallout or return trips) and determine what fuel suites you best. 

 

Good luck!