J3 Prop Length

[Sikorsky]

J3, standard SC gear, 850 tires, and on Baumann 1500 Floats most of the time. 90 hp Rolls Royce engine, which is basically a c90 with 9-1 compression, and the Lycon cylinder smoothing.

I've been told a 78-35 Catto is that best climb prop for this. How big of an issue is a 78" prop gong to be for ground clearance? Water Clearance? 76 is probably the safe bet but if I can get a little more bang for the buck, i'll go with the 78.

I have a short prop on presently.

Thoughts?

Zach

 

[mvivion]

J3, standard SC gear, 850 tires, and on Baumann 1500 Floats most of the time. 90 hp Rolls Royce engine, which is basically a c90 with 9-1 compression, and the Lycon cylinder smoothing.

I've been told a 78-35 Catto is that best climb prop for this. How big of an issue is a 78" prop gong to be for ground clearance? Water Clearance? 76 is probably the safe bet but if I can get a little more bang for the buck, i'll go with the 78.

I have a short prop on presently.

Thoughts?

Zach

Is the airplane certified or experimental?

MTV

 

[Sikorsky]

Experimental

 

[cubdriver2]

Might have what you want. Was on my buddies C90 J3

 

[KevinJ]

That looks like the ticket. I bet you could get away with a longer prop because of the nickel leading edge

 

[supercrow]

Just for information for what it's worth. Back in the early 80's I ran an 82-41 borer on a standard 150 super cub for several years with no problems on skis and 8:50's with standard length gear.

 

[Dan Gervae]

I have a 76 x 35 Catto on my Ex 11 and I tried it on my C90 powered Tcraft. I posted the results here somewhere I think, I’ll have to search it out. I think my 76AK-2-40 did a little better on the 90…I’ll find and post the static rpm results when I find them. The Catto spun higher rpm in my O200 static than Sen 76AK-2-40…. If I were you I’d get a Sensenich ground adjustable though….light weight and has options. Just my 2 cents

 

[hotrod180]

... How big of an issue is a 78" prop going to be for ground clearance? ....

There's a spec somewhere(for certified airplanes anyways) which calls out required prop ground clearance with the airplane in a level attitude. I seem to recall it's 9".

EDIT: that's 9" clearance with landing gear deflected, as per post #13 below. Thanks Gary.

 

[BC12D-4-85]

As Dan suggests, get this and never look back> https://www.sensenich.com/shop/airc...oming-o-235-ground-adjustable-stol-propeller/

Gary

 

[Jacob Papp]

The 80-34 Cato that Glenn referenced is the way to go… it squeezed every bit of power from the c90 and ran smooth. No issues for ground clearance with standard gear 8.50s

 

[Sikorsky]

Good information. I got the plane into flight level and measured stuff. With standard gear and 8.50’s there is 11.75” of ground clearance with the 80” prop. My concern is more so on floats chewing the water.

Z.

 

[skywagon8a]

Good information. I got the plane into flight level and measured stuff. With standard gear and 8.50’s there is 11.75” of ground clearance with the 80” prop. My concern is more so on floats chewing the water.

Z.

Attach a spray rail facing down from the inboard forward end of the chine on the floats. Extend the length to behind the propeller. This will turn the water pushed up by the float bottoms back down away from the prop. Most of the water which gets sucked up by the prop is first pushed upwards toward the center of the plane by the V shape of the float bottoms.

 

[BC12D-4-85]

This is a grab from CAR4a 1950...while suggestive it still has value. Some floats have very short struts (Aqua), others are longer (PK & EDO & Baumann). Longer = less water contact plus Pete's suggestion on spray rails helps. EDO 1320's and Baumann's with concave bottoms flare sideways and tend to throw water more in that direction than up like V-shaped hulls.

§ 4a.599 Propeller clearance. Propellers shall
have a minimum ground clearance of 9 inches when
the airplane is in a horizontal position with the landing
gear deflected as it would be under the maximum
authorized weight of the airplane. Propellers on
seaplanes shall clear the water by at least 18 inches
when the seaplane is at rest under the maximum
authorized load condition. A clearance of at least 1
inch shall be provided between the tips of the
propellers and any part of the structure.

Gary

 

[mvivion]

In my experience, the composite props with stainless or nickel leading edges are nearly impervious to water damage on floats. I’ve run three or four, and those leading edges aren’t affected at all by spray.

But if ‘‘twas me, I’d go the ground adjustable route. Same leading edges, BTW

MTV

 

[cubdriver2]

Zack check your PM

Glenn

 

[Dan Gervae]

It would be great to be able to test multiple props before buying…I’d love to know how much performance increase (or decrease) each prop provided….we are very lucky to have this forum to help us make our choices though.

 

[BC12D-4-85]

A friend with an EXP PA-18 has a Catto and Sensenich adjustable, plus tested a Borer on his O-320. I think it's a 160 but not 100% sure. Anyway he's flying the Sensenich mid-range pitch and prefers that design. Has good takeoff and better cruise. I'd expect similar with a C-90.

Gary