Tuesday, December 10, 2013

Techy Tuesday - Electric/Gasoline Hybrids Achieve Flight

A while back (2012) we had a good discussion about Hybrid Cars, Batteries and drive train options.  The comments add a lot to the story and a couple of comments mentioned that in many industrial systems, an internal combustion engine (ICE) is used at its best - to run a generator - and the electric motor is used at its best - to deliver lots of torque.  Zendo Deb brings the smart (as she always does) about several aspects.  Worth your time to read.  In particular:
Most cruise ships today, as well as a lot tug boats, ice breakers, military vessels and the like, use gas turbines (jet engines) to generate electricity. They use the exhaust to generate steam and more electricity. And they use the electricity to run everything - including the motive power to the boat. Trains have been diesel-electric since the 50s. You run the ICE or the turbine at high-constant speed, you use electric power to maximum torque at minimum RPM, and everyone is happy....
(and she goes on to discuss the liquid sulfur batteries big locomotives use and their poor fit into the way people use cars).

As you might imagine from me digging up that old post, this is exactly the approach taken by a consortium of companies claiming credit for the the first hybrid drivetrain to power a small airplane.  
Aerospace engineers at Siemens, Boca Raton, Fla., EADS, Herndon, Va., and Diamond Aircraft, London, Ont., Canada, are field-testing the DA36 E-Star, a plane that is a stepping-stone between gas power and a pure electric vehicle. The E-Star is the first aircraft to use electric power from a generator driven by a small gas engine. The two-seat, prop-driven plane’s serial-electric hybrid drive lets the aircraft take off quietly and cuts fuel consumption and emissions by up to 25%.
And they score extra geek points for using a Wankel rotary engine!  (animated engines view)
The plane carries a relatively small Wankel rotary engine from Austro Engines, Germany. It spins a generator, which, in turn, powers a 70-kW electric motor that turns the prop. The 28.5-lb motor gets additional electricity for taking off and climbing from a battery. The battery recharges during cruising. Overall, the plane uses 80 kW of power on takeoff and 65 kW during cruise. A new Siemens drivetrain cuts the airplane’s weight by 220 lb, which significantly extends its range.
I think I'm most impressed about them improving the weight efficiency of a small airplane this way.  General Aviation aircraft are a tough environment because they tend not to have much extra payload capacity.  They tend to be small and not very powerful.  The hybrid drivetrain has the effect of adding 220 lbs of payload for a given range or extending the range with the original ratings. 

(Side note:  does this look like a macho, rugged aircraft to you?  Looks pretty light and fragile to me).



  1. Boy, is this overdue.

    I might have mentioned this here before, but a great many moons ago I was involved in a development project for internal combustion reciprocating engines; we were using an engine not originally designed for racing as a racing engine, and, since the races were 60 minutes long, the goal was "how much horsepower can we get out of this thing for 63 minutes?" (quite a lot, as it turned out, except for the 63 minute issue - one weekend 4 crankshafts were quite literally ripped in half, exhausting the supply of both race and practice engines. 17K RPM to zero in under a second is not kind to crankcases, connecting rods, flywheels or pistons).

    The dynamometer data showed something interesting, though - as HP went up, fuel consumption per HP went down. The engine got more efficient within a continually-narrowing max-HP RPM range. That drove a lot of transmission development work (if you road raced motorcycles in the '70s the question was always "why does the Yamaha TZ350 have a 6-speed transmission" with the punch line "because the American Motorcycle Association won't allow a 20-speed..." Damn thing didn't need a throttle, an on-off switch would have worked).

    Anyway, years later, I got to thinking: a small, single-RPM, highly efficient turbo diesel driving a generator, assisted by a small battery pack, might be the ultimate hybrid. I think it was during the 1979 gas crisis Brock Yates and Smokey Yunick drove a Mercury Cougar equipped with a Yunick-created turbo diesel engine from Daytona to DC on something ridiculous like 10 or 12 gallons of diesel. Volkswagen is getting really impressive mileage out of its European turbo diesel Passats (EPA won't allow them here, but the American versions stretch a gallon, too http://www.autoweek.com/article/20130708/carnews/130709866), and that's with an engine that needs a wide RPM range for driveability. All that transmission work needed to manage a very narrow RPM race engine? It goes away with an electric motor for final drive.

    Copper wire is easier to run than drive shafts, and much lighter than differentials. Electric motors are getting smaller, and lighter, and automotive engineers are pretty darn smart now about computer-driven controls. An on-board power source doesn't eliminate the batteries needed for surge demands, but it reduces their number and allows them to be smaller.

    Aircraft run at a steady speed (and don't encounter hills), which is why the 70Kw output can easily recharge the batteries with a steady 65Kw system demand. Road vehicles operate in a different environment, but I think it's practical.

    I wonder if anyone is looking at this for Over-The-Road trucks? The diesel infrastructure already exists for them, and despite the hills, interstates are a good steady speed environment.

  2. The problem is it makes perfect sense in a ship or locomotive. It is an elegant solution to many of the problems for those types of complex and large (not to mention expensive) devices. But in cars it is nt so good. The batteries are too expensive and in fact dangerous to the public and dangerous to the environment. But what may be worse for most of us is they are too expensive. If we were able to today with one brush stroke eliminate most or all of the government regulations on automotive companies and eliminate the unions cars, nice cars, would cost about $4000. But even with the highly inflated and unjustified cost for an ICE car they are still half what you must pay for a hybrid or all electric car. Why pay $50,000 for an electric car that will only get you 80 miles from home before it quits?