Electric Power for High Performance Models
Introduction
At the start of this article, 08-02, I have very little practical experience with electric power for RC models. So why am I writing about it, when there are many others more knowledgeable? Well, I've casually read various articles on electric power over the years, but until recently, have not been impressed. I had many of the common misconceptions about it, including the idea that it is only useful for small "Indoor" types, powered sailplanes and small "Park Flyers". Since I began doing somewhat more serious research in June of this year, I've (happily) found that I was wrong.
Based on what I've recently seen and read, including text and video by Keith Shaw, long-time electric expert, I now believe that electric power is the perfect system for our 1/6th scale King Air B200 project. (I'll explain why, below.) This feeling was backed up by getting to know the other flyers in our club who fly electric, seeing their planes fly, and asking them a lot of questions about their experience. I've also been absorbing what I can by following the forums and articles at E-Zone, and Electric Jet Factory. Simply put, "I'm sold."
To do this right, I must become "Mr. Electric Twin". In the process, I'd like to prove to myself and others that electric power systems are not overly complex to assemble and operate, and since my experience with electric is limited, that makes me the perfect candidate. I intend to fly several other electric aircraft before the King Air is finished, so I'll have some experience by then.
For me to consider electric power, it has to meet the following criteria:
(Reliability and consistency are assumed, since that's the attraction of it in the first place.)
1. The system must have the power and duration to fly our B200 with authority... meaning that it must support a scale appearance, and not look "wimpy", like a "Park Flyer" type. On the other hand, it must not be so heavy as to harm the flying characteristics.
2. However powerful the system is, it cannot cause any radio interference.
3. The system must be easily repeatable, so that any of you can use it, if you like.
4. Both glow and electric power have "issues", which I'll describe and compare. The good points of the electric system must outweigh the bad points, to the extent that I have no doubt that it's superior.
For those of you who have shown an interest in future kits of the King Air, rest assured that the design will remain perfectly adaptable to glow or electric power. Since it will be entirely molded, it's simply a matter of changing the weight of the fiberglass, and a few internal parts.) We'll test both versions and publish the results on this site.
These are the reasons I've decided to give it a go:
Specific to our 1/6th scale King Air B200:
1. Everyone's biggest fear with a multi-engine aircraft (especially a twin) is an engine failure. If it happens at low airspeed and high torque/high P-factor, (at takeoff, for example) it's usually disastrous for the model. Electric power works all the time, and it resolves the problem of equal power output on both engines, too. (Notice how experienced twin glow flyers try to meticulously fine-tune and "match" their engines.)
2. The King Air is a turbine aircraft. Electric power sounds more turbine-like than any glow system. (A turbine-powered "turbo prop" setup is too heavy for this aircraft, and too expensive for me.)
3. Electric power allows us to completely hide the motors inside the scale nacelles, with no engine cylinder sticking down into the scale inlet or demanding a hole in the cowling. (The scale inlet ducts and exhaust stacks are sufficient for good cooling.)
4. The King Air has a rather long cantilevered structure inside the nacelles, to support the engines. If built for glow power, this area must be built strongly, mandating the use of either a heavy wood structure, or the use of more expensive composites such as carbon fiber. If built for electric power, a simple 1/8th inch plywood or fiberglass firewall and minimal support structure is perfectly adequate.
5. The King Air's wing center section must support the flight loads, two engines, and the main landing gear. The use of glow power means two heavy, vibrating engines, two fuel systems, and two throttle systems. If built for electric motors, which are lighter and virtually vibration free, the wing center section could be built much lighter.
6. The King Air does not have counter-rotating props. But, if we were to decide to use them, to improve performance, it's easily done with electric power, by simply reversing the wires to the motor and changing props.
Applicable to all electric aircraft:
1. It's dependable...No fiddling with fuel, mixture settings, glow plugs, starters, etc..
2. It's clean...No "goo" to attack the finish on your model, no "goo" to wipe off after flying, and no "goo" to gradually fuel-soak and weaken structures.
3. It's nearly vibration-free, enabling much lighter structures to be built.
4. Since the system is so reliable, the excess power normally built into glow-powered models can be reduced, which saves weight. This allows safer flight at more scale-like speeds.
Initial costs seem high, but really are not, when compared to glow power's fuel and maintenance. On a 1990 videotape called "Power for Performance", Keith Shaw mentions that he had been flying his large, scale, electric twin for over 9 years, without any engine maintenance! He noted that no glue joints had vibrated loose, no structures were fuel-soaked, and the model's exterior finish showed virtually no wear. Finally, he mentioned that although three people he knew of had built the same model for glow power, at a weight of 12 to 15 pounds, he was able to build his at 7 pounds!
Personal Interest:
1. I've been flying glow power for over 30 years, and consider this a worthwhile challenge.
2. If this works as desired, it'll give me the knowledge to convert my other projects to electric power too.