Busting an aerodynamic myth -- Planes don't fly due to Bernoulli Effect

[Arragonis]

Mr Adams...

There is an art, it says, or rather, a knack to flying.
The knack lies in learning how to throw yourself at the ground and miss.
Pick a nice day, it suggests, and try it.
The first part is easy.
All it requires is simply the ability to throw yourself forward with all your weight, and willingness not to mind that it's going to hurt.
That is, it's going to hurt if you fail to miss the ground.
Most people fail to miss the ground, and if they are really trying properly, the likelihood is that they will fail to miss it fairly hard.
Clearly, it is this second part, the missing, which presents the difficulties.
One problem is that you have to miss the ground accidentally. It's no good deliberately intending to miss the ground because you won't. You have to have your attention suddenly distracted by something else when you're halfway there, so that you are no longer thinking about falling, or about the ground, or about how much it's going to hurt if you fail to miss it.
It is notoriously difficult to prise your attention away from these three things during the split second you have at your disposal. Hence most people's failure, and their eventual disillusionment with this exhilarating and spectacular sport.
If, however, you are lucky enough to have your attention momentarily distracted at the crucial moment by, say, a gorgeous pair of legs (tentacles, pseudopodia, according to phyllum and/or personal inclination) or a bomb going off in your vicinity, or by suddenly spotting an extremely rare species of beetle crawling along a nearby twig, then in your astonishment you will miss the ground completely and remain bobbing just a few inches above it in what might seem to be a slightly foolish manner.
This is a moment for superb and delicate concentration.
Bob and float, float and bob.
Ignore all considerations of your own weight and simply let yourself waft higher.
Do not listen to what anybody says to you at this point because they are unlikely to say anything helpful.
They are most likely to say something along the lines of, 'Good God, you can't possibly be flying!'
It is vitally important not to believe them or they will suddenly be right.
Waft higher and higher.
Try a few swoops, gentle ones at first, then drift above the treetops breathing regularly.
DO NOT WAVE AT ANYBODY.
When you have done this a few times you will find the moment of distraction rapidly becomes easier and easier to achieve.
You will then learn all sorts of things about how to control your flight, your speed, your manoeuvrability, and the trick usually lies in not thinking too hard about whatever you want to do, but just allowing it to happen as if it was going to anyway.
You will also learn about how to land properly, which is something you will almost certainly cock up, and cock up badly, on your first attempt.
There are private flying clubs you can join which help you achieve the all-important moment of distraction. They hire people with surprising bodies or opinions to leap out from behind bushes and exhibit and/or explain them at the critical moments. Few genuine hitch-hikers will be able to afford to join these clubs, but some may be able to get temporary employment at them.

[redyaris]

1. The way it was explained to me, back in flight training, is that if you "do the math": calculate the total amount of lift from "accelerated air" (Bernoulli) vs the total amount of lift derived from forcing air down (F=MA), you'll wind up with the same number.

Did the explainer ever do the math?

[dcb]

Yah, this isn't a conspiracy. If you have a curved top wing it will contribute to lift, but pretty much all airplanes have the wing set at a certain angle of attack so it can "redirect" the air downward also.

I expect the contributions from bernoulli create less drag for the lift they create than changing the direction of the airflow. Hence why commuters use asymmetric airfoils, and I don't recall seeing a sailplane with a symmetrical airfoil (they are especially efficient).

Plenty of airplanes however, (i.e. stunt planes) have symmetrical airfoils and fly well rightside up or upside down. Now the angle of attack still makes a bit of bernoulli effect in reality, but air is being directed downward and newton takes it from there.

Having an airfoil also allows a steeper angle of attack without the flow seperating (stalling). So an airplane with just a curved top wing can nose up with less chance of a stall, a stunt plane can nose up or down and not stall (i.e. if (s)he is upside down and shoves the yoke forward)

[KamperBob]

It's worth noting that arched wings are much stronger than flat ones due to curvature. They flap less. Nature exploits curvature in many ways. There is more to learn from birds and fish.

[Joenavy85]

Originally Posted by KamperBob

It's worth noting that arched wings are much stronger than flat ones due to curvature. They flap less. Nature exploits curvature in many ways. There is more to learn from birds and fish.

exactly. it is possible to design a plane that flies solely on the Bernouli Effect, but it would take an immense amount of power to over come the drag of the airfoil design.

[winkosmosis]

I think the main reason the top of wings are usually curved is so flow attaches and stays attaches, then departs with a steeper angle. If the leading edge is razor sharp, air will hit it and never attach unless the angle is really shallow, so it has to be radiused. And then after the leading edge, the slope is shallow and gradually gets steeper so flow can remain attached.



http://scienceray.com/physics/wind-tunnels/

[Joenavy85]

^^^^^^^^What he said

[Quazar]

A factual title for this thread would be, the bernoulli effect isn't the only contributer to a plane flying.

However, it does not change that the bernoulli effect DOES contribute to a plane flying, so it not a MYTH. The fact that the OP has difficutly picturing it is not uncommon, may people have problems with the principal the the FASTER something moves, the less pressure it has, it seems contradictory. However, the speed of the plane, in combination with the redirection of air downward + decreased pressure above it causes it to lift.

If the bernoulli effect was A MYTH, it would take far more power then what is used to lift standard designed aircraft into the air.

[winkosmosis]

Originally Posted by Quazar

A factual title for this thread would be, the bernoulli effect isn't the only contributer to a plane flying.

However, it does not change that the bernoulli effect DOES contribute to a plane flying, so it not a MYTH. The fact that the OP has difficutly picturing it is not uncommon, may people have problems with the principal the the FASTER something moves, the less pressure it has, it seems contradictory. However, the speed of the plane, in combination with the redirection of air downward + decreased pressure above it causes it to lift.

If the bernoulli effect was A MYTH, it would take far more power then what is used to lift standard designed aircraft into the air.

Read the NASA article. The Bernoulli Effect is not what makes the plane fly. The air flows faster over the top of the wing, yes, because of the angle and the downward curve at the rear-- airflow on the bottom is compressed because it hits the underside and slows down relative to the plane. But the air speed difference is a tiny tiny contributor. It's not the majority or even a major portion of lift.

Redirection of flow is what creates lift.

If you know of a plane that can fly at 0 degrees wing pitch, post it.

[dcb]

I'm not quite ready to discount the bernoulli principle as being a significant contributor to lift.

One of my favorite RC sailplanes in my little fleet uses a SD7037 airfoil (pictured below). It is fast and has good penetration upwind (important when you don't have a motor), but it doesn't like slow very much.

But what I want to point out is that here it is drawn in normalized position, the leading and trailing edges are on the 0.00 line. So that when the air splits at the leading edge at this angle of attack, it should "rejoin" at the same exact height at the trailing edge. If there were no bernoulli, this would not create lift.

But it is creating quite a bit of lift. The zero lift angle of attack for the SD7037 is actually -3.29 degrees, meaning you have to lower the leading edge to get this to stop making lift.