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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 3/3/97:
Q:
Suppose you are in a windowless room aboard a modest-sized
wheel-shaped space station. The space station is spinning about its hub to
maintain normal simulated Earth gravity. What simple dynamics test(s) can
you perform to convince yourself that you are in space and not on the Earth?
No correct answers; the question stands another week!
Week of 3/10/97:
Q:
Suppose you are in a windowless room aboard a modest-sized
wheel-shaped space station. The space station is spinning about its hub to
maintain normal simulated Earth gravity. What simple dynamics test(s) can
you perform to convince yourself that you are in space and not on the Earth?
A:
One way is to try to spin a coin on the floor of your room. The coin
will not spin because, by conservation of angular momentum, a spinning object
tries to maintain its position in space, while the space station is
continually changing its position in space. Another way would be to observe
the effect that the Coriolis force, greatly exaggerated on the space station,
would have on the trajectories of objects thrown or dropped in the room.
Congratulations to Chris Miller.
Week of 3/17/97:
Q:
"We're coming up on Mach one," said Orville, as he flew the two-seat
supersonic jet interceptor higher and higher. "We should make sure our
variable-geometry convergent-divergent nozzles are configured to perfectly
expand the exhaust flow to ambient pressure. That way, we'll maximize
our gross thrust. We don't want to have any nozzle expansion losses when
we're trying to get through the transonic drag rise!"
"No," said Wilbur from the back seat. "We should open the nozzle exit
area so that the flow is a little overexpanded. We'll suffer a gross
thrust overexpansion loss due to pressure drag at the nozzle exit, but
that's all right. After all, it's not
gross thrust that we want to maximize!" Why is Wilbur's plan for
punching through the transonic drag rise likely better than Orville's?
A:
Because the installed net thrust (which is what
really matters from an overall systems perspective)
can be better when the nozzle is somewhat overexpanded.
Installed net thrust includes the external boattail drag penalty, which can
be very large, especially at transonic flight speeds. One method to reduce the
boattail drag of a convergent-divergent nozzle is to open up its exit
area beyond its ideal uninstalled value. Then the external flow
around the boattail surface produces less drag on the afterbody. So the
installed net thrust of an overexpanded jet can actually be better than
the installed net thrust of an ideally expanded jet!
Congratulations to Bill Strack.
Week of 3/31/97:
Q:
"Let's see now," the FAA aircraft certification engineer said to
himself. "95.4, 101.1, 97.8... add those together... Got it! 103.5!"
Is the engineer right? Or can't the FAA get good help these days?
No correct answers! The question stands one more week!
Week of 3/31/97:
Q:
"Let's see now," the FAA aircraft certification engineer said to
himself. "95.4, 101.1, 97.8... add those together... Got it! 103.5!"
Is the engineer right? Or can't the FAA get good help these days?
A:
The certification engineer
is correct if he is adding sound levels in decibels!
Congratulations to Arnie McCullers.
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