Engine Selection for Model Rockets

"We have a model rocket now. It's not painted, you know this. We will be painting it. But I want to talk a minute about engines. Because these things actually do fly. Here I have a pack of engines. Many manufacturers make them in the country. The engines come different price ranges, usually between five and ten dollars. You get three engines for three flights. The engines come in different designations. You will see half-A, A, B, C, and D for typically smaller-type rockets that I'm talking about. Those each mean that each time the number or the letter goes up, A to B, it doubles the strength of the engine basically. I have in my hand an engine called B. So this is a more powerful engine than A, and we'll use that B engine for this rocket, to fly it."