Download Laminar flow a reality PI Smiths flies wide-angle Hud

Laminar f l o w a reality
MCDONNELL DOUGLAS is testing
laminar-flow wing sections, which
could reduce fuel consumptiononlongrange flights by up to 40 per cent.
The sections could be in service by
1990, and the savings are relative to
widebody airliners in service today.
The company maintains laminar
How over the upper surface of the
wing by sucking in air, through millions of tiny holes. Only a small
amount of air is entrained, and the
energy needed to do this is vastly outweighed by the reduction in drag.
Laminar flow is a comparatively
old concept, easily demonstrated in a
windtunnel, but difficult to put into
practice. McDonnell Douglas now believes that it has found a way around
the difficulties. So far, all of the company's testing has been in windtunnels, but a leading edge section is
due to be flight-tested aboard a Nasa
aircraft next year.
Thin titanium sheet, pierced by
electron beam-drilled holes, is the
basis of the McDonnell Douglas section. Each hole is just 2-5 thousandths
of an inch in diameter, less than the
thickness of a human hair. They are
spaced 25 thousandths of an inch
apart, giving 1,600 holes per square
inch.
With such tiny holes, one of 'Lie
major difficulties is their susceptibility
to clogging. Protrusions of just four
thousandths of an inch could destroy
the laminar flow, so a clinically clean
surface is vital.
The company's answer is a retractable shield, deployed in front of the
wing during take-off, climb, descent,
and landing. These are the phases in
which particles are likely to be encountered—the air at cruising altitude being free of them. The shield
would double as a slat-like high-lift
device.
A further defence against contamination would be to spray a liquid
film over the surface, thus preventing
particles from sticking to it. Occasional
steam cleaning of the wing would
also be necessary.
The pierced titanium skin is
bonded to a composite substrate,
which is corrugated. The corrugations
serve as ducts for the air absorbed
through the skin. Completed panels
are then welded together, heated, and
formed against a smooth surface.
Laminar flow has powerful potential, since it is a saving which can be
exploited on top of the benefits of
new engines and aerodynamic design.
McDonnell Douglas estimates a 20
per cent fuel saving for laminar How,
relative to a new long-range airliner
designed today
A sect/on of the McDonnell Douglas laminarflow wing surface, overlaid by a paperclip.
Each hole is smaller than a human hair
PI
Below A wing exhibits a turbulent boundary layer over much of its upper surface {upper
diagram). The turbulent layer is triggered by surface imperfections and the adverse pressuregradient over the rear, upper-surface. By extracting small quantities of air, the flow can be
persuaded to remain attached to the upper surface {lower diagram). The resulting laminar boundary
is much less draggy
Smiths flies
wide-angle Hud
SMITHS INDUSTRIES has completed a series of test flights of its
latest diffractive optics headup display (DHUD) on board a Jaguar at
BAe Warton. The DHUD uses a
curved combiner glass incorporating
a laser-generated diffraction grating,
which acts as a mirror. This optical
system, which was developed by
Hughes Aircraft, gives a much wider
field of view than that on current Huds,
which use a combination of lenses and
mirrors. The instantaneous field of
view of this Hud is 33° by 22°.
Smiths claims that its DHUD is the
first one for which comprehensive
combat-aircraft performance data has
been obtained, and the company says
that several air forces are interested.
The test aircraft also had a Marconi
low-light TV sensor on board—one of
the DHUD advantages is that bright
raster images for nighttime flying
can be generated.
• The Marconi Avionics DHUD uses
three flat combiner glasses, and has
been selected for the USAF F-16 and
A10 night-attack variants.
The Smiths Industries diffractive optics headup
display has a wide-angle, curved combiner
glass with the minimum of support structure
to mar the pilot's view of the outside world.
The DHUD now awaits a retrofit or newaircraft application
EFFECT OF LAMINAR FLOW CONTROL
TURBULENT FLOW
INITIAL SMOOTH
(LAMINAR) FLOW
CONVENTIONAL WING
CONTINUOUS SMOOTH (LAMINAR! FLOW
FRACTION OF BOUNDARY LAYER DRAWN
INTO WING 3Y SUCTION TO PREVENT
ONSET OF TURBULENT FLOW
LAMINAR FLOW CONTROL WING
1208
R I G H T International,
IS May
1982