Space Shuttle Model In A Hypersonic Wind Tunnel

Mach 20 In A Wind Tunnel: Yes, It’s Rocket Science

Hypersonic speeds are defined by those exceeding Mach 5, and lately there’s been a lot of buzz about unmanned hypersonic vehicles making test flights. Vehicles returning from orbital flight also travel at hypersonic speeds as they do their best to transition back to the terrestrial realm. Before anything leaves ground though, these machines are tested in wind tunnels. [Scott Manley]’s video “How Hypersonic Wind Tunnels Recreate Mach 20” (embedded below) does a wonderful job of explaining the engineering behind wind tunnels for testing hypersonic vehicles.

While the earliest wind tunnels such as that used by the Wright Brothers were powered by simple fans, it is not possible for any propeller to surpass subsonic speeds. This is evidenced by there not being any propeller driven aircraft that can exceed Mach 1. Since an aircraft can’t reach those speeds with a propeller, it follows that a wind tunnel cannot be driven by propellers, fans, or any such device, and exceed Mach 1 wind speed, either. So it begs the question: Just how do they do it?

You might think that the answer lays in Bernoulli’s law – but it does not. You might think it involves compressing the air into smaller and smaller tubes and pipes. It doesn’t. As [Scott Manley] so expertly explains in the video below the break, it has quite a lot in common with actual rocket science.

You may be interested to know that we’ve covered some DIY wind tunnel builds as well as a small desktop wind tunnel in the past. While not hypersonic, they’re exactly what you’d want to have if you’re an aerospace hacker of any kind.

Thanks [Zane Atkins] for the tip!

Continue reading “Mach 20 In A Wind Tunnel: Yes, It’s Rocket Science”

The Old Ping-Pong Ball Levitation Trick


[Jacob] has put a slightly new twist on the levitating ball trick with his ping-pong ball levitation machine. We’ve all seen magnetic levitation systems before. Here on Hackaday, [Caleb] built a Portal gun which levitated a Companion Cube. Rather than go the magnetic route, [Jacob] levitated a ping-pong ball on a cushion of air.

Now, it would be possible to cheat here, anyone who’s seen a demonstration of Bernoulli’s principle knows that the ball will remain stable in a stream of air. [Jacob] proves that his system is actually working by levitating ping-pong balls with different weights.

A Parallax Ping style ultrasonic sensor measures the distance between the top of the rig and the levitating ball. If the ball gets above a set distance, [Jacob’s] chipKit based processor throttles down his fans. If the ball gets too low, the fans are throttled up. A software based Proportional Integral Derivative (PID) loop keeps the system under control. A graph of the ball distance vs fan speed is displayed on an Android tablet connected to the controller via USB.

When [Jacob] switches a heavy ball for a light one, the lighter ball is pushed beyond the pre-programmed height. The controller responds by reducing the fan speed and the ball falls back. Who said you can’t do anything good with a box of corn dogs?

Continue reading “The Old Ping-Pong Ball Levitation Trick”