Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: the4ork on February 11, 2008, 06:28:24 PM
-
im looking for info on these slats, not the principle of why they are there and how they work, but how they were manufactured into the wing...
from a design standpoint how were they incorperated into the aircraft and how they operate inside the wing...
in my head i picture them being spring operated? on some kind of guide they move along?
-
They're not spring operated, they just sit on ball bearings and are free to move on their own. Aerodynamic principals that I dont completely understand push them in and out, not springs. Positive and negative airflow or something like that.
-
http://109lair.hobbyvista.com/techref/systems/control/slats/slats.htm
No springs. Air pressure changes cause slats to open or close.
-
...damn annoying too...
-
Originally posted by Stampf
...damn annoying too...
I know how you feel. When I flew the K4 every time they would come out I felt that it would mess me up and throw me off, even if they did help me out.
donkey
-
Originally posted by Stampf
...damn annoying too...
When I changed soundpacks I kept thinking I was getting hit when the slats would open or bang shut!
-
im still not gettin out the mechanism works...
-
Do a search... type in 'discuss' and you'll find a thread with that title. It's got a lot of info on the slats... all the info you and I could ever hope to understand.
-
(http://img.villagephotos.com/p/2005-12/1114844/slat1.jpg)
(http://img.villagephotos.com/p/2005-12/1114844/slat6.jpg)
(http://img.villagephotos.com/p/2005-12/1114844/slat2.jpg)
(http://img.villagephotos.com/p/2005-12/1114844/slat3.jpg)
(http://img.villagephotos.com/p/2005-12/1114844/slat4.jpg)
(http://img.villagephotos.com/p/2005-12/1114844/slat5.jpg)
-
Note that the connecting rod (d) in second picture takes care that both arms move at the same time so that uneven pressure will not jam the slat if the outboard side of the slat wants to open but the inner part will not but the pressure at any part of the slat, if powerful enough, forces it to open evenly.
IIRC the system in Russian Lavochkins works differently so that the connecting mechanism is not needed. There's probably just two simple hinges that move sideways opening the slat. I'm not sure if the slats are linked, though.
-C+
-
Would say the Russian system of operation didn't need a connecting rod as a parallelogram doesn't need one. If one side of the slat moves it automatically pulls the other side. A simple no fuss design.
(http://img.villagephotos.com/p/2005-12/1114844/strut8r.gif)
-
Yep, thats what I remembered. It seems that the slats in right and left wing are not connected together either?
-C+
-
Ok, here is another question along the same lines;
How is the F86's wing slats compared to the 109? Same mechanism or was a completely different design?
-
Originally posted by Charge
Yep, thats what I remembered. It seems that the slats in right and left wing are not connected together either?
-C+
According to the information above, that is correct.
If they did indeed operate through air pressure it would seem logical that they would not be linked.
-
Originally posted by Delirium
Ok, here is another question along the same lines;
How is the F86's wing slats compared to the 109? Same mechanism or was a completely different design?
also interested in the same question, but also were the 110's slats operated the same way...
im just still not getting how all the linkage is hooked up and how the air pressure pops them open...
i'd like to incorporate them into an remote controlled 109 im building but im not getting it...
-
I suggest you use the sideways moving hinge. Its simple and reliable also in smaller scale and easy to make. Notice that you need the have the channel between the slat and wing at the corrrect angle. I don't think it needs to be accurately some specific degrees but the basic direction of flow needs to be right.
***
The accurate operation is not all clear to me either but the basic wing profile might give you a hint of how the pressure works on the surface of the wing at different speeds and angles of attack (AoA). If the profile is thick near the leading edge the profile usually tolerates more AoA but in turn provides more drag so the profiles used on fighters are usually a compromise to achieve both. The farther back you move the thickest point the less drag you willl have but at radical AoAs the wing stalls quicker since there is no profile surface to support the air flow.
My guess is that when the wing profile nears the stall a low pressure area builds up on the wing surface and rapidly shifts forward forcing the slat open. When the slat opens the high pressure underside the wing starts flowing (or "bleeding") on top of the wing compensating the pressure difference and uniforming the flow and thus preventing the stall. When the air pressure against the slat over comes the flow pressure through the slat opening the slat closes.
So it doesn't really work through giving more wing surface but just preventing a tip stall.
If a typical wing profile (wing tip) thickness is 9% (~11% in 109) of profile chord the profile itself has a rather low AoA tolerance of about 13 degrees of AoA (pulling out of hat) Where as the root with typical 15% thickness can tolerate about 16 degrees, so with slats you can expand this theoretically to 25 degrees. It is another matter if you have enough engine power to handle the drag caused by such AoA.
I'm not sure if I got it right so corrections are welcome.
-C+
-
The slat on the Me 109 started moving out at a Cl of approximately 0.8 at AoA circa 12 degrees and was supposed to move out gradually from there until fully deployed at Cl=1.25 AoA 18 degrees. The slat was then effective in keeping the flow attached up to an AoA of 30 degrees after which the Cl reduced gradually (no sharp stall of the airfoil section evident). Mind you this does not imply that you could fly the airplane to 30 degrees alfa, only that the 2D section could go so far and that the device was sucessful in keeping the flow attached over the aileron part of the wing until the inner portion lost it's lift thereby maintaining lateral control up to stall.
Source for slat operational data: Messerschmitt reports TB 33 and 34 on optimum slat kinematics, by Braun, 1941.
The function of the Me 109 slat was a tricky business though and required proper maintenance and there are Allied test flight accounts of the 109 in which the slat comes out unevenly and with a bang against the stop. This however was most likely due to faulty alignment of the slat (a gap) that greated a suction force which kept the slat closed until the leading edge suction overcame this and the slat went out with a bang.
Source for slat banging problem description: Fluid Dynamic drag (page 6-9) by Hoerner.
So if properly maintained the slats should move out nice and gradually :)
-
I thought it works quite abruptly by banging in and out but in Black 6 flying video it can be seen that the slat slowly slides in and out when the 109 flies along with the slower filming a/c.
-C+
-
Originally posted by Delirium
Ok, here is another question along the same lines;
How is the F86's wing slats compared to the 109? Same mechanism or was a completely different design?
Greg Goebel makes the following interesting comments.
F-86 swept wing and slats (http://www.vectorsite.net/avf86_1.html)
"This [early P-86] design got as far as a full-scale partial wooden mockup, unveiled at the NAA Inglewood, California, plant on 20 June 1945. It went no further, since by this time North American engineers knew that there was no way it could meet USAAF requirements. The straight wing couldn't achieve the required speed with the engines available at the time.
Aircraft engineers knew that a thin swept wing could greatly reduce drag and delay the onset of compressibility problems, but such a wing also led to serious stability problems at low speed. The hard data needed to resolve the issue was not available until early 1945, when the Allies captured research data on swept-wing flight from the Germans.
The Germans had conducted wind-tunnel tests on small swept-wing aircraft models as far back as 1940. By 1944, their work had demonstrated that swept wings offered substantial performance benefits. The main difficulty was that any swept wing that was efficient at high speeds tended to be unstable at low speeds. They experimented with a number of ways to deal with this problem, one of the most promising being a "slat" on the leading edge of the wing, which could be raised to change the airflow and generate more lift.
After the end of the war, aviation engineer George Schairer of the Boeing Company went to Germany to examine German aviation research. He was accompanied by the well-known Theodore Von Karman of the California of Technology, and Robert Jones of the US National Advisory Committee on Aeronautics (NACA, one of the precursor organizations of the modern US National Aeronautics & Space Administration / NASA). Schairer was extremely enthusiastic about the data he found on swept-wing flight, and not only proposed that Boeing use it on their new XB-47 long-range bomber, but that the information be provided to other US aviation firms.
Larry Green of NAA studied the materials and came to the conclusion that a swept wing was answer to improving the performance of the XP-86, and determined that a slat attached to the wing's leading edge and automatically extended at low speeds would solve the low-speed stability problem. Green and other NAA engineers convinced the president of NAA, "Dutch" Kindelberger, that the swept wing was the way to go, and on 18 August 1945, Kindelberger approved further studies on the concept. Within a few weeks, NAA engineers were performing wind tunnel tests on a 1/23rd scale model of an XP-86 with wings swept at 35 degrees. The results were extremely promising. After further tests, the USAAF approved development of the swept-wing XP-86 on 1 November 1945.
* Models were one thing, a flying aircraft another. Engineering the slats was troublesome, and in fact the NAA team went so far as to obtain slatted wings from the German Messerschmitt 262 jet fighter to get ideas. The first seven aircraft would actually use some Messerschmitt 262 slat hardware.
---
The first production batch of 33 aircraft was designated "F-86A-1". The second production batch of 188 was designated "F-86A-5", and featured a number of enhancements. While the F-86A-1 had a rounded front windscreen, the F-86A-5 had a flat front armor glass windscreen, and the canopy was now jettisoned using pyrotechnic charges. An improved leading-edge slat scheme was introduced, and there were a number of minor internal changes.
---
North American had only begun tinkering with the wing, however. Aerodynamic studies had shown that eliminating the leading-edge slat and providing a sharper leading edge on the wing provided substantial benefits in high-speed flight, though this led to "hotter" landing characteristics. To compensate for the hot landings, the wing was extended 15 centimeters (6 inches) at the root and 7.6 centimeters (3 inches) at the wingtip. The new wing, which also featured fuel tanks in the leading edge that increased capacity by 264 liters (70 US gallons), was known as the "solid 6-3" wing. The wing was incorporated into F-86F-25/30 production in midstream, and was also sent to Korea in kit form to upgrade most F-86Fs and a few F-86Es in service there.
---
The A-4 Skyhawk also used slats as well.
All the best.