denis parkinson Posted January 10, 2015 Author Share Posted January 10, 2015 I have finally got all the electrics installed after my forced Xmas break, and I have also got myself a watt meter. With a fully charged up battery (2200 3s lipo) running on a 10x6 electric prop, its showing up initially at full throttle as 320 watts at 24 amps..The wattage does start to drop slowly almost straight away, and I'm assuming that's normal. All up weight of the completely finished plane is a shade over 2 1/2 pounds, so I have lost around half a pound for the weight quoted on the plans. Looking back through the previous comments, it looks way over powered at 128 watts per pound, but obviously it doesn't have to be run anywhere near full throttle.. Just looking for your thoughts regarding wattage etc, before I get a calm enough day to maiden it. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted January 10, 2015 Share Posted January 10, 2015 Posted by denis parkinson on 10/01/2015 16:01:46: I have finally got all the electrics installed after my forced Xmas break, and I have also got myself a watt meter. With a fully charged up battery (2200 3s lipo) running on a 10x6 electric prop, its showing up initially at full throttle as 320 watts at 24 amps..The wattage does start to drop slowly almost straight away, and I'm assuming that's normal. All up weight of the completely finished plane is a shade over 2 1/2 pounds, so I have lost around half a pound for the weight quoted on the plans. Looking back through the previous comments, it looks way over powered at 128 watts per pound, but obviously it doesn't have to be run anywhere near full throttle.. Just looking for your thoughts regarding wattage etc, before I get a calm enough day to maiden it. If you downsize the prop (either diameter or pitch) then the current and hence wattage will drop, might well bring you back down to a more appropriate power level and prolong your flight times too Quote Link to comment Share on other sites More sharing options...
denis parkinson Posted January 10, 2015 Author Share Posted January 10, 2015 Cheers Dave, I'm used to IC power and all this electric wizzardry is totally alien to me. I have a 8x6 electric prop here but not sure if that would be too small..I'll order a 9 inch prop and see what the readings are with that. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted January 10, 2015 Share Posted January 10, 2015 Posted by denis parkinson on 10/01/2015 16:43:36: Cheers Dave, I'm used to IC power and all this electric wizzardry is totally alien to me. I have a 8x6 electric prop here but not sure if that would be too small..I'll order a 9 inch prop and see what the readings are with that. Chuck the 8x6 on and see what wattage you pull on that... can't hurt. I don't expect it will be enough but at least it will give you a clue what you will get on a 9" Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted January 10, 2015 Share Posted January 10, 2015 on a nice slow flyer like that a 10 x 5 might be a good fit, what motor did you end up with Dennis (for some reason the ebay links in your earlier post don't work), I'll run it through Ecalc and give you some idea of what to expect from different props. And yes wattage does drop off as the Lipo discharges, this is because there is less volts available and volts determines the motor max speed so as the volts drop off there is a reduction in speed and hence current and watts. Quote Link to comment Share on other sites More sharing options...
denis parkinson Posted January 10, 2015 Author Share Posted January 10, 2015 Frank, the motor I got was this one http://www.giantshark.co.uk/product/167837/e-power-bl2815-brushless-outrunner-motor-920kv With the weather as it is at the moment, all I can do is experiment..Oh and build Edited By denis parkinson on 10/01/2015 17:10:14 Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted January 10, 2015 Share Posted January 10, 2015 Denis, here you go 10 x 6 100% charged battery 22A, 9,200 rpm, 48ozs thrust 10 x 6 50% charged battery 20A, 8700 rpm, 43 ozs 10 x 5 50% charged battery 17A, 8,850 rpm, 37 ozs 9 x 6 50% charged battery 15A, 8,890 rpm, 33 ozs 8 x 6 50% charged battery 11A, 9,270 rpm, 25 ozs looks like you will be able to prop hang on a 10 x 6 Quote Link to comment Share on other sites More sharing options...
denis parkinson Posted January 10, 2015 Author Share Posted January 10, 2015 Cheers Frank and that's what I thought when I first tried the motor on full throttle. I couldn't believe how much power you can get from a small electric motor.. I'll give the 8x6 prop a go tomorrow and see how it pans out. I do have an old chunky 9x6 prop here, but I suppose it will be okay to use that just to check the power useage as long as its only for a few seconds.. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 10, 2015 Share Posted January 10, 2015 denis Whilst the Watts is useful to ensure you do not risk the electrics it is not the whole story. The prop pitch/diameter ratio does have an effect. Taking into account the type plane I would be tempted to go for the 10x5. By keeping the diameter but with a finer pitch you still get good static thrust, which is plenty, but the prop will 'off load' more in the air and will in effect limit the planes maximum speed or to put it another way you wont be using lots of power at full power trying to get a bit more speed on what is a fairly dragger airframe.. On the other hand get to near the stall and you will still have plenty of oomph! on tap without straining the electrics. I assume you are using e props. Quote Link to comment Share on other sites More sharing options...
denis parkinson Posted January 11, 2015 Author Share Posted January 11, 2015 Thank you Simon, and I have just put in an order for a 10x5 prop. I have a few builds lined up for the next few months, as well as converting some of my current models from IC to electric, so the extra props won't go amiss. Yes, I am using e props Quote Link to comment Share on other sites More sharing options...
robert Jones 14 Posted January 11, 2015 Share Posted January 11, 2015 Hi Denis, I am also new to electrics. I got lost in the discussions about current draw, MaHs,ohms, etc., so this is what I did: I looked at an electric plane similar to the one I was proposing, and chose the prop size, motor size,ESC, and battery that they recommended. Didn't necessarily get the exact same, but similar. One thing to be wary of is spinner diameter. Also it seems better to have a slightly over-amped ESC if in doubt. I have also found that 1300, 1800, and 2200 3S batts are interchangeable in my plane with a 30amp ESC. Not very scientific, but works for me. Quote Link to comment Share on other sites More sharing options...
denis parkinson Posted January 11, 2015 Author Share Posted January 11, 2015 Thanks Robert.. Up until now, all I have ever built is planes from kits using IC engines, but now I'm into scratch builds from plans that were designed well before the boom in electrics. I have a couple of large builds lined up, so I wanted to build something cheap and cheerful first, to gain some knowledge of electrics and how they work. The two planes I have lined up are a 60" Fokker DR1 and a 80" Tiger Moth, and I want to power them both by electric..The DB Sport and Scale website, does give details on what is needed to convert almost identical planes over to electric, so that will be my starting point for those 2 particular planes. The costs for the electrics however, are almost on a par with buying a good 4 stroke engine.. Quote Link to comment Share on other sites More sharing options...
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