Model rockets are small and simple compared to the rockets that launch into the vacuum of space. Yet model rocketry relies on many of the same basic principles of flight. In this blog post I will be talking about the wonders of model rocketry, and how it helped me understand how rockets work.
I’ll start off with the rocket engines that make model rockets fly. Model rocket engines are generally filled with either a gunpowder-like substance known as black powder or a more powerful propellant, ammonium perchlorate (AP), which was the fuel used in the Space Shuttle’s solid rocket boosters. Regardless of propellant type, these engines are designed to burn at a predetermined rate: too fast of a launch and the rocket airframe could shred apart (I’ve seen it happen!), too slow and the rocket could just sit on the ground without going anywhere. The length of the rocket’s burn and the amount of thrust it produces are dependent on the type and amount of propellant, the size of the combustion chamber and the shape of the rocket nozzle. All of these variables influence the thrust level and efficiency of any rocket, including those launched into orbit.
After selecting a proper motor, rocketeers must consider the problem of keeping a rocket stable. In model rockets, stability is generally enhanced with several fins at the base of the rocket. These fins increase drag near the back of the rocket, causing the less draggy (front) end to stay pointed straight up throughout the boost. (Think of holding an umbrella. As windspeed increases, the umbrella would turn so that its draggy end was opposite the wind direction.) If fins were not added to smaller rockets, they would fly very erratically. So, why do larger rockets not need fins? Generally, these spacecraft are steered by gyroscopes, which subtly alter the position of the rocket nozzle throughout boost to keep the craft pointed straight up. This procedure, known as “gimballing,” eliminates the need for fins.
Finally, rockets need to be recovered. Both large and small rockets are often recovered using parachutes. Many model rocket motors have a built-in “ejection charge,” which is a small blast that pops the parachute out a given number of seconds after launch. However, this approach has some problems: If the delay is too short, the rocket’s parachute may open too early, sometimes when the rocket is travelling upwards at hundreds of miles per hour. If the delay is too late, however, the rocket may plummet to the ground before it deploys the ‘chute. Some model rocketeers have added electronics to their rockets to solve these problems: sensors detect when the rocket is beginning to arc over, then deploy the parachute at the maximum altitude. Spacecraft use more sophisticated electronic equipment to deploy the parachute at exact altitudes, but the basic principle is the same.
All of these factors combine to make rocketry at all scales a very challenging but extremely rewarding pursuit. Rockets of all sizes require very specific conditions to fly successfully, and regardless of the rocket size, you can’t help but cheer when everything goes right.
Here’s a video of the “Inspire” rocket flying perfectly with
a video camera onboard…
http://www.youtube.com/watch?v=xcmn5o9QPzg Discuss this blog here: http://tinyurl.com/bloginspire12
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