# Rocket problem

• 01-20-2010
BobMcGee123
Rocket problem
I'm helping to teach an undergrad numerical methods course. The challenge was to design a rocket and implement a computer model to predict its maximum height. In years past we used off-the-shelf engines and the spec sheet thrust curve. This year we want to incorporate a laboratory aspect of the course, synthesize a potent fuel and launch a significant payload. The fuel has a specific impulse nearly 10x that of the off-the-shelf engines (at its most potent mix).

We may not just go for height. The professor wants to change the objective. Thusfar we've discussed:

- Turn the rocket into a rocket-propelled-aircraft. Predict how far the rocket must travel on a runway in order to take off, given a certain payload, wing span, chord, angle of attack, etc.
- Make two launches per team. One launch is with the straight fuel. The second launch expels the propellant through a nozzle. The shape of the nozzle is designed by each team to maximize the pressure drop through the engine, thus increasing thrust. The object then becomes to predict how much higher the second launch will go.
- Some other wacky ideas, one of which was to just attach a bunch of rockets to a shopping cart, load it up, and see how far it can be pushed up a hill

I'd like to hear some other ideas. I liked the second one, but the level of math required for nozzle design goes beyond what most people cover in their undergrad. The wing one was good, but seeing as how we're building everything I'm afraid they won't be stable.

And no, we aren't allowed to try to launch into space.
• 01-21-2010
crowe
Two words: Rocket Frisbee.
• 01-22-2010
Get the movie "October Sky". You'll love it, and it even touches on the nozzle design a bit. It's all about a young man's love affair with rocketry - and a true story.

Watch out for fuel - solid rocket fuel can be explosive if things go wrong. Rockets can and will go awry before, during, and after launch, and can start a fire or become a wayward horizontal projectile. :p

As a kid, I used to go with some friends out to the desert and we'd light off some solid fuel rockets - they were metal tubes 18-36 inches long, and they took off so fast, you could blink and completely miss the rocket's flight. Fuel was custom made, but not by us kids.

We made some super 8mm home movies of some launches, but finally quit in disgust - you could never capture the rocket in flight. One frame it was resting on the launch pad, and the next frame, it was gone; leaving just a trail of exhaust to show where it had gone.

Make sure your ingredients can not be classified as the ingredients for a bomb, and you have launch permission from the appropriate authorities.

The 1950's, this is not.

*Every team gets a standard nozzle
*And can make or request the fuel mix they want (weak to strong)
*And have the payload weight they request. Perhaps within a range of weights.

contest is to see which team can estimate their rockets performance parameters:

*greatest height
*total time of flight
*pass or fail on some automatic control - maybe parachute deployment on the way down
*most accurate guess on the landing spot.

Airplane idea just has too many variables, and controls. Straight up rocket launch has far fewer, and you can decide what to control by giving them required standardized parts, or not. The nozzle should be standardized perhaps.
• 01-22-2010
Salem
Well you could "just go for height".

But along the way, how about
- adding an Accelerometer to measure something, and use Telemetry to send that data back to base while it's happening (hard), or just record it locally for retrieval later on (easy).

Was each rocket powered for a reasonable amount of time, or was it just coasting all the way up after an initial big push.

- add a camera and parachute, and take some pictures on the way down.
• 01-27-2010
BobMcGee123
Quote:

As a kid, I used to go with some friends out to the desert and we'd light off some solid fuel rockets - they were metal tubes 18-36 inches long, and they took off so fast, you could blink and completely miss the rocket's flight. Fuel was custom made, but not by us kids.
Do you know what it was made of? We were looking at potassium nitrate (oxidizer) plus sugar (corn starch) for the low potent fuel for the undergrad class.

Quote:

Make sure your ingredients can not be classified as the ingredients for a bomb, and you have launch permission from the appropriate authorities.
Good point, because this stuff actually can turn rather...'negative.' I wouldn't be surprised if we got investigated by the DoHS. However, we've got everything we need in our chem lab (for both the low and high potent fuels) and you can actually get potassium nitrate quite easily online.

Quote:

- adding an Accelerometer to measure something
I like the way you think, because this also provides another approach towards validating the student work of developing an accurate thrust curve and numerical model (the initial validation is to predict and measure maximum height). My worry with the accelerometer is damage. The thrust curve for the low potent mix maxed out at 300 lbf for a 10 lb rocket, which can actually damage structural members, not to mention measurement devices.

The professor decided to stick with our traditional approach (off the shelf rocket materials) but have me develop the curriculum for next year. This means I'll be making the fuel, creating the thrust curve and attempting to develop the model. If it goes smoothly, it'll likely get used next year.

The professor also wants me to attempt to fire this underwater, as the solid fuel contains the oxidizing component (and I go to a maritime academy).
• 01-27-2010
MK27
Google ads is a crazy thing. I very rarely shop online or research products,* and as I rule, here on cboard, I get stuff about software development or sometimes games, often reflecting some specific, repeated term from the the thread (eg, the current "home server" thread: all hosting).

Now check this one out. I think it must be something more specific than just the word fuel, too :p Go, Bobby McGee!

* and I don't ride or have an interest in 'bikes, either.