Model Rocket Altitude Calculator

Rocket Inputs

Launch mass with motor, g

Burnout mass, g

Total impulse, N·s

Average thrust, N

Burn time, seconds

Body diameter, mm

Drag coefficient

Launch angle from vertical, degrees

Air density, kg/m³

Launch rod or rail length, m

Target rail exit speed, m/s

Pad elevation, m

Use loaded launch mass and expected burnout mass for better estimates.

Formula Used

The calculator uses a short numerical flight model. Powered flight uses thrust, gravity, changing mass, and drag.

Frontal area: A = π × (diameter ÷ 2)²

Drag force: D = 0.5 × air density × drag coefficient × area × velocity²

Powered acceleration: a = (thrust − drag − mass × gravity × cos(angle)) ÷ mass

Coast acceleration: a = −gravity × cos(angle) − drag ÷ burnout mass

The simulation stops at apogee when upward velocity reaches zero. It also reports a no drag reference value for comparison.

How to Use This Calculator

Enter the rocket mass with the loaded motor installed.
Enter the expected burnout mass after propellant is consumed.
Add total impulse, average thrust, and burn time from motor data.
Enter body diameter, drag coefficient, launch angle, and air density.
Add rail length and a target rail exit speed.
Press the calculate button and review the result above the form.
Use CSV or PDF export to save the launch estimate.

Example Data Table

Rocket	Launch Mass	Motor Impulse	Average Thrust	Diameter	Estimated Use
Small trainer	90 g	10 N·s	6 N	25 mm	Low field test
Sport rocket	180 g	20 N·s	12 N	35 mm	Common club flight
Payload model	350 g	40 N·s	22 N	50 mm	Altimeter practice

Model Rocket Altitude Planning Guide

A model rocket altitude calculator helps builders predict apogee before a launch. It turns motor data, mass, diameter, drag, and launch angle into practical flight estimates. The goal is not to replace field testing. The goal is to give a clear planning number before choosing a motor, delay, or launch site.

Why altitude estimates matter

Altitude affects recovery drift, visibility, delay timing, and range safety. A small rocket with a strong motor can leave a small field quickly. A heavy rocket may look powerful on paper, yet it can still leave the launch rod too slowly. Checking the numbers first helps prevent poor motor matches and unsafe starts.

What this tool considers

The calculator uses average thrust during powered flight. It reduces mass during the burn when propellant is consumed. It also estimates quadratic drag from air density, drag coefficient, and body area. After burnout, the rocket coasts upward until velocity reaches zero. That point is the estimated apogee above the pad.

Using realistic inputs

Good results need honest inputs. Use measured launch mass with the loaded motor. Use burnout mass after propellant is gone. Enter body diameter at the widest main section. Pick a drag coefficient that matches the design. Sleek rockets may be lower. Wide fins, rough paint, and external parts usually raise drag.

Reading the results

The result shows apogee, burnout velocity, coast gain, time to apogee, and rail exit speed. Rail exit speed is important because the rocket needs enough speed for stable flight. The delay suggestion compares coast time with burnout. It can help you choose an ejection delay, though manufacturer instructions still matter.

Limitations

This calculator uses a simplified one dimensional flight model. It does not model wind, thrust curves, spin, staging, weathercocking, rail friction, or changing drag with Mach number. Real flights can differ. Use the estimate as a planning guide, then confirm with altimeter data from actual launches.

Practical field workflow

Run one calculation for the planned setup, then test nearby motor choices. Save each result before launch day. Compare the printed estimate with altimeter readings after recovery. Over time, your own data will improve drag choices, delay choices, and field decisions for each rocket design safely.

FAQs

What is model rocket apogee?

Apogee is the highest point reached by the rocket. This calculator reports apogee above the launch pad and also adds pad elevation for an altitude above sea level estimate.

Which mass should I enter?

Use the full launch mass with the motor installed. For burnout mass, use the rocket mass after propellant is burned. Better mass values improve the estimate.

What drag coefficient should I use?

A smooth, simple model may use a lower value. Rockets with large fins, rough surfaces, payload pods, or external parts usually need a higher value.

Why is rail exit speed important?

The rocket needs enough speed before leaving the guide. Low rail exit speed can reduce stability and increase the chance of a poor flight path.

Can this replace an altimeter?

No. It is a planning estimate. A real flight altimeter gives measured data and helps tune future calculations for your exact rocket.

Does the calculator include wind?

No. Wind is not modeled. Wind can reduce vertical altitude, increase drift, and change the flight path, especially for light rockets.

What does the delay estimate mean?

It estimates coast time after burnout. Use it as a guide when comparing motor delays, but always follow motor instructions and safe launch practices.

Why compare with no drag altitude?

The no drag value shows an ideal reference. The difference helps explain how body diameter, air density, and drag coefficient reduce real altitude.