Pipistrel took the wraps off its latest iteration of what was originally called the Panthera, the hybrid variant of which has been renamed the HYPSTAIR, a pun that fails to diminish the significance of the achievement.
Pipistrel clams the most powerful aerial hybrid electric power train, powering it up on February 9 and making a mighty, but subdued noise, much of it coming from the specially-designed, five-bladed propeller.
Putting out 200 kilowatts (268 horsepower) at full throttle, the Siemens motor turned the propeller using first just the generator, and then the motor in low and high power modes. The propulsor (perhaps a new term to consider as hybrid power becomes a common operational type for electric aircraft) produces 100 kW (134 hp.) from the generator driven by a turbonormalized internal combustion engine, and the top rated power from the drive motor (150 kW continuous, or 201 hp.).
These impressive numbers allow the HYPSTAIR to achieve the same kinds of performance of which the original Panthera was capable with its Lycoming IO-390 engine. That engine could not run on automotive gasoline, though – part of Panthera’s initial specification.
Pipistrel calls the system “a new breed of aviation propulsion, which extends the range of all-electric aircraft while being environmentally friendly and quiet.” The firm explains the power system “can run in three modalities: electric-only mode using batteries, generator-only mode or hybrid mode combining both power sources. “
The system has a power density of five kilowatts per kilogram (3.18 hp. per pound), dual windings and four power controllers for reliability. The human-machine-interface, something Tine Tomazic has worked on for the last several years, simplifies the operation of this otherwise complex power train. The pilot controls power with a single lever with haptic feedback and views the system’s status and output on a new integrated cockpit display. The complete system will look and behave a great deal like a conventional aircraft’s FADEC (Full Authority Digital Engine Control) system.
Primary developers of the airplane and its power system commented on the demonstration of this new hybrid. Pipistrel CEO Ivo Boscarol, commented, “We are proud of what HYPSTAIR represents for the development of electric flight. It demonstrates the possibility for general aviation class aircraft to be electrically powered and it confirms the vision of Pipistrel – we were the first to design a four seat aircraft, the Panthera, which can be alternatively equipped with three different propulsion types: piston engine, electric motor or hybrid powertrain. Project HYPSTAIR represents a major step in the direction of a hybrid aircraft and an opportunity for Pipistrel and other general aviation aircraft manufacturers.”
Frank Anton, Head of e-Aircraft and the initiator of electric aircraft development at Siemens AG added, “Siemens is developing electric drive systems with highest power-to-weight ratio for aircraft propulsion. Only with innovation we can solve the problems of rising fuel costs, rising passenger demand and rising environmental regulation. Innovations developed for the HYPSTAIR hybrid-electric powertrain will be instrumental in making aviation more sustainable in the long run. As electric drives are scalable, we can expect that in the future also larger aircraft will use electric propulsion. The world is becoming electric, whether in the air, on land or at sea.”
Unveiled at the E2 Fliegen Symposium 2016 in Stuttgart, Germany, HYPSTAIR will undergo additional testing in the next few months. By the time Dr. Tine Tomazic of Pipistrel and Dr. Frank Anton appear at the Sustainable Aviation Symposium in San Francisco on May 6 and 7, There should be a great deal of new information to share with attendees.
Project HYPSTAIR has received funding from the European Union’s Seventh Framework Program for research, technological development and demonstration under grant agreement no. 605305. Project partners are Pipistrel d.o.o. Ajdovščina, Siemens AG, MBVision, the University of Pisa and the University of Maribor.
HYPSTAIR’s hybrid electric propulsion system that was tested on a Panthera fuselage this month has a range extender genset with a Rotax 914 engine. The 914’s 100 HP max continuous power output is reduced to about 80 HP by the time it goes through a generator, then AC/DC converter, then DC/AC inverter, then a motor, to spin a propeller shaft. So the Feb 2016 HYPSTAIR hybrid EPS has 200 kW peak power, 150 kW max continuous power until batteries are depleted, and about 60 kW max continuous power until mogas is depleted.
I doubt Pipistrel would be able to sell any hybrid Panthera with only 80 HP max continuous power in range extended mode (once batteries are depleted). I’d call that “limp home mode”. But that Siemens motor with 150 kW continuous power (or better yet, the Siemens 260 kW motor) would be great for the electro and hybrid Pantheras. Pipistrel just needs a more powerful genset for the hybrid Panthera.
(Editor’s Note: Bill Lofton’s EV Hangar is an excellent database of information on electric aircraft and components. It will be interesting to hear responses from both Dr. Tine Tomazic of Pipistrel and Dr. Frank Anton of Siemens about Bill’s concerns at this year’s Sustainable Aviation Symposium.)
After considering parallel hybrid (electric motor EM plus internal combustion engine ICE) vs. series hybrid with genset (EM plus ICE plus generator), I’ve come to the conclusion that for all single engine airplane conversions where the ICE and propeller were colocated and the hybrid powerplant and propeller will be colocated, parallel hybrid is superior to series hybrid with genset.
Almost all single engine airplanes that will be converted to hybrid electric should use parallel hybrid design.
Series hybrid with genset does have advantages when the ICE and propeller(s) won’t be colocated. So the e-volo VC200 and the EAN P2 Excursion need series hybrid with genset.
But a Panthera and other single engine airplanes with engine and propeller colocated are better with parallel hybrid than with series hybrid with genset. This is because a series hybrid 1) suffers 15% to 20% losses while converting engine power from mechanical to electrical and back to mechanical and 2) incurs cost and weight of generator and AC/DC converter(s), neither of which are the case for a parallel hybrid, which 1) doesn’t do that and 2) doesn’t need those.
Parallel hybrid has more power, is lighter, and has significant cost savings over series hybrid with genset.
In the case of the Panthera, compared to a series hybrid with genset conversion, a parallel hybrid conversion will have 15-20+ HP more ICE power reaching the propeller, plus save the cost and weight of a 100+ kW generator and a 100+ kW AC/DC converter. (Or two converters, as in Siemens’ design for failsoft.)
And a parallel hybrid can charge the batteries as well as a series hybrid with genset, because the motor is a motor/generator and can “regen” off the engine just like it does off the propeller during a descent. In both cases, the generator uses torque from the propeller shaft to convert mechanical power to electrical power that charges the batteries.
I understand that Airbus and Siemens are building toward hybrid propulsion of regional airliners, for which series hybrid with genset is a good solution. But a single engine airplane isn’t the place to showcase that technology.
Let’s work on parallel hybrid solutions for the single engine ultralight and experimental fleets. LSAs too!