Constant-Speed vs. Fixed Pitch
f1rocket said:
Yep, that's about right although the CS prop will be just slightly faster in cruise because it can pull more RPM....... At cruise, we are nearly identical with him just able to inch ahead of me.....
A CS prop will not necessarily be faster nor "pull" more RPMs. It depends on the fixed prop. Where the CS prop shines is climb, landing and overall efficiency. In the case of pulling more RPM, this is true on takeoff and climb. The higher RPM allows you to make more power. The chart from Hartzell shows this real well:
http://www.hartzellprop.com/kitplane/kitplane_certified_prop.htm Under performance click chart.
A good CS "how it works" Ref:
http://www.avweb.com/news/maint/185020-1.html
Constant-Speed vs. Fixed Pitch
Hartzell,
"Constant-speed propellers offer higher efficiency over a wider speed range compared to fixed-pitch propellers. With a fixed-pitch propeller, builders have to choose between a "climb" pitch and a "cruise" pitch. Choosing one results in a propeller system that compromises the other. The pilot has only a limited range of engine speed variation available to control the thrust of an aircraft equipped with a fixed-pitch prop. The ability to vary blade angle in a constant-speed propeller allows the engine to develop more power since rpm and power can be controlled independently at any air speed. This enables you to optimize both cruise and climb for maximum efficiency and performance."
A CS prop is limited by the governor, usually set @ 2700 RPM max. You can't exceed that RPM limited no matter what. Which is a nice thing; you don't have to worry about it. However, all things being equal, if you race a fixed pitch plane turning 2900 RPM, you might be at a speed disadvantage w/ a CS prop turning 2700 RPM, more RPM = more HP, more Go (HP=torquexRPM/5252).
There are many good fixed props to choose from today. A good option is the metal Sensenich, without the maintenance issues of wood, made for the RV and at a good price. Also, the factory can "tweak" or re-pitch a metal prop to fine-tune it for your needs. The advantage of wood is smoother operation, less likely to damage crank with a prop strike, and lighter. The down side, finnish is subject to erosion in rain and they req periodic re-torque. The Catto prop is also popular, but don't know anything about them except many like them. However one gent had a failure of his Catto and appeared to be a defect in a joint/bond.
RVator, 6th issue 20004, pg 11, Ken at Van's switched from a fixed to CS prop. He sounds like a grumpy old man. (Yea I said it)
His impression is a little negative in tone but admits he has not flown the new config much. Also he states with the heavier prop his CG moved Aft.
Confused? Me to. Despite his CG calc math error more weight on the nose will move the CG fwd. Can be a good thing or a bad thing.
Read all the many opinions, articles and look at your wallet. Only suggestion is
consider a purchase of an engine with CS capability even if you go fixed Pitched Prop to start. That way if you can change in the future if you want, and it will be a selling point and have higher resale. I would not use an electric prop due to maintenance of brush or slip rings. If your engine has a solid crank, go fixed. Hydraulic pitch control is reliable and req's little routine maintenance.
Cheers G RV-4 RV-7 (project O-360/CS prop)