Discuss.

[SgtPappy]

Just like Karnak said ... there was nothing very special about the elliptical wing. It was good because it had a good amount of wing area for the size of the tiny Spitfire, which gave it its turning. It was also very thin which was essentially more aerodynamic than a thicker, non-laminar flow wing.

It's just shaped like that for the sake of stuffing everything in, not because they thought it was magical.

The Tempest was fitted with a similar wing for the same reason. Those 20 mm cannon had to go somewhere and since they wanted it recessed in a thin wing, they got the same shape; albeit the wing was much larger so the cannon didn't jut out as much as on the Spit. They joked around saying that the only reason the wing was chosen was because everyone else was obsessed with the Spit's wing.

[Stoney74]

Originally posted by Motherland
notice that the 109 was never mentioned in the excerpt- and he was just trying to debunk the 'uber elliptical wing' myth.

Uh, end of the first paragraph you posted, the author began comparing the Spitfire wing with the 109.  Planform, thicknesses, aspect ratio...all were compared between the 109 and Spit.

[Motherland]

Originally posted by Stoney74
Uh, end of the first paragraph you posted, the author began comparing the Spitfire wing with the 109.  Planform, thicknesses, aspect ratio...all were compared between the 109 and Spit.

Woops. Missed that part when I was skimming back over it to check myself.

[Stoney74]

Originally posted by SgtPappy
...there was nothing very special about the elliptical wing. It was good because it had a good amount of wing area for the size of the tiny Spitfire, which gave it its turning. It was also very thin which was essentially more aerodynamic than a thicker, non-laminar flow wing.

It's just shaped like that for the sake of stuffing everything in, not because they thought it was magical.

Wrong.  After NACA's research was published, major aircraft manufacturers around the world began using it.  NACA stated that an elliptical wing would realize almost ideal spanwise lift distribution and reduce induced drag, with respect to the planform, to a minimum.  As a document, the research was the first published of its kind.  It was considered a breakthrough from a technology standpoint, as it was the first publication of such a monumental amount of research.  It was widely embraced as truth for a number of years--some still continue to repeat it almost verbatim.  That some of it was flawed was only considered after the War, and the debate over its legitimacy continues today.  The amount of specialized manufacturing was the main reason most manufacturers did not pursue elliptical wings, not because they didn't think the theory worked.  Even today, with the use of double tapered wings on the Lancair and Columbia production planes, designers are still chasing the theory of elliptical wings and ideal spanwise lift distribution.  There are differing opinions on its worth.

Further, wing thickness has nothing to do with respect to it being considered "laminar" or "non-laminar" (or properly termed, "turbulent").  You can have an aircraft with a wing that's 20% thick with respect to chord that uses a "laminar" airfoil.  The 2200 series airfoil used by the Spitfire is actually considered a "turbulent" airfoil.  The difference in the classification is a matter of how much laminar flow is achieved over the wing.  All airfoils create areas of both turbulent and laminar flow.  The turbulent airfoils only create laminar flow over a small percentage of the chord.  The laminar flow airfoils create much larger lengths of turbulent flow, and delay its formation to a point further back on the chord.  After a certain point, due to the geometry of the wing, the air becomes turbulent on either airfoil type.  The amount of laminar flow that is achieved is the basis for determining wheter a certain airfoil is "turbulent" or "laminar".  Perhaps a better description for them would be "high drag" and "low drag" airfoils, even though this could be confusing in certain circumstances.  The P-51 was the first WWII aircraft that I can find that took advantage of a "laminar" airfoil.  All of the rest, including the Typhoon/Tempest, 190, Spit, 109, etc., etc. used "turbulent" airfoils.

[Motherland]

Let me see if I've got this straight...
In a normal airfoil turbulence (turbulence is basically disturbed air, right?) is generated behind the wing. In a laminar flow wing, the turbulence is minimized (or is it completely eliminated?) From what I know about the P-51's performance, laminar flow wings are very low drag, but they do not produce as much lift as a traditional airfoil at low speeds, but seem to at higher speeds? Or is the Pony's highspeed maneuverability due solely to it's highspeed flaps and control surfaces?

If I got this horribly wrong, please forgive me. I find aerodynamics very intriguing, though I know little about it.

[Karnak]

Though later than the P-51, I seem to recall reading that the Ki-84 also had a "laminar" airfoil.

[Stoney74]

Originally posted by Motherland
Let me see if I've got this straight...

Let's start with a simple airfoil shape, one that's flat on the bottom and has a basic teardrop shape on top.  I wish I had a picture handy to illustrate, but alas...I went ahead and made this half way through the post...



Forgive the crude drawing.  

As the air hits the leading edge of the wing, it momentarily "stops" and then splits, with some air going under the wing, and other air going over the wing.  The air going over the wing accelerates as it travels up and over.  Ideally, we want the air to pass over the top of the wing in a smooth, "laminar" fashion.  The air closely follows the profile of the top wing surface.  But, since air has mass, and doesn't want to be disturbed...if the transition vertically is severe enough, the air can "trip" or "stumble" and become turbulent.  It is still attached to the wing--but swirling from being disturbed too much by the profile of the wing.  This happens on ALL wings--the difference is how far back along the top of the airfoil length (aka the "chord") the turbulence begins.  The turbulence can either be created by the front part of the chord, where it forces the air up, or be created by the middle of the chord, where it transitions from an upward motion to a downward motion, or can be created as the airfoil tapers down to the trailing edge.  All these different direction changes can cause turbulent flow, depending on the geometry of the wing.

What NACA tried to do was test whether or not they could force the air to remain laminar as far back along the chord as possible by changing the geometry of the airfoil.  The longer they could delay the air becoming turbulent, the less drag the airfoil shape would create, therefore reducing the overall drag of the wing caused by the airfoil geometry.  What they discovered was that there was a limit to how far back they could push the turbulent flow.  About 55% along the top of the airfoil was as far as they could force the turbulent flow and still have an airfoil that was useful for aircraft.  There are other shapes that can maintain laminar flow for their entirety, but they don't create enough lift to be considered for aircraft.  They usually possess some other nasty qualities as well that are beyond the scope of this discussion.

Anyway, when discussing the P-51's "low drag" wing, it basically was the first WWII fighter to use some of the airfoil shapes that pushed the turbulent flow further back along the top of the airfoil.  The result was a wing that caused much less drag than other wings designed before it.  I can't remember the actual percentage, but IIRC (don't have time to look it up), airfoil shapes that only maintain laminar flow for the first 25% or less are considered "turbulent" airfoils.  If the airfoil shape can maintain laminar flow for more than 25%, they are considered "laminar" airfoils.  Some laminar airfoils maintain the flow longer than others, but all are still considered laminar.

Depending on the camber, thickness, and chord length (wing width), a laminar flow airfoil can create as much or more lift than a turbulent section.  It depends on the geometry of the airfoil, wing, Reynolds number--a host of other considerations.  

Its late here, and perhaps another can chime in tomorrow while I'm at work.  I'll check back tomorrow and try to follow up with this post.

Do a Google Search on airfoils, airfoil design, airfoil selection, etc.  There are a bunch of good websites out there that explain this much better than my gross generalization above.

[dtango]

Stoney, pretty good descriptions above my friend .  I'm guessing you were looking for a diagram similar to the following:




As Stoney mentioned all wings have laminar and turbulent flows as depicted above.  When an object passes through a fluid (e.g. wing through the air) a boundary layer of flow forms along the surface.  This boundary layer has two characteristics: laminar flow (flow steady & layered) and turbulent (flow layers unsteady & mixed).  On a wing the boundary layer starts out laminar and then becomes turbulent at some point.  Viscous and pressure forces acting on the boundary layer directly impact where it is laminar or turbulent.  

Laminar flow airfoils attempt to increase the length of the laminar flow along the chord of the wing.  The shape of the laminar wing controls the pressure distribution across it to achieve more laminar flow.  Of course another factor that affects laminar flow is surface roughness which has nothing to do with shape.  The smoother the surface, the more likely you'll be able to lengthen the laminar flow.

==================
It's an over-generalization to say that laminar wings cannot produce as much lift as traditional airfoils.

One of the benefits of laminar airfoils are that they produce high Clmax for lower drag.  If you skim NACA Report 824 you'll find that NACA 6-series airfoils have max lift coeff. as high or higher than NACA 24- and 44- series airfoils.  Disadvantages of laminar airfoils are poor stall characteristics, suceptibility to surface roughness, higher pitching moments, and being very thin at the trailing edge which makes them more difficult to make.

==================
P-51 High-speed Maneuverability

I think the oft quoted comment about the reason for the P-51's high-speed maneuverability is because of it's combat flaps it can deploy at higher speeds.  To be honest I don't know where the idea that the Mustang had high-speed maneuverability comes from.  That being said, the 2nd not so obvious reason I believe that is totally overlooked comes from…you guessed it…the laminar wing .  

Most people are aware that compressibility effects drastically affects aircraft controls.  What is less obvious is that at high aoa's and moderate airspeeds compressibility effects can arise forming shockwaves on the wing that degrades an airfoil's maximum lift coefficient as well.  Thanks to gripen pointing it out to me years ago, there are some NACA flight tests that compare various USAAF aircraft that demonstrate that the Mustang's Clmax is not as drastically impacted by the degradation in lift due to compressibility.  Avoiding all the nasty physics, I believe basically the pressure distribution of a laminar flow wing allows it to delay the formation of shockwaves due to compressibility.

Tango, XO
412th FS Braunco Mustangs

[CAP1]

Originally posted by Motherland

I have no clue what it means, but it seems to suggest that the 109 should have a good angle of attack due to its wing slats. I honestly cant remember if it does in game (my hands are to ingrained with how far to push it to notice now) but my memory seems to suggest that it does not.

the leading edge flaps on the 109 don't actually create the space as pictured here, if i'm correct......but rather, they extens out and down, as the airflow attempts to seperate from the wing(this causes a negative air pressure on the leading edge). as they do this, they add camber, and a litle bit of area to the wing(almost like a fowler flap, but on the leading ege). by adding this camber, they increase the lift of the wing, and delay the onset of the stall.
 i haven't flown any of the german fighters in here enough to know if it is modeled that way or not in game.

<>

[dtango]

Cap:

I pretty sure that 109 slats are, well slats - meaning there is a gap.  The gap is necessary for vortex formation between the slat airfoil and the main wing airfoil.  Otherwise no downwash is created to reduce the spike in pressure peak toward the wing's leading edge at high aoa's.

Take a look at these pics as well:













Pics from the following sources:

http://109lair.hobbyvista.com/techref/systems/control/slats/slats.htm

http://www.rcgroups.com/forums/showthread.php?t=507614

Tango, XO
412th FS Braunco Mustangs

[Trukk]

I would take anything you read from Pentti Kurkinen, or "Penttiku" as I know him from WWIIOL with a large dose of salt.  I've never seen a guy spend so much time trying to prove an aircraft (ie the Bf-109) is uber compared to its contemporaries.

[Charge]

Thats a cheap shot Trukk but I know you enjoy it.

Penttiku was actually providing merely a counterforce to chronic infestation of "allied fanbois" who liked to elevate their views as a fact without actual knowledge of subject.

Of course he could have made his points more politely but then again the apparent ignorance from HTC finally was just too much. But at least he knew his facts and chose to say nothing if he didn't have enough info on subject -which cannot be said of his counterparts.

This conversation closely relates to "109's third wing" debate that took place in WW2OL forums. The modification to 109's flight model resulted in flight performance where 109 could not exceed 15 degrees AoA in any condition, where as data clearly states otherwise. Only the drag remained leading to naming them as "slatichutes" since they only slowed you down without any benefit to maneuvering.

When facing a Spitfire you had to make a decision whether to stay fast or you needed to go really slow with slats deployed to match Spitfire's turn If you stayed a bit too fast the Spitfire would out turn you quite quickly. After the flight model revisit you were as good as dead if you went slow making the Spit the Überride the fanbois always wanted it to be.

-C+

[Trukk]

It's my perception of the guy, take it for what it's worth.

I flew the 109 in WWIIOL and never had a problem with the slats.  They let you pull more AoA than the Spitfire, but that additional AoA cost you in drag.  So at high AoA with the slats deployed you had to get your shot in quickly because you were burning E fast.  But (like any aircraft) as long as you didn't play the Spitfire's game the 109 was very capable.

In the Tri-09 days, you could be really sloppy (heck you could out turn a H-75) but once they removed that extra wing you had to fly it smart.

Both sides have their fanboys and Penttiku is one of them.

[SgtPappy]

Originally posted by Stoney74
Wrong.  After NACA's research was published, major aircraft manufacturers around the world began using it.  NACA stated that an elliptical wing would realize almost ideal spanwise lift distribution and reduce induced drag, with respect to the planform, to a minimum.  As a document, the research was the first published of its kind.  It was considered a breakthrough from a technology standpoint, as it was the first publication of such a monumental amount of research.  It was widely embraced as truth for a number of years--some still continue to repeat it almost verbatim.  That some of it was flawed was only considered after the War, and the debate over its legitimacy continues today.  The amount of specialized manufacturing was the main reason most manufacturers did not pursue elliptical wings, not because they didn't think the theory worked.  Even today, with the use of double tapered wings on the Lancair and Columbia production planes, designers are still chasing the theory of elliptical wings and ideal spanwise lift distribution.  There are differing opinions on its worth.

Further, wing thickness has nothing to do with respect to it being considered "laminar" or "non-laminar" (or properly termed, "turbulent").  You can have an aircraft with a wing that's 20% thick with respect to chord that uses a "laminar" airfoil.  The 2200 series airfoil used by the Spitfire is actually considered a "turbulent" airfoil.  The difference in the classification is a matter of how much laminar flow is achieved over the wing.  All airfoils create areas of both turbulent and laminar flow.  The turbulent airfoils only create laminar flow over a small percentage of the chord.  The laminar flow airfoils create much larger lengths of turbulent flow, and delay its formation to a point further back on the chord.  After a certain point, due to the geometry of the wing, the air becomes turbulent on either airfoil type.  The amount of laminar flow that is achieved is the basis for determining wheter a certain airfoil is "turbulent" or "laminar".  Perhaps a better description for them would be "high drag" and "low drag" airfoils, even though this could be confusing in certain circumstances.  The P-51 was the first WWII aircraft that I can find that took advantage of a "laminar" airfoil.  All of the rest, including the Typhoon/Tempest, 190, Spit, 109, etc., etc. used "turbulent" airfoils.

I saw a report on a website supporting your statement on the elliptical wing... this is why Republic used it on many of their experimental post-WWI fighters right? For some reason, I've come to believe that the ellipse was all b.s but I guess I'm wrong.

Also, What i meant about the thin wing was that it was aerodynamically 'cleaner' than other wings of same, but thicker cross sections.

[Stoney74]

Originally posted by SgtPappy
I saw a report on a website supporting your statement on the elliptical wing... this is why Republic used it on many of their experimental post-WWI fighters right? For some reason, I've come to believe that the ellipse was all b.s but I guess I'm wrong.

Also, What i meant about the thin wing was that it was aerodynamically 'cleaner' than other wings of same, but thicker cross sections.

Sorry to be so blunt in my last response.  But, your absolutely right, and it wasn't just Republic, but they are a good example.  It's not so much that the elliptical wing theory is B.S. as it is that NACA used some questionable methods to arrive at that conclusion (source Ribblet GA Airfoils).  There are those out there that still believe in the elliptical ideal.  Some think it is more easily achieved with planform taper only, and some have begun to question whether aspect ratio is the larger factor in overall wing drag.  Peter Garison (Author of the Technicalities column in Flying Magazine) wrote an article a couple of months ago discussing whether or not taper even makes an appreciable difference or whether aspect ratio makes the largest impact.  There are as many opinions out there even among aerodynamic folks today.  We all see a lot of selectivity when folks quote aerodynamic evidence to support their claims about certain aircraft.

Thin wings are not necessarily aerodynamically "cleaner" than other wings of the same, but thicker section profiles.  The airfoil itself may have a lower absolute coefficient of drag, but they usually have narrow laminar buckets and a lower range of useful coefficients of lift (and overall lower Cl).  Not to mention that there is a difficult amount of math/wind tunnel use necessary to predict overall wing lift/drag versus the airfoil section lift/drag.  All the lift/drag information for each airfoil published by NACA was for 2 dimensional flow.  Since wings have 3 dimensional forces acting on them, there's much more involved to derive the actual efficiency of a wing.  Perhaps when I get home from work, I'll post some examples illustrating this.