Prop for CB-1 with O-290-D
Posted: Mon Apr 13, 2020 4:33 pm
Throwing this out for anybody in the propeller selection dilemma...
My Hatz has an O-290-D (125HP), and round cables instead of streamline wires so I'd expect slower cruise than others. When I bought it it had a Sensenich 76AM6-2-50 metal prop, 74" diameter x 50" pitch which I thought was a bit much. I wanted to replace it with a wood prop for various reasons, and I also hoped that a little less pitch would give me better climb with hopefully not too much speed loss. To make a long story short (the long version will be in a couple of upcoming Kitplanes magazine articles), I bought a 74x47 Sterba wood prop, which was still too much pitch (a wood prop generally needs a lower pitch than a metal prop because of the greater thickness and thus camber of the wood prop). After three reworks, it's down to 73½ X 44¼ and not quite as good as the metal prop, about 75 fpm worse climb but similar cruise speed at the same rpm. On the plus side, it weighs 15# less, doesn't have the AD that the metal prop has, runs smoother, protects the engine if it hits something, and just looks better. I get 2525 rpm climbing 760fpm at 60 knots (840fpm at 55 which is about Vy but 60 is comfortable), cruise 70kts at 2250, max out at 80kts at 2600.
If I was doing it again I think I'd start a 76x43 or 42 and work from there, it's easy to reduce a prop's pitch or diameter but not so easy to increase it. Though I'd love to borrow one of those 80" fine pitch Borer props the Super Cub guys use just to try...
My Hatz has an O-290-D (125HP), and round cables instead of streamline wires so I'd expect slower cruise than others. When I bought it it had a Sensenich 76AM6-2-50 metal prop, 74" diameter x 50" pitch which I thought was a bit much. I wanted to replace it with a wood prop for various reasons, and I also hoped that a little less pitch would give me better climb with hopefully not too much speed loss. To make a long story short (the long version will be in a couple of upcoming Kitplanes magazine articles), I bought a 74x47 Sterba wood prop, which was still too much pitch (a wood prop generally needs a lower pitch than a metal prop because of the greater thickness and thus camber of the wood prop). After three reworks, it's down to 73½ X 44¼ and not quite as good as the metal prop, about 75 fpm worse climb but similar cruise speed at the same rpm. On the plus side, it weighs 15# less, doesn't have the AD that the metal prop has, runs smoother, protects the engine if it hits something, and just looks better. I get 2525 rpm climbing 760fpm at 60 knots (840fpm at 55 which is about Vy but 60 is comfortable), cruise 70kts at 2250, max out at 80kts at 2600.
If I was doing it again I think I'd start a 76x43 or 42 and work from there, it's easy to reduce a prop's pitch or diameter but not so easy to increase it. Though I'd love to borrow one of those 80" fine pitch Borer props the Super Cub guys use just to try...