Model Rocket Altitude Predictor

This page is obsolete. There is a newer version available.

Please don't link directly to this page. Link to http://www.markworld.com/ which never moves.

Multi-Stage Version

Experimental

A user's motor version is also available.

This page drives a rocket simulation program which will project the peak altitude and other flight profile information about a multi-stage model rocket. A single stage version is available at http://webalt.markworld.com/altitude.html.
First read the disclaimer.
Then fill in the requested information about your rocket.

For each stage, you can select up to 3 motor sizes and specify a quantity of each size. Leave the quantity blank for unused motor sizes or stages.
Masses specify the launch mass of each stage and everything that will be lost when it is ejected. The sum of the individual stage masses entered should equal the launch mass of the entire vehicle including motors and propellants.
Staging delays are specified in seconds from stage start. A stage ejects and the next stage ignites after this delay.
Cd for each stage is the entire vehicle including that stage.

When all appropriate data is filled in, click the LAUNCH button to start the simulation and receive the results.

Rocket Name
Body Diameter	millimeters
	First Stage	Second Stage	Third Stage
First Motor Size
Quantity of First Size
Second Motor Size
Quantity of Second Size
Third Motor Size
Quantity of Third Size
Staging Delay	seconds	seconds
Mass	grams	grams	grams
Cd
Parachute Delay	seconds from launch (optional)
Chute Diameter	millimeters (required only if ejection delay specified)
Launch Angle	degrees from vertical
Launch Altitude	meters MSL

Not sure what to use? Try this two-stage example.

This simulation uses a number of approximations to simplify the amount of data you have to input. For instance, there is no attempt to simulate the effects of winds and the drag of your rocket is calculated with a simplified transonic drag model. A better multi-stage simulation would also use the length of each stage to evaluate friction drag along the body tube.

The default Cd of .75 should be pretty close for a typical, rocket-shaped, model vehicle with three or four average sized, airfoil fins a good smooth finish and a typical launch lug. For other vehicle geometries, you may need to supply a different Cd. See John S. DeMar's excellent Model Rocket Drag Analysis for more information.

I originally obtained the motor thrust profiles by measuring the curves printed on the manufacturer-supplied data sheets for several Estes and Aerotech motors. Then I found out that someone had already done this for a couple of hundred motors. You can find the motor database HERE. The program interpolates (linearly) between time/thrust data points. If you would like to see a motor added, Email the thrust profile as a set of time (in seconds) and thrust (in Newtons) data points in the same format as mine.

People often ask me the "formula" used by this calculator. Well, the best answer is F=MA. This calculator uses numerical integration which is how lazy programmers with fast computers do calculus. If you want to see how a real man does it, check Randy Culp's Analytical Solution! He's also done the math for the multi-stage case. Check Randy's Space Exploration Home Page for his latest.

Disclaimer:
Because of the approximations used, the large number of uncontrolled real-world variables influencing rocket trajectory, and the very high probability that there are bugs in this experimental program, I cannot accept any liability for the failure of your actual rocket flight to conform to this projection.

Claimer:
I hope you enjoy the program and let me know how its projections match any actual flight measurements you may make.

with comments, corrections, and bug reports.
Visit the Mark Sullivan home page for more technical hobby resources
or the Teeniem�nde Rocketry Club