Timothy Ward Posted May 18, 2020 Share Posted May 18, 2020 Hi, I am a complete beginner in the field of prop selection so please bare with me. I have managed to obtain a T-motor F20 II motor and a 4.7x4" 2-blade propeller for free, and was wondering if they would be a workable fit together. I am planning on scratch building a very small park flyer type aircraft, and I am not planning (and don't have the flying confidence) to go extremely fast. Obviously this motor is designed for twitchy fast FPV usage; I am planning on setting a throttle curve that won't let it exceed about 40%. The motor manufacturer recommends a 3x4 Tri blade prop, but obviously that's for FPV drone usage. Would the longer 4.7x4 prop, with only 2 blades, be workable? They are compatible in terms of fitting size etc. Thanks for any help, I can clarify anything if needed. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted May 19, 2020 Share Posted May 19, 2020 Just ran the motor through Ecalc something like a 6 x 3 2 blade prop on a 2s lipo maybe a better option, at WOT this gives 9amps, 290g thrust and 37mph pitch speed at 12,900 rpm. A 4.7 x 4 gives 6.5amps, 250g, 57mph at 15,000 rpm at WOT at 40% throttle thrust will be under 70g A lower KV motor would be a better choice turning a larger prop at lower rpm. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted May 19, 2020 Share Posted May 19, 2020 Franks figures are spot on Timothy, so let me support that I have 2 18" span homebuilds, weighing just over 100 grams Flying 2S 300mah lipo, On 6 x 3 prop on both, with 9gram and 15 gram motors respectively The 1st model esc 6A is the best throttle response, rarely needing full throttle, the gentler flyer The 2nd model, upgraded to 10A esc is more aerobatic, but a tad overpowered Quote Link to comment Share on other sites More sharing options...
Dickw Posted May 19, 2020 Share Posted May 19, 2020 As the others have said, a lower kv motor and larger prop would be more sensible for a park flyer. However, your combination could be made to work with care. I use a similar setup - the 20" span model in the attached photo has a 3200kv 9gm motor with a 4x4 prop and uses a 2s 300 mAh Lipo (model weighs 89gms). Most of the flight is on half throttle, including launching, and full throttle is only for continuous verticals. It is fast and somewhat "lively" and I am not sure I would reccomend the combination to anyone other than an experienced flyer. Dick Quote Link to comment Share on other sites More sharing options...
Timothy Ward Posted May 19, 2020 Author Share Posted May 19, 2020 Posted by Dickw on 19/05/2020 12:23:40: As the others have said, a lower kv motor and larger prop would be more sensible for a park flyer. However, your combination could be made to work with care. I use a similar setup - the 20" span model in the attached photo has a 3200kv 9gm motor with a 4x4 prop and uses a 2s 300 mAh Lipo (model weighs 89gms). Most of the flight is on half throttle, including launching, and full throttle is only for continuous verticals. It is fast and somewhat "lively" and I am not sure I would reccomend the combination to anyone other than an experienced flyer. Dick Thanks for the reply. I thought as much, I'm probably going to give it a go with the least throttle I can manage, but if it becomes unworkable then I'll splash out on some more parts. Quote Link to comment Share on other sites More sharing options...
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