This one is very special to me...the NASA AD-1 Oblique Swing Wing Concept.

In case you weren't aware, supersonic flight is really difficult. Generally speaking, you need a pointy airplane to go supersonic, with a very low aspect ratio wing. Wave drag, which occurs in the supersonic regime, generally relates to the ratio of span to length, b/l. This number should be as small as possible to reduce supersonic drag, and with a lower drag you have a much more efficient aircraft.

Seems pretty simple right? Make a stick! Well, there's a problem: sticks generally don't do well at slow speeds. So all those pretty delta wings, like the Dassault Mirage, while excellent at high speed are incredibly dangerous at low speed and extremely inefficient. This was the downfall of Concorde - great at Mach 2, mediocre subsonic.


So how do you fix this? Variable geometry. I'm sure all of you are familiar with the F-14 Tomcat:

It has a really neat trick: the wings can be swept at different angles. Interestingly, it's actually computer controlled to automatically sweep starting at Mach 0.8 and being fully swept at Mach 1.2. Neat-o. The F-111 Aardvark and Panavia Tornado do this as well.


So, lets just do that, right? Well, even unswept, these planes aren't great at low speed, and those two mechanisms are two points of failure and really heavy. Now what?

A brilliant engineer by the name of R. T. Jones came up with a genius solution: what if we sweep the whole wing? This accomplishes a few things:

Because of the nature of a shockwave, which I won't get into too much here, the leading edge of an oblique wing is always seeing subsonic airflow. So your wing can now use supercritical airfoils, making it really efficient! And by swinging the whole wing, you get a very large, high aspect ratio lifting surface at low speeds, making the aircraft very efficient and giving it excellent flying qualities at low speed.

NASA built the AD-1 to test this concept. While not capable of supersonic flight, the AD-1 did it's job very well. The oblique wing works! Only problem: when you pitch, you roll. This is easily fixed with a control system. Otherwise, the airplane is truly a shining example of a proof of concept: a strange concept, built and flown and proven to be valid.

Here's some pictures, and a video of the AD-1 sweeping its wing:

Notice that the wing is fully swept, at 60 degrees here:

The AD-1 currently hangs in the Hiller Aviation Museum outside of San Francisco.

I mentioned at the beginning that the concept is special to me: I designed an aircraft based on it for my senior design project. Called the Aethos, it was a supersonic aircraft capable of carrying a 2000 lb satellite launching rocket to 60,000 ft to launch the satellite into space. I chose the oblique swing wing because the airplane had to carry the rocket 1500 nautical miles, so I kept the overall size of the aircraft down by maximizing efficiency. It's 40 ft long and 40 ft wingspan

Hope you enjoyed this little review of, in my opinion, the most interesting NASA proof of concept ever produced.

Tune in next week for the aircraft with the greatest name of all time.