Answer 1:
This is a good question. I assume here you want
to compare the drag on Earth and in space. The
short answer is the total drag will be much
smaller.
The drag in aircraft is complicated and
consists of many contributions that resists the
motion of aircraft. I will talk about a few type
of drags:
1) Parasitic drag. It is the resistance
force the aircraft experience when it is moving
inside the medium, which is air in this case.
There are several contributing factors that
determine the drag force: the form of the
aircraft, relative velocity, the density of the
medium (air).
a) form drag: If you have a really bad
design with a large cross section along the motion
direction, you will certainly experience stronger
resistance because of the air, which means larger
form drag. This part will not depend on where you
are, in space or on Earth.
b) skin friction: when the aircraft moves
inside the medium, it will experience the
friction. This type of drag will depend on the
relative velocity. The higher the relative
velocity, the stronger skin friction will be.
If the wind is blowing in the same direction, the
drag due to the sink friction will certainly be
smaller and vice versa. Of course, the skin
friction will also depend on the air
density. Think about that, if the density is
close to zero, as in space, little or no friction
will exist. So in short, the type of drag will
be much smaller in space with almost zero air
density.
2) Lift induced drag: If an airplane
wants to fly and stay in air, you need the
wings (and other parts) to create the lift to
counter the gravity, otherwise it would be
extremely difficulty for an airplane to stay in
air. The lift will also project part of its force
against the moving direction. Such force is called
lift induced drag. This type of drag will
be inversely depend on the air density in a
reasonably range. However, this type of force
will be much smaller when the relative velocity is
much larger. Assuming everything is the same, you
would expect larger lift induced drag. But in
reality, since on Earth you need large speed to
create lift to counter the gravity, lift induced
drag is not that big. While in space the gravity
is much smaller, thus it does not require that
amount of lift to counter the gravity, therefore,
I would say the lift induced drag is also much
smaller in space.
3) Wave drag: This is the drag we have
when the aircraft travels at the transonic and
supersonic speed due to the presence of
shock waves. In space, the air density is
close to zero. No shock waves will come into
existence because the lack of air. This this type
of drag will also be much smaller in space.
In summary, the total drag in space will be
much smaller.
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