Battery Takes Wing with Hybrid Electric Drive

I'm skeptical this type of hybrid system has much chance of being widely adopted.

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Hybrid systems in road based ground transportation make sense in large part because regenerative braking can recoup a lot of otherwise wasted energy. It also can make sense to extend the range of electric vehicles.

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The thing braking is not as significant in planes as it is in cars. Even though takeoff requires more power, there is very little variation in power over a whole flight, especially compared to a typical trip in an automobile. That takes away a major reason for investing in a hybrid system.

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Weight is also at a premium on planes. Every extra pound in copper windings and batteries is a pound less of cargo. While you may be able to get away with a smaller engine and maybe slightly less fuel, my guess is that the total weight will be heavier than a similarly powered non hybrid system.

I agree. This appears to be the least likely application for a hybrid electric system. If batteries ever achieve an energy density similar to a liquid fuel, then all bets are off.

Actually I can think of one even less likely - a battery powered rocket.

Yeah. I think technology will have to improve beyond the point that we see widespread conversion of diesel electric locomotives to battery (car) incorporating hybrids before hybrid planes ever become a realistic competitive option.

I will respecfully disagree on this one. They German fellow from Siemens specifically stated that the payload expectations were met. Planes typically use a considerably greater level of power during climbout, yes, and cruise conditions can be set up to vastly conserve "fuel". My question is, during descent, could the propeller not be "feathered" to keep spinning with torque from wind pressure, and operate the electric motor as a generator once again, even without the gas powered engine being online?

Usually descent and approach slowing is considered to be the two greatest "energy" wasters in flight, by necessity. Surely there is an aeronautical engineer who can figure out a way to <safely> exploit this to recharge a hybrid during descent, and essentially convert this part of the system into a speed brake. Maybe dive flaps with small wind turbines built-in? I don't know. Sorry if this appears off the wall and slightly tongue in cheek.

Thank you for detailing an alternate point of view.

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You make good points, but I remain skeptical. While the Seimens employee certainly has access to more details, he also has strong motivation for communicating this project as a success.

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Betting on recouping energy by having the props spin the motors as generators doesn't seem like a sure thing. There are a couple problems.

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First, the foils used on props are not of symmetrical in cross section. Attempting to use a typical prop as a wind turbine isn't going to be very efficient, since the camber will be in the wrong direction.

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The second problem is, with the exception of situations that require steep descent for some other reason, adding resistance will be of set by having to cruise further before beginning the descent. The amount of time the typical flight could regenerate would be fairly short just before landing. And if the plane reverses thrust landing, that is again, not a time when regeneration will be available.

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One of the things that helps to make hybrids payoff is typically the engine is shut off when regenerating. But for a plane having full power dependably available is a safety issue for planes. I doubt the engine will be shut down, whether turbine or piston.

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Even when battery technology has evolved to the point that hybrid planes are viable, I doubt there will be much regeneration involved, not only for the reasons above, but also because with any possible regeneration occurring at the very end of the flight and the possibility of charging batteries from cheap power through the grid will likely be very attractive.

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That leaves us back at the situation where the benefit of running a smaller engine at its optimal speed, must offset the additional weight and cost, probably without much if any help from regeneration. That is a case very similar to large ships, but as far as I know it hasn't taken off in that arena.

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NASA has experimented with small turbines that take advantage of the wing tip vortices to generate enough power to obviate the need for the APU. That system wasn't so much for regeneration as it was an attempt at dealing with energy lost to vortex induced drag. Since those turbines are purpose made and not affecting the available power, perhaps that might be a viable approach.

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I still expect to see a railcar that can be added behind diesel electric locomotive that with minimal alterations to the original system will provide storage and regeneration benefits widely adopted, before widespread adoption of hybrid passenger aircraft.

With your last comment, I believe hydraulic hybrids offer the best weight to energy capture ratio of all regenerative braking systems out there. These hydraulic systems may also hold that title for rerelease of that captured energy. Last I heard, over 40% capture for hydraulics compared to 26% for electric capture in a honda insight.

I would be willing to bet a suitable hybrid hydraulic motor/regnerator system could be incorporated with a small, highly efficient opposing piston engine to accomplish everything this hybrid electric does at even less weight overall. The added benefit is that hydraulic motors have evolved to a high level of reliability, efficiency, and instanteous power that electric simply can't touch. I see that the electric drive part of the electric hybrid has all the climb power it needs, but look at how long the wings are to achieve this. Consider building one with wings more typical of a conventional two-seater, and still producing the same or more lift using hydraulics.

I believe hydraulic hybrids have issues with high speed, (at least I remember they did when I read about them a few years back [keep under 45 mph for effective results]. Higher coefficient of friction was probably the issue, and noise issues were also brought up concerning use in passenger cars.

We have not been reading the same stuff. Also, consider this: the speed has nothing to do with the performance of a hydraulic motor at a given rpm in an airplane. The motor only needs to spin the prop with sufficient torque to maintain optimal rpm for a given pitch angle of the prop, under what is considered to be "normal power", with perhaps a little extra for "emergency power". I still think some energy recovery is possible by converting wingtip vortical drag as suggested by tinac, or by having an advanced prop design that could totally reverse pitch, probably not the best idea on that one.

I think there is also a lot of potential in hydraulic hybrids. I haven't heard much about UPS hydraulic hybrid delivery vehicles since they were rolled out a couple years back. I wonder how that has unfolded?