Wing Loadings: The Idiots Guide? (1 Viewer)

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Claidmore, a fixed slot would increase drag (either a device put in front of the wing or a slot cut into the wing), yes, but the automatic stats are operating beyond the wing's normal flight envleope. Without the slats the wing would exceed critical AoA and stall much earlier.

There is a small period in AoA where the slats begin to extend prior to where the wing's normal Clmax, which I would assume would increase drag somewhat compared to an unslatted wing, but this region is relatively small.

If the slats were extended all the time (ie when unnecessary) it would certainly be detrimental, but that's the point of a slat rather than a slot: they are only in use when needed.

And this:
The same article says that leading edge devices increase drag, but the lift/drag ratio is improved.
seems rather odd to me.
To improve the L/D the increase in lift provided by the increased AoA acheivable with the slats would have to be greater than the coresponding increase in drag.
It's also in direct opposition to that chart I listed.
 
Sorry but you're wrong Claidemore,

The leading edge slats allow the aircraft to fly at a high angle of attack (lower speed) by accelerating the air between the slat and the wing (venturi effect).

Also where would the extra wetted area come from exactly ?? The slats don't just magically appear, when the extend they leave behind the space where they once sat remember ;)


Soren, the surfaces of the trailing edge of the slat and LE of the wing are not exposed when the slat is retracted, so there is an increase in the area.
 
Soren, the surfaces of the trailing edge of the slat and LE of the wing are not exposed when the slat is retracted, so there is an increase in the area.

The only increase in area would be from the underside of the slat, cause the circumference of the wing has been reduced bythe slat popping out. So we're talking about a ridiculously small amount of extra area, something which has a microscopic on the drag in turns.
 
When the slat extends, you now have two leading edges, the one on the slat itself, and the one in the hole where the slat was sitting, plus you have the underside of the slat. You now have 3 surfaces where there was only one. On the 109 for example, the slat is 40% of the wings leading edge? That certainly isn't microscopic.

If a fixed slat causes drag, then a retractable slat will cause an identical amount of drag when it is extended into the exact same position as the fixed one. When there is no requirement for maximum speed simple fixed slats are used. It is the need for speed that requires a complicated mechanism for retractable/extendable slats.

From the US Centenial of Flight Commission:
At low angles of attack, the slat is flush against the wing leading edge and reduces drag at high speeds compared with the fixed slot.
and:
There are two types of slots—fixed and automatic. With the fixed slot, the leading-edge slat is mounted a fixed distance from the airfoil. Its main disadvantage is that it creates excessive drag at high speeds.
According to some sources, when the slat extends, it does not accelerate the air, it smooths out the vortex caused by the high aoa, so the wing does not stall. Other sources explain it as accellerating the air via the venturi effect.

So....from a Zenith Air STOL design page:
The disadvantage of leading-edge slats is that the air acceleration in the slot requires energy (it creates additional drag). While many STOL designs utilize retractible leading-edge slat devices, the additional weight, complexity, reliability issues and cost of such systems minimize their feasibility for use in light aircraft and their overall effectiveness.

From yet another online source:
The disadvantage of the slots and flaps is that they produce higher drag.
Since the high lift coefficient is only needed when flying slowly (take-off, initial
climb, final approach and landing) some designers use retractable devices,
which closes at higher speeds to reduce drag.

The amount of drag caused is directly related to the percentage of clmax, and at lower percentages there can be no net increase in drag, it is when the aircraft approaches clmax, that there is a drag penalty.

Besides, if the slats increase lift, and increased lift equals increased drag, there really is no argument.
 
SOmthing to note: In the case of a fixed slot, it isn't necessarily in front of the wing like an extened slat, rather it is a channel cut into the wing itsself with the LE of the wing being continuous. (ie. on the SBD, Me 163, modified on the Fokker D.XXI)

And this still increases drag.



But Claidmore, my point on the slats is that (for all practical comparisons) an unslatted wing wll have the same drag as the slatted wing when compared below the stall of the normal wing.
When you get to the stall you can no longer compare the wings as one will be stalling (with the acompanied massive drag increase of the stall) and the other will still be well below the stall thanks to the slats.

(now, there is the small region where the slats -of the airpressure operated type- are begining to deploy before they are really helping, which I would assume put the clean wing in the advantage, but this is a very small range)

The amount of drag caused is directly related to the percentage of clmax, and at lower percentages there can be no net increase in drag, it is when the aircraft approaches clmax, that there is a drag penalty.

Besides, if the slats increase lift, and increased lift equals increased drag, there really is no argument.

If you compare the drag of the slatted wing's CLmax to the unslated wing, that's not a valid comparison as the unslated wing will be achieveing a considerably lower CLmax at a much lower AoA. (at which point the slated wing should be no greater in drag)
And again, at higher AoA the clean wing would be stalled.

Now if you make a comparison to a larger (say 30% greater area) clean wing with a smaller (full span) slatted wing of similar AR, airfoil, and planform things are a bit different, but a comparison can be made. The unslated wing should have a higher lift to drag ratio, while producing the same lift, but there would be penalties as well as the larger wing should be heavier, and will be longer in span. So the larger wing will have a poorer roll rate, will partially negate the greter lift/drag by adding weight, and will result in lower level speed due to the greater area. (the slats will tend to add to maintainence costs though, and may have other problems -ie the early 109's)
 
When the slat extends, you now have two leading edges, the one on the slat itself, and the one in the hole where the slat was sitting, plus you have the underside of the slat. You now have 3 surfaces where there was only one. On the 109 for example, the slat is 40% of the wings leading edge? That certainly isn't microscopic.

If a fixed slat causes drag, then a retractable slat will cause an identical amount of drag when it is extended into the exact same position as the fixed one. When there is no requirement for maximum speed simple fixed slats are used. It is the need for speed that requires a complicated mechanism for retractable/extendable slats.

From the US Centenial of Flight Commission:
and:
According to some sources, when the slat extends, it does not accelerate the air, it smooths out the vortex caused by the high aoa, so the wing does not stall. Other sources explain it as accellerating the air via the venturi effect.

So....from a Zenith Air STOL design page:

From yet another online source:

The amount of drag caused is directly related to the percentage of clmax, and at lower percentages there can be no net increase in drag, it is when the aircraft approaches clmax, that there is a drag penalty.

Besides, if the slats increase lift, and increased lift equals increased drag, there really is no argument.


good summary claidmore.

Soren is right about describing the 'energy' feature of a retractable slat - when the AoA reaches the point of deployment it is because it is high enough to start separation of flow on the wing area downstream. When the slat pops open it does enable high energy freestream to 'reattach' flow behind the slats - hence maintain lift for another degree or two of high AoA.


The Fowler flap acts in a similar way, when deployed it privides high(er) energy airstream at the trailing edge of wing/leadin edge of the flap to enhance the lift distribution
 
k. k. I see your point. :) I guess my point is that when the slat deploys, there is a drag penalty, so in combat, the plane with the slat doesn't enjoy a magic carpet ride, there is a price to pay.
This is part of why I feel that LE slats in a prop driven fighter, were of questionable value (as far as ACM). In a jet, where there is much more thrust available, they make better sense. Since only a few prop driven fighters used them, and they are common as hens teeth on jet fighters, it seems that the designers agree.

And your last paragraph illustrates the reason why some WWII fighters used the (semi) elliptical planform, to keep parasitic drag to a minimum.
 
As I understand it, the elliptical (or tapered) planform is to minimise induced drag, not parasite drag. Parasitic drag being most affected by the airfoil (and its thhickness) used and the overall area of the wing. (hence the P-51's wing, Tempest, Me 262, P-80 etc.)


But now that I bring it up, what are the major factors on turning performance at high speed? (say, 400+ mph sustained -particularly for the jets-) Does the wing's AR and planform still play a big part? Is induced drag still a major factor, or is parasitic drag the main factor. (with wave drag possibly coming onto the scene, depending on the a/c we're looking at -and the altitude/air temp)

At high speed the slats wouldn't really come into the equation as you wouldn't be getting near Clmax (G-forces being the limiting factor). At least untill you get into swept wing fighters which may get into the stall region near the wing tips. (or if you have an aircraft with exceedingly high wingloading)
 
As I understand it, the elliptical (or tapered) planform is to minimise induced drag, not parasite drag. Parasitic drag being most affected by the airfoil (and its thhickness) used and the overall area of the wing. (hence the P-51's wing, Tempest, Me 262, P-80 etc.)

KK - parasite drag is everything else other than induced drag, drag caused by unsealed airlerons, open wheel wells, antenna masts, trim drag of deflected rudder/elevators,...


But now that I bring it up, what are the major factors on turning performance at high speed? (say, 400+ mph sustained -particularly for the jets-) Does the wing's AR and planform still play a big part?

Yes - but at high speed thrust is huge as well as wing design (thickness).. Every thing needs to be focused on energy retention for a/c designed for high speed manueverability. Ultimately today the limiting factor is the pilot's ability to sustain 9+G as the airframes can handle 12+

Is induced drag still a major factor, or is parasitic drag the main factor. (with wave drag possibly coming onto the scene, depending on the a/c we're looking at -and the altitude/air temp)

At High speed for subsonic a/c parasite drag is key. Wave drag/transonic effects for WWII airfoils started in .55 Mach and propeller efficiency was also a factor for WWII designs. Tip speeds had to be kept below .9+Mach

At high speed the slats wouldn't really come into the equation as you wouldn't be getting near Clmax (G-forces being the limiting factor). At least untill you get into swept wing fighters which may get into the stall region near the wing tips. (or if you have an aircraft with exceedingly high wingloading)

The slats come into play near stall (local). For post WWII a/c the stall AoA for the thin wings were much lower than classic WWII airfoils.
 
On the parasitic drag comment, my point was that this:
And your last paragraph illustrates the reason why some WWII fighters used the (semi) elliptical planform, to keep parasitic drag to a minimum.
Is incorrect.
 
There's no drag penalty with the slats Claidemore, they are there to increase the lift when needed. The only increase in drag which occurs is that which stems from the increase in lift. And as for the reason why not all WW2 piston engined fighters featured them (slats), you're own theory just doesn't hold any truth to it. The reason not all fighters in WW2 featured slats is because they were complicated devices to mass produce and prepare the wing for, adding complexity to the design and reducing production rates, and because not all designers were aware (Or convinced) that they were needed.

Moving on to your theory about wetted area;

When deployed the slats DON'T add much wetted area at all, nearly nothing infact. Remember that the wetted area is the exposed surface area of the entire a/c, and since the slats are set 'in-place' at the wing LE they will, when they deploy, leave behind a "hole" where they used to be situated, which will actually reduce the circumference (And therefore SWA) of the covered area. Thus the only extra wetted area will be the backside of the slats, which apart from being a VERY small overall area, is positioned so that the wind just rides right alongside it, which means a very close to ZERO increase in Cd0. (Probably a factor of 0.0001 or 0.00005)

Thus NO, the slats don't add any drag when they deploy, they delay the stall by reenergizing the boundary layer increasing the lift critical AoA by ~25%. It's a brilliant device, hence whey nearly every fighter (And most a/c in general) since WW2 features auto LE slats or flaps.
 
There's no drag penalty with the slats Claidemore, they are there to increase the lift when needed. The only increase in drag which occurs is that which stems from the increase in lift. And as for the reason why not all WW2 piston engined fighters featured them (slats), you're own theory just doesn't hold any truth to it. The reason not all fighters in WW2 featured slats is because they were complicated devices to mass produce and prepare the wing for, adding complexity to the design and reducing production rates, and because not all designers were aware (Or convinced) that they were needed.

Thus NO, the slats don't add any drag when they deploy, they delay the stall by reenergizing the boundary layer increasing the lift critical AoA by ~25%. It's a brilliant device, hence whey nearly every fighter (And most a/c in general) since WW2 features auto LE slats or flaps.

You are wrong Soren. Every source I have quoted on leading edge slats disagrees with you, as well as other knowledgeable contributors to this forum. You have provided no sources other than your own assertations as usual.

As for WWII designers not being aware of LE slats, it was 20 year old technology, and it was used where needed, for example on the Westland Lysander, which needed STOL capabilities, the application where LE slats actually are useful in a prop driven plane.

And yet again, your own arguments prove the point: extended slats = increased lift, increased lift = increased drag, ergo.....extended slats = increased drag.
 
You are wrong Soren. Every source I have quoted on leading edge slats disagrees with you, as well as other knowledgeable contributors to this forum. You have provided no sources other than your own assertations as usual.

Christ :rolleyes:

You're the one who is wrong Claidemore, and terribly so.

For the very last time:

ANY increase in lift means an increase in drag, it is Cl dependant! Everything else being equal a wing with a higher Clmax produces a higher Cdi as-well. The slats themselves don't add any drag at all, all they do is increase the Clmax critical AoA of the wing. What is it about that you don't understand Claidemore ???

And as for sources, I have provided plenty, and some of the same as you, all which agree with what I say while to the contrary totally disagree with what you think!

As for WWII designers not being aware of LE slats, it was 20 year old technology, and it was used where needed, for example on the Westland Lysander, which needed STOL capabilities, the application where LE slats actually are useful in a prop driven plane.

You're so terribly wrong. Slats weren't used on all a/c in part because of ignorance regarding their usability and because of their complicated manufacturing requirements, thats it. And you will find nothing and no'one to support your own ridiculous theory.

There's a reason nearly every a/c (not just fighters!) have been equipped with either auto LE slats or flaps ever since! Get that through your skull man!

:rolleyes:

And yet again, your own arguments prove the point: extended slats = increased lift, increased lift = increased drag, ergo.....extended slats = increased drag.

OMG :lol:

Do you realize what it is you're argueing ???

What you're saying is that a high Clmax is a bad bad thing in a turnfight, which just couldn't be more wrong!
 
Christ :rolleyes:

You're the one who is wrong Claidemore, and terribly so.

For the very last time:

ANY increase in lift means an increase in drag, it is Cl dependant! Everything else being equal a wing with a higher Clmax produces a higher Cdi as-well. The slats themselves don't add any drag at all, all they do is increase the Clmax critical AoA of the wing. What is it about that you don't understand Claidemore ???

This is a good tutorial
STOL Wing Design

and explains why (correctly) that leading edge slats DO increase drag with the introduction of high energy air over the airfoil.


And as for sources, I have provided plenty, and some of the same as you, all which agree with what I say while to the contrary totally disagree with what you think!

Well, not all agree with what you are saying above..

You're so terribly wrong. Slats weren't used on all a/c in part because of ignorance regarding their usability and because of their complicated manufacturing requirements, thats it. And you will find nothing and no'one to support your own ridiculous theory.

Slats were designed in parallel by Gustav Lachmann and Handley Page in 1919. Page got the patent by having Gustav come to work for him.

Various aircraft such as the Hampden, the Lysander and the Storch. Retractable Slats were complicated as Soren says and necessary for high performance a/c. Most designe engineers were not sufficiently convinced that a small increase in stall angle, or lower landing speed was worth the cost


There's a reason nearly every a/c (not just fighters!) have been equipped with either auto LE slats or flaps ever since! Get that through your skull man!

I believe the discussion was about the aerodynamics of the slats and application in subsonic (sub transonic) aircraft in WWII with medium aspect ratio wings?

:rolleyes:



OMG :lol:

Do you realize what it is you're argueing ???

What you're saying is that a high Clmax is a bad bad thing in a turnfight, which just couldn't be more wrong!

I didn't see him argue that. I saw a discussion that said the benefit carried certain penalties, namely more drag when deployed.

I agree, greater ClMax is good at low speed.
 
Nope, the links agree with what I've been saying Bill, none so far disagree, not even the page you linked.

Here's the quote:
The disadvantage of leading-edge slats is that the air acceleration in the slot requires energy (it creates additional drag). PS: The illustration shows slots, which do create drag (except in tight turns) as they're fixed.

And what also requires energy to emerge ? Lift! From which the drag originates!

The increase in drag stems directly from the increase in Clmax.

That means that the slatted wing producing a CLmax of 1.5 doesn't feature anymore drag than the unslatted wing producing the same Clmax.

The point being, it is NOT the slats which create extra drag, it IS the extra lift which they allow to be created which creates the extra drag, cause: Drag is the direct byproduct of lift!

Slats were designed in parallel by Gustav Lachmann and Handley Page in 1919. Page got the patent by having Gustav come to work for him.

No arguments there and there never has been.

I agree, greater ClMax is good at low speed.

And more importantly in tight maneuvers.
 
Bill said:
I didn't see him argue that. I saw a discussion that said the benefit carried certain penalties, namely more drag when deployed.

Well here's what he said, which is just flat wrong:

This is part of why I feel that LE slats in a prop driven fighter, were of questionable value (as far as ACM). In a jet, where there is much more thrust available, they make better sense. Since only a few prop driven fighters used them, and they are common as hens teeth on jet fighters, it seems that the designers agree.

And your last paragraph illustrates the reason why some WWII fighters used the (semi) elliptical planform, to keep parasitic drag to a minimum.


Or would you call that correct Bill ?
 
To make it even more simple for those of you who don't quite follow yet:

We have to equal sized wings, but with different airfoils, one emphazising speed (Wing B) the other high lift (Wing A), and therefore the Clmax of the two wings are different. Thus wing A obviously produces the most lift and therefore obviously also more drag.

So which wing is best for turn fighting ?? Wing A with the higher CLmax ofcourse.

However being the smart humans that we are we decide to put slats on Wing B, increasing its Clmax to the same as that of Wing B.

Now which wing is the most efficient ?? Wing B ofcourse as it now features just as high a CLmax as Wing A while at the same time retaining lower drag in straight flight. And drag in turns is no greater than that of Wing A cause it features the same Clmax and therefore Cdi.

So how exactly does one conclude that the slats themselves increase drag ?? The answer is one can't or he will be wrong.

Hence why a/c designers all over the world all suddenly put slats on their a/c when they understood all the benefits.
 
Nope, the links agree with what I've been saying Bill, none so far disagree, not even the page you linked.

Here's the quote:
The disadvantage of leading-edge slats is that the air acceleration in the slot requires energy (it creates additional drag). PS: The illustration shows slots, which do create drag (except in tight turns) as they're fixed.

Fixed slats would create more lift and drag throughout the turn regime - shallow and tight - than the equivalent non-slotted wing.

And what also requires energy to emerge ? Lift! From which the drag originates!

I believe you are repaeating the point Claidmore and I made to support slats having a penalty of more drag (than same wing w/o slats deployed)

The increase in drag stems directly from the increase in Clmax.

Claidmore made that point and I supported it.. your point is?

That means that the slatted wing producing a CLmax of 1.5 doesn't feature anymore drag than the unslatted wing producing the same Clmax.

But for the same wing Clmax IS greater for the deployed slats and the corresponding drag to the deployed slat CLmax is greater for the deployed slats than both the CLmax and Drag of the undeployed slat configuration



The point being, it is NOT the slats which create extra drag, it IS the extra lift which they allow to be created which creates the extra drag, cause: Drag is the direct byproduct of lift!

You continue to agree with what Claidmore said



No arguments there and there never has been.



And more importantly in tight maneuvers.

Then why are you arguing?
 
To make it even more simple for those of you who don't quite follow yet:

We have to equal sized wings, but with different airfoils, one emphazising speed (Wing B) the other high lift (Wing A), and therefore the Clmax of the two wings are different. Thus wing A obviously produces the most lift and therefore obviously also more drag.

So which wing is best for turn fighting ?? Wing A with the higher CLmax ofcourse.

Soren - where are you trying to take the discussion (which you introduced) of turn efficiency being a function of WL divided by CLmax?

However being the smart humans that we are we decide to put slats on Wing B, increasing its Clmax to the same as that of Wing B.

The smart humans will conclude that the configuration at the velocties compared which has a higher wing L/D at that velocity is the wing with the higher efficiency. The smart ones will also note that every airfoil has a different slope of CL to AoA, a different CLmax, and all are influenced by aspect ratio. The greater the AR, the steeper the slope of CL to AoA - but further complicated by the fact that for the same airfoil the greater AR ,while having a higher CLmax, will stall at a lower AoA.

These are facts - what do you wish to do with them in your manuever thesis of Clmax having anything to do with 'efficiency' when applied to Lift Loading

Sources for WL/Clmax = efficiency? when in fact it equals a pressure at one velocity?
 

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