7 Flight Mystery and Aerodynamic Principles
453
Fig. 7.9 Hot air balloon made of linen by the French Montgolfier brothers
achieved a successful flight was invented by the Montgolfier brothers. The
Montgolfier brothers burned a kind of grass or other substances under the
balloon, and the heated flue gas enters the balloon. The density of the hot
flue gas inside the balloon is less than the cold air outside, which creates
buoyancy and causes the balloon to lift-off. The principle of hot air balloon
and Kongming lantern is the same. As long as the buoyancy is greater than
gravity, the balloon can fly off.
Another simple device that is driven by the upward movement of hot gas
is the Chinese trotting horse lamp (as shown in Fig. 7.10), the principle of
which is similar to that of a balloon. People light candles in the lamp, when
the candles burn for a certain period of time, the temperature of the gas
inside the lamp will rise. At this time, the lamp will rotate. The lampshade
is painted with different people riding the horse. People see the painting on
the rotating lampshade as if the horse keeps going backwards, so it is called
trotting horse lamp. How does the upward movement of the hot air flow
rotate the lampshade? From the schematic diagram of the lamp, when the
candle is ignited, there will be an upward movement of hot air inside the
453
Fig. 7.9 Hot air balloon made of linen by the French Montgolfier brothers
achieved a successful flight was invented by the Montgolfier brothers. The
Montgolfier brothers burned a kind of grass or other substances under the
balloon, and the heated flue gas enters the balloon. The density of the hot
flue gas inside the balloon is less than the cold air outside, which creates
buoyancy and causes the balloon to lift-off. The principle of hot air balloon
and Kongming lantern is the same. As long as the buoyancy is greater than
gravity, the balloon can fly off.
Another simple device that is driven by the upward movement of hot gas
is the Chinese trotting horse lamp (as shown in Fig. 7.10), the principle of
which is similar to that of a balloon. People light candles in the lamp, when
the candles burn for a certain period of time, the temperature of the gas
inside the lamp will rise. At this time, the lamp will rotate. The lampshade
is painted with different people riding the horse. People see the painting on
the rotating lampshade as if the horse keeps going backwards, so it is called
trotting horse lamp. How does the upward movement of the hot air flow
rotate the lampshade? From the schematic diagram of the lamp, when the
candle is ignited, there will be an upward movement of hot air inside the