Esch
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- Feb 19, 2012
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Reading this forum I've learned a lot more about fixed pitch props than I knew before (especially following some of the links). I don't have much experience flying FP airplanes, and all my acro has been with CS props, so bear with me.
First off, a question about pitch. I know this number is supposed to represent how far the prop would "screw" through the air with no slippage. Given a pitch of 61 inches and 2700 rpm, that comes out to 156 mph. Does this represent a theoretical upper speed limit for level flight? And if so, how is the prop producing enough thrust to overcome drag if there's no slippage? Does the camber of the prop alone produce this? I guess what I'm asking is whether pitch is measured for a "zero-lift AOA" for the prop blade, or just some convenient geometric reference where the prop is still producing lift at that angle.
The second question is about overspeed. Say you're at redline rpm in level flight at 8,000 ft or so and you push the nose over. Obviously you're going to overspeed the engine/prop as gravity adds to your airspeed. I imagine if you retard the throttle towards idle, your speed won't increase quite as rapidly since the slipstream has to fight against piston compression and frictional losses to windmill the prop. With a fixed pitch prop, is this hard on the engine? I know you can use a CS prop as a kind of air brake, but wasn't sure how this differs with a FP regarding the stress to the engine.
Finally a question about preferences. For an aircraft that spends most of its time doing aerobatics and less time on cross countries or sight seeing, do you lean towards fine or coarse pitch, and do you prefer 2 or 3 blades (let's assume an O-360 is the engine in question)?
First off, a question about pitch. I know this number is supposed to represent how far the prop would "screw" through the air with no slippage. Given a pitch of 61 inches and 2700 rpm, that comes out to 156 mph. Does this represent a theoretical upper speed limit for level flight? And if so, how is the prop producing enough thrust to overcome drag if there's no slippage? Does the camber of the prop alone produce this? I guess what I'm asking is whether pitch is measured for a "zero-lift AOA" for the prop blade, or just some convenient geometric reference where the prop is still producing lift at that angle.
The second question is about overspeed. Say you're at redline rpm in level flight at 8,000 ft or so and you push the nose over. Obviously you're going to overspeed the engine/prop as gravity adds to your airspeed. I imagine if you retard the throttle towards idle, your speed won't increase quite as rapidly since the slipstream has to fight against piston compression and frictional losses to windmill the prop. With a fixed pitch prop, is this hard on the engine? I know you can use a CS prop as a kind of air brake, but wasn't sure how this differs with a FP regarding the stress to the engine.
Finally a question about preferences. For an aircraft that spends most of its time doing aerobatics and less time on cross countries or sight seeing, do you lean towards fine or coarse pitch, and do you prefer 2 or 3 blades (let's assume an O-360 is the engine in question)?
