Lift the Ban on Supersonics: No Boom

 [[{“value”:”Boom, the supersonic startup, has announced that their new jet reaches supersonic speeds but without creating much of an audible boom. How so? According to CEO Blake Scholl: It’s actually well-known physics called Mach cutoff. When an aircraft breaks the sound barrier at a sufficiently high altitude, the boom refracts in the atmosphere and curls
The post Lift the Ban on Supersonics: No Boom appeared first on Marginal REVOLUTION.”}]] 

Boom, the supersonic startup, has announced that their new jet reaches supersonic speeds but without creating much of an audible boom. How so? According to CEO Blake Scholl:

It’s actually well-known physics called Mach cutoff. When an aircraft breaks the sound barrier at a sufficiently high altitude, the boom refracts in the atmosphere and curls upward without reaching the ground. It makes a U-turn before anyone can hear it. Mach cutoff physics is a theoretical capability on some military supersonic aircraft; now XB-1 has proven it with airliner-ready technology. Just as a light ray bends as it goes through a glass of water, sound rays bend as they go through media with varying speeds of sound. Speed of sound varies with temperature… and temperature varies with altitude. With colder temperatures aloft, sonic booms bend upward. This means that sonic booms can make a U-turn in the atmosphere without ever touching the ground. The height of the U varies—with the aircraft speed, with atmospheric temperature gradient, and with winds.

….Boomless Cruise requires engines powerful enough to break the sound barrier at an altitude high enough that the boom has enough altitude to U- turn. And realtime weather and powerful algorithms to predict the boom propagation precisely.

Here is the crazy part. Civilian supersonic aircraft have been banned in the United States for over 50 years! In case that wasn’t clear, we didn’t ban noisy aircraft we banned supersonic aircraft. Thus, even quiet supersonic aircraft are banned today. This was a serious mistake. Aside from the fact that the noise was exaggerated, technological development is endogenous.

If you ban supersonic aircraft, the money, experience and learning by doing needed to develop quieter supersonic aircraft won’t exist. A ban will make technological developments in the industry much slower and dependent upon exogeneous progress in other industries.

When we ban a new technology we have to think not just about the costs and benefits of a ban today but about the costs and benefits on the entire glide path of the technology.

In short, we must build to build better. We stopped building and so it has taken more than 50 years to get better. Not learning, by not doing.

In 2018 Congress directed the FAA:

..to exercise leadership in the creation of Federal and international policies, regulations, and standards relating to the certification and safe and efficient operation of civil supersonic aircraft.

But, aside from tidying up some regulations related to testing, the FAA hasn’t done much to speed up progress. I’d like to see the new administration move forthwith to lift the ban on supersonic aircraft. We have been moving too slow.

Addendum: Elon says it will happen.

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