Questions
1. Next time you take a flight, obey the following :
i. Don’t flush the plane toilet while seated.
ii. Carrying Mercury is prohibited.
iii. Laptops and CD-players are banned during take-off.
iv. and in case, you are a pilot, you are not allowed to have beards.
Are these rules justified?
2. In many events, athletes do take advantage of reduced aerodynamic drag that occurs on hot
days and at high altitudes. This reduction in aerodynamic drag, for example, has been
attributed to help U.S. athlete Bob Beamon (in Mexico City, 1968) to break the world long
jump record by almost 2 ft! Can one argue that an airplane will experience better performance
trying to take off from a high altitude runway on a hot day?
3. During high-speed maneuvers in modern fighter aircrafts, pilots experience centrifugal forces
equivalent to many times the force of gravity. When this happens, blood can pool in body’s
lower extremities and the pilot is susceptible to blacking out. A G-suit counters this problem
by squeezing the pilot with expandable bladders to keep more blood in the upper body. The
U.S. Navy’s Blue Angel pilots, however, choose not to wear them. Why?
4. In June 1918, 25 fighter aircraft prototypes were tested before members of German Air
Force. The overall winner was Fokker D-VIII, a monoplane having plywood-covered wings
with excellent strength and structural rigidity. The German Air Force placed an order for 400
aircrafts with a request that the rear wing spar be strengthened even further. After 20 of these
aircrafts were delivered in July 1918, several were quickly lost in flight when the wings tore off
at high speed. Time to blame the structural engineers! Those poor fellows again performed
the ground test, this time the wings loaded with sand bags to ultimate strength – what a
surprise! The airplane passed all of the static tests! Can you solve the mystery?
5. In the world of aircraft, does sun ever rise in the west?
6. During cryogenic testing at NASA’s National Transonic Facility (NTF) wind tunnel, operators
spray cryogenic liquid Nitrogen into the flow upstream of the fan. Why?
7. Is it possible to see “earthrise” or “earthset” from the moon?
8. Stealth aircrafts are supposed to be aircrafts difficult to detect. Perhaps you will be surprised
to know that exterior lights are attached to the Stealth and they are turned on when it tries to
be ‘stealthy’! Can you guess why?
9. Richard P. Feynman, the great Nobel Prize-winning physicist, called it “the most important
unsolved problem of classical physics”. What is it?
10. Through his spyglass, in 1609 Galileo observed Saturn’s rings. He publicly announced it.
Nobody believed him. So Galileo asked them to see it in their own eyes (using his spyglass).
But it happened other way round! Nobody could see the rings (including Galileo himself). Was
Galileo a liar?
Answers
1.
i. This has the danger of being vacuum-sealed. In 2001, a passenger flying across the
Atlantic on a Boeing-767 became vacuum-sealed to a toilet seat after flushing.
Engineers were later able to pry her loose only after the aircraft landed!
ii. Mercury corrodes Aluminum-alloys (what planes are largely made of).
iii. They emit electro-magnetic (EM) radiation which can interfere with aircraft’s sensitive
navigation instruments’ signals during the first 10,000 ft.
iv. Pilots must be clean-shaven. It’s not a style issue; a beard would stop the Oxygen
mask from fitting tightly enough, if the cabin pressure suddenly drops down.
2. No, the high altitude would translate into a long take-off run due to thinner air. Although drag
is less on a hot day at high altitude, so is lift. Also the low-density air results in a reduced
mass flow rate through the engine. So thrust is penalized. Shortest take-off runs occur at low,
cool altitudes.
3. The suits are restricting and uncomfortable, preventing the Angel pilots from performing
precision flight. Instead they keep their body in excellent shape with vigorous training. When
high ‘g’ occurs, they squeeze their abdominal muscles – something they master during
training session. Normally they can sustain up to 5g without any problem.
4. This may be the first documented case of a static aero-elastic phenomenon known 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 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, the aerodynamic twisting torque exceeded the elastic restoring
torque and hence the blunder. Solution : Strengthen the D-VIII’s front spar so that the
torsional axis remains ahead of the aerodynamic center, as was in the original design.
5. Yes. If the aircraft is heading west faster than the Earth rotates, it would appear to the
occupants of the plane that the sun was rising in the west. Here is one such experience filed
in NASA archive. Jerry Glasser and Ted Ross once took off after sunset in an SR-71. They
flew a westerly course and since the day/night terminator travels at only about a thousand
miles per hour at the equator and the SR-71 (a supersonic spy plane) travels much faster
than that, they watched the sun rising in the west. After a while, they turned south, the sun set
again. Later in the mission, they headed west again and observed the sun slowly rise over the
horizon. Perhaps they are only people to see sunrise twice a day, both at west!
6. To vary the Reynolds’s number by altering density(ρ). This allows the model size to be
smaller and/or velocities to be lower to achieve the necessary transonic parameters.
7. No, due to earth-moon tidal forces, the moon’s rotation long ago became synchronized with
its revolution about the earth. Therefore, to an observer at a given site on the moon, the earth
will always appear in the same point in the sky.
8. During day, we can see aircrafts because they are darker than the sky. Brightening them with
lights make them less visible. Stealths match their luminance with that of the sky (In fact, it
can vary its luminance since you might get a situation when overcast sky changes to sunny
sky). Modern Stealths use electro-optical photo-sensor which turns on and adjusts the hightech
illumination devices automatically.
9. Turbulence.
10. Because Saturn is tilted, when its rings are facing Earth edge-on they “disappear” from our
view. We now know this happens every 14 years or so. But poor Galileo was questioned
about his sanity when rings “disappeared” and then “reappeared” a few years later.
(Courtesy:Wings 2006 By IIT KGP)
