An avweb flash entitled Smaller Aircraft Tails Possible caught my eye back on December 5th.
It linked to a story from CalTech, called Sweeping Surfaces for Greener Planes – relating how researchers at that eminent institution hope to reduce tail sizes (and weight, and drag, and fuel consumption) by using active flow control air to supplement the authority of a smaller rudder at low airspeeds.
Changing the ending
Apart from the earliest strut-and-wire designs by Wrights, Voisins, Farman, Cody, Curtiss, etc, most aircraft have been some variation on a winged tube with a bit sticking up at the end. So for most of the world’s population, that flying ice hockey stick format is just what planes look like.
But, after nearly a century of flying tubes, the shape of airplanes is changing. A little thinning at the back might be the start of something much bigger.
Aircraft designers and engineers are finally free from the restrictions of building with metals, and so we could be watching when shiny white tubes finally disappear from the airport ramp.
Like most things, it won’t happen overnight. Boeing, Airbus, Embraer and others are still churning out brand new tubes that will still be flying in 40, 50, even 100 years. But at the pointy end of aeronautics, places like NASA, no-one bothers with that layout much any more.
Their vision is clearly based on blended wing bodies and ultra-streamlined, boom-reducing supersonics.
Welcome to the new jet age
Just consider a few of these designs in NASA’s current crystal ball. None look much like a conventional airliner. One day soon A380s will be as ‘classic’ as a DC-8; and B787s will look as ‘evocative’ as an L749 Constellation.
The true next generation airliners will likely trace their heritage to the extensive and hugely successful X-48 test program that wrapped up in April 2013. More than a hundred X-48A, B and C test flights proved the efficiency and controllability of Boeing’s Hybrid Wing Body (HWB) design.
But that’s not all. Around the same time, a team of aerospace engineering students from NASA’s 2012 and 2013 Aeronautics Academies dug out the work of eminent German aerodynamicist Ludwig Prandtl and set to work on that other holy grail of aeronautic efficiency –the flying wing. (Do click the link and read about Prandtl. My goodness!)
By combining Prandtl’s theories on lift distribution with the equally amazing Richard T. Whitcomb’s breakthrough winglets, the ones that turn tip vortices into an apparent thrust, the team were able to create a flying wing that didn’t generate adverse yaw when rolled.
You remember adverse yaw from your primary flight training, right? To turn an airplane, a down-going aileron increases the lift being produced by the outside wing while an up-going aileron reduces lift from the inside wing. And the plane rolls.
But with lift and induced drag being generated together, the outer wing gets draggier at the same time as inner wing gets less draggy, so the aircraft yaws away from the turn as quickly as it rolls into it.
That’s why planes have tails and tails have rudders. (And pilots have feet.)
Long, high-aspect ratio wings, like those on a sailplane, provide masses of leverage for this adverse yaw. So while taildragger instructors talk about ‘waking your feet up’ on the ground, in a sailplane your feet have to wake up and waltz the aircraft around the sky.
Meanwhile, back at Dryden
The Academy teams’ flying wing didn’t just overcome adverse yaw, it also demonstrated pro-verse yaw, giving it the controllability that has always been an achilles heel for flying wings – and without any tail at all. Or a fuselage, for that matter. You can watch the video here.
I guess the next stage is to apply active flow control to the non-lifting wingtips, to reduce their size to a minimum.
These are exciting times. If you take photos of airliners, you really are capturing scenes with nostalgia built into them. If you love older aircraft, they’ll only become more vintage and their numbers will increase.
Mind you, it’s a long time before we’ll see a Boeing 747 achieving the same rarity and appeal currently enjoyed by the B-29, Vulcan or, to varying degrees, any number of other rare birds.
So guess where we’ll see blended wing body and flying wing forms really take off? In the military? Sure. They like speed, stealth and, well, new stuff. But the real driver will be (drumroll, please) air freight. Although you could include munitions in that category if you felt the need.
What the people want
Air freight used to be the pasture that old airliners were put out to. These days, companies like FedEx and UPS buy jets right off the line. And the demand for fast, global distribution isn’t about to go away. So anything that helps drive the efficiencies of delivering your books and fresh lobster – by reducing drag, saving fuel, and maximising load space – will be a hit. From drone sized right up to heavy jets, the immediate future for HWBs has got to be in haulage.
Besides, we might still ‘lose a few’ as the new designs mature. With freight, the cost of that is heavy in cash, inconvenience and pilots’ lives – but not, at least, passengers.
So my instinct is that our trusty, proven and fondly-maligned flying hockey sticks – especially the big white ones – will be with us for a while yet.
Remember, we humans are a funny lot: The biggest problem facing Hybrid Wing Body designers and operators may be that we simply aren’t yet ready for the windows to get any smaller or further away. Is there a technology for that?