ORIGINAL: Sport_Pilot
--- you cannot accelerate to a higher speed without thurst. Thrust is Delta V * Area (of blades). Leaving out a few details of course.
Getting back to propellers -- the number of blades is irrelevant to discharge velocity,& hence speed --
wrong, you cannot get the speed with the same area without increacing power. You have to decrease the area, once you decrease the area, then the extra blades help increase the thust.
In the case of your Bearcat example, it is up against theboth clearance & RPM limitations so it is forced to use a 5-blade prop. If it had adequate ground clearance to swing a larger diameter 4-blade prop of the same pitch as the smaller diameter 5-blade that you are so entranced with -- it would generate MORE thrust than with the 5-blade & would certainly accelerate faster & likely be able to go slightly faster.
I never said anything about 5 bladed props, in fact I think the Rare Bear has a 4 blade prop. It has plenty of excess prop clearance.
However, the blades could possibly fail through excessive centrifugal loads.
Centrifigal loads, you are really pulling at straws. Think sonic.
The 2-blade fixed-pitch prop on the Supermarine S-6B float plane was quite sufficient to transmit well over 2,000 HP and push it to 407 mph. That is a FLOAT plane with floats, braces, struts & wires hanging out in the breeze going more than 400 mph. If they could have gone faster with a multi-blade prop it would have been fitted instantly -- except that the multi would have been slower.
I think the supermarine was a bit before these things were worked out, I don't know how much of this they knew back then, but I don't recall 400 MPH speeds from that era, not saying you are wrong. Just that 300+ MPH would seem more likely.
When I think about it the Reno racers may not be the best example, if I recall correctly multiblade props are at a speed advantage at altitude, or more so. Both the Reno racers and the Schnider cup was at low altitude.
You cannot accelerate without delta-V, regardless of thrust. You can inrease delta-V without increasing thrust -- which is what you do with a smaller diameter higher-pitch prop. The thrust is often actually less in those cases
Actually you are wrong --- you can increase speed with the same area by increasing pitch (delta-V) -- up to the limit imposed by the required power. Try it yourself -- put a flat pitch prop on your model & measure the speed -- change to a steeper pitch prop with the same blade area -- you will go faster, despite a possible decrease in power.
Tip Mach number is important for prop efficiency, but tips can actually go supersonic in many cases without failure, whereas centrifugal loads impose absolute mechanical limits on prop RPM.
The Supermarine S6B set a world speed record of 407 MPH -- with a 2-blade fixed-pitch propeller.
Speed is always dependent upon power, regardless of altitude. The ability to deliver power at high altitude is indeed dependent on propeller blade area. Since propeller RPM can't be increased due to tip speed & mechanical limits, & diameter has the same limitations, as well as practical limits on size, therefore more blades are the answer -- but that is not different from the low-level case.