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To make a rubber band plane fly, is there a limit to the number of twists, for both the speed and the distance. I am using a 1/8 x 3 1/2 band.
Question Date: 2019-02-15
Answer 1:

Twisting the rubber band does work on the band and stores potential energy in it, meaning the capacity for the band to do work has increased.

When the rubber band is allowed to unwind, the band does work and that potential energy is converted to kinetic energy, which is energy of an object in motion.

High speed means having a lot of kinetic energy, and reaching large distance means the kinetic energy has caused the plane to travel very far. Thus, for both speed and distance, having more potential energy means being able to reach a higher value. A twisted rubber band is essentially a torsion spring, for which the stored energy U can be calculated with
U=1/2*k*T2, where
k is the torsional spring constant, and
T is the angle of twist.

From this one can see that increasing the number of twists (increasing T) will always increase the stored energy. This means that there is not a limit to the number of twists to increase either speed or distance: more twists increases the potential energy and enables greater speeds and distances (until the rubber band is twisted so many times that it breaks of course).

BUT, here is another aspect to consider (a twist, if you will): for a given amount of energy (i.e., for a given number of twists), reaching the highest speed prevents having the largest distance. High speeds require high thrust, which is obtained by having the propeller rotate very quickly. Objects moving through fluids experience drag though, which is essentially friction due to moving through the fluid.

Drag converts the kinetic energy of the propeller and plane into other forms, such as heat and sound, in which case that energy is not pushing the airplane forward.

Because drag increases with velocity, moving fast reduces efficiency (more potential energy is ultimately lost to drag instead of being used to push the aircraft forward). So to reach a large distance it is generally better to fly slower for a longer period of time (like this one).


Answer 2:

I am sure that this depends on how the plane is designed, and not knowing the exact design I can't answer that for you. It also probably depends on the type of rubber used for the band, as there are multiple types of rubber. I can tell you that rubber has a limited tensile strength, so if you twist it too far, it will break. The limit to the number of twists definitely depends on the type of rubber that you use, though.

The best thing that I can tell you to do is to experiment and find out for yourself!



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