Comment on why do reverse thrusters work on an airplane, but a fan on a sailboat doesn't work?
truthfultemporarily@feddit.org 2 weeks ago
The reverse thruster is force originating from the plane pushing against the air.
The fan on the sailboat is force originating from the boat pushing against the boat.
Karmanopoly@lemmy.world 2 weeks ago
Onomatopoeia@lemmy.cafe 2 weeks ago
Imagine 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 2 weeks 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 2 weeks 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.
gastroglizzy@piefed.social 2 weeks ago
It works by redirecting the flow of outgoing gas forwards.
This may shock you to learn, but typing your question into a search engine and reading any Wikipedia articles in the results is something you can do yourself; it’s much faster and more accurate than asking random strangers on the internet.
ianhclark510@lemmy.blahaj.zone 2 weeks ago
Hey dipshit, I think you’re lost, the community is called ‘nostupidquestions’ not ‘I want to gargle on CIA cock’
Karmanopoly@lemmy.world 2 weeks ago
snooggums@piefed.world 2 weeks ago
The reverse thrusters redirect the air coming out in the opposite direction, so it is like turning the fan in the opposite direction.
A sail catches the air to pull the boat along and some of it bleeds off, but it does not direct any air backwards to propel the ship forward.
remon@ani.social 2 weeks ago
And both work, the sail is just a very inefficient trust reverser so you hardly get any thrust from it. Just remove the sail and use the fan directly.
AnAmericanPotato@programming.dev 2 weeks ago
They tested the fan on a sailboat on MythBusters, and were shocked that it actually worked. mythresults.com/blow-your-own-sail
It didn’t work well, but it did work.
gastroglizzy@piefed.social 2 weeks ago
“The idea works if you just remove this half and reverse the other half.”
Kyrias@lemmy.ca 2 weeks ago
I prefer Lemmy to Reddit but the userbase here is way more insufferable.
remon@ani.social 2 weeks ago
Well yeah, because the sail is not needed at all, you just need the fan.
A jet engine is just a very powerful fan anyway, so nothing else is needed.
The sail would just be a very inefficient reverser.
paraplu@piefed.social 2 weeks ago
Can you push your car while sitting inside it? That’s essentially what your boat picture depicts. Could you turn around the fan and push the other way? Sure, then you end up with an airboat. Or better yet you turn the fan around and stick it in the water.
Although this could just be another of your physics trolling questions, where you just want to argue in the comments. Apologies if that’s a different user and I’ve mixed you up.
Hacksaw@lemmy.ca 2 weeks ago
I mean sure, maybe there is no difference. But then, like the plane you’re better off not using the sail and just pointing the fan the opposite way so it pushes the boat fwd.
The engine on a plane pushes the airplane forward. The reversers redirect a portion of the thrust forward slowing the aircraft down. The best thrust reversers get MAYBE 50% efficiency. On the boat there is no reason to throw out half the fans thrust.
That’s combined with the fact that the sail isn’t an effective thrust reverser and that the worst case efficiency is negative. If you don’t redirect enough air backwards you won’t even overcome the fans thrust let alone produce a net reverse thrust.
gastroglizzy@piefed.social 2 weeks ago
This is the correct answer.