Helicopters were once billed as an alternative to fixed-wing aircraft, especially as a short-haul airliner – but noise, vibration and fuel-efficiency got in the way. Can a radical re-design turn things around?
When helicopters first appeared in our skies in the 1950s, they were
touted as the transport of the future; an aircraft which could take off
and land in a car park or the roof of a building and fly us high above
our traffic-clogged streets.
Congested roads and airways would be a
thing of the past, the thinking went. Fleets of helicopters could whisk
us safely and efficiently to our destinations. But helicopters proved
to have their drawbacks. They are much less fuel-efficient than planes.
They are noisy, and vibrations make them uncomfortable to travel in.
In
the meantime, fixed-wing aircraft won out. Conventional planes can
carry larger loads faster and further than helicopters, and in more
comfort for passengers. But they require long runways and therefore,
bigger airports.
At London’s Heathrow,
for instance, a plane uses the runway every 30 seconds or so. Airports
like these are bad neighbours; noisy and polluting, and have to be
situated some way outside city centres, adding to travel time. And we
need more and more of them.
If helicopters can be re-designed, then they might provide an alternative, cutting congestion and opening the skies to us all.
“They
could operate at heliports constructed at other transport centres, like
train stations or on top of freeways” says Carl Russell, an aerospace
engineer at Nasa Ames Research Center.
Full-tilt
Nasa
may be best known for space exploration, but its aeronautics division
is doing some cutting-edge research into a new generation of air travel.
Their mission is to “solve the challenges in the air transportation
system: air traffic congestion, safety, and environmental impacts.”
‘Compound
aircraft’ have been investigated in the past, for direct
city-centre-to-city-centre travel, but with little success. In the
1950s, the British-built Fairey Rotodyne was developed as a kind of
flying bus. It had a conventional-rotor for vertical flight, and two
propellers on stubby wings for horizontal flight.
It showed
promise, but development was cut mainly due to politics and
cost-cutting. Test flights highlighted a number of engineering
challenges, in particular the noise from a jet air system used to power
the rotors.
Now Nasa designers are using tilt-rotor technology to
design a machine that will carry around 90 passengers and travel 1,000
miles (1,600km).
The Large Civil Tilt Rotor (LCTR) looks like a
plane, but with two huge rotors at the end of each wing instead of small
propellers. For take-off and landing those rotors are parallel to the
ground just as in a helicopter. Then during flight, they swivel forwards
to act like huge propellers. “The entire nacelle [the streamlined engine housing] at the wingtip will actually tip forward with the rotors,” says Russell.
Right now it’s an engineering concept, and Nasa are doing wind tunnel tests of various components.
The
LCTR is designed to work using existing infrastructure. That means it
could use airports, but not clog up runways. Short and medium-length
trips could be taken on a tilt-rotor, leaving just the long-haul flights
using large fixed-wing aircraft.
Need for speed
Another
major drawback of helicopters has been their speed, or rather lack of
it. Compared to fixed wing aircraft, helicopters are the snails of the
sky.
The limit for a conventional helicopter – big rotor on top,
small rotor at the back - is somewhere in the region of 170-190 knots
(315-350km/h or 185 to 220 mph). The LCTR is designed to fly at 300
knots (555 km/h), which is a significant increase in speed.
“That’s
why we have to go to these different type of configurations because
you’re just not going to get it with a conventional design,” says
Russell.
But to build an even faster helicopter is going to take another huge leap in engineering.
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