A question on aircraft propellers?
3 blades would provide more thrust, if the application is a high power one. Your requirement of same RPM and diameter would impose a wider chord for single and twin blade solutions to get the proper area (or solidity as this is called in the case of propeller), and that means the blade would be less slender. But, within limit, a slender (high aspect ratio) is better as it provides more lift (equal to thrust in the case of a propeller) for the drag (which has to be over come by the engine power). That said, for a limited power application, a 3 bladed propeller may be inefficient and end up producing less propulsive force than a 2 bladed propeller. It is a matter of balance.
Question about propeller aircraft?
Most propeller aircraft are expected to have their propeller spin at nearly the same RPM, irrespective of power; a fairly narrow band that would range from 900 to 1200 RPM, and that is because any faster and the tips will spin at supersonic speed, leading to a decrease in efficiency. So, to go from a low power to a high power setting, the power of the engine is adjusted, which produces more torque, with the propeller moving to a higher pitch. So that is why: the pitch of the propeller is how the power is modulated, as opposed to having the RPM change.
Prop produces most power when aircraft is stationary?
I see where you are going with the Helo comparison. The fault in your logic is that the Helo doesn’t so much rely on displacing air downwards to fly as a fixed wing displaces air aft. The rotary wings (as Igor Sikorsky called them, a more accurate term than rotor blades) work more like the wings of your light a/c than the propeller. They generate lift by moving air over them as they rotate. This is why translational lift is greater. The speed of the air over the rotary wings increases with increased forward velocity. Therefore more lift is generated. Notice we call it lift not thrust.
Contra-rotating propellers, turbulence?
First, since contra rotating propellers have been used, not sure if I can say widely but used... I'm not sure if I can ask this question but I would like to know. Doesn't contra-rotating propellers introduce a great probability of turbulence occurring if not guarantee because the blades "smash" into each other as they rotate in opposite directions on the same shaft? And isn't air compressed between the blades? Or is it simply sucked through? I am concerned about the abrupt change in direction I would think of the air following the curvature of the blades... Can someone shed some light for me?
Why are the leading edges of an airplane propeller curved?
One of the things that made flight possible was the realization that an aircraft propeller is essentially a rotating wing. As it rotates, it uses the same principles as a wing to generate force with the air. It's exactly like lift, but since it's directed backwards to drive the plane, we call it thrust. The Wright Brothers were the first to implement that curve to give a propeller variating incidence along the blade's length. This is important because the tip of the propeller is moving faster than the inner portion. This lets the propeller generate thrust along it's entire length. If the propeller were the same angle along it's entire length, it would be stalled along part of it and would be generating much less thrust. Basically, the curve is there to ensure that every inch of the propeller blade is most efficient at the propeller's intended speed. It's interesing to note that the Wrights' propeller was so carefully engineered that it operated at between 70 and 75 percent efficiency. The most efficient modern props operate at 85% efficiency. In 100 years, we've only improved props by 10%. The propeller as a wing was one of the innovations that made flight possible. In fact, the Wright Flyer would not have flown at all with any previous propeller designs. The prop's chord and curvature of leading edge, trailing edge, etc all vary between different propeller designs for best efficiency at designed speeds. A great example of this is a highly swept prop as mentioned in some of these answers. Getting any more specific than that would be pretty hard without seeing the specific prop the question refers to.
An airplane engine starts from rest; and 2 seconds later, it is rotating with an angular speed of 300 rev/min.?
ω = 300rev/min*2π rad/rev*1min/60s = 31.4 rad/s Now ω = αt so α = ω/t = 31.4 rad/s/2.0s = 15.7 rad/s^2 so θ = 1/2*α*t^2 = 1/2*15.7*2^2 = 31.4 rad which = 31.4 rad*1 rev/2 π rad = 5.0 rev
What is free shaft turbine in aircraft propulsion?
@Bradley a "free-shaft turbine" is a component of the engine, the engine usually being a turbo-shaft or turbo-prop type engine, the turbine component running free of the compressor drive-shaft, as opposed to a "fixed turbine," being driven solely by the combustion chamber exhaust gases, and responsible for converting that gas energy into mechanical energy. sorry, but it really vexes me when people refer to the whole engine as being a turbine, it is not, any more than a whole computer being "the processor."