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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 5/8/00:
Q:
You are cruising in a commercial jet at 35,000 feet. You
look out your window. It's a nice day with the sun shining
overhead. You look along the span of the wing and
are surprised to see an irregular blur of light and shadow
dancing back and forth above the wing. You are just about
to cancel your order for a second martini when you recall
details from your compressible fluid dynamics class. What
did you remember?
A:
I remember that even while traveling at subsonic speeds
in an airliner, the local flow velocity over the wing can
reach the speed of sound (or higher) and produce shock waves.
What you're seeing is a weak shock produced by traveling faster
than the critical mach number for that wing.
Congratulations to Frank Brown.
Unless you're William Shatner in the "Nightmare at 20,000
Feet" Twilight Zone episode, you're seeing a shock wave!
As Frank wrote, there are often regions around the
wing surfaces where the flow has been accelerated to supersonic
speeds. When this occurs, there is a weak shock wave at the
downstream boundary between the subsonic and supersonic flows.
If the conditions are right, you sometimes can be lucky enough
to see the refracted light from the shock wave with your naked eye.
- The Aeroquiz Editor
Week of 5/15/00:
Q:
An aircraft hangar at the top secret Area 51 contains
5 Vogon flying saucers equipped with planetary demolition
beams. All together the hangar contains 14 Vogon saucers,
8 saucers with demolition beams, and 2 saucers that are
neither Vogon nor have demolition beams. How many flying
saucers are in the hangar?
A:
Wow! The government is hiding 19 flying saucers in that Area 51 hangar!
As stated, there are 5 Vogon flying saucers equipped with planetary
demolition beams. To have a total of 14 Vogon saucers, there must
be 9 additional Vogons that are not equipped with this popular planetary
annihilation package.
Since it's also stated that the hangar contains 8 saucers with
demolition beams, there must be an additional 3 saucers that are
not of the Vogon type that have the beam. This brings the running
total to 17.
Finally, there are 2 other saucers that are neither Vogon nor have
demolition beams. Total: 19 UFOs.
Congratulations to Brian Kitchen.
Week of 5/22/00:
Q:
In a normal airplane landing, the pilot approaches the runway
at a reduced throttle setting and "flares" (stalls) the airplane
just before touchdown. This is to ensure that the vertical sink
speed and contact forces are very small. Some pilots, however,
do not flare their airplanes when landing. In fact, they approach
at a high throttle setting and fly right into the runway at high
speeds. Yikes, who are these people and what are they doing?
A:
These pilots are Naval aviators.
Upon touching down on the aircraft carrier, the pilot will apply
full throttle. If the tailhook grabs an arresting cable, then
the airplane will come to a complete stop regardless of throttle setting.
Should the hook miss the cables, then the full throttle setting is
required to "bolter" or take off again in a very short distance.
Congratulations to Steve Cook.
Week of 5/29/00:
Q:
With your collar turned against the cold, you exit the
terminal gate, hurry up the portable stairs, and climb into
the airplane that will take you home. This scheduled flight
will be a long one for an interstate hop, but it is still within
the normal range of the regional twin turboprop that will be
your home for the next two and a half hours. "Full flight," you
mumble under your breath as you walk down the aisle. And indeed
it is -- every seat but yours on the 30-passenger turboprop
is occupied. As you settle into your seat, you look out
your window and notice the ground crew topping off the fuel
tanks. Just as you are about to turn your attention elsewhere,
you see an airline employee come out of the gate and walk
towards your plane. He enters the cabin and runs his hands
through his disheveled hair before he speaks. "Sorry about
this, folks. We can only take twenty passengers on this flight.
I'm going to have to ask for volunteers to stay behind."
"That's unexpected," you think. "They wouldn't have scheduled a
full flight if they knew in advance that there was some sort of
problem." You think for a moment. "Oh, of course!"
What is the most likely reason for having to off-load passengers?
Can you find the clue?
A:
They are facing a strong, unexpected headwind, which will mean
filling the tanks to the maximum capacity for such a
long flight. Hence the need to off-load passengers.
Congratulations to Nicolas Cousineau.
Since it was a scheduled flight, with presumably correct payload
calculations carried out well in advance, the reason for off-loading
passengers must be due to something sudden and unexpected.
Since it's a cold day, the reason couldn't be a sudden heat wave
(which would lengthen the takeoff field distance, possibly beyond
what was available, due to wing lift and engine thrust penalties).
Quite a few people suggested that the cold weather increased the
fuel's density (and since the tanks were topped off, that may have
put the airplane weight over the maximum weight allowed). But
that's unlikely, since airframe designers consider
those effects. Also, having to off-load ten passengers and baggage
amounts to about 2000 pounds -- that's a big increase in fuel weight
for an airplane that carries only a few thousand pounds of fuel!
The real reason? Sudden forecasted headwinds along the route.
Remember the airline employee's disheveled hair?
- The Aeroquiz Editor.
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