The best thing about space is that every little detail of anything is just the tip of an iceberg made out of tons of talent and engineering and people that battled problems and solved them succesfully. Science is awesome

I'm surprised Destin from Smarter Every Day didn't get summoned when you said "laminar flow" at 1:25.

I love how Scott walked us through the thinking process of how to build a hypersonic wind tunnel. I had similar questions at each stage and he answered them immediately.

Really cool how a single image can spark curiosity and learning about some very interesting science. Great video Scott.

Man, I wish I was a kid again. I was desperate for science explainers like Scott in the pre-internet 90's. I remember just having to take a book's short description of this phenomena for granted, but not really understanding it until decades later in college.

I studied aeronautical engineering years ago, and got to use a wind tunnel for a project, it was subsonic, but we also had a blow down supersonic wind tunnel, that one worked by decompressing a chamber, and compressing another, and quickly releasing the pressure, and using a trigger to start a camera to record the shock waves around the model in the test section :)

Some of us look at a cat video on youtube and still can't explain in simple terms what a cat is. Scott Manley sees one 50 year-old picture and, in a few minutes, explains multiple mind-blowing scientific facts via the same cat video delivery platform.

Never in a thousand years would I have ever thought to use an electron beam to ionize the gas flow in a wind tunnel to see such things on reentry simulations. The people who come up with this stuff truly have amazing minds. They basically turned the model itself into a kind of neon sign to let the gas alone show the flow and density patterns. Truly genius whoever came up with that.

I FINALLY understand how converging/diverging nozzles work! Something about this explanation made it click for me

"But in the end, after testing, it was vastly more successful at converting aviation fuel into noise pollution" How much do I like these sarcastic quotes 😁

When you said "Fifty year old photo", I had to quickly do the math in disbelief of my actual age. I felt my whole day slip down a peg, on the pretty good scale of painlessly enjoyable. :) Rock-On Dr. Scott ! Always cool facts, keeping it sharp.

1:10 I visited the Eiffel wind tunnel a couple of years ago. It’s still in use for wind speeds up to 120 km/hr. You can actually walk into the tunnel - it’s person sized! For bigger objects to be tested they make a scale model. They had recently used it to test the stability of drones.

This was a fascinating topic and a fabulous job explaining it.

This was amazing. It's this kind of content that makes this my favorite KZfaq channel! Technical content well explained without treating the viewer either as an idiot or requiring we actually do the calculations.

Impressive! I am ashamed to say I am supposed to know all this ( I do really) but would trip over myself trying to explain it to the layman. Scott does a great job leading you through the subject starting from the basics, explaining the issues and they way they have been resolved to achieve Mach 20. I am very impressed.

Scott, I teach engineering to high school students, and one of the classes is Aerospace engineering. I can't tell you how much I've learned from your videos, and I'm incorporating as much as I think high school seniors can understand into my classes. Thanks so much!

We just covered wind tunnels and flows in my aerospace engineering course! It feels awesome to really understand everything going on in this video.

"Bernoulli's most obvious law" I love that! This stuff is also yet another example of the science that needs helium that we keep hearing about.

Thanks Scott ! This was a reminder of a great job I had in late 80's in Rocket Test for ARC ( now Aerojet I think ) that had a huge "Air Facility" as it was called in those days. I think it was an amalgam of ex NASA equipment that allowed them to test fire not models, but the actual full size SM-2 Standard Missile recreating it's entire flight profile while the motor operated, generating performance test data to qualify systems for manufacturing. They even had an expansion system around nozzle's exit to recreate lower external air pressures at altitude. It was a blowdown system with about a dozen immense tanks on railroad cars that took days to fill with the required compressed air it expended in tests. They literally flew the missile in a high speed wind tunnel while the rocket motor operated in real world test conditions ! They also did extensive ramjet testing with same facilities. I sometimes wonder if any of that stuff is still being used to test next gen systems currently ?

Fascinating topic, completely agreed. If I may, the "Schlieren Photography" is pronounced "sh-leer-en". Schlieren is the German word for wisps or swirls, such as you get when a drop of mechanical oil glistens on a swirling patch of water in light. Not as critique, simply as pronounciation help for the future.

My university has a mach 10+ wind tunnel, it doesn't run for very long though. I would love to get to use it one day.

Such a cool episode! As soon as you mentioned expansion after the restriction area to increase velocity I was like “WAIT a second… thats exactly the same principle as…” and a few seconds later you mention rocket nozzles. 🤣

As a mechanical engineer, I have often said to disbelieving laymen, that engineers are some of the most creative people alive. This video does a good job at validating that concept. Thank you Scott.

"50 year old photo featuring the Space Shuttle in a helium electron beam excited wind tunnel". I was 10 when we landed on the moon in 1969. That was only 52 years ago. I love this example of 50 year old serious work we and others were and are doing that is very much out of my training and scope. Kudos to the scientists, engineers, programmers, project managers, inventors.... all those people working hard in the area they aspire to and love that is making a difference in our world.

This must be one of your best videos ever. Really succinct explanation and enjoyable narration.

I am often impressed by how good and specific to the subject the visuals in these videos are. How do you usually go about finding the right images?

Forget the wind tunnels, I never understood the rocket nozzle throat thing until now, many thanks for that clear and simple explanation of how fluid physics adjusts relative to sound speed!

Brilliant lecture, as always, we're waiting for a long overdue shock wave dynamics video as promised in plutonium implosion devices, looking forward to that Scott! Peace from North Wales

I follow this channel since early ksp journey. After a casual course about the topology of fuel injection in rocket engine, here we go: a casual course about the engineering problems of high velocity wind tunnels.

I wish they had lessons like this in school. It covers so many topics and in an interesting and engaging format! It seems like schools are more interested in confusing children instead of teaching them.

I live 5 miles from Langley and have seen all of that equipment up close and personal many times Now after nearly 50 years It is awesome to know how it works thank you Scott great work!!

dang that's a nice thumbnail

WOW this was insanely interesting, and a testimony of how aparently simple things, are in reality much complex, specially when you push for the limits.

As a aerospace engineering technician at Langley Research Center for 36 years our job was to install instrument and run the wind tunnels. I worked and operated in over 20 wind tunnels during my career. The 20” Mach 20 Helium tunnel shown here and described by Scott was described accurately for the reason for the use of Helium gas. After purification of the helium gas we increased the gas pressure I believe ( sorry I retired 20 years ago) 3000 psi. When the isolation valve for the tunnel to the vacuum sphere was open the 3000 psi helium supply valves were opened and the gas raced thru the orifice and generated Mach 20. No heating of the helium was required. Many years were spent in this and other NASA facilities to develop the final shuttle shape. I also worked in the Mach 6 2’x2’ tunnel air in the D wing of Gas Dynamic building 1247 at Langley. To develop Mach 6 with 600 psi air the air was heater to about 425 + degrees to insure the air would not become liquid as it accelerates to Mach 6 thru the nozzle which causes a drop in temperature. If not hot enough the air would liquify into air and droplets of air and invalidate the data. So if we used air at Mach 20 what temperature of the air would be required to prevent liquefaction- above my pay grade but probably several thousand degrees. So what material in the structure of tunnels valves and hardware would be required to withstand those temperatures - materials we did not have therefore helium was used. I point I noticed in the comments I was technician and had the the immense honor of working with some of the brightest aerospace engineers and managers in our country - these brilliant engineers these public servants worked tirelessly long hours with pay well below many other in the private sector and were true patriots.

Scott… I’ve watching your videos for sometime now and just wanted to say THANK YOU. I love your how you explain technical things and you make the viewer never to feel dumb. This particular video was fascinating as I never thought about hypersonic testing requirements before. Keep up the excellent work that you do for us!!!!!

Its Friday afternoon, and I learned more about hypersonic wind-tunnels. It is great that school honed my skills at acquiring knowledge I will never need in real life. I quite enjoyed that.

Very well explained, Scott. I love that Saturn-5 rocket model! Seeing it takes me back to when I was a kid, watching Apollo 11 land on the moon.

It took me 7 minutes of watching this video before I realized Scott was wearing merch.

Hi Scott - why are you so awesome!!! This is once again an amazing story about several amazing physical effects. KEEP IT COMING!

Speaking of wind tunnels, please please feel free to use our open source wind tunnel to use for schools and other activities or just for yourself to have fun. You can find it in our channels. Go ahead and enjoy it.

This was awesome. It's great to see how some of the more analog science approaches were done when we didn't have the simulation technology we have now. Thanks for sharing Scott!

Awesome lecture, Prof. Manley. Thank you for breaking through the complexities of this and all the fascinating subjects you cover and making their fundamentals understandable.

Simple but deep explanation of gas dynamic, compressible flow & wind tunnel as well. Great job 👍👍

“converting aviation fuel into noise pollution” is such a fantastic descriptor omg

Thank you Scott, most interesting. That image is just amazing. I too have seen a transonic shock, on the inner wing of a B-747-400. In my case it was visible as a stable distortion standing up above the wing surface - exactly the height I had read about as the optimal trade-off between increased fuel burn due to mach drag rise and flight time. I called over the cabin attendant - thinking she would find it as interesting as I did. No, she thought I was expecting the plane to crash or something. I still do not understand how a person who is in the airline industry can be so incurious about aerodynamics... and maybe more than a little ignorant. I took several photos, but thanks to several changes of residence, I do not know where they are now.

When growing up in Madison, AL, I used to live down the road from Wyle Lab’s wind tunnel. I think they helped NASA test the shuttle’s aerodynamics there. Whenever Wyle conducted a test, there was always a low-frequency sound that made all the windows rattle. I can definitely see why now after watching this very informative video.

That's amazing. Being able to put together a whole bunch of different processes and principles to create something that lets you *see* the density of the air, and do it under such extreme conditions... I never fail to be impressed by ingenious solutions like this.

Great video. In case nobody else has mentioned it, I recommend the book "Facing the Heat Barrier" by T.A. Heppenheimer. The first part of the book goes into some detail about the different wind tunnels developed during the early years of the space age, and why they were necessary. It's an absolute must-read if you are interested in how the problems of heat were solved for ICBMs, Apollo, the X-15 and Space Shuttle.

This is way more interesting than I expected. The nozzle based design like in a rocket and the liquification of the air after Mach 4 blew my mind. Btw Schlieren is a German word meaning something like a line of smudges on a surface. It's pronounced more closer to Shlee-ren then what you said.

Excellent discussion of basic wind tunnel operations. As an aero engineer it was a fun review. The US Air Force has a facility in Tullahoma, Tennessee that has wind tunnels that run tests from sub sonic to hypersonic. I walked through the the test section of the transonic tunnel that could hold very large scale models (about 20’) for testing.

Usually when you explain the physics behind certain complex topics no I have to watch it a couple of times before I get it but this video I was able to understand pretty much everything you said in one watch. It's a testament to how well you know this topic as you are able to explain it so simply.

That was a great explanation, really interesting stuff!

I think the reason for using Helium is that, temperature being proportional to the kinetic energy of gas molecules mv^2/2, the lower the mass of the molecule, the lower the temperature (and energy) needed to achieve the same velocity. That is why Helium needs much less heating than air to reach Mach 20. I think this was also used to fire a hypersonic Helium pellet gun in some video.

I know for a fact that I will never deal with wind tunnels in my whole life, but the joy of learning new things and adding new questions after them is so pure and sweet that I can not miss it. And you, dear Scott, have a special part in this whole story. thank you.👍❤️

Quality content once again. Informative, fun and easy to follow. You're among the best creators to follow on YT. Thanks Scott !

Thank you, Scott, for this excellent lecture on these amazing subjects. I thought I understood windtunnels from back in uni but never realized hypersonic speeds present such extreme challenges. I loved to hear you describe my line of thoughts just when I started seeing the similarity of rocket nozzles! That was a great trick! It makes me wonder which came first - the hypersonic windtunnel or the rocket nozzle? But again, massive thanks for this awesome post! 👌

Hi Scott. Helium and Hydrogen both have negative joule-Thompson coefficients, which mean they actually heat up in stead of cool down when throttled through an orifice. Maybe that is part of the reason for using Helium here as well. Thanks for an awesome video as always!

Just absolutely impressive… you know your material extremely well when you’re able to describe it to the layman. That’s the sign of subject matter expert!

Wow, maybe your best explained video to date, storytelling-wise. Great pacing, great narrative, well done Scott!

Again one of the best videos ever. Nobody does it better than Scott! Thank you very much for the simple, comprehensible and very interesting information about what seems to be a simple computer animated image, but is in fact far more!

I was amazed to discover that the Germans had a Mach 5 wind tunnel in Penemunde. I guess this was a high priority article for operation paperclip, seeing how rare and sofisticated these things are. Still, to think they where doing this kind of engineering almost 80 years ago.... Mind blowing.

The ‘ie’ “Schlieren”-technique is actually pronounced like the ‘ee’ in the English word “eerie”. (Sorry, but it is a German word. It literally means “smears”. And while Germans don’t know everything, they sure know everything better.) BTW: I noticed that Scott’s eyes looked weird in some videos. Now I know why: it is the reflection of the circular light he is using in his recording set-up. Nice video with interesting details. Thanks!

Love your channel Scott. Been watching you for years. You have such a firm grasp on technical topics that you make them sound simple and obvious with your clear explanations, even if the topics are actually quite subtle. Bravo.

Would absolutely love you to do a few videos or a playlist on the basics of fluid dynamics, these videos are so well explained, I feel it could be really helpful for a lot of people

helium at Mach 20 is pretty hardcore

Bernoulli might be spinning in his grave over all the misunderstandings of his theory... but no physicist can agree on how he spins.

Fascinating! One of the best videos I have seen on this channel. 👌🏾🙏🏾

I always come back to your channel every once in a while because it’s exactly just technical enough while also not feeling like a lecture Keep up the good work Scott!

My fluid engineering teacher taught me "the only way to convert subsonic flow into supersonic flow is the throat of a duck" QUACK!

Was more succesful at turning aviation fuel into noise pollution xD

You are amazing when it comes to explaining things with great illustrations and graphics. Thank you.

Fascinating topic! It amazes me how you always come up with great videos I didn't even know were a thing, thank you a lot for your work Scott

"Schlieren" is pronounced "Schleeren" not "Schliren

It's amazing all the complex engineering that went into taking that photo. Great explanation of it!

Perfectly explained! I didn't even think of how many problems had to be solved to achieve this...

In 1968 I was stationed at NAS Moffet Field were Nasa Ames Research center. The wind tunnel would keep us awake ,great stuff

Your technical storytelling skills are unrivaled, sir. That is some dry matter to explain, but it was super-engaging, chapeau!

Very interesting - and a very complex subject explained so well I thought for a moment or two that I almost understood it... I love the variety on this channel - you never know what's going to pop up or when. Definitely the best YT science and tech channel.

That is really amazing. I saw the low speed wind tunnel at Langley, decades ago. There is (or was) a KZfaq film about how its giant, wooden propellers were built. I hadn't given much thought about supersonic, much less hypersonic, tunnels. Your explanation of the problems and solutions for these is fascinating. I really enjoyed it.

Amazing insight. It was a beautiful abstract image initially, but knowing all this just makes it that much more awesome.

I’m taking a compressible flow class this semester and it’s cool hearing you talk about this stuff while I’m learning about it.

Awesome video. From someone who has been working in everything from a 7'X10' 100PSF low speed tunnel to a MACH 6 quiet tunnel to a MACH~'we're not sure just how fast we can go" Hypersonic Expansion Tunnel using a Helium slug. Now my days are spent developing new laser based analytical techniques for hypersonics research. This was a fantastic explanation of how wind tunnels work and why there aren't too many hypersonic facilities.

Well done, Scott. As an Aerospace engineer who has tested in wind tunnels all over the country, I get so infuriated at the regular media in talking about hypersonic. Of course they wouldn't begin to understand your discussion. Thanks.

Brilliant video, well told with just enough history to explain the need for it and the problems it was trying to solve.

Wow. That was way more complicated than I would have imagined! Fascinating too!

Always quality information from yuo, Scott. My inner nerd appreciates your efforts to make rather complex matters easy to understand.

Well done! This is definitely a top 10 of your videos.

The inlet velocity of the project Pluto cruise missile nuclear reactor (ram jet engine) at the Nevada Test Site test facility needed to be Mach 3 @ 2000 degrees to PREVENT meltdown of the flow-through reactor. The engineering in that monster building and equipment was INSANE! There was a 50 acre area covered in air tubes made from something like naval rifle barrels, pumped up with submarine compressors to provide airflow for a 5 minute test. The air tank field fed four huge tanks filled with 2” stainless ball bearings that would be heated to 2000 degrees. I visited there in 2000.

I was an apprentice at the NGTE Pyestock supersonic wind tunnel (now a cow pasture). Thanks for updating me a little. Sixty years. . .

For me, this has been the best explanation of any scientific/engineering concept ever, so thanks man!

I'll tell you what. This past Thursday here in Kansas, it felt like we were in a hypersonic wind tunnel. Driving down the road, the paint on my car became an ablative heat shield. Seriously, on Thursday in Kansas we had steady 40 mph winds with gusts over 60 mph, all of that with a blue sky and not a cloud in sight.

Thanks Scott, for the follow-up to the Fluid Dynamics 101 I took a couple decades ago. It's always fascinated me and I really expanded my knowledge with your video. Well done!

Haven't caught up with your vids in a while. This one rocked! Thank you!

You are sooo becoming my favorite YTer- I'm totally hooked!

A good example of air changing temperature with pressure change can be seen in places that use pneumatically actuated machinery. It's common to have bell-style water traps inline just before the line goes into the machine. The compressor releases high pressure air into the distribution lines, cooling it in the process. From there if the atmospheric conditions are right, generally meaning the local dew point, the now colder air causes water to condense in the distribution lines, then the air flow pushes it downstream towards places you really do not want water going. The bell traps basically use gravity to catch it before it causes trouble. The bells are usually made from a clear polycarbonate so the operator can see if they're filling up. During the muggiest days with high dew points, it's not uncommon to have to drain the water multiple times a day.

This might be one of your best videos. You explain it very well, even things that I as a trained engineer didn't know.

Great explanations. I performed NDT inspections on a hypersonic wind tunnel back in 2013. It was an awesome place and thing to see. The pressures were massive.

Very cool lecture, Scott. Having grown up in the Space Shuttle era, and not far from Edwards AFB to watch the shuttle land and be transported off on the back of the modified 747 - this is the most beautiful image I have seen. Thanks for finding and sharing it.

Great video! Lot's of stuff I knew (and some I didn't), but hadn't put together into the application of a wind tunnel!

One of the only channels I like the videos before I even watch them. Thanks Scott