Comment on why do reverse thrusters work on an airplane, but a fan on a sailboat doesn't work?
Onomatopoeia@lemmy.cafe 4 hours agoImagine standing on the boat and pushing on the sail.
Which is the same as the fan pushing on the sail.
The force is all contained in the boat.
remon@ani.social 3 hours ago
Not all air is contained on the boat, it is pushed away from the boat by the sail. Since that air has mass it will produce and equal force pushing on the sail, aka trust.
Trust reverses are fans mounted on the plane pushing against the plane and they work just fine.
A sail is just a very inefficient deflector of air, but the principle is the same.
cecilkorik@lemmy.ca 3 hours ago
For what it’s worth, a thrust reverser is also a very inefficient deflector of air. It’s better than nothing, and jet engines produce a lot of thrust, so even inefficiently reversed it still provides a significant amount of reverse thrust which happens to be quite useful for slowing down an aircraft when there’s minimal weight-on-wheels or on slippery runways, but it’s still only a tiny fraction of what the engines produce in normal operation for forward flight.
A fan blasting air at a sail is also quite inefficient, but as other comments note, it does technically work. It just works so poorly for the amount of energy you’re putting into the fan that you’d probably be better off rowing or just using the sail properly.