Controllable Pitch Propellor

[Steppenrig]

Anyone ever tried to build a CPP for their model? If so, can you throw some ideas or suggestions my way?


I've been toying with the idea of a simplified helicopter type setup. Any thoughts?

Cheers

Dave

[HMAS]

What dia prop/ screw?
back when I wuz young & motivated
I did it on a 2 screw tug. but did not find any improvement over a fixed screw & a speed controller allowing forward & reverse.
However on a marinized 10cc gloplug engine running at a fixed speed it came into its own.
The heli head will be easier & possibly better, than my old ideas.
I'll dig up some piccys if I can find them to see wot I did.

[Sean Hert]

IIRC, didn't Robart or Robbe experiment, unsuccessfully, with one?

[HMAS]

I thought they had one that worked ?? I must admit mine was large scale & sloppy, so the tolerances they worked too would have been a lot tighter,therefore harder to do

[Steppenrig]

Pics would be fantastic if it's convenient.

Cheers

Dave

[fooman2008]

would be interesting since every ship in the Navy that is gas turbine uses variable pitch screws.
I was on a Sprucan, and we had a valve failure and locked up the screw at 101% pitch (war emergency), was lots of fun when ship weaved 25 deg off course regardless of what I did on the helm. Normally a Sprucan would turn 55rpm until about 11 knots (I think?) just varying the pitch of the screws. Made it a real joy to try and tie to a buoy (Hong Kong) since the screws are never perfectly flat always moving ever so slightly.
We ended up going from Pearl Harbor on one screw (they removed the blades on the bad screw), called ourselves the navy's largest frigate.

The best way to vary the pitch would be hydraulic, I would think (like full scale), but making a system like that would also be quite the challenge.

[Admhawk]

The simplest way would be to have a hollow shaft with a push rod in the center. This would attach to pivots on the blades which would rotate them as you moved the rod fwd and back. You would have to work out a way for the blades to attach to the hub, be free to rotate and have an off center rod that goes into the hub to be pushed by the center push rod. You'd get about 40-50 degrees of rotation this way, which should be enough. The shaft would need a gear or belt at the drive end to offset the motor so that the rod can come out and attach to a servo. Awful tight tolerances for a 1/96 or 1/72 scale model.

[fooman2008]

just had a thought....try something like a heli swash plate, with a hollow shaft and push rod down the middle? Belt drives are not that hard to find in R/C cars and that gives you the end of the shaft clear for variable pitch actuation. You will have to make sure that you support the end of the shaft with a bearing or bushing to prevent it from waving around but it does sound feasible, though probably not in small scale. The real joy will be machining the hub to be able to accept the screw blades and keeping them from wobbling. You ought to try and find a pic or two from a shipyard (Grumman SeaSystems perhaps?) showing decent view of the screw hub and the mountings for the blades. The blades on a Sprucan are taller than I am (6foot 5in) sitting on a pallet on the flight deck, and if I recall right had 20 something huge brass screws holding the blades on. One which they dropped to the bottom of Pearl Harbor, along with about half the attachment screws at one time or another stripping off the blades.

[oneslim]

Here is how the R/C airplane guys do it.

http://www.rcuniverse.com/magazine/arti ... cle_id=716

[Laurent]

This is how a french guy did it on his trawler model :
http://modelisme-naval-radiocommande.ac ... riable.htm

the pictures are self explanatory ...

hereby a little video of the same propeller :
http://www.zippyvideos.com/6017937106742876/p1100659/

Regards ,

Laurent

[Steppenrig]

Thanks for the links guys,

This is gonna be on the back burner for a while until my CG(X) and my experimental turbine get built, possibly have a refit next year some time that incorporates some of these ideas.

Dave