Can anyone explain the basics of a "Constant Speed Prop"
From FlightSim
Q:
a) about the lever in the cockpit and how do you know where to keep it?
b) scenario (takeoff from sea level to 20,000 ft) where do you keep it (lever) at sea level and where do you keep it at 20,000 ft?
A:
A constant speed prop is a prop that always turns (once it's up to speed of course) at the same speed (doh ). The power it puts out is controlled not by increasing the speed it turns but by changing the angle of the blades.
Rod Machado has posted an excerpt from his Private Pilot Handbook that explains constant-speed props (used on piston-engine aircraft) as well as anything I've read.
You can also find good explanations of the constant-speed propeller typically used on piston-engine aircraft in The Pilot's Handbook of Aeronautical Knowledge (free pdf download). See Chapter 3 "Aerodynamics of Flight" (see p. 3-21ff. for "Basic Propeller Principles") and Chapter 5 "Aircraft Systems" (see p. 5-4ff), including the section "Turboprop" (p. 5-30ff).
For more information about using the propeller controls, see "Constant-Speed Propeller" in Chapter 11, "Transition to Complex Airplanes" (p. 11-4ff.), in The Airplane Flying Handbook (also a free pdf dowload).
McCauley, a leading propeller manufacturer, also has good basic information on its Web site.
These are just some of the (mostly) free aviation resources related to aircraft, training, and flight operations that you can find on the Web.
While I can't help you on how to use the power lever and prop control in a turboprop, I will address how it's used in a piston-engine aircraft.
a) On takeoff, you want the prop lever full forward (fine pitch) for max available RPM. After you've lifted off (and retracted your gear, if applicable) and you have a positive rate of climb (and you've cleared all obstacles), you would then retard the throttle a bit followed by reducing the RPM a bit to your climb setting.
Let's take a real world Bonanza, for example (Mooney, Baron, etc. are similar) at sea level. Before takeoff your prop control should be full forward, then you taxi onto the runway and add full throttle, watching the manifold pressure carefully, if it's a turbocharged engine, to not exceed max allowed. After liftoff and gear retraction, you would bring the throttle back to about 25" MP and then bring the prop back to about 2500 RPM, where you'll leave it for the remainder of your climb. Any needed power adjustments during climb will normally then be made only with throttle (unless you have a compelling reason to go to full power, then you'd put prop full forward again). You will probably need to add throttle periodically during the climb to maintain 25" MP, since the air density decreases as you climb. With turbocharging, you probably won't need this other than minor checks to see that nothing has changed, until you're rather high, probably between 12,000 and 18,000 feet, depending on the aircraft. If your takeoff (in a non-turbocharged engine) is above about 4,000 feet, you can probably forego the throttle reduction after takeoff and just retard the RPM, since you won't be able to get MP above about 25" or so at full throttle.
After you've leveled off, you can leave the prop at 2500 RPM, if you wish, adjusting power only with the throttle, but for additional economy and to make it a bit quieter in the cockpit, you can reduce the throttle to about 23" MP and then the prop to about 2300 RPM (or even a bit lower on both, if you wish). It would be rare to reduce RPM below about 2100 or so. If you need to climb again, other than small altitude changes, it would be best to increase RPM back to 2500, then add whatever throttle you need to maintain a reasonable rate of climb.
When descending, you may leave the RPM at your cruise setting, if you wish, until reaching somewhere near pattern altitude, or even until you are established in the traffic pattern. During this descent, you'll want to periodically check the manifold pressure to be sure that it doesn't increase appreciably above the cruise setting (you're descending into more dense air, so MP will tend to increase as you descend).
On the downwind leg, or wherever you're doing your pre-landing checks, you'll want to go back to the max RPM (lever full forward) setting, in case you need to do a go-around, or otherwise need high power, making all other power changes with the throttle. You'll want to leave the prop at max throughout the landing and taxi to parking, and not change it (other than a runup) until you are again ready for takeoff.
b) The same as in a) -- leave it around 2500 RPM until you level off. Obviously you'll need turbocharging to reach 20,000 feet, so you'll want to watch your manifold pressure carefully during climb. In this scenario, you'll also need to carefully watch engine temperatures, since turbochargers generate a lot of heat.
