Der Fachbegriff dafür ist Höllenkinematik

February 10, 2024 11:27 AM

The AK-X (in German) is a radical experimental flying-wing sailplane being designed and built by Akaflieg Karlsruhe. A YouTube playlist documents the progress so far (and introduces some of the many students working on it), but if you want a comprehensive overview, take in this Presentation about the AK-X at our 95th Anniversary Celebration - Let's Talk about Flying Wings (also in German with good subtitles), summarising the many engineering challenges faced. For a Wikipedia-powered glossary and some background, there's

Some concepts:

• An akaflieg is a student aeronatical engineering club found nearly exclusively at some German technical universities. While some akafliegs are dedicated to flying only, several others do some truly world-class experimental aircraft engineering, often for sailplanes. Forschen, Bauen, Fliegen (research, construction, flight) is the official motto of several akafliegs and the ethos of the century-old movement (in German).

• Sailplanes or gliders aren't the hang-gliders or paragliders known to many: they're fully rigid aircraft built for the recreational enjoyment of unpowered flight. Optimised for gliding capability and speed, the graceful, drag-minimising, broad-winged design found on most sailplanes reflects the tireless pursuit of flying efficiency: so, a natural target for an akaflieg. A high-performance modern sailplane can glide for over 50 metres without losing more than one metre of altitude.

• A flying wing (nurflügel auf Deutsch) is an aircraft form that lacks a tail or a fuselage. (By that score the AK-X might not seem a flying wing as there's a big pod where the pilot sits, but if Akaflieg Karlsruhe are calling it Der Nurflügel on their homepage then I am going with it.) There have been flying-wing gliders many decades ago (most famously the Horten H.1 through Horten H.VI plus several Northrup test articles), but the conventional planform has prevailed.

As they claim that the tailboom and tail assembly account for 10% of a sailplane's overall drag, Akaflieg Karlsruhe hope they'll achieve performance gains by omitting it altogether. They've been working on the AK-X since 2010 and the first flight is probably a few years off still.

posted by tss (9 comments total)

My favorite flying wing was a concept that explored oblique design by rotating the engines instead of the wing.
posted by Brian B. at 12:05 PM on February 10

Zeppelins are always the go-to for filmmakers to easily posit an alternate universe for viewers, but I’d love to see someone use flying wings instead. It’d be awesome to see an airport with massive passenger wings at the gates.

This project looks very nifty. Best of luck to them.
posted by los pantalones del muerte at 12:16 PM on February 10

This is a cool design exploration! It's been .. more years than I want to admit, I think about 15.. since I flew a sailplane, but this looks like it would be fun to fly, and incredibly performant relative to what I used to fly (most of my hours are in trainers and relatively low-performance ships -- 2-33s, 1-26s, and a Grob 103). Wishing the akaflieg luck with the continued development!
posted by Alterscape at 3:34 PM on February 10

Sailplanes can be launched by winch. Makes propulsion cheap and even carbon neutral. Something I'd like to try some day.
posted by Mitheral at 4:27 PM on February 10 [1 favorite]

This is a truly excellent project! Another really cool glider project is NASA's PRANDTL-D that is applying lessons learned from birds (and from lots of math, simulation, and glider experience).

For anyone interested in trying out sailplanes, here's the Where To Fly map from the Soaring Society of America. (Sorry, the map is US only.)

(I am a glider pilot. Also a glider tow pilot.)
posted by phliar at 4:46 PM on February 10 [3 favorites]

Ohh, so the wings are raked backwards. I thought from the intro page that they raked forwards, which would have done all sorts of things to the crosswise airflow. And likely make it impossible to control.

(Also: am I the only mefite who saw the name of the student organization and thought: “We must perform an akaflieg!”?)
posted by scruss at 5:25 PM on February 10

I'm just thinking this is almost the perfect plane for Cathy Guisewite.
posted by symbioid at 6:00 PM on February 10 [1 favorite]

Thanks for posting this.

I was a glider pilot for many years, and an instructor for a few, but am long since lapsed and haven't kept up with the latest developments, so I didn't know anything about this project.

I was always fascinated by flying wings - they're extremely efficient in theory, but so hard to engineer in practice. I even built and flew a couple of radio controlled Zagi-type designs, which really brought home how hard it is to achieve good flight characteristics towards the edges of the flight envelope; yaw control in particular was extremely difficult to get right, just as you'd expect.

But the sheer purity of the concept has always been so tantalising, and the Horten brothers proved it was viable for sailplanes all the way back in the 1930s. I got to see the Horten H.VI at Udvar-Hazy up close a few years back and it's one of the most beautiful aircraft I've ever seen - yet it remained a technological dead end for the next 80 years.

So I'm really glad that someone is finally pursuing this direction again. The presentation in the video is excellent, and covered every aspect of the project to just the right degree to satisfy my curiosity. The whole effort is extremely impressive and I'll definitely be following their progress now.
posted by automatronic at 6:12 PM on February 10 [3 favorites]

Sailplanes can be launched by winch

It is a very fun ride for about 30 seconds, with an added overlay of "must keep the airspeed in the correct band, or terrible things will happen." Winch launch is more of a European thing, most north american clubs use aerotow, but if you have a chance to take a winch launch, highly recommend. The main downside with the winch is that you're only a bit above pattern altitude at the end, so you'd better be good at finding lift, or you're just going to drop back into the downwind to land and do it again. My logbook has exactly enough launches for the endorsement (and at this point, I've lost that skill and would have to repeat the endorsement for safety), but I'd gladly do more given the opportunity.
posted by Alterscape at 10:08 AM on February 11 [1 favorite]