Calin Cologan and George Bye staged a joint press event on the Sunday evening before AirVenture started. Held in the Redbird Tent on Wittman Field, it drew hundreds who saw the Redbird flight simulators and a Diesel-powered Cessna, but were stopped short by the yellow and blue Sun Flyer, a single-seat proof-of-concept version of what will soon be a two-seat battery/solar training aircraft.
Forming a new firm based on the strengths of PC-Aero in Germany, and Bye Aerospace and Redbird Flight Simulators in America, they promise an electric training aircraft for the near future. Unlike the tandem two-seaters PC-Aero is developing in Germany, American Electric Aircraft Corporation will produce a side-by-side craft, often preferred for communication between instructor and student.
In this Da Vinci Institute presentation, George Bye discusses the keys to performance for his aircraft, which include clean aerodynamics, high efficiency, a light carbon structure, and solar energy. Nest will come a “big performance step – endurance” – and possible perpetual flight like that demonstrated by the much bigger, less practical Solar Impulse and being approached by Eric Raymond’s Solar-Flight Duo.
Part of AEAC’s strategy is to use proven off-the- shelf components, advanced technology, miniaturization, and emerging aerospace design to bring a complete, modern machine onto the training scene. The strategy will bring flexible, innovative, and scalable design and manufacturing techniques to the fore, enabled by an experienced team with years of aerospace expertise.
Stealth is Good for Civilian Aircraft, Too
Sun Flyer, as with other electric aircraft, has several aspects that make it commercially-viable for training or unmanned use, including a low heat signature that comes from the lack of hot exhaust. Large, wide propeller blades turn slowly, giving half the acoustic signature of conventional small General Aviation aircraft. The unobtrusive nature of the airplane allows the unmanned version to stay, listen, and watch – highly attractive to the Defense Department.
This leads to a concept developed by Bye and Gologan, StratoAirNet, a persistent network of medium-to-high altitude aircraft that can provide applications in “communications, border patrol and homeland security, maritime search and rescue, visual and thermal reconnaissance and forward air control. Potential civil applications include traffic control, pipeline and power line inspection, aerial law enforcement, wildlife and natural resource monitoring, forest fire detection, weather monitoring and aerial photography.”
Characteristics that allow low-cost surveillance equate to reasonable operational costs for flight schools. Part of that is the low empty weight of the concept airplane, 150 kilograms (331 pounds), with batteries adding 80 kilograms or 176 pounds to that. In the surveillance version, this allows a payload of 150 pounds. For the trainer, LSA-type numbers will prevail, with an empty weight of 280 kilograms (616 pounds) empty weight including batteries, a payload of 200 kilograms (440 pounds), and a flying weight of 600 kilograms (1,320 pounds). The poster at the Redwing tent showed a power output from the Eck/Geiger HPD-25 motor of 26 kilowatts (34.8 horsepower) continuous and 30 kW (40.2 hp.) peak power for a limited time.
The nine-kilogram (20-pound) motors give twin-motor safety with single-motor operation. Dual controllers add about two pounds to the power system. Two throttles can be individually operated, or combined to use the full power of both motors for takeoff or climb. Since the clean, light airframe requires only six kilowatts (8 hp.) to maintain level flight at 50 knots (57.5 mph), the airplane should be able to stay aloft for over three hours on its 18 kilowatt-hour battery pack at that speed. At full throttle(s) it can climb 700 feet per minute. Of course, normal training regimens will include tough-and-goes, maneuvers, and higher-speed operations that will reduce that best-glide-speed type endurance. Some indicators show a 52-kW (70-horsepower) version of the dual motor may be available, which would certainly enhance climb performance.
To augment that, the airplane has Solar World thin-film photovoltaic cells that can add a maximum of up to 1.3 kW of energy. These cells add minimal weight for their 7 square meters (75.3 square feet) of conservatively-calculated area. According to Calin Gologan, “The cells weigh about 0.5 kilogram (1.1 pounds) per square meter, the layers 0.2 kg (0.44 pounds).” Wiring adds about 0.1 kg (0.22 pounds). This totals about 0.8 kilograms (1.76 pounds) per square meter, or about 0.16 pounds per square foot. The seven square meters of solar cells thus add about 12.3 pounds to the aircraft’s weight. Since they are 22-percent efficient, Calin calculates them as providing 220 Watts per square meter, or a maximum of 1.54 kW, about 20-percent of the energy required for low cruise. Calculations for endurance are based on the currently installed batteries and their 250 Watt-hour per kilogram performance. AEAC anticipates having 400 Watt-hour per kilogram batteries soon.
The cells cost about 350 euros ($465) per square meter, two layers of thin glass laminations which form a flexible and protective matrix cost about 660 euros per square meter, and this totals about $1,000 euros ($1,330) per square meter ($124 per square foot). The solar cells add 7,000 Euros ($9,310) to the cost of the airplane, but allow free recharging of the batteries as the airplane is parked, and add to the endurance and range in the air.
Note that Charlie Johnson estimates a price for the two-seat trainer at under $180,000, certainly not out of touch with the market or out of line with other LSA-type aircraft. AEAC has a truly disruptive card up its sleeve, though – an operating cost of $10 per hour, including an hourly allowance for battery replacement. Calin, George and Charlie all hope this will lead to a resurgence in flight training and a rebirth of the General Aviation market. Coupled with new aircraft promised from Airbus and rising interest in electric ultralights, we may soon witness a quiet buzz at our local flying fields.