• Jul 3, 2011
Siemens, along with Diamond Aircraft and EADS, have built a custom aircraft equipped with a series hybrid propulsion system. The trio unveiled the two-seat airplane, dubbed the DA36 E-Star, at the 2011 Paris Air Show in late June. Siemens says the aircraft's revolutionary series hybrid technology cuts fuel consumption and emissions by 25 percent, compared to today's most fuel-efficient airplane propulsion systems.

Based on Diamond Aircraft's HK36 Super Dimona, the E-Star's propeller is powered by Siemen's 70 kW electric motor. A small Wankel engine, supplied by Austro Engine, acts as a generator, supplying juice to the electric motor. Siemens says that fuel consumption is exceptional due to the combustion engine spinning at reduced RPM. An on-board battery pack, provided by EADS, gives the lightweight aircraft a boost in power during takeoffs and climbs. That battery pack is then recharged while cruising. During initial test flights, the DA36 E-Star was airborne for two hours.

[Source: Siemens]
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Joint press release by Siemens, Diamond Aircraft and EADS

World's first serial hybrid electric aircraft to fly at Le Bourget


Siemens AG, Diamond Aircraft and EADS are set to present the world's first aircraft with a serial hybrid electric drive system at the Paris Air Show Le Bourget 2011. The two-seater motor glider successfully completed its maiden flight on June 8 at the Wiener Neustadt airfield in Vienna, Austria. The aircraft was built by the three partners to test the hybrid electric drive concept. In the future, the technology, which is intended for later use also in large-scale aircraft, will cut fuel consumption and emissions by 25 percent, compared to today's most efficient aircraft drives.

Air traffic accounts for some 2.2 percent of CO2 emissions worldwide. For this reason, aircraft, too, must become more efficient. One possible solution – which Siemens and its partners Diamond Aircraft and EADS are testing in the DA36 E-Star motor glider – is to electrify the drive system.

"A serial hybrid electric drive can be scaled for a wide range of uses, making it highly suitable for aircraft as well," said Dr. Frank Anton, the initiator of electric aircraft development at Siemens. "The first thing we want to do is test the technology in small aircraft. In the long term, however, the drive system will also be used in large-scale aircraft. We want to cut fuel consumption and emissions by 25 percent, compared to today's most efficient technologies. This will make air travel more sustainable."

The motor glider, which is based on Diamond Aircraft's HK36 Super Dimona, is the only aircraft of its kind in the world. It is the first to use a so-called serial hybrid electric drive, which has been utilized to date only in cars, as an integrated drive train. The plane's propeller is powered by a 70kW electric motor from Siemens. Electricity is supplied by a small Wankel engine from Austro Engine with a generator that functions solely as a power source. A Siemens converter supplies the electric motor with power from the battery and the generator. Fuel consumption is very low since the combustion engine always runs with a constant low output of 30kW. A battery system from EADS provides the increased power required during takeoff and climb. The accumulator is recharged during the cruising phase. "The serial hybrid electric drive concept makes possible a quiet electric takeoff and a considerable reduction in fuel consumption and emission," said Christian Dries, the owner of Diamond Aircraft. "It also enables aircraft to cover the required long distances."

The electric motor glider successfully completed its first flight at the Wiener Neustadt airfield in Vienna, Austria on June 8, 2011. "On the long way to hybrid electric-powered commercial aircraft, the maiden flight of the DA36 E-Star is a small step and at the same time a historic milestone," said Dr. Jean Botti, Chief Technical Officer and member of the Executive Committee of EADS.

The next development step will be to further optimize the entire drive train. Siemens scientists are currently working on a new electric motor that is expected to be five times lighter than conventional drives. In two years, another aircraft is expected to be equipped with an ultra-light electric drive. Siemens' Drive Technologies Division has already used integrated drive trains in other applications like marine drives. The knowhow gained in these areas has now been applied in the aviation industry as well. Combined with the corresponding product portfolio, the components of the drive train can be optimally adjusted to one another.
The DA36 E-Star will be exhibited at the Paris Air Show Le Bourget in a flight demonstration every day from June 20 to June 26, 2011.


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    • 1 Second Ago
  • 38 Comments
      Dan Frederiksen
      • 3 Years Ago
      not sure a plane is an obvious application for a series hybrid but ok to experiment. they might gain more from a ducted fan instead of free propeller. the aerodynamics looks pretty good but tandem seating instead of side by side can be better.
        • 3 Years Ago
        @Dan Frederiksen
        Engineering an aircraft is much more involved than you seem to think.... Electric motors have a nice torque curve, but real ones don't match the ideal-torque model that a lot of blog readers and writers use when discussing motors, so the gearing probably does put the electric motor into a sweet spot, or it carries the forward-force of the propeller better than the motor itself. Aero guys would go direct drive whenever they can, because the weight of the gearbox that far ahead of the CG has a big effect on the aircraft. Anyway, please please please talk to a real aero engineer before you "go gearless". There is a lot to think about. I wouldn't have pegged an aircraft is an application for a serial hybrid, either, because the engine runs at 60%+ power for almost the entire flight. But Wankels are compelling for aviation because of their light weight, but they like to spin fast and general aviation propellers like to spin around 1500-2300rpm (to avoid the tips of the propeller going transonic, and the bigger the prop the slower it turns, and wrapping a shroud around a conventional GA prop isn't full real solution) -- so this system probably was intended to be a Wankel transmission with a little extra oomph for climbout. But, seriously, I ready your comments here every day and I wouldn't fly in an aircraft that you built with your arm-chair engineering.
        • 3 Years Ago
        @Dan Frederiksen
        Side by side isn't necessarily an issue. Granted, that machine probably doesn't achieve a truly laminar air flow, but a wider aircraft with a laminar flow or very close to it will be more efficient than a narrow, tandem seating arrangement if there is too much drag due to a non-laminar flow of air around the plane.
        BipDBo
        • 3 Years Ago
        @Dan Frederiksen
        Actually, a ducted fan is less efficient than an open propeller. The advantage of eliminating tip vortices is outweighed by the drag caused by the duct housing. A typical jet liner uses a turbo fan engine; a jet engine that drives a ducted fan. About 90% of the thrust comes from the fan. Only a small portion of thrust comes from the combustion chamber. The ducted fan housing has 2 purposes. The first is to reduce nooise since many commercial airports are surrounded by neighborhoods. The second purpose is to allow the aircraft to fly at near sonic speed. At these high speeds, the tips of the spinning turbine blades are actually traveling above the speed of sound. Without the fan housing, this would create shock waves. Even on jets as fast as the supersonic SR-71, the fan housing expands the airstream to slow the intake air down to subsonic speeds before it hits the turbine. The most efficient aircraft engine that I know of is the turboprop, which is a jet engine that powers a propeller with variable pitch blades. It is slower and noisier than a turbofan, but very reliable and efficient. My father served in the Coast Guard as a mechanic who maintaned these engines. I have many happy memories playing in the aircraft hangar and in the shop, my dad explaining to me the purpose of all the bits and pieces of these wonderful machines. I think that my love of machines was cultivated in that shop. Anyway, a lot of research is currently taking place to build a "open rotor" jet, which is essentially turbo prop engine that offers the speed and low noise of current turbo fans, but up to 30% improved fuel efficiency.
          BipDBo
          • 3 Years Ago
          @BipDBo
          I'm no NASA engineer, but if we are talking about whom we know, I guess I can say that many of my college professors were former NASA engineers. Even though my degree was in mechanical engineering, I did a lot of research into aerodynamics, mostly in airfoils. I've also done a bit of reading on the subject of aircraft propulsion. To be fair, ducted fans are more efficient in certain applications, but not generally for forward thrust of low speed aircraft. For one, a ducted fan is better for near sonic speeds as I previously stated. Another example is this 'hoverbike": http://www.autoblog.com/2011/06/10/hoverbike-concept-combines-motorcycle-with-helicopter-w-video/ The first reason a ducted design wins on the hoverbike is that the rotor housing does not induce much drag because it is not traveling through the air at high speed. The second reason, is that this design requires two small diameter rotors. Two much larger, inline, counter rotating, overhead rotors for this hoverbike would be much more efficient, but then it would just be a tail-less helicopter. It is not only important to define the application, but also to define what you are holding constant when comparing your apple to your orange. When given a limited diameter, a ducted fan will be more efficient under many conditions. To a point, the larger the diameter of a propeller, the more efficient it will be, increasingly so the lower the speed. A helicopter has a maximally sized main rotor in order to maximize efficiency. For the same reason, a prop plane has tall landing gear and a high propeller driveshaft to allow for a very large propeller diameter. When the weight of the entire assembly is constant, an open propeller will generally win out because it can have a large diameter and remain light weight. Aside from all of this, a ducted fan on a single engine pull prop plane would create quite a visual obstruction. Run this by your NASA bud. I'd like to know if I have the wrong understanding on the subject.
          Dan Frederiksen
          • 3 Years Ago
          @BipDBo
          I have it on decent authority that a ducted fan is more efficient. a nasa guy developing concept planes. what's your source?
      • 3 Years Ago
      My make sense for possibly reducing noise around some airports.
      • 3 Years Ago
      I'm no expert, so I could be completely wrong about this, but here goes: 1. with a multi-cylinder engine, you have alot of moving parts - but if a part fails, the other cylinders continue to work. 2. with a wankel engine, you have very few moving parts , but each of them is absolutely vital - if a part fails, the engine dies. This isn't something you want to happen in midair.
        • 1 Year Ago
        And in Fact - I have driven an RX7 - With Aftermarket Turbo - which after 3 months and 30,000 hard driven Kms (20,000 miles) roasted the Apex Seals - (the flat bars at the tips of the three points of the Rotor) and they warped, then one broke. the biggest problem - was that idle or minimum RPM went up from 500 - 700 RPM - to 2500 RPM - Meaning - it took that much power to keep it running. True - it was a 2-rotor variant - but it also was the old 12A Model - not as strong as current designs. In loosing the Apex Seal - I effectively lost 2 complete Combustion Spaces. Try and keep your usual V6 Running after loosing all compression and breaking the rings on 2 pistons side-by-side! As found on the website for Austro Engine - the unit is a Single Rotor Wankel - so it might not have the same failure mode survival as mine did - but also - I am sure that the little 40.4 kW Engine - is not being pushed as hard as mine was - since I had the added turbo that bumped up the factory 100 Hp to 205 Hp - which was used a lot more than just for Sunday drives - but a few of them too, along with Mostly Mountain Driving on twisty two-lane roads, when not on the Freeway!
        • 3 Years Ago
        In practice, that may not be as much of an argument as you might like. 1. If a critical part of a standard aviation piston engine fails, the whole engine quits operating. If you're lucky, you might get partial power for a while. 2. There are a lot more parts to fail in a conventional engine. Corollary: Two engines are not more reliable than one, in actual practice. 3. In the system described in the article, the wankel engine's failure doesn't mean that the prop stops spinning immediately. You may have several minutes to land at a nearby airport or, at worst, several more minutes to choose a spot on which to land.
      goodoldgorr
      • 3 Years Ago
      That seem to be a very efficient electric generator.
      fly by wireless
      • 3 Years Ago
      I've been mulling something like this since last year, but this configuration. What I've been thinking about is having 2 engines as generators and 1 or more electric motor driven props. This would open up SOOOOO many possibilities in aircraft design because the engine placement (heaviest single part) dictates your design. Now you can put the engine(s) in far more possible places in the craft since the actual propulsion can be done elsewhere. I'd soooo love to see a Eurofighter-like light plane with its engine amidships and the prop in the back! I see great things coming out of this development!
      goodoldgorr
      • 3 Years Ago
      That seam to be an efficient electric generator.
      Dan Frederiksen
      • 3 Years Ago
      the way you can know I'm smarter than you is that I would have considered the irony that you aren't an aircraft engineer either yet you correct me. please please please think a little.
      Rotation
      • 3 Years Ago
      I don't see why the CO2 from air traffic is brought up here. Most of that CO2 comes from commercial flights. This system is not going to replace jet engines mounted under a wing, so it isn't going to affect commercial flights. You're not going to save fuel by burning it in an ICE, generating electricity and then driving props/fans with that electricity versus burning in a jet engine and producing thrust and shaft output driving a front fan producing more thrust. Maybe if this used a fuel cell instead of an ICE it could be more efficient? Then it could perhaps compete with a jet?
        • 3 Years Ago
        @Rotation
        Because "lowering CO2" is like an invocation or prayer in the Green Religion. Like saying "Peace be upon him" whenever your say Muhammad. It doesn't make any sense, but if you don't say it your coreligionists get offended.
        • 3 Years Ago
        @Rotation
        It won't compete with jet engines, because the fixed-pitch propeller on the front of this aircraft is the wrong tool for going fast. It's the right tool for a small general aviation aircraft (which has a lot of uses), but going over about 140mph isn't one of those uses.
      A3TDI
      • 3 Years Ago
      Interesting. Two observations: wankels aren't known for great economy; is it used for their lighter weight or do they have a economical sweet-spot at cruise (e.g. diesels)? Reductions are great in concept, but are common points of failure and require aggressive inspection to keep maintained down later in life (often not done). This one looks like a beefy belt; wondering if TBO has improved on these?
        Chris M
        • 3 Years Ago
        @A3TDI
        All internal combustion engines have an optimal speed for efficiency, including Wankels, but even at the optimal speed, efficiency of Wankels is less than for piston engines at their optimal speed. I suspect that the savings in weight might make up for the lower efficiency, though.
      Dan Frederiksen
      • 3 Years Ago
      I'd probably also go gearless for the motor. should be some percent to gain there
      Levine Levine
      • 3 Years Ago
      It's really cold even at 10,000 feet. Battery power is almost useless.
        Chris M
        • 3 Years Ago
        @Levine Levine
        I rather suspect that they don't put the battery outside the plane where it would be exposed to such cold. With a little insulation, there are places inside the fuselage that stay quite warm even at that altitude.
        montoym
        • 3 Years Ago
        @Levine Levine
        I agree with the other comments here as well but also add that the batteries are only used for take off and climb out. So, by the time the cold has gotten to the batteries, they are well past the point of being needed during that flight anyhow and they are just being recharged. Also, being someone who lives at over 6,000ft and spends a lot of time at 10k ft and above(not even counting the times I've been in a non-commercial plane), I can tell you that 10k ft isn't really an elevation where temperature is a problem. The typical equation for figuring temperature differences is about 3.5 degrees F per 1000ft in elevation change. So, if it's 90F at sea level, you'd figure about 55F at 10k ft, not really a big deal. It's once you get into much higher elevations that you start to run into sub-zero temps pretty much all the time. Higher elevations than planes like this are meant to be flown in. Looking up the specs for the HK36 Super Dimona, it seems to have a ceiling of 17k ft (for the 115hp turbocharged model). It might be even lower for the non-turbo model due to the air density differences at higher altitudes, I don't know though based on the info I found online. Either way, this isn't a plane that's going to be spending a lot of time at high altitudes. Check out the website for the NOAA's Aviation Weather and look over the Temps Aloft section. They give temps as Celsius so some conversion is required, but it will help to show you that the temps don't really dip into really low territory until you get around 18k ft and above or so. http://aviationweather.gov/adds/winds/
        GoodCheer
        • 3 Years Ago
        @Levine Levine
        "cuts fuel consumption and emissions by 25 percent" But never mind measured results. I'm sure you're right.
        • 3 Years Ago
        @Levine Levine
        In practice, heat rejection is by far a greater problem than excessive coolth in aircraft operations. Given Wankel's fairly hot operating exhaust, routing a bit past the batteries should be more than enough to keep them happily warm. In fact, you'd want to be able to route the exhaust away if they get too warm. Not that 10,000' is all that cold. Adiabatic lapse rate (depending on humidity) runs betwee about 2.5 to 5 degrees F/1000'. So subtract 25F to 50F from sea level temperature at 10,000'. It's not all that cold.
        • 3 Years Ago
        @Levine Levine
        Have you ever been to 10,000 feet? The temperature really depends on the day. If it's a hot day, 10,000 feet is usually comfortably cool. I think you're confusing 10,000 feet with FL40.... Also, batteries don't become useless with cold -- they're just not as good.
      Roy_H
      • 3 Years Ago
      Doesn't make much sense to me. Hybrids work well for cars especially in stop-and-go traffic. Airplane engines run at almost constant speed, so no gain by going through the generator/motor transformation. They said this allowed the motor to run slower, surely a simple planetary gear would be more efficient?
        erhcanadian
        • 3 Years Ago
        @Roy_H
        An airplane needs more power to take off than during flight. A single engine airplane might need 175hp for 1 minute, and 75hp for 59 minutes. If a hybrid system can provide a boost for just a minute of two during takeoff, the airplane could use a much smaller and more efficient ICE engine!
          • 3 Years Ago
          @erhcanadian
          Good point. But, efficiency cruise is usually around 60% power for Cessnas and Pipers -- though it depends on the aircraft, and the pilot's patience. The highest efficiency is right around best-glide speed (obviously), but most people don't get in an airplane to go 60-70mph In your example, you'd likely need 175hp for 5-10 minutes, 105hp for 3 hours 15 minutes, and then 40hp for 5-10 minutes. I agree with your major point, I'm just quibbling with your numbers a bit. :-)
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