Understanding Aerodynamics

[Howard Rush]

I just got my copy of Understanding Aerodynamics, a new book by Doug McLean, a modeler and the smartest person at Boeing: http://www.amazon.com/Understanding-Aerodynamics-Arguing-Physics-Aerospace/dp/1119967511/ref=sr_1_1?ie=UTF8&qid=1356045394&sr=8-1&keywords=understanding+aerodynamics .  In the two hours I've had the book, I think I learned why PJ's vortex generator locations work, why other locations he tried didn't, that the explanation we all were taught about Reynolds number (the ratio of inertial to viscous forces) is wrong, and why the skies are not black with biplanes. 

The book has surprisingly little math.  It covers a lot of stuff of interest to modelers: how wings lift, how air flows and what you can and can't do about it, wingtip devices and other esoteric doodads like riblets.  It has only a page or so specifically about low-Reynolds-number airfoils, but it's a very interesting page. It's probably most useful to somebody who studied aerodynamics in school, but was left bewildered about how it all fits together.  That's most of us who have worked in aeronautics. Folks who learned aerodynamics from magazine articles and books written for pilots will be dismayed to learn that everything they know is wrong.  Doug has spent a lot of effort explaining "the real physics", and in doing so refutes a number of popular misconceptions.

[Dave Denison]

Thanks Howard.  I "need" one more item under the Xmas Tree. Also, something to read during the rainy months. Information is a wonderful thing

Happy Holidays.

  Dave.
 ama41041

[Chuck_Smith]

Thanks Howard,

Appreciate the tip.

Re number - only time I ever use it is in Buckingham Pi theory for dymamic similarity. It explains why a 1/4 scale Cub flying at 20mph doesn't behave anything like a full-size at 80mph. I've personallly witnessed laminar flow a Re over 2x10^6, so yeah, I'll agree it's a poor predictor of flow transition.

Chuck

[Tim Wescott]

Airplanes fly because rapidly moving air sucks.

Helicopters fly because really strongly vibrating things experience and anti-gravity effect, and as anyone who's ever tried to keep bolts tight on helicopter-borne equipment knows, nothing vibrates like a helicopter.

[Chuck_Smith]

Airplanes fly because rapidly moving air sucks.

Helicopters fly because really strongly vibrating things experience and anti-gravity effect, and as anyone who's ever tried to keep bolts tight on helicopter-borne equipment knows, nothing vibrates like a helicopter.

Especailly a UH1 with the M6 package!

[John Sunderland]

One thing I understand is that everything I built since the age nine flew....how well was a matter of experimentation and observation and time....and it always cost money! This book sounds interesting with something new and pertinent in it.

[Kim Mortimore]

Fortunately, Amazon allows you to read a fairly large sampling of the text online.  I was lost on page one, and the following pages were pretty much the same, otherwise I would have been happy to fork over the 80 bucks.

Howard, you gave us a smattering of teasers in your description of the book.  Any chance you might be willing to discuss in language accessible to us ordinary mortals some of the discoveries, insights, etc. to be found in the book?

[Howard Rush]

I was lost on page one, and the following pages were pretty much the same, otherwise I would have been happy to fork over the 80 bucks.

I'm currently lost in chapter 3.  I paid more than $100 for it, the price of being the first kid on my block, I guess.  OK,  I'll try to write some more after I slog a little further. 

[Kim Mortimore]

I'm currently lost in chapter 3.  I paid more than $100 for it, the price of being the first kid on my block, I guess.  OK,  I'll try to write some more after I slog a little further. 

No hurry.  Much appreciated.

[Ted Fancher]

Folks who learned aerodynamics from magazine articles and books written for pilots will be dismayed to learn that everything they know is wrong.  Doug has spent a lot of effort explaining "the real physics", and in doing so refutes a number of popular misconceptions.

Well,  no wonder none of my airplanes fly!  At least now I know why. 

I was getting tired of hitting spectators on the soles of their shoes while I was convinced  I was actually doing overhead eights.  And the spectators were confused because they were looking up when they got hit and afterward wondered why the didn't see the airplane coming.  It's all clear now. 

Ted (learned to fly but didn't know why) Fancher

[EddyR]

" If you can make something work with incorrect information then the correct information is only partially correct"
Famous quote from School Yard aeronautic engineer ,Me
EddyR

[Kim Mortimore]

How about a mud wrestling match between Howard and Ted to determine the King of Aerodynamikul Theory?

[Howard Rush]

Folks who learned aerodynamics from magazine articles and books written for pilots will be dismayed to learn that everything they know is wrong. 

This is a bit of an overstatement, as some of you have noted.  I haven't seen anything that Doug wrote that contradicts anything I've seen that Ted has written.  This isn't a book on stability and control or airplane performance, but about nitty-gritty fluid mechanics.  This book doesn't address the usual stunt topics.  Other than learning better the stuff I sat through in school, I hope to find out from it how to fix hunting and where to put vortex generators. 

Doug does go out of his way to refute the "simplified" explanations of how wings work that we all read as kids: the "equal transit time" explanation of lift, the idea of Bernoulli and Newton being at odds or of having separate, equivalent explanations, the Coanda effect as an explanation of why air follows the curve of an airfoil, and particularly about causality between pressure and velocity over a wing.  He justifies treating air as a continuum, from which you can calculate stuff, rather than as particles, which won't get you anywhere.  He straightens us out about what Reynolds number is.  It ain't the ratio of inertial to viscous forces, as I've heard and passed along. 

Reading all that junk probably didn't do us much harm, but it did get in the way of us being able to figure stuff out.  We learned the "equal transit time" explanation of lift, but pretty much dismissed it as irrelevant when we saw that symmetrical airfoils work and that airplanes can fly upside down.  It's sorta like teaching kids that babies come from storks.  It's a quick explanation, but it's wrong and leaves out some kinda interesting phenomena.