Comment by namirez
2 years ago
Not quite true! Modern airplanes are way more complex. First of all, all modern airplanes have supercritical airfoils which go back to the 60s and 70s. Secondly, the airfoil of the wing root is typically different than the wing tip. Finally, new composite wings are adaptive during flight. They change their shape slightly to maximize efficiency.
Case in point would be modern gliders (sailplanes). One simple parameter that describes their aerodynamic performance is the maximum achievable Lift/Drag ratio, and that dimension-less ratio has climbed from ~30 in the 1960s to as high as 75 today. That means modern gliders can, using the same altitude/energy, go over 2 times further horizontally. The L/D is not the ultimate decider of performance but it is quite representative of the aerodynamic performance improvements.
BTW, all lift based flying objects have an L/D ratio (which depends mainly on the airspeed), this includes birds, fighter jets, commercial airliners; and the discrepancies can be pretty interesting. For example if one looks at the L/D of the Concorde vs a subsonic jet it becomes clear why it was so damn expensive to operate. Or why the U-2 looks like a glider :). I cannot find any aerodynamic performance data on any famous long endurance (>24h) unmanned drone, but I bet it's rather high as well.
> Concorde
Another good example is the space shuttle. It does actually glide back down. But it glides like a brick at first (1:1 during its initial braking into the atmosphere), and then like a less dense brick (2:1 while it's still supersonic), and then like a brick with shitty wings (a whopping 4:1 or whatever on final approach). Which is about what the Concorde is during landing, 4:1, yea.
Pretty crazy stuff
(Obviously the space shuttle was a tradeoff for, you know, getting it into orbit via rocket)
Your numbers are right but your analogies are misleading. I get “glides like a brick” is hyperbole, but you’ve added enough detail I can see people taking it seriously.
A brick’s L/D is much worse than 1:1. I’m seeing people say 1:10 online, but I can’t find a source and I think that’s incredibly high. A real brick is going to tumble and essentially not make any lift.
A less dense brick will have the same L/D. L/D is about the shape, not the mass.
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I saw the space shuttle land once. From my perspective, it seemed to drop like a rock (fast!) and then as it got closer to the ground, it started "flying". I'd never seen anything like it.
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I personally give the space shuttle a little slack on the aerodynamics department when I remember that it enters the atmosphere at nearly Mach 25, and is big enough to produce two separate sonic booms. It was probably a very wasteful design (burdened by the military requirements), but it's like nothing else we've ever built!
The case with gliders and U2 and the max L/D is due to the wing aspect ratio (look up the formula for drag polar). Modern aircraft have much higher L/D because they have long skinny wings and these wings are possible because we moved from aluminum to carbon reinforced composites.