In the last post I discussed simple ways that you can modify most paper aeroplanes so they fly in a straight line. Those techniques can improve the directional stability of virtually any paper aeroplane with minimal modification to the fundamental design.
However, if you’re designing your own planes there is more you can do. So let’s add another technique to the list in the previous post:
4. Shifting the centre of gravity forwards relative to the longitudinal centre of the fuselage
In the previous post the paper aeroplane we used as an example was the classic dart, where the centre of gravity was right in the centre of the longitudinal axis of the plane. However, using certain simple folding techniques you can shift the centre of gravity. This can be used to give even a perfectly rectangular fuselage a certain level of directional stability.
The reason why this works is the same as the reason in the last post. As you will see in the diagram below, the surface area ahead of the centre of gravity is smaller than the surface area behind the centre of gravity. This means the ‘weather vane’ effect occurs again, just as it did in the earlier example.
An ultra simple way of doing this is to add a paper clip to the nose of the plane; however, I like my paper aeroplanes to be made out of one sheet of paper alone, without additions, sticky tape or cutting.
If you are subjecting yourself to the same constraints, you can shift the centre of gravity along the longitudinal axis of the plane by making sure there is more paper (or mass) ahead of the longitudinal centre of the plane than behind it. You can do this by using any one of a number of folds. For example, when making ‘The Lion‘ paper aeroplane, at the part where you fold the paper over itself and back towards the end of the instructions, that moves the centre of gravity forward relative to the longitudinal centre of the plane, because there is more mass ahead of the centre than behind it. In fact, all the paper aeroplanes up on the site so far, with the exception of The Classic Dart, use some folding technique to shift the centre of gravity of the plane forward.
I should note that, generally, shifting the centre of gravity is not the only technique you should use to produce directional stability. This is not because it is a poor technique in theory, it is simply because there are limits on how much you can shift the centre of gravity using folding techniques alone without sacrificing other useful aerodynamic features of a design.