Homemade Solid Rocket Nozzle

[Farhan]

Hello everyone. My simple question is that how am I going to determine a nozzle throat diameter of any given homemade solid rocket motor? 

[Panel]

It depends on the size, propellants, the altitude/speed you want it to reach.

You'll need more details to calculate.

 

[Dfthu]

You also might have to decide what's the max temp so you can choose the material to make it out of.

[lajoswinkler]

There are too many variables. You need an experimental approach. Use different sized diameters and observe the effects at static tests. Start with the widest, then decrease the diameter. Expect explosive failure at one point, so take cover.

Use a kitchen scale as a dynamometer. Secure the motor over it.

[fredinno]

11 hours ago, lajoswinkler said:

There are too many variables. You need an experimental approach. Use different sized diameters and observe the effects at static tests. Start with the widest, then decrease the diameter. Expect explosive failure at one point, so take cover.

Use a kitchen scale as a dynamometer. Secure the motor over it.

"experimental"= "Kerbal

Isn't there an equation for calculating nozzle diameter?

Edited March 31, 2016 by fredinno

[lajoswinkler]

1 hour ago, fredinno said:

"experimental"= "Kerbal

Isn't there an equation for calculating nozzle diameter?

There is, but as I've said, there's too many variables when you don't work with professional... anything.

[More Boosters]

Don't, you're going to get yourself hurt.

The engine is one of the more delicate parts in a model rocket and you should just leave that to professionals until you get really, REALLY good at amateur rocketry.

[B787_300]

Some first things

Experimenting with rocket motors can be very very dangerous.  be safe when doing it.  A good rule to follow is "ALWAYS ASSUME IT WILL EXPLODE, WITH A FORCE 3 TIMES A GREAT AS YOU EXPECT"

 

So Nozzle design is pretty in depth.  And it sort of depends on what material you want to make it out of and what type of motor you are making.  Graphite is the best all around one followed by metal and occasionally clay.  Estes Motor nozzles are hardened clay. Most composite motors are graphite. Most main nozzles from liquid engines are metal.  

A good place to start is braeunig.us.  Other good resources are books like Huzel and Huang.

[More Boosters]

Man just don't do it. Let your dreams stay dreams.

 

For now.

[StrandedonEarth]

On 3/30/2016 at 2:41 PM, Farhan said:

Hello everyone. My simple question is that how am I going to determine a nozzle throat diameter of any given homemade solid rocket motor? 

As others have said, rocketry on any scale is a dangerous business. When the space program was young, many people, mostly young people, were maimed or killed trying to make homemade rockets. Estes and other model rocket engine makers got their start by making safe, predictable model rocket engines for aspiring rocketeers to use, so they could fly their own rockets without burning down or blowing up their house, or blowing off a hand or losing eyes or heads.

Unless you are working in a fireproof lab with all required safety precautions, and you know exactly what you're doing, don't do it!

[Mazon Del]

In a similar line of thinking, what about the thought of machining a nozzle, and having it mounted to the rocket such that the motor's exhaust must flow through it? Of course stand back before you light it off.

[fredinno]

5 hours ago, B787_300 said:

Some first things

Experimenting with rocket motors can be very very dangerous.  be safe when doing it.  A good rule to follow is "ALWAYS ASSUME IT WILL EXPLODE, WITH A FORCE 3 TIMES A GREAT AS YOU EXPECT"

 

So Nozzle design is pretty in depth.  And it sort of depends on what material you want to make it out of and what type of motor you are making.  Graphite is the best all around one followed by metal and occasionally clay.  Estes Motor nozzles are hardened clay. Most composite motors are graphite. Most main nozzles from liquid engines are metal.  

A good place to start is braeunig.us.  Other good resources are books like Huzel and Huang.

What are the advantages and disadvantages of different nozzle materials?

[B787_300]

35 minutes ago, fredinno said:

What are the advantages and disadvantages of different nozzle materials?

Welcome to the world of Aerospace Materials.  Ill point you to a very nice NASA paper on the topic.  " PERFORMANCE OF ROCKET NOZZLE MATERIALS WITH SEVERAL SOLID PROPELLANTS"

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660015713.pdf

Even though it is from 1966 still reasonably good although I dont recognize the propellant names.  

Short answer is Graphite (look at Loki Research) or Graphite with Phenolic. 

[Farhan]

Thank you everyone, my hertiest gratitude. So let me specify, when I say a homenade rocket motor I mean more or less 100 gram of powdered KNO3-Sugar propellent stuffed into a 5 inch long PVC (dia 1/2 inch). I live in Bangladesh so everything is very much expensive and there is no such thing as readily available rocket motors. So I have to build everything from scratch. However I experimented with it before and I know the dangers. Apart from that experimenting with motors is very time consuming plus expensive and I am now giving attention to the airframe. So I need someone to tell me at least a rough estimation of nozzle throat so that it has enough thrust to lift itself off the ground rather becoming a stationary flair so that I can proceed with experimenting the body tube framing. Thank you.

Edited April 1, 2016 by Farhan

[lajoswinkler]

12 hours ago, More Boosters said:

Don't, you're going to get yourself hurt.

The engine is one of the more delicate parts in a model rocket and you should just leave that to professionals until you get really, REALLY good at amateur rocketry.

How is he going to learn if he doesn't try?

This is a very safe hobby if one takes reasonable caution. I've performed a huge number of static tests and I had only one explosion (not unexpected, though) because of one special fuel mixture.

 

Nobody expects to start with large engines. You start small and gradually increase the fuel masses and engine sizes. Don't be one of those nanny state guys that would ban sticks from children because they can impale themselves on them.

[Farhan]

Thank you thank you again everyone who gave their valuable opinions. But let me draw your kind attention to the fact that I have already done experimenting with rocket motors a few years back. I experimented with the KNO3 candy and it was not as easy in my place (Bangladesh) as it is in the west because first of all the materials are not cheap and second our weather is so humid that fuels got degraded in a matter of minute. I also had to use glycerin instead of Karo, kerosene stove and so on so forth. However knowing my situation you all could easily understand that I need as much information as possible from other experiments to reduce my hassels and costs as I am pretty sure that there have  been much experiments done already. And I need to cut down unnecessary expenses and if any of you can estimate a rough calculation about the nozzle throat of a homemade motor I specified in my previous comment then I would be more than obliged. Thanks again.