Leading edge flaps ?

A slat (a worldwide term) is just one type of leading edge device as stated in all the text above. Slats are even used in GA aircraft such as the Rallye and the Tiger Moth.

Theres another name for this leading edge flap besides slat. I think slat must be a british term or something.

cool…have fun… 😎

true, if the programs not up to the job then its not worth anything….but the program they have at uni is good enough for our purposes I suppose…needless to say we wont be doing much full vehicle 3d dynamics….as a matter of interst I’m going to put the nose section of the F22 into the prog (CFX5) with a sting and measure (and at least view) the vortex pattern created by the nose chine.

coanda

don’t fall into that trap…full vehicle 3D NS numerical solution is often wrong and can only get you visualizations. I guess what you’re talking about is 2D flow (airfoil cross sections)….then ok…

I think i am in the lucky position of both experiencing these devices in flight and learning about them through my aerospace degree.

You’ll see that there are certain advantages over certain types of leading edge devices.

Leading edge devices are useful not only in terms of lift, but perhaps more critically in reducing the effective angle of attack of a flapped airfoil.

A flapped airfoil it can be proven stalls before a none flapped airfoil (in the more well known sense of TE stall, as most airfoils in general use have ‘nice’ flow appreciative curved leading edges).

The way in which this can easily by shown is by drawing a line from the trailing edge to the leading edge of an airfoil with and without some kind of flap extension.

Thus you will see that the flapped wing has an effectively higher angle of attack.

with a drooped leading edge it can be seen that this same angle of attack is reduced as the leading edge of the airfoil is lowered.

another advantage of leading edge slats is the increase in speed produced through the ‘throat’ of the system between the trailing edge of the slat and the leading edge of the rest of the wing. this increases flow speed in this region and provides a more laminar flow over the wing at higher angles of attack, which otherwise would increase the chances of flow transition(and leading edge flow seperation) leading to the stall from an artificially ‘sharper’ leading edge.

Perhaps another way of thinking of a wing with leading edge device and a flap is to remember the shape of first world war (and indeed the wrightflyer craft) airfoils. nothing more than a curved sheet in practice.

in this case pressure differential and thus lift occurred because of the low pressure vortex occuring within the confines of the undersurface of the airfoil and the free stream flow. The sharp leading edge partly permitted flow breakaway and the free stream kept that vortex in place. in effect this completes the airfoils shape and provided the shape required for lift.

High lift devices do increase drag in increased frontal area drag besides drag due to lift.

There is more than one way of explaining what ‘lift’ fundamentally is and those ways are sometimes applicable in one area only (the vortex theory is useful in symmetrical airfoils with nil angle of attack for example) and situations occur when more than one theory will provide the same equally valid result.

However as i progress through my course (only 5 months left now) I have come to see that using CFD as a tool for analysis really is the best way to achieve the required results as by using the navier stokes equations there are no ‘conditional’ equations and you can solve everything you want at the same time. Computing power is however still a severe restriction.

hope this helps some what!

coanda

I think I now see where the difference lies, Vortex. You (the engineer) sees the actual occurance at that moment in time whereas I (the pilot) see what that effect allows me to then do (i.e. to then use the advantage of having deployed the device)!

Originally posted by wysiwyg
I fully agree with you about the leading edge devices allowing the increase of angle of attack beyong the usual stalling angle however the graph quite clearly does show a large INCREASE in lift coefficient with leading edge device deployment.

Well, depends on how you see it i guess. From practical and engineering perspective, it doesn’t. In engineering perspective, the component of the leading edge device does not increase lift significantly because if you integrate the Pressure of the entire wing with respect to the area then you’ll see that the leading edge portion only accounts for say 10-20% of the lift (typical, and sometimes negative) at any instance. Practically it also doesn’t because an aircraft don’t just magically becomes at a different angle of attack…at least in continuum theory. When a pilot lowers the leading edge flap, the wing still stays pretty much at the same AoA since the time constant for the change in forces to rotate the wing is on the order of seconds. But, as i mentioned before and as you’re suggesting, the use of the LE devices “allows” the attainment of higher AOAs which means higher lift. Notice this is very different from a flap…where at the same AoA, a flap clearly increases the lift significantly, LE devices or not…until stall of course.

Elp, i thought you’re in the military…that’s a “SIR” to you 😀 😀 😀 😀 😀

GREAT! I only never understood these graphs about take off speeds, weights and t° and height etc…. :p No need to explain :s

Turning = Lift

Here’s a web tutorial put together by the fine folks at NASA that discusses lift, wing shape and lift devices.

http://www.grc.nasa.gov/WWW/K-12/airplane/shape.html

Here’s a complete list of the guided tours they have online.

http://www.grc.nasa.gov/WWW/K-12/airplane/guided.htm

Will that be on the final test Mr. Vortex ? 😀