Just wondering. Is there a constant speed prop available for RC aircraft?

Not a true constant speed prop, but there is a variable pitch prop for electrics only. With it, pilots have performed reverse 3D maneuvers like hovering nose down.

There is some R&D going one with larger turbo prop models, I'm not certain if there is a production variable pitch prop available yet.

As for the middle of the road, glow engines, I haven't seen anything in that range.

There were one or two variable pitch designs made for glow engines about 30-35 years ago.

http://www.warbirdpropdrives.com/4436.html

If this one makes it into production I will have to have one on a TF P51

A couple years back, I purchased a set of plans for a P&W Wasp Jr 1/6 scarle engine. Included is a set of plans for a consant speed prop for that engine. The designer sells carbon fiber blades for the prop, and you can make a 2 or threee blade setup. The prop is a 20" with a 16 pitch at 6000rpm down to a 5 pitch at 3300. This is bigger that any thing I'm flying now but I've been toying with scaleing it down. There is even an option for a hyd cylinder setup to provide an overide on the spring loaded setup with weights. You can see a view of the two blade version here
http://ph.groups.yahoo.com/group/R_a.../view/372a?b=4

This is R_and_engines under Yahoo groups. I think you will have to join to see the photo section.

Don