Technology

#Supersonic flights are making a comeback — and they still won’t be cheap

#Supersonic flights are making a comeback — and they still won’t be cheap

United Airlines has announced it will purchase up to 50 Boom Overture supersonic jets for commercial use by 2029, heralding the return of supersonic passenger flights nearly 20 years after the Concorde was decommissioned.

Supersonic planes halve the time it takes to fly from New York to London, from seven hours down to 3.5 hours, but such airliners were abandoned following Concorde’s final flight in 2003. Concorde had become financially unworkable after a high-profile crash in 2000, combined with excessive ticket prices, high fuel consumption, and increasingly high maintenance costs.

If Boom’s supersonic aircraft is to succeed, it will depend on overcoming these issues that derailed Concorde. So can it be done?

Breaking the sound barrier

Supersonic flights are so called because they travel faster than the speed of sound. To do this, the aircraft must break through the sound barrier, which requires an efficient aerodynamic design to reduce drag, and considerable thrust from powerful engines to overcome the turbulence caused by shock waves.

Breaking the sound barrier produces a loud sonic boom.

Breaking the sound barrier also requires engines which burn through lots of jet fuel – one of Concorde’s key drawbacks and something that’s only become more contentious in recent years. You’d therefore expect Boom, which is in the prototype stage of developing the Overture, to concentrate its designs on increasing fuel efficiency.

The Colorado-based company is likely to choose between a turbojet and turbofan engine. A turbojet produces all of its thrust from its exhaust gas when it is moving at faster speeds. A turbofan engine, meanwhile, derives most of its thrust from the amount of the air it accelerates with its fan blades. The amount of this air defines the engine’s “bypass ratio”.

Higher bypass ratio turbofan engines are more fuel efficient than turbojets. Their lower exhaust speed makes them quieter, but they tend to be larger, resulting in higher drag at supersonic speeds. This drag penalty has outweighed the efficiency of turbofans for prolonged supersonic flight in the past.

A good compromise might be a low bypass turbofan with an afterburner, which injects additional fuel to significantly increase the available thrust, and is commonly used on military jets. Such an engine was used in early production versions of another supersonic passenger jet, the Russian Tupelov Tu-144, but was too inefficient because it needed to keep firing its afterburners to maintain supersonic cruise.

A Russian supersonic jet in flight
Close

Please allow ads on our site

Please consider supporting us by disabling your ad blocker!