Seaplane prop question ?

[cropduster]

I have an F-21 on a new set of Baumann 1500's and still have the original Sensenich 72CK-0-50 prop on it. It seems to eat up a lot of the lake on takeoffs and and am only able to develope 2450-2500 rpm, which is 250rpm short of the red line of 2700. I just took it off and sent it up to Propworks to get it twisted 3 degrees shallower which should help considerably, but here is my question. I know many Cessna and Supercub drivers on floats put on much longer props than land airplanes. I know it's not certified, but I am wondering if a Sensenich 76AM6-2-44 for a PA18 supercub with the same 0-235 lycoming engine as my F-21 has would be the real ticket. I don't know much about the different engine-prop do's and don't do. I just flew with a guy yesterday in his supercub, and he said he had a ( pencil prop ) on it , that was a cut down version of the one for a piper pawnee spray plane, and boy did that thing pull us out of the water! Anybody with prop experience please respond.

[T-Rex]

Re: Seaplane prop question ?

T-Rex has a c-85 so I don't have any direct personal experince with the O-235, but I do work as a mechanic at Surfside Seaplane Base. In general you want to go as long as you can and for pitch as flat as is practical. I'me not a fan of blasting off the water and then cruiseing along at 80mph. You should be able to hit redline and maybe go a little over when straight and level. Every RPM you give up on take off is horsepower you are not makeing. Some planes here will hit redline on a static run up and many come within 50 to 100 rpm. The Sen. 76AM-2-44 sounds like that would preaty good but look on the Cub Type Certificate and see what is approved. It should be an easy Field Approval if the prop is approved on a Cub with the same engine. The best thing to do is try one out if you can before you buy or overhaul one. This can be a little trickey to get someone to pull their prop off so you can try it but most floatplane guys are preaty easy going. How are you liking the new floats?

Brad

[cropduster]

Re: Seaplane prop question ?

Thanks Brad, I think they will be great after I get this prop thing figured out, although I flew with a friend of mine last weekend, and he has the Baumann 2100's on his PA-18, and I noticed he is not as underfloated with his as I am with the 1500's. I think if I could have found a set of certified floats in the 1650-1750 range, it would have been closer the the correct bouancy. I am going to try and get a response from Steve Long, from AK, on this forum as to the kind of prop his runs on his F-21.

[gcgilpin]

Re: Seaplane prop question ?

I think you should be looking for a pitch of around 42-44 on a 115 HP lycoming.

[cropduster]

Re: Seaplane prop question ?

I am going to try and get a one time approval for a Sensenich 76AM6-2-44, that is approved for the PA-18 with the 0-235 engine. I just got my 72" repitch to 48, but it is not enough. I'm still lacking about 75 to 100 rpm

[gcgilpin]

Re: Seaplane prop question ?

So you got an RPM increase of about 100 by changing the pitch from 50 to 48? Sounds about right.