Andy C Posted April 5, 2021 Share Posted April 5, 2021 (edited) So I am part way through building my DSC Fly Baby and need some help in selecting power source and battery please. Its quite an old design and information I can find on its plan, build notes box and also the web is that the following were suggested power sources. .049 to .074 engine 035 cobalt or 05/075 ferrite electric motor such as the DSC 075 Hyperthrust motor .05 to .075 electric motor with 6 or 7 cells battery Wing area is shown as 275 sq inches I have also found on outerzone: reference to a more recent build using Firepower 450 Sport motor (1100kv) and 1800mAh battery on a 9x4.5 prop but it has not follow up info on whether it actually flew. And a link to an old RCME article written by the designer Ted Davey which gives more details, weight ready to fly as 34ozs and a wing loading of 16.8oz per square foot and he uses an 8x4 prop. Many Thanks Edited April 5, 2021 by Andy C Quote Link to comment Share on other sites More sharing options...
Dad_flyer Posted April 5, 2021 Share Posted April 5, 2021 I don't know the model, but in one of my models the 049 replacement is a 1900kv Overlander 2826 on 2s with an 8x4. Gives about 70W and a 1000 to 1300 mAh is a long flight. You want something more than that. The same motor on a 9" prop would take the motor to its limit at 100W ish. Quote Link to comment Share on other sites More sharing options...
Jonathan M Posted April 5, 2021 Share Posted April 5, 2021 You could always ask George at 4-Max for his suggestion - he really knows his beans... and his volts! Quote Link to comment Share on other sites More sharing options...
PatMc Posted April 5, 2021 Share Posted April 5, 2021 Andy, I converted my "Henry" motor glider design from a Cox 049 to a 400 can brushed motor running on 7 cells nicads driving a 5x3 folder or 6x4 fixed prop. Later that was upgraded to a 57 gm 1022kv BL motor on 3s 2200 (1st generation circa 12c) lipo battery that actually weighed the same as the nicads. This combo drove a 9x5 folder at 9000rpm pulling 11.3A for 115W & transformed the model performance. This is Henry with the brushed motor. The BL motor mentioned is no longer available so I was going to suggest a larger more powerful 76g Keda 2217/16 1050kv which I use in my Amigo 2 but that also seems out of production now. However this DYS motor has similar weight & kv so should give similar performance. In the Amigo the Keda turns a 9x5 folder at 10000rpm, 14A for 165W using a 3s lipo. Battery size in the Amigo is from 700 to 1400 mAH (depending on the wind speed) but I only power on for about 25 -30 secs per launch. I suggest that a 3s 1300 - 1500mAH might be adequate capacity for your Fly Baby. Quote Link to comment Share on other sites More sharing options...
Andy C Posted April 8, 2021 Author Share Posted April 8, 2021 Thanks guys for the replies. Quote Link to comment Share on other sites More sharing options...
Andy C Posted April 9, 2021 Author Share Posted April 9, 2021 @PatMc - Out of interest, is there science behind your suggestions? What calculations are required to arrive at the power source being suitable please? Thanks Quote Link to comment Share on other sites More sharing options...
PatMc Posted April 11, 2021 Share Posted April 11, 2021 (edited) @Andy C - my rationale goes as follows : in the OP suggested power for the design included .049 to .074 engine. My Henry design initially flew quite well on an .049 & as mentioned the subsequent conversion to brushed electric /nicads gave similar performance using a 5x3 or 6x4 prop. Converting to a 57gm brushless with very low "C" rated lipos driving a 9x5 prop transformed the performance at the same time increasing the duration (over an hour per charge was normal but it is a motor glider). This BL/lipo combo using a 9" prop was now delivering power at a level similar to a pre schnurle .09 engine driving a 7" prop. The Keda motor using modern 3s lipos in the Amigo gives about a 40% increase in power using the same 9x5 prop, no doubt due to it's increased dimensions & weight. The DYS motor linked is similar in size, weight & Kv to the Keda therefore I would expect similar power output from it using the same prop & lipos. As for duration, I normally reckon for a typical sports model to use a battery capacity that would give, theoretically at least, about 5 - 6 minutes of full power. From experience I've found this actually allows a much longer flight time without depleting the battery overmuch. Edited April 11, 2021 by PatMc Quote Link to comment Share on other sites More sharing options...
Andy C Posted April 15, 2021 Author Share Posted April 15, 2021 Excellent, Thanks for the response. Quote Link to comment Share on other sites More sharing options...
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