Hey guys! Jon from Fly8ma.com and today we're talking about the
four forces of flight. How these gigantic machines get off the ground. So how does
an airplane actually get into the air and what forces are acting upon it when
it's flying through the air. So there's four fundamental forces. We'll focus on
each one. So we see this gigantic Boeing 747 lift off the ground. There's four
fundamental things that are acting on it. The same as the four forces that are
acting upon our little Piper Cherokee here as it rolls down the runway and
takes off. We'll get right to it.
So let's define the four forces that are always acting upon an airplane whether
it's taking off flying through the air or coming in for a landing. The four
forces are thrust, which comes from the engines, the propeller, or the jet engine,
drag, that tries to slow the airplane down and fights against those engines,
the lift keeping the airplane in the air, what's
holding it up the wings, and the weight of the airplane. Notice we don't
say gravity, but we say weight of the airplane acting in the opposite
direction, fighting against that lift, trying to pull the airplane down towards
the ground. Now it's important to note that these forces don't ever bend or
change the angle that they're pulling in. Thrust will always directly oppose drag
and lift will always directly oppose weight. So regardless of the bank or the
pitch of the aircraft, you're always going to have lift directly opposing
weight and thrust directly opposing drag. Now let's take a look at these forces as
they act upon the airplane as we're flying along straight level here say at
100 miles an hour and we have our four forces all in equilibrium the airplanes
level at a thousand feet in 100 miles an hour and then we accelerate the airplane
say to 150 miles per hour and as we speed it up as we accelerate it then we
must have more thrust than drag as it accelerates now once we get to say 150
miles per hour and we're stable again at cruising along at 150 then we're back to
the four forces being equilibrium lifts equals weight and thrust is equal
engrossed able at 150 miles per hour in a thousand feet now let's go ahead and
look at four forces when we're climbing or descending and so here's the tricky
part if we take our airplane and we want to start climbing say we're at a
thousand feet we're going to go ahead and go up to 2,000 feet then we need to
accelerate upward generate more lift than wait and the airplane starts
accelerating upward now once we get to say 500 feet per minute up weight and
lift will then equal again and we'll continue to climb upward so we are
climbing getting higher but we're not accelerating upwards so the
our forces are always equal when you're an unaccelerated flight unaccelerated so
if you're stable at 100 miles per hour in 500 feet a minute going up then the
four forces are equal lift equals weight thrust equals drag if you are
decelerating accelerating or if you go ahead and stop climbing from say 500
feet per minute and level off then momentarily your lift will be less than
weight so that you can decelerate your upward motion and level off at say 2,000
feet here and then you resume level on accelerated flight in the four forces go
back to being equal so as we look at our Piper Cherokee here rolling down the
runway as we accelerate down the runway we have more thrust than drag the
airplanes increasing its speed and we don't quite have enough lift to get off
the ground so we have less lift and wait until eventually we have enough airspeed
to generate enough lift we get more lift than weight in the aircraft leaves the
ground starts climbing upward and then eventually once we're established in
climbing flight the four forces are equal we're stable at 85 miles per hour
or climbing at say 500 feet per minute and everything's stable if four forces
are equal as we're climbing upward now even as we approach to land here the
four forces are actually equal we're descending at 500 feet per minute
our airspeed stable at 80 miles per hour and as we come down get close to the
ground we'll start to ease back on the controls that increases our lift on the
wings decelerating us as we come down to the ground is try to level off close the
ground it also increases drag which makes the airspeed slow so that we
touchdown right about 60 miles per hour in as close to a zero rate keep per
minute descent as possible as we roll out here drag is greater than thrust
because of the powers at idle more applying brakes and the aircraft slows
down it generates less and less lift and settles down onto the wheels and stays
nice and stable on the ground what you ultimately need to remember here is that
there's four forces that act upon every airplane flying through the air lift
weight thrust and drag and those four forces are often equal unless the
airplane is a seller rating either up-down or forwards
or backwards if it's an unaccelerated flight all four forces are equal even if
it's climbing or descending hope you found this helpful
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