HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 18, 2003, 04:41 AM
Registered User
Joined May 2002
239 Posts
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 ?
yclui is offline Find More Posts by yclui
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 18, 2003, 05:01 AM
Registered User
Peter Khor's Avatar
Mostly in Norman, OK
Joined May 2002
1,868 Posts
Speed vs. Rate of Climb.
Peter Khor is offline Find More Posts by Peter Khor
Reply With Quote
Old Dec 18, 2003, 11:31 AM
Registered User
Joined May 2002
239 Posts
Thanks. Is it possible to elaborate a bit ?
yclui is offline Find More Posts by yclui
Reply With Quote
Old Dec 18, 2003, 11:48 AM
Registered User
Peter Khor's Avatar
Mostly in Norman, OK
Joined May 2002
1,868 Posts
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.
Peter Khor is offline Find More Posts by Peter Khor
Reply With Quote
Old Dec 19, 2003, 12:04 AM
Registered User
Joined May 2002
239 Posts
Thanks, Peter. It makes sense to me now.
yclui is offline Find More Posts by yclui
Reply With Quote
Old Dec 19, 2003, 09:17 AM
Registered User
96S14's Avatar
Calgary, Alberta, Canada
Joined Oct 2002
739 Posts
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.

Ryan
96S14 is offline Find More Posts by 96S14
Reply With Quote
Old Dec 19, 2003, 09:46 AM
Registered User
Joined May 2002
239 Posts
It certainly doesn't help a bit but a lot! Thanks, Ryan.
yclui is offline Find More Posts by yclui
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
big prop, gear drive v. small prop, direct drive RD Blakeslee Power Systems 2 Jan 25, 2008 03:46 AM
When to use a geared or a direct drive prop? nanoflite Scratchbuilt Indoor and Micro Models 7 Sep 27, 2004 10:47 PM
Why small prop & direct drive on Zagi's? Solcat Foamies (Kits) 4 Apr 22, 2004 06:38 PM
Direct drive small prop vs. geared big prop? TEM Parkflyers 1 Sep 14, 2003 06:39 AM
Direct Drive 550 vs. Geared with Big Prop Greg Covey Electric Sailplanes 15 May 15, 2001 11:51 PM