# Laminar Flow Control



## Zipper730 (Jun 15, 2020)

This is quite fascinating: There was research into this as early as 1941?

https://www.nasa.gov/centers/dryden/pdf/88792main_Laminar.pdf


----------



## tyrodtom (Jun 15, 2020)

There was research before 1941.
Remember the NA-37 ( what developed into the P-51) first flew on October 40, so there was research out there before that.

error, that's NA-73.

Reactions: Like Like:
1 | Like List reactions


----------



## swampyankee (Jun 15, 2020)

The idea of sucking away a turbulent boundary layer predates 1935 (see Schrenk, O, "Experiments with suction-type wings", Aug 1935 originally published as "Versuche mit Absaugeflugeln," Luftfahrtforschung. Vol. 12, No. 1, pp. 10-27, March 28, 1935.  https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930094644.pdf This is one of many examples of aeronautics' internationalism before WW2) or look at this list: NASA Technical Reports Server (NTRS)

Reactions: Like Like:
1 | Agree Agree:
1 | Like List reactions


----------



## Odoaker (Nov 24, 2020)

Can someone explain to me in a simple way how a laminar wing lifts an airplane? I always thought an airplane wing had to be convex at the top and flat at the bottom. This causes a difference in air velocity at the top and bottom. And that causes the pressure difference. But when I look at the P-51 wing, I have the impression that it is equally convex at the top and bottom. See figure: 

http://historynet.com/wp-content/uploads/2015/07/air_flow.jpg


----------



## pbehn (Nov 24, 2020)

Odoaker said:


> Can someone explain to me in a simple way how a laminar wing lifts an airplane? I always thought an airplane wing had to be convex at the top and flat at the bottom. This causes a difference in air velocity at the top and bottom. And that causes the pressure difference. But when I look at the P-51 wing, I have the impression that it is equally convex at the top and bottom. See figure:
> 
> http://historynet.com/wp-content/uploads/2015/07/air_flow.jpg


Just the angle of attack generates lift.

Reactions: Agree Agree:
1 | Like List reactions


----------



## tomo pauk (Nov 24, 2020)

Paging 

 drgondog
...


----------



## drgondog (Nov 24, 2020)

The NAA/NACA 45-100 airfoil has camber also but the first statement above is correct - positive AoA generates the lift/pressure distribution


----------



## Odoaker (Nov 24, 2020)

pbehn said:


> Just the angle of attack generates lift.



Unfortunately, I still don't understand how it works. Where does the pressure difference over the wing and under the wing come from?


----------



## tyrodtom (Nov 24, 2020)

Just roll your car window down, at speed, stick your hand out the window at a angle.

Then you'll have some understanding how the angle of attack can generate lift .

Reactions: Like Like:
1 | Agree Agree:
1 | Like List reactions


----------



## pbehn (Nov 24, 2020)

Odoaker said:


> Unfortunately, I still don't understand how it works. Where does the pressure difference over the wing and under the wing come from?


The speed of the aircraft, as trodom posted, try holding a piece of card out of a car window at 45degrees. A plane like a P-51 is doing circa 100MPH at take off at normal flying speeds around 300MPH you get a lot of lift from a small angle of attack. When I was a kid some of my friends had static line aircraft, some were just a thin and narrow plywood board with a prop and motor, the "wing" had no aerofoil shape at all, not even pointed leading and trailing edges.


----------



## BiffF15 (Nov 24, 2020)

Odoaker said:


> Unfortunately, I still don't understand how it works. Where does the pressure difference over the wing and under the wing come from?



The distance over top of the wing is great than the difference under it. With symmetric airfoils via AoA.

How do symmetrical airfoils generate lift?


----------



## Odoaker (Nov 25, 2020)

tyrodtom said:


> Just roll your car window down, at speed, stick your hand out the window at a angle.
> 
> Then you'll have some understanding how the angle of attack can generate lift .



When I was a kid I used to think that this is how an airplane wing works. But then in school during the lesson I heard that the "lift" of the plane is the result of the difference in airspeed over the wing and under the wing. And that for the same reason a strong wind lifts the roofs of houses (because they are convex at the top). So ... something must be wrong with school education.


----------



## Odoaker (Nov 25, 2020)

pbehn said:


> The speed of the aircraft, as trodom posted, try holding a piece of card out of a car window at 45degrees. A plane like a P-51 is doing circa 100MPH at take off at normal flying speeds around 300MPH you get a lot of lift from a small angle of attack. When I was a kid some of my friends had static line aircraft, some were just a thin and narrow plywood board with a prop and motor, the "wing" had no aerofoil shape at all, not even pointed leading and trailing edges.



I always thought that was how a rocket's "fins" worked. The rocket cannot change the direction of flight because it "wants" to have the lowest possible resistance in flight. And these "fins" force it - as long as the rocket is flying very fast. But the wings of an airplane - as they taught me in school - are quite a different matter than the "fins" of a rocket.


----------



## Odoaker (Nov 25, 2020)

BiffF15 said:


> The distance over top of the wing is great than the difference under it. With symmetric airfoils via AoA.
> 
> How do symmetrical airfoils generate lift?



"the exiting airstream is deflected downwards." - it reminds me more of a rocket fin or elevator fin on the tail of an airplane. If I understand this text correctly (maybe wrong). George Cayley explained the phenomenon of flight in a different way. Or maybe I get it all wrong.


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> I always thought that was how a rocket's "fins" worked. The rocket cannot change the direction of flight because it "wants" to have the lowest possible resistance in flight. And these "fins" force it - as long as the rocket is flying very fast. But the wings of an airplane - as they taught me in school - are quite a different matter than the "fins" of a rocket.


That depends on the type of rocket, a simple childs rocket using water goes up because of its centre of gravity and the drag of the tail fins. A fire work needs a wooden stick to move the centre of gravity behind the centre of thrust. On a proper rocket like a V2 or Saturn V the thrusters steer the rocket they are adjustable and move based on info from gyroscopes and computers. On the first stage of Saturn V it had 5 rocket motors, the 4 outside steered only the centre motor was fixed. Anything moving very fast has momentum but also has massive forces on it. A Sidewinder missile only has small "wings" but they generate the lift to keep it flying horizontal and turn at up to 25G if required. The wings of early aeroplanes had classic aerofoils using a differential in air pressure to create lift, many airplanes in the supersonic era have wings like a blade.


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> "the exiting airstream is deflected downwards." - it reminds me more of a rocket fin or elevator fin on the tail of an airplane. If I understand this text correctly (maybe wrong). George Cayley explained the phenomenon of flight in a different way. Or maybe I get it all wrong.


With due respect to the great George Cayley, he was writing years ago and was actually discussing gliding, though he did have ideas on propulsion, he could only theorise about it. Cayleys "glider" did not use a cambered aerofoil, there is a replica at "The Yorkshire Museum" picture from wiki


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> When I was a kid I used to think that this is how an airplane wing works. But then in school during the lesson I heard that the "lift" of the plane is the result of the difference in airspeed over the wing and under the wing. And that for the same reason a strong wind lifts the roofs of houses (because they are convex at the top). So ... something must be wrong with school education.


At school they were perhaps teaching the whole subject of relationships between pressure volume and temperature (Boyles Law etc), generating lift by increasing velocity over the top of the wing and therefore reducing pressure is one example of it.


----------



## Odoaker (Nov 25, 2020)

So, in short, the P-51 wing works like flat board outside the window of a fast moving car? OK, but if making a wing is so simple, why before did people get unnecessarily tired and make more complicated wings? If an engine and a simple board are enough ... ?


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> So, in short, the P-51 wing works like flat board outside the window of a fast moving car? OK, but if making a wing is so simple, why before did people get unnecessarily tired and make more complicated wings? If an engine and a simple board are enough ... ?


You are only discussing lift, the other issue is producing lift without producing drag in two structures (wings) that can contain 180 gallons of fuel, 6 machine guns and ammunition and have the beams strong enough to support 9 times weight of the plane when making a tight turn. If you stick a card out of the car window at the same time as pushing your hand up it pushes it backwards, that is the drag. The P-51 wing was incredibly sophisticated and took years of wind tunnel research into plastic flow, pressure gradients and other "stuff" I barely understand about gases and thermodynamics.

Reactions: Like Like:
1 | Agree Agree:
2 | Like List reactions


----------



## Odoaker (Nov 25, 2020)

pbehn said:


> You are only discussing lift, the other issue is producing lift without producing drag in two structures (wings) that can contain 180 gallons of fuel, 6 machine guns and ammunition and have the beams strong enough to support 9 times weight of the plane when making a tight turn. If you stick a card out of the car window at the same time as pushing your hand up it pushes it backwards, that is the drag. The P-51 wing was incredibly sophisticated and took years of wind tunnel research into plastic flow, pressure gradients and other "stuff" I barely understand about gases and thermodynamics.



It is definitely a complicated matter. As I heard, the PZL.37 was used partially symmetrical airfoil by accident and out of necessity. The constructor had to fit the bombs inside the wings. But he was highly skeptical. He believed that an airplane with symmetrical airfoil would fly worse. As it turned out, he flew quite well, but his "father" didn't understand it. So - before that people had to think that symmetrical airfoil was a bad idea. What's more - the Germans captured PZL.37, the Soviets captured PZL.37 and ... they did not copy this idea. And they certainly had smart engineers too.


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> It is definitely a complicated matter. As I heard, the PZL.37 was used partially symmetrical airfoil by accident and out of necessity. The constructor had to fit the bombs inside the wings. But he was highly skeptical. He believed that an airplane with symmetrical airfoil would fly worse. As it turned out, he flew quite well, but his "father" didn't understand it. So - before that people had to think that symmetrical airfoil was a bad idea. What's more - the Germans captured PZL.37, the Soviets captured PZL.37 and ... they did not copy this idea. And they certainly had smart engineers too.


The success of the P-51 wasn't because its aerofoil was symmetrical but because of its contours and point of maximum thickness.

Reactions: Informative Informative:
1 | Like List reactions


----------



## Koopernic (Nov 25, 2020)

Odoaker said:


> Can someone explain to me in a simple way how a laminar wing lifts an airplane? I always thought an airplane wing had to be convex at the top and flat at the bottom. This causes a difference in air velocity at the top and bottom. And that causes the pressure difference. But when I look at the P-51 wing, I have the impression that it is equally convex at the top and bottom. See figure:
> 
> http://historynet.com/wp-content/uploads/2015/07/air_flow.jpg



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.

Reactions: Like Like:
1 | Winner Winner:
1 | Like List reactions


----------



## MIflyer (Nov 25, 2020)

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.

Reactions: Like Like:
1 | Agree Agree:
1 | Like List reactions


----------



## swampyankee (Nov 25, 2020)

One hopes no one is repeating the "Bernoulli effect causes lift."


pbehn said:


> At school they were perhaps teaching the whole subject of relationships between pressure volume and temperature (Boyles Law etc), generating lift by increasing velocity over the top of the wing and therefore reducing pressure is one example of it.



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

Reactions: Agree Agree:
1 | Like List reactions


----------



## drgondog (Nov 25, 2020)

Couple of thoughts,, re: Mustang wing through P-51K (but not the LW F/G/H) - NAA/NACA 45-100 airfoil.


Had 1.29%* Cambe*r 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. 
I cover all of this and more in my new book Appendices - including the development and tools and methods to arrive at the airfoil co-ordinates beginning with
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.

Reactions: Like Like:
2 | Winner Winner:
1 | Like List reactions


----------



## special ed (Nov 25, 2020)

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.

Reactions: Like Like:
1 | Like List reactions


----------



## pbehn (Nov 25, 2020)

swampyankee said:


> 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


Thats why I thought it was part of teaching the basic laws of physics rather than how an aircraft flies.


----------



## Odoaker (Nov 25, 2020)

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."


----------



## pbehn (Nov 25, 2020)

drgondog said:


> Couple of thoughts,, re: Mustang wing through P-51K (but not the LW F/G/H) - NAA/NACA 45-100 airfoil.
> 
> 
> Had 1.29%* Cambe*r 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.
> ...


I knew something like that would happen, back to google.


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> 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."


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.


----------



## Dana Bell (Nov 25, 2020)

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

Reactions: Like Like:
3 | Informative Informative:
1 | Like List reactions


----------



## MIflyer (Nov 25, 2020)

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.


----------



## Odoaker (Nov 25, 2020)

Looks like I opened a Pandora's Box ... Because my question caused an avalanche of higher math and some mysterious words. But, to put it simply: the wings of the Blériot XI could have been quite flat? And symmetrical?


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> Looks like I opened a Pandora's Box ... Because my question caused an avalanche of higher math and some mysterious words. But, to put it simply: the wings of the Blériot XI could have been quite flat? And symmetrical?


If you can get such a wing to warp to provide control.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Nov 25, 2020)

pbehn said:


> 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 ... ?


----------



## Zipper730 (Nov 25, 2020)

Odoaker said:


> When I was a kid I used to think that this is how an airplane wing works. But then in school during the lesson I heard that the "lift" of the plane is the result of the difference in airspeed over the wing and under the wing. And that for the same reason a strong wind lifts the roofs of houses (because they are convex at the top). So ... something must be wrong with school education.


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.

Reactions: Like Like:
1 | Like List reactions


----------



## pbehn (Nov 25, 2020)

Odoaker said:


> 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:
> 
> ...


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.

Reactions: Like Like:
1 | Like List reactions


----------



## Koopernic (Nov 25, 2020)

drgondog said:


> Couple of thoughts,, re: Mustang wing through P-51K (but not the LW F/G/H) - NAA/NACA 45-100 airfoil.
> 
> 
> Had 1.29%* Cambe*r 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.
> ...



You have books? Give me a link please.


----------



## Koopernic (Nov 25, 2020)

MIflyer said:


> 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.



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.


----------



## Odoaker (Nov 26, 2020)

pbehn said:


> 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.



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.


----------



## pbehn (Nov 26, 2020)

Odoaker said:


> 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.


Sorry, I thought you were serious, it seems you are trolling.


----------



## drgondog (Nov 26, 2020)

Koopernic said:


> You have books? Give me a link please.


 
Amazon.com : P-51B Mustang North Americans Bastard Stepchild

Reactions: Winner Winner:
1 | Like List reactions


----------



## Odoaker (Nov 26, 2020)

Zipper730 said:


> After all, how could you fly upside down if AoA didn't matter?.



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.


----------



## MIflyer (Nov 26, 2020)

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.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Nov 26, 2020)

MIflyer said:


> 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.



I understand. It is interesting. I didn't know an airplane could work like this.


----------



## drgondog (Nov 26, 2020)

Odoaker said:


> 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.


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.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Nov 26, 2020)

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?


----------



## tyrodtom (Nov 26, 2020)

I realize you're not a pilot or a engineer. 
But I wonder what you thought process is for starting out the test with the model in a vertical dive ?


----------



## pbehn (Nov 26, 2020)

tyrodtom said:


> I realize you're not a pilot or a engineer.
> But I wonder what you thought process is for starting out the test with the model in a vertical dive ?


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.


----------



## Simon Thomas (Nov 26, 2020)

...


tyrodtom said:


> I realize you're not a pilot or a engineer.
> But I wonder what you thought process is for starting out the test with the model in a vertical dive ?


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.

Reactions: Bacon Bacon:
1 | Funny Funny:
1 | Like List reactions


----------



## Odoaker (Nov 27, 2020)

tyrodtom said:


> I realize you're not a pilot or a engineer.
> But I wonder what you thought process is for starting out the test with the model in a vertical dive ?



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.


----------



## XBe02Drvr (Nov 27, 2020)

Odoaker said:


> .. 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.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Nov 27, 2020)

XBe02Drvr said:


> 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.



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?


----------



## XBe02Drvr (Nov 27, 2020)

Odoaker said:


> But difference in airspeed over the wing and under the wing was really not necessary at all?


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?

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Nov 27, 2020)

XBe02Drvr said:


> 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.


----------



## Odoaker (Nov 27, 2020)

XBe02Drvr said:


> I curvature (camber) IS necessary for lift, .



So how to understand this story? This "ordinary plywood" used by Heiniman probably had no curvature? 



MIflyer said:


> 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.
> 
> ...


----------



## Dana Bell (Nov 27, 2020)

The important part is that Heiniman rounded off the leading edge - at a normal angle of attack, all lift is generated forward of the wing's maximum thickness. Aft of that point, the wing exists only to reduce pressure drag.

Cheers,



Dana


----------



## Simon Thomas (Nov 27, 2020)

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.

Reactions: Like Like:
2 | Like List reactions


----------



## Odoaker (Nov 27, 2020)

Dana Bell said:


> The important part is that Heiniman rounded off the leading edge - at a normal angle of attack, all lift is generated forward of the wing's maximum thickness. Aft of that point, the wing exists only to reduce pressure drag.
> 
> Cheers,
> 
> ...



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.)


----------



## Koopernic (Nov 27, 2020)

Odoaker said:


> 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.)



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.


----------



## Husky (Nov 27, 2020)

How is lift produced?


----------



## MIflyer (Nov 27, 2020)

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.

Reactions: Informative Informative:
1 | Like List reactions


----------



## XBe02Drvr (Nov 28, 2020)

XBe02Drvr said:


> curvature (camber) IS necessary for lift


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.


Odoaker said:


> 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?


Yes, that is a stall.



Odoaker said:


> 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.


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.

Reactions: Like Like:
1 | Like List reactions


----------



## ThomasP (Nov 28, 2020)

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.


----------



## Odoaker (Nov 28, 2020)

ThomasP said:


> A lot of the paper airplane examples use flat wings .



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?




Edit:

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.



MIflyer said:


> 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.



But these elements were probably not used during the flight?


----------



## ThomasP (Nov 28, 2020)

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.

Reactions: Like Like:
1 | Like List reactions


----------



## MIflyer (Nov 28, 2020)

"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.


----------



## Odoaker (Nov 28, 2020)

ThomasP said:


> 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.



MIflyer said:


> " The leading edge slats might be used during hard maneuvering, such as in air combat. The flaps, probably not.



So, during the flight, where did the lift come from?


----------



## pbehn (Nov 28, 2020)

Odoaker said:


> I get the impression that a model made of heavier materials needs a bigger lift.


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).


----------



## XBe02Drvr (Nov 29, 2020)

Odoaker said:


> But these elements were probably not used during the flight?


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.



MIflyer said:


> The leading edge slats might be used during hard maneuvering, such as in air combat. The flaps, probably not.


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.



Odoaker said:


> So, during the flight, where did the lift come from?


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.

Reactions: Like Like:
1 | Like List reactions


----------



## MIflyer (Nov 29, 2020)

XBe02Drvr said:


> 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.



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.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Nov 29, 2020)

MIflyer said:


> 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 .



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.


----------



## XBe02Drvr (Nov 29, 2020)

MIflyer said:


> 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.


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.


----------



## XBe02Drvr (Nov 29, 2020)

Odoaker said:


> 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.


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.





Odoaker said:


> 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.


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.


----------



## XBe02Drvr (Nov 29, 2020)

MIflyer said:


> 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.


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.


----------



## Odoaker (Nov 29, 2020)

XBe02Drvr said:


> 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.



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 (Nov 29, 2020)

Odoaker said:


> 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.



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.


----------



## Odoaker (Nov 29, 2020)

MIflyer said:


> Okay, to do experiments like that you are going to have to build yourself a wind tunnel .



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.


----------



## Odoaker (Nov 29, 2020)

MIflyer said:


> 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.
> View attachment 603236
> View attachment 603237



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.


----------



## Odoaker (Nov 29, 2020)

MIflyer said:


> 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.



If I understand you correctly, your plane on the runway has zero AoA and zero lift. And during the flight?


----------



## MIflyer (Nov 29, 2020)

Odoaker said:


> If I understand you correctly, your plane on the runway has zero AoA and zero lift. And during the flight?



Give it a little back pressure and up she goes, but the elevator trim is limited to reduce the severity of stalls. It will stall but recovers on its own even if you keep the wheel back, after which it will stall and recover again. And it cannot spin.

_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. _

A Fowler Flap is indeed nice, if rather complicated as well as expensive and heavy.

Reactions: Like Like:
2 | Like List reactions


----------



## Odoaker (Nov 29, 2020)

I modified my model again and used thin sheet steel wings. It is not visible in the photo, but there is a thin sheet of metal underneath that black fabric. I threw the model out the window, it flew about ten meters straight, lowers the flight about half a meter and ended its flight trapped in the branches of a tree. But it's hard to experiment with such a model. The connection of the sheet metal wings to the cardboard fuselage was extremely unstable. To be precise, there was no joint at all, just a sheet of metal was pressed into the gaps in the cardboard. I will make the next model more solidly.








ThomasP said:


> 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.



That's what worries me. My sheet metal wing model was flying straight but for a short distance. I am afraid that over longer distances, he could slow down and fall.


----------



## tyrodtom (Nov 29, 2020)

Back in the 50's when I was a kid they had small wood gliders for 5 to 10 cents.
3 pieces of about 1/8 inch balsa wood.
A fuselage with the vertical stabilizer in one piece, two slots, one for the wing to slide through, and one at the rear for the horizontal stabilizer.
You didn't have to add any weight at the front, you adjusted the CG by sliding the wing back and forth in it's slot .
Later I learned you could add dihedral to the wings by putting hot water on the center, and bending gently.
With properly adjusted wings, with a little dihedral in them, and a gentle launch, you could get some quite long flights even on a slightly gusty day.
I learned soon if you wanted a stable, long, flight. Send it off as close to stable flight as you can.

Your home made glider, IMO, is just way too heavy, for it's small wing spread. 
Even if you do get your stability issues sorted out, your flights are all going to be pretty short.

They probably still make those little balsa wood gliders, though I'll bet they cost a lot more, look online. 
They'll teach you some very small adjustments can make some big differences in flight performance.


----------



## Odoaker (Nov 30, 2020)

tyrodtom said:


> Your home made glider, IMO, is just way too heavy, for it's small wing spread.



But what's heavy about it? Mainly wings. If I make bigger wings, they'll be even heavier.

I can also keep the current wings, but give a smaller, lighter fuselage. Then the wings will be proportionately "larger". But this fuselage is already ultra-light.

I have seen models similar to the one you are talking about. Of course, during my childhood these models were made of some kind of plastic. But for me, the main "challenge" is to make something that glides, not to buy a model in a store. And I would like to make it from "commonly available" materials, and not some rare and unavailable in a normal home. I saw a movie where a guy makes a polystyrene glider model (anyway, terribly over engineered, the guy worked like Mitch Leary). But in my opinion, the polystyrene model is the easiest way. This is how to make a model out of paper. Rather, I mean some elements from old furniture etc.


----------



## Odoaker (Nov 30, 2020)

MIflyer said:


> 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.



How was it with the P-51? When he was standing on the runway or in the hangar, did he have zero AoA or non-zero AoA?


----------



## tyrodtom (Nov 30, 2020)

At least look at those models, you might pick up some tips.
You also could look at some videos of aircraft taking off.

A p-51 is tail dragger, so when it's sitting on the ground it has a very nose up AoA. so it accelerates down the runway until the tail provides enough lift to lift the tail to a near neutral AoA, then it accelerates to flying speed , gently dips it's tail to a slightly nose up AoA, and it lifts off.

Reactions: Like Like:
1 | Like List reactions


----------



## MIflyer (Nov 30, 2020)

Yes, taildraggers have even been described as airplanes with "Take Off Gear" since when sitting on the runway the angle of attack is already positive. Tricycle gear airplanes have "landing gear" because in that three point attitude they tend to want to stay on the ground, although some much more so than others.


----------



## Odoaker (Nov 30, 2020)

tyrodtom said:


> At least look at those models, you might pick up some tips.
> You also could look at some videos of aircraft taking off.



I saw, but still do not know, whether a flat wing with a slight non-zero AoA will work. Of course, I believe that in a military jet it can work because a powerful engine will give a lift with a small AoA (without stalling). And, perhaps, in some absurdly light model at low speed, this will also be the case. The model can weigh so little that a minimal lift force will lift it. But I am thinking of a model made of something like a plastic ruler.



tyrodtom said:


> so it accelerates down the runway until the tail provides enough lift to lift the tail to a near neutral AoA, then it accelerates to flying speed...



And during this acceleration, what is the AoA? If the pilot didn't do anything (besides just keeping speed), the plane would be traveling on the runway "forever"?


----------



## MIflyer (Nov 30, 2020)

Most taildraggers will fly off the runway when it gets going fast enough. Tri-gear airplanes might or might not.

Reactions: Like Like:
1 | Like List reactions


----------



## Reluctant Poster (Nov 30, 2020)

Incorrect Lift Theory

Wings do not simply rely on Newton’s Third Law. 
Lift from Flow Turning


----------



## tyrodtom (Nov 30, 2020)

Odoaker said:


> I saw, but still do not know, whether a flat wing with a slight non-zero AoA will work. Of course, I believe that in a military jet it can work because a powerful engine will give a lift with a small AoA (without stalling). And, perhaps, in some absurdly light model at low speed, this will also be the case. The model can weigh so little that a minimal lift force will lift it. But I am thinking of a model made of something like a plastic ruler.
> 
> 
> 
> And during this acceleration, what is the AoA? If the pilot didn't do anything (besides just keeping speed), the plane would be traveling on the runway "forever"?


 
Near neutral, about 0 AoA. Less drag .
The pilot is not just keeping speed, he's accelerating.

You really need to watch some videos.


----------



## Odoaker (Nov 30, 2020)

tyrodtom said:


> The pilot is not just keeping speed, he's accelerating. .



Of course, but I was talking about the theoretical situation: the pilot draws maximum power from the engine, the plane accelerates to the maximum, but the pilot does not lift his nose up.


----------



## tyrodtom (Nov 30, 2020)

Odoaker said:


> Of course, but I was talking about the theoretical situation: the pilot draws maximum power from the engine, the plane accelerates to the maximum, but the pilot does not lift his nose u



I don't understand what you're asking.
The pilot either lifts the nose to a slightly positive AoA, or he runs off the runway into the bushes. 
He'd have to do it deliberately, because the faster the aircraft goes, the less he'd have to lift the nose to climb.


----------



## gumbyk (Nov 30, 2020)

I think one of the problems here is that you are wanting a 'one size fits all' answer, when there isn't one. I've flown tricycle aircraft that would run off the end of the runway if you didn't do anything, and I've flown them that would happily get airborne by themselves. If in the landing configuration there is enough of an angle of attack that there is some lift then it will fly, if there isn't, then it won't.
Likewise, there are tail-wheel aircraft that won't fly unless you lift the nose, either due to lack of power to accelerate to flying speed, of the fact that the wing is stalled in the three-point configuration. The Tiger moth will barely get airborne.

As for flat plates - take a look at the tailplane of a cub ,or Tiger - no aerofoils there


----------



## Odoaker (Nov 30, 2020)

tyrodtom said:


> I or he runs off the runway into the bushes.



This is the scenario I asked about. You see, earlyer I thought it was impossible at all, because every plane has a Clark Y airfoil and if it starts going fast on the runway then it MUST be a lift (even if the pilot is dead). And now I know that I was wrong because:



gumbyk said:


> I. I've flown tricycle aircraft that would run off the end of the runway if you didn't do anything



The second thing:



tyrodtom said:


> As for flat plates - take a look at the tailplane of a cub ,or Tiger - no aerofoils there



Honestly, I wasn't expecting a convex on the tail at all. I thought the tail of the plane is kind of medieval war dart (with the difference that, of course, the rudder and elevator are movable). But I wonder if it is possible a flat "main wing" - as in this picture:

http://www.ericbrasseur.org/glider_physics_28.gif

The author of this drawing seems to think it might work. BUT the weight and speed of this "airframe" are not given. When I made such a model with a flat plastic ruler as a wing - I did not notice any lift.


----------



## Odoaker (Nov 30, 2020)

tyrodtom said:


> Your home made glider, IMO, is just way too heavy, for it's small wing spread.



Thanks for the advice. This time I made such a model and the effect was quite good. The wing spread is proportionally larger here. So a flat ruler can, to some extent, act as a wing. I have the impression that AoA was greater here than in the Internet project. But despite this, the model flew very correctly without a stall. Perhaps during the flight the tail rose higher and the nose dropped lower, and therefore the AoA was smaller. It should also be noted that this ruler is not perfectly flat. It has a light convex, although of course a lot less than the Clark Y.


----------



## XBe02Drvr (Dec 1, 2020)

Odoaker said:


> perhaps, in some absurdly light model at low speed, this will also be the case. The model can weigh so little that a minimal lift force will lift it. But I am thinking of a model made of something like a plastic ruler.


If you're trying to make a hand launch glider to fly at hand launch speeds, weight is your enemy. "Absurdly light" is a basic requirement. I spent most of my teen years building flying models, including many gliders, ranging from 20 CM wingspan hand launch featherweights to 2 and 3 M tow launched and slingshot launched big gliders. These were all built out of balsa wood, most framed and covered with tissue paper, but some (including up to 2 M) with solid balsa wings formed by gluing flat pieces together at an angle and sanding them to a cambered airfoil shape. These solid wing gliders did not perform as well as the balsa frame and tissue paper ones, because they glided faster and at a steeper down angle than the built-up ones, but they were more durable in the inevitable collisions with trees, buildings, and the earth itself. I got a lot of exercise chasing after some of the larger balsa and tissue "floaters", as they would sometimes catch thermals and gain altitude, extending the glide while the breeze carried them away. One of them landed on the hood of a school bus that was stopped to let a few kids off, startling the driver.
What I learned:
WEIGHT IS YOUR ENEMY!
WING CAMBER IS NECESSARY.
CoG LOCATION IS CRITICAL.
IT'S ALL ABOUT LIFT/DRAG.
THE HEAVIER IT IS, THE FASTER IT GLIDES.


----------



## Odoaker (Dec 1, 2020)

XBe02Drvr said:


> If you're trying to make a hand launch glider to fly at hand launch speeds, weight is your enemy. "Absurdly light" is a basic requirement. I spent most of my teen years building flying models, including many gliders, ranging from 20 CM wingspan hand launch featherweights to 2 and 3 M tow launched and slingshot launched big gliders. These were all built out of balsa wood, most framed and covered with tissue paper, but some (including up to 2 M) with solid balsa wings formed by gluing flat pieces together at an angle and sanding them to a cambered airfoil shape. These solid wing gliders did not perform as well as the balsa frame and tissue paper ones, because they glided faster and at a steeper down angle than the built-up ones, but they were more durable in the inevitable collisions with trees, buildings, and the earth itself. I got a lot of exercise chasing after some of the larger balsa and tissue "floaters", as they would sometimes catch thermals and gain altitude, extending the glide while the breeze carried them away. One of them landed on the hood of a school bus that was stopped to let a few kids off, startling the driver.
> What I learned:
> WEIGHT IS YOUR ENEMY!
> WING CAMBER IS NECESSARY.
> ...



You're right about everything you write, but I'm still trying to get the ruler and other items found in my desk to glide  I know there will be no "best" flying structures possible. The last model thrown (rather gently, not at high speed) from a height of 10 meters flew some 30 meters ahead and landed quite gently. I estimate that the pilot had a chance to survive the landing without any broken legs, although there were of course 4 nails in the role of the "pilot".

BTW BV40 is just an interesting "glider"! The pilot is surrounded by steel armor. Landing speed: 125 km / h. You think something like this could land in a field or a meadow?


----------



## Odoaker (Dec 1, 2020)

MIflyer said:


> Give it a little back pressure and up she goes, but the elevator trim is limited to reduce the severity of stalls. It will stall but recovers on its own even if you keep the wheel back, after which it will stall and recover again. And it cannot spin.



And how do pilots solve the problem of changing the center of gravity? I mean, when some extra passenger takes a seat behind your back.


----------



## MIflyer (Dec 1, 2020)

Odoaker said:


> And how do pilots solve the problem of changing the center of gravity? I mean, when some extra passenger takes a seat behind your back



You use the trim for level flight adjustments. And if you do the CG calculations and the passengers put you outside the allowed envelope, you do not let them get in the airplane.

Actually, Aft CG is better for efficiency. The tailplane provides Negative Lift to counterbalance the Positive Lift provided by the wing. Moving more weight aft decreases the amount of Negative Lift required to keep the airplane balanced. The bad news is that Aft CG is much more likely to cause the airplane to stall and spin and be unrecoverable.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Dec 1, 2020)

MIflyer said:


> You use the trim for level flight adjustments. And if you do the CG calculations and the passengers put you outside the allowed envelope, you do not let them get in the airplane.
> 
> Actually, Aft CG is better for efficiency. The tailplane provides Negative Lift to counterbalance the Positive Lift provided by the wing. Moving more weight aft decreases the amount of Negative Lift required to keep the airplane balanced. The bad news is that Aft CG is much more likely to cause the airplane to stall and spin and be unrecoverable.



In some TV program they said that during World War I - in two-seater airplanes - the pilot flying alone had to take a sandbag as ballast. Then the designers changed the pilot's seat and the problem was solved. Can you explain to me what this is about?


----------



## MIflyer (Dec 1, 2020)

Never mind WWI, in the J-3 Cub the pilot has to fly from the back seat if there is no passenger. So that's not unusual.


----------



## tyrodtom (Dec 1, 2020)

Odoaker said:


> In some TV program they said that during World War I - in two-seater airplanes - the pilot flying alone had to take a sandbag as ballast. Then the designers changed the pilot's seat and the problem was solved. Can you explain to me what this is about?



You've got it backwards.
In early WW1, most 2 seat aircraft had the pilot in the rear, the observer was ( with a gun maybe) in the front.
That way if the pilot had to do no CG adjustments, if he flew solo, because the front seat was at the approximate CG.
But I'm sure you can see the problem with the observer up front , right under the wing where all the support struts are.
A bad combination when trying to shoot a MG.
So they eventually got smart, put the pilot up front, the observer in the rear, where he had a better location for using a gun.
But these early aircraft didn't have a adjustable stabilizer to compensate for a changed CG. So the aircraft with the pilot in the front had to add weight to the rear if they flew solo.
Look at a early WW1 BE-2, most had the pilot in the rear, late war BE-2s and most other 2 seater aircraft had the positions changed.

Reactions: Like Like:
1 | Like List reactions


----------



## pbehn (Dec 1, 2020)

MIflyer said:


> You use the trim for level flight adjustments. And if you do the CG calculations and the passengers put you outside the allowed envelope, you do not let them get in the airplane.
> 
> .


Ive been on a few flights in small aircraft (Short Skyvan type) where passengers have been asked to move from the rear to the centre.


----------



## gumbyk (Dec 1, 2020)

Odoaker said:


> In some TV program they said that during World War I - in two-seater airplanes - the pilot flying alone had to take a sandbag as ballast. Then the designers changed the pilot's seat and the problem was solved. Can you explain to me what this is about?


Most ww1 aircraft that I've seen didn't have any form of trim system, so the elevator authority was limited. During ww1 this wasn't a problem, as the only time you'd be flying a two seater aircraft alone would have been ferrying it, or a test flight.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Dec 2, 2020)

MIflyer said:


> You use the trim for level flight adjustments. And if you do the CG calculations and the passengers put you outside the allowed envelope, you do not let them get in the airplane..



So another question. It has always interested me. How do pilots solve the ice problem on the windscreen inside the cabin? As a driver, I know that the ice outside is less of a problem - you can cover the windscreen with a fabric or use different substances. But inside the car, that's impossible (these substances smell a lot and drip onto the inside). And pilots must have some solution to this problem, because in war movies they often (after an alarm) run to the plane and have clean windows, no ice.


----------



## tyrodtom (Dec 2, 2020)

About any military aircraft has a ground crew, crew chief, etc.
Guess who cleans the windows, and a thousand and one other tasks on the aircraft to keep it mission ready ?
And once he's airborne, most aircraft meant for high altitude flight has very good defrost systems.


----------



## Odoaker (Dec 2, 2020)

tyrodtom said:


> About any military aircraft has a ground crew, crew chief, etc.
> Guess who cleans the windows, and a thousand and one other tasks on the aircraft to keep it mission ready ?



I have no doubts - when it comes to planned missions. But it's hard for me to imagine that there is always someone sitting in the cabins at the airport scraping ice from the windows. There must be some other "smarter" way here. And what does the owner of a private plane do? Also scratches the ice inside the windscreen and the ice falls on his seat? No, that's too stupid. There must be some wise solution to this problem. Additionally, my guess is that the windscreen in airplanes can be "a bit" more expensive and complicated than in a car and such an expensive glass must not be scratched with a tool (even some car owners find it too risky).


----------



## tyrodtom (Dec 2, 2020)

I'm not sure you're reading my whole answer.
Nobody scraps ice off plexiglas windows.

I've never owned a private plane, but I have rented them.
If the weather is so bad you're having a hard time getting the aircraft ready to fly, you probably shouldn't even be thinking of taking it off the ground.
Because once you're airborne it's likely to get worse.
A lot of people have died ignoring that fact.


----------



## MIflyer (Dec 2, 2020)

Odoaker said:


> How do pilots solve the ice problem on the windscreen inside the cabin?



In a typical jet aircraft. hot, high pressure bleed air is taken from the compressor section of the engine, cooled by running it through a heat exchanger that uses ram air from outside, and then expanded through a cooling turbine to produce cold air. The aircrews then mix in some of the still hot bleed air to attain a suitable cockpit temperature. Typically, after the cold air comes out of the cooling turbine it is run through a water separator, which is kind of like a perforated funnel with a cotton sock over it.

Now, how does that prevent the canopy from fogging up when the aircraft descended to lower altitudes? Well, sometimes it does not, the F-4 being an example. This was surprising considering that the F-4 is unique in that it has two air conditioning packs, one for avionics and one for the cockpit. But the reason it has two is that when they added the 2nd seat and added the Sparrow missiles as the primary weapon the only room they had available was the place where the 20MM guns were supposed to go. Now, the air conditioning system will eventually clear out the moisture, but if you have just turned final "eventually" may be far too long. 

Hot bleed air is also used for rain removal by blowing it across the front of the windshield. I had some "fun" figuring out what was wrong with an F-105 rain removal regulator that would turn into a foghorn when it either needed some special adjustment or we had a technician running the test cell decide to ignore certain set-up details.

On some aircraft they put a very thin layer of gold across the windshield and pass a electric current through it to keep the transparencies warm enough to get rid of any ice.


----------



## gumbyk (Dec 2, 2020)

Odoaker said:


> I have no doubts - when it comes to planned missions. But it's hard for me to imagine that there is always someone sitting in the cabins at the airport scraping ice from the windows. There must be some other "smarter" way here. And what does the owner of a private plane do? Also scratches the ice inside the windscreen and the ice falls on his seat? No, that's too stupid. There must be some wise solution to this problem. Additionally, my guess is that the windscreen in airplanes can be "a bit" more expensive and complicated than in a car and such an expensive glass must not be scratched with a tool (even some car owners find it too risky).



WW1 ground crews were up and about well before pilots, getting the aircraft ready. Ice accumulation on the ground wasn't really too big an issue, it only forms in the presence of visible water vapour (cloud/fog), so if it was forming while you were waiting, you were grounded due to the visibility anyway.

I've never seen ice on the inside of a modern aircraft windscreen, the humidity is generally too low inside the cabin for visible vapour, so no ice. Modern aircraft do have heaters, just like cars and this can normally be redirected onto the screen if needed.


----------



## Odoaker (Dec 2, 2020)

As far as I know the planes of that time (WW1) had open cockpits (only windscreen) so the humid and warm air probably didn't collect inside and it didn't condense on the windscreen. I mean, for example, Bf 109 used in winter.



gumbyk said:


> Modern aircraft do have heaters, just like cars and this can normally be redirected onto the screen if needed



But how fast does the engine warm up and you have warm air? From my experience: after 15 minutes of driving, not earlier. Often, warm air appears when ... you don't need it anymore because you've just arrived at your destination  Maybe during the war they put some kind of electric heater in the cockpit and it was warm all the time? (at least, warm enough that there is no ice inside) ? But where to get electricity for such an electric heater under Stalingrad? Also a weak theory ...


----------



## Odoaker (Dec 2, 2020)

XBe02Drvr said:


> If you're trying to make a hand launch glider to fly at hand launch speeds, weight is your enemy. "Absurdly light" is a basic requirement.



However, I did notice a problem with that light models (made only of thick paper + small metal ballast). They are very sensitive to the wind. They fly nice, but only indoors without wind. There is no point in using them outdoors, as they are in the air for quite a long time, but the flight direction is completely random. How did you solve this problem with your models?


----------



## gumbyk (Dec 2, 2020)

Odoaker said:


> As far as I know the planes of that time (WW1) had open cockpits (only windscreen) so the humid and warm air probably didn't collect inside and it didn't condense on the windscreen. I mean, for example, Bf 109 used in winter.
> 
> 
> 
> But how fast does the engine warm up and you have warm air? From my experience: after 15 minutes of driving, not earlier. Often, warm air appears when ... you don't need it anymore because you've just arrived at your destination  Maybe during the war they put some kind of electric heater in the cockpit and it was warm all the time? (at least, warm enough that there is no ice inside) ? But where to get electricity for such an electric heater under Stalingrad? Also a weak theory ...


It's almost immediate - most light aircraft have the heat exchanger off the exhaust. If your car takes that long to warm up, you need to check the thermostat; I've just done the school run - 4km total, and the car was a operating temp well before I got home.
Honestly, it's not a problem as you seem to think it is. You may get some condensation, but in my experience, even with a good frost on the outside, there isn't ice inside the windscreen.


----------



## tyrodtom (Dec 2, 2020)

There is no way to answer questions accurately with such wide reach.
WW1 ? WW2 ? Civilian aviation ? Military aviation ?

Then to how did they have flight operations in Stalingrad, in the winter .
Everything on the Eastern front was primitive, to start the engines in the cold they erected tents around the engine, and built a fire under them.
Sometimes the Russians thinned their oil with gasoline, set the gas on fire . When done right, in the extreme cold that would only heat the oil up enough to flow and let the engine turn over. When done wrong, as I'm sure it happened sometimes, it resulted in a big fire, and maybe a execution .
Finally the Russians squeezed them down to such a small area, they didn't have room left for aircraft to land.

And then back to a home made model glider ?
And none of it has anything to do with laminar flow control .

You might need to move this out of the technical section to another.


----------



## MIflyer (Dec 2, 2020)

Light aircraft are mostly air cooled, so all that needs to warm up is the thin metal assembly that acts as a jacket around the exhaust manifold. And since they are air cooled they is no water to warm up, either. Note that before takeoff for carburated engines we check to see if the carb heat is working; if it is not working because things have not warmed up enough, you run the engine until it does.

Reactions: Like Like:
1 | Like List reactions


----------



## Odoaker (Dec 2, 2020)

gumbyk said:


> It's almost immediate - most light aircraft have the heat exchanger off the exhaust. If your car takes that long to warm up, you need to check the thermostat; I've just done the school run - 4km total, and the car was a operating temp well before I got home.
> Honestly, it's not a problem as you seem to think it is. You may get some condensation, but in my experience, even with a good frost on the outside, there isn't ice inside the windscreen.



So maybe it's just some particular problem with my car. In fact, the other two cars in my family have this problem less. But I figured it must be a hassle for a pilot when he is ordered to jump on a plane and fly immediately. And I heard a soldier's story about how in his air unit there was suddenly such a training evacuation of all planes. Many of them were completely unprepared to fly, but an order is an order. The idea behind the exercises was that World War III suddenly began and the airport would be destroyed in a moment. The unit that evacuated more planes within the specified time wins.


----------



## gumbyk (Dec 2, 2020)

Odoaker said:


> So maybe it's just some particular problem with my car. In fact, the other two cars in my family have this problem less. But I figured it must be a hassle for a pilot when he is ordered to jump on a plane and fly immediately. And I heard a soldier's story about how in his air unit there was suddenly such a training evacuation of all planes. Many of them were completely unprepared to fly, but an order is an order. The idea behind the exercises was that World War III suddenly began and the airport would be destroyed in a moment. The unit that evacuated more planes within the specified time wins.


As I understand it, aircraft were run up at the beginning of the day by ground crew, to ensure that they were ready to go.

Jet aircraft are a different story, you can just get in, start it and go. Piston aircraft need to be run up to ensure that they are making adequate power.


----------



## Odoaker (Dec 2, 2020)

gumbyk said:


> As I understand it, aircraft were run up at the beginning of the day by ground crew, to ensure that they were ready to go.



I'm afraid not necessarily. The soldier said that the mechanics and pilots were terrified and that some planes had numerous technical problems during take-off - precisely because they were not prepared. But the Soviet command was not worried about the lives of the soldiers. The generals were proud that the planes took off quickly under conditions of total surprise.


----------



## tyrodtom (Dec 2, 2020)

I was stationed at a Seymour Johnson AFB , NC, in 1966, a SAC base.
They would have alerts where all the B-52s and their tankers had to get in the air within a certain specified time limit.
I don't remember what that time limit was.

But when they occurred everybody for miles around knew it.
My barracks was over a mile from the SAC ready pad, when those 12 or so B-52s and a tanker each started up, we had to yell at each other to be heard over the noise.
And in the back of your mind was always the thought , is this just a drill ? or ???.

If it was a drill, they called it off when all the B-52s reached their assigned altitude, and location for refueling.

The tankers would come back first, that's when we'd be sure we weren't all about to become crispy critters.

Just one failure to successfully get all the aircraft in the air within that time limit would at least result in the relief of the squadron commander.'
There were no excuses accepted.

That was how the USAF did it in 1966, I have no idea how the Soviets did it.

Reactions: Like Like:
1 | Like List reactions


----------



## XBe02Drvr (Dec 2, 2020)

Odoaker said:


> There is no point in using them outdoors, as they are in the air for quite a long time, but the flight direction is completely random. How did you solve this problem with your models?


By paying attention to wind direction and areas of probable "lift" from thermals or upslope air movement.
First, I would trim a large (1-2 M wingspan)
glider to fly in a very gentle turn, so that in still air it would circle within 300-500 M of where I launched it.
Second, I would launch from the upwind side of a large open area, so as it circled it would drift into the open area.
Third, I did a lot of running to keep the dang thing in sight when it threatened to liberate itself from my posession. I have retrieved gliders from trees, rooftops, rivers, the tops of parked semi trucks, a barnyard, and a baseball park grandstand. I was a nordic ski racer and jumper and a track and field athlete in high school, so running came naturally.
All that experience in second guessing the behavior of the air became valuable later in life when I became a flight instructor in gliders.

Reactions: Like Like:
1 | Like List reactions


----------



## gumbyk (Dec 2, 2020)

Odoaker said:


> I'm afraid not necessarily. The soldier said that the mechanics and pilots were terrified and that some planes had numerous technical problems during take-off - precisely because they were not prepared. But the Soviet command was not worried about the lives of the soldiers. The generals were proud that the planes took off quickly under conditions of total surprise.


That comes down to the attitude of higher ranks, American and British had ground crews warming the aircraft, as they didn't consider pilots or aircraft an expendable resource.



tyrodtom said:


> I was stationed at a Seymour Johnson AFB , NC, in 1966, a SAC base.
> They would have alerts where all the B-52s and their tankers had to get in the air within a certain specified time limit.
> I don't remember what that time limit was.


The difference between jets and piston engines there. A turbine is happy to go from 0 to full power in as long as it takes to start. A piston engine needs time to warm up.


----------



## pbehn (Dec 3, 2020)

gumbyk said:


> That comes down to the attitude of higher ranks, American and British had ground crews warming the aircraft, as they didn't consider pilots or aircraft an expendable resource.
> 
> 
> The difference between jets and piston engines there. A turbine is happy to go from 0 to full power in as long as it takes to start. A piston engine needs time to warm up.


In the UK in the BoB there was no such thing as an unexpected raid. There were some cases where planes were caught on the ground, or were taking off as the raid took place but the aircraft and pilots were ready to go from sunrise.


----------



## Odoaker (Dec 3, 2020)

tyrodtom said:


> I was stationed at a Seymour Johnson AFB , NC, in 1966, a SAC base.
> They would have alerts where all the B-52s and their tankers had to get in the air within a certain specified time limit.
> I don't remember what that time limit was.
> 
> ...



Well, yes, but here's the "problem" - if the planes are to take off safely, they have to be checked somehow - and then the exercises are no surprise. Unless this unit is required to be on constant alert. As far as I know, units in the Warsaw Pact were divided into two types: "pact" units were to be able to react quickly. And the rest of the units did not have such readiness, such good discipline, and good equipment.


----------



## Odoaker (Dec 3, 2020)

tyrodtom said:


> And then back to a home made model glider ?
> And none of it has anything to do with laminar flow control .
> 
> You might need to move this out of the technical section to another.



Because the "problem" is that I already found out from you how a symmetrical wing could produce a lift and completely different questions appeared in my head. I would have to open a few other threads to stay organized. But I guess that's my last question at this point, so ...


----------



## Odoaker (Dec 3, 2020)

gumbyk said:


> That comes down to the attitude of higher ranks, American and British had ground crews warming the aircraft, as they didn't consider pilots or aircraft an expendable resource.



I know many examples of how silly the communism was, for example Piper Cub were destroyed because they were "western" and the witnesses should not see them, but this is off-topic.


----------



## XBe02Drvr (Dec 3, 2020)

Odoaker said:


> I know many examples of how silly the communism was, for example Piper Cub were destroyed because they were "western" and the witnesses should not see them, but this is off-topic.


An airplane! Privately owned??! And free to fly anywhere its owner wishes and see what can be seen???!! An existential threat to state security!!! A temptation to thoughtcrime!!!!


----------



## pbehn (Dec 3, 2020)

XBe02Drvr said:


> An airplane! Privately owned??! And free to fly anywhere its owner wishes and see what can be seen???!! An existential threat to state security!!! A temptation to thoughtcrime!!!!


Well someone did land next to Red Square in one, I believe someone did in Berlin too but cant find it in a search. Mathias Rust - Wikipedia


----------



## tyrodtom (Dec 3, 2020)

Odoaker said:


> Well, yes, but here's the "problem" - if the planes are to take off safely, they have to be checked somehow - and then the exercises are no surprise. Unless this unit is required to be on constant alert. As far as I know, units in the Warsaw Pact were divided into two types: "pact" units were to be able to react quickly. And the rest of the units did not have such readiness, such good discipline, and good equipment.


I don't think you've ever been in the military, and you're listening to a lot of rumors.
Maybe things were different in your part of the world, but in my part , and in my time in the military we or they kept a pretty good constant check on their equipment, right down to your boots.
They didn't just set equipment out in a field and hoped it would start when it was needed, I can't imagine any thinking military doing it any other way.

And those SAC alerts were completely random, nobody knew when they would occur.
One time we had them two days in a row, then no more for more than a month.
Good weather, bad weather, daytime, 3 in the morning, you never knew when they would occur.


----------



## pbehn (Dec 3, 2020)

XBe02Drvr said:


> By paying attention to wind direction and areas of probable "lift" from thermals or upslope air movement.
> First, I would trim a large (1-2 M wingspan)
> glider to fly in a very gentle turn, so that in still air it would circle within 300-500 M of where I launched it.
> Second, I would launch from the upwind side of a large open area, so as it circled it would drift into the open area.
> ...


My brother had a set of encyclopedias, one section on aviation had plans on building simple gliders to quite complex ones. The most complex was quite large with a hinge and a spike to locate a launching string. Instead of being thrown it was launched with a tow string like a kite, the string kept the hinge and the main wings in a climb configuration, when the string went slack the wings moved into level flight trim and a cam dropped the string. It all looked great but since there is always more wind here at 50-100ft than ground level it seemed like a great way of donating some balsa and tissue to the next county.


----------



## pbehn (Dec 3, 2020)

tyrodtom said:


> There is no way to answer questions accurately with such wide reach.
> WW1 ? WW2 ? Civilian aviation ? Military aviation ?
> 
> Then to how did they have flight operations in Stalingrad, in the winter .
> ...


It was also extremely cold as not experienced in the West, if you have to drain all fluids every evening from a plane and use heaters on everything to start up, keeping a wind shield ice free isn't really a big issue.


----------



## XBe02Drvr (Dec 4, 2020)

pbehn said:


> Instead of being thrown it was launched with a tow string like a kite, the string kept the hinge and the main wings in a climb configuration, when the string went slack the wings moved into level flight trim and a cam dropped the string.


For my larger gliders I used a tow line or a sort of slingshot consisting of two tent stakes driven in the ground and a ten foot length of flight rubber engaged in a simple L-shaped hook under the glider's CoG. I could get about 250 feet of altitude with a 300 foot line, and due to the wind's low level gradient I usually didn't have to run very much once the glider got 100 feet or so of altitude.
Location of the tow hook was critical. Too far forward, and the glider wouldn't climb very much, and too far aft would cause it to rear up and stall, dropping the tow line at low altitude, usually with impact damage to the forward fuselage and snapping the rubber bands that held the wing on. And yes, I did occasionally donate one to the next county. What the heck, balsa, tissue,and Ambroid were cheap back then.

Reactions: Friendly Friendly:
1 | Like List reactions


----------



## ThomasP (Jan 1, 2021)

re:"And yes, I did occasionally donate one to the next county. What the heck, balsa, tissue, and Ambroid were cheap back then."

LOLOLOL


----------

