hello everyone. I just recently bought a new electric plane that it will probably take me a while to get around to building. I am a new guy when it comes to electric and I don't know much about selecting the right componants to keep everything happy without blowing the whole thing up. I got a douglas dc6b mainliner civilan airliner from pats custom models. The model has a target weight of 26-28 ounces and has a 60" winspan. now I'm not sure what this means but the power system that pat used on his model was 4x GWS 4:1 IPS drives with 8-6 props on a 2 cell 2100mah lipo pack. The only other thing I know about his setup is that he used one esc for this plane. I'm not sure how that works but it sounds nice to save weight because its a stickbuilt plane. Now Pats plane flew pretty nicely, but it has been said that the system flies his plane nicely but there isn't really any power in reserve. I always like to have a little extra power in reserve to be able to get out of trouble is need be. I wanted to setup a motor system for this plane but don't know where to begine. I though about brushless but then read that you have to have an esc for each motor so 4 escs would add a lot of weight. and my other question is if using 4 escs how would you hook one battery to the full setup ? I don't have a wattmeter or anything like that so I would like to simply be pointed in the direction of going out and getting a battery esc and the for motors for this plane. One thing I almost forgot to menstion is that the plane must use 8 in props because the inner motors on each wing pannel do not have enough clearance to the fuselage for a 9 in prop. I would have gone to my local hobby shop to have him point me in the right direction but because the only hobby shop around this area and hes going out of buisness today being his last day open and I have work yet another day I cant do that. so all your help would be nice thanks. Also I was looking at different motors totally confused. I see speed 400 I see for an example 33/18/4100 thats that compared to the speed 400 ? again I'm a newbee to electric power but no newbee to airplanes or flying.

Hi Crazedman,

Just for future reference, carriage returns are free on rcuniverse so feel free to use a few next time

Okay - you have a few things to learn and figure out. Addressing some particular points in question:

1. Yes you need a separate ESC for each brushless motor, and yes they probably weight about 1/2 an ounce each.
2. Don't worry about the extra weight. A cheap brushless outrunner will, configured correctly, produce about 50-75% more thrust versus a speed 400 electric brushed motor. In short, much much more efficient which should, provided you really aren't pushing your wing loading, increase your power more than enough to compensate for the extra weight.

Choosing the right motor(s), prop, and battery for an application is a bit like choosing the right gear in a car. It might seem a bit complicated the first time you do it, but after a while you get a feel for it. Now - you've already told us you can't go bigger than an 8" prop - that's great - we can use that as a design input. You've also told use the plane weighs about 1.75 pounds - great - another design input.

For electric planes we use the concept of "watts per pound" to figure out how much power is needed to fly. It does depend on the type of model, but 120w/lb will fly just about anything (although it is a bit lame for an aerobat/3d/warbird it will fly on that power). So, applying that to your weight, we need 210watts. That's another design input.

So, we know:
- you need to spin no larger than an 8" prop
- you need 210watts total power
- you are going to use 4 engines (by the way, a multi-engine model is perhaps not a good way to start in electrics - having four motors just makes understanding what is going on that little bit harder).
- So , each motor needs to produce in the order of 60w
- Assume you want to stick with 2s to save the weight penalty over 3s.
- At 2s you need to get about 8A out of each motor (60W/7.4v, because watts=amps x volts, therefore amps = watts/volts).

So, a brushless outrunner around 1250kv (revs per volt) spinning an 8x4, or 8x6 should give you around 8A on a 2s. Good news - some cheap cheerful little 1250kv outrunners will be lighter than speed 400s easily helping to make up for the weight of the extra controllers. (this bit I figured out by going and looking at some manufacturers charts of motors and props they spin plus amp draw at that speed)

Make sure your main battery can handle providing amps at 240/7.4 = 32A (maybe a little more for a margin of safety).

Oh, and read these for next time perhaps:
http://www.rcuniverse.com/forum/m_7100376/tm.htm
http://www.wattflyer.com/forums/showthread.php?t=24238
http://www.oz********.com/2007/01/el...ic-flight.html
http://www.oz********.com/2007/09/gu...low-heads.html
http://www.oz********.com/2008/02/el...c-numbers.html

Cheers,
Oz.

Everything you want to know about electric flight
http://www.rcuniverse.com/forum/m_7100376/tm.htm

Read the article about choosing a power system.

thanks for the help this is partically helpful for me. I am starting to get some of an understanding of the whole electric world. I was reading a lot the last few days and I have read that first thread that you posted. I will continue to read more. i am pretty versed about batteries and well aware of the laws of lipo batteries although I have never had any need for one till now. question nomber 2 will I need to go out and buy myself a watt meter before I go fly the plane just to make sure everything is working good ? I also was wondering about the wiring of hooking one battery up to all 4 motors ? As far as a battery goes it seems like a battery of that capacity means that I will have to disable the escs built in escs and power the radio with its own battery because what I have read so far the esc will not be able to handle the amp output needed to the radio to power the 4 servos recquired to operate this airliner. And granted a quad engine would complicate the setup a little more to understand whats going on. this is not my only electric project as I also have a bare bones from modelair tech that requires a speed 400 motor. that airframe is 2" wide, is 16oz, has a 160 sg inch and 30" wingspan. Im thinking about using something like the electrifly ammo 12 30 3850 inrunner and the best battery I can get to fit in the small little airframe.

yes ed thank you for the thread I read your whole forum and probably will reread it all again. that is helpfull

Glad you found it useful.

ok applying a little of my new found info I have put together a power system for the bare bones I mentioned in post #4. a rehash the plane is a model airtech speed 400 plane. it has a 160 sq inch wing and a 30"wingspan, its 16 ounces and its has a 2" wide airframe. new tell me what you guys think of this power setup for the plane. I have chosen a 8 cell 9.6 v 650 Mah electrifly NiMh pack, a Great planes silver series 8A brushless esc 5v/1a bec, and a great planes Ammo 20-30-2650 in runner brushless motor. I didnt pick a prop yet but I was hoping I can use a 5x5 .


http://www3.towerhobbies.com/cgi-bin...2&I=LXGBN1&P=K

http://www3.towerhobbies.com/cgi-bin...2&I=LXKSY2&P=K

http://www3.towerhobbies.com/cgi-bin...2&I=LXLWW4&P=K

I've got a feeling an 8.4v batt driving a 2650kv might be a fraction hot on a 5x5 - maybe drawing around 11A or so - you would really need to measure it to be sure.