Fred said: "If a three bladed prop is so much better than two ..."
Here is my point: EVERY turbo prop engine I have ever seen is a 4 bladed prop. AND they are constant speed with beta mode (most of them allowing reverse thrust). So if 2 blades was THAT much better, than they would not go to the expense to make a 4 bladed hub with adjustment. I don't know what a hub for a Pratt & Whitney PT6 costs, but the replacements for an IO 540 when I was teaching exceeded $20,000 a piece, and that was for a 2 bladed. Closer to home, almost every Ultralight I have seen run 3 or 4, and some run 5 bladed props, running similar engines to KR's, and with similar horsepower to ours. Sorry Peter, but the P51 was running a version of the Rolls Royce Merlin Engine (not the stated Radial, but an inline 12 cylinder) which developed close to 1500 hp, and no 2 blade at the time could put that kind of thrust to the air. I bought a text written by an aeronautical engineer, called How to Build Your Own Propeller, I believe that I got it from AS&S (ok no flaming the vendor), and he is the one that stated that a 3 bladed prop would perform some 17% better, that a 4 bladed prop nearly 20% better, etc... This is qualified of course with some critical comparison factors being the same. No matter what you have been told by the "local" guy, my research is showing that the crowd pleasing 2 blade prop is used most by the lower end hp and torque guys almost completely due to cost and weight benefits. Most of you direct drive guys cannot run the average 4 blade due to weight, and might be too close to run a 3 blade. Also, the additional thrust developed by the additional blades may cause some lower torque engines to bog down, and actually lose thrust. Randy, common sense says that additional blades make more thrust, or no one would install them. I can illustrate literally hundreds of planes that have benefited from multi-bladed props, slow and fast. Also be aware that many sources of information about props relates to certified aircraft that cannot even change their original prop without an STC. C152, and C172 have 2 blades due to price and use. For the cost they best fit the bill. Most VW guys have to run a wooden prop due to cranks cracking otherwise. I suspect that may be the long term consensus for the Corvair as well. I cannot argue that for the money, nothing beats a well made 2 bladed wooden prop, if it matches the engine. Yes a multi-blade will always make more drag than a 2 blade, no argument. Larry said, and I don't disagree that under ideal matching, a 2 blade should out perform a 3 blade in cruise, especially under 200 knots with lower hp engines (say under 150 hp). But, I have seen the actual results of the same plane with the same engine, swap a 3 blade where a 2 blade was previously, and it out climbed said 2 blade with no other modifications. The author of my book said so also, and I have seen the fpm results. It was not done just to look good. Cessna comes standard on the C-182 with a 3 bladed Hartzell constant speed prop. There is no way they would incur the extra cost unless there was a solid benefit. Mark L. said it a little while ago; encourage anybody doing solid true experimenting. They are how we got this far to begin with. The Light Sport Airplane, and Ultralight guys are leaving us in the dust with updates. There are guys running engines on Trikes that make more torque than the VW or Corvair, and that is what makes thrust not hp, and are continuing to make hundreds of hours, with fuel injection, computer controls, re-drives, and multi-bladed props. I am not knocking anybody here. I am just saying, if there are good solid ideas that other flyers are proving, maybe we should give a hard look to how they could benefit us as well.... Colin Rainey N96TA brokerpi...@bellsouth.net
