Sorry, I thought you were serious, it seems you are trolling.
Laminar Flow Control
- Thread starter Zipper730
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drgondog
Major
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I didn't think it didn't matter. I even read about some plane that had the ability to change the AoA to make it easier to take off from the carrier. But I thought convex is always necessary. Smaller on faster planes, larger on slower ones. In other words, I thought "flat convex airfoil" was the only type of airfoil. When it comes to upside down flights, I thought it was possible because of the powerful engine (same as a rocket can fly "upside down.") But if you are right, the wings can be completely flat and such a structure has some lifting force. I have to check on the model. Of course, the words about the "tenth floor" are a simplification. I mean great height above the ground (not in the city center ...) That's actually all for now. I thank those who wrote the things that were interesting to me.
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MIflyer
1st Lieutenant
The shape of the wing - its cross sectional profile - on my Ercoupe, combined with its angle of incidence as set on the fuselage, means that it goes from no lift to considerable lift with a small amount of change in angle of attack. When properly rigged - and many out there are not - you can go down the runway at full power and the airplane will sit there moving fast, with its wheels on the runway. Pull back on the wheel just a little and .. Zoom! Up you go. On landing it is the same way; you can fly the airplane "in close formation" with the runway, get the wheels on the surface, and chop the power, without fear of it ballooning up. Of course, Th proper way to land it is just like any tricycle gear airplane, MLG on first, and then have the nose come down, applying some brake when the MLG hits if there is some crosswind.
I understand. It is interesting. I didn't know an airplane could work like this.
drgondog
Major
The wing can be flat, but the leading edge should not be square - ever. Boundary layer separation ensues much faster with 'flat' leading edge. Trailing edge should be tapered.
I quickly made a plane model with flat wings and non-zero AoA. I dropped it from the second floor. The effect was this:
model-03
Someone may say, "Well, not bad, before it crashed, he tried to correct the flight!" But theoretically, let's say it was the tenth floor. Even in this scenario, I don't believe in a successful flight. Rather, I expect something like this:
model-04
But - I'm not a pilot, I'm not an engineer, maybe I'm wrong?
model-03
Someone may say, "Well, not bad, before it crashed, he tried to correct the flight!" But theoretically, let's say it was the tenth floor. Even in this scenario, I don't believe in a successful flight. Rather, I expect something like this:
model-04
But - I'm not a pilot, I'm not an engineer, maybe I'm wrong?
To compare to the aviation industry standard of a half house brick. Any human development that doesn't stay in the air longer and/or cover more distance in a horizontal plane than a hand thrown half house brick is a step backwards. Or to add to the millions of internet events that never happened.
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Simon Thomas
Senior Airman
...
That is how a wingsuit operates. There is no reason it can't be analysed with the same rigor as other forms of aeronautics, such as groundhogs.
That's a very good question. I remember that my friend from school had a model of an airplane that, in the same situation, initially dived, but then started to fly horizontally and quite far. It had some ability to "self-stabilize" without remote control devices.
But, yesterday I read this page:
2. Basic Aerodynamics
... and it turns out my teacher at school was probably right (here the author also writes that the wing must have a curvature, because then the air flows faster over the wing and this reduces the pressure). And earlier on this forum other people wrote that this is - if I understand correctly - a misconception about how planes fly.
I know it's a bit confusing, but both statements are actually true: curvature (camber) IS necessary for lift, AND lift is produced by deflecting the air downward, NOT by the so called "Bernouli effect".
The purpose of the curvature is to allow the airflow to stay attached in laminar fashion to the wing top surface as the angle of attack increases as long (in time) and as far back (in distance) as possible with increasing angle of attack before it detaches into turbulent flow (Stall). This requires that the airflow not be asked to turn too sharp a corner, as that is what will detach it. Your flat board with it's square leading edge can't assume much angle of attack before the air just can't bend around the corner any more.
Now let's look at your nice curvaceous airfoil cruising along at a moderate (cruise flight) angle of attack. At the point where the curved leading edge of the airfoil first meets the relative wind there's a stagnation point where the air is split into top surface flow and bottom surface flow. The greater the angle of attack, the further down the curvature of the leading edge this stagnation point moves, and the greater the distance difference between top flowpath and bottom flowpath becomes. This means that at the trailing edge recombination point the higher energy top surface air is going to deflect the newly recombined airflow downward. This is called downwash and produces both lift and drag. The higher the angle of attack, the greater this downwash will be, up to the angle of attack where the top surface airflow can't "make it around the bend" anymore, and delaminates into turbulence, causing a huge increase in drag and loss of lift. This is the CRITICAL angle of attack, and this behavior is called a STALL. The airplane quits flying and becomes momentarily a ballistic object. Gravity sets in and an immediate move to regain control is necessary. Reducing the angle of attack by stuffing the nose down is the antidote to this particular malady. Facing a windshield full of treetops as your stomach floats up into your ribcage is guaranteed to get your attention the first few times, but it has to become an automatic response.
Hope this has made it all a little clearer for you.
So if I make the wing from a flat board and increase the angle of attack, the air above the board will stop flowing "nicely". That's the problem? And the P-51 could fly because its wing was deflecting the air downwards, but the air above the wings still flew "nicely". But difference in airspeed over the wing and under the wing was really not necessary at all?
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The higher energy airflow over the top surface is what deflects the recombined air at the trailing edge at a downward angle, creating downwash and lift. This only happens at a positive angle of attack for a symmetrical airfoil where the top flow path is longer than the bottom one. If AoA is zero, both flowpaths are the same, there is no downward deflection of the air leaving the trailing edge, and no lift is generated.
So yes, higher airspeed over the top surface is necessary to generate lift. Whether this lift is a result of "Bernoulli" or "downwash" is largely a matter of semantics, as both explanations are oversimplifications to explain what happens without diving too deep into fluid dynamics. The downwash explanation seems to be the current preferred choice, as it does a better job of explaining ground effect, the reduction in drag that occurs when a plane flies less than one wingspan height above the ground.
Make sense?
It makes sense, although I would like to install a colored smoke generator above and below such a wing and see what happens to the smoke. The best option: a different color of smoke on the top of the wing and a different color underneath. But your theoretical description also gives me some idea.
So how to understand this story? This "ordinary plywood" used by Heiniman probably had no curvature?
Simon Thomas
Senior Airman
X-Foil is a rather useful tool for seeing what is going on around an aerofoil. https://web.mit.edu/drela/Public/web/xfoil/
For windows, download XFOIL6.99.zip and unzip it into a folder. It doesn't need installation - it can simply run in the folder.
It isn't the most user-friendly software, but it gets easier as you get familiar with it. I am still a novice after more years than i would like to admit.
I took screenshots of the pressure vectors around an NACA 0012 aerofoil (I guess I should say airfoil, but old habits die hard) at 0° and 4°.
To help you get started on x-foil. Run xfoil.exe and then type the following, with an enter after each line. (obviously don't enter the comment)
NACA 0012 [selects symmetrical NACA aerofoil at 12% thick]
OPER [moves to operating point mode]
V 6E6 [uses viscous mode and sets reynolds number to 6E6 - you can use whatever Re you want]
A 0 [calculates performance at an angle of attack of 0 degrees]
CPV [brings up pressure plot as above]
You can try different angles of attack by typing A and then the AoA. It takes negatives.
You can also put in a Cl and it will figure out the AoA. e.g. type C 0.4 and it sets the Cl to 0.4 and works out the AoA
The really interesting part is you can type in VELS and put in the co-ordinates of any point and it gives you the cp, q, u and v at any point. I recommend not looking at a point inside the aerofoil.
Xfoil has a huge number of features for working with aerofoils. The GDES menu allows you to play with the thickness and camber. The MDES menu allows you to smooth out an aerofoil, which is very helpful if you only have a limited number of X/Y points. you can add flaps.
Youtube has some good tutorials on using Xfoil - if you choose poorly you will get some that my 14-y-o made me record for his youtube channel.
For windows, download XFOIL6.99.zip and unzip it into a folder. It doesn't need installation - it can simply run in the folder.
It isn't the most user-friendly software, but it gets easier as you get familiar with it. I am still a novice after more years than i would like to admit.
I took screenshots of the pressure vectors around an NACA 0012 aerofoil (I guess I should say airfoil, but old habits die hard) at 0° and 4°.
To help you get started on x-foil. Run xfoil.exe and then type the following, with an enter after each line. (obviously don't enter the comment)
NACA 0012 [selects symmetrical NACA aerofoil at 12% thick]
OPER [moves to operating point mode]
V 6E6 [uses viscous mode and sets reynolds number to 6E6 - you can use whatever Re you want]
A 0 [calculates performance at an angle of attack of 0 degrees]
CPV [brings up pressure plot as above]
You can try different angles of attack by typing A and then the AoA. It takes negatives.
You can also put in a Cl and it will figure out the AoA. e.g. type C 0.4 and it sets the Cl to 0.4 and works out the AoA
The really interesting part is you can type in VELS and put in the co-ordinates of any point and it gives you the cp, q, u and v at any point. I recommend not looking at a point inside the aerofoil.
Xfoil has a huge number of features for working with aerofoils. The GDES menu allows you to play with the thickness and camber. The MDES menu allows you to smooth out an aerofoil, which is very helpful if you only have a limited number of X/Y points. you can add flaps.
Youtube has some good tutorials on using Xfoil - if you choose poorly you will get some that my 14-y-o made me record for his youtube channel.
I don't understand that. What is "normal" AoA? Where does a lift come from? If that plywood had zero AoA, there was no lift (I think)? If this plywood had non-zero AoA, the airflow over the plywood should be "disturbed" (I think?)
(I would add that the problem is probably not that you write unclearly, but I have to translate it from English into my native language, and aerodynamics is not a conversation about walking in the park with the dog. So - I can sometimes have trouble understanding certain sentences.)
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I wouldn't impute too much on the Heinemann plywood plank story though it is instructive. With a rounded leading edge it's likely the flat plank wing generated good lift and good lift to drag ratios however past a few degrees, say 3 degrees the plank airflow would start to separate and stall. Much of lift would disappear and the drag would go up massively.
A well curved wing would last till about 16 degrees before stall began to develop. If given a slat it might go to as much as 25 degrees. An ultra thin supersonic wing might stall at 12.0 degree but would have less zero lift drag (ie parasitic drag) but be harder to construct and contain little room for fuel.
Laminarity in the boundary layer as opposed to turbulence within the boundary layer doesn't. matter much in terms of lift so long as the turbulent boundary layer average flow is still in the same direction as the wing upper surface. If it thickens too much the average flow separates and no longer follows. Drag goes up, downwash reduces. Laminarity reduces only skin friction drag which is only one aspect of drag.
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