Compressed Air Rockets – The Physics Behind the Flight

3 10 2008

I’ve been thinking about how the rockets work and which forces are involved in making the fly.  After some help from Will, Matt, Ben, and Blake, I was finally able to come to the equation that governs the flight of the paper rockets.

h = (P.rocket – P.atm)*A*x/(m*g)    eq. 1

h = height of the rocket

P.rocket = Pressure of the rocket inside or the pressure of the rocket launcher compressed air tank

P.atm = Pressure of the atmosphere

A = Cross-section of the rocket body (not the fins)

x = the length of the rocket body that is in contact with the launch tube

m = mass of the rocket

g = gravity

  • Note 1 – m*g = Weight,  So for those working in English units you just way your rocket and subsitute it for the m*g term.
  • Note 2 – make sure that your units are consistant.  NASA has made catastrophic errors and lost millions of dollars due to conversion errors don’t let this happen to you!  =)

Using the equation

In order to keep things simple I added in a conversion factor so that the answer will be in feet after you plug in the values. The equation then becomes

h = (P.rocket – 14.7)*A*x/(12*W)    eq.2

where

h =(ft) height of the rocket

P.rocket = (Psi) Pressure of the rocket inside or the pressure of the rocket launcher compressed air tank

14.7 psi = (Psi) Pressure of the atmosphere (@sea level)

A = (in^2) Cross-section of the rocket body (not the fins) = (π*d^2)/4

x = (in) the length of the rocket body that is in contact with the launch tube

W = (lbs) weight of the rocket

Examples

I’d run through some calculations but I need a digital scale that is small enough to measure the rocket.  I’d suggest buying one that has the capability to measure in grams because you will be a better resolution.  Then you can convert it over to pounds.

More to come!

Advertisements




Compressed Air Rockets (Part2)

13 09 2008

So what this project is missing is two things. The first thing and most obvious is paper rockets. We’ll cover that later. Right now I wanted to describe how to make a detonation box or the ignition switch.

Most of the parts can be found at Radio Shack.  The part they may not have is the illuminate momentary push button, but they have plenty of buttons that aren’t illuminated.  The parts that are needed are detailed below:

Material:

9 Volt Battery

Single Pull Single Throw Switch

Momentary Push Button (LED illuminate if possible)

Binding Posts

Solderless Banana plugs

Altoids tin (or any other brand or some sort of enclosure)

This is what the final design will look like.

Note:  The binding posts are not shown in this picture.  That was thought up after the picture.  When I get the chance I will update the picture and take some pictures of the guts.





Compressed Air Rocketry (Part 1)

12 09 2008

Compressed Air Rocketry is well….just that rocketry using compressed air.  I got this idea from my friend Blakestradamus.  He has build these before and is quite the wizard.  He was going to build one for some cub scouts that were coming over to his house to investigate engineering careers.  I told him that I wanted to build one and that we could be two for twice the cost!  What a deal!

I’m going to try and detail everything that I did to assemble the Compressed Air Rocket Launch Pad.

All of the materials can be picked up at your local hardware store.  They should have all of these parts, but if not you can alter the design to the parts that are at your disposal.

Materials:

2″ PVC Tubing  – about 5 feet.  This will be cut into 3 different pieces.

2″ PVC End Cap – 1

2″ 90° Elbow – 2

2″ coupler – 1

2″ to 1″ Reducer – 1

3/4″ slip / 1″ threaded joint – 2

1″ Sprinkler Valve – 1

1″ 90° Elbow / 1/2″ threaded  – 1

1/2″ thread/slip joint – 1

Compressor air hose connector – 1

Other materials not shown

PVC primer

PVC glue/cement

Links/References

NASA Paper Rockets

Rocket Templates

Air Power Rockets