The Woracle

Business jets have them, more airliners are getting them, now the US National Research Council says the US Air Force's KC-135 and KC-10 tankers would benefit from them. Developed by NASA in the 1970s, winglets are becoming a hot item in the hunt for fuel savings.

An NRC committee was asked by the USAF to look at its inventory and identify which aircraft might be good candidates for drag-reducing winglets. The committee evaluated the fleets that burned the most fuel - in decreasing order the C-17, KC-135, C-5, KC-10 and C-130 - and ranked them in terms of priority and potential benefit from wingtip modifications. The KC-10 and KC-135 were ranked "high", the C-5 "medium" and the C-130 "low".

Surprisingly the C-17, which already has winglets, gets a relatively positive "medium/low" ranking - because the committee believes it should be possible to design a better wingtip these days.

The USAF's next tanker? (NASA photo)

Cirrus Design, maker of the popular SR22 piston single, has taken the wraps off its first jet - which it calls simply "the-jet" - and Flight correspondent Jeff Decker was there. We have all been wondering where the single Williams turbofan would be located - in the fuselage, like Diamond's D-Jet, or at the base of the fin, DC-10-style, like the Piper Jet?

Well it seems the designers looked elsewhere for inspiration. Cirrus chief executive and co-founder Alan Klapmeier gives a nod to Northrop's iconic V-tailed Global Hawk UAV - but I see echoes of Heinkel's He162 , a German single-engine jet fighter that emerged late in the Second World War. Sometimes referred to as the Salamander, the He162 was called the Volksjaeger, or "People's Fighter", because it was designed to be simple, cheap and easy to build in large numbers.

Well "the-jet" is designed to be easy for an owner to fly (more a jet-powered SR22 than a small business jet), at "around $1 million" is relatively affordable in aircraft terms and Cirrus is hoping to build them by the hundreds.

the-jet, by Cirrus
the He162 (NASM photo)

Fingers firmly crossed, but it looks like NASA will put the unique and beautiful F-16XL back in the air to support supersonic sonic-boom research. The cranked-arrow wing fighter last flew at NASA Dryden 10 years ago, but both aircraft - the only F-16XLs built - have since been kept in flyable storage.

Taxi tests could begin soon. “We’re blowing off the dust and putting air in the tires,” a NASA spokesman tells my colleague John Croft.

Supersonic elegance (F-16XL #1 - NASA photo)

We are all wondering what the next Airbus and Boeing narrowbodies will look like, but NASA is already looking beyond that - waaaay beyond that, to airliners that could enter service in 2030-35.

The agency is holding a pre-proposal conference in Washington DC on 29 November as a precursor to inviting bids for advanced concept studies of what it calls "N+3 Generation" subsonic and supersonic fixed-wing transports.

Under NASA's revitalised Fundamental Aeronautics programme, N equals Now and is represented by today's CFM56-powered Boeing 737. N+1 is aircraft that could enter service in 2012-15. They would still look fairly conventional. N+2 is aircraft that could enter service in 2018-20. They could look like Boeing's Blended Wing Body, or this...

N+3 is way out there, and no-one yet knows what the aircraft could look like. Well NASA has some ideas, but it is not revealing them. It also has some targets. For a subsonic 160-seater they include noise 81dB below Stage 3, NOx emissions 80% below CAEP 2, fuel burn 50% lower than the 737 - and a 70% reduction in field length to allow access to more runways.

Realistically, NASA doesn't expect all of these targets to be met in a single vehicle. They are what the agency calls the "corners of the trade space" - what could be possible if the design is focused on that target.

There is no "N" for a supersonic airliner, except Concorde, but NASA's N+3 metrics for a 100- to 200-seat airliner include an efficient Mach 2 cruise where supersonic flight is unrestricted and a low-boom Mach 1.6 over land, airport noise 20-30dB below Stage 3 and a 6,000nm range. Far out, indeed.

NASA has sent me a two-CD set (how seasonal!) on its revitalised Fundamental Aeronautics programme. One is the presentations from the programme's recent annual meeting (saved for later posts). The other is a 12-minute movie produced by the programme and entitled "Today's Research...Tomorrow's Flight".

I have shamelessy ripped some clips from the DVD to show you some of the concepts NASA is using to focus its research. The first of these is the cruise efficient short take-off and landing (CESTOL) airliner. NASA's idea is that, by reducing take-off distance, aircraft can use runways that are too short for today's A320s and 737s, increasing the capacity of existing airports. Steeper departures and approaches will also reduce noise. The challenge is acheiving STOL without sacrificing cruise speed and while meeting tomorrow's tougher noise and emissions limits.

NASA's targets for an "N+1"-generation subsonic airliner, to enter service in 2012-2015, include a 33% reduction in field length relative to the 737. For the N+2 generation (2018-2020 EIS) it is 50%, and for N+3 (2030-2035) it is a whopping 70% reduction. Technologies include over-wing nacelles and circulation-control wings to increase lift and reduce noise. Not sure Airbus or Boeing are ready to go quite this far with their next-gen narrowbodies...

A look at the direction of NASA's supersonic research under its Fundamental Aeronautics programme makes an interesting comparison with its High-Speed Research programme, cancelled in 1999. The focus of HSR was the High-Speed Civil Transport, a 300-seat, Mach 2.4 airliner intended to fly at supersonic speeds only over the oceans.

NASA's HSCT - a 1998 vision of a 2015 SST

NASA's renewed supersonics effort takes a more incremental approach, setting targets for three generations of high-speed transport: a business jet that could enter service by 2015; a small airliner by 2020; and an "efficient multi-Mach aircraft" that could see service by 2030-35. The latter is the closest analogue to the late-1990s HSCT.

What is different this time round is the greater emphasis on efficiency and the environment. The overall goal is a 30% improvement in efficiency over HSR and all three generations are expected to be low boom, allowing supersonic flight over land. NASA has set a "corner of the trade space" target for sonic boom of 65-70PLdB, compared with more than 100 for Concorde.

NASA's "N+1 generation" is similar to the quiet supersonic business jets currently being studied by Gulfstream and others. The N+2 "vision vehicle" is intriguing: a 35- to 70-seat supersonic airliner with transatlantic range at Mach 1.6-1.8 - very reminiscent of the "business express" aircraft once talked about as a possible successor to Concorde.

NASA's Icon - a 2007 vision of a 2020 QST

Things to note about this reference design, which I think is called "Icon", is the telescoping nose spike for sonic boom suppression, the engine location for noise shielding and the return to variable geometry for airport performance. (Boeing's 1960s SST, the 2707, started out with a swing wing, but ended up a delta like the HSCT.) Here's NASA's visualisation of the concept:

Like it or not, the blended wing-body airliner will not go away. Those that like the BWB point to its aerodynamic and structural efficiency, its ample volume for passengers, cargo and fuel. Those that don't point to its lack of windows. non-circular pressure vessel and edge-of-the-envelope flying qualities. But if the world starts to take the environment seriously, and demands that aviation dramatically cuts its fuel consumption, emissions and noise, where else can airlines go? Solar-powered passenger-carrying airships?

Here is NASA's vision of one possible future:

There is an interesting chart from a recent NASA presentation that illustrates the BWB's fundamental attraction - for the same volume it has a third less surface area than a conventional tube-and-wing airliner. And less surface area means less friction drag. The same presentation also charts the evolution of BWB designs, from the 800-passenger, 7,000nm-range monster conceived by McDonnell Douglas in the early 1990s to Boeing's X-48B subscale demonstrator.

The X-48B is the culmination of research begun in the late 1990s and using a 450-seat BWB as the reference design for a series of small-scale windtunnel models to investigate the configuration's challenging flight dynamics. There was to be a 14%-scale, 35ft-span low-speed flight demonstrator, the X-48B, but it was cancelled by NASA when aeronautics fell out of favour. Instead, Boeing and Cranfield built the 8.5% X-48B, which first flew in July 2007 (watch the video here).

Where next? Well NASA has funded Boeing to investigate the noise benefits of a BWB. It is also funding Boeing, MTI and UCI to mature the blended wing-body design concept produced by the UK/US Silent Aircraft Initiative ... Cal Poly, meanwhile, will refine its concept for a 100-seat hybrid wing-body STOL airliner under NASA grant.

The Silent Aircraft Initiative was a three-year effort by the Cambridge-MIT Institute to develop a credible concept for a 2025-timeframe airliner that would be inaudible outside the airport boundaries (see Flight's story and a video here). Cal Poly's concept is a 2020s-timeframe, low-noise, powered-lift airliner designed ease airport congestion by using shorter runways. And, guess what, neither is a tube with wings.

Interesting news: NASA's associate administrator for aeronautics Lisa Porter is leaving the research agency to become the first director of the Intelligence Advanced Research Projects Activity (IARPA) - a DARPA for the spooks. It's a great move for the striking Porter, who came to NASA from DARPA in 2005 to head the agency's new aeronautics directorate. But what does it mean for NASA, and US aeronautics research?

NASA administrator Mike Griffin says he will "find a successor, but not a replacement" for Porter. I agree, but I don't think a "replacement" is needed. She has stopped the rot in US aeronautics research, after its years of decline, and put in place a programme that will allow the US to hold up its head on the global aero R&D stage.

On a personal note, I found Porter challenging to interview (it was always by phone, not in in person, I should make clear). She was extremely focused on the process of revamping NASA's aeronautics programme and on building it around fundamental research. As an old aero guy, I think she succeeded, as previous posts on this blog should illustrate.

So I wish Ms Porter well in her new job. If you want to know more about IARPA - or as much as they will say without having to shoot you - check out this story from Signal magazine.