Fast Sugar Propellant

[NickC]

how much do machinists charge to make nozzles? I've never priced it, I know this machinist that has big cnc machines and he said he do it for me for the cost of materials when he had some off time.


-in what product do you get glycerin from at the grocery store?

[Ray]

Its expensive to have one nozzle made...if you make 100 it'll start to get cheaper...

You can buy nozzles that are already made, but the throat isn't drilled from a lot of sources.

Loki Research

Missile Works carries Purple Woody hardware, but you'll have to call them.

Aerocon Systems

Binder Design also makes them but doesn't advertise them on his page...

You'll notice that all of these are sized to fit specific cases...they may or may not work for the PVC motors you are building...I think Aerocon makes some stuff for PVC motors (casting liners, liners) but I don't know about nozzles.

[NickC]

what is the thickness of those casings? i assume they just take an aluminum tube and turn some circlip grooves in it?

[Ray]

Pretty much...but each casing is unique in its wall thickness.

29mm - 0.058
38mm - 0.083
54mm - 0.095
75mm - 0.115
98mm - 0.188

29 mm is 1.125" x 0.058 wall tubing, 38mm is 1.5" x 0.083 wall tubing.

54mm starts life as Schedule 80 aluminum pipe. 75mm starts life as 3" x 0.125 wall tubing, 98 mm starts life a 4" x 0.250 wall tubing. Each of these sizes is then turned down for the right wall thickness. Standard depth for the snap ring (circlip) is 1/2 wall thickness and its usually placed 1/4" or so from the end of the motor.

All tubing is 6061 T6 aluminum.

If you get creative you can do these on your own...We cut grooves with a slot cutting saw that has a bearing that determines depth of cut. OD is turned on a wood lathe...

Its worked so far, and our 2 grain 75mm casing had a trip to 1470 PSI without failure....our 5 and 6 grain 75mm casing have gone over 1100 PSI for brief periods of time with out failure. You should hear the ROAR of a composite motor at around 1000 PSI.

[Greg O'Bryant]

Glycerin is found in the pharmacy department for skin care. The Kroger brand is pretty cheap for what you get. Is there any way that you could use a brass or copper fitting from the hardware store as a nozzle? If not I will just cast some out of clay and try cementing them into the case like I did with the propellant.

[Greg O'Bryant]

Ray for the casings do they use the standard 6061 tubing stock or do they use the seamless tubing?

[Ray]

Seamless tubing. The seam in the other stuff will prevent you from getting the liner in.

Of note, the 2" schedule 80 pipe is frequently the wrong size for the liners...the best way to get it is to take some liner down, find some that fits and buy that...of course, you'll have to buy it from a local dealer that is willing to let you trial fit prior to buying, not all will allow that.

For those of you that are not aware, the difference between pipe and tubing is that for Pipe the OD is controlled, tubing, the ID is controlled.

[NickC]

and the OD of the casings, say a 75mm casing, is it a true 75mm?

[marksteamnz]

http://www.cncprototyping.co.nz/HobbyItems.html
I do graphite nozzles occasionally but I'm moving away from hobby stuff. To many flakes who would rather pay for a name brand with poor design at a higher cost than my parts.

Its expensive to have one nozzle made...if you make 100 it'll start to get cheaper...

You can buy nozzles that are already made, but the throat isn't drilled from a lot of sources.

Loki Research

Missile Works carries Purple Woody hardware, but you'll have to call them.

Aerocon Systems

Binder Design also makes them but doesn't advertise them on his page...

You'll notice that all of these are sized to fit specific cases...they may or may not work for the PVC motors you are building...I think Aerocon makes some stuff for PVC motors (casting liners, liners) but I don't know about nozzles.

[NickC]

is the aluminum tubing on onlinemetals.com seamless?

[Greg O'Bryant]

I tested some more end burners this weekend. None of them worked, they kept blowing out the nozzle after a second or two. The rush of the exhaust is really powerful and definitely looks like they should work. I have just been cementing the nozzle into place without the end cap. I will try this next but first I have some other things I want to try. I finally found a good glue that will cement paper directly to the PVC pipe. This way I should be able to bond the nozzle and the propellant directly to the casing wihtout the need for an end cap.

[Greg O'Bryant]

It worked!! My end burner finally worked. I tested a motor with a reinforced nozzle and it worked! I don't have any way to measure the thrust. Does anybody know a simple way to do this so I can get an idea of the burn time and power output of this engine? Or can I guesstimate what it is doing if I take into consideration the burn time, mass of the propellant and nozzle throat diameter? By the way the sound of it was quite impressive for it being such a small engine:)

[Ray]

This is about as simple as you can get...works fine for small motors. It only requires some lumber and a video camera.

Good luck.

[Greg O'Bryant]

This might be the end for the end burner:(. I just don't think that it has enough mass flow to really do much. My initial reason for wanting to make an end burner was to get a longer burn time. As I am finding out it might be a lot easier to work with a slower burning propellant. I made a batch of propellant last night out of corn syrup and glycerin for the fuel. It had some pretty interesting properties. The burn was slow but complete. The cool thing was that it was workable even to relatively cool conditions (175 degrees) and it stuck to paper like glue. So no bonding problems. My last question may sound like a stupid one and I may have over looked it something in all of my studying, but what is the ideal web thickness/grain length for a bates grain?

[Ray]

well, in general, given a "standard" core, the length is about 1.5 times the diameter.

You don't have to be precise, 1.5 times will get you close. If you model the motor in BurnSim or a spreadsheet from Nakka (on his D/L page) you can tweek to make a neutral burn profile.