Canards!

lynx white screenex

Lynx has a tail-less design that eliminates the weight and complexity of an additional set of airfoils, but it didn’t start out that way. The original design had canards!  Now,  a single set of double-delta wings with large vertical stabilizers at each end allow for a sleek, simplified airframe that makes the Lynx the sports car of spacecraft.

In the coming weeks, we’ll discuss how our subsonic wind tunnel test program has shaped the design of Lynx, and much more.

Schlieren photographs

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Above is an image of of the Lynx supersonic wind tunnel model being photographed using the ‘schlieren’ technique. You may have seen this photo in a press release after some of our earlier supersonic wind tunnel tests.

‘But what is schlieren?’ you ask.

As it turns out, schlieren photography is the brain child of German physicist August Toepler, who in 1864 developed the technique to analyze and understand supersonic motion. “Schlieren” in German means streak “streaks.” As is visible in the image above, shock waves appear as streaks across the image emanating from the edges of the model. These streaks reveal changes in air density around our wind tunnel model, and this helps to determine where geometry changes will be needed for improved aerodynamic performance in a given environment.

A schlieren image is captured using a sharply focused collimated light that is reflected into a camera from a curved mirror on the other side of the model. Where airflow is affected by the model, the air density changes, causing the beam to refract differently in low pressure areas versus high pressure areas. Think of heat mirages during the summertime, these are an every day example of that same principle!

Next week we will take a break from the technical and introduce you to some XCOR’ians.

XCOR Lynx: DIY Aerodynamics


Engineer Mike Valant drives an XCOR wind test truck back and forth on the taxiways of the Mojave Air and Space Port during a test series.

In 2009 XCOR built a highly precise sub-sonic wind tunnel test model of the Lynx. For some preliminary data before actual wind tunnel visits, we ran tests using our ‘DIY truck tunnel’ as shown above. The truck and its fixtures include precisely instrumented appendages, structures and bit of computing and data recording capability. We also used the truck tunnel after the sub-sonic wind tunnel tests to experiment with some additional design features before returning to the real tunnel a second time.

By the way, this is not the first time that this particular technique has been applied in Mojave and “other places” in the Antelope Valley for aerodynamic development. We wish we could say we invented this technique but we did not. It has been used for many years by both neighbors in Mojave and neighbors to the west and south of us.

Stay tuned tomorrow as we answer your questions and update you on where you can find us on the road!

XCOR Lynx: Aerodynamics–Supersonic wind tunnel tests

LITT TUNNEL

In this image, XCOR engineer Brandon Litt makes final preparations to a Lynx supersonic wind tunnel model before performing a test at the storied NASA Marshall tri-sonic wind tunnel in Huntsville, Alabama.

NASA TUNNEL

Above, a NASA Marshall spaceflight engineer tests a similarly sized supersonic wind tunnel model of the Space Shuttle in the same facility during the early years of the Shuttle program. The results of the Shuttle tunnel tests were critical to the go-forward decision to build and fly the Space Shuttle.

We believe that test pilots and customers alike require confidence that the spacecraft they fly on has been evaluated and tested extensively prior to flight. And in this day and age, many rely on computer simulation to be sure that their aircraft can perform at the level required.

XCOR used Computational Fluid Dynamics (CFD) and other software analysis tools to design the shape of the Lynx aeroshell. However, things really accelerated when we were able to perform a series of seven subsonic and supersonic wind tunnel test campaigns at United States Air Force (USAF) and NASA labs.

Typically, the faster the tunnel, the smaller the available space. Supersonic wind tunnel models are traditionally smaller than their subsonic counterparts due to the available space in supersonic tunnel test sections. The models must not only fit, but have room to change pitch and yaw inside the tunnel without approaching the side walls of the tunnel. If the model is too close to the walls, edge effects from the walls can be picked up in the data, and ruin the test.

Because supersonic wind tunnels are so small, Lynx models themselves must be highly precise to adequately simulate the full scale spacecraft. The models have many pieces that are interchangeable to test different configurations of the vehicle. For example, a model may have 5-10 different nose shapes, 5-10 different permutations of wing aileron settings, and so on. Because of this, the models can become quite expensive, sometimes approaching several hundred thousand dollars.

Because the actual Lynx is so much smaller in real life than the Space Shuttle attached to the solid rocket boosters and center fuel tank, the Lynx model shown above is actually much larger (almost 3-4 times larger) in scale than the Space Shuttle model.

Tomorrow we answer some of the week’s questions and let you know where you can find XCOR on the road in the near future. In particular, we’ll have some updates for future appearances of XCOR team members and the Lynx full scale model.

XCOR Lynx: Aeroshell 101

Thursday Aeroshell
The Lynx aeroshell shape demonstrates why author Michael Belfiore calls it a “Space Corvette”

As discussed, Thursday 9am Pacific is the time each week that we discuss aerodynamics, modeling, simulation, test process and results. [Note: we delayed today's post by 20 minutes to make room for some other excellent news from our neighbors].

Developing the outer aeroshell for Lynx has been a long and detailed process. From early concepts to wind tunnel tests and “schlieren” shockwave photographs, we will give you a visual tour of what it is like to design an airfoil for a spacecraft, and hear from the people who are doing just that.

XCOR uses computer modeling, simulation, and analysis tools in the aeroshell development process. We have also used subsonic, transonic and supersonic wind tunnels to test and analyze the aeroshell design from very low speeds up to over Mach 4. This will continue into actual flight tests, where we will use an incremental “expand the envelope” approach from slow speed taxi tests to supersonic flights.

This is the approach most aircraft have used for over 100 years, including the rocket aircraft predecessors of Lynx like the Bell X-1 and the North American Aviation X-15.

Tomorrow, find out how you can communicate with us and share what you learn with others.