# Supersonic Speed Measurement With A Sound Card

You might think that if you have a need to measure the speed of a projectile that is too fast for your high-speed camera, you would have to invest in some significantly expensive equipment.

That was the problem facing [Nick Moore], and the solution he arrived at is extremely elegant in its simplicity. He’s arranged a pair of foil tapes in the path of the projectile, as it passes through them they break, and he measures the time between those breaks. The clever bit though lies not in the tapes, but in how he measures the timing. Instead of relying on a lab stuffed with equipment, he’s using his computer sound card. The outputs send a tone through each tape to the inputs, and using Audacity he can capture both tones and measure the time between the end of each one on left and right channels.

In the video below the break he demonstrates measuring the speed of a supersonic particle at 496.5 metres per second, which for such relatively simple equipment is rather an achievement. He could certainly improve his resolution by increasing the sampling frequency, but we are guessing that the choice of 48 kHz owes much to the quality of his sound card. Still, to achieve this with such a relatively basic piece of equipment is a neat achievement.

# Why No Plane Parachutes? And Other Questions.

This week I was approached with a question. Why don’t passenger aircraft have emergency parachutes? Whole plane emergency parachutes are available for light aircraft, and have been used to great effect in many light aircraft engine failures and accidents.

But the truth is that while parachutes may be effective for light aircraft, they don’t scale. There are a series of great answers on Quora which run the numbers of the size a parachute would need to be for a full size passenger jet. I recommend reading the full thread, but suffice it to say a ballpark estimate would require a million square feet (92903 square meters) of material. This clearly isn’t very feasible, and the added weight and complexity would no doubt bring its own risks.

# Retrotechtacular: Don’t Balk at Pitch-Up in the McDonnell F-101 Voodoo

The McDonnell aircraft corporation’s F-101 Voodoo was a lean, mean, supersonic machine capable of going from tarmac to 40,000 feet in about two minutes. But for all its innovation and engineering, the Voodoo had a common problem of pitch-up. That is, the swept-back wings of the Voodoo created a tendency for the plane to nose upward very sharply, negating the pilot’s control.

McDonnell assures Voodoo pilots that this problem is easily overcome with a cool head and a solid foundation of know-how about the issue. This training film is meant to provide that foundation, exploring the causes of pitch-up and the prescribed methods for recovery with and without deployment of the drag chute.

The drag chute is always the recommended route to help correct the craft. This is especially true for a full-scale pitch-up situation. Recovery is possible without the drag chute, however. The altitude lost in recovery is proportional to the altitude at the time that pitch-up occurs. That is, the lower the altitude of the craft when pitch-up occurs, the less altitude is lost in getting back to straight and level flight.

# Retrotechtacular: Supersonic Transport Initiatives

In the early days of PBS member station WGBH-Boston, they in conjunction with MIT produced a program called Science Reporter. The program’s aim was explaining modern technological advances to a wide audience through the use of interviews and demonstrations. This week, we have a 1966 episode called “Ticket Through the Sound Barrier”, which outlines the then-current state of supersonic transport (SST) initiatives being undertaken by NASA.

MIT reporter and basso profondo [John Fitch] opens the program at NASA’s Ames research center. Here, he outlines the three major considerations of the SST initiative. First, the aluminium typically used in subsonic aircraft fuselage cannot withstand the extreme temperatures caused by air friction at supersonic speeds. Although the Aérospatiale-BAC Concorde was skinned in aluminium, it was limited to Mach 2.02 because of heating issues. In place of aluminium, a titanium alloy with a melting point of 3,000°F is being developed and tested.

# Wall climbing robot uses supersonic grippers

Watch out Spidey, there’s a new wall climber in town!

Researchers [Matthew Journee, XiaoQi Chen, James Robertson, Mark Jermy, and Mathieu Sellier] recently unveiled their wall climbing wonder bot at the 2011 IEEE International Conference on Robotics and Automation. Like most other wall climbing bots, theirs operates on the Bernoulli principle to keep it stuck to the surface, but that’s where the similarities end.

Unlike other Bernoulli-based climbers, this robot’s gripper never actually touches the surface it is climbing. The researchers were able to accomplish this feat by designing a specialized gripper which forces air through a 25 μm gap, creating a very powerful low pressure vortex. The gripper’s design compresses the air by shape alone, causing the air flow to reach speeds of Mach 3, without relying on powerful pumps or increased air volume.

The researchers state that their supersonic gripper can support about five times the weight of a conventional Bernoulli gripper, and as you can see in the video below it also has no problem climbing a wide variety of surfaces.

Window-washing Roomba, here we come!

[via Make]