Directional stability 3: Swept or Delta wings
Let’s add one more factor to our list of features that keep paper aeroplanes flying straight.
5. Design your plane so that it has swept or delta wings.
Why does this work?
Well lets look at two wings configurations, one straight, one swept.
The diagram below shows both configurations flying straight forward, with zero yaw and zero sideslip. In this scenario, both sides of the straight wing configuration are presenting equal frontal surface areas to the oncoming air. This is also the case for both sides of the swept wing configuration.
Note: for simplicity’s sake let’s assume that the centre of gravity of each wing configuration is right at the very front of the centre of the wing. The centre of gravity is denoted by the pink dot in the diagrams.
However, let’s say the plane starts to yaw by 45 degrees.
Again in the situation the each side of the straight configuration continues to present exactly the same surface area to the oncoming air. This means that the yaw is not corrected.
However, in the swept wing configuration, the side on the outside of the yaw is presenting a greater surface area to the air than side on the inside of the yaw. This helps correct the yaw by pushing the swept wings back into the original position as seen in the first diagram.
Actually, there is more going on than described in this article; however, this is intended as a very basic introduction.