Quote:
Originally Posted by Cougar
...I would think that it largely depends on the initial relative velocity of the {paper airplane} and the molecules in the atmosphere. At high enough relative velocities, any interaction with even the "uppermost" atmosphere would turn your paper airplane to toast.
Grains of sand have different aerodynamics than paper airplanes, but they're also pretty light, and it may be instructive to recall that grains coming in at very high speeds spectacularly combust into fireballs visible from the ground...
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The small "grain of sand sand" meteoroids illustrate an object:
(1) With a low ratio of surface area to mass
(2) On a steep reentry angle (30 degrees typical)
(3) At very high velocity (11 to 71 km/sec)
...will burn up
None of these apply to a paper airplane or a balloon reentering from earth orbit.
As opposed to a tiny meteoroid, a paper airplane:
(a) Has a high ratio of surface area to mass
(b) Is on a shallow reentry angle (1 degree)
(c) Is going much slower on average (7.8 km/sec)
For the airplane, the faint air drag at entry interface would cause aerobraking and rapid deceleration due to the large surface area, low mass and kinetic energy.
Compare a tiny "grain of sand" meteroid to a paper airplane:
Consider a reentering spherical meteoroid that is 1 cubic millimeter, specific gravity of 3 g/cm^3 (average), moving at 15 km/sec on a 30 degree entry angle (also average).
The cross-sectional area is 1.2 mm^2, and the mass is .003 grams. The ratio of cross-sectional area to mass is 4 square cm per gram, or 0.5 lb per square foot.
Kinetic energy is given by KE = 1/2 * m * v^2, so the sand grain's kinetic energy is 33,750 Joules.
Compare this to a paper airplane, mass 3 grams, wing area 500 square cm, reentering from orbital velocity of 7.8 km/sec.
The paper airplane's ratio of wing area to mass (wing loading) is 0.012 pounds per square foot, or 40 times lower than the "grain of sand" meteoroid.
The paper airplane's kinetic energy is 91,260 Joules, 3x the tiny meteor, but dispersed over 41,000 times the surface area.
The paper airplane must only dissipate 182 Joules per square cm, vs the meteroid's 2.75 MILLION Joules per square cm. That's why the tiny meteroid burns up.
I don't know for sure a paper airplane would survive, but it seems conceivable once you think about the physics involved.