# How high can an aircraft fly? **URL:** \ **Category:** Factual Questions\ **Created:** [June 17, 2018, 5:57pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273 "2018-06-17T17:57:20Z")\ **Posts on this page:** 12\ **Page:** 2
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [June 18, 2018, 3:36pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/21 "2018-06-18T15:36:45Z")
> [@Machine\_Elf](#): > > 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? I don’t know, I would guess they were ballistic. They used thrusters to maneuver when the control surfaces wouldn’t work. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 18, 2018, 3:50pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/22 "2018-06-18T15:50:59Z")
> [@Machine\_Elf](#): > > 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? The X-15 conducted both altitude and velocity tests. In the altitude tests it was operating primarily as a rocket with a reaction control system necessary at some altitude. By then the wings were no longer functioning as common foils anymore, they were just deflecting air downward in a 45 degree attitude. Velocity tests maintained the airplane mode more of the time. The wings acted like foils and aerodynamic control surfaces were in use, and gaining maximum altitude wasn’t the goal of those tests. The Karman line defines the point where the an aircraft would need to exceed orbital velocity for aerodynamic surfaces to work. I don’t think anything that could be considered “Today’s technology” could approach that line. If I understand it correctly (not the best bet you could place) existing rocket technology is a more efficient way to push an aircraft to orbital velocity at a much lower altitude and velocity. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [June 18, 2018, 4:55pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/23 "2018-06-18T16:55:23Z")
> [@Jacquernagy](#): > > An [interesting interview](https://youtu.be/RSOaKaFIgAs) 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. It’s worth noting that the SR-71’s maiden flight was 54 years ago. Remarkable is an understatement. ---
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [June 18, 2018, 6:11pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/24 "2018-06-18T18:11:15Z")
They’re pushing for 90,000’ at the Perlan Project. In a glider, btw. ---
**Author:** ![Corry\_El](https://avatars.discourse-cdn.com/v4/letter/c/ecae2f/32.png) [@Corry\_El](https://boards.straightdope.com/u/Corry_El)\ **Post date:** [June 18, 2018, 6:45pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/25 "2018-06-18T18:45:09Z")
> [@Machine\_Elf](#): > > For sustained flight? Not likely. The SR-71 can handle aerodynamic heating at ~2000MPH; [according to this chart,](https://image.slidesharecdn.com/highspeedaerodynamics-091209082849-phpapp02/95/high-speed-aerodynamics-57-728.jpg?cb=1260347465) 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](https://en.wikipedia.org/wiki/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. The core of air breathing self propelled hypersonic research is basically how to deal with very high stagnation temperature at hypersonic speeds. Especially considering that that’s why supersonic combustion ramjets are needed., which have been perhaps the most central element to self propelled hypersonics research, and elusive to build, but now coming into hand as a technology. Scramjets would be the most fundamental difference between the combined turbine/subsonic combustion ramjet engines of the SR-71 and turbine/subsonic combustion/supersonic combustion ramjet engines on a projected SR-72. The main reason you couldn’t build an a/c with the SR-71’s technology that was a lot faster wasn’t necessarily skin heating, but how hot the intake air gets when you slow it down to subsonic speed for combustion, then raise the temperature further with combustion. The scramjet eases that restriction by allowing combustion with cooler supersonic flow. Skin heating is also a real issue of course, but again some hypersonics research projects have been specifically to test new materials and techniques to make sustained hypersonic flight practical in term of leading edge heating. ---
**Author:** ![joema](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@joema](https://boards.straightdope.com/u/joema)\ **Post date:** [June 19, 2018, 9:35am UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/26 "2018-06-19T09:35:30Z")
> [@MichaelEmouse](#): > > 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?.. In theory a scramjet-powered vehicle could sustain flight up to about 75 km (246,000 ft), this graph from STUDY OF AN AIR-BREATHING ENGINE FOR HYPERSONIC FLIGHT, Author: Marta Marimon, September 2013: [![](https://photos.smugmug.com/photos/i-PJ74Jsm/0/db5c1d0e/M/i-PJ74Jsm-M.jpg) ](https://photos.smugmug.com/photos/i-PJ74Jsm/0/db5c1d0e/M/i-PJ74Jsm-M.jpg) Actual test vehicles using scramjets have flown briefly at 110,000 ft (33.5 km): [NASA X-43 - Wikipedia](https://en.wikipedia.org/wiki/NASA_X-43) To take off from the ground would require a “combined cycle” engine which transitioned between turbojet, ramjet and scramjet mode. This was envisioned for the X-30 but was never built: [Rockwell X-30 - Wikipedia](https://en.wikipedia.org/wiki/Rockwell_X-30) However ground-launched, scramjet-powered vehicles are still planned. The altitude would very with the mission need, but 75 km has been discussed as the theoretical upper limit of scramjet operation. > **[Aerojet Rocketdyne To Build Zero-to-Mach-6 Engine](https://www.popularmechanics.com/military/aviation/news/a28577/darpa-aerojet-rocketdyne-hypersonic-jet-engine/)** > > The turbine-based combined cycle engine will combine elements of a turbojet for low speeds and a dual-mode ramjet and scramjet from supersonic and hypersonic flight. ---
**Author:** ![Spiderman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spiderman/32/230_2.png) [@Spiderman](https://boards.straightdope.com/u/Spiderman)\ **Post date:** [June 19, 2018, 2:12pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/27 "2018-06-19T14:12:23Z")
> [@Corry\_El](#): > > 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. The Red Bull Stratos went to 39k. ---
**Author:** ![rbroome](https://avatars.discourse-cdn.com/v4/letter/r/838e76/32.png) [@rbroome](https://boards.straightdope.com/u/rbroome)\ **Post date:** [June 19, 2018, 9:15pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/28 "2018-06-19T21:15:05Z")
> [@Spiderman](#): > > The Red Bull Stratos went to 39k. I assume your units are meters? From wiki: " With a final altitude of 38,969 m (127,851 ft)\* (23.3884 miles)," ---
**Author:** ![Corry\_El](https://avatars.discourse-cdn.com/v4/letter/c/ecae2f/32.png) [@Corry\_El](https://boards.straightdope.com/u/Corry_El)\ **Post date:** [June 20, 2018, 1:34am UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/29 "2018-06-20T01:34:12Z")
> [@rbroome](#): > > I assume your units are meters? > From wiki: > " With a final altitude of 38,969 m (127,851 ft)\* (23.3884 miles)," Right. I assumed the OP meant heavier than air aircraft, that was a balloon, but I guess a balloon is a lighter than air aircraft. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [June 20, 2018, 1:45am UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/30 "2018-06-20T01:45:50Z")
The U2 climbed to 70,000 ft. and top speed at 500mph. The U2S is still in service. > **[Lockheed U-2](https://en.m.wikipedia.org/wiki/Lockheed_U-2)** > > The Lockheed U-2, nicknamed "Dragon Lady", is an American single-engine, high altitude reconnaissance aircraft operated from the 1950s by the United States Air Force (USAF) or the Central Intelligence Agency (CIA). It provides day and night, high-altitude (70,000 feet, 21,300 meters), all-weather intelligence gathering. > Lockheed Corporation originally proposed it in 1953, it was approved in 1954, and its first test flight was in 1955. It was flown during the Cold War over the Soviet Union, Chi... ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [June 20, 2018, 2:04am UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/31 "2018-06-20T02:04:59Z")
Rex Kramer: [talking on the phone to the airport control tower] No, we can’t do that, the risk of a flame-out is too great. Keep 'em at 24,000. … No, feet. ---
**Author:** ![BrotherCadfael](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@BrotherCadfael](https://boards.straightdope.com/u/BrotherCadfael)\ **Post date:** [June 20, 2018, 1:30pm UTC](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273/32 "2018-06-20T13:30:47Z")
> [@AK84](#): > > 100 km. The Space Shuttle was an aircraft when it reentered the atmosphere. The space shuttle isn’t an aircraft. It’s a brick with wings. [Previous page](https://boards.straightdope.com/t/how-high-can-an-aircraft-fly/816273.md?page=1)