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Thread: Choosing rotor diameter

  1. #1

    Choosing rotor diameter

    Being new to rotorcraft, I have a few questions. How do you determine the right diameter rotor to use? Am I right in assuming that the larger the rotor on a given gyro, the slower the rotor would turn in flight, and the smaller the rotor, the faster it would have to turn in the same circumstance? Would the smaller rotor require more forward speed, or just a greater angle of attack? Which would cause more drag? Would the faster turning rotor significantly increase the speed at which the retreating blade would stall? Is there a rotor rpm which is considered too fast? Too slow? I live at 4200 ft elevation, so what impact would that have on rotor choice? Thanks for any light you all can shed on my questions.

  2. #2
    Jay
    A word of caution, I am not an expert, but have learned something from many hours with these forums and many websites. When you buy your rotor all your questions can be answered if you've picked a quality manufacturer like Dragon Wings or Skywheels, and there are others of course. Look at PRA's manufacturers list. My understanding is that about 300 rpm is the average rotor speed, and a smaller rotor will turn faster with a given load. Speed will change during flight as well. Skywheels.com/selection.html shows some great info.They show, for example, that a 28 foot rotor will support from 800 to 1,000lbs. The formula for rotor disc loading is aircraft weight divided by Pi-R-squared (the formula for area of a circle). Apparently the desirable numbers are from 1.2 to 1.8 lbs/square foot of disc area. I have read that Chuck Beatty, one of the foremost experts in the business, recommends an angle of attack of 5 degrees. At 4200 ft the air is thinner so that will certainly make a difference. Plane weight, rotor diameter, blade geometry, angle of attack, speed, drag, air density, and power are all inter-related, so it gets pretty complicated, but there are tried and true ways to get it done. I know Ernie Boyette flies every set of Dragon Wings rotors before he ships them so you'll be happy. Others may too. Good Luck.
    Jim

  3. #3
    Jim
    Thanks for the info. I am a long way from being ready to buy a gyro, but there is so much to learn. Replies like yours sure help with the learning process!

  4. #4
    PRA Secretary JOHN ROUNTREE 41449's Avatar
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    Hi Jay and James that was a great post.

    Jay most of the manufactures of gyroplane have selected the rotorblades that they fell are best for their rides so most go with the ones they put on the rides.
    However some owners just like to use others blades then they buy those.
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