Let's say you want to build a RC hovercraft, based on a real recreation hovercraft having these specifications :
Dimensions : 3 meters long, 1.8 meters width, 1.5 meters height
A total weight of 260 kilograms (180 kilograms dry weight, 10 kilograms of fuel, 70 kilograms for the pilot)
30 horsepower motor
1 - Determine the scale of your RC model
To get a compact RC hovercraft, we'll say its lenght will be 50 cm. Therefore, its scale will be 1/6.
According to this scale, its width should be 1.8 meters / 6 = 30 centimeters, and its height 1.5 meters / 6 = 25 centimeters.
2 - Determine the power needed by your RC model
Make the conversion from horsepower to watts. As 1 horsepower = 736 watts, 30 horsepower = 22080 watts.
Calculate the cube of your models scale : 6 X 6 X 6 = 216.
Then, use this result to divide the numbers of watts : 22080 / 216 = 102 watts.
3 - Determine the maximum weight of your RC model
Like before, we will divide 260 kilograms by the cube of your models scale : 260 / 216 = 1.2 kilograms.
This is quite a heavy weight, giving you the possibility to set a heavy NIMH battery on your model.
That's it, the final specifications of your RC hovercraft are :
50 cm lenght, 30 cm width, 25 cm height, a power of 102 watts and a maximum weight of 1.2 kilograms