Rocket Nozzles

[DIYMark]

If theres anything that irritates me most with rockets, its nozzles!

 

I don't know what to do. Some rockets just use a clay plug and drill a hole it it. Others have full blown CD nozzles. While most just have a diverging cone and thats it.

 

At this scale of rockets I'm pretty sure just a diverging cone is adequate seeing as its already got a "converging' section (to a certain degree) Because even with out a converging cone (flat), the nozzle still converges the gases to the nozzle throat - rather abruptly, but it still does.

 

So anyway. Personally I would like my rockets to have a full CD nozzles as it should increase performance (Only slightly) and the added mass is negligible as I see it. The only issue is machining it. I'd most likely run out of patience machining a little complex spindle and stuff it up!

 

Anyway, I found some stainless steel scrap and made an end burner tooling set for 16mm ID (electrical conduit size ).

 

I haven't made a base as of yet because this tooling I made it more like a prototype and all I really wanted to do was to make a nozzle then cut the rocket in half to see it in a cross section view

 

Anyway here it is.

 

All of the "Stuff"

http://img135.imageshack.us/img135/2645/thelotak9.th.jpg

 

Spindle

http://img529.imageshack.us/img529/1391/spindlelg7.th.jpg

 

Nozzle

http://img355.imageshack.us/img355/8027/nozzleyf3.th.jpg

 

Back of Nozzle

http://img294.imageshack.us/img294/9681/nozzlebackjk0.th.jpg

 

How the internals of the Nozzle are (I just lined up the parts to visualize the internals of the Nozzle)

http://img186.imageshack.us/img186/9711/setupon1.th.jpg

 

Rammer/Drift (No award to who can guess what its made from )

http://img186.imageshack.us/img186/3382/rammerem0.th.jpg

 

The Drift is just a bolt because I didn't have any adequate rod.

 

This tooling will be enough to make a couple of rockets from just to test and if its successful I might have to buy some SS and machine it all up properly (Ill make a core burning and end burning set of tooling )

 

Man this SS is expensive stuff! When I got some a while ago its was $50 for half a meter for 30mm Round Bar (Mind you it was meant to be some top sh!t marine stuff).

 

Anyway, the outcome was pretty good because I used non ground up cat litter (just straight from the bag so it was a bit chunky). I also rammed this one (Test sample) a bit too hard and the PVC started to bulge - however it did not snap. Lastly the finish on the clay in nice and smooth and as glossy as the PVC its self.

 

Finally, whats everyone else's thoughts? What kind of nozzles do you use? How much do you think a CD nozzle will improve performance compared to a hole in clay nozzle?

 

N.B. - The Diverging half angle is 17.5*, the Converging half angle is 35* and the Nozzle diameter is 3.5mm.

 

...and not that it means anything but if you blow from the intake to the exhaust of the nozzle it makes an awesome whistle hehe

[Swede]

I like your tooling. I think you did a great job with it. I may be weird, but I find making tools to be a lot of fun. The picture showing the form of the nozzle "lined up" is interesting, and I'll bet it'll make a very effective nozzle. I never really thought much about optimizing the convergent portion. Most of the tutorials at best have a divergent cone, and that's about it. That's what I did with my 4 ounce tooling I cranked out recently.

 

About the only problem I can see with your convergent/divergent setup would be the need to have a pretty exact amount of nozzle mix. Too much and the choke point might be too big, too little and the tooling clashes without compressing the clay enough. But once you know how much mix to use, I bet the nozzles perform as good as anything out there.

 

I haven't tried kitty litter yet. I bought some bentonite and it looks like a lifetime supply, there's so much of it. The clay, plus some grog-like material, and wax (toilet ring wax) seems to work well, no nozzle failures yet. It doesn't seem to matter if I just use a mallet, or use a press, the stuff just works well.

 

Curious, with your high-performance nozzle tooling, why not produce a cored motor and REALLY get some max performance out of it? Have you flown any motors made with this tooling yet? It looks good!

[DIYMark]

Hey I like to make tools too Hell even just making swarf is fun!

 

You’re right on the Clay issue. Its has to be pretty exact! I'll have to weigh out how much to sue then use that as a base line.

 

At the moment I just use kitty litter for nozzles and they seem to work fine. I have noticed that the clay is a little damp so when the rocket is in use the water kind of cools the nozzle and prevents erosion.

 

As of yet I haven’t made any rockets with this particular set of tooling (its intended for a BP end burner) however I'll try to make a Cored KNSU rocket this after noon. Id have to ram the motor then drill the core (Can’t really "extend" the spindle) anyway that will kill some time for me later today

 

And this weekend I’m hopefully getting some balsa to make charcoal. If not ill try newspaper or “napkin” – some YouTube videos showed good results with newspaper/napkin – however one guy used cork charcoal and it was faster than willow?!

[DIYMark]

Well I made a rocket with my tooling from yesterday and It worked great - I used catalyzed KNSU and it had a short (~0.5 second), powerful burn time.

 

However, the converging cone doesn't extend to the ID on the case making it a bit hard for gases to flow. So I'm planning on making this some time...

http://img49.imageshack.us/img49/2286/cdnozzlesp9.th.jpg

 

Its pretty close to the Wolter End burner tooling just that I've made a larger Nozzle Dia and made it into a core burner. Ive added a small 1mm lip to the rammer to help push the clay down rather than around the rammer had I used a straight taper.

 

And as of now I'll most likely stick to cored rockets - because I don't need super fast BP and this tooling will almost be interchangeable with BP and KNSU. But knowing me I'll probably get bored one day and make a end burner jig the same as this (Just smaller nozzle Dia).

 

Oh and BTW the CAD software I used is Alibre Design (Only the trial version but still a handy bit of kit~)

[FrankRizzo]

Very nice start Mark! You've come to the correct conclusion, your convergent section needs to be a full inner casing diameter to decrease turbulence. With a smaller diameter, the exhaust gases are turbulent around the flat section surrounding the nozzle entrance and conduct a significant amount of heat to the casing wall at that point. You'll have have burn-thru problems when making engines that have longer thrust duration (end burners).

 

A good start is a 30-degree half-angle for the convergent section & 20-degrees for the divergent exhaust. That little lip on the nozzle forming ram is absolutely crucial. The swearing and muscle strain that you lose far outweighs the tiny bit of casing erosion.

 

Also, dry your clay and/or add a bit of dissolved wax to it if you plan on storing your motors before using them. If the humidity decreases, the clay will shrink and you might have bonding issues. Granted, with casing deformation like what you've got right now locking in the nozzle, that probably won't be a huge issue. It's more so a problem when using paper tubes (a more environmentally friendly casing).

[DIYMark]

I think that if I stick my cat litter in a coffee mill for a second or two I can use a smaller lip (0.5mm) as the clay will be able to fit between the smaller lip and ID easier. However the lip differnece isnt for performnce (will help a bit though) but mainly because it'l look better too

 

Thanks for the Angle dimentions. Ive drawn a few sketches using the 30*/20* and they seem spot on (It try them in CAD later).

 

Also, at the moment I'm using PVC for tubes but Id like to use paper simply because its more enviromentaly friendly. BUT is there any substitutes for Kraft paper? I maybe able to get just plain old brown paper - inst that Kraft paper?

[FrankRizzo]

I think that if I stick my cat litter in a coffee mill for a second or two I can use a smaller lip (0.5mm) as the clay will be able to fit between the smaller lip and ID easier. However the lip differnece isnt for performnce (will help a bit though) but mainly because it'l look better too 

 

Thanks for the Angle dimentions. Ive drawn a few sketches using the 30*/20* and they seem spot on (It try them in CAD later).

 

Also, at the moment I'm using PVC for tubes but Id like to use paper simply because its more enviromentaly friendly. BUT is there any substitutes for Kraft paper? I maybe able to get just plain old brown paper - inst that Kraft paper?

The lip serves to *prevent* the clay from squeezing up between the casing wall. It doesn't need to be very big...just so that the force is directed straight down near the case walls instead of slightly outward like it would if you extended the angle all the way to the edge. If the clay does squeeze up between them, it locks the rammer in place and makes removing it extremely difficult. That little flat spot around the perimeter of the convergent section will create a bit of turbulence, but it won't cause any significant problem.

 

Brown paper grocery bags are usually a decent quality Kraft paper, but the stuff you'd find at department stores for wrapping parcels is usually a low quality recyled Kraft. Rolling you own tubes is fun, but once you get going making rockets, it's much better to just buy your tubes premade and use the time you save doing something else like making nice shells as headers.

 

The best paper tubes are sold by Jim Biersach @ http://hobbyhorse.com/pyro_tubes.shtml

[psyco_1322]

Well thanks for that info on that lip Frank, I always wondered why that seemed to be on all the tooling I see. Kinda left it off my universal tooling, ill put one on later. I have a spindle thats a bit oversized and about no good.

 

Dan Creagan suggested to use a 30 degree angle of the inside nozzle and a 60 degree for the outside nozzle. That may only be for core burners though.

[DIYMark]

I was hoping to make a smaller lip and to do this finer clay would be needed. Anyway Ive re designed the Tooling in CAD with the 20*/30*angles...

 

http://img46.imageshack.us/img46/74/nozzlecdjz0.th.jpg

 

Doesn't look right to me. Ill try the above nozzle posted before and just change the divergering cone (to 15* and a tad bit shorter).

[DIYMark]

Well this is better!

 

http://img206.imageshack.us/img206/3142/nozzlecdgg1.th.jpg

 

Its using 30* in the front and 12.5* half angle in the back.

[FrankRizzo]

You fellas should read the posts by Andrew on this thread over at UKR:

 

http://www.pyrosociety.org.uk/forum/index....opic=2370&st=15

[DIYMark]

Thanks for the link! No wonder I could never find that kind of info looking through Google! The damn thread title is "Idea about Rocket Fuel" but they branched off topic (a bit ) into rocket nozzles.

 

Anyway heres the latest progress...

 

http://img206.imageshack.us/img206/4642/18175449av6.th.jpg

 

http://img206.imageshack.us/img206/4743/75633480pj8.th.jpg

 

http://img90.imageshack.us/img90/5141/54431136kq7.th.jpg

 

http://img90.imageshack.us/img90/6195/67775941rz8.th.jpg

 

And their made from steel *Ducks for cover * I know they might spark but I'll take my chances (until I can find some better material) The steel is fro man old Go Kart axle that was hardened, however this steel machined so beautifully it was like Brass. Small swarf that would chip break and leave an awesome finish - its possibly some leaded steel alloy I think. And I didn't have any wet and dry sandpaper so 120 Grit painters sand paper and 1800RPM on the lathe worked great (Did this on the main part of the spindle. The rest is done at 800 RPM).

 

Tomorrow I plan to make some charcoal and test this tooling using KNSU.

[Swede]

If it is leaded steel, that would account for its ease of machining. If anything, the lead content will help keep potential sparking down. 12L14 is low carbon as well. But still - the thought of that steel banging on ceramic chunks/grog near the nozzle - can you say "flint and steel?" Please be careful!

[FrankRizzo]

Very nice, sir! On that last picture showing the fit between the nozzle forming ram and the the spindle, does the ram stop at the point where you've got it placed? If so, ream out the rammer bore slightly until it's able to travel all the way down to the divergent nozzle forming section of the spindle. That way, you have the ability to tune the throat length for each batch of propellant. A longer throat can lead to CATO's.

 

Because your tooling is steel, make absolutely sure to press a full increment of fuel above the spindle with the holed rammer before switching to the flat rammer. If you switch too early, you run the risk of pinching fuel between the tip of the spindle and the rammer face and having an accident (and mangling your spindle if nothing else). Also, NEVER USE TITANIUM in your fuels while using that tooling!

[psyco_1322]

Very nice tooling you got there Mark. Hope that works as nice as it looks.

 

Titanium in a coffee grinder is cool looking, until it starts to scare you when you think of it possible igniting. It was some big o needles from Firefox......anyone else have these?

[DIYMark]

Thanks for the comments Guys! And as a safety measure the hollow rammer is drill right through - makes cleaning easier too.

 

The tooling "use" is yet to be known. We went to the tip to get rid of gardening stuff/clippings and we decided to stop at the "Tip Shop". There I found some 3 huge rolls of fax paper and a container of wine bottle corks - all for the pricey sum of $2

 

The cork was for charcoal - it's "meant" to burn fast.

 

The paper was for making casings (A 460mm wide 340meter roll of 80gsm Kraft cost $50 here!)

 

The cork charcoal was cooked in a paint tin with a hole in it over fire until no more methane (flames) were produced (Hence no more reaction - charcoal is done). The can was shook frequently too. And to answer the question - Its crap.

 

The milled meal powder wont burn unless you have 100grams on the ground, light 5 matches at once then immediately stab them into the pile. Then if your lucky and the stars line up, it may ignite which then it will smoke, bubble like lava then ooze yellow crap everywhere. Amazing

 

I guess the people who said cork charcoal is good were referring to actually using the tree's wood - not the cork its self.

 

Anyway, that aside I made some tubes. They work okay but I rolled a revolution of paper around the former, put a strip of glue, the rolled till I had the right size then taped it shut - not exactly the best way as they telescope out

 

So my first rocket blew its top cap. the second was a fountain - the motor was primed with KNSU dry mix (no meal left) then the motor turned its self into an end burner.Which inst any good with a core burner configured nozzle. The third blew its nozzle. The nozzle cant exactly be rammed harder because the paper will blow out (I'll need to make a sleeve).

 

However my last (Possibly best motor) sounded awesome. Its was like a large scale R Candy motor. It would have a little quiet shhhh sound as it ignited, then a slight pause, then a roaring SHHHHHHHHHHHHHHHHHHH shortly followed by a huge bang as it catoed - WOW I invented the self reporting rocket !

 

So I need to make a sleeve for ramming my rockets. Or I could use PVC but I'd prefer paper tubes. Also my rockets catoed at the last moment once it was nearing the maximum pressure zone. I could tone down the propellant but I want to squeeze the last ounce of power from these! (Hence the full CD Nozzle). So its time to improve the tubes/make a sleeve.

 

BTW all the rockets/tooling till now have been 16mm ID and 125mm long

[psyco_1322]

If I wasnt so confusing with every other sentence being spaced out I would say you have a fuel problem. Are you using the crappy bp made from the cork or is this sugar based? If its sugar than sounds like your getting dross and crap plugging up your nozzle and causing catos. If its the bp then just throw it away, yellow ooze doesnt fly rockets.

 

When making your tubes you should definately apply glue all over the paper from where you first start the roll, or else you get a rolled up piece of paper and not a tube worth using.

[tentacles]

ARISE, dead thread!

 

So I'm making up some rocket tooling for BP (and whistle, once I pry the spindle dimensions out of FrankRizzo).. And I'm wondering what angles I should use on the divergent nozzle former.. I'll be using taper pins for the actual core, same as the latest tooling from Tyler.

 

Frank, by the way, does Tyler have a couple taper pins I could buy off him? Otherwise I'll order some from mcmaster, along with some dowel pins for star plates.. One thing at a time, though. I could trade him a 4" (I think?) piece of .754 stainless to replace some of those brass nozzle formers that stripped out. Or just pay him, or buy him beer.

 

From what I've gathered, reading this thread and the one over at uk pyro, is that the divergent cone should be around 20 degrees half angle. But what should the convergent cone be? 45 degrees? I plan on putting a smooth fillet transition from the divergent former and the spindle..

[Aquarius]

I make my own metal tooling on a bench lathe.

Usually I make the prototype out of brass, and the "work horse" out of stainless steel or silver steel. And I press, no ramming any more.

 

An uneducated guess is to keep the half angles at 30 and 15 degreees, at least I do. This is borrowed from David Sleeters book.

 

30 and 15 degree halfangles make 60 and 30 degreees full angles, if this is unclear..

[tentacles]

Silver steel sounds like an insane choice to me - why would you go with tool steel for rocket tooling? You almost might as well go with hot rolled steel.. Silver steel is roughly equivalent to O1 oil hardening tool steel.. carbon content isn't too high but that stuff sparks readily. Stainless makes sense, however.

 

To me, brass is awful expensive to use as a prototype material - why not aluminum? 2024 actually holds up very well as rocket tooling, the extra hardness helps a lot there. We've noticed that whistle rockets release from 2024 spindles more readily than with 6061 spindles. I would imagine the same to be true for 7075 aluminum as well.

[Aquarius]

Hmm, should have explained better, I guess..

The silver steel for base base and spindle for the endburner, brass spindle on coreburners and SS rammers on both.

I have used some aluminum T-6xxx on some tools, but I find it too soft for pressing or ramming.

 

I got a lot of SS and silver steel lying around, scraps form work and the junkyard. Spindles made out of brass are not that expensive, as I make the base and the spindle as two different parts. Less swarf, lower cost and a lot quicker than making it from one solid rod.

 

In the base I centredrill a hole to attach the tapered spindle and thread the other end. I then screw the base an spindle to my hydraulic press and start pressing.

Makes it easy and quick to change the setup when needed.

[psyco_1322]

Well I just ordered a bunch of T6 6061 to make some tooling out of. For what I can tell its what Rich makes his out of. Since what I have bought from him seems to hold up nice, or good enough for my abuse, thats what I went with.

[Aquarius]

Nothing wrong with T6, the only thing to remeber is not to let your drift become too long on the smaller sizes or they will bend/flex with heavy ramming.

What sizes are you building Psyco?

[tentacles]

Nothing wrong with 6061, but 7075 machines a bit nicer and it's stronger, roughly equivalent to 1020 (mild) steel, although stiffer. 2024 is similar to 7075, mostly the differences are in the alloying elements and 2024 essentially cannot be welded. 2024 is less prone to stress failure than most of the high strength alloys - although I'm not sure in what way. Likely it has to do with repeatedly loading the material to a high percentage of it's yield strength. (In other words, Not Important To Us)

 

By the way, the "T6" or "T6511" just refers to the state of the hardening. 6061 is a hardenable grade of aluminum, one which is typically shipped in the hardened state (T6, T6511). You can anneal it by baking it in an oven or using a torch to heat it around 950F, just below melting - visually, the surface will take on a dull sheen. You can stop heating and allow it to cool, it will be annealed. After annealing it will be far more formable, ie bend it into shapes. You can re harden it by baking it for some hours at an elevated temperature, or you can achieve T5 hardness by simply aging it.

 

One more edit for the road: Apparently a great way to test when you've got the aluminum hot enough to anneal it is to mark the area with a black sharpie, and when the mark starts to disappear, it's hot enough and you can take the heat away.

 

edit: Here's some very good info:

 

"Found 6061, interesting stuff. Heat to 750F, cool 50 degrees per hour to

500F and it is -T0 (annealed). Heat to 975F long enough to get even

temp, quench in water (or water spray for large items) and you have -T4.

Age harden by heating to 320F for 16 hours or 350F for 8 hours and you

have -T6. If you let -T4 sit for several years, it will gradually drift

to almost -T6"

 

Here's a detailed description of aluminum tempers, although it doesn't really describe any annealed states: http://www.engineersedge.com/aluminum_tempers.htm

 

Yes, I realize none of this has anything to do with rocket nozzles.

Edited December 19, 2008 by tentacles

[psyco_1322]

OK, thats great to hear.

 

Need to make rammers mostly, for my 1/2" whistles. Will likely be making some kind of 3/8 tooling just for the fun of it. Going to make a completely new 3/4" whistle spindle, and rammers. Then possible look at getting things set up for moving up to 1" whistles, depends on how easy I blow up these 3/4" ones. I have the tubes, but I didn't order the stock to make a complete set of 1" tooling. I'll try to get some end burner tooling made for several sizes also. I have lots of turning to do