Feb 27, 2004, 02:47 PM Jody Bradshaw Salisbury, North Carolina, United States Joined Feb 2004 1,061 Posts Question What is the difference in the GW/EPS-300C (2/1/A/B/C/D)? GWS lists GW/EPS-300C (2/1/A/B/C/D). All these different models. What's the difference?2/1/A/B/C/D
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 Feb 27, 2004, 03:30 PM Motor Maniac Orange County, CA Joined Feb 2002 2,875 Posts These are the different gear ratios. Why they use both letters and numbers to designate the gear ratios is beyond me. Note that the ratios for the EPS-400 are different from the EPS-300, as are the IPS (DX). With enough time you may end up memorizing the more common ones (C=5.33, D=6.6, B=4.4 or so, A=3.75). The higher the gear ratio the larger the prop it can spin, which tends to be more efficient than spinning a smaller prop faster.
 Feb 27, 2004, 05:06 PM Jody Bradshaw Salisbury, North Carolina, United States Joined Feb 2004 1,061 Posts Prop size. When figuring prop size is the 1st # the length and the 2nd # the aggresivness of the pitch on the blade? Give me an example, Of say a 12x4. Last edited by JMBRAD; Feb 27, 2004 at 05:08 PM.
 Feb 27, 2004, 06:32 PM Registered User Chattanooga, Tennessee, United States Joined May 2003 27,210 Posts The best analogy for 'pitch' is to imagine your 12x4 prop is (a bit like a corkscrew) rotating in a mass of Jello. For each complete revolution of the prop it will move forward 4". A 6" prop would move 6" and so on. "Pitch speed" is important in flying planes at a suitable airspeed and can be calculated from an equation, simplified as: pitch speed (mph) = rpm x pitch (inches)/1052. Cheers, Phil
 Feb 27, 2004, 06:43 PM Jody Bradshaw Salisbury, North Carolina, United States Joined Feb 2004 1,061 Posts Thanks Phil. Are there any free programs similar to Motocalc that calculate flight times given a particular motor, prop, and battery?
 Feb 28, 2004, 08:39 AM Registered User Chattanooga, Tennessee, United States Joined May 2003 27,210 Posts

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