Research different types of airplanes that you want your design to be modeled after. For example, if you want to design fighter jets, you would research vthe F-16 and the F-22. Pick one jet that you want your design to resemble.
Research and record the length and width specifications of the airplane you want your design to resemble. For example, you should find the length and width of wings, propeller, wheels, tail and engines. The more specifications you include, the more detailed and accurate your design will be.
Choose a scale ratio. For example, you could choose a ratio of 100:1. This means that for every 100 feet on the real airplane, you draw 1 foot on your design. You don't have to choose feet as the unit. Another example is a ratio of 600:1; for every 600 inches, you draw 1 inch on your design.
Convert the specification on the real airplane into the ratio specifications you will use for your design. For example, if the wingspan is 100 feet on the real airplane and you have chosen a ratio of 100:1, your new specification is 1 foot.
Sketch out all of the specifications on a sheet of grid paper using a ruler. Label all of the airplane components with the original specifications, including length and width.
Add new details to your design that make it different from the original airplane. For example, you could add another set of wings to make it a biplane. The only thing that needs to remain the same is the length and width specifications so that the math concept of ratio stays intact. Everything else is up to your imagination.
Label any additions that you have made to the airplane with the correct specifications. For example, if you added a set of wings that were each 6 inches long using the 100:1 ratio, you need to label it as 50 feet because 6 inches is half of 1 foot and 50 is half of 100.