# How Does the Shape & Size of the Fins Affect the Flight of a Rocket?

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Most rockets have some kind of fin system in the back to help stabilize the rocket. This is true for any kind of rocket, whether it is a missile, hobby rocket or space rocket. The size and the shape of the fin on the rocket affects the overall performance, speed and height that the rocket obtains. There is a great deal of math behind the physics of rocket fins, but the principles involved are not difficult to understand.

## Purpose

The purpose of rocket fins are to stabilize a rocket and help it continue in a certain direction without wobbling, falling, flipping over or suddenly changing direction. The fins also help control the speed of the rocket as it lifts into the air. Without fins, a rocket would be much less aerodynamic, which would interfere with the rocket’s ability to shoot high and straight into the air. For a rocket to be successful, it must have fins that can help the rocket keep its intended trajectory.

## Size

The size of the rocket fins can have a large effect on the performance of the rocket. Fins that are too small will not provide any stability, and the rocket will then be at the mercy of the elements and will likely fall to the ground suddenly. Fins that are too large will cause the rocket to have too much drag, which will prevent it from flying as high. The best way to determine the correct size of a fin is to tie a 6-foot piece of string to the middle of the rocket. Place the proposed fins onto the back of the rocket. Spin the rocket around in a circle by the end of the string. If the rocket remains stable, then the fins are the correct size.

## Shape

The shape of the rocket’s fins actually have less influence on the rocket than many people think. Typically, the longer and thinner the fins, the better stability they will provide, but this is not always the case. Most fins are triangular in shape, but other shape variations are also used. The shape of the fin will change the way that the rocket pushes against the air. The larger the profile of the fin, the greater the drag on the rocket. Streamlined fins will help the rocket cut through the air.

## Number

The number of fins can affect the performance of a rocket. The fins need to be evenly placed around the rocket to distribute the weight of the rocket and the air drag evenly. As long as there is an even space between the fins, it does not matter how many there are. One fin will not provide enough stability, but two or more fins will provide enough stability for most small-sized rockets. Many people use between three and four fins for maximum stability.