Leading Edge Slats on the Me-109

[taildraggernut]

Originally Posted by Crumpp

You are not discussing anything civilly...you are just making insults.

I am being very civil, if you have taken insult from that then I believe you are a touch over-sensitive......I believe that comes with instability

Originally Posted by Crumpp

First of all, you do not understand the fundamentals of LE slat aerodynamics.

Now that is an insult.

Originally Posted by Crumpp

Quit using wikipedia as your source. It is not credible and in this case is just plain wrong as the author does not understand boundary layer mechanics.

Oh come now, that 'Stop using Wikipedia as a source' is too cliche, used as a cheap attempt at discrediting in many internet debates, there is nothing wrong with that article.

Originally Posted by Crumpp

In boundary layer mechanics, we have two portions, laminar and turbulent.

Laminar flow is the last thing you want on the outboard portion in a stall. Laminar flow is low energy. That is why it is low drag AND subsequently, low lift.

Slats work by increasing turbulent flow not laminar flow. Turbulent flow portion of the boundary layer is high energy and high lift!.

optfly.iaa.ncku.edu.tw/aftdesgn/lect16.pdf

The laminar flow is not the purpose of the slats, it is the increase in turbulent flow boundary layer which delays the onset of the stall..

http://history.nasa.gov/SP-4103/app-f.htm

I suggest you read this article, it will help you understand boundary layers and the effect of skin friction and subsequent separation due to turbulence.

Extracts from the article......I hope NACA are a more credible source for you rather than wikipedia.

The flying qualities of wings can be enhanced in two ways, and boundary-layer control can help in both. The first is to decrease drag; the second is to increase lift. The most desirable way to decrease drag is to maintain laminar flow within the boundary layer and prevent a transition to turbulent flow.

Over a normal wing, the boundary layer remains laminar over only a small portion of the wing chord before breaking up into turbulent flow. The area of turbulent flow experiences significantly greater skin-friction drag than the laminar flow.3

Finally, however, the boundary layer on the upper surface breaks free of the wing altogether, reducing lift drastically. This is known as stalling. If the boundary layer can be kept from separating, the maximum lift of the aircraft can be increased, an important consideration in increasing takeoff-weight capacity and reducing landing speed. Furthermore, the same energizing of the boundary layer that delays separation can also help to maintain the boundary layer in fast laminar flow, increasing total lift even at low angles of incidence.

Originally Posted by Crumpp

No stall = NO SPIN! Hence, the spin resistance found in slats and the reason engineers used them as an early anti-spin device.

They are spin resistant because they allow for control inputs that would normally result in a spin. One can easily see this in the RAE report.

Spin resistance is not anti-spin.....anti would suggest there is complete protection and that is simply not the case.

in case you were doubtfull that slats are a boundary layer control device heres more stuff from NACA..

http://history.nasa.gov/SP-367/chapt4.htm

Slots.- The maximum coefficient of lift may be increased through the use of a slot formed by a leading-edge auxiliary airfoil called a slat. Figure 63(a) illustrates the operating principle. When the slot is open, the air flows through the slot and over the airfoil. The slot is a boundary-layer control device and the air thus channeled energizes the boundary layer about the wing and retards the separation. The airfoil can then be flown at a higher angle of attack before stall occurs and thus get a higher...

Boundary-layer control.- Another method of increasing CL,max is by boundary-layer control. The idea is to either remove the low-energy segment of the boundary layer and let it be replaced by high-energy flow from above or by adding kinetic energy to the boundary layer directly. Both of these methods maintain a laminar flow for a longer distance over the airfoil, delay separation, and allow one to get a larger angle of attack before stall occurs, and thus a higher CL,max The slot was shown to be one means of passing high-energy flow over the top surface of a wing.

Originally Posted by Crumpp

Flow separation from the top of the airfoil, i.e., stall, results from the loss of the kinetic energy in the boundary layer due to viscous shear and an adverse pressure gradient. A turbulent boundary layer is better able to delay flow separation than a laminar boundary layer because of the higher energy associated with the turbulence. For this reason it is better to have a turbulent boundary layer over the airfoil. Vortex generator are put on the top surface of a wing for the purpose of forcing the early transition of the boudary layer to turbulent.

Vortex generators are using a completely different method, the 'turbulence' they are creating is simply in the form of vortices to draw in energy to a portion of the airflow.

http://www.aerospaceweb.org/question...cs/q0228.shtml

The advantage of wing devices that create vortices is that a vortex adds energy to the airflow and increases its forward momentum. This momentum encourages the airflow to remain attached to the surface of the wing at higher angles of attack than it would otherwise. As a result, the wing is able to continue generating lift in conditions where it would have stalled. This behavior is particularly advantageous on high-performance military aircraft that need to be extremely maneuverable at high angles of attack in combat. The advantage for commercial airliners is increased safety since the plane is less likely to experience a wing stall during critical stages of flight like takeoff and landing.

The method by which these vortex devices work can be better understood by studying the above diagram of vortex generators on a wing. A vortex generator is much like a miniature wing perpendicular to the main wing. These generators are mounted at an angle of attack to the airflow over the wing so that each creates a vortex off the exposed tip, much like a trailing vortex created by a wing. The above example shows vortex generators aligned in opposite directions so that the vortices they create rotate opposite to each other. These vortices serve to increase the speed of the downstream airflow so that it is "entrained" to follow the sharp curvature of the deployed flap and remain attached to its surface. Otherwise, the airflow would likely separate from the flap causing a loss of lift.

Now hopefully you will be able to explain to us all exactly what are the mechanics involved in complete stall/spin avoidance once a slatted wing has been taken beyond it's maximum angle of attack?