Beginner's Guide to Aeronautics | Hacker News Reader

Beginner's Guide to Aeronautics

grc.nasa.gov

121 pointsrnjailamba17 comments

This link is old. The new one is this: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/. I know that sometimes old links are gold, but I can't tell if this is really the case.

Grumble — both this site and the newer one someone else posted [1] link to an old and somewhat misleading diagram of how an airplane wing works [2].

The problem with the diagram is that the "lines" both ahead of the wing and behind the wing are pretty much flat — as if the air ultimately returns to where it was as the wing moves through it (to be fair, the lines are a little wobbly in the diagram).

That's misleading because if the wing has a net force upwards (ie lift), then the air must have a net force downward. You can't invent forces out of thin air (literally, in this case :). Yes, there's Bernoulli’s principle and all that, but fundamentally: if the wing is pushed up, then the air must be pushed down. The mechanism for how that happens is a separate discussion.

This is an issue that has been debated back and forth for a long time, so I don't want to re-hash it in this comment, but I think it's fair to say at a minimum that those diagrams are misleading, and fly (ha) in the face of Newtonian laws of physics.

I expect better from NASA.

Here's good short Veritasium video on the subject: https://youtu.be/aFO4PBolwFg?t=13

Also good: https://www.youtube.com/watch?v=HmDYbnGnhpA (part 1), https://www.youtube.com/watch?v=21YB4qCvIK4 (part 2), https://www.youtube.com/watch?v=iE27CXLXbp0 (part 3)

[1] https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/

[2] https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/aer...

Honestly, I don’t think you are reading the diagram well.

The lines are streamlines, i.e. tangential to the flow velocity at each point.

They are not straight flat lines so they do show that there _is_ a change of momentum (that is, a force) being applied to the air.

And the air in turn is pushing back on the wing. These are the normals also depicted on the diagram.

You could be right, though the diagram is not well-labeled so it's hard to say for sure. What's the big black arrow at the left-hand side? Direction of flow?

It would be nice if the accompanying text made any mention of deflection of air downwards, but it doesn't.

I take some solace that the spotty explanations in the text (eg: a single mention of Euler's Equations without any other reference) will send a curious reader to better sources.

I’m very certain that the curved lines are streamlines.

The black arrow is labeled “Free stream velocity” meaning that, in absence of any perturbation, that is the direction that the air would freely follow. I.e. it would go in a straight line.

There is a mention of flow turning as the source of lift here [0] but the page you mention is taking the more mathematical approach of defining lift as the integration of pressure over the wing area.

I agree that the diagram could be better, most aerodynamics textbook diagrams could be :)

[0] https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/wha...

EDIT: I just reread the page with a bit more time and I have to disagree, it’s a very good explanation of lift, although it is a bit more technical than a layman’s. I can’t see anything obviously wrong with it, except that it doesn’t mention more advanced topics (e.g. turbulence).

So what? They are taking about the forces on the wing, not the surrounding area!

Is there something of the like but for orbital mechanics? Out of all the engineering that is nearly superhuman to get us to do everything we do in space, there's something about the knowing that "if I point it at this direction, in 3 days time, going this fast, it'll hit this object in 4 days" that I just find utterly fascinating but am hopelessly ignorant about.

Kerbal Space Program. The original is more refined at this point, the second one will eventually have better tutorials, but if you watch Scott Manley videos you'll have the basics in no time. Then there's Dover Press with Fundamentals of Astrodynamics. Fun for everyone.

As of today, I think the best way to learn orbital mechanics is playing Kerbal Space Program.

BMW and do the exercises by hand with pencil and paper.

I'm a professional astrodynamicist, and I can echo the other commenters about KSP. I used it to study in my undergrad. I don't know of any way to get a better intuitive understanding of how the thrust directions affect trajectory, honestly.

Yes. Kerbal Space Program. When you can get the small green men to the Mun and back, it will be time for you to leave.

https://youtu.be/PbMP0lo4A2o

https://youtu.be/WkU08pXUPKc

https://youtu.be/9OMvpSLHm4Q

https://youtu.be/j_57NSlkzt4

Several of the links there need to be updated. I just emailed them to let them know, so you don't have to.

thank you!

This is excellent: "See How It Flies": http://www.av8n.com/how/

Related link https://www.grc.nasa.gov/www/k-12/airplane/ covers Hypersonics, Beginner's Guide to Kites, Kid's Page explaining how airplanes and jet engines work, Beginner's Guide to Model Rockets, Beginner's Guide to Propulsion, Aerodynamics of Baseball, Aerodynamics of Soccer. It has some repetition with respect to the main link.

Great Interactive Simulations here: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/bga...

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