With hypersonic transport, we’d be able to travel to any part of the world in 3 hours
or less.
Let’s talk about the challenges and ideas behind making this a reality.
Going hypersonic means traveling at a speed more than five times the speed of sound, which
would be Mach 5 or 3,835 MPH.
I recently made a video about the development of supersonic commercial airliners, but even
as those are yet to be released, several governments and private companies are currently engaged
in a race to hypersonic flight.
The official record for fastest manned jet aircraft has been held by the Lockheed SR-71
Blackbird since 1976, a reconnaissance plane capable of flying above Mach 3.
Experimental hypersonic planes have been flown in the past, but all have been powered by
rocket engines or rocket boosters, which are extra heavy because they require carrying
the oxygen used to fuel them as well as being extremely inefficient and not particularly
reusable.
What we are talking about in this video is the development of a manned hypersonic jet
aircraft that can take off, fly, and land on its own like a regular airliner or fighter
jet can.
Sounds simple enough.
But as we learned when discussing supersonic jets in a previous video, weird stuff happens
at high speeds that make certain thresholds a complicated hurdle to cross.
There are three main problem areas that must be overcome to successfully build a hypersonic jet
What materials to use, how to design the craft, and the proper engine to use.
Standard commercial aircrafts are made of aluminium because it’s a strong, lightweight,
and inexpensive material.
Unfortunately, an aluminium plane would melt at hypersonic speeds as would common stronger
materials like steel.
Heat on the body of the plane can reach temperatures of up to 5,000 degrees Fahrenheit and up to
12,000 degrees Fahrenheit in the engine.
This is partly explained by the skin friction created by the airplane pushing air out of
the way at five times the speed of sound, which is called aerodynamic heating.
Heat is also produced by shockwaves created when travelling above the speed of sound,
which is a rapid compression of air caused by air literally not being able to get out
of the plane’s way fast enough.
As you can imagine, this also produces massive drag, which not only affects the speed of
the aircraft, but can also damage materials and reduce its lifespan.
But Julián you might be saying, that’s my name by the way, we’ve sent a plane into
space before, you may have heard of the Space Shuttle that took people to the ISS and back.
What was THAT made out of and why can’t we just build hypersonic planes out of the
same material?
That’s a great question, and a convenient segue thanks for asking.
Mainly, space shuttles and hypersonic Earth-bound planes have significantly different uses.
Space shuttles are designed to make a small number of trips, whereas hypersonic jets would
be making several flights per day and traveling within the Earth’s atmosphere at hypersonic
speeds for relatively long periods of time.
Spacecrafts solve the issue of extreme aerodynamic heating caused by reentering the Earth’s
atmosphere at high speeds using tiles made of different materials based on the amount
of heat the part of the plane they were on would be facing.
Which you’ve probably heard referenced to as a heat shield.
While this worked well for the few minutes it takes a space shuttle to reenter the Earth’s
atmosphere, it doesn’t work quite as well for a hypersonic airliner travelling for hours
at a time, because the space shuttle tiles while extremely poor conductors of heat are
also very fragile.
The main focus of the research into these materials is focused on some sort of ceramic
tiles reinforced by carbon-carbon material at the points getting the brunt of the heat,
the nose and leading edges.
But these materials can be rather susceptible to damage from debris, which as shown by the
Space Shuttle Columbia disaster can be extremely dangerous.
The Space Shuttle Columbia itself used ceramic tiles and reinforced its leading edges with
carbon-carbon material.
It was damage to this heat shield from debris that lead to its destruction upon reentry.
Clearly, engineers will have to come up with a material that is much much safer if we ever
want to see hypersonic flight become a reality.
It seems for now, however, the answer is creating more durable ceramics.
British and Chinese scientists working together made a breakthrough last year with a new process
for creating carbides, which are ceramics formed by combining carbon with other materials.
They start with reinforced carbon-carbon, which is a matrix of carbon reinforced by
carbon fibres, then using a process called reactive melt infiltration they infuse the
carbon-carbon with zirconium, titanium, more carbon and boron.
The carbon-carbon structure absorbs these materials and the resulting material is a
carbide that retains the flexibility and strength of the original carbon structure but with
much higher resistance to heat.
In fact it’s about 12 times stronger than zirconium carbide which is currently used
to dissipate heat in things such as drill bits and reusable rockets.
There is a lot more progress needed in materials before it’s safe to use on a hypersonic plane.
Following the materials and heat issue, although not unrelated, is that of what engine do you
use on a hypersonic plane to maximize fuel efficiency and actually achieve the necessary speed?
There are four kinds of engines one might consider: turbojet, ramjet, scramjet, and
rocket engines which we already discarded as an option at the beginning of this video.
In my video on the comeback of supersonic planes, I discuss why a turbojet engine is
best to achieve supersonic speeds.
However, a turbojet engine doesn’t cut it if you want to fly at hypersonic speeds because
it caps out around Mach 3.5, short of the Mach 5 requirement to go hypersonic.
In part two of this video I’ll go into the challenges of the proper engine to use and
how to design a hypersonic airplane.
If you’d like to see sneak peeks of part two and other videos I’m working on and
see my plans for this channel, please check out my Patreon and like this video because
you made it to the end.
Until next time, I’ll see you in the future.