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this post was submitted on 14 Oct 2026
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No Stupid Questions
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No such thing. Ask away!
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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.
This is the correct answer.
In my mind there is no difference in these setups
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.
But the air is not contained on the boat, it is pushed away from the boat after hitting the sail. Since that air has mass it will produce and equal force pushing on the sail, aka thrust.
A jet engine with deployed reverses is just a fan mounted on the plane pushing against the plane but it works just fine.
A sail is just a very inefficient deflector of air, but the principle is the same.
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.
What about this?
You need a magnet thrust reverser
Put another magnet on the front of the truck and the magnets reverse thrust one another for maximum results
This guy screws
And both work, the sail is just very inefficient as a trust reverser. Just remove the sail and use the fan directly. You can rotate the entire fan if you want to reverse.
They tested the fan on a sailboat on MythBusters, and were shocked that it actually worked. https://mythresults.com/blow-your-own-sail
It didn't work well, but it did work.
"The idea works if you just remove this half and reverse the other half."
I prefer Lemmy to Reddit but the userbase here is way more insufferable.
It's a venn diagram of people banned from reddit and people who think they're too good for reddit, what do you expect.
Haha, good point.
Just wait, what does that make us?
Insufferable.
Checks out.
Well yeah, because the sail is not needed at all, you just need the fan.
A modern commercial jet engine is just a very powerful fan anyway. You move air backward, you move forwards. Works just as well on boat as on a plane.
The sail would just be a very inefficient reverser.
Yeah, so inefficient as to be completely ineffective. In other words, "it doesn't work".
No, it's not completely ineffective, just very ineffective.
If you blow enough air at a sufficient sturdy sail you can absolutely generate trust from the airflow the sail deflects.
But you'll be more efficient if you remove the sail and just point the fan in the other direction.
You'd be even more efficient if you put the fan under the boat and push the water instead of the air.
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.
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.
https://en.wikipedia.org/wiki/Thrust_reversal
But it isn't as fun
You know that everyone knows that Wikipedia and search engines exist, right? People don't post questions on forums because information doesn't exist elsewhere. It's because of the social factor.
Besides, Wikipedia isn't perfect, and search engines have gone to shit
Hey dipshit, I think you’re lost, the community is called ‘nostupidquestions’ not ‘I want to gargle on CIA cock’
How is the sail in this pic any different?
It is redirecting the flow of air from the fan
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.
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.