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Multidisciplinary
Design, Analysis, and
Optimization Branch
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EDUCATIONAL ACTIVITIES: THE NASA AEROQUIZ
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Week of 4/5/99:
Q:
During World War II, aircraft designer and scientist Dr. Barnes Wallis
developed a 9250 pound cylindrical bomb that was used against heavily-defended
German dams. On raids against three dams, British Lancaster bombers
approached their targets at treetop level where they released the bombs
while rotating them backwards at a rate of 500 rpm. They skipped along
the river surface to the dams and exploded near their bases. Using
detailed trajectory calculations, Wallis determined that the skip bombs had
to be deployed at altitudes of exactly sixty feet. Using the technology
available at the time, how did the Lancaster pilots know when they were
at this precise altitude during their bombing runs?
A:
They had two spotlights, one at each end of the aircraft, and canted
downward and inward. The proper altitude was reached when the two
roundels of light would touch.
Congratulations to Nicolas Cousineau.
The Dambusters Raid was one of the most brilliant, albeit costly, air
attacks of World War II. Eight of the nineteen Lancasters failed to return.
53 aircrew were killed, while three survived to be taken prisoner.
The destruction of the Mohne and Eder dams caused widespread flooding and
interrupted industry, communications, and various utility services.
- The Aeroquiz Editor.
Week of 4/12/99:
Q:
Pratt & Whitney's F119 jet engine powers the U.S. Air Force's new
air superiority fighter - the F-22 Raptor. Remarkably, the F119 is able to
spool up from idle speed to full thrust in only two seconds. Aside from the
obvious performance benefits of pilots getting their power on demand, this
quick response is also good for prolonging engine life. Why?
A:
It helps to avoid "high cycle fatigue" of the turbomachinery's airfoils.
Fan or compressor airfoils have several natural excitation frequencies that
correspond to their geometry and composition. As the shafts spool up in
rotational speed, they pass through several excitation frequencies
corresponding to pressure fields and wakes interacting with struts, stators,
and other internal objects. The airfoils can begin to resonate at these
critical speeds, with potentially disastrous results if too much time is spent
at those conditions. Since the resonant frequencies are usually on the order
of 1 to 10 kHz, billions of vibratory "stress cycles" can build up in just a
few dozen hours. Turbomachinery designers use Campbell diagrams to describe
these effects, and recommend avoiding these shaft speeds.
No one got the correct answer!
- The Aeroquiz Editor.
Week of 4/19/99:
Q:
The year is 2030. The Martians, having monitored Earth's radio
transmissions for well over a century, have adopted baseball as their favorite
pastime. The Mars Stars have challenged your team to a winner-take-all
game of interplanetary domination on a neutral venue: the desolate surface of
the moon. Your two ace pitchers, Roger Clemens Jr. - with his blistering
fastball, and Tom Glavine Jr. - with his unhittable breaking ball - have
comparable statistics. Who should start?
A:
Start the fastball pitcher because the breaking ball will not curve
without air.
Congratulations to Ronnie Gladden.
Go with the heat. But just to show that conventional wisdom isn't always
accurate, the only no-hitter to date in the thin air at Denver's Coors
Field was the "Nomo No-No" on September 17, 1996, by LA's curve ball thrower Hideo Nomo.
- The Aeroquiz Editor
Week of 4/26/99:
Q:
You wouldn't expect a nineteenth-century lighthouse to launch itself
into orbit. Or would you? Why?
A:
One of the most interesting structures at Cape Canaveral is a lighthouse
built shortly after the Civil War. From a distance, it looks so much like
a rocket that many people have mistakenly waited for it to launch. In the
image below, a real rocket is shown lifting off behind the lighthouse.
No one got the correct answer!
- The Aeroquiz Editor
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