Cox Medallion .051 NFFS Special
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I've been asked about propellors for the Lucky Lindy model many times. Recently flyer and friend Bob Sowder asked them, and below is how I answered. Of course there are many other engines and props that will work well for the Lucky Lindy. What's here summarizes my own experiences over the years. TheAeroSmith Bob: As far as my own experience, the prop that has flown the FAI sized LL the very best has been an APC C-2 8X4. There areseveral different props carrying the 'C-2' tag. I've asked them about that, and only gotten an answer that's incorrect; was told that the C-2 (or other) is for the mold for that prop. I have at the very least, two different APC 8X4's that say they are C-2's. Obviously, they didn't come out of the same mold. The very earliest of the 8X4 APC (C-1) flew the model very well. A later version, a C-2, looks similar, but has a beefier hub and has less Scimitar shape. That one I've used most. That's also the prop that I blew apart at about 9 seconds out, which made the model look and sound as though it had been hit by a rocket. I now have epoxy/glass/carbon props of this version. I thinned the hub area some, and did a very thorough job matching the blades for thickness, width, balance, pitch, and tracking. This one won't come apart without some serious provocation. If there's an interest, I may make up a dozen or so to sell. I think they will have to sell for about $20 each + mail to be worth spending the time on the project. That's a lot for a prop, but if the model doesn't explode, it's really cheap. There is a newer 'C-2' that is much more conventional looking...pretty straight blades. I think it may be the best of the bunch, but I have to make a 'glass one before I'll fly it to see how it performs. As soon as I can get some altimiter testing done with the new prop, I'll let you know the results. Bob |
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| Several props used on the FAI Lucky Lindy. | ||
 Difference between APC props seen in the side view. |
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 Some information on prop tip speed and how to calculate it might be of interest to some. This data courtesy of P.Ponk Aviation (www.pponk.com). To determine propeller tip speed: Prop Diameter X Pi / 12 X RPM X 60 / 5280 = Tip Speed in MPH
Example: 86" prop turning at 2800 RPM To determine the speed of sound: Example: 59 degree F. day To determine propeller tip mach speed: |
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