End Burning Questions

[DIYMark]

Hi Ive recently made some decent Meal Powder (After 24H of Ball Milling it wont burn any faster...) and Ive tried to make a few rockets.

The problem is that I can make core burners fine. Today I fired a D size one [Not sure of impulse - but it was bloody loud] and this is all good and fine.

But the problem is end burners! Ive seen end burner tooling for sale and assuming this means that making end burner rockets is possible I tried to make one.

But no matter what I tried, any end burner I make doesn't work [That is using Super Fine Meal Powder 75:15:10 [AKA 15:3:2] ratio].

They sit there not even making enough lift to carry its self and the stabilizer stick!

So I was wondering if its possible (or in other words) do people make end burning BP rockets?

Also, what are Estes/Quest motors like? End or core burners? If they are end burners why dont mine work?

Thanks if you can help out.

[Rocket Doctor]

Estes motors are end burners, they use to have core burners (b14'S).

Carl at Semroc would be the guy to ask about6 motors, you can contact him at carl@semroc.com

[DIYMark]

Thank You :D

Ill give him an email

[tbzep]

You might get good information from a pyrotechnics forum. Our BP motors are just evolutions of the lift motors for large fireworks.

[jj94]

I don't make my own motors, but you may be able to increase thrust significantly if you use different nozzles. I can't say what dimensions would be best for you as I don't have a clue, but try experimenting until you find one that you like.

[shockwaveriderz]

The best BP rocket motor site that I have found is here:

http://www.apcforum.net/

Most modle rocket endburner are actually cored endburners; ie thay have have small core or combustion chmaber formed into the bottom of the propellant grain.


If this Bp worked with a core burner skyroct type engine, I'm unsure as to why it wouldn't work as a cored endburner. Does you endburner have a core in it? Most skyrocket cored rocket motors use a slow 60/30/10 mix while endburners use a faster 75/15/10.

What does your endburner do? just sit there smoking? but not porducing any thrust?

whats teh nozzle look like? simple cylindrical core? or a more CD type nozzle ?

terry dean

[DIYMark]

At the moment is has been a TLAR (That Looks About Night :) ) rocket.

My core burners I made had a 40mm long core with 20mm in front of it un cored.

Once burnt you could hear the cored bit work. It was extremly loud (Im surprised the motor didnt CATO; but I did make the tube extra thick and packed the powder as hard as possible). But once the core burnt out it was like only a fraction as loud and the spark trail was 1/4 as long as it was when the core was there.

What Im saying is it was a noticeable difference between the cored part burning and the un cored.

The nozzles at the moment are just cylindrical holes (Via drill bit) because I dont want to machine my rocket tooling just yet untill i have a better ideal of what size nozzle I'll be using. Once knowing this ill machine up proper CD angles and have a real nozzle :D

At the moment after further reading on the APCforum (went there last night and found some good info). It seems that i may have made the nozzle stoo big :o

One guy made 3/8 Id rocket (End burner) and had a 2mm nozzle! So it seems I've been making nozzles too big :mad:

Ill try again tonight (ball mill will be about done then) and make a smaller nozzle end burner.

BTW my previous rocket sat there burning (had a little trail of flame/spark) but didnt make much if any lift.

Also would any one know the nozzle diameter of and Estes C Class rocket? or any other class for that matter? My test engine will be about C size so having a rough idea of what nozzle diameter would be good.

[shockwaveriderz]

At the moment is has been a TLAR (That Looks About Night :) ) rocket.

My core burners I made had a 40mm long core with 20mm in front of it un cored.

Once burnt you could hear the cored bit work. It was extremly loud (Im surprised the motor didnt CATO; but I did make the tube extra thick and packed the powder as hard as possible). But once the core burnt out it was like only a fraction as loud and the spark trail was 1/4 as long as it was when the core was there.

What Im saying is it was a noticeable difference between the cored part burning and the un cored.

The nozzles at the moment are just cylindrical holes (Via drill bit) because I dont want to machine my rocket tooling just yet untill i have a better ideal of what size nozzle I'll be using. Once knowing this ill machine up proper CD angles and have a real nozzle :D

At the moment after further reading on the APCforum (went there last night and found some good info). It seems that i may have made the nozzle stoo big :o

One guy made 3/8 Id rocket (End burner) and had a 2mm nozzle! So it seems I've been making nozzles too big :mad:

Ill try again tonight (ball mill will be about done then) and make a smaller nozzle end burner.

BTW my previous rocket sat there burning (had a little trail of flame/spark) but didnt make much if any lift.

Also would any one know the nozzle diameter of and Estes C Class rocket? or any other class for that matter? My test engine will be about C size so having a rough idea of what nozzle diameter would be good.

See Tn-2 in the Estes MRN JAN 1971 for C6 nozzle dimensions. http://www.oldrocketplans.com/mrn/mrn_v11_n1/MRN_V11_N1.pdf

hth

terry dean

[DIYMark]

Success!

Firstly thank you for the PDF! It was a great read :)

Secondly, I just took out my freshly milled BP, Made a quick case and packed it.

My nozzle was 3mm (First mistake) and I did a static test. It seemed to work good but wasn't too convincing.

So I made another motor and strapped it to a stick. This time the rocket had a 2.5mm nozzle (Still drilled clay; nothing special). I strapped it to a stick (Well actually 2 because the ones I had were to small to balance the motor). I sat it in a jar in the backyard (Second mistake) and lit it.

Because of the 2 joined sticks they wern't exactly rigidly bound to together or straight and the moment rocket make a tiny bit of thrust just as the motor was been lit it moved its self and swung around in the jar and decided to point its self at the the neighbors rather than the empty yard!

The thing shot out of the jar and 3 meters above the ground it was traveling horizontally and because the stick wasn't straight it spiraled like a rifled bullet!

It cleared the neighbor and then landed in the next neighbors tree. It was almost perfect! The motor had just stopped burning before it entered the tree :D

And on that note i will never test motors/rockets in the back yard again :o

Anyway, it worked great :cool: So now ill machine up some tooling.

Ill probably make 3 sets - Small bottle rocket, Skyrocket (Really a bottle rocket on steroids) then one capable of lifting a shell/payload.

Once again thank you to the people who replied.

[shockwaveriderz]

diymark:

I'm attaching a little BP Skyrocket motor toling calculator I found someplace on the web.

Its for cored burners not enburners but it may be of some use.

May I suggest that you get propep/guipep(perform a google) and perhaps AeroIsp as they will help you in desiging your cored and cored endburners motors better.

An important factor in ecored endburners is a function known as Kn which is an area ratio between the throat area and the burn area ..Kn's for small cored endburners for typical Estes cored endburners are around 22... a typical Kn for a cored skyrocket may be on the order of 7!.


Also for skyrocket cored motors the nozzle diameter is usually 1/3 the "bore" which is the ID of the casing.

I was wondering why your cored motor didn't CATO with 75/15/10 and the fact that you used a way oversized nozzle explains that.

If you use the 1/3 rule with that 75/15/10 mix it will probbaly CATO.

I've forgotten what length to nozzle ratio should be in realationship to casing diamter but I'll look it up and post it for you.

[DIYMark]

Lol, I was surprised it didnt CATO aswell - but the large nozzle and heavily rammed mix might have stopped that (plus I made the case 1/4" thick hehe :p )

Thank you for the BP tool! It saves alot of messing around. Just puthet ID in and done :D

At the moment im googling propep and guipep

Thank You

[shockwaveriderz]

IDIYMark;

Yes I'd say it was the combo of the wall thickness and nozzle diameter.

I just wanted to mention a few more things:

1. add about 2% water to your mix ..it will help with your compression; plus it lowers the burn rate very slightly

2. without going overbaord, the higher press pressure you have will result in a lower burn rate higher press pressure = slower burn rate

3. check out this document: http://www.jacobsrocketry.com/free_manual.htm it has some very good info in it.

4. if you want to play around with nozzle design this is really good for being free:

http://www.engapplets.vt.edu/fluids/CDnozzle/cdinfo.html



good luck


hth

terry dean

[DIYMark]

Thank you for the free manual link and nozzle applet.

The manual has some great charts in back for rocket dimentions in terms of ID