counter-rotating props

[kitnut617]

Lecture time (it doesn't hurt, honestly.)

Counter-rotating props are fitted to twins: one rotates clockwise and the other anti-clockwise.

Contra-rotating props are fitted to a single engine (or, in the case of a Gannet, two driving a single shaft).

Now is that right, contra props have two shafts too, one is hollow where the other solid one rotates in it

In the case of the Gannet, which did have two engines, one connected to the front propeller and the other connected to the rear propeller. Which is why they could shut down one engine and feather the prop. So would this be a counter rotating prop or a contra-rotating one :lol:

[Bob Perry]

The most familiar examples of counter rotating props might be the P-38 Lightning and the DH Hornet. They're not nearly so exotic as contra rotaing props.

[agboak]

Correct, that should not have been a common shaft but a common axis of rotation. The Gannet really does foul up standard thinking, doesn't it?

It is interesting to wonder why some twins got away without counter props whereas others didn't. It helps to have a big tail (or two), I guess.

[kitnut617]

Correct, that should not have been a common shaft but a common axis of rotation. The Gannet really does foul up standard thinking, doesn't it?

It is interesting to wonder why some twins got away without counter props whereas others didn't. It helps to have a big tail (or two), I guess.

It's also interesting that some twins which had counter rotating props had them rotating in different directions too, the P-38 for instance when viewed from the front, the starboard engine turned counter-clockwise and the port engine clockwise, while the DH Hornet when view in the same direction, the starboard engine turned clockwise and the port one counter-clockwise.

There was an article in SAMI a few issues ago which had a build up of the MPM Hornet Mk.21 and I had noticed that the builder had put the props on the wrong way around and wrote to the Editor about it and he posted my letter in a later issue.

One of the resident columnist picked up on it and explained how when the aircraft had one engine out, the way the props turned made it easier to fly on one engine. But it didn't explain why the P-38's had a different rotation to the Hornets or whether it was harder to fly on one engine.

It's interesting too that the all P/F-82's except the P-82B (both props turning the same way), had the props rotating the same as the P-38

Edited February 6, 2007 by kitnut617

[Slartibartfast]

The P/F-82 wouldn't get off the ground when first tested as the prop wash blanked the lift from the wing center section. North American reversed prop rotation and all was right with the world.

[kitnut617]

The P/F-82 wouldn't get off the ground when first tested as the prop wash blanked the lift from the wing center section. North American reversed prop rotation and all was right with the world.

Now that's interesting to know, thanks