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seems rather odd to me.The same article says that leading edge devices increase drag, but the lift/drag ratio is improved.
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.
and: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.
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.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.
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.
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.
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.
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)
Is incorrect.And your last paragraph illustrates the reason why some WWII fighters used the (semi) elliptical planform, to keep parasitic drag to a minimum.
On the parasitic drag comment, my point was that this:
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.
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.
Christ
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?
OMG
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!
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.
I agree, greater ClMax is good at low speed.
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.
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.
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