NASA's X-59 plane is aiming for a sonic thump, not a boom

Pilot James 'Clue' Less is ready to take to the skies

Feature Sitting in the hangar of Lockheed Martin's famous Palmdale, California Skunk Works facility is one of the oddest aircraft ever to take shape: the X-59 that's looking to revive supersonic travel over land.

The X-59 is a very strange looking bird. It's 99.7 ft (30.4 m) long with a 29.5 ft (9 m) delta-style wingspan – but the first third of the aircraft is all nose. That elongated proboscis is designed to pierce shockwaves created when aircraft top the speed of sound, and by doing so reduce sonic booms to a more muted sonic thump that won't deafen folks on the ground.

X-59 aircraft (pic: Lockheed Martin)

Earlier this month, NASA fired up the X-59's engines for the first time ahead of next year's test flights. The Register caught up with the project’s head of propulsion, Ray Castner, and test pilot James L Less – aka "Clue" – to learn more about this amazing aircraft.

The Register: James, I have to ask about your call sign. Where did you get it?

Less: I've been Clue since my first squadron in the Air Force over 20 years ago. I walked in, they took a look at my name, and they just said, "OK, we've got to come up with something good."

The Register: It seems like you're basically taking an F-18 engine, F-16 undercarriage, and then the rest of the plane is custom-built. Is that correct?

Castner: That's true. It is a fully new aircraft with parts from all kinds of other airplanes, mostly to save budget and cost. If you can get anything you can reuse, that saves money.

The Register: Does that go for the lack of a forward windscreen? It's got to be unusual relying on cameras alone.

Less: The cockpit of the X-59 is designed around the rear cockpit of a T-38 Air Force trainer. So we didn't have to develop it all from scratch and test it. The canopy, canopy jettison mechanism, and then the ejection seat are all things that, if we had to do those from scratch, would be a lot of development. So we just used what's in the T-38 – they took the blueprints for that rear cockpit and then built a whole plane around it.

This is not the first airplane that you couldn't see straight forward out of – Charles Lindbergh had to hang his head out the window to see where he was going. We didn't want to have to do that. So this camera system will actually make it – in theory – just like looking out the front window. We have a big high-definition TV monitor right in front of us, and the picture is nearly what they call "conformal." If I were looking through a transparent window right there, that's what I'd be seeing.

The Register: The design of the craft is most unusual – the extended nose and tail in particular. How does that help with sonic booms?

Castner: I've sat through countless meetings about the sonic-boom design. And actually, before the X-59, we'd done some wind tunnel testing on what would be a next-generation supersonic transport.

The whole concept for aircraft shaping for sonic booms is about managing the volume of the airplane and the lift – because sonic booms are all about lift and volume. So if you can manage that energy, then the human ear will hear that sound as a softer sound.

And it's really all based on advances in computational technology. We have all these supercomputers that can analyze thousands of designs in a month. And they can basically optimize the shape of the aircraft, and that's really the secret sauce, how boom optimization works.

Less: The nose of the airplane and the tail of the airplane put out the strongest sonic shocks normally. And that's the boom that you hear. And then there's a whole bunch of smaller shocks along the whole length of the airplane. And as those all travel to the ground, they kind of merge together into the front and the back, and that's the loud boom that you hear.

The point of the long, straight, new nose, skinny airplane is to spread all those little shocks out so that they don't merge together as they go to the ground. And as Ray was saying, it's energy. It's the same amount of energy in the sound, but it's spread out over the length of the airplane instead of into two short sections: nose and tail.

The Register:Is this design practical for commercial aircraft?

Castner: NASA is pretty confident. Right before we designed X-59, we've done both computational and wind tunnel tests on vehicles that would be scaled up towards 60-passenger aircraft. NASA feels confident that that technology can be scaled up to a full scale commercial supersonic aircraft – but the X-59 is needed to demonstrate that and to collect that data.

The Register:So when's the first flight?

Less: From a flight test standpoint, we mainly just have to make sure we're safe. So I won't say how many flights, but we will fly fairly quickly, and assuming we keep moving through that envelope, we will get supersonic without too much delay. That's obviously the goal. So we're hoping to do the first flight early next year.

The Register: So assuming a successful flight, what happens to the data for this? Is this shared with the industry?

Less: One is the human response to the public survey data. When we're done testing this airplane we're going to go fly around the country and get people's response to the sonic thump. That data will go to the Federal Aviation Administration and any international regulatory boards to show them that we've got the data saying you can change your rules. Instead of being a hard speed limit, the limit will be based on sound.

The other set of data we're going to get is all those computer tools that Ray was talking about that were used to design this. We're going to go and measure the results and go back and refine those tools even more based on real-world results. And then those tools are available to any US manufacturer that wants to try to use it and make a low boom aircraft. ®