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The Speed 400 Revolution

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tex2html_wrap100 Electric-powered RC has come a long way since its advent in the early 1970's. At that time, making an RC plane fly at all under electric power was considered a huge, if novel, success. Now, electric powered planes that yield excellent performance and duration are almost commonplace, although still a minority compared to their glow-powered brethren.

Even as recently as 1995, I had always assumed that the future of electric RC was aimed, as glow power had been, towards the ``bigger is better'' adage. At larger sizes, electric power holds its own easily against glow-powered planes in terms of power and endurance. Most well-designed .40 sized planes can be converted to electric power using 12-24 cells and (geared) motors of comparable power to glow engines. And you only have to witness a 1/4 scale Sig Cub flying with a geared Astro 60 and 14x8 prop on 32 NiCad cells to be captured by the beauty of electric power on large scales.

But since 1995, the largest growth in electric flight has been in the small-scale, generally classified as ``Speed 400'' after the inexpensive Graupner motor that started the craze. In fact, this growth has led to a renewed interest in small RC planes, even down to what are now called ``park flyers'' that can be flown in large backyards and parks. These planes typically have 30'' to 45'' wingspans, roughly comparable to .02 to .049 glow screamers. Speed-400 pylon racers typically use 6 to 8 of the 500 mAH ``AA'' sized NiCad cells (i.e. the type you probably use in your transmitter), run direct drive at high RPMs with a suitable 5x5 propeller. Sport planes might use a geared-down Speed 400 to spin a larger 8x5 or 9x5 prop at lower RPMS for more thrust. 1.5-meter gliders, often in the ``Hand-Launched Glider'' category, might use a folding prop and a further-geared Speed 400 motor to spin a 10'' or 11'' propeller for maximum thrust at low airspeeds.

The advantages of these small planes are many - they are quiet, inexpensive and convenient. They can be flown just about anywhere, and somewhat larger multi-engine designs are a cinch. Well designed small models fly very nicely and aren't substantially ``squirrelier'' than larger models, although many don't handle high winds as well as their larger brethren. Let's look at three different Speed 400 examples to see what can be done.

Aside: Remember that electric motors don't ``have'' a fixed amount of power like a glow engine. Instead, they have a very broad power range, limited only by the point at which the motor starts smoldering. :) For example, a high-quality ``25'' class motor might act like a glow .25 on 14 cells, direct drive, with a 9x6 prop. But it could also have the power of a .53 four-stroke, geared down to swing a 12x8 prop on 16 cells. It could generate as much power as a 1.20 four-stroke on 28 cells using a 14x8 prop, but it would be operating past specs and wouldn't last long. It might leave a nifty smoke trail though. :)




next up previous
Next: Sailplane Example Up: Front Page Previous: From the Puckerbrush...

Craig Kulesa
Fri Dec 1 16:54:18 MST 2000