Breaking the Sound Barrier: Shock Waves, Drag Rise, and the Physics of Transonic Flight

Why is it so difficult for aircraft to fly near Mach 1?

In this short video, I use Stallion 3D to look at transonic flow around an aircraft. The example starts with the Bell X-1, the first aircraft to break the sound barrier in 1947. The main idea is simple: as an aircraft approaches the speed of sound, the airflow does not change smoothly. The drag can rise sharply.

This speed range is called the transonic regime. In transonic flow, part of the air around the aircraft can still be subsonic, while another part has already become supersonic. This can happen directly on the surface of the aircraft. That is what makes the problem important for aircraft design.

When shocks form on the aircraft surface, the pressure distribution changes quickly. The forces on the airplane are found by adding up the pressure over the surface. If the pressure changes sharply before and after a shock, the aircraft can see a large increase in drag. This is one reason wave drag becomes important near the speed of sound.

The flow can also become unsteady. A shock wave may move back and forth on the aircraft surface. That motion can create unsteady aerodynamic forces. In some cases, those forces can contribute to structural vibration or other design problems.

One common way to reduce transonic drag is to sweep the wing. Wing sweep reduces the effective Mach number seen by the airfoil section and helps delay some of the strongest transonic effects. This is one of the reasons swept wings became common on fast aircraft. The video is a simple look at this problem using Stallion 3D CFD.

More information can be found at Hanley Innovations ➡️ https://www.hanleyinnovations.com 

Thanks for watching

Patrick 

Transonic Aircraft Design and Analysis

Transonic Accuracy with Stallion 3D

Transonic aircraft design is difficult because small changes in sweep, airfoil shape, angle of attack, and Mach number can produce large changes in pressure distribution and drag. Stallion 3D is designed to capture these effects with high-fidelity CFD, giving engineers a practical way to compare configurations before committing to expensive testing or redesign. In the example (see above picture), two similar wings with the same span, chord, aspect ratio, and area show very different drag results at Mach 0.85, demonstrating how sweep can strongly influence transonic performance.

This level of differentiation is important for CCA UAVs, small business jets, rockets, and other high-speed vehicles operating near or through the transonic regime. Stallion 3D can help identify how design choices affect shock behavior, pressure drag, skin friction drag, and aerodynamic loading. The goal is not just to create colorful flow images, but to produce useful aerodynamic forces, moments, and coefficients that guide design decisions.

The accuracy edge of high-fidelity CFD comes from resolving the physics well enough to separate meaningful design differences. For transonic aircraft, that means being able to evaluate sweep, airfoil selection, angle of attack, and geometry changes with confidence. Stallion 3D gives small teams and engineering groups a way to bring this type of analysis into early design trade studies, where better aerodynamic answers can reduce risk and improve the final vehicle.

Please visit the following link for more information about Stallion 3D:

➡️ https://www.hanleyinnovations.com

As always, feedback is welcome.  Thank you.

Best regards,

Patrick

eVTOL Aerodynamics - How to analyze an aircraft in the cruise configuration with 6 prop rotors.

 

Follow the step to compute lift, drag, aerodynamic moments and induced power for the eVTOL cruise configuration.

1. Here is the breakdown on how to analyze an eVTOL aircraft using Stallion 3D.
2. Click the design menu to import the STL geometry.
3. Next, choose the eVTOL CAD file. The STL file can be either ASCII or binary.
4. In the position tab, choose STL location to place the geometry to the exact design coordinates.
5. Set the dimensions in the size scale tab. Be sure to click the box to set up the automatic grid sizing. Then click okay.
6. Click design menu and top view and visualization view geometry to verify the design was correctly imported. To model prop wash and compute the ideal power, we can add six actuator discs.
7. Click the actuator discs menu.
8. Start with the inboard starboard propeller. Enter thrust location, direction, inner and outer disc radii.
9. Choose linear thrust distribution.
10. Click copy and then add disk.
11. In the disk 2 dialogue, click paste to fill the box with the copied information.
12. Change only the Y center of rotation sign to negative to create the inboard port rotor disc.
13. Click add disc to continue the process.
14. Enter the information for the outboard starboard prop rotor.
15. Copy and paste to the port rotor and change the sign of the Y center of rotation to negative.
16. Complete the process for both the starboard and port tail prop rotors.
17. Run the CFD with a target cell count of over 1 million cells.
18. At sea level conditions, set the angle of attack to 2.5° and the speed to 200 mph.
19. The results show a combined power of 360 kW for the speed and angle of attack settings.
20. In addition, the lift to drag ratio is 13.2. Learn more at hanleyinovations.com.

Please visit https://www.hanleyinnovations.com for more information.