The Future of Flight: Hybrid-Electric VTOL Aircraft

nasa-greased-lightning-10-foot-drone-640x480It may look like something a dedicated hobbyist built, and sound like something cheekily named, but NASA’s new electrical vertical take-off and landing (VTOL) machine is a very serious venture. Known as the GL-10 Greased Lightning, this unmanned hybrid-electric aircraft is the agency’s proposal for a vehicle that one day replace the reigning champion of VTOL – the helicopter.


The G-10 is in part the result of the recent strides made in electric propulsion, which is made possible thanks to the growing power and energy density of batteries allows for some very efficient hybrid-electric aircraft designs. With eight prop engines mounted on the two main wings and another two mounted on the tail, the vehicle swivels them into vertical position for takeoff and landing, and then horizontal for conventional flight.

nasa-greased-lightning-prototype1While it’s not particularly hard to create an aircraft capable of VTOL, it has so far proven to be very tough to create an aircraft that can also efficiently cruise through the air after taking off vertically. The helicopter is the only common example of a VTOL aircraft that can also cruise acceptably, but at a cost. Compared to other aircraft, an everyday helicopter has a much lower-lift-drag ratio, which means it burns more fuel, has less range and can carry less weight.

However, electric propulsion allows for much more efficient designs, since vehicles no longer have to accommodate large fossil fuel-powered engines or manage the mechanical stress across the airframe. Instead, they can rely on smaller, more efficient, optimally placed electric motors, and without the mechanical complexity of big jet engines, it suddenly becomes a lot easier to have wings and propellers that can swivel between horizontal and vertical. pure-electric aircraft do exist – in the form of quadcopters – hybrid-electric designs with longer range are generally of more interest to military and commercial groups. In the case of NASA’s Greased Lightning, there are two small diesel engines in the body of the aircraft that turn electric alternators that constantly recharge the lithium batteries. This theoretically gives the GL-10 the same range and duration as a modern plane alongside its VTOL capability.

Interestingly, NASA also says that such a hybrid-electric design is “scale free” — meaning the same principles could be used to revolutionize everything from helicopters, to military UAVs, to massive jetliners. Much like hybrid-electric cars, the concept is set to revolutionize an entire fleet of aircraft designs that could be far more efficient than they currently are. One party who is sure to be interested in the possibilities is the US military, with its ever growing fleet of UAVs.

For now, Greased Lightning only has a wingspan of 3 meters (10 feet), and on its first test flight  – which took place on National Aviation Day, August 19 – it was tethered. Untethered flights are planned for later in the year, an event which is sure to be a media sensation and produce some viral videos!




The Future of Flight: Morphing Wings

morphing-wingsSince the Wright Brothers developed the world’s first airplane, scientists and aerospace engineers have understood how important airflaps and wing design are to ensuring that a plane is able to achieve lift and land safely. During and after World War II, additional lessons were learned, where the sweep of a wing was found to be central to a plane achieving higher service ceilings and air speed velocities.

Since that time, many notable improvements have been made, but some strictures have remained the same. For example, conventional wings suffer from the problem of being fixed in a single position, which makes some aspects of performance possible but other things extremely difficult. In addition, flaps have remained virtually unchanged over the years, relying on hinged joints that are limited and vulnerable.

flexfoilIn both cases, the answer may lie in flexible and seamless materials, leading to wings that can change shape as needed. Such technology could not only enable better performance, but remove the need for hinges and gears. Towards this end, Michigan-based FlexSys has developed a way to optimize wing aerodynamics with FlexFoil, a seamless variable geometry airfoil system.

In development since 2001, FlexFoil is made from what is described only as “aerospace materials,” and is seamlessly integrated into the trailing edge of the wing. Based on a technology known as “distributed compliance,” the morphing structure integrates actuators and sensors that, according to Flexsys, results in “large deformations in shape morphing with very small strains.”

flexfoil1According to a 2006 paper co-written by mechanical engineer Dr. Sridhar Kota (the FlexFoil’s inventor), the foils are:

optimized to resist deflection under significant external aerodynamic loading and are just as stiff and strong as a conventional flap.

What this translates to in real terms is a tolerance of over 4500 kg (10,000 lbs) in air loads and the ability to distribute pressure more evenly throughout the wing, resulting in less strain in any one area. It is also said to reduce wind noise by up to 40 percent on landing, and to lessen build-up of both ice and debris. But the biggest benefit comes in terms of fuel economy.

flexfoil2When retrofitted onto a wing, FlexFoil can reduce fuel consumption by a claimed 4 to 8 percent, with that number climbing to 12 percent for those wings that are built are the system. What’s more, the technology could be applied to anything that moves relative to a fluid medium, including things like helicopter rotor blades, wind turbine blades, boat rudders, or pump impellers.

FlexFoil was officially introduced to the public this week at the AIAA (American Institute of Aeronautics and Astronautics) SciTech exposition in Washington, DC. Plans call for flight tests to be performed this July at NASA’s Dryden Flight Research Center, where the flaps of a Gulfstream business jet will be replaced with the foils.

Check out this video of the airwing design and what it does here:

morphing-wings1To be fair, this is not the only case of flexible, morphing aircraft in development right now. In fact, NASA has been looking to create a morphing aircraft concept ever since 2001. So far, this has included collaborating with Boeing and the U.S. Air Force to create the Active Aeroelastic Wing (AAW) which was fitted to the F/A-18 Hornet, a multirole combat jet in use with the USAF.

But looking long-term, NASA hopes to create a design for a morphing airplane (pictured above). Known as the 21st Century Aerospace Vehicle, and sometimes nicknamed the Morphing Airplane, the concept includes a variety of smart technologies that could enable inflight configuration changes for optimum flight characteristics, and is an example of biomimetic technology.

morphing-wings2In this case, the biological design being mimicked is that of a bird. Through the use of smart materials that are flexible and can change their shape on command, the 21st Century Aerospace Vehicle is able to shape its wings by extending the tips out and slightly upward to give it optimal lift capability. In this configuration, the inspiration for the aircraft’s wings is most clear (pictured above).

But once airborne, the aircraft needs a wing that is capable of producing less wind resistance while still maintaining lift. This is why the wings, upon reaching and service ceilings in excess of 3000 meters (10,000 feet), the wings then contract inward and sweep back to minimize drag and increase airspeed velocity.
Though this program has yet to bear fruit, it is an exciting proposal, and provides a glimpse of the future.

Be sure to check out NASA’s video of the CAV too, and keep your eyes on the skies. Chances are, jets that utilize smart, morphing surfaces are going to be there soon!