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EADS Concept Diesel-Electric Hybrid Helicopter Features EcoMotors OPOC Engines; Up to 50% Less Fuel Consumption Than Conventional Twin-Turbine Helicopter

The hybrid helicopter concept. Click to enlarge.

EADS Innovation Works is presenting a concept helicopter with a diesel-electric hybrid propulsion system at the ILA Berlin Airshow 2010, 8-13 June.

The diesel-electric hybrid concept is one of the projects grouped under the name of eCO2avia by EADS Innovation Works. Highly efficient electrical motors driving the rotors, combined with OPOC (Opposed Piston, Opposed Cylinder) diesel engines (earlier post), reduce fuel consumption and emissions by up to 50% relative to a conventional twin-turbine powered helicopter.

The main components of this hybrid system are multiple diesel-electric motor-generator units, a pair of high-performance batteries and a power electronics unit controlling the energy flows for best efficiency. The OPOC diesel engines, designed and built by EcoMotors International in the US, offer a fuel economy improvement of up to 30% compared to today’s helicopter turbine engines.

The OPOC engine is a two-stroke turbocharged diesel engine in which the intake and exhaust ports are at opposite ends of the cylinders. As the pistons move, the exhaust slits are open before the intakes and turbochargers blow air through the cylinders to push out the exhaust gas and fill them with clean air. Since the engine needs positive pressure to do this, the turbochargers have electric motors to power them at low rpm when exhaust energy is low.

The pistons are connected to a short crankshaft, located between the two opposed cylinders. The volume formed between the two opposed pistons is the combustion chamber. These design features are the key to an OPOC engine’s power-to-weight ratio being as high as 2 kW/kg.

The OPOC engine’s power output shafts are fitted with advanced, weight-optimized generators delivering electrical current to a power electronics unit, which manages the distribution of the electricity to the electrical motors driving the main rotor and the tail rotor as well as the other user systems on the helicopter.

The speeds of the electric motors driving the rotors can be adjusted individually and controlled for best efficiency. The multiple OPOC engines run at their most fuel-efficient operating point during the cruise phase.

The batteries can store sufficient energy to enable the helicopter to take off and climb or approach and land on electrical power alone. For flight safety reasons, the OPOC engines run at idle during these phases of the flight.

Several different kinds of combustion engines could be integrated into such a hybrid system, EADS notes.

A tilting main rotor enables the helicopter’s fuselage to remain at its optimum alignment with the airstream, minimizing aerodynamic drag and thereby reducing the power demand and the fuel consumption.

Running on biofuel made from algae (another eCO2avia project), the amount of carbon dioxide released during flight is about equivalent to the amount absorbed by the algae during their growth phase, EADS says. This, the company says, opens up the possibility of carbon-neutral flights.

The engines also emit up to 40% less NOx and very small amounts of sulphur oxides (ca. 10 ppm vs. 600 ppm for normal Jet A1 fuel/kerosene), due to the very low nitrogen and sulphur content of the biofuel compared with fossil fuel.

Several different kinds of combustion engines could be integrated into such a hybrid system, EADS notes.



Have they also found a way to reduce the ICE noise and vibration level?


Why Hybridize? There will be no stop-start or regenerative braking so you don't gain the traditional car hybrid advantages. I would have thought the load would have been in a narrow enough range for a helicopter so that you could get away with an ICE and a single-speed gearbox. So why hybridize?

Herm Perez

There should not be much vibration with an OPOC.. instead of a heli I would like to see this in light duty pick up trucks.

Nothing is going to beat the lightness of a turbine.


This makes a funky kind of sense. These OPOC engines, on paper, are incredibly efficient gen sets. I agree, I'd like to see them as gensets in medium duty serial PHEVs, but hey, if this gets them more research attention, that's probably good.


Seems like a daft idea. Love to know the power/weight ratio of this thing. Seems fairly space inneficient too judging from the pic. Except for a very narrow military requirement of low noise (on pure electric power) I can't see this as at all viable.

Roger Pham

This opens up the question of serial hybrid or parallel hybrid?
The serial gas electric hybrid that they are proposing will be way too heavy and inefficient to implement. Having a large electric motor, generator, power controller will take up too much weight.

However, imagine a kind of hybrid like the Toyota HSD, which functions like a CVT using electric motors, in which the weight of electric motor, generator and power electronics will be cut to half.

Why hybridize helicopters? Because the rotor needs to turn faster in high speed flight and can turn slower in hovering or low speed flight to conserve power. Rigid rotor design can allows variable rotor speed without the inherent vibration problem associated with articulated rotors.
The energy stored in the battery will greatly facilitate autorotation in case of engine failure, making the helicopter much safer. This allows single engine helicopter to be just as safe as a twin-engine helicopter at lower cost and higher fuel efficiency.

A more fuel-efficiency aircraft will carry less fuel, permitting more payload.


"EADS Concept Diesel-Electric Hybrid Helicopter Features EcoMotors OPOC Engines; Up to 50% Less Fuel Consumption Than Conventional Twin-Turbine Helicopter" sounds worth flying.


Toyota HSD would suck in this application. Very low specific power of the ICE (due to the Atkinson cycle), a power split transmission and two electric machines. It sounds very heavy to me. Eventually, a helicopter is probably not the best application for a diesel engine. A long-distance aircraft would be a better application, since the engine weight penalty could be offset by less fuel load. But, to make this happen, we would need a well-developed propfan too that would enable cruising speeds similar to jet planes.


electric motors need not be very heavy. The 280 HP Tesla motor weighs just 70 pounds.

Roger Pham

Who is saying anything about Atkinson cycle engine? The engine used here is OPOC, a relatively light-weight two-cycle engine. It's just that the transmission will be electrical CVT to reduce fuel consumption. All helicopters have transmission already, albeit a single-speed transmission (gear reduction unit). A significant part of the helicopter gross weight will be fuel weight. Reduction in fuel weight will allow for higher power propulsion weight.



You are incorrect. You can recover most of the accent energy on decent. This was proven in a recent hyrid experiment aircraft. For short hops that could be a huge fuel savings.


If you save 30% in fuel, that makes up for the heavier engine/genset. Direct drive the rotor and get rid of the transmission, even more weight saved and safer too. Rotor speeds were quoted backwards, you want slower rotor speeds for high speed forward flight, the tip speed of the advancing rotor blade is a major part of a helicopter speed limitation. With a tilting motor/mast and rotor system, they may be able to get rid of the articulation. No gear box needed for the tail rotor, just a good motor and fly by wire, maybe double windings and inverter boxes for redundancy, helicopters can land without a tailrotor as long as they have forward speed. When I first read the title I thought this was another dumb idea, but with all the flapping bits and gear train on a normal helicopter that are critical to flight safety, a tilting electric motor with a battery backup sounds like it could work...

Roger Pham

Remember the "retreating blade stall" phenomenon? This happens when the helicopter flies fast enough that the retreating blade can no longer produce enough lift to sustain the aircraft. This will make the nose of the copter pitch up, the copter will slow down and the retreating blade will again have enough airspeed to sustain the aircraft. To fly fast in a copter, the blades' rotational speeds must be fast enough that the retreating blade has enough airspeed.

A gear reduction unit will always be needed, since the main rotor turns so much slower than any possible motor or engine.

Tilting the mast is only to keep the body aligned with the wind to reduce drag. This has nothing to do with the articulation of the main blades. Even with rigid rotors, the blade or the blade root must flex in respond to changing forces. This is accomplished by elastomeric bearings in modern multi-bladed helicopters instead of fully-articulated couplings of earlier era.

Gear box for the tail rotor is still a much lighter and lower-cost method for transmission of power from the engine.

Herm Perez

perhaps an application for a small tilt rotor similar to the V22 Osprey, the electric setup would simplify the transmissions. Something like the helicopters in the movie Avatar. This would give a you the high speed advantages of a tilt rotor without the complexities of dual turbines and transmissions in a small heli.. but electric motors and generators are still heavier than a transmission.


I once read that the OPOC engine will be 45% more efficient in a class 8 trucks than a conventional engine.Since those trucks are diesel, so the claim is that OPOC engine is 45% more fuel efficient than the diesel in those trucks. Assuming those engines are 25% efficient ,that will make OPOC 70% fuel efficient.Now, in this article, an OPOC hybrid would be 50% more fuel efficient than a normal twin rotor turbine ,and a non hybrid version would be 30% more efficient than an helicopter turbine engine. The way they throw around words like 45% more ,50% greater just doesn't make any sense to me;The simple reason is this ,45% more, 50% greater would mean that this OPOC stuff is between 70% to 90% fuel efficient,and to me that is total crap.I would be amazed if at the end the engine gets 15% better mileage than a normal diesel engine.


Ben: Correct me if I'm wrong but if you increase the efficiency a vehicle with 25% fuel efficiency by 45% it will only reach 36.24% efficiency (25% x 1.45 = 36.24%. That's a long way from 70%.

Very few ICE vehicles have reached 45% in regular use.


HarveyD: You are totally right if we were talking about 25% efficiency .Advanced diesel are about 52% efficient,so if you improve that by 45% ,we get an engine which is 75.4% efficient.


Going to have to brush up on my cyclic and collective.


Ben: entropy increases in combustion don't allow that; there is an irreducible minimum of waste heat from the engine due to the chemical processes.

I'm skeptical about the usefulness of electric drive for the main rotor. It's just added weight, and another point of failure. Using twin OPOC engines with a redundant mechanical drive would appear to offer more fail-safes.


Ben: I have to agree with you that the newest slow speed very large marine diesel can be 47.6% to 52.6% efficient under ideal conditions. (between 160 to 160 g/Kwh). However, under operational conditions they rarely do more than 45% because it is very difficult to keep them operating at their ideal sweet spot for long periods of time.

Assuming that 45% is possible (occasionally) in a heavy truck, increasing that efficiency by 45% = (45 x 1.45 = 65.25%). That would happen only when the heavy truck is operating at the engine sweet spot, about 30% of the time. However, even 50% to 60% would be much better than the 30% that most diesel trucks are currently getting.

Roger Pham

My calculation reveals that the most OPOC can improve on peak BTE (break thermal efficiency)is around 20-23%, or 1/2 of what they are claiming of 45%.

However, in part-load when the modular OPOC engine can deactivate 1/2 of its two modules, thereby totally eliminating the friction there altogether, the part-load efficiency of a typical heavy-duty turbocharged diesel engine at 30%-35% perhaps may be improved by 45% to around 43%-50% BTE with turbocharging and some turbo-compounding when running at its peak BTE, now that the active module is running at its peak efficiency spot. Perhaps this is where the 45% gain in efficiency comes in. Quite feasible.

Henry Gibson

The main advantage of an electric transmission is full power from the engine at any time it is needed at any aircraft speed or propeller speed. Another advantage is operating at maximum engine efficiency at any aircraft speed. The propellers can also operate at the highest design thrust at any engine speed if the power is available and also at the most efficient thrust. There is no reason for any battery in the main power circuit of such an aircraft. Multiple OPOCs even of different sizes or even a turbine generator for very high power low weight are more suited to flight than a battery.

Model aircraft are now using many electric motors, and I have been trying to promote a hybrid electric model for many years. The large IC engines now used in model aircraft would be suited for a tiny emergency range extender for an electric automobile of any size. You would be surprized how much faster one horsepower is than walking even in a large electric car. One horsepower is good enough for a constant five miles an hour or more in an electrically operated PRIUS. The Tesla may do a little better.

The electro-turbo-supercharger gives very high power density to this engine that I have been mentioning for years for use a range extender in electric cars, and it also gives very quick power response. The electric part of it can be used as a generator to put more power into the propellers when available, and conversely power can be robbed from the propeller to accelerate the turbo for more power. There is no limit to the supercharging of a diesel engine except the need for cooling.

The lightest weight motor/generator that can be made is a switched reluctance machine, and it does not use any moving magnets or moving conductors. It has high redundantcy and is already being used where reliable motors are used in aircraft. The switching semiconductor circuits are simple and thus more reliable. and they can be made redundant. Such motors can also continue to operate at lower power with a failure of one or more phases, and a shorted winding will not burn up the motor. ..HG..

Henry Gibson

The use of a turbo-electric-supercharged diesel engine means that there is a very high altitude limit to this aircraft in conjunction with a longer range. ..HG..


Replacing, in the above application, the OPOC engine with the pattakon OPRE engine, everything improves.

The OPRE with two counter-rotating electric generators is not only absolutely rid of inertia vibrations (like a Wankel rotary engine), but it is also absolutely rid of combustion vibrations (torques) on its mounts.
In the case of the OPOC or of the Wankel electric generator set (or range extender), each combustion-expansion creates a strong pair of forces on the engine mounts.

The OPRE has extended piston dwell at the combustion dead center - some 20% as compared to the OPOC - which means higher revs and higher power density. It also means improved fuel efficiency at specific revs because of the additional available time for the injection and the combustion of the fuel at high “compression” conditions.

The multiple modules is applicable to OPRE too.

The lubrication and reliability of the OPRE are better because the thrust loads are taken away from the hot cylinder walls and away from the ports. In comparison, the lubrication of the skirt of the inner exhaust piston of the OPOC is anything but easy or efficient (the piston skirt abuts on the hot cylinder, onto the bridges among the exhaust ports, oil is lost at the exhaust etc).

The synchronizing mechanism between the two crankshafts of the OPRE remains completely unloaded in application of divided load, like the electric generation set.

Yet, in case the two crankshafts of OPRE seem as a disadvantage, the PatOP engine, which is the single crankshaft version of the OPRE, is the next reasonable selection (opposed-piston, single-crankshaft, single-cylinder, full balance of inertia forces and moments, extended piston dwell etc ect).

For more, take a look at web site.

Manousos Pattakos

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