While we wait (with increasing patience or impatience depending on our personalities) for the next round of battery developments to make pure electric airplanes a reality, hybrid possibilities abound. The definition of “hybrid” might not be as coherent as those used for automobiles. Some “hybrids in this entry allow extended letdowns following a primary engine failure. In that case, the added electric motor/generator gives extra minutes to find a safe landing space. While both motor and primary engine are operational, the system acts much like an automotive hybrid system, both motor and engine combining outputs for added power, or the electrical portion recharging batteries while the engine maintains cruise power.
Some are more like automotive serial systems, an engine-driven generator charging batteries which power the propulsion motor. Pipistrel, though the Hypstair project, has a 200-kilowatt (268-horsepower) unit ready for test flights in 2017, according to Tine Tomazic, Director of Research and Development.
Several Flying Now
Several years ago, Flight Design in Germany attached a generator/motor setup to a Rotax engine. The electrical add-on would assist in takeoffs, charge batteries while in flight, and take over as a primary power source if the gasoline engine failed. This same hybrid approach applies to similar current systems.
Mounted on a Tecnam P92, the Axter Rotax/electric motor combination allows up to 15 minutes of 40-horsepower flying if the Rotax fails. That should be enough to find a landing area and make a safe letdown. The Spanish company now markets the powerplant with a variable-pitch propeller.
This Israeli system had a brief moment in the spotlight, but seems not to be included in the company’s lineup at this time. Ashot Ashkelon manufactures many aerospace components, and their hybrid system is shown in coverage of their displays at the Le Bourget Air show in 2015. The system is markedly similar to Axter’s.
E-Genius’s Hybrid System
e-Genius has been flying with its add-on pod for over a year now, and tests show predictions of 1,000 kilometer (620 mile) trips are doable. The 20-kilowatt generator burns five liters per hour, and is turned on after e-Genius has gained sufficient altitude to make its added sound level imperceptible from the ground – a practice that seems perfect for a noise-conscious world.
Close to Flight
Equator’s Hybrid System
Both the Equator P2 and e-Genius rely on the Aixro/Engiro hybrid generator-motor system for flight. Equator’s units include a 60 kilowatt-hour generator powered by an Aixro Wankel engine, and the motor at the propeller puts out 100 kilowatts (130 horsepower). Thomas Brodreskift and his crew recently fired up the system and all looks well for its eventual flight tests.
As Tine Tomazic explains in an interview with AVWeb’s Paul Bertorelli, This most powerful of hybrid systems, destined to make the modified Panthera a high-performance hybrid.
This micro-turboalternator drives a lightweight permanent magnet generator, which the makers claim consumes only one pound of fuel per hour per kilowatt output. Its claimed power-to-weight ratio is “1.7 kilowatts per pound, six times the specific power, or 12-15 times the energy density of lithium polymer batteries.” The design places the power turbine driving the bypass flow at the front of the combustor rather than at the engine exhaust. A compact recuperator recovers heat from the exhaust decreases fuel consumption.
Given company figures, a 20-kilowatt microturboalternator would weigh under 12 pounds and consume 20 pounds (three gallons) of fuel per hour at full output. This performance possibly led to the project garnering funding from DARPA and NASA.
DARPA Funds Liquid Piston
Using its High Efficiency Hybrid Cycle (HEHC), The Liquid Piston X Engine has few parts and three combustion events per rotor revolution, resulting in tremendous power density, according to its makers. One of these coupled to a compact generator may prove useful for ultralight-type aircraft. Whether fuel consumption becomes an issue remains to be seen at this point.
NASA’s Forays into Hybrid Power
In the video here, Mike Ricci, Vice President of Engineering at Launchpoint Technologies shows off a few of the company’s offerings. As interviewer Lee Teschler, Executive Editor at Design World points out, Launchpoint is a NASA contractor, apparently involved with several recent projects.
Launchpoint’s portfolio shows extremely light generator sets, using off-the-shelf components from the model aircraft industry as starting points. With the redundancy inherent in hybrids, less-expensive components could prove to be viable and at least nominally reliable. Used in pairs or greater numbers, they could be a low-cost answer for light aircraft such as ultralights, self-launching sailplanes or motorgliders.
Promise for Near-term Solutions
Hybrid systems are a possible answer for near-term solutions to making aviation cleaner, if not totally pollution free. Many entries and their combinations at all power levels make tempting excursions into researching these possibilities an exciting challenge. We’ll have examples in new entries soon.