|
|
Multidisciplinary
Design, Analysis, and
Optimization Branch
|
|
|
| |
EDUCATIONAL ACTIVITIES: THE NASA AEROQUIZ
|
|
|
| |
|
| |
Week of 5/3/99:
Q:
In June of 1918, 25 fighter aircraft prototypes were tested before members
of the German Air Force. The overall winner was the Fokker D-VIII; a parasol
monoplane having plywood-covered wings with excellent strength and structural
rigidity. A production order was placed for 400 aircraft. For these
production aircraft, the German Air Force required that the rear wing spar
be strengthened even further, as required by design practices of the time for
conventional strut and wire-braced wings. After 20 of these aircraft were
delivered in July, 1918, several were quickly lost in flight when the wings
tore off at high speed. In ground tests, the wings were loaded with sand
bags and tested for ultimate strength. Much to the consternation of engineers,
the airplane passed all of the static tests. What was causing the airplane
to shed its wings in flight?
A:
Sounds like drag divergence.
Congratulations to Dan Shedd.
This may be the first documented case of a static aeroelastic phenomenon
know as aerodynamic divergence. When an airplane flies, the force of the
air on the wing at certain angles can cause the leading edge to twist upwards.
According to Anthony Fokker's autobiography, the strengthening of the rear wing
spar caused the torsional axis to move rearward and downstream of the wing's
aerodynamic center. When it reached a certain critical dynamic
pressure (dependent on airspeed and altitude), the aerodynamic twisting torque
exceeded the elastic restoring torque and the wing became statically unstable.
The solution to the problem was to strengthen the D-VIII's front spar so that
the torsional axis was ahead of the aerodynamic center as it was in the
prototypes.
- The Aeroquiz Editor
Week of 5/10/99:
Q:
On April 25, 1999, two Canadian Twin Otter airplanes strafed
northeast Ohio. But it was not the kind of attack you might think.
Interestingly enough, it was actually done at the request of Ohio's
Department of Health. The targets: raccoons. What happened?
A:
750,000 chunks of fish meal were dropped over 1700 square miles
of northeast Ohio. Wedged inside each piece was a small pouch of raccoon
rabies vaccine. The raccoons that eat the bait become vaccinated.
It is all part of the semiannual drive to stop the westward spread of
raccoon rabies.
No one got the correct answer!
- The Aeroquiz Editor.
Week of 5/17/99:
Q:
Sometimes mechanical shaking devices are deliberately connected to
an airplane and turned on. Why?
A:
To simulate vibrations experienced in-flight, and thus test and
observe the way the airplane (or a specific part) reacts to such vibration.
Congratulations to Andrew Field.
Ground vibration testing is often done on airplanes in support of
airframe flutter analysis to verify calculated vibration modes. Flutter
is a devastating self-excited dynamic instability sometimes encountered
in flight and must be avoided at all costs. Analysis of the vibrational
modes measured in a vibration test is valuable in airframe structural
design so that the aircraft never experiences flutter.
- The Aeroquiz Editor.
Week of 5/24/99:
Q:
Air travel by zeppelin was effectively ended in 1937, when the
rigid airship Hindenburg burst into flame while landing in Lakehurst,
New Jersey. The use of hydrogen as the lifting gas has long been blamed
for the disaster. It was assumed that some ignition source, likely
lightning or some other electrical discharge, caused the extremely
flammable hydrogen to ignite. Recent studies, however, place the
blame on a much different flammable material. What was it?
A:
It was the doping (glue) compound used in the covering of the skeletal structure.
Congratulations to Daniel Shedd.
According to research done by NASA and reported in the Smithsonian's
Air and Space magazine, the culprit is likely the highly flammable
fabric that covered the dirigible. Many characteristics of the incident
are not consistent with a hydrogen fire: it did not explode, but burned
very rapidly in omnidirectional patterns; it remained aloft and upright
for many seconds after the fire began, which indicates that the hydrogen
did not burn immediately; falling pieces of the fabric were aflame and
not self-extinguishing; and the flames were very bright and colorful,
whereas a hydrogen fire makes no visible flame. And no one smelled garlic,
the scent of which had been added to the hydrogen to help detect leaks.
The Hindenburg fabric was found to be made of a cotton substrate with an
aluminized cellulose acetate butyrate dopant. The fire characteristics
are consistent with a huge aluminum fire. The brightness of the space
shuttle's rocket boosters are an example of aluminum-based combustion.
It was likely the extreme flammability of the Hindenburg's fabric envelope
which caused the disaster and not the hydrogen gas inside.
- The Aeroquiz Editor.
Week of 5/31/99:
Q:
The Mach 3 SR-71 spyplane flies so fast that the airframe in the
vicinity of the fuel tanks can reach five to six hundred degrees Fahrenheit.
To withstand these high temperatures, an extremely low vapor pressure
fuel called JP-7 was formulated specially for the SR-71. JP-7 is so hard
to light, you could extinguish a cigarette in a dish of it. With such a
high flashpoint, how is the engine started?
A:
A chemical called TEB is used to create a chemical reaction which
ignites the JP-7.
Congratulations to Ryan Verwest.
Triethylborane, or TEB, is
a chemical that spontaneously burns at high temperature upon contact with
air. A supply of TEB is used to ignite the JP-7 at engine start-up and
when turning on the afterburners.
- The Aeroquiz Editor.
|
|
|
|
