geared drive + big prop or direct drive + small prop ? - RC Groups
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Dec 18, 2003, 05:41 AM
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geared drive + big prop or direct drive + small prop ?

I am totally new to the F5X stuff and one thing I have observed is that that F5D models always go with small props (e.g. 5X5) while big props ( e.g. 15X15 ) seems to be the de-facto standard for F5B ships. Is there any any reason for that ?
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Dec 18, 2003, 06:01 AM
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Peter Khor's Avatar
Speed vs. Rate of Climb.
Dec 18, 2003, 12:31 PM
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Thanks. Is it possible to elaborate a bit ?
Dec 18, 2003, 12:48 PM
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Peter Khor's Avatar
Sorry for the curt reply couple of hours ago

Look up the F5B rules, in short you only run the motors outside of the course, and for a very short time (there is a penalty for how much motor run you make), and in that time you want to get to altitude as fast as you can. For pylon racing F5D motor is on all the time over a level course and you want a combo that will give you duration and speed.
Dec 19, 2003, 01:04 AM
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Thanks, Peter. It makes sense to me now.
Dec 19, 2003, 10:17 AM
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96S14's Avatar
It's also a pitch speed thing. F5D is very fast, so they spin a small prop very, very quickly with a less pitch. By having this small prop though, thrust is generally down, but they are never climbing anyway.

In F5B, climb is the name of the game, so they spin a large, efficient prop much more slowly and get tons of thrust. They make up for the lack of revs at the prop (due to the gearbox reduction) by increasing the pitch of the prop.

Hope that helps a bit.

Dec 19, 2003, 10:46 AM
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It certainly doesn't help a bit but a lot! Thanks, Ryan.