I'm the editor of the newsletter of a Milwaukee Area Radio Control club. Over the past year or so, I've put together a series of articles on medium powered electric models. These articles have been compiled to the attached 14 page PDF document.
The article covers the following items:
Four Stroke 70 Sized Electric Powered Models Chapter I ---------Definition Chapter II --------Field Charging Issues Chapter III -------Selection of Hanger 9 Showtime 50 Model Chapter IV -------Get Computer Software Help Chapter V --------Evolution from Geared Astro 40 to Hacker A50 Motors Chapter VI -------Results Chapter VII ------BEC (Battery Elimination Circuits) Issues Chapter VIII -----Power output vs Four Stroke 70 Glow Engines Chapter IX -------Electric Power Prop Unloading Chapter X --------A123 Cells Chapter XI -------Showtime 90 Design Chapter XII ------Electric Cost Issues Chapter XIII -----Battery Life Span Chapter XIV -----How to Kill a Lipo/A123 Pack Chapter XV ------Editors On Board Monitor Chapter XVI -----Charging Lipo/A123 Packs
This article may be of some benefit for those club members seeking to advance to medium sized electric models.
Excellent article, Dennis. I haven't tried A123 cells yet, but they are a possibilty for my giant scale project, though it will initially fly with 6S2P 5000 Zippy H lipo's (actually, 4 3 cell packs, which can be used as 3S in other models, for economy). You've written a good, common sense approach to the subject.
How much current are you planning on pulling? I've found that about 25-30 Amps per A123 cell is a good average amount of current to pull out of them. Go much higher, and your flight time gets rather short.
What ever you do, don't ever short an A123 pack out. The pack will ALWAYS win. (Don't ask how I know!)
One of these days, I'm going to add to my fleet of 12 ready to fly electrics, and try a Biplane! To give you an idea on how these perform, I've got a lead sled CAP232-46 model that weighs in at 7 pounds, with 30 ounces per square foot. Power is a Hacker A40-10L with a 16X12 APC-E prop, and 5S2P A123's. It gets off the ground in about 30 feet, and climbs up at about 50 degrees out of sight.
These are a couple of my recent large A123 powered foamy projects. They are not glow conversions, but they illustrate the point just as well I think
The Mega Capricorn weighs about 6.5 pounds (havent actually weighed it yet but thats close) and runs off a 6S1P A123 pack. Peak power is in the 8-900 watt range but flight times are a solid 6 to 7 minutes the way I fly. I spend most of the flight loafing along at 1/4 to 1/2 throttle.
The XXL Polaris runs off 6S2P A123 packs. It only weighs 7.5 pounds but the average power draw is a good bit higher. Peak power is 1250 watts and flight times are 8-9 minutes max. I tend to spend a lot more time at 3/4 to full throttle with this one. It looks better going fast
Larry, Ive followed your threads on both those models, and saw that they both perform very well, indeed!
Dennis, I hope to draw no more than 40A on my big Bird Dog, for a little over 1000W, but that will only give me a very scale power loading of about 50W/lb, as the r.t.f. weight will be about 20 lbs. I can't do much to lighten the model, as it's already built, and formerly ran on a large twin gasser. The 6S2P 5000 pack will be mounted right up inside the firewall, and may not add enough nose weight for this 108" span monster, but I've got to see if it can be done. She does have fully functional flaps, and I think I may be relying on them for both take-off and landing. My experience with large models of scale slow-fliers is that they don't need huge power to weight to perform like the real thing. The D VII in my avatar weighs a hair over 10 lbs, wing loading is 13oz/sq.ft., and power loading is only 60W/lb., and she'll do everything the real one could, which is all I want from a scale model. WW I fighters should NOT prophang!
bradt Dennis, I hope to draw no more than 40A on my big Bird Dog, for a little over 1000W, but that will only give me a very scale power loading of about 50W/lb, as the r.t.f. weight will be about 20 lbs. I can't do much to lighten the
You can run that 6S2P A123 pack at 55-60 amps all day with no problem. To give you an idea on power, that pack will turn a 16X12 APC-E prop at about 5900 RPM using a Hacker A50-16S motor. This setup hauls my 8 pound Hanger 9 Showtime 50 up at about 50-60 degrees until you can no longer see the model. The take off run is about 30 feet or so on short grass. It pulls about 48 Amps out of the battery. Flight time is limited to about 7 minutes, which takes about 60% out of the battery after a very acrobatic flight. I've found that the current drops to about 15 Amps or so just keeping it in the air, so at that current level, the model could fly 15 minutes completely discharging the battery.
Note that these A123 batteries quit like a glow engine! When they reach total discharge, they just quit, like in 15-20 seconds! (That is hard on them, as well as the Lipo batteries. Did it once though, the battery came out just fine, but landed the model off the field.)
I used to go to my local field, complaining about my "Underpowered Electrics" then take off in 25 feet and climb out at 45 degrees, and make 80 MPH passes over the field. That with an 8 1/2 pound airplane. Guess our club members got wise, these Electrics ain't what they used to be! More than a few of them went electric.
My question deals of what kind and size Volts/mah, battery would be good for a speed 400 electric motor on a Mini Telemaster. I want to get my grand kids to fly out at the ranch. Don't need to Out of Sight (OOS in old free flight days) performance -just a simple school yard flyer. Thanks and try to send responses to my email firstname.lastname@example.org