Contra-rotating propeller and other concepts.

[Evoman]

As this propeller forum has gotten some what style I thought of getting a more active discussion going to revive it. It seems like the more interesting topics have mostly been taken place over in the EDF section. I thought of starting a new thread in an effort to not only get more discussion but more ideas flowing on more interesting and innovative propeller airplanes as potential future models.
There have been two British Royal Navy carrier based turbo prop models that as of late have caught my attention because of their interesting contra-rotating propeller set up. These being the Westland Wyvern and the Fairey Gannet.





The Fairey Gannet in particular in the most interesting because it featured twin turbines each powering a propeller each. This layout not only makes it twin engine but an optimal set up as it would not suffer the typical ill effects of a twin when one engine fails because both propellers are mounted in the center.
This concept at first seemed complex for RC use but as I discovered there have already been scale electric power plants recreated complete with variable propeller pitch. So it appears to not be that terribly complex to point of being undo-able.
A contra-rotating propeller electric RC model would actually be beneficial for its extra thrust with both motors running for take off and high speed runs while still being able to be efficient giving more flight time by turning off one motor when just cruising. Add to that the optimal redundancy of twin center mounted props and it makes for a very good and reliable setup.

[Parky]

There have been some dual motor, coaxial counterrotating setups sold. Maxx Products, Aeo and Model Motors have all done them. I am not sure what is still available however.

The issue for shutting one down is that you really have to feather the stopped prop (i.e. align the blades almost fore-aft) or that prop has a lot of drag in the flow field of the other prop. Its worse than a normal twin with one stopped, since the flow speed by the prop is higher than free stream.

A big issue is noise. Closely spaced counter rotating props are pretty loud. Much louder than the same two motors set up as a conventional side by side twin.

And, with both motors running, the efficiency is less than side by side props of the same diameter.

The reason they were popular in the era of the planes you show above is because they are all Navy planes, and the counter rotating setup cancels the engine torque.

Bob

[fhhuber]

Contra-rotating props are the big thing in Pattern Aerobatics competition now.

Cancelled torque helps them get the same roll rate both directions and the same spin rate both ways.

The electric power systems used in Pattern Competition approach being equal to a DA 50.

[Evoman]

There have been some dual motor, coaxial counterrotating setups sold. Maxx Products, Aeo and Model Motors have all done them. I am not sure what is still available however.

The issue for shutting one down is that you really have to feather the stopped prop (i.e. align the blades almost fore-aft) or that prop has a lot of drag in the flow field of the other prop. Its worse than a normal twin with one stopped, since the flow speed by the prop is higher than free stream.

Bob

That is why airplanes like the Fairey Gannet had variable propeller pitch so that the pitch could be adjusted as to not cause drag. Even in these videos you can see that the builder of the RC contra-rotating props designed it to scale complete with variable propeller pitch for that very reason. The whole process could be programed in a tiny controller board that would adjust the prop pitch accordingly when ever one of the motors is shut down automatically.

[F106DeltaDart]

I'd love to see someone make a Gannet someday. The only one still flying, XT752, was based a few miles from home back in MN at the New Richmond Airport in WI. Got to see it fly a few times, and it is one impressive beast! The Z wing wing fold would be the icing on the cake! I've thought about scratch building one, but the scarcity of good quality affordable coaxial setups is problematic.