![]() ![]() ![]() Each blade has a leading edge (impacts the air first) and a trailing edge. The root sections of each propeller blade come together at the propeller hub. A blade has a root and a tip, where the tip is located the outer-most region of the blade. This should come as no surprise as a propeller blade is essentially a twisted, rotating wing. The terminology used to describe the various parts of a propeller blade are very similar to that of a wing. Momentum is the product of mass and velocity and you can think of the thrust generated as the reaction to the acceleration of a column of air with a diameter equal to that of the propeller.įigure 1: Momentum transfer from propeller to air is responsible for thrust generation Propeller ForcesĪ propeller produces thrust through a momentum transfer from the propeller to the air by the rotation of the propeller blades. If you are interested in a more technical discussion on how to size an engine and propeller then you are encouraged to read this post, where a propeller and engine combination is specified for a conceptual light sport aircraft. ![]() ![]() At worst, this could produce an inherently dangerous aircraft that may struggle to get airborne and could be prone to a complete engine or propeller inflight failure. A poorly chosen propeller-engine combination will at best result in an aircraft that does not meet the performance requirements outlined by the aircraft designer. Engine and Propeller CombinationĪ propeller does not operate in isolation but rather must be designed to work in unison with the aircraft’s engine. We will discuss the forces generated by, and acting on a propeller, the variables associated with propeller design, the types of propellers in use, and how the propeller should be operated and managed in flight. This post will focus on the propeller and should provide a good overview of all aspects associated with light aircraft propellers. This rotational motion is then be converted into a forward thrusting force by the propeller which powers the aircraft forward and is required to balance the drag produced by moving through the atmosphere. I am going to post these symptoms in a different subject area.An internal combustion engine is designed to convert the reciprocating motion of the pistons into rotational motion at the crankshaft. Then it began to cut out and surge at anything above 4600, then 4400 then 4000. At first all was great, throttle response was good, no surging, could cruise at 4600 - 4800rpm for minutes at a time. This prop is now my baseline.Īnother problem showed up though after a while. Not too bad for aluminum but I think I can do better with props that are put there. Running the numbers in a prop calculator it seems I am getting about 18% slip using 4800 rpm at 48mph. Speed by the speedometer in the boat (I think someone besides me ended up with my handheld GPS, grrr) was much higher this time, was approaching 50 bouncing a little from 48 or so. Boat still would not porpoise as I would expect, but that's ok, accepting this as "by design" from Bryant. I could only hit the rev beep when I trimmed up just a tad too much and the revs climbed with no speed increase, obvious it was close to blowing out. I had a good hour's run in, playing with trim at top rpm's quite a bit at first. Prop has good bite at holeshot, not stellar but as expected for the basic design. When I was backing out I could tell a difference immediately, the boat moved much "sooner" with much less throttle. I was able to get out on the lake and run the new Michigan Wheel Vortex 21p aluminum prop. ![]()
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