Turning a propeller around doesn't change it's direction of rotation.

[halfeye]

I was thinking about this while trying to sleep, and was surprised to realise the above.

If you have a propeller blade like front \ back, if you turn it around, it's back \ front. If for some reason you need a propeller with blades that go front / back, you need an entirely different propeller.

[NichG]

This is why every toolbox needs a Klein bottle...

[Lord Torath]

Yup, taking a clockwise-turning propeller and installing it backward will leave it as a clockwise-turning propeller.

It is my understanding, though, that the leading and trailing edges of propellers are not the same. You probably won't get the same performance if you install the propeller backward (if it will even let you install it that way).

[halfeye]

This is why every toolbox needs a Klein bottle...

Yeah, I thought it was a fun and interesting fact, but not obvious until you think about it.

[Yora]

It's the same as how you can screw a nut on a bolt regardless of which side of the nut you use. Instead of twisted propeller blades on the outside, there's a spiral thread on the inside.

[Rockphed]

If you have a propeller that can be installed backwards, it can probably be run just as efficiently backwards as forwards. Ceiling fans frequently have perfectly flat vanes precisely so they can have their rotation reversed at will. It lowers their efficiency by a bit, but the utility of being able to changing a fan that pushes air down in the center of the room to one that pulls air up in the center of the room is worth it.

[Imbalance]

Next time, just imagine turning the boat around instead, and you'll probably fall asleep faster.

[halfeye]

Next time, just imagine turning the boat around instead, and you'll probably fall asleep faster.

Boat?

[DavidSh]

Boat?

These days, I think most propellers are on boats (submarines included), but I suppose there are also propellers on airplanes, airships, and the occasional forms of propeller hat. What did you have in mind?

[halfeye]

These days, I think most propellers are on boats (submarines included), but I suppose there are also propellers on airplanes, airships, and the occasional forms of propeller hat. What did you have in mind?

As Peelee says of himself, I think I'm funny.

The actual application was a pedal powered ekranoplan, so boat isn't entirely wrong, but it's not entirely right either.

[Trafalgar]

Yup, taking a clockwise-turning propeller and installing it backward will leave it as a clockwise-turning propeller.

It is my understanding, though, that the leading and trailing edges of propellers are not the same. You probably won't get the same performance if you install the propeller backward (if it will even let you install it that way).

For boats and ships, propeller blades have an airfoil shaped cross section to maximize performance. So installing one backwards will greatly degrade thrust and efficiency. Shafts are usually tapered, however, which makes putting the prop on backwards impossible.

It's pretty common, though, for someone to accidentally put a left handed prop on a right handed shaft and not realize it until the boat is in the water.