Boom: The Future of Supersonic Flight?

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We are often told how loud super sonic booms
are, but rarely actually get the chance to hear it for ourselves. One of the rare timas where a boom was heard
in an American city occurred in 2010 when a small floatplane entered restricted airspace
over Seattle when, former US President, Barack Obama was visiting. Twin F-15 Eagles were scrambled to intercept
the floatplane and in the process broke the sound barrier over the greater Seattle area. The low flying aircraft created a boom strong
enough to shake homes and was heard as far as south Washington state and caused a huge
surge in calls into local emergency services centres. This phenomenon of sonic booms is one of the
key limiting factors that caused the Concorde to be an economic failure, but high flying
aircraft don’t create near as loud booms as the sound energy is dissipated as it travels
through the air. The other limiting factor, preventing the
Concorde from achieving economic success was it’s fuel economy. When comparing it to one of it’s major competitors,
the Boeing 747, it consumed about 50% more fuel, carried a quarter the amount of passengers,
and had about half the maximum range.The range was so poor, the plane was basically limited
to transatlantic flights as it couldn’t cross the Pacific Ocean and and was banned
from flying over land, as a result to those pesky sonic booms. Although the entire airplane was treated like
first class, flight tickets were still very high compared to competitor first class offerings,
and it was difficult to find enough people to pay those prices regularly. Although the Concorde was, for all intents
and purposes, a safe and successful aircraft for the entirety of its 27 year career, there
were more than a handful of reasons the aircraft was officially retired in 2003. Growing pressure from the British and French
governments, concerns about fuel costs, the lack of route options and the simple shortage
of mass market potential simply killed this iconic aircraft. For the next generation of supersonic aircraft
to succeed they are going to have to overcome these challenges and this exactly what Boom
Technology plans to do. Boom is a startup company aiming to create
a 45-passenger civilian supersonic transport aircraft to fly up to Mach 2.2 at a price
comparable to a business class ticket on a regular airline.The laws concerning supersonic
flight over land are still in place, so their plans are currently focusing on creating economically
viable transoceanic flights. Like a London to New York flight that would
take just 3 hours 15 minutes with a price of $2,500. A San Francisco to Tokyo flight that would
take just 5 and a half hours and cost $3,250 each way or an LA to Sydney route with a flight
time of 6 hours and 45 minutes at $3,500 each way. These are still extremely expensive flights,
but they open up the possibility of getting a early morning flight in LA, arrive in Tokyo
for a business meeting over Sushi and being back in time to tuck your kids into bed. Time is money for many people. Boom are currently developing two aircraft. An all-premium class airliner and a geometrically
similar two seater jet called the XB-1. The XB-1 will be a 1/3rd scale demonstration
aircraft, intended to be a test bed and proof of concept for the larger airliner The team, don’t just have the advantage
of hindsight guiding their design. When the Concorde was being developed computers
weren’t really used for design work. Everything was done on paper and tested in
wind tunnels. Today the engineers at Boom have incredible
design software allowing them to quickly develop prototype designs and have powerful computational
analysis software that can test the designs the same day, without pouring money into building
a scaled prototype and paying for wind tunnel hours. This allows them to tweak the design to the
finest detail to create the most efficient aircraft possible. What once took days and thousands of dollars
to test, takes a single engineer a couple of hours. This coupled with carbon fibre reinforced
plastics is allowing the design of the Boom Supersonic airliner to be lightweight, be
shaped perfectly and perform well at the high temperatures of supersonic flight. So beyond these advantages, what are the differences
between the Concorde and Boom? Boom believe that a 30% increase in fuel efficiency
would reduce operating costs sufficiently to allow a viable business model. The Concorde consumed 16.7 litres of fuel
every 100 kilometres per passenger, but the Concorde had an average passenger capacity
of about 100 with 25 rows with 4 seats in each. Boom plan to have just 45 passengers each
getting their own window seat and aisle access. Creating a much more enjoyable experience
over the cramped interior of the Concorde, but it also makes that target of a 30% decrease
in fuel consumption per passenger much more difficult. Let’s look at some of the design features
they are introducing to achieve this goal. Both planes feature an extremely thin delta
wing, named after the triangular greek letter delta. This design feature is essential to allowing
the wing to function at both subsonic and supersonic speeds. If you watched my video about Why Plane Wings
are Angled Backwards, you will understand why sweeping the wing is incredibly important
for planes that travel close to the speed of sound, but it’s important for planes
breaking the speed of sound too. As an object approaches the speed of sound
it experiences a sharp increase in coefficient of drag and as explained in my Greatest Innovations
in Formula One video the drag force on an object increases with the square of the velocity,
so creating a streamlined aircraft is incredibly important for supersonic aircraft, especially
when fuel efficiency is paramount. Intuitively we want to minimise the cross-sectional
area of the aircraft to reduce drag, but we also want to minimise the changes in cross
sectional area along the length of the plane to reduce the wave drag. If we compare two shapes with the same maximum
cross-sectional area, but one is smoothed and other has a sudden change in cross sectional
area, we can see the later has a much high coefficient of drag as it enters supersonic
speed. So the plane’s fuselage is narrowed where
where it meets the wing, as the wing increases the cross sectional area of the plane at that
location. This is called the Area-Rule. Sweeping the wing backwards decreases the
coefficient of drag significantly at transonic and supersonic speeds too and the Delta wing
allows for a sweep angle of up to 70 degrees, while also allowing for a very thin wing,
thanks to the large chord and short wingspan. The Delta wing performs well at low speeds
too, as a result of unique swirling vortices that form on the uppers surface of the wing. On a traditional aircraft’s wing a swirling
vortex is formed only at the wing tips. On a delta wing they form on nearly the entire
wing surface and produces a considerable amount of lift. This is particularly apparent on damp days
where the vortices can be seen forming on the upper surface of the wing, due to the
water vapour condensing in the low pressure vortex The Delta wing gains additional lift, particularly
on landing, as a result of the ground effect where the downwash of the air between the
wing and the ground creates a cushion of air. But generating lift using these technique
needs a large angle of attack, and The Concorde’s angle of attack on landing was so high that
the nose of the plane needed to be tilted downwards to allow the pilots to see what
they were doing. I imagine Boom are just employing a camera
to help the pilots see on landing. Boom also uses a chined fuselage, which helps
maintain the centre of lift as the plane gains speed. As a supersonic plane gains speed, the the
centre of lift tends to move backwards, creating issues for the balance and control of the
aircraft. A chine is a ridge that extends from the wing,
you can see a similar shape on the SR-71. This structure generates more lift at supersonic
speeds than subsonic and thus helps hold the centre of lift location. The engines may be the most interesting part
of the design, with a variable geometry inlet. At supersonic speed the air is efficiently
slowed to the ideal subsonic speed for the engine, with digitally-controlled movable
surfaces precisely shaping shock waves to achieve ideal compression at a range of speeds
and flight conditions. The Concorde used Turbojet engines, which
were superior for supersonic flight over turbofan engines, as they have a much smaller frontal
area reducing drag. The Russian supersonic jet Airliner Tu-144
initially used turbofan engines, but later changed to turbojet and gained a significant
increase in efficiency. But todays engines are much more efficient
and Boom can reach their performance targets with a medium bypass turbofan engine, which
also reduces the noise on takeoff and landing. An important trait to allow the plane to land
in many airports. Boom isn’t just some concept plane like
the Aurora D8, shown previously. It is an actual plane in development and the
company closed a $33 million dollar round of investment last March
.If the flight tests of the 1/3rd scale XB-1 next year prove successful, we could be in
for a reemergence of civilian supersonic flight in the near future. Thanks for watching. So last week I spoke about why Hover is such
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