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randy echtinaw wrote:
Gentlemen,
I am building an acro rated single seat biplane that the designer has limited the max. engine size to IO-360. I am surmising that this engine limitation is based on weight and airframe maximum speed. I have decided to use rotary power and am slowly developing a plan as to what I will use. I am looking for a little more help going "vertical." The rotary weight (less) will be a bonus. I am not an engineer and am not even related to one so my question:
Can I go to a P-port 2 rotor in the 230-240 hp range if I do not exceed the max. airframe speed.
Thank you,
Randy
It's like real estate, except 'prop diameter, prop diameter, prop diameter'. I'm no aero engineer either but I do hear them talk about stuff like 'mass flow' increases with increases in prop diameter. Vance Jaqua, who contributed to the design of the KIS kit a/c, published a chart several years ago showing prop efficiency for various diameters at various speeds & it's pretty amazing what extra diameter can do, especially if you're stuck with fixed pitch.
I don't know if Tracy or Ed flew their 68" props on the 2.85-1 gearboxes but if they did they could give you an idea on how much difference extra diameter makes on the same power. I believe that both are now running 74"-76" diameter with radical increases in climb performance.
Relatively small increases in prop diameter result in large increases in climb ability. Consider that 160 hp in a 2seat helicopter will lift the a/c & 2 people straight up.
Talk Tracy into making you a gearbox with the 3-1 ratio or talk to Ken Welter http://homepage.mac.com/rotarycoot/ about one of his belt drive reductions & build long gear legs for prop clearance.
Charlie
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