4 ms·

A propeller in air is fundamentally just like a roller on the ground, but with some efficiency loss.

• gibba999 5y ago
  I understand that. However, that's not something I find easy to explain to a someone who doesn't understand that. The analogy is a little distant. For example, "some efficiency loss" is complex and a little bit inaccurate. It's not just efficiency loss: - In the mechanical analogy, I can extract infinite power from a board moving at a given speed. There is no upper bound on the force the board can apply to me. - In the case of a fan, there is an upper bound on the power which can be extracted given a specific air speed, even given perfect efficiency. Now, it's possible to correctly argue that as the fan size increases, I can make a closer and closer to this analogue. However: - Once you start making arguments like that, cognitive load increases, and beginners start to drop off. You need to keep more and more steps in your head. - And more often than not, an imprecise argument simply reinforces or introduces some misconception, rather than giving an honest understanding. I think a force*distance argument (which is probably a clearer way of stating the argument I was making above) has the virtues of: 1. Being 100% precise 2. Being compact enough someone who understands force, power, and energy can keep the whole argument in their head