Aircraft

NASA harvests slow moving air to increase next-gen aircraft efficiency

Artist's rendering of NASA’s concept aircraft, STARC-ABL, which utilizes advanced propulsion technologies to decrease fuel usage, emissions and noise
Artist's rendering of NASA’s concept aircraft, STARC-ABL, which utilizes advanced propulsion technologies to decrease fuel usage, emissions and noise
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Artist's rendering of NASA’s concept aircraft, STARC-ABL, which utilizes advanced propulsion technologies to decrease fuel usage, emissions and noise
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Artist's rendering of NASA’s concept aircraft, STARC-ABL, which utilizes advanced propulsion technologies to decrease fuel usage, emissions and noise

As part of its New Aviation Horizons initiative, NASA is developing a series of new X-planes that include one concept that uses the air flowing along the fuselage to reduce fuel consumption. The Single-aisle Turboelectric AiRCraft with an Aft Boundary-Layer (STARC-ABL) propulsor harvests a jet airliner's boundary layer to provide more thrust with a 10 percent increase in efficiency.

The Aviation Horizons initiative is intended to study a number of ideas for the next generation of commercial aircraft, including a quieter supersonic passenger plane, blended wing designs, and new, more efficient, greener propulsion systems. Among these is the STARC-ABL concept being developed by Jim Felder and Jason Welstead at NASA's Glenn Research Center in Cleveland, which is an advanced turboelectric configuration that combines turbofan jets with a boundary-layer ingesting (BLI) engine that encircles the stern of the aircraft fuselage.

In a conventional aircraft, the boundary layer is a cocoon of slow-moving air that clings to and flows along the fuselage. Though this does help to reduce friction, as it flows off the rear of the aircraft, the boundary layer breaks up into turbulence. In the STARC-ABL concept, the BLI engine is a giant ducted fan that encircles the stern of the fuselage while the aft control surfaces are moved to a top of the T-shaped empennage. As the boundary layer flows backward, the fan collects it, accelerates the air, and turns it into thrust.

To power the fan, the 737-like aircraft has two slightly smaller underwing engines that not only provide thrust, but also about 3 megawatts of electricity for the BLI engine as well as the other flight subsystems. The BLI provides 20 percent of takeoff power and 45 percent of cruising power. Despite its weight and the need for the other two engines to power it, NASA says the BLI may improve fuel efficiency by 10 percent.

Currently, NASA engineers are working on the STARC-ABL's aerodynamic efficiency, engine optimization, weight compensation, and safety and operational requirements. If the project goes as scheduled, a subscale STARC-ABL concept will undergo initial ground tests at the space agency's Electric Aircraft Testbed (NEAT) at Plum Brook Station in Sandusky, Ohio.

Meanwhile, other X-plane configurations will be explored as part of a year-long study to create a next-generation, hybrid or turboelectric aircraft concept that could fly within 20 years that uses less fuel while generating less noise and fewer emissions.

"During the 12-month cycle, we'll work with the teams to take a deep dive into their hybrid and turboelectric aircraft concepts," says Amy Jankovsky, NASA's AATT subproject manager. "These concepts will provide in-depth, detailed analyses of the propulsion and electrical systems, and we will recommend technology development paths for their concepts."

The video below shows how the BLI works.

Source: NASA

STARC-ABL Animation

7 comments
myale
So if you lose an engine you lose thrust from it and you lose the generation capacity which drives the rear engine so you lose thrust from this also - so assume there will be excess capacity to pick up an engine loss - which larger engines can do.
EH
It's an eminently workable idea which could be retrofitted to existing models. The ducted fan uses air that has been pulled up closer to the aircraft's speed by drag against the fuselage, so requires less energy to push out the back, thus saving fuel. Turbine engines have trouble handing the turbulence in the boundary layer, ducted fans do not. It should be reversible as well, making an excellent air-brake usable at any speed, which most air-brakes / thrust reversers cannot. Keeping the traditional empennage may not be needed, with a larger fan the control surfaces could be integrated with the duct and still have lower drag than the traditional layout plus the fan size shown.
CraigAllenCorson
"about 3 megawatts of electricity" Seriously? Three MEGAwatts? I think somebody has misplaced a decimal. If not, then we need to fly one of these things to Puerto Rico immediately, get that island back up and running again.
Don Duncan
Could this rear fan work on a car?
Craig Jennings
3 megawatts is only ~4000 hp Mr Corson. Not much vs 70-80 tonne of plane :)
MD
Hybrid Aircraft here we come.. So the Under wing units are to be "optimised" for 2 regimes, Takeoff power and in-flight Electricity generation (while supplying ~28% of cruise thrust each.) The tail unit, boundary layer Ingester is one example of a distributed thrust system. It may even be able (should) to regenerate to appease those wanting all passenger aircraft to fly noise abatement approaches. Just where to store all those regenerated Joules becomes an Engineering problem to solve. (humungous bank of SuperCaps, ready charged for the next takeoff in 1 hour. something like 12GJ of energy need to be stored - 2MW over 10 minutes ("conservatively" _only_ need ~20000F at 1000V, I think this well exceeds any storage capacitor bank EVER made) Please correct any errors in my "back of napkin calculation".
over_there
It looks like it was made purely to satisfy the requirments of funding for a hybrid aircraft. wouldnt you just put another jet engine back there. Heaps of turbine engine operate in turbualance think about helicopters and you can put fans on them.
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