what might look like a step backwards is
actually two giant steps forward on the
future path of advanced aircraft engine
since 1941 the Lewis Research Center has
developed an international reputation
for its research on jet propulsion
systems however in 1977 the researchers
at Louis began to take a new look at the
propeller their challenge was to combine
the efficiency of the propeller with the
power of the turbine engine what has
evolved is ATP the advanced turboprop
project
Keith severs manager of the NASA
advanced turboprop project office at the
Lewis Research Center back after World
War two jets for the thing the coming
thing her powers were very efficient in
those days but they couldn't go fast it
couldn't go to high altitudes and quite
frankly they were not jazzy like jet
engines and which gave way them to
turbofan engines and high bypass ratio
engines and when fuel was cheap people
didn't worry much about it 10 cents a
gallon as long as they get speed high
altitude capability which the air
transport system required propellers
just kind of withered on the vine for 20
or 30 years the Arab oil embargo of the
early 70s not only hit American
consumers at the corner gas station but
was also reflected at the airline ticket
counter due to the soaring price of jet
fuel in 1973 the price of a gallon of
jet fuel was 12 cents and represented
one-quarter of the direct operating cost
of the jet by 1979 the price had risen
to 63 cents a gallon and represented
half of the direct operating cost in
1981 the cost of jet fuel was over a
dollar eight cents a gallon with the
rising fuel prices a fuel efficient
propeller engine again became the object
of an aeronautical propulsion research
effort the researchers objectives were
to develop a powerplant that would be
fuel efficient dew point eight mach
cruise at 35,000 feet operate at a
reduced noise level
these propellers look a lot different
there are very highly swept they're very
thin compared to old propellers and the
thing it hits you first is they're eight
to ten blades on these are rather than
three or four is that you've been
accustomed to in the past and what the
sweep doesn't in the propeller end of
finis is is to reduce the drag losses at
the higher tip speeds and higher Mach
numbers also helps to reduce the source
noise of the propellers the higher blade
count and we've loaded these blades up
much higher than old propellers so we
get a lot more power at a lot smaller
diameter and this saves weight on the
propeller say it's weight on the engine
and it also packages better on the
aircraft earlier two turbo props were
limited both in horsepower and in flight
speed mainly because of the
compressibility effects that occur at
the propeller tips with the recent
advances in computer design technology
we are now able to optimize the blade
shape to minimize the compressibility
effects occurring at the blade tips
allowing the planes to fly faster up to
six hundred miles an hour and at higher
altitudes up to 35,000 feet as you
approach the speed of sound you run into
a problem where the apparent pressure
that you're trying to push through
suddenly takes a quantum leap and
because the blades are very large in
diameter to 13 feet in diameter the tip
speed is upwards of 800 feet per second
which is just under Mach 1 or the speed
of sound as you try to push through that
Mach 1 range you run into this
compressibility factor it's almost like
running into a brick wall with the blade
the blade construction is now a
composite type arrangement where you
have a metallic leading edge such as
aluminum and a graphite epoxy resign'd
internal construction that allows the
blades to be very lightweight and
cause they're lighter weight minimizes
the centrifugal stresses that occur when
the propeller system is rotated at
12,000 rpm ultimate goal is to save fuel
commercial aircraft and also military
aircraft were it can be applied and this
fuel saving is very dramatic compared to
the fuel burn that aircraft have today
such as a 727 737 that type of air cream
aircraft a prop van driven airplane can
do the same mission that like forty to
fifty percent of the fuel that they use
today if you look at just the u.s. fleet
existing today for medium to short range
aircraft I'm talking 727 737 is dc-9s
md-80s those aircraft in a typical year
burn about 5 billion gallons of fuel if
these aircrafts were equipped with pop
fans they could do the same mission
they're doing today and save two to two
and a half billion gallons of fuel per
year
propeller-driven airplanes have
traditionally been noisy advanced
turboprop researchers are tackling the
problem of trying to build a turboprop
to rival the relative quiet and
smoothness of the ship well we've had to
look at the entire aircraft as a system
we didn't look just at sticking a new
widget called a prop fan on them better
look at what to do they do to the rest
of the aircraft and particularly we're
concerned about passenger comfort it
doesn't matter how much fuel was saved
if people don't like it or they're
uncomfortable sound vibration and
they're not going to write it so it
won't matter so part of our project goal
is to to make sure that people have the
same comfort that they're used to on
today's wide-body aircraft in addition
we're concerned about community noise
these things are allowed and we have to
provide the technology sort of the
equivalent existing far 36-yard stage
three regulate
by around airports and communities
most the time we really don't even know
what's running inside the cockpit it's
that quiet and we're only what 15 feet
away from after several years of wind
tunnel and static engine testing a full
flight test of the advanced propeller
system was held on May 19 1987 at
Lockheed Georgia company in Marietta
Georgia so far operation has been very
good everything is about as predicted
that the engineers had predicted from
their initial assessment of the program
we haven't really had any big surprises
I should say when you pull the prop fan
in and add power to it the pilot really
knows it but there again this airplane
wasn't really designed to fly with an
engine out on a on the left wing but
again what our engineers predicted is
pretty much what's happening with the
airplane so I'd have to say so far it
looks good so far it looks very good if
all goes to plan prop fans will probably
be fitted on short to medium range
aircraft we hope to have as a part of
the project goal to have a technology in
hand by the end of 1980s so that
industry the engine people the aircraft
people can make marketing decisions
because it involves a lot of private
capital that's a make sure breaks our
company so the way things are proceeding
right now it looks like Boeing and
McDonnell Douglas are aiming for new
aircraft injuries so with prop vans in
say the 1991 92 93 timeframe
you