During the autumn of 1947, the sleek orange form of the Bell X-1 “Glamorous Glennis” dropped clear of its B-29 mothership and lit its four chambered XLR-11 rocket engine. The flight that followed marked a milestone in aviation history as the X-1 and pilot, Charles “Chuck” Yeager successfully completed the first controlled supersonic flight.
The lives of many pilots had been claimed during World War II by the little understood effects of compressibility on an aircraft as it approached the speed of sound and the X-1 was built for the purpose of investigating this flight regime. With only a vague idea of what to expect, the X-1 test pilots and engineers bravely pushed the speed limit leading to the momentous flight on 14th October 1947.
The Bell X-1
Had computer simulation been feasible back then much of the danger could have been reduced allowing the engineers to know what to expect and to design the aircraft to cope predictably with supersonic flight. One big issue was the loss of control as an airframe approaches the speed of sound. Because the air cannot get out of the way of the aircraft fast enough, the air “piles up” in front of aircraft fuselage, wings and tailplane forming shockwaves which severely disrupt the flow over those surfaces and can cause the flight controls to lock in place.
With this anniversary in mind I chose to honor the achievement of Chuck Yeager and the X-1 by simulating this first supersonic flight using ANSYS AIM 18.2. After finding a suitable geometry I was able to import the model into geometry editing and prepare the geometry for simulation. I was then able, with relative ease, to create a flow domain around the X-1, mesh and perform a compressible fluid flow analysis. Using AIM expressions I created a transient function for the flow around the X-1 which accelerated the flow from M0.8 up to and settling at M1.06 over a period of 10 seconds.
Pressure contours around the airframe at Mach 1.06
The image above shows the pressure contours around the airframe and one can clearly see a number of shockwaves created by the nosecone, the chine above the canopy, the wing leading edge and the leading of the fin. The image below shows a different view by displaying the Mach number as viewed from above. It’s easy to see how the air is being “bunched up” in front of the nose and the leading edges of the wings as it is attempting to get out of the way of the airframe.
Mach number contours on the airframe and a plane cutting through the wings
ANSYS AIM 3D model Bell X-1 airplane mach number contour.jpg
These results give an interesting insight into the airflow around an experimental aircraft from another era in aviation history but using modern technology. As the aerospace industry continues to develop the latest air and spacecraft, they can do so with the confidence provided by pervasive simulation, something in which ANSYS excels.
Many thanks to Cornel Alexa who produced the original CAD model of the Bell X-1 kindly gave permission for the publishing of this article.
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