Monday, September 18, 2017

Did I Call It, or Did I Call It!

by John Patrick Conway, Jr.



I'm sorry, but I just cannot help myself...

Though I'm fully cognizant of my propensity to
go on at length with most of my posts, this just speaks for itself. While spinning thru a news feed, I came a cross an article whose title was simply begging to be clicked on. It emanates from Bloomberg and it's written by a guy named Max Abelson...and the fetching caption whose siren call I could not resist:

"Obama Goes From White House to Wall Street in Less Than One Year"

Read it...or don't. I really don't give a fuck. I just wanted to rub the world's nose in it...


A...ha-ha-ha-ha-haaaaaaaaaaa! (sigh) Yeah....OK.



Copyright September 18, 2017. All rights reserved.





Sunday, September 17, 2017

Swimming In A Sea Of Media Red Herrings

by John Patrick Conway, Jr.




After the "shocking" defeat of Hillary Rodham Clinton by Donald Trump in the 2016 presidential elections, the news media and political scientists were all over themselves issuing what appears now to be a series of empty Mea Culpa, my bad, and should've seen it coming acknowledgements followed by promises to really open themselves and listen to the rank and file, hence. I remember thinking at the time...yeah, right. Sure you will. Once the shock wore off, though, and with the reality of the next four years staring them in the eye, it didn't take long for these same people to demonstrate the insincerity of their words as they clearly decided to take a page from the Republican playbook under the title of "Obstructionism" and run with it.

If you tune into the Sunday morning talking heads, Cable News, or even the Evening News, it's all about what a bastard Trump is; it's all about the Russian's penetrating DNC emails and the threat to our "national security" that they pose; it's about this, that, and every other mother fucking thing under the sun so long as it deflects any light shining upon the truth of what just happened.

This past week Hillary Clinton came out with her new book and issued a statement beforehand owning the loss of the presidency in 2016...then turned right around and leveled her finger at misogyny in general, and at Bernie Sanders in particular, and laid the blame at their feet. I mean, really, come on...is it any wonder why this woman lost?

Lets start with the Russians eavesdropping in on DNC emails. Yeah, security is important. That's why the U.S. Air Force still uses 5 inch floppy discs for boot sequences when initiating launch of land based ICBMs. Understanding the grave threat posed by malicious hackers, there has never been a direct electronic link allowed into this system, thank God. But the truth is, whether you are willing to admit it or not, the Russians provided the American people with an invaluable service, and ultimately the truth of what Donald Trump was claiming all along...that the very process of winning the Democratic nomination was pure theater. It demonstrated that there did, in fact, exist a state of collusion to deny every registered Democrat a vote, equal in weight, regardless of economic or political primacy, and that it emanated from the very top of the machine: Congresswoman Debbie Wasserman Schultz.

Now, don't get me wrong. I didn't buy the song and dance Bernie Sanders was putting on in 2016, and for the very same reasons I didn't buy then Senator Barak Obama's mantra on "change" back in 2008 (See my entry dated September 16, 2011, titled: Thoughts on an article by James Carville). It appeared to me at the time that Bernie was just making a gratuitous play upon the sensibilities of those discontented masses that comprised the Occupy Wall Street crowd...which I counted myself as one. As things turned out my suspicions of Barak Obama's lack of political prowess proved to be all to well founded, and I wasn't having it again. Be this as it may, the fiasco that was the Democratic National Convention in 2016 did not have any affect upon me personally. I withdrew my name from their rolls long ago. But it did show, in full view of an already beaten down America, the naked truth about how their government really functions: privileged puppeteers and those who they animate with strings of gold that were spun upon the looms of corruption.

So, anyway...thanks Ivan, and fuck you too. Lets see you do the same with Putin. God knows that fucking prick has been murdering everyone who dares attempt to bring Russia back into the light of peace and freedom. I just knew Perestroika and Glasnost were a flash in the pan...

As for Hillary Clinton's assertion that misogyny played a part in her defeat...well, duh! But here's the thing, Hillary...can I call you Hillary (in case you ever happen to read this post)? The thing is, and there really isn't any getting around this...nobody likes you and, judging from the results of the 2016 election, nobody trusts you.

Throughout the entire election cycle you made no attempt to distance yourself from the image of a bought and paid for political lackey, but that's cool...it's who you are. But don't ever assume to accuse Americans of making the wrong or uninformed choice. It is you, and others like you, whose arrogant behavior constituted an affront upon the dignity of those who ultimately sealed your fate and sent you and yours packing. The writing is on the wall, and that goes for the Republicans as well.

And another thing. Before you go fishing for some left wing sympathy by calling out us "basket of deplorables" as the bane of your presidential campaign and its, shall we say lethargic pace of gathering momentum, you might first consider that even among many women who would love nothing more than to see a female executive in the White House, you're not exactly what they had in mind anyway. Never mind the polls on this, I'll never forget the observation of one woman who stated in public, out loud so everyone could hear, that given the choice between you as the first female President and a yeast infection...she would've gone with a protracted regimen of anti fungal treatments. Now, not being a woman, I don't exactly know what that entails but I'm guessing it isn't all that pleasant...

If anyone wants a really well thought out laundry list of reasons why the Democrats were able to snatch defeat from the jaws of victory last November, then I encourage you to watch on YouTube Chris Matthews' observations on election night when it became obvious that Trump was about to eat Hillary's lunch. It's short, simple and straight to the point. No bullshit.

Donald Trump maybe a liar and a Snake Oil Salesman, but in his own simple minded way he recognized what most Americans were crying out for...and he closed! That's what a salesman does...he is always closing. What was the takeaway from the film: Glengarry Glen Ross? Always be closing!

America says, "Capital is shipping our jobs overseas to pad their margins, and those few of us who are still left with jobs are not benefiting from any trickle-down!" and the Donald says, "Fuck NAFTA! I'll bring those jobs back. Vote for me!"

America says, "I cannot afford Health Care. The copays, coinsurances and deductibles will absolutely bankrupt me!" The Hump says. "That's what Americans get for voting Obama into office. I'll repeal and replace Obamacare. Vote for me!"

America says, "The economy is picking up, productivity is increasing, I'm working longer hours and/or multiple jobs, and yet every payday I'm forced with the choice: Do I pay the Rent, or feed my family?" The Donald says, "It's those foreigners working off the books and not paying their share. I'll deport them the hell out of here. Vote for me!"

Americans are not blind and stupid, though they pretend to be sometimes so they do not have to admit to themselves that the Great American Experience is showing signs of fissure. Just as clearly, their confidence has been shaken; they're not sure enough about themselves and the character of their government officials to see this Caterpillar of a country blossom into the Butterfly that is the enduring promise of the American spirit. But when there exists a clear lack in leadership, a refusal of our "elected" officials to even admit the true nature of the problems facing most everyday Americans, then they will always turn to the least objectionable choice who is asshole enough to tell them what they want to hear in the hope that, somehow, he/she may actually get lucky and follow through.

Well, if it wasn't clear before it most certainly is now. The Democrats and the Republicans have exhausted whatever go juice they may have enjoyed in the past with their respective bases. The Democratic votership did not hand the Republicans a victory; they handed their own leadership a defeat. They were done being taken advantage of and they've made that clear in no uncertain terms. Outraged by the treatment of Bernie Sanders and his supporters, they dug their heels in and refused to fall in and close ranks behind Crooked Hillary. 

Likewise, the Republican votership did not hand their leadership a victory; they handed them Donald Trump who ran on the premise that the Republican leadership had abandoned them which, of course, they had. The rift that has been growing between the haves and have-nots had reached the point where the party's exploitation of social prejudices, among other things, could no longer overcome the reality of their rank and file's daily lives. The party's embracing of corporate entities that saw illegal immigrants as a source of cheap labor to be exploited did not hold well with them and, at the very least, they appreciated Trump's candid, in your face, tell it like it is manner. Say what you will, the man came out swinging and never stopped until all who stood in his way were consumed. If there was ever a clear demonstration of confidence projecting strength, this was it.

Some of you out there reading this maybe wondering where I land on all of this. If you've read the previous entries of this blog then you must be aware that I have been, for some time, registering my disgust with the state of politics within the United States by taking back the power of my vote with write-ins for "None Of The Above" (see my entry dated June 2, 2012, title: A Vote For None Of The Above!). However, in the last election held in 2016, I did cast a vote for someone. Though I still voted NOTA on all other races, I made an exception solely for Office of the President of the United States. I voted for...Jill Stein.

It's not that I found Dr. Stein a perfect candidate; I don't believe that any exist. In fact I almost did not cast a vote in her favor because I found her running mate to be a radical. But she is an articulate, educated woman whose platform resonated in sympathy with my values. Her persona stood in direct contrast to the opportunistic, and megalomaniacal vibes put out by Hillary Clinton and Donald Trump. From Health Care, Military Spending and Corporate/Bank reformation to Education and Student Loan Debt, she broached with me a threshold that had not been reached in quite some time. And, yeah, I knew full well that there wasn't a snowballs chance in hell of her winning, but that wasn't important. What mattered most was that there existed on the ballot someone I could vote for and not feel the need to shower afterword. I voted and was still able to look myself in the mirror the next day. For me, personally, it was a win nonetheless.

So now almost a year has gone by and what has happened? Well, lets see. The Democrats have gone nuclear attempting to spin their humiliating defeat. True to form, its been more of the same with them. After using the tired old excuse of compensating well connected members by commissioning a study of just what went wrong, as if they didn't already know, the conclusions drawn apparently obviated the need to change course in any real and meaningful way. I'm not going to get into the details...I'll just piss myself off. 

Hillary Clinton is attempting to regain some composure, testing the waters I suspect for another try and, if not for her, then possibly her Daughter...? I mean, you've got to be kidding me with this fucking dynastic bullshit.

The news media has been wetting themselves for months attempting to demonize every goddamn thing President Donald Trump says, does, doesn't say, doesn't do. And lets be honest about this...he's making it way too easy for them. But, hey, if it takes the heat off the Democrats and focuses it squarely upon Trump...mission accomplished.

As for the Republicans...well, well, well. What a tangled web we weave. Coming as no surprise to anyone fit to feed themselves and visit the toilet unassisted, it turns out that after eight wasted years of out and out obstructionism, the Grand Old Party is truly bereft of any forethought and talent in identifying and implementing a viable alternative to the euphemistically titled: Affordable Health Care Act. In fact, they never had anything in the hopper, nor did they ever really give a shit, either. For them it was OK if you could afford Health Care, and if you couldn't...well, that was OK, too. Just as long as they were not called upon to pay anything.

Without getting into this too deeply, I'll will say just this: Both sides are equally fucked in the head where this topic is concerned.

The Democrats for trying to cater to the interests of an Insurance Industry that demanded to have their profits subsidized by taxpayers even in markets where there would never be any profits to be had...for whatever reason.

And the Republicans for their indifference to those whose rights were systematically trampled upon, time and again, by a an Insurance industry which saw to it that, by keeping their thumb pressed upon the scales, they could dictate not only the terms of an individuals health care, but the manner in which they may, or may not, meet their contractual obligation(s).

The truth is, Health Care is not an insurable commodity. Sorry. Don't blame me. It never was, and it never will be. Everyone, and I mean everyone, will get sick or injured and, eventually, reach an infirm state of health. It has never been a question of if, but rather when. The mathematics upon which the concept of insurance pivots is that of probability and statistical analysis over some given period of time, and as one ages the costs of justifying an insurance company's bet that the policy holder will not claim benefits beyond the point of premiums paid increases exponentially. Unless there exists a surplus of healthy policy holders who can subsidize those who are not, and still allow the Insurer a reasonable profit, well...you get the idea.

The real problem is that Insurance companies are all about profit. Yeah, they'll sing you a song about how they are an important corner of society serving a real economic need blah, blah, blah. Forget about the fact that they are attempting to gamble with real lives of real people who think and feel. To them, we're all just amalgamations of set-data points. Another truth about the Insurance Industry is that its very existence breeds corruption, and inflates the costs of related goods and services.

So now what? Well, I'll give it to Bernie on this one. At least he's persistent. Nationalize it. How we going to pay for it? Simple. Take the money that was earmarked for propping up the militaries of unworthy "allies" like Israel for example. If they wish to conduct open warfare upon civilian populations instead of negotiating peace in good faith and on fair and equitable terms then fuck them! I don't care anymore. Seriously, with friends like them who needs any enemies?

And lets not kid ourselves here about the debt limit. Since when has that stopped the United States Government from spending money that they never had in the first place and effectively pulling it out of thin air at taxpayer expense? You never hear anything about it from Republicans as long as it's going to Boeing, Lockheed, Northrop-Grumman, Newport News, Ingalls Ship Building and General Dynamics. Or to provide subsidies to Oil and Natural Gas companies for whatever reason I can't even begin to imagine. Yeah, ExxonMobile! I'm talking to you Fuck-Nuts! So don't even try and test my patience.

Whoa! I need to chill a second. OK, now where was I...? Oh, yeah. Red herrings. So over this past year the liberal media (for such it is with the soul exception of Fox News) has effectively tried to bob and weave, duck and cover, drop and roll, point and deflect...whatever it took to re-engineer the truth in terms amenable to the Democratic Party line, and the sick thing is they may actually be getting away with it because there doesn't seem to be anyone around willing to hold their feet to the fire.

As for those who voted for the Donald, well, all I can say is I hope you enjoy the show. Hey, I understand why you did it, but if at the end of his third year you don't see those "American Jobs" coming back to energize the middle class, and if you do not see yourselves bringing home a wage that leaves you free from living hand to mouth...don't come crying. He never had any intention of serving anyone but himself. In the end he will not accept responsibility. He will, however, blame everyone and everything under the Sun for his failures...just like Hillary Clinton.

Poor babies. Trump will return to his daily life, business as usual, playing golf and with billions of dollars to comfort him. Hillary will have the resources of the Clinton Foundation to keep her warm and fuzzy.  And you? Well, you're four years older; four years closer to finding a way to send your kids to college, or four years closer to a retirement you cannot afford. All because you didn't have the courage and strength to vote for a third party candidate who you just knew couldn't win...and who wants to be a loser like that anyway? Hummm....



Copyright September 17, 2017. All rights reserved.

Thursday, July 27, 2017

The Propagation of Aerodynamic Falsehoods Within The Flight Training Industry...

By John Patrick Conway, Jr.

Acknowledgement! Its been sometime since I posted to this blog, but I haven't forgotten a promise I made around the time of my last submission to dedicate my next post to a friend and coworker who actually followed this site with a modicum of interest. At that time we were working the same truly shitty job at an equally shitty company. So to Anna "from Humana" Rosario, this one is for you. Sorry it took so long.

This paper is an attempt to arrest misleading and false interpretations of aerodynamic theory on two fronts. First is the definition of angle of attack where the deflection of flaps is concerned; the second has to do with understanding how the addition of leading edge camber influences the aerodynamic character of an airfoil. The fact that the flight training industry has been allowed to propagate inaccurate myths of technical issue in case of the former, and that have been allowed to go unchecked for so long by the aviation community, is really inexcusable. Whether this has to do with a fear of standing up and exposing oneself to ridicule, or everyone just relying upon time to work things out by themselves, is another matter entirely. But I will say that, given the degree to which these circumstances have been allowed to exist, I'm of the opinion that some serious soul searching among aviation's professional caste is in order here. That having been said...

Back in the late 1980's, while still an undergraduate at Embry-Riddle Aeronautical University, I noticed that the flight training manual put out by Jeppesen included an expanded definition of angle of attack (AOA). The graphic within this text showed a revised interpretation where the chord line used to define AOA continued from leading to trailing edge even as the trailing edge flap was deflected. This, I remember thinking at that time, was an embarrassing error for an otherwise respected source of basic aeronautical knowledge, and one which would surely be corrected once someone within the aviation community (i.e., NASA-Langley, The FAA, Aeronautical Engineers, etc.) made them aware of their mistake. Then, not long ago, I was surfing Youtube and came across some educational videos on this very subject. To say that I was surprised to see this myth has propagated to such an extent would be an understatement. I also noticed that some pilots who had uploaded videos would incorrectly attribute the deflection of ailerons as instruments by which they alter the wings AOA, as opposed to its camber. I searched the Internet for a PDF download of a relatively late publication of Jeppesen's manual and, lo and behold, the error remained! Worst of all, in having done an Internet search regarding this issue, I was horrified to find an "Ask A CFI" message board where CFI's responding to the inquiries of confused students on this very subject were reciting answers that appeared to come directly from Jeppesen's manual, stating that flap deflection increases both camber and angle of attack. This is unacceptable, especially coming from those who are suppose to know better, but obviously don't.

The glaring issue at hand is the definition of angle of attack with flaps deployed. The graphic employed by Jeppesen, and others, shows the chord line running from leading to trailing edge as the flap is being deflected, but this is incorrect. The definition of angle of attack is that angle between the airfoil's chord IN ITS CLEAN CONFIGURATION and that of its relative wind. Flap deflection has no influence upon altering AOA as suggested by the above referenced video - only the aerodynamic character of the wing itself. All NACA airfoil profiles (plots of lift coefficient vs. angle of attack) are based upon this understanding. You may ask how I know this for sure...fair enough: while studying as an undergraduate, my Basic Aerodynamics class did the low pressure wind tunnel studies where we confirmed, among other things, airfoil forces and pressure distributions in both basic and flapped configurations vs. angle of attack.

Below you will find those elements of my article contradicting said theory as laid down by current flight training orthodoxy. What follows is an edited post I made within the comments section of that aforementioned video on Youtube and, because of the article's length, it went deleted as spam. I also sent a copy to Jeppesen via the contact link of their website. That was a few weeks ago and I still have not yet received a reply. But before I go any further, a little historical background may be a good idea here.

Back in 1915, the government of the United States established what was then known as the National Advisory Committee for Aeronautics (NACA); a federal agency charged to "undertake, promote, and institutionalize aeronautical research."[1] It was the forerunner to what is now the National Aeronautics and Space Administration (NASA). Anyway, with this mandate in hand, one of the research efforts NACA endeavored upon was to fingerprint the sectional profiles of airfoils in terms of lift coefficient vs. angle of attack. However, when it came time to plot the influence of camber altering devices (i.e., flaps and ailerons) it was decided to do so in a manner where the effects of camber alone could be studied independently of AOA. Another reason for this went to the heart of the definition of AOA as that angle between an airfoil's chord and its relative wind, and the choice of flap-type used within these studies. As was explained to me as an undergraduate, the split flap was used because its physical properties were identical to all profiles then under study and, that by effecting an increase in lower wing camber alone, the combined influence of Reynolds Number and gradient of the upper surface pressure distribution critical to airflow separation went relatively undisturbed. This served the purpose of evaluating cambered airfoil performance with the least amount of contravening elements by which to distort analysis. Additionally, and not the least of which, the deflection of a split flap would technically yield two trailing edges, thus giving rise to an ambiguity as to which trailing edge constituted the reference point for defining chord and its corresponding AOA.

This previous point also begs the question as to how it is anyone could've confused Jeppesen's definition of AOA with the reality of the situation when almost all airplanes utilize semi-span flaps. Using their, Jeppesen's, definition of a reference chord by which to establish AOA just streams the obvious contradiction that now there exists two angles of attack for the same aircraft under such circumstances...one for the flapped sections, and one for the unflapped sections...?!?!

In all fairness, though, Jeppesen is not the only resource that has bought into this unfortunate mischaracterization; I've seen others. But Jeppesen was the first that I can recall off hand and, given the fact that for a vast majority of civilian trained aviators whose first exposure to aerodynamic theory was their manuals, I hold them responsible for rushing into print unsubstantiated theory.*

Clearly, the NACA engineers chose wisely by fixing the referenced chord for AOA to that of an airfoil in its clean (basic) configuration, thus eliminating superfluous elements that, when combined, would complicate analysis of an airfoil's performance with overlapping duplications of effort to describe the same thing. Hence, the influence of camber and camber distribution alone could be studied independently, and exclusive of all other factors.

If you should doubt this, then I encourage you to examine the two dimensional NACA section profile of, say, a symmetrical airfoil like that of the NACA 0009 with and without trailing edge flaps (an excellent reference here would be NACA Technical Report No. 824 and is downloadable for free on the internet). You'll notice that the zero lift coefficient occurs at zero degrees AOA in its basic configuration (as do all symmetrical profiles). However, notice the AOA that produces a zero lift coefficient with trailing edge, split-type flaps of 20% chord (as per NACA convention) deployed 60 degrees. Depending on airfoil thickness, this will usually land somewhere between negative 5 and negative 15 degrees AOA, inconclusive. However, in the case of the NACA 0009, this would be found at negative 12 degrees using a Reynolds Number of six million.[2] Now picture trying to reconcile this with an airfoil using the Jeppesen definition of AOA with flaps deployed. To begin with, the 60 degree deflection of a 20% chord flap would, by Jeppesen's reasoning, automatically yield an 11 degree AOA should the airfoil's inclination not be changed in any way. So what NACA plotted as a negative 12 degree AOA is now actually a negative 23 degrees! Doesn't seem too likely...does it? Clearly under those circumstances this would result in a negative lift coefficient. The negative 12 degree value obtained by NACA referenced an AOA defined by the chord line of its airfoil's basic section.

Still not sold? Lets look at it from a zero degree AOA perspective. Using the same NACA plot for the 0009 section, a 60 degree deflection of a 20% chord split flap will raise the section lift coefficient from zero to about 1.35 (Reynold's Number is still six-million). Makes sense in what was once a symetrical profile is now a cambered one. Using the Jeppesen definition, though, by holding a zero degree AOA would still produce a 1.35 lift coefficient, but in actuality what is happening is the airfoil is at a negative 11 degrees AOA and a miniscule 0.1 lift coefficient.

Still not convinced? Lets look at the condition of maximum lift coefficient. Using NACA's reasoning, the 0009 section with 60 degrees deflection of a 20% chord split type flap will produce a maximum lift coefficient of 2.1 at just over eight degrees AOA. Using Jeppesen's reasoning, eight degrees AOA would still hold the profile at a negative three degrees. Now, anyone who flies knows that's just not so...unless, of course, your aircraft is rigged with a negative angle of incidence and I can't think of one at the moment that ever has.

The other issue at hand, though not as immediately pressing as that of the aforementioned, is an almost total lack of understanding where the influence of leading edge camber is concerned. It's a subject that only seems to get any attention in aerodynamics courses focused directly for engineering students...and even then the subject is only briefly glossed over. Whether this is by luck or design I am unsure. The extent of leading edge high lift device theory, where the training of aviators is concerned, appears limited to fixed and aerodynamic slots and slats, the latter of which tends to be aerodynamically neutral in its application of effecting leading edge camber, anyway. So all that needs to be said about its influence upon airfoil performance is that it simply extends the reach of that curve defining the relationship between lift coefficient vs. AOA without altering its slope (same as the trailing edge flap in that manner) to some higher value for both. This may be all well and good, but it completely misses out on an opportunity to show how the application of fixed leading (and trailing) edge camber can be employed to alter the span-wise distribution of pressure upon a wing. The problem here, I suspect, has to do with the fact that the application of fixed leading edge camber is not as straight forward as that of its trailing edge counterpart. Its application does influence the slope of that relationship, and that slope is rarely consistent throughout the airfoils usable range with leading edge flaps deployed (see NACA Technical Note 1277). That having been said, I will try to, in as much as possible, attempt to offer a somewhat simplified explanation of how varying degrees of fixed leading edge camber can alter the aerodynamic character of a two-dimensional airfoil section, and perhaps offer a useful example of its application within the realm of three dimensional flight.

One last thought before you continue. This exercise is in no way a means by which to place myself above others as a sage of aeronautical liturgy...if you will. My motivations are simple and forthright: to pass along to others what my understanding of the truth is. Alas, if I am to share the same sky with others, then I'll feel a lot better if we're all reading from the same script. Perhaps, too, I'm splitting hairs; maybe no one else really gives a flying-fuck as to all this technical mumbo-jumbo, but I really don't believe that. I believe most aviators share not only a love of flight, but a thirst for knowledge of what got us where we are today...and what keeps us here, safely.

I have to admit that "high-circulatory" flight (aka: high-lift flight) was a favorite subject of mine, personally. It fascinated me, and lent proof to the assertion that all the energy theory presented within those Physics courses I endured actually had applicability to real world situations; an appreciation that, for the most part, went realized after the fact but endures to this day, growing stronger with time. It would explain why I've chosen to elaborate, at length, the importance of this subject to those who fly.

So, to that end, lets examine what camber is more closely and how it functions. All pilots are familiar with its definition, but why is it so important?

Well, look, most conventional airfoils at moderate to high angles of attack will show peak suction to exist at around 5 to 0 percent leading edge chord, forcing the airflow over a commanding portion of the wing to do so in the face of an adverse pressure gradient. The immediate ramifications of this truth will be a loss of kinetic energy within the "Boundary Layer." If this thin layer of air immediately adjacent to the wing is allowed to stagnate, higher pressure air from behind the wing can wedge its way back under the retreating stream, into the partial vacuum responsible for sustaining lift, and precipitating airflow separation beginning at the trailing edge and working its way progressively forward as AOA is increased; an aerodynamic condition known as stall.

The addition of positive camber is to soften this pressure gradient by drawing peak suction further aft along the wings' upper surface, effecting an increase in the Reynolds Number above the airfoil as a whole. This allows the airflow traversing the upper surface to do so under the influence of a favorable pressure gradient for a greater percentage of the chord than otherwise possible, energizing the boundary layer, and distributing pressure (and velocity) in a more efficient manner. Both leading and trailing edge flaps do this but with a critical difference. So to study their influence independently upon an airfoils' performance we need to be explicitly clear as to what that datum of reference we measure against will be, which is to say: angle of attack.

Out of an abundance of caution, lets first define lift coefficient. Simply put, it is a dimensionless ratio between a wing's ability to circulate airflow in such a way that it will precipitate a difference in pressure about its surface area relative to its free-stream dynamic pressure (kinetic energy per unit volume of a working fluid - q). In other words, it is a measure of a wing's ability to extract the kinetic energy of its airstream, per unit volume, and convert it into doing the useful work of supporting an aircraft in flight, and it does this in two ways: changing its angle of attack, or by altering the character of its aerodynamic profile.

All fluid-dynamic forces, and their moments, are distilled to some difference in static pressure applied about a surface area:

F = (delta-p) S

But how does one account for the individual influence of changing angle of attack and wing/airfoil configuration? The answer is to multiply this expression by a ratio of unity using dynamic pressure (q) and grouping the terms in a coherent manner amenable to a ratio form of the equation:

(q/q) F = (q/q) (delta-p)  S

Now you have: F = [(delta-p)/q] q S = CF q S

Solving for the force coefficient: CF = (F/S)/q

Since the forces of lift and drag are Pythagorean components of aerodynamic force, we can express them in like manner. But what is of immense importance here is that these subcomponents of lift and drag are first defined by the relationship of the wing relative to its direction of motion...its angle of attack, and this is why we should be perfectly clear as to its definition.

That having been said, lets get back to the topic: How does altering the sectional profile of an airfoil alter the relationship between lift coefficient (CL) and AOA.

By adding camber aft of peak suction, you augment circulation in a way that increases section lift coefficient per unit angle of attack, raising the curve that plots CL against AOA as a whole and shifting it to the left, thus lowering its critical AOA (critical alpha) in the process. The reasons why this is has to do with the very nature of airflow itself. You see, below two hundred knots, and/or 20,000 feet, the airstream does not carry sufficient energy to create sensible discontinuities in flow-density about an aerodynamic structure; airflow is assumed to be relatively incompressible within these limits. So the extension of trailing edge flaps, while holding AOA constant, serves to displace a greater volume of air per unit time and, since nature abhors a vacuum, the surrounding atmosphere rushes in to fill the void.** So by distributing pressure (and, hence, local velocity) in a more efficient manner, the airfoil can draw from within its airstream a greater delta-p per unit q. The loss in critical AOA, however, is a consequence of forcing the airflow through a greater curvature in the presence of some adverse pressure gradient, thereby achieving that critical gradient responsible for precipitating stall sooner rather than later.

The addition of camber forward of peak suction generally has the opposite effect assuming the angle of leading edge deflection is greater than the airfoil's AOA: it lowers section lift coefficient per unit angle of attack, dropping that same curve defining CL and AOA down, but it also tends to increase the slope of said curve. This point is key and deserves some elaboration, so in order to provide a quick visualization of things we should first revisit some basic aerodynamic theory.

In his excellent text on applied aerodynamics, Aerodynamics For Naval Aviators, Hugh Harrison Hurt, Jr. outlines a pivotal truth common to all airfoils of identical cross section, and I'm paraphrasing here: that for any given angle of attack, relative pressure distribution, within compressibility limits, is a constant. Meaning that points of stagnation, peak suction, or points representative of free-air static pressure remain fixed and unchanging upon that surface. Therefore, each possesses the same coefficients of lift and drag regardless of their relative size, or the magnitude  of "q" contained within the airstream.[3] Why this is of any concern is central to my explanation of how leading edge flaps influence the aerodynamic character of an airfoil.

Imagine two flat plates within the same airstream, and at equivalent angles of attack. One has a chord line 90 percent of the other. Since they share identical cross sections, their pressure and velocity distributions are also identical, as are their respective force coefficients. But because one is 10 percent larger, it will carry 10 percent greater aerodynamic load. Now assume the larger of these two flat plates possess a hinged leading edge flap of 10 percent chord, and the flap is deflected by an amount equivalent to the airfoil's angle of attack. The leading edge flap is aerodynamically null and now produces exactly (or near so) not only the same force coefficients, but the same aerodynamic load as the smaller of the two. Here is where the leading edge flap differs markedly from its trailing edge equivalent.

With the deflection of trailing edge flaps, there is always in increase in section lift coefficient per unit AOA, and the curves that define CL vs. AOA never cross; their slopes generally remaining parallel to one another. Not so for leading edge flaps. While holding AOA constant, leading edge flap deflection angles between zero degrees and that of the airfoil's AOA will actually show a small increase in lift coefficient per unit AOA. However, as the deflection angle approaches the airfoil's AOA, streamlining the leading edge flap with the relative wind, the CL starts to drop and approaches its initial value. Here the two curves cross (see NACA Technical Note No. 1277). As deflection angle continues to increase beyond the airfoil's current AOA, the lift coefficient drops off. At some value the crossing point of the two curves extends beyond the clean airfoil's critical angle, and now the flapped section always holds a lower section lift coefficient for all angles of attack attainable by its basic section. But because leading edge flap extension beyond current AOA repositions peak suction aft along the airfoil's chord, this contouring effect allows the airfoil to reach angles of attack and lift coefficients otherwise unattainable.

The deflection of leading edge flaps beyond its null angle unloads the wing in its immediate vicinity, but because airflow is forced thru a greater curvature in the presence of a favorable pressure gradient, circulation increases in like manner, and kinetic energy within the boundary layer is augmented to the degree of staving off airflow separation to some higher critical (stalling) angle of attack, along with a commensurate increase in maximum lift coefficient. So, although the curve that defines the relationship between CL and AOA does drop, and slope increases, it also extends its reach beyond that which can be achieved by the airfoil in its clean configuration.

Now, this loss of lift per unit AOA is not necessarily the bad thing some may first presume when you consider the fact that, by manipulating the slope of a wing's leading edge, outboard along its semi-span, you can balance out what would otherwise be a natural asymmetry in the span-wise distribution of pressure characteristic of wing planforms of high taper and/or sweepback...especially with sweepback.***

It may interest you to know that in the case of the latter, a swept wing of increasingly greater sweep angles, with a taper ratio of unity, not only physically places the tip vortex further away from a greater percentage of the wing's area, the airflow trailing from the inboard sections of the wing will tend to wash up and around the outer sections so as to fill the void in trail created by the outer span as AOA is increased. This induces a counter-rotating vortex that not only endeavors to weaken the tip vortices, but serves to align the airflow in the immediate vicinity of the tip, reducing the downwash within its domain to a greater extent than with respect to the wing as a whole, thus giving rise to the aforementioned discontinuity which ultimately rears its ugly head in the form of induced drag, to say nothing of the loss in controllability as span-wise flow increasingly erodes away at aileron control and the wing's effective lifting surface area.[4]

And since I'm on the subject, here's another cool application that lends to their utility as camber altering devices: on some modern high performance aircraft, differential deflection of leading edge flaps can be scheduled (via air data computer) to counter the torsional deflections imposed upon outer-span wing panels by ailerons at high-q if the wing's airfoil is characteristic of high fineness ratios (i.e., low thickness to chord ratios) which may otherwise result in reduced roll rates and, at the extreme end of the performance envelope, aileron reversal.
  
A little FYI, but I diverge.

P.S.

I will be uploading some charts at a later time to aide in visualizing the finer points of my thesis above. I'm having a time of it trying to locate professionally drafted ones that are in the public domain. If I cannot, then I'll construct them myself and upload them ASAP. 




1. Wikipedia entry: The National Advisory Committee for Aeronautics (NACA)

2. NACA Report No. 824, page 132.

3. Aerodynamics For Naval Aviators, page 20. Hugh Harrison Hurt, Jr.

4. Phantom Over Vietnam, page 224. John Trotti - Paraphrase from Glossary entry: AOA

*  Sanderson's flight training manuals, and those published under the auspices of Jeppesen, are in my opinion among the very best resources of condensed subject matter on the topic. This is just one of those issues that I feel should've seen better editorial vetting on a technical level.

** Incidentally, you may recognize this as the basic manner in which the concept of lift is initially presented to flight students. A symmetrical airfoil will only produce a net lifting force when given some AOA to induce a "net circulation." Having done so, a displacement within the fluid occurs that can not be tolerated by nature which commands, in and of itself, a continuity of flow that is manifest in the accelerating nature of the enveloping fluid upon the airfoils' leeward surface. A cambered profile takes advantage of this truth by forcing an asymmetry in displacement but with a lower broaching angle, allowing for the same amount of lift but at a lower AOA. In this instance the displacement occurs, in whole or part, by virtue of the airfoil's cross sectional shape (camber) as opposed to being entirely attributed to AOA. All other factors being equal, this translates into less drag for any given amount of lift and serves to reflect camber as an application of applied fluid-dynamic efficiency.

*** Trailing edge camber can also serve as a means to the same end in controlling the span-wise distribution of pressure on about a wing. In fact, within the realm of fixed geometry, what is being described here is the aerodynamic principle of span-wise airfoil variation. However, I'm limiting the scope of span-wise camber distribution to that of its leading edge within the body of this article so as to isolate its individual contribution(s).

Copyright April 22, 2017. All rights reserved.