I hope I convey my point probably, but why do planes go so many thousands of feet in the air? Is it faster that way, or could they achieve similar flight times at a lower altitude?
Does it have something to do with the curvature of the earth?
In: Engineering
Planes travel faster the higher they go. Which in turn means less fuel consumption. Which in turn means less expenses.
Air is thinner at higher altitudes, which mean they face less drag(air resistance.
Ever put your had out the window while driving and notice it has a tendency to be pushed back? Well imagine that but with an airplane, being slowed down by the air.
Technically planes could operate at similar speeds at lower altitudes, but the problem is its less fuel efficient due to the engines needing to work harder to maintain speed, so it costs more money, and it could create noise problems for those on the ground.
They don’t *need* to, but it’s much more efficient if they do. Run 100ft in a line. Then run 100ft in a pool. It’s much harder in the pool because it’s thicker
Wait, since air is so thin at 30,000ft, is there enough oxygen to run the engines?
Whatever plane you have runs at as high of power as it runs at (
POWER
=THRUST (important later)), and as I can guess that anyone could guess thrust has something to do with speed (also relevant later… but let’s assume 100٪ throttle/thrust–>same thing (ultimately)).
All airplane wings have a fixed airfoil. The airfoil is what provides lift.
LIFT
= ALTITUDE (ultimately).
So the trick with understanding those two variables at once and relative to each other is:
the FASTER and airplane goes the
HIGHER IT CAN go until it reaches air thin enough such that at its given (max?) speed (as defined by how much it’s being PUSHED by the (given)) thrust with the fixed airfoil it cannot go any higher… on the other hand it’s going as fast as it can go because the thrust is there but no energy is going into Rising the altitude anymore
So what does the airplane do with the extra energy not being used anymore to push it upwards… it converts it into SPEED.
So what do modern ( think all ) airplanes do? They set their throttle for maximum engine efficiency and leave it theren which provides X amount of
THRUST, which provides X amount of
ALTITUDE which provides X amount of
SPEED… ultimately.
This is why modern airliners (physics wise relatively equal to each other) always fly at 30 some thousand feet at 600 and some miles an hour. THRUST.
Typical cruise numbers:
0.84 Mach at 31000 feet is 314 knots (361 mph) indicated airspeed.
That’s about 623 mph over the ground / true airspeed.
If that same plane were flying at sea level it would be covering ground about half as fast.
Air molecules passing an airplane are like tennis balls thrown at you.
You can overcome 100 tennis balls thrown at you at 50mph, or chose to overcome 1 tennis ball thrown at you at 500mph, the energy you have to fight is the same.
So by going higher, there is less air (less tennis balls) so you can sustain a higher speed.
Others have explained the “air is thinner higher up” thing well enough, so I think I’ll add a cool FYI which 5 year old me would have loved to have learned.
When fighter planes are shooting radar-guided missiles at each other, the primary way you defend yourself is to turn around and dive into thicker air close to the ground. Missile rockets do not last forever, so if you make the missile maneuver through dense air long enough, they will lose their energy and eventually fall out of the sky.
Source: Too many DCS videos.
Adding to all the comments about aerodynamic efficiency, airliner jets on very short flights will climb all the way to their cruising altitude and stay there for a few minutes before descending all the way down. It is worthwhile in the fuel savings to do that than cruise at a lower altitude.
Have you ever hit a goose at mach 2? Fury and feathers, dude.
Latest Answers