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AERODYNAMICS MICHAEL GUBISCH LONDON
Rotor blade pressure may
hold key to dynamic stall
DLR revisits experiments from 1940s to test effect of air discharge on flight control
German aerospace research
centre DLR is experimenting
with modified helicopter rotor
blades which discharge pressurised
air through small holes
along the leading edge to dampen
airfoil vibrations and increase aircraft
manoeuvrability.
Main rotor blades tend to stall
in the part of the rotation cycle
when the airfoil travels in the opposite
direction to flight. Such
dynamic stall happens particularly
in high-speed forward flight
or fast manoeuvres.
The airfoil not only loses lift
and drag increases when the airflow
becomes turbulent, but the
rotor construction is also subject
to vibrations and significant strain.
This limits the top speed and manoeuvrability
of helicopters, particularly
at high altitudes.
Releasing air from the holes in
the leading edge can reduce the
turbulences and substantially
dampen the associated pitchdown
momentum of the rotor,
says DLR.
The scientists tested a 1m (3ft)
fixed rotor blade in the transonic
windtunnel of DLR’s Institute of
Though great efforts necessarily
go into improving the machinery
of flight, it is sometimes
worth remembering there remains
much to be learned about
the most important component of
all: the human crew.
Speaking to a packed house on
7 February at the Royal
Aeronautical Society in London
about the training regime he
hopes will one day earn him selection
for an International Space
Station mission, European Space
Agency astronaut Tim Peake was
asked whether, 50 years into the
space age, we fully understand
Sensors measured air pressure changes 6,000 times per second
Aerodynamics and Flow Technology
in Göttingen, which can
simulate air speeds from about
540kt (1,000km/h) to Mach 2.2.
The blade was equipped with
42 holes of 3mm diameter to discharge
the pressurised air, as
well as 74 sensors to measure air
pressure changes across the airfoil
6,000 times per second. As a
next step, DLR wants to test a rotating
blade and verify the previous
results.
The research team envisions
an application which can be
the physiological effects of
weightlessness. His answer surprised
the crowd.
Just last year, he said, it became
evident that about 20% of men
who make long-duration space
flights – of six months or more –
suffer permanent eyesight degradation.
That is, after returning to
Earth they remain short-sighted
and may need to wear glasses or
undergo corrective laser surgery.
The theory being considered
is that in microgravity, blood and
fluid pressure in the legs is necessarily
lower than on the
ground, and that pressure is dis-
manually activated by the pilot in
critical manoeuvres to enhance
the helicopter’s performance.
The idea of influencing aircraft
aerodynamics by discharging pressurised
air from airfoils goes back
to the 1940s, when experiments
were conducted in Göttingen.
Karl Richter, who is head of
DLR’s “STELAR” (stall and transition
on elastic rotor blades)
project, says that the windtunnel
experiment was the most elaborate
dynamic stall control assessment
internationally. �
tributed elsewhere; astronauts
on the ISS tend to have puffy
faces, says Peake, and it may be
the case that pressure on the retinas
flattens them, in some cases
permanently. Women are not affected,
it appears. This discovery
begs the question, what other effects
of spaceflight have we yet
TECHNOLOGY
TESTBED
‘Responsible’
eye-in-sky set for
return to testing
Boeing’s Phantom Eye highaltitude,
long-endurance testbed
is ready to fly again – following
a hard landing after its first
flight in June 2012.
Strengthened landing gear and
software and hardware upgrades
will enable higher-altitude tests
from NASA’s Dryden Flight
Research Center at Edwards AFB,
following 40kt (75km/h) taxi tests
on its launch cart on 6 February.
The 150ft (46m) wingspan aircraft
is capable of carrying a 440lb
(200kg) payload and features
what Boeing describes as an “innovative
and environmentally
responsible liquid-hydrogen propulsion
system creating only
water as a by-product”.
The objective is to stay on station
for up to four days at up to
65,000ft. The June 2012 flight
ended in a mishap when the
landing gear dug into the
Edwards lake bed and broke.
“We’ve drawn on Boeing’s experience
to come up with a solution
using our tactical fighter aircraft
landing systems as an example,”
says chief engineer Brad Shaw. �
FLIGHT MEDICINE DAN THISDELL LONDON
Warning – weightlessness can ruin your eyesight
It may be the case
that pressure on the
retinas flattens them,
in some cases
permanently
DLR
Track the progress of development
programmes at
flightglobal.com/aircraft
to encounter? A typical stay on
the ISS is six months and the
spaceflight endurance record is
437 days, set on the Russian station,
Mir. If a mission to Mars is
ever undertaken, the crew would
be away from Earth for a minimum
of 18 months.
Peake, a UK army major who
still flies Boeing Apache helicopters
for the Territorial Army, speculated
that genetic screening may
become a necessary part of astronaut
selection. �
Commentary about the spaceflight
sector is on our blog at
flightglobal.com/hyperbola
19-25 February 2013 | Flight International | 21