And the pilots aren’t behaving like nincompoops.
“Light” typically refers to aircraft with no cabin differential at all - IOW, unpressurized aircraft.
Due to decreasing air density the engine develops less power as altitude increases. Due to the same decreasing air density, the required speed to maintain enough lift to support the aircraft also increases, which means it takes more power to fly.
At some point the two curves cross, and the airplane no longer has enough power to fly. This does not normally induce a stall. Because of the way nearly all airfoils work, they are less efficient right at stall than at a little bit higher speed (known as max L/D…L=lift, D=drag) So to max out the altitude you need to be at max L/D, not hanging on the edge of a stall.
So you take off, firewall the throttle, and lift the nose and climb at max L/D. As your altitude increases, you have to progressively lower the nose (reduce climb rate) to maintain speed. Eventually you reach a point where your climb rate at that speed is zero and you can’t go any higher. You can try to keep climbing, but raising the nose will increase drag more than lift, so you don’t gain anything. Keep it up, and you will stall the airplane.
Stall doesn’t mean you die. It means either that you are not going fast enough for the wing to generate enough lift to offset the load, or that you have forced the wing’s angle of attack beyond it’s max-lift angle of attack. You can recover from the stall either by decreasing the load (relaxing back pressure on stick) or diving a bit to increase speed.
You can get a little higher by building up a little speed in a dive, then gently pulling up to a fairly sharp angle, then maintaining a zero-G pushover. By maintaining zero G you can go way below the airplanes normal “stall speed” without actually stalling…which explains the complex wording in the above 'graph. You are essentially going ballistic, and trading most of your kenetic energy for altitude.
So that is for piston powered light aircraft. I think there was at least one Lear Jet that the maximum ceiling was due to a mach limit. As air density decreases stall speed increases, and eventually that stall speed got reached up near sonic velocity where the airplane had issues due to compressiblity effects. Supersonic aircraft need special design features, and in general they have poor efficiency at lower speeds.
At full speed, the engines were more like ramjets than conventional turbojets, with the spikes and bypass gates serving to keep the inlet shock in the right place for that to work.
A good point. The pilot who stalls his airplane while trying to reach maximum altitude will not have climbed as high as the pilot who maintains trouble-free controlled flight at the airspeed that requires the lowest power (which is called best glide speed or max L/D speed).
The pilot may not have a choice. The typical mission profile of the U-2 had almost the entire flight within the “coffin corner”, and (according to Wiki) spent most of the time at 5 knots over stall speed.
Don’t start that shit in here, you two. :mad:
Yes. Well actually the engines are always a form of augmented ramjet. At subsonic speeds the ramjet combustion is like a conventional afterburner. At supersonic speeds the spikes use shock compression to turn the whole thing into a ramjet. At some velocity the internal turbojet is optimizing the inlet and outlet conditions instead of providing significant thrust. I was pretty sure that was what the post I referenced meant, but the numbers are all over the place for how much thrust is produced in ramjet mode. 70:30 make sense for how much compression comes just from the inlet spikes instead of the internal turbojet.
FYI, the X15 had a reaction control system (and obviously couldn’t be stuck in space as it reached nothing like orbital velocity)
Which is not to say that any possible thing you did with it would have led to a survivable reentry of course, and at least one dude died after reaching 266 000 feet - which made it a space flight, just by the USAF definition at the time (50 miles) - in one.
Orbital velocity is the speed needed to stay in orbit. What’s stopping an X-15 from just continuing away from the planet?
When the Lear 55 first came out, it was the highest jet at the time.
With no passengers, we could hit 51,000 feet in about 12 minutes IIRC.
You just don’t do it at a 70 degree angle the whole way. It sounds like these potato heads in the CRJ were playing MIG chaser or something equally foolish.
I’ve bumped into the sides of the envelope enough to know that it’s usually best to be more conservative than your average fighter pilot. I’m still here after 4,500 hours, and intend to stay that way.
A little thing called gravity.
It’ll come back down again; |orbital velocity at altitude x| = |escape velocity at altitude x|.
(Not strictly speaking due to non circular orbits but it’ll do)
that would only really apply if you were circling the planet. the X-15 was a rocket. the only limiting factor is fuel. As long as the rocket is producing more thrust than weight it should continue away from the planet with ever decreasing gravitational loads regardless of speed.
Not so much. Wikipedia claims a 2.0 thrust/weight ratio, so it could easily overpower gravity without any lift at all.
What stops it from going where noone has gone before is the same old problem all spaceflight has: fuel. Or, more accurately, the efficiency of the conversion from fuel mass to thrust.
By “light” I meant a lightly loaded aircraft, not a small GA aircraft.
Much dumber question than the OP: when I read “ceiling” in connection with aircraft, I thought it meant what the Weather Channel shows along with temperature and other current conditions.
Since it apparently doesn’t, just what is the Weather Channel talking about there?
The height of the cloud base.
Ben Rich’s (the head of the Lockheed Skunk Works after Kelly Johnson) biography mentions a bit about the U-2. In addition to what you write, he quoted a pilot saying that steep enough turns in the U-2 at altitude would give you an overspeed buffet in the outside wing, while the inside wing would be experiencing stall buffeting. And yet, it was not unknown for pilots to spend 10 hours in the thing, which strikes me as an amazing feat of concentration.
The U-2 was reportedly a very unforgiving plane to fly and killed more than a few pilots. Didn’t the Taiwanese Air Force have a very difficult time during their use of the U-2 to overfly the People’s Republic of China, with multiple crashes and deaths?
Wow. Many differences between that story and the Air France jet that went down off the coast of Brazil a few years ago, but this sentence happens to apply equally well to both:
“But as an automatic system tried to push the nose down, to gain speed and prevent the stall, the pilots, for reasons that are unclear, overrode it.”
(For Air France, just substitute “other pilot” for “autopilot”).
I wonder if there’s a common factor here – some instinctual thing which makes some pilots want to keep their nose up when they know intellectually speaking it’s the wrong thing to do?
Well, that’s a topic for another thread.