N1BZRich(at)AOL.COM
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 Posted: Thu May 24, 2007 6:34 am Post subject: Best prop |
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Jim,
I will also post this to the Lightning group as it might be of interest to others.
As far as my experience goes (with my airplane and the other Lightnings I have flown), Ryan is right on. I have been very pleased with the Sensenich props, both wood and carbon fiber, that have the "ZK" blade profile. Note - that is the only blade profile that I have flown, but I do know that Nick has tried others and is currently testing a different blade profile on a fixed pitch wooden Sensenich. Also, all of the Sensenich props that I have used have been 64 inches in diameter, but I have tried pitches of 51", 53", 54" and 55 inches. I am currently flying the 55 inch and have about decided I still need another inch of pitch on 31BZ. With the 55" pitch I can still over speed the engine rpm limit at 5000' in level flight. I have not tested it higher than 5000' but will probably do that soon. Most of my prop data for the other pitches had been done at 5000 so that is where I do my comparison testing. Having said the above, let me make a few other comments.
First, it seems to me that the ground adjustable carbon fiber prop (pitch set at 54 inches) is about the same at the fixed pitch of 54 inches UNTIL you get to the speed regime above 160 mph or so. Above that speed (and I can only guess as to why) it is just not as efficient or fast. On my airplane (your mileage may vary) I lose about 8 to 10 mph on top end. I say about 8 mph because various test have resulted in various results (probably due to OAT) with the loss of speed varying between 6 to 15 mph. I think it has to do with the carbon fiber blades being stiffer. Also the total weight of the carbon fiber prop with the aluminum hub is certainly heavier. I also seem to burn slightly more fuel when this prop in on.
Second, the wooden fixed pitch props seem to run slightly smoother than the carbon fiber prop did for me. Note - I had one of the very early ground adjustable props and later ones may be better. But for me, the smoother run, the lighter weight, the less fuel burn, and the faster speed all point to me using a wooden Sensenich.
Third, both the white painted wooden and carbon fiber props seem to not like to be flown in the rain. The paint on the leading edge erodes - at least on the outer 12 inches or so. I know they have changed the way they paint the carbon fiber ones based on what I saw at Sun-N-Fun. They now leave the metal leading edge (nickel?) unpainted and that should help. They look good that way. The wooded props with the clear wooden finish do not seem to have this problem - at least I have not noticed it. So I am thinking the next prop I order will have the wood finish. Kind of looks "neat" to me in an "out of the ordinary way" to have a wood looking prop on a faster airplane.
Fourth, as I mentioned above I am currently testing the 64ZK55 wooden Sensenich. Top speed at 5000' with spring like OATs (and holding the rpm to 3300) seems to averaging about 185 mph TAS or so, but my engine will still turn up to 3400 or more if you let it go past redline. Take off rpm is down maybe 50 rpm but the takeoff roll is a rapid acceleration and still short (less than 500' even with two on board and full fuel - I live just above sea level), so I can still add another inch of pitch and still get off short.
Lastly, why would someone try for a "top speed" prop when you almost never run the airplane at top speed. To my way of thinking, on a clean airplane like a Lightning (or 31BZ), that "top speed" prop will result in a faster and / or more fuel efficient cruise speed at the speed or rpms that you do use for cruise. Also, the Lightning, with the short take off roll and low stall speed, can get in and out of short fields even with a "speed" prop. I normally only use the first 1000' of runway for my airplane here in Virginia at the two airports I have hangars at. Both have a turn off taxiway at 1000'. If it is gusty I might use 1500' to turn around, but 31BZ will float if you get a 3 know gust. The Lightning wing is so much better in this respect that sea level operation out of a 1000' runway (with good approaches) by a proficient pilot should not be a problem.
Bottom line: You don't have to settle for a compromise prop or you don't have to pay the dollars for a constant speed in order to get max performance from a Lightning.
Blue Skies,
Buz
See what's free at AOL.com.
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