We still don't understand how airplanes fly

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Xyla Foxlin
3727 W. Magnolia Blvd. # 174
Burbank, CA 91505

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[SEO]

Retired USAF WC-135 and B-52H flyer here. We always described "noise" as the means of sustained flight, because when the noise stops, the jet goes down. Also, helicopters fly because they're so ugly the earth repels them. To fly as an individual, you have to throw yourself at the earth - and miss. (Thank you, Douglas Adams and Arthur Dent!)

[andy-in-indy]

The Simplistic Laws of Aeronautics:

1st Law of Aeronautics - Given enough thrust, anything will fly
2nd Law of Aeronautics - If you want to fly straight, the ass end has to want to go slower than the front end
3rd Law of Aeronautics - Down is easy. "Where?" and "How Fast?" require some forethought.
4th Law of Aeronautics - Lift is when the top and bottom can't decide how much they want to fall.
5th Law of Aeronautics - Controlled flight is all about levers
6th Law of Aeronautics - The faster you go, the harder it is to go faster.

[mrford]

My five year old daughter just went from talking excitedly about playing in the other room to sitting quietly and listening intently to your explanation about flight and lift once I clicked this video. Not sure if that'll continue for the series you mentioned, but thanks for the 10 minutes of an example for her of a woman who knows what they're talking about. "Oh, and say 'she loved this video.'" :D

[Auchioane]

more videos please xyla and that quote near the end pure gold and explains me in a nutshell:
"Sometimes you dont need to fully understand everything you can just keep trying new things and experimenting until you figure out something that works."

[UnlikelyToRemember]

every kid who has ever stuck his hand out a moving car intuitively understands how to generate lift

[MitchD]

Xyla's birds and the bees talk is way different than my parent's version.

[philso]

I am sure I am not the only one who would appreciate a video from you about blimps and dirigibles

[mattkillough]

PhD in applied math here. It is true that we don't have a general theorem that guarantees global existence of a sufficiently smooth solution to the Navier-Stokes equations (the partial differential equations that describe motion of a viscous fluid) under all conditions. But its also true that we can write down exact solutions under various simplifying assumptions, and/or asymptotic limits which gives us a pretty solid understanding of lifting wing theory and drag. Combine that with the computer modeling you mentioned, and you have pretty thoroughly understood physics.

[BustedByDaFeds]

This girl is so adorable and smart. I bet her parents are so proud of her. Thanks for this content, I'll be sharing this to my daughters.

[PhilG]

Flashback to Engineering School! I used to solve Bernoulli's Equation many times a day at work while doing pipe system design. Fluid Mechanics/Dynamics of fluids with SPGR usually greater than or less than water. Water is easier because so many of the terms essentially become "Multiplying by One"!

The way aircraft wing function was described to US was that as the air flows over the top of the wing, the air molecules have farther to travel and spread out, making the air on top of the wing less dense than the air under it. Fewer molecules pressing "down" on the wing than pressing "up" from under it. Net force "up" = "lift".

But then there are other factors that come into play like Turbulent vs Laminar flow (Reynolds numbers).

So many times I'd ask one of my PhD professors a question and they'd reply: "That's beyond the scope of this course." Which over time I concluded meant: "I don't know."

BTW your video on the FAA was posted on an R/C hobby board I frequent in the "Life the Universe and Politics" sub-forum, colloquially known as "The Basement", which unfortunately is where the "discussions" are usually between the "Trolls" and the "Normal People" (like me).

The Trolls all insist your ticket should be pulled permanently and go on to take shots at YOU for the "personal details" the "inspector" chose to focus on, etc. Pretty much echoing the bias HE showed. The rest of us came to your defense (and *I* am probably the only one of them who actually HAVE seen your vids before)!

One Engineer to another: "Nils Illigettimi Carborundum!"

[donalddepew]

Retired Aviator here. Great video, especially the Bernoulli principle definition. All through the many check rides and written tests I’ve been subjected to, the FAA isn’t the smartest set of tools in the shed. But in order to obtain the type certificates, licenses and ratings, ya just have to play the game so to speak. Xyla, I hope your medical issues with the FAA gets cleared up soon. Great Video!

[MrDaveWhitney]

Your embedded ad is by far the best I've seen in any YouTube video. The entertainment factor alone was worth it!

[amdbarton]

Navier-Stokes mentioned! Fun fact: the official Millennium Prize problem statement doesn’t even require that NS be solved. It ‘simply’ requires that you prove that *solutions exist* or *solutions do not exist*. As a chemE, I’d love to see that done in my lifetime. Maybe one day we will!

[HeidiandFranny]

I went to UF in the 80's (ASE), the explanation we got was that the wing pushes on the ground (I guess through the air). That, and the wing's job is to redirect the flow downward upon exiting the trailing edge. It is one of the things that pushes down on the stab to counteract the forward CG position, adding to a positive pitch stability. I think I like the second explanation about redirecting the flow. It is more helpful for how the airplane as a whole moves through the air. Thanks for a fun video :)

[JimHoward]

I earned my aero degree in 1974, and our instructors mocked the pressure differential theory that the FAA loves. First we reviewed why Bernoulli even bothered to come up with his laws.

In 1783 Bernoulli was trying to calculate the flow of fluid through pipes. Not wings. How did he do it? He applied Newtons second and third laws of motion. That should be a hint.

What we had to do was apply Newton to the airflow across a surface. Turns out if you do that you can show that airplane lift is really a product of the amount of air that is pushed down times the acceleration of that air due to angle of attack. AKA F=ma.

As a byproduct of this fact is that if you put pressure sensors on the top of the wing they will indicate a lower pressure you can calculate using Bernoulli’sf formula.

But that’s the wrong way for pilots to think about what the wing is really doing. And the Newtonian mental model explains why flat or symmetrical wings work, and why planes can fly upside down.

And if you what induced drag is (drag caused by lift) this explains why a fighter that wants to accelerate as quickly as possible will usually reduce AOA to the point of zero lift .

There are many other subtle factors, but as pilots we should be thinking about deflecting air mass, not what a pressure sensor in the wing might read.

Note with respect to the boundary layer: some aircraft, mostly high-performance jets, have boundary layer control system, s such as the hard wing F-4s. For those pilots some understanding of how the boundary layer behaves is probably worth revealing to them, but not to the typical airline or general aviation pilot.

Most significant second order factor is the tendency of moving fluids to stick to a curved surface called the Coanda effect, followed by boundary layer effects. But as engineers, we should not confuse pilots with those secondary effects.

Pilot should be taught to envision the way, the wing is pushing down air, resulting in an upwards force is the right mental model for them to have.

Then the nonsense thinking. that two air particles have some kind of quantum entanglement that makes them want to meet each other at the end of the wing and crazy shit like that is avoided.

[erichurst]

Xyla: Should I do a video on

the Internet: YES

[jamespettit]

Well, we know Helicopters beat the air into submission.

[KrisBendix]

Your airplane content is very uplifting. 🛫

[jacobbaumgardner]

“Understanding Aerodynamic Lift” by The Efficient Engineer is by far the best explanation on this I’ve ever seen. Of course, as said, there’s no unified theory, but man this video was by far most comprehensive and easy to understand.

[rmqjjhl]

This is so good! So much profound insight about the nature of models, theories, engineering and physics wrapped into just over 10 minutes! I really appreciated how you embraced the uncertainty and didn't just "pick a side". I am personally SO excited for more videos about the physics of flying! You rock, Xyla, you rock!