The success of the P-51 wasn't because its aerofoil was symmetrical but because of its contours and point of maximum thickness.
Laminar Flow Control
- Thread starter Zipper730
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The upper part of the wings convexness ie it's camber is mainly there to ensure the airflow ie boundary layer doesn't separate. The boundary layer can be laminar(excellent) or turbulent but attached (still very good). So long as it's attached the wing is making ift. A symmetrical biconvex wing with a razor leading edge like used on the Miles M52 will still produce good subsonic lift.
For many years scientists thought that flight would be impossible because the Lift to Drag ratios of planks were just too poor.
Supersonic aircraft tend to have symmetrical wings to avoid uneven shockwave formation.
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MIflyer
1st Lieutenant
Ed Heiniman had a student working on what airfoil to use for the A-4. The kid went off and Heiniman did not hear from him for a number of weeks. He went to see what was going on and found the student doing detailed wind tunnel studies on multiple airfoils, trying to figure out which cross section was best, and getting rather confused. He had a number of different airfoil sections he had run tests on and could not figure out which one was best
Heiniman took a piece of ordinary plywood, cut it to the shape of the A-4 wing, rounded off the leading edge, and had the student run wind tunnel tests.
"How much difference in the results in that plywood and the other sections you tried?" asked Heiniman.
"Not much at all." replied the student.
"Well, there ya go." replied the great designer.
Heiniman took a piece of ordinary plywood, cut it to the shape of the A-4 wing, rounded off the leading edge, and had the student run wind tunnel tests.
"How much difference in the results in that plywood and the other sections you tried?" asked Heiniman.
"Not much at all." replied the student.
"Well, there ya go." replied the great designer.
swampyankee
Chief Master Sergeant
- 4,031
- Jun 25, 2013
One hopes no one is repeating the "Bernoulli effect causes lift."
Probably. A lot of teachers have used the Bernoulli theorem to explain lift. It's a nice story, but it's also wrong. Lift is caused by the deflection of the airflow. You can see this by looking at a different lifting surface: the wing on sail boat, where there is no difference between the length of the trip on the suction and pressure sides
Probably. A lot of teachers have used the Bernoulli theorem to explain lift. It's a nice story, but it's also wrong. Lift is caused by the deflection of the airflow. You can see this by looking at a different lifting surface: the wing on sail boat, where there is no difference between the length of the trip on the suction and pressure sides
drgondog
Major
Couple of thoughts,, re: Mustang wing through P-51K (but not the LW F/G/H) - NAA/NACA 45-100 airfoil.
desired pressure distribution, CM and CL vs AoA
While some small laminar flow properties were achieved (largely by manufacturing processes in fabrication, flush rivets and sealing/priming and sanding leading 40% Chord. the truly dominant values were Low Drag, delayed Mcr and location of shock wave to max T/C which greatly reduced effect of moving CP aft of 25% Chord. The P-51 just didn't have severe pitch down issues at critical Mach.
- Had 1.29% Camber WS 0 through 215, T/C constant 37.2% - then 1.34% at tip chord t tip. The Tip Chord differed in mac TC at 48.01% to mitigate some low speed stall issues.
- T/C at root, WS=0 was 16.13%, tapering to 11.46% at WS=215.
- Geometric twist - total 1 degree 53 minutes 6.43 seconds. + 0.59 minutes 56.46 sec at WS=0; -0.53 minutes 9.7 sec at WS 215.
desired pressure distribution, CM and CL vs AoA
While some small laminar flow properties were achieved (largely by manufacturing processes in fabrication, flush rivets and sealing/priming and sanding leading 40% Chord. the truly dominant values were Low Drag, delayed Mcr and location of shock wave to max T/C which greatly reduced effect of moving CP aft of 25% Chord. The P-51 just didn't have severe pitch down issues at critical Mach.
special ed
2nd Lieutenant
- 5,731
- May 13, 2018
In flying model airplanes, an exact symmetrical airfoil is used for stunt flying because it acts the same upside down as right side up. Fullscale aerobatic airshow aircraft use completely symmetrical airfoils. In models, a flat bottom airfoil is more difficult to make a smooth stable level flight, while a semi symmetrical airfoil still functions well upside down and in upright flight allows the flyer to groove the plane in level flight.
Thats why I thought it was part of teaching the basic laws of physics rather than how an aircraft flies.
I understand the idea that a non-zero angle of attack causes the plane to be lifted up. Indeed, when there is flat cardboard outside the window of a fast moving car, this effect can be achieved. But how is such "wing" different from the tail elevator? I remember the movie about the history of building the Avro Canada CF-105 Arrow. There is a scene where a guy makes a paper plane as a "model". Then I thought: "OK, such a >>plane<< can have wings made of a flat sheet of paper because it is light, gravity does not pull it strongly to the ground, but a real heavy plane is another matter, it must have some lift effect."
I knew something like that would happen, back to google.
It only works at high speed and there is no free lunch. Cant find a picture of an Arrow landing but this is how Concorde landed at approximately 160Kts. it needs a large AoA to generate the lift even at those speeds because it was built to cruise at Mach 2. A paper dart can only hold together at throwing speeds, use an elastic band and it becomes a piece of paper again.
Hi Zipper,
As the other posters have noted, fluid dynamics is a pretty complicated subject. For the best laymen's understanding, I recommend you look up the lectures of Ascher Shapiro on U-Tube. Schapiro was an MIT professor with an amazing ability to put scientific and engineering principles into easy-to-understand terms. His explanation of laminar vs turbulent flow on a golf ball was the first time anything in fluid dynamics made any sense to me. (You might also look for his paperback book Shape and Flow on Amazon.)
Note that the P-51 had what was considered a laminar flow wing, not a laminar flow control wing. Both wings were being developed in the late-1920s, with the laminar flow wing using its shape to delay the onset of turbulent flow, while the LFC wing used a motor and span-wise slots in the upper wing surface to suck down the boundary layer to reduce pressure drag. The most effective use of an LFC wing was the X-21, a heavily modified B-66 flown in the late 1960s.
Anyhow, hope this helps!
Cheers,
Dana
As the other posters have noted, fluid dynamics is a pretty complicated subject. For the best laymen's understanding, I recommend you look up the lectures of Ascher Shapiro on U-Tube. Schapiro was an MIT professor with an amazing ability to put scientific and engineering principles into easy-to-understand terms. His explanation of laminar vs turbulent flow on a golf ball was the first time anything in fluid dynamics made any sense to me. (You might also look for his paperback book Shape and Flow on Amazon.)
Note that the P-51 had what was considered a laminar flow wing, not a laminar flow control wing. Both wings were being developed in the late-1920s, with the laminar flow wing using its shape to delay the onset of turbulent flow, while the LFC wing used a motor and span-wise slots in the upper wing surface to suck down the boundary layer to reduce pressure drag. The most effective use of an LFC wing was the X-21, a heavily modified B-66 flown in the late 1960s.
Anyhow, hope this helps!
Cheers,
Dana
MIflyer
1st Lieutenant
Completely aside from the airfoil effects, separating the boundary layer from the rest of the flow had some important benefits. Note that the P-51 grew an upper lip on its belly intake. The P-38 had a lip added to the side mounted radiators, which improved cooling without reducing radiator size. The P-80 had splitter plates added to the jet intakes, to eliminate duct rumble that came from the boundary layer and outer air mixing in the intake duct, as well as providing a suitable air source for the ECS cooling.
If you can get such a wing to warp to provide control.
The rudder and elevator on the tail are not enough? (maybe you are surprised that I do not understand it, but I rarely fly with planes and only as a passenger, not a pilot)
And another question: if I make such an airplane model:
model-01
... (flat wings, but "enlarged" angle of attack) and mount the engine in it, will it fly correctly? Let's say "the wings" are the center of balance. Of course, I mean "generally correctly", in the sense of: it will take off and move forward ... ?
- Thread starter
- #36
Basically you're dealing with both variables acting together in tandem.
1. A wing without camber can still produce lift as a result of angle of attack: As the angle of attack goes up, the coefficient of lift goes up with it, up until the critical angle of attack is reached (which is where the wing stalls). After all, how could you fly upside down if AoA didn't matter?
2. The shape of the wing has effects on all sorts of things such as the critical angle of attack, the degree of turbulence over the wing under what conditions, what the maximum mach number it can operate at, structural strength, and lift to drag ratio across speed.
I am not a pilot or aviation engineer, there are some who post here as you have seen. The Bleriot XI flyer only had elevator controls on the tips of the rear elevator I doubt if that would give anywhere near enough, would you fly it? Probably would, why not give the wings some dihedral to help self levelling and have them straight with the elevator used to give a small AoA. One aircraft I know was built like your model was the Armstrong Whitworth Whitley - Wikipedia It was good for take off and landing but in level flight meant a nose down attitude which was very draggy.
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You have books? Give me a link please.
One of the more interesting applications of active boundary layer control re air intakes is given in "Secret Messerschmitt Projects". One of the "lightweight emergency fighters" being evaluated in Germany along with the Focke Wulf Ta 183 was known as Messerschmitt P.1011. It was proposed to use a 200hp suction compressor driven of the 1300kg thrust engine to draw of the boundary layer to the side intakes instead of using splitters. They built a half scale model and tested it in a high speed wind tunnel and the results were excellent. It consumed a small percentage of engine thrust but made up for it in lower drag. One big advantage was it hid most of the intakes from the front where gunfire was expected.
It's interesting what you write. Now I am thinking of building such model from chipboard or plywood. In this case, tilting the nose down should not cause a big problem, because "fuselage" is just a flat plate. I wonder if something like this will glide if I drop it from the tenth floor.
