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.
For black powder motors, the letter after the delay time is meaningless. Estes put the "T" designation to refer to "tiny." When Estes first produced the "T" size motors, they only had two sizes. At this point in time, the "T" just causes confusion, because a letter is used on composite and high-power motors to designate the type of propellant and the color of the flame produced by the motor. Since these are black powder motors, a letter isn't really needed. The "T" size motor are sometimes referred to as Estes mini-motors.
Engine Diameter and Length
Unfortunately, the engine diameter and length are not included in the type code printed on the side of the rocket. So before you can pick an engine from the charts, you have to refer back to the rocket kit itself, and see which engine diameter it can use. Do that first. Most kits can accept different length motors, so that is not an issue. The most important thing when selecting a rocket engine is the diameter, and then the "type" designation.