CURRENT POSITION: STAGE 3 OF 4
3.1
STAGE 3: CHOOSE WITH CONFIDENCE
With an assembled airframe, you face a logistical decision: engine selection. Using an overpowered motor in a small field guarantees the loss of your rocket. Using an underpowered motor guarantees an unstable, dangerous flight. Make choices based on data.
3.2
UNDERSTANDING ENGINE CODES
A standard model rocket engine is defined by a code, such as B4-4.
- The Letter (B): Total impulse (total power). Each letter doubles the power of the previous letter. A 'B' engine is twice as powerful as an 'A' engine.
- First Number (4): Average thrust in Newtons. This dictates how quickly the rocket comes off the launch pad. Heavy rockets need high average thrust.
- Second Number (-4): The delay time in seconds between motor burnout and the ejection charge firing.
3.3
ENGINE CLASS COMPARISON
| Class | Total Impulse (N-sec) | Typical Altitude (Standard Rocket) | Field Size Required |
|---|---|---|---|
| 1/2 A | 0.626 - 1.25 | 100 - 200 ft | Small Park (200 sq ft) |
| A | 1.26 - 2.50 | 300 - 400 ft | Football Field |
| B | 2.51 - 5.00 | 500 - 800 ft | Large Field |
| C | 5.01 - 10.00 | 1,000 - 1,500 ft | Wide Open Area |
| D | 10.01 - 20.00 | 2,000+ ft | Extensive Farmland |
3.4
PROCEED TO NEXT STAGE
You have mastered low-power classification. It is time to look at the larger scope of amateur aerospace.
BEGIN STAGE 4