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.
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!
Engineer Mark Street assembles a sub-sonic wind tunnel model Lynx, which was used at the U.S. Air Force test facility at Wright-Patterson Air Force Base near Dayton, Ohio.
In addition to computer modeling with computational fluid dynamics, wind tunnel models provide the necessary real-world data that together informs the final shape of the vehicle. We will cover all of these topics and more in the near future.
Tomorrow we cover some questions from the week, and update you a bit later on where you can find us on the road.