10/22/02

My interest in building my own motors flourished when I started buying big motors and realized how expensive they were. Then I found out how cheaply they could be made.  After some dismal tries with Ammonium Nitrate motors, I finally talked to Ted Proseus about his AP motors.  A few weeks later, and I was down there casting grains.  Alot of people have helped me out:

Ted Proseus - The guy who got me going.  The guy I brainstorm with.  He puts up with my 10 calls a day.

Jeff Taylor - Makes absolutely fantastic snap ring cases.  No more Kosdon for me!

Sean McAndrew - Set me up with some great formulations.  If Sean had the chance, he could do this professionally. 

Marty Wright - My dad....and a polymer chemist.  Not a bad contact to have!  He is the buffer between my gray area hobbies and my mother, the eternal worrywart. 

John Gustavsen - Another mad scientist.  He is my rubber ball...I bounce EVERYTHING off his brain.

Erik Hall - My partner of Ozark Aerospace.  He makes all the electronic doohickeys run properly.  Another rubber ball for my wild ideas.   

The guys on AROCKET list.  Man are you a bunch of smart geeks.  Heheh.  Me too. 

So how does one make a motor?

First, a few basic terms:

"Kn" - This is super important.  It is the ratio of the burn area to the nozzle area.  If your Kn is too low for a certain propellant, it will never come up to pressure.  If it is too high, the motor will keep accelerating the burn and eventually overpressurize and CATO.

"Web"  -  The measurement from the edge of the core to the edge of the propellant.

"Burn Rate" - The rate at which the motor burns.  This is measured generally by taking  (web / burn time).

"Grain Type"  -  What the geometry of the propellant is.  Most of my motors are Bates Grains.

"Solids Loading"  -  The % of metal / oxidizer to binder / curative. 

Secondly, some equipment:

1. Plastic spoons and cups - Buy them by the millions

2. Tongue Depressors - Work great for scraping.  A billion would be a good number.

3. Aluminum Bowls - For mixing.

4. Wooden spoons - again for mixing unless you can afford a....

5. Kitchen Aid mixer - Nice to have.

6. A good scale.  I use and Acculab VIR-2400.  I could not live without a Tare function, but a triple beam may work ok.

7. Proper liners and casting tubes.

8. Chemicals - More on this later.

So, what goes into a motor?

An AP motor is basically 2 things.  Fuel, and an oxidizer.  The motors I make use Ammonium Perchlorate (AP) as the oxidizer, and the binder, HTPB, as the fuel.  Thsoe 2 things together will burn very nicely.  To make the propellant do different things, we add different chemicals to the mix.    My basic propellant, Tiger Tail, is a formulation made up by Ted Proseus.  It consists of:

Per 100 grams:

HTPB R45-M   18.6g
Aluminum 400 mesh   2.0g
Ammonium Perchlorate (200 µm)   77.1g
HDI curative   2.3g

ISP:  about 185 (1.79 NS/g)

That's it!