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This is my presentation for the Third Annual Electrical Aircraft Symposium at the Hiller Aviation Museum in San Carlos, CA. I have added several links that were not in my original notes, but that I hope will help guide readers to form their own conclusions, and possibly add to the core of knowledge we hope to collectively build. San Carlos, April 24, 2009 1 This presentation is an expansion of a talk I gave at the 2008 Tehachapi gathering of the Experimental Soaring Association. Dr. Brien Seeley heard that presentation and asked me to do a similar show for the 2009 San Carlos CAFÉ symposium. San Carlos, April 24, 2009 2 “The many experiments made during this last quarter of the nineteenth century have given considerable impetus to the question of guida ble bllballoons. The cars furni sh ed with propellers attached in 1852 to the aerostats of the elongated form introduced by Henry Giffard, the machines of Dupuy de Lome in 1872, of the Tissandier brothers in 1883, and of Captain Krebs and Renard in 1884, yielded many important results. But if these machines, moving in a medium heavier than themselves, maneuvering under the propulsion of a screw, working at an angle to the direction of the wind, and even against the wind, to return to their point of departure, had been really ‘guidable,’ they had only succeeded under very favorable conditions. In large, covered halls their success was perfect. In a calm atmosphere they did very well. In a light wind of five or six yards a second they still moved. But nothing practical had been obtained. Against a miller's wind-- nine yards a second--the machines had remained almost stationary. Against a fresh breeze--eleven yards a second--they would have advanced backwards. In a storm--twenty-seven to thirty-three yards a second--they would have been blown about like a feather. In a hurricane--sixty yards a second--they would have run the risk of being dashed to pieces. And in one of those cyclones which exceed a hundred yards a second not a fragment of them would have been left. It remained, then, even after the striking experiments of Captains Krebs and Renard, that though guidable aerostats had gained a little speed, they could not be kept going in a moderate breeze. Hence the impossibility of making practical use of this mode of aerial locomotion. “With regards to the means employed to give the aerostat its motion a great deal of progress had been made. For the steam engines of Henry Giffard, and the muscular force of Dupuy de Lome, electric motors had gradually been substituted. The batteries of bichromate of potassium of the Tissandier brothers had given a speed of four yards a second. The dynamo-electric machines of Captain Krebs and Renard had developed a force of twelve horsepower and yielded a speed of six and a half yards per second. With regard to this motor, engineers and electricians had been approaching more and more to that desideratum which is known as a steam horse in a watch case. Gradually the results of the pile of which Captains Krebs and Renard had kept the secret had been surpassed, and aeronauts had become able to avail themse lves of motors whose lihlightness increase d at the same time as thiheir power.” Robur the Conqueror, Jules Verne San Carlos, April 24, 2009 3 Harpers Magazine, in 1901, published this cartoon, with this telling caption. Often, because no immediate commercial reward can be gained from a new invention, there is no reward or recognition for the inventor. Often, since existing technologies are adequate to dissuade hopeful visionaries from wasting their time in the new field, promising alternatives to the current reality are neglected. San Carlos, April 24, 2009 4 This book, a compilation of articles from Popular Science and Popular Mechanics magazines of the 1920’s and 1930’s, reflects on the folly of trying to predict the future. Almost none of the predicted marvels in the book came to pass – many are still awaiting an entry in the hoped-for world of the future. San Carlos, April 24, 2009 5 As with all generalities, my outline is subject to occasional excursions into areas of related interest, if not strict adherence to the categories shown. San Carlos, April 24, 2009 6 Following a heart attack in April, 2004, I had time to recuperate and engage in leisure reading. On a trip not authorized by my doctor, I had my daughter Beth drive me to a favorite magazine shop in Portland, Oregon, where I purchased the current edition of Quiet Flyer, which featured Rob Honeycutt’s amazing Extra 330L. I was able to deduce that a 28-pound airplane that could hover had to be putting out at least 28-pounds of thrust. It turned out to be better than that, and I was able to conceive that these little model electric motors could power a sustainer power pack for sailplanes. Assuming a 524 pound AUW sailplane with even a modest 25:1 lift to drag ratio, it would require only 20.96 pounds of thrust to maintain altitude at its best l/d speed. San Carlos, April 24, 2009 7 One has the option to select a single large motor or two or more smaller motor to get the desired thrust. Rob Honeycutt used twin Hacker motors in his successful Extra 330L, using a speed reduction drive to the prop. Hacker followed up with multiple motors in geared drive arrangements – a twin-motor item and a four-motor design that produced 87 pounds of thrust through a 30-inch propeller, and cost $2,995. Because the four motors required four electronic speed controllers and four battery packs, it and the twin-motor system shown above were soon replaced byyg larger, sing le motor desi gns. http://www.hackerbrushless.com/ San Carlos, April 24, 2009 8 Most model motors in the size ranges of interest in this presentation are brushless, and are either inrunners or outrunners. Inrunners are built like traditional brushed motors, but take their speed control from an electronic speed controller. Outrunners reverse the major parts of the inrunner motor, with the stator mounted in a fixed, central position, and the rotor spinning around in the outer casing of the motor. The propeller is fastened to the spinning casing, a great deal like the configuration of WWI rotary engines. Taking signals from the speed controller, the motors outer magnets are turned on an off at 120-degree phased intervals. Each time a pole is activated, it draws the rotor toward it. The speed controller acts as the interface between the battery and the motor. Since the battery is always at the same voltage, the controller has to modulate that power to allow the motor to turn at different speeds. A series of MOSFET transistors act as switches in the sppyeed controller and vary the width of the pulses sent to motor. San Carlos, April 24, 2009 9 Electronic speed controllers (ESCs) must be carefully matched to the intended motor. Brushless motors do not receive electricity directly from the batteries that power them, but have that current modulated by an electronic speed controller. There are several features of electronic speed controllers typically used in model aircraft that we should consider. If the full voltage from the batteries was passed uninterrupted to the motor, the motor would run at whatever speed the available voltage allowed. For determining how to match a motor and propeller, a motor performance parameter, kV, or revolutions per minute per volt, will be helpful. Motors vary in their kV rating, depending on size, number of windings, poles, etc. How do we vary the amount of electricity which passes into the motor? The best control would allow everything from the motor not turning over at all to a full-throttle, full power run. An electronic speed controller (ESC) enables this, with some limitations, usually at lower RPMs. An ESC works as a switch, usinggg high-spp(eed MOSFETs (metal oxide semiconducting field effect transistors) to switch the current on and off. The motor receives only pulses of electricity that are allowed through by the controller as the MOSFETS turn on and off. The power received by the motor is based on how “wide” the pulse is, San Carlos, April 24, 2009 10 “The servo signal is a simple digital pulse. It spends most of its time at a logic low (0 V). About every 20mS it goes logi ic highhi h (3 to 6VDC) and then quickly kl goes low again. It is this tiny window of logic high time, called the pulse width, that gets the attention of the servo. Please refer to the drawing. The period labeled "A" is called the frame rate. In the example it is repeated every 20mS (50 times per second), which is quite typical for most radio systems. Modern servos define center as a 1.5mS pulse width, as shown by detail "B" in the drawing. Full servo rotation to one side would require that this pulse width be reduced to 1.0mS. Full rotation to the other side would requirrequiree the pulse width to increase to 2.0mS . Any pulse width value between 1.0mS and 2.0mS creates a proportional servo wheel position within the two extremes. The frame rate does not need to change and is usually kept constant. The servo will not move to its final destination with just one pulse. The servo amp designers had brilliantly considered that multiple pulses should be used to complete the journey.

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