Nitrocellulose Rocket Fuel

[Axt]

Whenever I try to find information on nitrocellulose rocket propellant
its always stated thats its never used in hobby rocketry, but i know
its had a lot of military use.

Why is this? wouldnt smokeless powder derived double base propellant
be more energetic then blackpowder? Is any isp values available for
"gun grade" double based smokeless powder?

I know one factor is its slow burn rate, but I also know its burn
rate is far more dependant on pressure then blackpowder.

So couldnt the slow burn rate be overcome by adding a small booster
charge of blackpowder to both give the rocket initial velocity and
boost the pressure to promote the faster burning of the
nitrocellulose/nitroglycerine fuel?

So you would have a solid pellet containing the first 10-20mm of
compressed blackpowder then say 100mm of Double based smokeless cast
on top, the blackpowder would launch the rocket and raise the pressure
to a level where it is sustained by the nitrocellulose/nitroglycerine
combustion.

Its just a thought that could give longer flight time then typical BP
engines.

What do you all think?

[nbk2000]

NC is used with Nitrous Oxide in hybrid motors for high power model rocketry.

[NickSG]

Even though i have never made any rockets with NC, i think that you would have to have a small nozzel. I dont know how much faster NC burns under confinment, but i still think it would be slow enough to need a small nozzel, even though it makes more gasses that BP produces.

[CyclonitePyro]

I can think of a much better use for nitrous oxide :D

Nitrocellulose burns much faster in confinement than in the open, more so than most propellants, like you said. I don't think the problem with these rockets would be getting the pressure up more so than using a strong enough casing to handle the pressure. If you can get it to work without building a pipe bomb, than you will have a powerfull rocket.

[EP]

Makeshift Arsenal mentions something like this under the name "shotshell rocket". Basically you mix the SP with BP, 4 parts smokeless, 1 part black. This is dampened with acetone, pressed into the shotshell wad and dried. This is jambed backwards into the shotshell casing and glued in, with the primer hole acting as the nozzle. Never tried it myself, but it claims "the rocket is remarkably fast and reaches a great altitude, most of the time you wont be able to keep your eye on it."

If you have/can get the file, check it out. Its the only time I've seen directions for a rocket with that propellant, but I've heard some military rockets use a variation with smokeless powder.

[a_bab]

I once tryed to use a shotgun shell as a rochet engine. I removed the primer, and I inserted a fuse instead. Also I applied fins to "the rocket" and even a cone. Well, it didn't worked AT ALL. The quantity of the SP is quite small in these shells, but it burned a few seconds though. I guess it's a matter of the speed of burning.

[Microtek]

With NC/NG propellants you need a ratio of about 1:1 by weight, so you'll need to make some extra NG.
I have done quite extensive experiments with this and found that an Al tube 10 mm ID, 12 mm OD, 30 mm length with polyester putty as endplug and 2.8-3.5 mm nozzle with cored grain works quite good.
The most remarkable thing about it is that no exhaust can be seen except a very dull glow at night. When launched during the day, the noise ( which isn't very loud ) is the only indication that something is happening. Except for the movement of the rocket of course.
On the other hand, performance is not spectacular either; KClO4 propellants are much better, especially in acceleration and top speed.
There is also a problem with casting the propellant grain as acetone solutions of NC/NG or just plain NC will form cavities in the grain as the acetone evaporates. This usually leads to CATO.
I have developed a method of overcoming this problem as follows:
- Prepare a bath of acetone in a container that can be closed ( such as a jam jar.
- Add 50 parts NG to the acetone with stirring.
- Add 50 parts acid free NC to the bath a little at a time to ensure optimal mixing and colloidonization. Leave the mix overnight with occasional stirring to obtain a homogenous mass.
- Spread this mass out in a thin layer to evaporate. This will produce a sheet of propellant that is free of cavities ( if the evaporation was done without heating ).
- Cut the sheet into strips as wide as your engine will be long and as long as possible.
- Choose a core size and obtain a tool of this diameter ( drillbits are useful here ).
- Roll the strips up on this tool as tightly as practical, using more than one strip if neccessary to reach the ID of your motor casing.

The propellant grain produced in this manner is very robust as compared to pressed or cast grains as it is virtually impossible to crack due to its flexibility. Also, the nozzle size can be chosen independently of core diameter.
If desired, supplementary oxidizers of fuels can be added to the acetone solution to regulate burn rate or power. In this manner I have added a KClO4-whistle mix to obtain a hybrid between my usual high-powered but fragile rockets and the robustness of this system.
Alternately, differentiated propellant compositions can easily be employed by using strips of different composition. For instance, an initial short strip of a fast-burning composition could be the first to be wound up on the tool and then slower ones could follow to give a fast burst of acceleration to build up some speed and then a long steady burn to get good range and low signature.

[Crazy Swede]

Just a comment to the initial question why dubbel base propellants are seldom used in small rockets.

As the performance requires narrow nozzles to achieve greater burning chamber pressures, the motor casing must be stronger which adds undesirable weight and also increses the risk of shrapnel in case of a CATO.

Also, ordinary double base powders are brittle and can be dangerous to use at low temperatures if cracks develop.

If you add a bp booster the smokeless powder will burn better but as soon as the bp is gone, the pressure will drop and the smokeless powder will start chuffing.

Of course you could use smokeless powder, or any other slower burning composition, to make some kind of base bleed effect to add lenght to the rockets flight after the main rocket motor composition is consumed.

[Axt]

I posted this question on a number of rocketry forums, the most meaningful responses thus far are here, will be expanded upon if there are more responses - <a href="http://guns.ft100.com/html/nc_rockets.txt" target="_blank">http://guns.ft100.com/html/nc_rockets.txt</a>

Thanks Microtek, a very interesting response! the rolled strips idea is great and as you stated, can be adapted to many uses, its hard to think up questions since you covered most I can think of, read this and feel appreciated :cool: .

What is the reason for needing a 1:1 ratio and have you tested lower percentage nitro such as found in DBSP (approx. 7:3~6:4)?.

My criteria I will be attempting for are such -

- Uses only bought smokeless powders (no making nitro for me).
- 18mm ID PVC casing (up to 3 layers thick, each layer safe to 260psi + ~30%)
- end burning (hopefully) or only an initial short core.
- 3+ sec burn time

These are pretty much decided upon, since anything else takes away the quick and dirty rocket im hoping for, performance is second to production.

To minimise voids ive found its best to create a filter out of cloth into this put large grained NC then pour the solvent over the powder. This way you arnt disolving any NC (that gets used) and the large grain size when compressed wont shrink up, since you are just sticking the grains together rather then disolving them. Cylindrical powders seem best to avoid the voids, though the only I have on hand are single based.

I punched up a couple engines today using the 18mm ID PVC with a 5mm nozzle, they arnt as such meant to fly, more to see the results to improve upon - only getting betters always a morale booster :) should also show if the PVC/nozzle will hold up to the heat.

#1 is a SBSP cast with MEK inside the 18mm ID pipe, 90mm long with 40mm core.

#2 is the same cast SBSP but with with BP 4:1 as stated above, 75mm long with 10mm core.

I made another to cut open in a few days to make sure that the MEK has evaporated, if its right i'll clamp the others in a vice and see what happens.

[irish]

a method I've experimented with is to use multible cored cast nitrocellulose, primed with a small amount of ball powder(about three mm ) between the propellant and the nozzle. the propellant is cast then drilled evenly from bottom to top,
the problem is getting the number, size etc of holes just right to avoid the above mentioned pipe bomb effect. when they work they are very very fast :D but so far most just go bang.
I cannot test them at the moment due to bushfire risk here :( but if it ever rains again I will post the results of the next batch.
IRISH

[Axt]

Yeh.. shes as dry as chips here too irish, actually I attempted to use BP/epoxy in an engine today fireed in a vice to see if it would work as the booster. It exploded sending a fireball streaking through the air starting a fire where it hit, lucky theres no grass left to burn!

On the plus side SP/epoxy makes an absolute crapload of smoke, could possibly be used at the end of flight to mark where the rocket is in the air.

Irish, what casing and type of smokeless were you using for the rockets.

[irish]

hi axt
the caseing is thick paper tube rolled in three parts one (20-30 Cm) is rolled with out glue then two more of about 30 cm glued full lengeth, any strong paper will do as long as the middle bit is a different one. this is for a 10 mm core rocket.
the propellant is any double base powder I've got at the time. getting the size, depth and number of holes just right is my problem at the moment.
my aim is an even pressure increase and long flight time.

[Microtek]

One thing to bear in mind is that when using end-burners, the casing must be able to withstand prolonged exposure to the hot gasses.
With core-burners, the gasses only come into contact with the propellant burn-surface and the nozzle.