How To Design A Plane To Fly At 100,000 Feet? 

Fun fact: the U2 flies so high in the atmosphere, it can fly into the temperature inversion in the stratosphere, meaning the speed of sound actually increases again and it can go even faster without exceeding its limitation on laminar airflow. It also makes a very weird flight performance/ coffin corner envelope.

Scott has a way of plucking obscure but interesting stories out of subjects well studied by most of his audience.

Coincidentally, I've just been reading the latest _Aeroplane_ magazine, which has an interview with USN vet, entrepreneur and record-setter Doug Matthews. In 2013, doing time-to-climb class records in a P-51 Mustang, he hit 42,300 feet (unpressurised cockpit, no pressure suit...). As he was passing 40k, he overheard this convo between an airliner and Miami Centre: "Miami, Delta 1479, requesting our descent." "Delta 1479, I'm going to give you a slight delay. There's an aircraft crossing your nose at 40 and climbing out. It's a WWII fighter." "Say again, Miami?" "There's a North American P-51 climbing through your altitude." "Oh. _Wow..._ "🤣😎😎😎

I supported Helios and Pathfinder during the record flight. It got to 97,000 feet at a flight speed of 35 mph. In a head wind of 40 mph it could fly backwards at 5 mph and gain altitude. PMRF had a runway wide enough for it to take off, I was on the side of that runway as it took off.

The more I learn about the U-2 the more I respect the pilots.

Not sure if you've ever looked, but on an airline flight, if the sun angle is parallel to the recompression shocks on the upper surface of the wing(s), they will cast a refractive shadow on the wing. It's pretty easy to see once you spot it and watch it shift for and aft as the airflow changes from speed and/or turbulence.

I used to work for the company that designed and flew Helios on the team for the successor aircraft Sunglider. The guys who had worked on Helios back in the day were always annoyed that everyone brought up the 1 mishap they had, but not the dozens of flights that went off without a hitch both before and after Helios. Seeing the proprietary design methodology for that type of aircraft was amazing. It's like the ultimate extreme of aircraft engineering.

Fascinating video. Your closing comment reminds me of an incident in which an F-15 suffered damage to its right wing in a training accident. Just how much damage was impossible to tell because the spray of leaking fuel obscured the pilot's view. The pilot considered ejecting when his plane became uncontrollable and tumbled out of the sky; but he found that above a certain speed, he could regain control. So he decided to attempt to land it. He found that his stall speed had roughly doubled, so he had to land at twice normal landing speed. After landing, on attempting to finally ascertain just how much damage there was to his right wing, he discovered to his shock that he _had no_ right wing! His reaction was to say "Huh! I guess with an F-15, if you get it going fast enough, you're a rocket and you don't _need_ wings!"

"The science of getting really high". I have a friend that does that. It usually ends in an empty fridge lol

Watching the video at around 06:40 I remembered that that propeller in front of the plane is actually a fan. It keeps the pilot cool. If it stops you can actually see the pilot sweating..

if I remember correctly, "coffin corner" on the U2 is around 6 knots. In other words, there's a 6 knot difference between stalling and falling out of the sky or ripping the wings off.

That’s a really good video and captures all the main points. All I would add is that stall speed does start to increase if you climb high enough; it only stays constant up to about 10,000 ft then slowly increases due to Reynolds number (viscosity and density related) effects until about 35,000 ft, at which point Mach effects start to become dominant. Because a given Mach number has a decreasing IAS as you climb, this means the wing suffers low speed “shock stall” at high angles of attack (AOA), but typically at lower AOA than a normal stall. As an example, an aircraft that stalls at 100 kt IAS at sea level could stall at 130 kt at 40,000 ft. This problem gets worse until the top of the tropopause, about 65,000 ft, at which point the stall speed for a subsonic aircraft starts to reduce again slightly due to stratospheric temperature increasing with altitude. This phenomenon is exploited by the U-2, as shown in the video, allowing it to climb in a very narrow flight envelope with just a few kt between stall and limiting Mach number. On the high speed side, ultimately it is aerodynamic heating that limits things, for the airframe structure and particularly for air-breathing engines. Scram jets help here, but they are fiendishly difficult to get right. Keeping combustion going in supersonic airflow is really hard to do! Ultimately we might see aircraft that can sustain Mach 4, or possibly Mach 5, but much above that is highly unlikely. As for altitude, 100,000 ft is really the limit for conventional aircraft. Much above that and you need reaction control systems because control surfaces don’t work. And or course, at 63,000 ft is the Armstrong limit, above which you have to wear a pressure suit to survive, and even before then you need pressure breathing for oxygen if the aircraft pressurisation fails. That’s why Concorde had such small windows, and also why even the most advanced business jets don’t fly above 55,000 ft. You have to ensure they can get down to 15,000 ft in the event of cabin depressurisation, before the passengers die of oxygen starvation.

The story about the Perlan project is actually quite fascinating. I heard a lecture on it once. It took a lot of effort and some very special meteorological conditions to reach these insane altitudes. Enough stuff there for a whole separate video…

My wife and i are currently staying on the 10th floor in a resort at North Myrtle Beach. I've been watching the scene for a couple of days and there are several navy ships of various sizes on the scene. Today I've been watching off and on through binoculars and there are also two CH-53 Stallion variants flying very slowly at a low enough altitude to kick up visible spray, obviously "mowing the lawn". I guess they are determined to get every fragment of the balloon's instrument package possible, no matter how long it takes. One of them just now flew in to Grand Strand Airport, (CRE) right behind us and landed. The process has been both interesting and boring to watch.

Jet engines do not push against the air anymore than rocket engines do... unless you are talking about turbofan engines. Perhaps a bit more clarity would be useful here... Love your stuff... keep it coming!

I believe I may have taken part in the highest air-to-air 'kill". During my exchange tour from the Air Force to Navy Test & Evaluation Squadron Four (VX4) I was part of a detachment of three F-14s which flew from Eglin AFB (my previous home base). The purpose of this deployment was to test the then new AIM-54C Phoenix missile which was undergoing operational testing. The target for this test was an AQM-81A Firebolt which was undergoing development to meet an Air Force requirement for a high-altitude, high-speed aerial target. For our intercept the Firebolt was launched from the vicinity of MacDill AFB and was at 97,000 ft. and Mach 3 over the Gulf of Mexico. We used three F-14s to ensure that at least one of us would have an opportunity to launch a Phoenix (I was designated at the number #2 shooter). We climbed to 40,000 ft. and GCI provided us information on the target at 140 nm. We accelerated to Mach 1.5. The lead F-14 got a radar track at 90 nm. (two minute from launch) and we started our pull-up at approximately 65 nm. with a missile launch at approximately 40 nm. When the AIM-54 launched we were topping out at 50,000 ft. and the target was still almost 50,000 ft. above us which was a distance of 8 nm vertically (this was the highest I had been in a F-14)

There were rumours an EE Lightning zoomed up to 85,000 feet. This shot past and was observed by a U2 at that time. The maximum heights of some of the bombers of the sixties, Canberra. Vulcan, Victor was set by human factors, cold and more importantly the oxygen supply specs. A bomber designed to cruise at 50K feet plus with maybe 10 ton payload can obviously climb higher with a zero bomb load. Teddy Petter designed a high aspect winged high altitude fighter in WW2, the Welkin. The problems he encountered persuaded him to design a high speed high altitude bomber, the Canberra, with a low aspect high area wing. The US stretched the concept with bigger wings and engines as a precursor to the U2.

An aircraft that I sorta missed in this overview is the Grob G 850 Strato 2C , an experimental research aircraft build for Germany's DLR. It had a really unusual engine setup, using Teledyne piston engines that were pressure fed by turbine sections of PW127 turboprop jet engines. Current altitude record for piston powered flight at 18,552 m (60,866 ft). It's a real oddball that sadly did not have a long career, and now stands on the manufacturers airfield.

I thought the U-2 was based on the F-104 too, but that was an early prototype, the CL-282. For the U-2 they threw out everything F-104 based. Kelly Johnson was quoted as saying the only thing left over from the 104 was the rudder pedals. Super interesting rabbit hole to go down! Thx for the content, amazing as always.

The Sr-71 is clearly the master of the "go fast by having a LOT of power" segment, but what is rather interesting is where all that power comes from. Thanks to it's clever inlets being able to leverage the incoming dynamic pressure and turn that into static pressure, at a M3.0 cruise the inlet is actually providing 70% or more of the total forward thrust. ie the higher static pressure behind the inlet tries to actually push it forwards out of the airframe and as a result actually puses the thing along! Of course, ultimately the energy is all coming from the fuel being burnt in the engine, and the engine must be running and removing that high pressure air from behind the inlet for this trick to work, however this way of seemingly getting something for nothing can be somewhat difficult to get ones head around initally 🙂 These high dynamic range inlets (and the classic long delta wing drag characteristics) are what enabled both the Sr-71 and Concorde to achieve lower fuel consumption the faster they went, which is also extremely counter intuitive. The fact all this was worked out in the late 1950's and early 1960's with very basic analysis, calculation and test equipment is truely mind boggling (to someone that these days routinely records nearly a thousand channels of data at >1KHz on a simple passenger car development test.....)

Really liking the additional airplane videos you've been doing since going for your private pilot's license Scott. Gives me some more appreciation for them and for the engineering challenge of flying in general.

This is one of the best expositions of high-altitude flight I have ever heard. You even covered the fact that Mach number is the critical factor above 25,000ft.

I was in the US Navy from 1961 to 1966 as an Aviation Tech. We talk to one another about what we hear over the radio. One tech formally stationed in Japan relates this story while checking the radio and heard this transmission - permission to come down to 100,000 ft!

The A-12 at Battleship Park in Mobile relatively briefly had a sign stating that that particular aircraft had been an altitude in excess of 100'k, 108 IIRC. The next time I visited, the sign had been changed, with no reference to the altitude. When I inquired, the guy only said that they had been "asked" to change it.

I remember seeing James May going for a flight in a U-2 and a lot of the numbers on the flight instruments were classified until not that long ago. The altitude and climb speed schedule in the U-2 flight manual looks a lot different than the performance charts for a 172. 😎

One of the very rare times, as a pilot, that I already knew most of what you were explaining and was waiting for you to get to the good stuff.

As an old, retired corporate jet pilot, let me compliment you on your excellent explanations. You nailed it. Fly Safe!

I don't recall ever seeing more actionable information packed into a shorter presentation that this, Scott. Very well done, Sir.

Gosh, Scott, I think this episode was one of your most interesting and informative to date. Good stuff!

Oh, a rare Australian intro!

I had never considered the speed difference induced by a simple turn maneuver causing one wing to exceed its Mach limit (and potentially the other wing to simultaneously drop below its stall limit)... coffin corner, indeed.

F-104 starfighters had zoom climbed over 100k feet before 1960. A later variant with a small rocket booster and managed 119k Fun to know mach 3.3 at 80k is equivalent to less than 400 knots at sealevel as far as aerodynamic forces go.

The insane speeds of the SR-71 is why is was so expensive. Titanium was used in order to survive higher air friction while staying lightweight, and this was difficult to mine, refine, and machine. Also they were consuming half the world's supply, so they had to set up a shell company to buy some from the Soviets.

As a pilot this video brings me joy. 1. Because my flight instructors across all my certificates taught me well clearly! 2. I can fully understand and comprehend all of the info in this video!!!!

Most informative video. A high performance fighter can zoom climb above the altitude that aerodynamic control is effective and become ballistic. Reaction controls become necessary to maintain correct angle of attack, yaw and roll during the ballistic portion of the flight.

I sat here for 17 minutes thinking he was going to show us how to make LSD or something to get really high, I feel cheated

What? No-one else commenting on the inverted intro animation ?

Scott, I love to watch you going through the “aha” moments in flight training, and these videos on aerodynamic fundamentals. Also, having known a lot of pilots, instructors, examiners, etc.. I think you’ve got the perfect disposition / demeanor for flying.. Namely you’re a monumental skeptic .. and that’s a life-saving characteristic in flying. 😊 Be safe ! 💸

Oh Scott. How I love your videos. Beautifully tailored to those of us who didn’t get beyond A level science. Fantastically simplified, pitched and delivered. Thank you. I find this fascinating.

Other high altitude compensations are low bypass engines, ramjets, and eventually scramjets. Higher bypass engines lose effectiveness more quickly at altitude. The SR-71 did go above 85k, and it was more than capable of it. Due to its speed, ramjet, and lifting body it was well designed for those altitudes.

The Mach 2.1 F-104 Starfighter baby! 31.6Km (just under 104,000 feet) Such a cool plane! I have been to 51,120 feet in a LearJet back in the 80's. Was cool to be that high back then as there wasn't many private jets going that high. Then the other way I have been down to -131' in altitude in a sub! 😁👍 Keep up the good work.

Finally someone talks abaut sailplanes! The power of nature is often underrestimated. The pearland 2 wing is actually an modified version of an dg505,which is an farely standart glider when it comes to performance.

Great thumbnail Scott. Love getting high on science with ya!

I'll push back on your statement at 2:10 about helicopters not having wings. They do indeed have wings. Rotating ones. But a rotor blade generates lift in exactly the same way as a fixed wing does; airflow at some angle of attack over an airfoil. Hence the classification as "rotary wing" vs "fixed wing".

I love the SR-71 footage sporting the LASRE linear aerospike test! Perhaps an upcoming video on that?

Corporate jet pilot here. Andrew at Rocket Ranch Boca Chica TX shared this with me and he had questions and an interesting conversation ensued about the characteristics of sound, speed of sound, air density, humidity, altitude. He records sounds at a high level and was so interesting to listen to where he comes from technically. I love all the interactions that evolve from the vastly different people who are drawn like moths to a flame that is SpaceX. Thank you for this excellent video and the conversation it created. You do great work.

Entertaining and informative as always. Very enjoyable, thanks Scott.

Nice summary and quite complete but you missed one. NASA's WB-57. It is a design that pre-dates the U-2. A licensed version of the English Electric Canberra bomber, I watched it sampling the exhaust plume of the Delta Rocket carrying the LandSat 7 to orbit when I was part of the group invited for the launch. It was atypical for it to be such a gorgeous day at Vandenberg as you are aware. On the bus going back to work at Santa Barbara Research Co.a co-worker noticed the aircraft and asked aloud about how high it was. I remembered that I had read up on it, and told him its "party trick" was its ability to exceed 60,000 ft.

I read where the speed limit of the SR-71 was the thermal limit of the air-frame. Even titanium gets soft when cooked to 800 degrees C. Mach 3.1 was deemed safe, while 3.4 was reached in emergencies.

Fantastic, Scott! Thanks for the lesson! 😃 Stay safe there with your family! 🖖😊

I remember way back when this channel was about exploration in Eve Online. I too have moved on from that time in my life, but the "Fly safe" always brings me back.

The Lockheed F-104 Starfighter introduced in 1958 Was running level intercepts on U2s at 70,000 ft in the 1960s. The highest altitude reached by an F-104 was over 100,000 ft. An intercept flown at 65,000 ft has been possible since at least 1960.

A limit that should be considered is the human limit. The Armstrong limit is roughly 60,000 to 62,000 feet. Humans cannot go above this altitude without a pressure suit or in an unpressurized craft without dying. That's why U-2 pilots (and the old SR-71 pilots) wear pressure suits. A pressurization failure would kill them otherwise.

I recall reading about U-2 pilots making a gentle turn and the inside wing is in stall buffet while the outside wing is in Mach buffet. Insane!!

Ahh, this brings be back to my Fluid-mechanics times. Loved playing with wind tunnels and pushing limits of wing designs and impellers.

The F22's glorious air combat kills make the cost well worth it...

Man this was quite the interesting video, got to learn some new terms/concepts like Zoom climb, which sounds pretty cool to get an aircraft up to higher altitudes quickly.

I like your aviation content. Keep it coming!

Aerodynamics has always interested me, and this is a great video! Scott has the ability to get all those itty-bitty details right.

Really enjoyed this one, very informative thanks :-) Suggestion for another aerodynamic related one would be the black art of Dynamic Soaring.

Well, Reynolds number is very important. This can influence the aerofoil choice and wing aspect ratio. Picking the correct engine and the ramps for flight at that height is important.

well done! i enjoy these educational side-trips into the physics of things.

Awesome video! I really enjoy hearing your take on the physics and engineering of these topics!

Absolutely love your video. As a glider pilot and plane enthusiast in general, I find your explanations "grounded" and easily understandable. Thanks, Scott.

Solar powered HAPS gliders are being discussed again to provide communication with lower lag than satellite internet like starlink etc. Really enjoyed this video, thanks

1:24 - hmm, kind of borderline whether you could say a helicopter stayed aloft just from its engine when it's got those big rotating aerodynamic surfaces -- the blades of its rotor(s) -- which kind of are a type of wing. The NASA Lunar Landing Research Vehicle (aka flying bedstead) would seem a better, if not so well known, example of flying from pure engine power.

Scott Manley the only dude that can take a crazy event like this, and turn it into some KSP discussion lol. I love this guys channel. Always can count on him to make my day lol

Great job as usual. Thank you Scott!!!

The XB-70 was rated at 77.000 ft but the prototypes, especially number 1, had many issues that limited performance. If it was properly developed into production I am sure it would have gone much higher, perhaps matching the SR-71/A12.

Jet engines don't "push against the air" any more then rocket engines do. The actual mechanism is action and re-action. The air being forced backwards has mass and pushing it backwards results in an equal and opposite reaction.

Really good and informative video Scott. Love your info videos! All the best

You have to really love the information this gentleman puts out really learn a lot keep it coming

Hey Scott! Love your videos and your deep explanations and different perspective. Can you do a deep dive on the soviet N1? Everyone compares Starship to N1 and Saturn V, but would love to know more about how it really stacks up. Thanks

KSP 2 KERBAL PLUSHIE?!?!?!

Another great video from Scott 😎

Great video. I listened to it whilst driving my car with the phone screen off. Came across perfectly. Thanks again.

Ok.. A glider that can reach 100,000 feet .. unpowered .. is freaking amazing.

There's an SR-71 on display at my local air museum. I don't think people realize just how large they are. I know I was surprised when I saw it in person.

Good episode Scott, thanks. Lots of fun/unusual facts and data.

Your pronunciation of Caproni was spot on!! Love your videos!

Use Balloons, if that doesn’t work, more Balloons, I miss airships though, they aren’t even that dangerous anymore

I think the title may be missing a word

4:05 For your discussion : on a twin engine aircraft a blue line is also marked: It is the engine out best rate of climb speed, meaning the indicated airspeed( actually CAS) requiring the least power, to achieve climb, irregardless of the altitude. That helps to determine the highest altitude to make 100 ft/min, but only for propeller airplanes.

A terrific video about high altitude and "high" speed flight. Thanks, Scott.

I was sad to see that the Lancair Evolution wasn't actually a Lancer Evo with wings

I used to think that if you were in a helicopter and the engine stopped you would be toast. But then I learned about autorotation and realized that you might be better off in a helicopter that lost power than a plane. I’m sure autorotation is tricky to master but you can get to the ground safely.

Thanks Scott I really enjoyed that, that was a great video!

Scott, Very well researched and presented video - I leaned lots of interesting stuff, many thanks, fly high, Eamon

It was really breathtakingly interesting (coz thin air…) Aerodynamics become very complicated at higher speeds and altitudes, it is hard to imagine how planes like sr-71 was developed in 1950s, considering the fact that first electronic calculator was created in the early 1960s

You literally wanted to say "the operating manual for my Space Craft" 6:25 You almost said the quiet part out loud. Great video. Your videos are more interesting now you are flying yourself too. Well done.

Oh in airplanes, I'll watch anyway because anything Scott does is good.

I was wondering about exactly this after the balloon news. Would also be interested in hearing about the missile itself which must have gained another 40,000ft before finding its target - impressive. Edit: I was wrong, balloon was at 60-65k ft, not 100k ft like I originally believed.

Simple: Smoke weed.

Mulatu Astatke playing and Scott Manley telling and explaining is A++

Very nicely done. Like Scott, I’m a student pilot but also an enthusiast of all things aircraft and space. I have a special love of the SR-71 too.

Good description of coffin corner - to elaborate on the last piece of it, the idea is the low speed buffet near the stall and the high speed buffet from high mach number can coincide, meaning you don't know whether you're going too fast or too slow.

Great Video, Scott! I only disagree on one thing: although helicopters use engine power to directly drive their rotors, they don’t use engine thrust to defy gravity, but simply to move their rotor blades through the air, which are pretty comparable to airplane wings in the way the generate lift: an aerodynamic surface that moves through the air (or call it ‚fluent‘ to also cover Mars helicopters) and generates lift this way. The same limits of stall, flutter and Mach number apply as to a conventional fixed wing.

Very interesting Scott. Thank you!

Enjoyed that, Scott. Thank you.

Thanks Scott, always fascinating.