The Gift of Lift
As long as weight is greater than lift, you're grounded. But if you can create lift greater than your aircraft's weight, you're
ready for takeoff. Simple enough, but easier said than done. Unlike weight (which, thanks to gravity, is always exerting
itself), lift isn't exactly self-motivating. We have to create it ourselves. Generally, we do this by forcing air around an
"airfoil," like a wing.
Thrust or Bust
Thrust is a mechanical force that propels objects forward. Aircraft create thrust in different ways. We can't be
sure how your chosen craft will work, but Newton's third law of motion ("to every action there is an equal and
opposite reaction") will no doubt be key. By propelling gases, such as plain old air, backward, an aircraft's
engines generate the thrust that pushes them forward.
Jets and rockets use explosive chemical reactions to blast gases backward, and all that gas backwardness
generates equal and opposite forward thrusting. Propeller-based aircraft, on the other hand, use internal
combustion engines to rapidly spin blades that behave like rotating airfoils. The faster a propeller spins, the faster
it propels air backward--and backward blowing leads to equal forward thrusting.
What a Drag
If weight is a downer, drag is a stopper. Drag is the aerodynamic force that opposes an aircraft's motion
through the air. Air is something and not nothing after all. And when any two objects slide past each
other, they generate friction, which siphons off kinetic energy (motion) and converts it into heat. The
more friction, the more energy the sliding objects lose, and the more they slow down.
Major Tom to Pound Control
When it comes to flying, weight is actually the easiest force to deal with, because its effects are
relatively constant and easy to measure. Every aircraft has a mass. We measure gravity's pull on that
mass as weight, and, since gravity is basically constant here on Earth, so is the aircraft's weight (at
least until it starts adding passengers, or burning fuel).
Getting an aircraft airborne is basically a matter of generating enough lift to overcome its weight. Of
course, one way to help do that is to lighten the load as much as possible from the start. Hence all
aircraft parts are made to weigh the minimum while still safely doing their jobs, and airplane designers
try to remove all unnecessary components from their crafts. Keeping an aircraft "fit and trim" simply
makes the job of lifting it easier.