ESTES ES1601 B4-2 STANDARD ROCKET ENGINE PACK

The Estes B4-2 engine is single stage engine designed for model rocket flight. This engine is a standard engine designed for flights in rockets weighing less than 4 ounces, including the engine. Each package includes 3 engines, 4 starters and 4 plugs.

3 – B4-2 Engines
4 – Starters
4 – Starter Plugs

Technical Specifications

• Total Impulse

5.00 N-sec

• Time Delay

2 Seconds

• Max Lift Weight

4.0 oz (113 g)

• Max Thrust

13.20 Newtons (3.0 lbs)

• Thrust Duration

1.10 Seconds

• Length

2.8 in. (7 cm)

• Diameter

18 mm

• Weight

.66 oz. (18.7 g)

• Propellant Weight

0.27 oz (7.6 g)

What do all the letters and numbers in the the motor name mean?

Lets take an example so you can see how to read the charts. As an example, we'll look at the "1/2A3-2T" motor. 

Breaking it down, we have four bits of information. "1/2A," "3," "2," and "T"

The first letter, "1/2A," in our example, is the power level classification of the motor.  The "1/2" power band, as the chart to the right shows, is greater than .625 Newton-seconds of Total Impulse, and less than 1.25 Newton-Seconds. The maximum power doubles from one letter to the next. So a "B" motor can have twice the power of a "A" motor; which means it will fly approximately twice as high.

Remember, think of power as the size of the fuel tank. The tank doesn't have to be totally full. So An "E" motor isn't required to have the maximum of 40 N-s of total power to still be classified as an "E". It just has to have greater than 20 N-s but less than 40 N-s. This gives us the power-bands (shown as the colors in the chart to the right).

The first number after the power letter is the average thrust level of the rocket measured in Newtons, equivalent to 0.225 pounds of force. That means in our example, the motor has an average thrust of 3 Newtons during the entire burn time. If you were driving a car, you could relate average thrust to the amount of pressure you push on the accelerator pedal. The harder you push, the higher the average thrust of the motor, and hence the higher you'll accelerate the rocket. If you want to go fast, choose a high thrust motor. If you want to get good economy (longer travel distance), choose a lower average thrust motor. 

For example, a B6 and a B4 would have the same amount of fuel in the tank. But the B6 burns it faster, and hence the rocket will reach a higher speed. The B4 motor burns the fuel slower, and like in your automobile, you'll get more distance out of the fuel that is burne

The number after the dash is the length of time in which the "delay" charge burns before it allows the ejection charge, which deploys your parachute, to go off. Delay allows time for the rocket to coast and slow down so the parachute doesn't rip out of the tube at ejection. In our example, the rocket would coast for 2 seconds before deployment.

Most single-use motors give a hard number for the delay, and you will need to purchase the appropriate one for your kit. Some loadable, larger single use or reloadable motors will often have a maximum delay that, with a specially designed tool, you can use to shorten the delay to what is best for your rocket. Look at the "Max Delay" statistic for that particular motor.  If it is an N/A, or not listed, you cannot adjust the delay.