How It Works-Amazing Vehicles

NORTH

AMERICAN

X-

Mission fl ights

199

Top altitude

107,960m (354,200ft)

Fatalities

1

Top speed

7,274km/h (4,520 mph)

Climbing rate

305m/s (1,000ft/s)

Propulsion

Reaction Motors XLR99 rocket

Aerodynamic challenges

The engineering challenges for high-speed

aircraft are surprisingly similar to building the

world’s fastest cars. Drag is still public enemy

number one. As an aircraft approaches the speed

of sound, the gas fl ow ing around the plane grows

more v iscous, ‘sticking’ to the surface and altering

the aerodynamic shape of the craft. A ny friction

with that high-velocity stream of gases will cause

bone-rattling turbulence, incredible heat and

shock waves. To achieve the best aerodynamic

profi le, supersonic planes have swept-back wings

that stay safely inside the cone of a supersonic

shockwave. The F-14 fi ghter jet can pull its wings

in tight for maximum speed and stretch them out

for greater control at lower speeds. Supersonic

craft are also made from lightweight materials

like aluminium to further reduce drag.

Of course, you’ll never reach supersonic speeds

without serious engine power. X-1, the fi rst plane

to break the sound barrier in 1947, was propelled

by a rocket, but modern turbojet engines like the

Concorde’s four Rolls-Royce turbofans, are also

capable of supersonic fl ight. Hypersonic fl ight – ie

greater than Mach 5 – has its ow n unique set of

challenges because gas molecules begin to break

apart and create multiple overlapping

shockwaves. Experimental hypersonic designs

such as the Falcon HTV look more like wingless

sci-fi vehicles than traditional planes.

The fastest-ever manned

aeroplane made its record-

setting fl ight 47 years ago. In the

early days of the Space Race, the

X-15 was designed to test the

limits of aeronautical

engineering at the edge of

space. Built like a short-winged

fi ghter jet, the X-15 packed a

rocket under its hood. To fl y,

it would hitch a ride on a

massive B-52 up to 13,700 metres

(45,000 feet). Dropped from the

bomber, the X-15 lit its liquid

propellant rocket capable of

500,000 horsepower. The X-

only carried enough fuel for 83

seconds of powered fl ight – but

it was enough to rocket its pilots

into the record books.

Other speed demons... in the air

Fastest unmanned plane

Falcon HTV-2, 20,921km/h (13,000mph)

Blackbird SR-71, 3,185km/h+ (1,979mph+)

Virgin Galactic’s SpaceShipTwo, 1,752km/h (1,089mph)

Fastest jet aircraft

Fastest space plane

The HTV-2 test fl ight lasted about

nine minutes, before heat damage

forced the mission to be terminated

Rocket engine

The XLR99 engine was throttled,

which meant thrust could be

adjusted from half to full.

Short wings

Stubby wings create less air

resistance to allow for greater speed,

but make an aircraft harder to control.

Drop-off tanks

When the second iteration of the X-

was damaged on landing, the fuel

tanks were redesigned to fall away.

Nose wheel

The front wheel could not be

steered so the X-15 had to land on

a lake bed rather than a runway.

Oxygen supply

As there is so little oxygen at the

edge of space, the X-15 had to

take its own for burning fuel.

WORLD’S FASTEST

MANNED AIRCRAFT

Outer fuselage

To cope with the extreme heat

of high-speed fl ight, the X-

had a chromium-nickel skin.

DID YOU KNOW? To simulate a missile flight, US Air Force researchers built a rocket sled that reached 10,325km/h (6,416mph)