NOT SO FAST, Bill Berson

[Bill Greenwood]

In the long 7 page discussion of AOA indicators, Bill Berson wrote that
"wings stall at less angle with flaps down" and by angle it is clear that he means angle of attack.

I disagreed and thus Bill gave a reference to Langewiesche as his source and specificly tells me to "go to page 166 for the proof and a chart listed as figure 13-2. "

So I did just as he said, and got my copy out, looked at it, and I don't see it. One of us Bill's must have a different version of the book or have a vivid imagination.
First of all there is very little discussion of flaps in the whole book. There is no chapter on flaps, there is only 2 short references for a half page each on page 83 and 256 and neither mention angle of attack at all. He writes, "Flaps have the double purpose of lowering the airplane's stalling speed," etc.

Next the whole chapter of which p166 is part of, is titled The Ailerons, and has no mention of flaps. Yes, it talks about aileron effects on stall, but that is not the part I wrote about or am writing on now. An aileron and a landing flap are not the same thing.

As for proof in the "figure 13-2", once again, it is not in my book, The illustrations are not numbered at all and there is not one that shows a graph for stall speed as higher with flaps down. Mine is copywrited 1944 and renewed 1972.

So Bill Berson, as they say in legal circles, which Bill has the true bill?

Now if anyone wants to comment on this, besides the other Bill, fine, but I'd ask you to keep it on this specific point which is about the affect of FLAPS , (not ailerons) on stall speed and the angle of attack. And my discussion here is only this point , not about if AOA indicators are good or which brand is best, that was the other topic.
Thanks, Bill G

[Bill Berson]

To Bill Greenwood,
The figure 13-2 is in this web link:http://books.google.com/books?id=i8rNn1vFEd0C&pg=PA199&lpg=PA199&dq=flap+stall+angle&source=bl&ots=u1xDNZgE72&sig=nJ3GcqFGvXoontoc70zFWnOML6s&hl=en&sa=X&ei=guDjUOGWJqaRiAKSqYHYBQ&ved=0CDIQ6AEwATgU#v=onepage&q=flap%20stall%20angle&f=false

[Bill Berson]

It's true, The book Stick and Rudder does not have a chapter on flaps. That why I used the aileron as an example.

For more details:
I would also suggest a careful reread of Ron Blum's post #55 here:http://eaaforums.org/showthread.php?3262-Angle-of-attack/page6&highlight=Angle+attack

[Bill Greenwood]

Well, Bill, as least we agree with what I wrote, in that page 166 on Langeweiche does not say, and has nothing to do with flaps and stall speed.
I may not be as young as I used to be, but I was the best reader in my elementary school and just went to the FAA Dr. today and passed my eye test at 20-20 with no glasses.
By the way, I was also probably the worst dancer in my school, and I might be the worst computer guy on this forum, but you can't win em all.

Now as for the figure 13-2, and your pages from the Rich Stowell book, well I just don't read it the same way you do. He talks about stall speed and bank angle for instance. Nowhere do I see a straight forward statement that says ,"Flaps make a wing stall at a lower angle of attack", and I am talking just landing flaps down vs clean, nothing about changing g loading or weight or bank angle or ailerons.
If he has that simple phrase somewhere that I missed please quote it.

I have heard Rich speak at EAA, and if I go to his lecture this year, I will ask him that specific question.
I do like his simple PARE spin recovery idea, and it works in the planes I have flown, but I have also heard and even read on this forum that some acro guys dispute it and like to bring up a few airplanes that it may not work on.
I have phoned a couple of current CFI friends. All agree that flaps lower the stall speed, just as I am saying and as Langweiche is saying. But they are not sure when you phrase it only on angle of attack,and they start to hedge their statements. One thinks flaps don't change the stall angle of attack at all, but like me he can't see how they would make it stall at a lower angle.

Just seems to me if a plane with flaps down can fly at a lower airspeed without stalling than when clean, it must indicate that it can fly at a higher angle of attack before stalling than if clean.

I, of course, may be wrong. I once voted for Nixon, and once bought a VW Rabbit and both proved to be defective.

[Matt Gonitzke]

Bill G.-

Go find a copy of Theory of Wing Sections by Abbott and Von Doenhoff and look at the CL vs. AOA graph for any airfoil in it. You'll notice that the CL vs. AOA curve peaks at a lower AOA and higher CL with the deflected flap than the clean configuration.

[Bill Berson]

Thanks Matt,
I just got out my copy of Theory of Wing Sections to find a reference to quote.
You beat me to it.

[Victor Bravo]

In the long 7 page discussion of AOL indicators,



AOL indicators include:
1) receiving hundreds of useless computer disks in the mail weekly,
2) being inundated and besieged with hundreds of offers and purchase opportunities when all you're trying to do is check your e-mail, and
3) being viewed as a little less educated and computer savvy by the rest of the internet world.

AOA indicators, on the other hand, give you information about an airplane wing's angle of attack. :)

[Bill Greenwood]

Matt, I don't have a copy of the book on wing theory that you refer to, and won't order one just for this.
I did look up the authors info, lot's of credentials but a long time ago.

So I have three questions:

1. Are you saying that the peak of CL which I understand is lift, is where the stall occurs?

2. Since that book is about theory, is there anywhere in the book that refers to a real airplane test in actual flight, and has a simple direct statement to the point that Bill Berson made, which was,
"wings stall at a lower angle with flaps down"

3. If flaps do what you and Bill B say, then why do many airplanes take off with partial flaps? It seems under your way, they would be handicapping themselves and setting the plane up to stall sooner, ie at a lower angle of attack than clean?

I may be dense and of course have not flown with AOA indicators, but rather airspeed indicators for all these years, and I don't read a lot of design or theory books, more of Pilot Notes or flight manuals which tell you the airplane performance, but re airspeed.

Thanks, Bill G.

[Bill Berson]

Bill G.
I think it is important as a pilot, that you understand how a down aileron can initiate a stall.
You seem to refuse to think about ailerons. But from a pure physics point of view, the aileron is virtually the same as the flap.
You need to know this.

[Matt Gonitzke]

Bill G.-

3 answers (hopefully):

1. Yes. Here is a picture of one page of the book for reference:
http://www.boatdesign.net/forums/attachments/boat-design/41848d1269979580-naca-sections-naca-0012.jpg

2. There are methods to transform a 2D airfoil CL vs. AOA graph into one for a 3D wing that are described in other books. These theories and equations are used to design aircraft and have been for decades. If they didn't properly capture this behavior, we wouldn't be using them.

3. I'm not sure what you mean by 'sooner'. Flap deflection will decrease the stall speed. The points during the takeoff at which you rotate, begin climb, etc are based on airspeed. The angle of attack associated with that airspeed will vary based on flap deflection (and other things). I use 10 degrees of flaps in a single-engine Cessna to shorten my takeoff roll on short runways. More lift is produced at that flap setting, and the increase in drag is not enough to offset this benefit.

[Bill Greenwood]

Bill Berson, I am aware that a down aileron makes drag, but our discussion (or at least my part of iT )was only about the effect of flaps. Flaps, IN PRACTICE, are not the same as ailerons. There are at least 3 differences: flaps are lowered the same on both sides, (unless there is a malfunction such as the fatal one in Tusnami) and partial flaps also make lift as well as drag. Finally most landings, unless there is a crosswind, are made with flaps down, but ailerons neutral.

I was talking about flaps, not all the other variables. We could even use drag from a pilot's big ears if we wanted to get away from the main topic.
What if Obama was to pilot an open cockpit Pitenpol and not wear a hat? Or what if Vincent Van Gough flew one?

And believe it or not, I have managed to fly with some luck for 34 years by using ailerons rather than worrying about them. I have even flown a gas powered model airplane that didn't even have ailerons, only rudder, and not knowing any better they still fly.

[Flyfalcons]

Typical airfoil Cl graph:

http://flysafe.raa.asn.au/groundschool/flapcl.gif

[Bill Berson]

,

I was talking about flaps, not all the other variables. We could even use drag from a pilot's big ears if we wanted to get away from the main topic. .
Flaps and ailerons are both camber changing devices. If the wing is flying very close to critical stall angle and the pilot suddenly lowers the flaps or aileron, that portion of the wing will instantly stall.
In the case of flaps, it usually doesn't matter much when both the inboard wing areas stalls from the increased camber with flap deployment since the nose just pitches down straight ahead.
It is much worse when the down going aileron causes a stall because the plane usually tips upside down.(the controls seem to the pilot to have reversed)

I suppose the fact this didn't kill you in 34 years may be because you apparently flew well behaved and forgiving airplanes that have nice features to prevent this. ( such as aileron differential) Not all planes have these features.

My comments are not just for you.
These comments are also for others here that would rather think than die. (stole that line from Langewiesce's book)

I give up.

[Bill Greenwood]

Bill B., I think you have shown me the light.

I'll trade my Bonanza in for a Wright Flyer Model B.
No ailerons at all and no flaps, thus no danger of a flap or aileron deflection inducing a stall.
Now, the density altitude here in Colorado might be a bit of an issue, but I am sure some intrepid EAA member can come up with a turbocharger for that 4 banger.

Obviously, I am trying to bring a little levity into the discussion and I don't want you to take it personally when I questioned the concept as you wrote it.

You might find it hard to believe, but actually I am close to the point of saying that, odd as it seems, you may be correct about flaps lowering the AOA at stall.
To be sure, I hope to find a plane with an AOA indicator and go try a few stalls both Vs and Vso.

[Flyfalcons]

You don't need to Bill. The research is out there already.

[Ron Blum]

Don't know if anyone will read this post as it is 8 months after the original posting, but a reference to me in a discussion (and actually in a positive light) is awesome :o) Bill B is correct in his statements (as he agreed with me ... again, :o) In addition, Bill G is correct in that deflecting flaps also lowers the stall speed. For Bill G, I hope the following two points help as to why the stall AOA is lower with the flaps deflected. 1) Because the down flap adds camber to the "local" airfoils (those are the airfoils that are ahead of the flap), the air must work harder in that area to follow the increased camber. Since the air has to work harder, it separates at a lower AOA. 2) In addition, the AOA remains referenced to the original chord line. If we were to draw a new (unflapped) airfoil that looked just like the original airfoil with the flap deflected, the increased camber would make it stall at a lower AOA. Note: This happens to be how some CFD programs analyze "simple flapped" airfoils. ------------------------ --------------------------- ------------------ ------------ ---------------- ---------------------------------------------------- ----------------------------------------- ----------------------------------- ------------------------------- -------- ----- ---- ---- ----This brings me to a question I'd like to pose to y'all. Would anyone be interested in articles on like the "Top 10 Airplane/Aerodynamic Myths"? Suggested topics are very welcome. I'd start a new forum, but I'm not sure how to. Heck, if I new how to start a new paragraph, I would do that, too! Thanks, Ron

[Matt Gonitzke]

This brings me to a question I'd like to pose to y'all. Would anyone be interested in articles on like the "Top 10 Airplane/Aerodynamic Myths"? Suggested topics are very welcome. I'd start a new forum, but I'm not sure how to. Heck, if I new how to start a new paragraph, I would do that, too! Thanks, Ron

Yes, please! :D

[Jim Hann]

Flaps and ailerons are both camber changing devices. If the wing is flying very close to critical stall angle and the pilot suddenly lowers the flaps or aileron, that portion of the wing will instantly stall.
In the case of flaps, it usually doesn't matter much when both the inboard wing areas stalls from the increased camber with flap deployment since the nose just pitches down straight ahead.
It is much worse when the down going aileron causes a stall because the plane usually tips upside down.(the controls seem to the pilot to have reversed)

I suppose the fact this didn't kill you in 34 years may be because you apparently flew well behaved and forgiving airplanes that have nice features to prevent this. ( such as aileron differential) Not all planes have these features.

My comments are not just for you.
These comments are also for others here that would rather think than die. (stole that line from Langewiesce's book)

I give up.

Bill, spot on! I taught in the good ol' (I use that descriptor loosely) Piper Tomahawk. It does a fantastic job of demonstrating this. I had many former Cessna pilots put the Traumabird into an incipient spin because they would deflect the ailerons while practicing or demonstrating stalls.

[Ron Blum]

I taught in the good ol' Piper Tomahawk.

What does the Tomahawk use for stall warning?

I have also heard horror stories about the stall/spin characteristics of that airplane. What are your thoughts? Thanks! -Ron

[Bill Greenwood]

Jim and Ron, talking about the Piper Tomahawk brings me back to my early days as a student pilot with Nugs Madriaga, National Air College at San Diego Montgoemery Field, in summer/fall of 78. I took my first lesson in a Tomahawk, it seemed a little tinny so I swithched to a Cherokee 140, but I knew enough, (barely) to know I wanted to do spin training even though it was not FAA required. I remember asking my CFI if he was sure he knew how to do spin revovery and he said yes, so we went up to about 8000 and I stalled it power off,kept the wheel back and hit full rudder. It broke for sure and surprised me as how much it rolled and dropped the nose into the spin, as opposed to jsut yawing. The spin was stepp enough that I was almost standing on the pedals, but it came out with normal recovery promptly. We did a couple and much of what I learned was not to spin a plane anywhere down low.
I am pretty sure we did not have chutes then, I wasn't that knowlegeble, and within the next few months there was one or more fatal accidents with students and/or CFIs spinning into the ground in the Tomawhawk and an A D came out that required some strips on the wing that ours didn't have.
As they say, "Live and learn" and I learned from this and we were lucky enogh to live also.
I have since done a lot of slow speed/stall training in most everything I have flown, and I have done spin/s recoveries in Piper J3, and Super Cub, Decthalon Stearman, T-34, Spit MkIX, etc. I have not spun a T-6, but have done lot's of stall training in them and they are an excellent trainer for this.

[Ron Blum]

Bill G. I think that you hit on a very important spin characteristic that most people (especially those that see it for the time unexpectedly) miss is that the nose drops dramatically. BUT, a nose low attitude doesn't mean that the airplane is recovering/recovered. AOA could still be high, and the wing could still be stalled. I would venture to guess that the first time that a pilot sees this unexpectedly, he/she will continue to pull ... and wonder why the nose won't come up! And the airplane is still stalled.