Published on August 26th, 2019 | by Nicolas Zart0
CleanTechnica Special: Verdego Aero Eric Bartsch On Hybrid Electric Plane Design
August 26th, 2019 by Nicolas Zart
I recently caught up with Eric Bartsch from VerdeGo Aero to talk about the differences between electric vertical takeoff & landing (eVTOL) aircraft and electric conventional takeoff and landing (eCTOL) aircraft. If you recall, we previously announced that VerdeGo stopped the development of its eVTOL aircraft to focus instead on designing powertrains for other eVTOL and eCTOL aircraft makers, a valuable way to enable more urban air mobility (UAM).
VerdeGo Aero Providing A Cleaner Way To Fly For Aviation Companies
Electrifying aviation is a complicated topic that is evolving quickly. Here on CleanTechnica, we’ve been reporting about eVTOL and eCTOL aircraft for 3 years now, watching it mature. It’s always a treat to sit down and talk with the movers and shakers of this new cleaner aviation industry.
Eric Bartsch is the CEO of Verdego Aero and started with the notion that there is a serious need for an aviation diet before 100 to 300-seat air taxis cover thousands of miles on batteries alone. All high-capacity hybrid-electric air commuters chose a hybrid platform for reason. Until battery energy density shrinks enough, the aim to reach pure electric flight is out of reach or impractical, so the transition is starting with hybrid drivetrains, much as the automotive market did 20 years ago. But that isn’t to say that aviation didn’t start its electrification a long time ago. It did so through a different route that deserves an article unto itself.
Eric says he led VerdeGo Aero through a strategic pivot away from developing an aircraft and towards developing enabling technologies for the entire market in order to help airlines and other aviation companies develop their own aircraft using VerdeGo’s hybrid-electric powertrains.
The concept started as a way to accommodate a wide variety of aircraft VTOL and CTOL designs, with both fixed-wing and rotary-wing aircraft of up to 7,000 lb. Many computations and tests later, they developed the VerdeGo Aero Integrated Distributed Electric Propulsion (IDEP) system.
Verdego Aero Perfectly In Between eVTOL & eCTOL Markets
Essentially, VerdeGo Aero ideally positioned itself as an enabler for the eVTOL and eCTOL industries.
“The challenge when converting any conventional aircraft to either hybrid-electric or battery-electric power is the risk that the conversion process results in an aircraft that is materially worse than the original one.”
The problem with the notion of hybrid is that it is associated with being inherently “green” regardless of the application. While automotive hybrids were designed for stop-and-go traffic, airplanes weren’t. The rolling, wasted energy from cars is recuperated through a regenerative braking system. This is more difficult with airplanes since there are no stoplights and no stop and go traffic. Add to this that airplanes already recover all of this energy when throttling back well before landing. The result is that trying to justify a hybrid installation on an existing aircraft might not yield the energy savings expected. You end up with an aerodynamically identical aircraft with the exact same amount of thrust through all phases of flight as it had before.
Hybrid aircraft takes mechanical energy from an engine, converts it to electricity using a generator charging a heavy battery pack, and then uses the electricity for electric motors. If the aircraft isn’t also being changed to benefit from the unique aspects of hybrid propulsion, then a bunch of heavy components have been added fo no clear purpose with energy loss in each stage of the conversion. This is where Eric’s VerdeGo Aero parts ways with other companies proposing to convert existing airframes to hybrid tech.
Eric says the net result when converting an existing aircraft to hybrid is usually more weight, less efficiency, and greater complexity than before. In the end, an aircraft is already designed with efficiency maximized. If it was powered by conventional propulsion, then it was optimized for that. It’s difficult adding more to something that is already specialized. He sees potential corner cases or niche markets for hybrid conversions, however.
Where hybrids make more sense are from a clean sheet design perspective. Distributed electric propulsion systems provide an array of thrust that can be placed anywhere to ideally control the airflow over the aircraft. The propulsion and attitude control systems can merge together with safety redundancies. Eric feels this is where hybrid design can maximize the benefits that the system provides.
Finally, Eric ends with this analogy:
“When jet engines came into existence in the 1930s and 1940s, they were a huge revolution in aircraft propulsion. The jet engine opened up huge potentials to design an aircraft around a new set of propulsion capabilities to do things that were previously impossible. We wouldn’t have the 747, A320, Eurofighter, or F-22 without the jet engine. However, just because the jet was revolutionary does not mean it was relevant to all missions and aircraft designs. For example, the Cessna 172 is a great airplane design that has stood the test of time. Attaching a jet engine to the top of a Cessna 172 would not make it a better aircraft. In fact it would make it significantly worse because the fuel tanks, aerodynamics, aircraft configuration, and mission are all wrong for a jet engine. This is often the case when force fitting hybrid-electric or battery-electric powertrains to existing airframes that were optimized around something else. The result is rarely satisfactory.”
eCTOL aircraft designed around a hybrid electric system and also designed around distributed electric propulsion have the potential to achieve higher efficiency with propulsion redundancy levels not possible with conventional propulsion today. They are a stepping stone until battery density shrinks enough to allow to 200 to 500 passenger aircraft replacing today’s jetliners. But the hybrid tech needs to be used where it’s useful, and focused on maximizing value in some way.
VerdeGo Aero is focused on matching aircraft architecture, propulsion systems, and different missions to enable broader use of this transitionary tech toward fully electric VTOL and CTOL aircraft.
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