Laminar Flow Control
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MIflyer
1st Lieutenant
Well, because the A-4 was a carrier airplane, Heinemann knew very well that the wing would have an slatted moveable leading edge and flaps on the trailing edge. When deployed hose features largely overcome any built-in curve on the wing surface.
The F-86A had leading edge slats but on the F-86F they got rid of that in order to extend the wing leading edge in a fixed position and improve high speed turning. But they used long runways.
The F-86A had leading edge slats but on the F-86F they got rid of that in order to extend the wing leading edge in a fixed position and improve high speed turning. But they used long runways.
I wasn't quite correct here. Camber IS necessary for ADEQUATE lift. A flat board will give you zero lift at zero angle of attack, and some deflection lift if you give it a little AoA, but it won't take much AoA without stalling.
Yes, that is a stall.
That is what they do in wind tunnels. There are numerous videos on the internet showing this and allowing you to see how the air behaves at various angles of attack and speeds. Way better than a verbal description.
ThomasP
Senior Master Sergeant
Hey Odoaker,
I would like to suggest that you try using paper airplanes to help answer some (most?) of your questions. The are many good books and some instructional videos (on or off the internet) that give very good explanations of how different wing shapes effect flight. There are also many paper airplane books that do the same, and a few videos that use paper airplanes to illustrate. Plus it is usually makes it much easier to visualize what works and how it works, particularly for the non-aeronautical engineer/non-physicist. There are some written by aeronautical engineers for engineers (some of which are quite technical) and some for non-engineers (usually less technical). Some of the books go through the different wing planforms step-by-step (ie straight-swept-delta (including camber and twist), traditional tail control surfaces vs canard control surfaces, LEX/chines, etc) and even illustrate things like the need to balance center-of-lift vs center-of-gravity in order to allow stable/controlled flight. A lot of the paper airplane examples use flat wings, but the more complex paper models use different cambers and even ~airfoil sections. I did a fair amount of paper airplane building when I was in my teens and twenties, and I found it quite helpful in understanding the effects of delta wings, variable sweep wings, and lifting bodies.
I would like to suggest that you try using paper airplanes to help answer some (most?) of your questions. The are many good books and some instructional videos (on or off the internet) that give very good explanations of how different wing shapes effect flight. There are also many paper airplane books that do the same, and a few videos that use paper airplanes to illustrate. Plus it is usually makes it much easier to visualize what works and how it works, particularly for the non-aeronautical engineer/non-physicist. There are some written by aeronautical engineers for engineers (some of which are quite technical) and some for non-engineers (usually less technical). Some of the books go through the different wing planforms step-by-step (ie straight-swept-delta (including camber and twist), traditional tail control surfaces vs canard control surfaces, LEX/chines, etc) and even illustrate things like the need to balance center-of-lift vs center-of-gravity in order to allow stable/controlled flight. A lot of the paper airplane examples use flat wings, but the more complex paper models use different cambers and even ~airfoil sections. I did a fair amount of paper airplane building when I was in my teens and twenties, and I found it quite helpful in understanding the effects of delta wings, variable sweep wings, and lifting bodies.
Of course, as a kid, I made paper airplanes that only had flat wings. Just like in this scene below. But the paper is light. Can you make such a flying model out of thin sheet metal or chipboard?
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On the Internet some author claims that such a flat wing model should fly:
http://www.ericbrasseur.org/glider_physics_28.gif
But this is almost the model I threw from the window (the main difference was that my model had an inverted V-tail, because it was easier to make, and inverted, because I wanted the weight rather under the model). And it "flew" almost like a thrown brick.
But these elements were probably not used during the flight?
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ThomasP
Senior Master Sergeant
Hey Odoaker,
Yes you can make similar models out of thin (very thin) sheet metal, but the problem is that with every thing else being equal (ie same dimensions and geometry) as the density of the material used goes up so does the velocity needed to keep it flying. The minimum flying speed will go up by the square root of the difference in weight. Another problem you will run into is keeping the airframe stable, just like you do with the paper airplanes. Because you do not have movable control surfaces it will be difficult to maintain the proper AOA and velocity combination needed to maintain a glide. However, as with paper airplanes, you should be able to bend either the after surfaces of the main wings (if highly swept or delta) or the tail plane surfaces (if the main wings are low-moderately swept or straight) to get the correct downward (or in some cases upward) force at the aft end of the model. The idea is to get the model to move at a velocity that will allow it to operate within its glide ratio (since there is no power source other than the initial throw and subsequent gravitational pull).
If you would like to use wood I would suggest modeler's plywood or balsa - you can usually find it at model railroad stores and the more in depth plastic model stores. Some craft stores will carry it as well. Or you can order it online through many websites.
If you build a paper model that flies right first, and then transfer the pattern to the thin sheet metal or thin wood, you will be more than half way to getting the balance of forces right. Hope this helps.
Yes you can make similar models out of thin (very thin) sheet metal, but the problem is that with every thing else being equal (ie same dimensions and geometry) as the density of the material used goes up so does the velocity needed to keep it flying. The minimum flying speed will go up by the square root of the difference in weight. Another problem you will run into is keeping the airframe stable, just like you do with the paper airplanes. Because you do not have movable control surfaces it will be difficult to maintain the proper AOA and velocity combination needed to maintain a glide. However, as with paper airplanes, you should be able to bend either the after surfaces of the main wings (if highly swept or delta) or the tail plane surfaces (if the main wings are low-moderately swept or straight) to get the correct downward (or in some cases upward) force at the aft end of the model. The idea is to get the model to move at a velocity that will allow it to operate within its glide ratio (since there is no power source other than the initial throw and subsequent gravitational pull).
If you would like to use wood I would suggest modeler's plywood or balsa - you can usually find it at model railroad stores and the more in depth plastic model stores. Some craft stores will carry it as well. Or you can order it online through many websites.
If you build a paper model that flies right first, and then transfer the pattern to the thin sheet metal or thin wood, you will be more than half way to getting the balance of forces right. Hope this helps.
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MIflyer
1st Lieutenant
"But these elements were probably not used during the flight?"
The leading edge slats might be used during hard maneuvering, such as in air combat. The flaps, probably not.
The leading edge slats might be used during hard maneuvering, such as in air combat. The flaps, probably not.
If you build a paper model that flies right first, and then transfer the pattern to the thin sheet metal or thin wood, you will be more than half way to getting the balance of forces right. Hope this helps.
I get the impression that a model made of heavier materials needs a bigger lift, a bigger lift needs larger AoA, and a larger AoA with a flat wing ... But maybe I am thinking wrong?
This time I modified the model a bit and added a very heavy ballast to the front (brass "monster pen"). Obviously I had to take care of the balance so I moved the wings forward and the tail was very long. I threw the model and it had good flight stability. As the model completed its flight and I approached the landing site, I saw that the brass pen hit the ground as deep and precise as a spear. This surprised me as the pen was not very pointed. But that was the main problem: a model with such heavy ballast flew through the air almost as fast as a spear, only a little slower. And the flight distance was probably similar. It was not a model airplane, but a spear with wings and a V-tail. The flight stability was very good, the model was fast and poor made, but it did not break down when hitting the ground many times (there were many tests), the wings did not break, but what's the point of making wings and tail if the ordinary spear "flies" almost identical? Sure, I could have increased the AoA, but you understand perfectly well what I was afraid of.
So, during the flight, where did the lift come from?
Don't confuse weight and density. Metals are generally "heavier" than paper because they are dense and the applications we have for metals and papers mean we can pick up most things made of paper but many things made of metal need a crane to lift them. Aluminium cooking foil is very "light" which you may think is because aluminium is light, it isn't, it is because you can roll aluminium foil very thin. Gold is much more dense than paper or aluminium but can be rolled so thin one ounce (25.4g)of gold can cover 300square feet (28 square meters).
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Yes, they were used in various phases of flight. In climb, descent and level flight, all these "high lift devices" would be retracted. In any high angle of attack situation, such as a high G combat turn or an approach to landing, the automatic leading edge slats would deploy whenever the AoA exceeded approx 3/4 of the the critical (stall) AoA. The flaps would be extended during the approach to landing and partially extended for a heavyweight takeoff.
The leading edge slats on the A4 were free floating and would be held retracted by aerodynamic forces at normal operating angles of attack In flight. When the AoA approached the the critical angle, the stagnation point would drop below the leading edge of the slat, and the "reverse flow" of air over the curvature of the leading edge would cancel the pressure of relative wind holding them shut, and they would start to "fall" forward on their curved rails which ran on ball bearing rollers, opening a "slot" that allowed the airflow to follow a more moderately curved path to the top surface of the wing.
On the ground the slats always hung down by gravity in the extended position. Pilots doing their preflight inspection would grab the slats, push them shut, and let them slide back out, feeling for binding or excess friction, and comparing the friction and extension rate side to side. The last thing you could want is to get an asymmetric slat extension in a high G turn In a dogfight.
From the AoA and the camber of the airfoil. The A4 had a rather small wing for the weights it was capable of operating at, and flew in a pretty pronounced nose-high attitude at just about anything less than never-exceed speed. An A4 carrying a maximum ordnance load looks like a caricature of a tiny toy airplane strapped to a huge cluster of bombs. Lightly loaded, it had the thrust to weight ratio to be a startling performer for its time, much to the chagrin of the occasional unwary Vietnamese MiG pilot.
MIflyer
1st Lieutenant
And the A-4 was even used by the Blue Angels, for a while, due to the oil crunch in the 70's, which made it embarrassing for the military aerobatic teams to be flying the F-4. The USAF switched to the T-38 in that same timeframe. Aside from the amount of gas used, it also was nice for you to have an airshow that stayed in the same county.
I recall IDF pilots saying that the Mirage was always so smooth but in the A-4 when the slats came out, it would be "Bang!" and the pilot's helmet would hit the canopy.
Funny thing was, the A-4 basically outlived its successor, the A-7. I guess the TF-41 engine had a lot to do with that.
What people often do not realize is that a flat or symmetrical wing still uses Bernouli because when it is at a suitable angle of attack a wing still creates a situation where the air has to go faster over the top than it does the bottom.
Now, for supersonic flight, you are talking shock waves being formed, so the lift generated is a whole 'nuther situation.
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OK, so in your opinion, such a model should glide?
http://www.ericbrasseur.org/glider_physics_28.gif
Why has this issue become so interesting to me? I have materials at home and in my garage like this:
flat
It is quite light and very stiff but I have a feeling I can't make a convex airfoil out of it. If I try to bend it more, this material will probably break in two.
BTW I don't understand something about "Bernoulli". Air should go faster over the wing than under the wing, right? So if I take a flat piece of cardboard (zero AoA), take air in my lungs, and blow over that cardboard, should it go up? But - nothing like that happens.
Therefore, honestly, the theory of air deflecting thanks to AoA seems to me more understandable. Obviously the non-zero AoA cardboard goes up when I blow on it. But I couldn't build a flat wing that would allow my model to glide.
After the Blues switched to the A4 (due to a series of fatal accidents, more than the fuel issue), the Thunderbirds came to Key West (on Navy Day, no less) to rub the Navy's nose in what their spanking new F4Es could do. This was only two weeks after we had been treated to The Blues first rather tentative public show in their A4s, which I must admit was not very impressive.
I was standing next to a bunch of VF101 F4J instructors and heard the comment: "I fly that airplane every day, and I KNOW it CAN'T do that!!" as the full six plane formation came by in a low speed "dirty pass" with everything hanging, doing a formation slow roll so low that the two wingmen barely cleared the water WITH THE LEADER INVERTED! They even retracted their tailhooks in unison as they passed through inverted right in front of the crowd, to rub it in a little more.
I suspect this was getting back at the Navy for designating Boca Chica's shortest (7400 feet) runway as the active for The 'Birds arrival show, forcing each plane to land singly and take the overrun arresting gear due to their high touchdown speeds. (Navy: 130 kts, AF: 165 kts) No fancy formation landings in Navy Country! They floated 1/3 runway length just flaring for landing! VF101 always planted their birds in front of the initial arresting wire, which was half a carrier deck (500 feet) from the runway threshold. If you "flew the ball", that's where it would put you. Us flying club types used to get a kick out of flying the ball.
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Your cardboard is too stiff and heavy and your relative wind (your breath) isn't strong enough. Try a facial tissue or a piece of toilet paper and see what happens.
If your cardboard is hanging straight down and you're blowing horizontally across the top of it, of course it won't come up, because your airflow is "stalled", not laminar. The angle of attack of your breath relative to the cardboard or facial tissue needs to be no more than 10 or 15 degrees. Try resting the far end of your cardboard or tissue on a table top and raising the end you're holding just two or three centimeters above the table, and blow over it.
Try this. Use your light, stiff material for the bottom surface of your wing and cut ribs of some very light, stiff material to your desired airfoil shape and glue them to the top surface of your wing bottom. Now glue some kind of light, strong, flexible material such as tissue tracing paper over the curved top surface of your ribs. You have now created a wing. If you can get some thin sheets of balsa wood, it would be ideal for making ribs and making your flat bottom, or even an undercambered one, which will perform better in a glider. Be sure your glider balances at about 1/3 of the chord dimension of your wing. Good luck.
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Unless you're a certified dwarf, your helmet-to-canopy clearance in the A4 is pretty minimal. It gets pretty narrow above shoulder height, and "headbanging" is a pretty common occurrence. Ever notice the canopy similarities between the Douglas X3, the Douglas F4D, and the Douglas A4? Ed Heineman loved that A-frame style greenhouse.
You see, I also like the idea of a flat wing because it doesn't require any ribs.
This time I made a "glider" that had a slightly convex airfoil. Of course, it was possible because the model was made of thick paper. On the front it had a ballast made of coins placed between the nails.
model-paper
The model had some gliding ability, but the flight distance was rather short.
MIflyer
1st Lieutenant
Okay, to do experiments like that you are going to have to build yourself a wind tunnel. Simple - but you'll have to figure out how to hang the airfoil in a manner that will not impede either the lift or the drag - and that part ain't. The US put the wing in the tunnel upside down, making it much easier to measure the lift, since you did not have to both suspend it and measure the lift acting upward. When Fred Weick went to Germany in the late 1930's the Germans asked him about that. He told them it was a tough problem that NACA was struggling with as well. He did not tell them about putting wing sections in upside down.
I saw the Birds in the F-4's twice, I think. The best time was at Aiken, SC, where they performed right over the airfield. You could look right up into the burners of the F-4's when they did a straight up climb for the bombburst. That was just before they put restrictions on flying over the crowd.
I'm not that desperate (and so rich). Anyway, I believe in this phenomenon because I can see that the spray gun is working. The very fast airflow sucks paint from the tank below.
When I look at the drawing you posted, I have the impression that this FOWLER FLAP is the best, because the wing still has an "even" shape, in a sense, this flap "enlarges" the wing. It looks nice.
If I understand you correctly, your plane on the runway has zero AoA and zero lift. And during the flight?
