REPORT STYLE & COLOUR // FEATURE NAME
DISPATCHES FROM THE FRONT LINE
OF AEROSPACE TECHNOLOGY
BY DAVID AXEBOEING HAS
ITS OWN
IDEAS FOR
A MACH-5
SPYPLANE
110 April 2018 //^ http://www.combataircraft.net
notably industry magazine Aviation Week. The
Boeing concept relies on a so-called ‘combined-
cycle’ propulsion system that lumps together
conventional jet turbines with powerful ramjet
engines. The turbines accelerate the vehicle past
the sound barrier. At high supersonic speed, the
turbine shuts down and the ramjet takes over.
The competing demands of supersonic and
hypersonic ight dictate this dual arrangement.
‘It’s a really hard problem to develop an aircraft
that takes o and accelerates through Mach 1 all
the way to Mach 5 and beyond’, Kevin Bowcutt,
Boeing chief scientist for hypersonics, told
Aviation Week.
The most e cient engine for transonic and
low-supersonic ight is a turbine with a narrow
inlet that compresses the air. But the kinds of
ramjets that sustain ight faster than Mach 5
don’t compress the air. Therefore, they need
wide inlets. One major challenge for Boeing
— and Lockheed, too — is designing a single
inlet that can e ectively feed air to both engine
types. For its work on hypersonic propulsion, the
company has partnered with Orbital ATK.
Heat is also a problem. ‘Extreme heating
from air friction requires hypersonic vehicles
be made of very high-temperature materials
and structures that are both light and durable’,
Boeing spokesperson Brianna Jackson said.
‘Integrating the engines and airframe in a
manner that achieves high performance across
a very large operating envelope exacerbates the
design challenge.’
In developing the Valkyrie II, Boeing is drawing
on its experience with high-speed vehicles
stretching back decades. The North American
XB-70 bomber prototype, which ew between
1964 and 1969, could cruise faster than Mach 3.
For the Valkyrie II, Boeing reportedly borrowed
elements of the XB-70’s inlet design.
More recently, Boeing’s X-51 — a hypersonic
missile demonstrator with a ramjet-like
propulsion system that last ew in 2013 —
gave the company’s engineers an opportunityto integrate airframes and engines for
Mach-5 ight.
While Boeing continues to re ne the Valkyrie II
concept, the company hasn’t actually committed
to building a functional vehicle. ‘Boeing is not
currently developing a hypersonic airplane’,
Jackson said. ‘However, we continue to conduct
several studies around hypersonic technology.
There will need to be further advances in several
technology areas before an actual aircraft is
feasible.’
But if Boeing does proceed with construction of
a Valkyrie II demonstrator, it already has a pretty
good idea how it might look. The company has
displayed a scale model of a hypersonic drone
that has the same elongated wedge shape
that Lockheed’s own SR-72 does. Bowcutt told
Aviation Week that, in demonstrator form, the
Valkyrie would be roughly the size of an F-16
ghter — that is, around 50ft from nose to tail.
Bowcutt said that an operational version of
the same vehicle would be much larger, with
roughly the same dimensions as Lockheed’s
107ft-long SR-71 Mach-3 spyplane, which retired
from US service in the late 1990s and inspired
the current SR-72 e ort.
Jackson said that it could be decades before
today’s hypersonic concepts produce a
working, front-line warplane: ‘While it would
be premature to speculate precisely when
hypersonic ight will be a reality, it is fair to say
that it could be feasible looking 10 to 20 years
into the future.’While Boeing
continues to refi ne
the Valkyrie II concept, it
hasn’t committed to building
a functional vehicle.
An artist’s rendition of Boeing’s
Valkyrie II concept. BoeingI
N EARLY JANUARY 2018, Boeing
announced that it is developing a concept
for a hypersonic reconnaissance and strike
drone that could compete with Lockheed
Martin’s own SR-72. Both Boeing’s Valkyrie
II and Lockheed’s ‘son of Blackbird’ could be
capable of cruising at speeds exceeding Mach
5, potentially allowing them to evade all but the
most sophisticated enemy defenses.
Since Boeing o cials revealed the Valkyrie II
concept at a Florida trade show, details of the
possible design have appeared in the press, most110 Cutting Edge C.indd 110 16/02/2018 10:12