How do planes fly so high in a thin atmosphere if they need lots of air to generate lift?
In: 0
The answer is speed. (And plane weight+design).
But “ordinary” planes can fly on certain altitude only on certain speed.
They fly at the optimal height they were designed for, thick enough to get lift, thin enough to have the benefits of less friction
There’s enough air at the altitudes they fly, which is dependent on speed and wing shape and size. Thin atmosphere isn’t no atmosphere, and if a plane presents enough wing surface and generates enough forward thrust to keep enough high pressure air under the wing to generate lift, the plane will fly. Of course, for each plane, there is an altitude that is too high, but until they reach that point, they’ll fly.
Speed mostly. As you go up in altitude, the air gets less dense. In turn the plane moves faster through the air to generate lift. In the aviation world this is the difference between indicated airspeed and true airspeed.
Not that its very ELI5 but if you look at the formula for lift, velocity is squared. It is one of the biggest factors to creating lift for a plane. Wing area/design would be the next big factor.
The short answer is speed. The long answer is much more complicated.
Lift is calculated as L=½ρv²S(cl), thus, double the speed 4 times the lift. At high speeds, usually Mach 0.3 and higher, we have to correct the lift coefficient because the air actually compresses.
This new lift coefficient is (cl)=(cl₀)/√(1-M²). This correction works up to M≈0.7, where most aircraft start to go transonic. Because 1/x gets pretty big pretty quick for fractional x, we really just have to worry about maintaining the speed necessary for being in the compressible flow regime.
If we go any faster, the corrections for transonic compressibility require lots of calculus, linear algebra, and looking things up in a database. Supersonic becomes easy again because we can use theories that let us just look things up on a table.
This is where turbine engines really shine. The compressor stage of a turbine engine is incredibly effective at compressing air to produce a combustible mixture (which in turn can be exhausted to produce thrust). These engines also produce an incredible amount of thrust for their size. But because they continuously burn fuel, they burn a lot of it.
[deleted]
Latest Answers