The SR-71’s flight ceiling is around 26km, if you dedicated an aircraft to doing little more than flying high with today’s technology, how high could you get?
A few parameters:
The aircraft doesn’t have to be manned, stealthy, fast or particularly long-range, it only has to be reusable and carry a payload of 10-1000kg.
The aircraft’s take-off/launch can be assisted by tug, catapult, rocket booster or anything else but the main portion of the flight has to be air-breathing with the aircraft’s own engine(s) only.
Flight ceiling is to be calculated according to level flight, not zoom climbs.
I presume you would end up with an aircraft designed around its air intake(s), like a giant maw flying through the air.
Is that its flight ceiling in level flight with only its air-breathing engine(s) being used at that time? The question isn’t about what’s the highest altitude that counts as being in the atmosphere, that’s easy to look up.
Read the linked article. The Karman line is the theoretic limit for aircraft flight. Because of that, some people use it as the definition of the edge of space.
With a strict construction of “today’s technology” the answer might be 110,000 ft., reached by the NASA X-43. I don’t know if it was in level flight at that point, but aircraft like that are trying to get as close to orbital velocity as possible and aren’t performing zoom climbs.
I’m not asking about the theoretical limit for aircraft flight.
Thanks. There is some ambiguity about “today’s technology” as there may be a prototype somewhere in a lab that isn’t large scale production-viable at this time which seems to describe a lot of scramjet tech. I’m surprised the X-43 doesn’t have a bigger air intake.
Those engines rely on velocity to take in enough air. The intakes wouldn’t get much larger. These aircraft do have to be designed around the intake though, it has to be optimized for the max velocity they want to reach. Variable intakes are being considered but even the current technology is still a kind of dicey and frills like that won’t show up for a while.
"The highest commercial airliner altitude was 60,000 feet by Concorde. The highest military air-breathing engine airplane was the SR-71 — about 90,000 feet. The highest airliner flying today reaches 45,000 feet. The highest business jet flying today reaches 51,000 feet. "
May 28, 2017 Ask the Captain: Highest altitudes for planes - USA Today
According to the flight information on the screen in front of me, I reached over 50,000 feet on a commercial flight from Vancouver to Hong Kong (maybe Tokyo?) about 15 years ago.
A quote of 110,000 ft for an unmanned hypersonic test vehicle has been mentioned. Various other air breathing test vehicles of relatively recent years have been quoted as seeking operation at 100-150k ft. Presumably if the goal was for some reason to maximize the altitude it would be more like 150. The caution there is how much of the vehicle’s climb to high altitude is via the airbreathing component v rocket booster, though not to be confused with concepts for boost-glide hypersonic vehicles with have no airbreathing engines but would ‘fly’ (be steered aerodynamically) at up to 200k ft. As of now no air breathing test vehicles are reusable AFAIK and the focus in the US for operational systems is to make missiles out of them. The quoted planned altitude for the potential hypersonic, definitely reusable (and manned) SR-72 is quoted as similar to that of the SR-71 (often quoted at 85k~26km but some sources say the SR-71 could fly somewhat higher), just twice as fast.
The alternative way to extremely high altitude is slow, very low wing loading solar powered propeller a/c. The Helios a/c flew at around 97k ft climbing there completely on its own.
I wasn’t sure about including the reusability requirement. So, missiles could rely on air-breathing propulsion up to 45km and aerodynamically steer up to 60km? Aside from defense against ballistic missiles, what could be the uses of an air-breathing missile with a 45km flight ceiling? How about a missile with 60km altitude aerodynamic steering?
How might they get the SR-72 to go twice as fast as the SR-71 while at substantially the same altitude?
Is the SR-72 likely to actually be produced in the next few decades? I thought the SR-71 was mainly a stopgap measure until the US got a solid satellite constellation. It’s always going to be easier to make an anti-air missile that reaches n altitude than have an aircraft fly at that same altitude.
For sustained flight? Not likely. The SR-71 can handle aerodynamic heating at ~2000MPH; according to this chart, peak temperatures at the nose and leading edges would have been well under 1000F (windshield glass reportedly reached 600F). Double the speed, and you fall off of that chart: peak temps will be well over 2000F, probably closer to 3000F. A heat shield can protect a vehicle from those kinds of temps during a transient event (e.g. a ballistic reentry from space), but ISTM it would be difficult to protect against those temps for a sustained flight (e.g. 1-2 hours). In addition, all that extra weight and bulk would make it awfully hard for an aircraft to maintain level flight in very thin air.
IIRC, the U-2 has a performance envelope that is so extreme that at operating altitude, there is only a 10 mph difference between going too slow and it stalls and too fast and it goes supersonic, tearing the wings off.
If they engineered a U-2 with swept-back wings, it could go higher.
The problem (for the U-2) with going faster is not aerodynamic stresses, but a change in lift characteristics that can cause a stall and subsequent loss of control. Aerodynamic breakup may or may not happen after that.
An interesting interview with a longtime SR-71 pilot, Lt. Col. Maury Rosenberg. This video contains every bit of information you could possibly want to know about that remarkable aircraft.
I thought the speed and height of the SR-71 were still classified.
The X-15 a few times flew to over 100km, high enough that the control surfaces no longer worked, and pilots on those missions were given astronaut wings.
Were the wings generating enough lift to sustain flight at that altitude, or was the entire aircraft (and not just the control surfaces) basically ballistic until they descended into thicker air?
