Oh blah blah.. You are trying to say a feather will hit the ground the same time as a lead balloon. I don't think so.

You missed the point completely.

k. explain why an airplane wing stalls if bernoulli is in affect one hundred percent of the time. is lift being produced because of bernoull's effect on a falling coke machine? does not bernoulli's principal requira a laminar flow over the upper surface to lower the pressure the fluid exerts on that surface? when separation of this 'boundary layer' as we call it in the flying business, such as happens during a stall, where does bernoulli apply after the point of separation on the upper surface of the stalled wing????

you're right jeannie. but i'll wait for his explanation of why an airplane wing stalls or how bernoulli's principle suggests that a falling coke machine produces lift without the adhesion of a boundary layer before i comment further. i think you'll agree that bernoulli's effect damn sure does not apply one hundred percent of the time.

Bernoulli gives the mathematical relationship between speed and pressure in an ideal fluid. All airfoils stall, that is part of the relationship. Separation into turbulence is part of the relationship. Spoilers to reduce lift is part of the relationship. It is always combined with kinetic energy.

What does NOT happen is that a bullet would get aerodynamic lift in flight and cause it to stay in flight longer than one simply dropped to the ground... as you posted. You are pretending to understand a topic that you obviously don't understand at all.

And as to the question of the feathers and lead. The density was not given so air resistance isn't a factor. Lead can be foamed to take up much more volume and feathers can be compressed. A pound of lead and a pound of feathers have the same attractive force to the Earth from gravity and will attempt to accelerate to the Earth at the same rate.

Two asteroids in space at the same distance from the Earth will do the same if they are at the same distance from the earth.

All objects at the same distance from the Earth will tend to fall towards it at the same rate minus the DIFFERENT effects of air friction, which in most cases is minimal.

Bernoulli effect does not just describe the lift on an airfoil. It describes the flapping of a flag, the trajectory of a golfball, and the failure of the Washington Tacoma Narrows Bridge.

http://www.youtube.com/watch?v=j-zczJXSxnw

but you said bernoilli is in effect one hundred percent of the time on every object. so what is happening on the upper surface of a wing or any airfoil, flag, feather, coke machine, whatever, after the point of separation of the boundary layer??? you're doing great with wiki, youtube searches and whatnot, now can you simply explain how bernoulli is in effect in that portion of the upper surface of an asymetrical airfoil design during a stall aft of laminar flow disruption??? what goes on behind the spoilers, speed brakes, lift dump devices, that you brought up??? is bernoulli in effect one hundred percent of the time aft of those devices??? how is the speed of the fluid in question, air if we're talking about airplanes, accelerated on the upper surface of a wing if not due to it's adhesion to the upper surface causing it to travel a greater distance from the wing's leading edge to trailing edge than does the air flowing below the wing??? what happens to the air on the upper surface of the wing when spoilers are deployed??? why do you not see spoilers on the bottom of airplane wings??? i've been reaching for the handle that deploys the 'boards' all these decades in vain????? they really don't work to bust up that boundary layer on which bernoulli's principal depends??? ah well, passengers always complained spoilers messed up the ride during descent anyway???



whoa, horsey!!!! you've been saying all along that bernoilli's principle is in effect on every object one hundred percent of the time. so help me understand the topic. is a bullet not affectd aerodynamically in flight or not??? what is the purpose of rifling in a gun barrel??? why would anybody want a bullet to spin on it's way to the target???



you are absolutely, positively and magnificently correct, of course. i indeed do stand corrected. having never actually seen feathers bound to the same density of lead i just assumed that when he talked about dropping feathers from the empire state building he was talking about a simple bunch of feathers. but you set me straight on that, huh?



so the speed of the two asteroids have no effect??? why then have many, many asteroids that make up the van allen belt not impacted earth when others whose origin was not even within our solar system have??? oh, you might say it's all about trajectory i suppose, but then why does every asteroid that comes within the distance of the van allen belt and not on a collision course with earth not enter orbit along with those asteroids that make up the belt? the asteroid is now at the same distance as several asteroids, no? so why does one asteroid pass on through the solar system and continue it's journey and the van allen asteroids are stuck in orbit about the sun??? obviously air friction has nothing to do with it does it??? or does it????



and yet bernoulli's principle does not affect a bullet in flight.... uh huh...

That is a really long post to defend the fact that you got the physics wrong, got it wrong again, and tried to use Bernoulli to cover it up and got Bernoulli wrong in the process.

You went into great detail explaining the aerodynamic effect on a bullet to explain how it holds the bullet in the air and a bullet fired horizontal would stay in the air longer than one simply dropped to the ground at the same height.

For a pilot, you don't seem to know that a bullet doesn't have any wings or any airfoil surfaces to hold it in the air so the fired bullet would simply fall to Earth at the same rate as the one dropped. All your bologna to confuse the issue is apparently to hide the fact that you really don't understand high school physics and made flat wrong statements.

Whatever references I have made to websites is to give you some references to simple high school physics. I don't need them because I studied physics in college.

Bernoulli acts 100% of the time on objects in motion in an ideal fluid. A bullet would have high negative forces on all cylinder surfaces but since the bullet is symmetrical, all of those forces cancel out since they all operate equal and opposite to each other. The force on the front of the bullet would be high and the force on the rear of the bullet would be low causing most of the drag which causes a bullet to slow down during flight. None of these forces keep the bullet in the air one instant longer than the one dropped from the same height.

I could go into parasitic drag, flat plate area, and calculation of drag coefficients from Reynold's numbers but it is beyond the scope of this discussion.

For a pilot, you know less about aerodynamics than most pilots. The guys at the hanger got a good laugh about this yesterday.

As to asteroids in the Van Allen belt? Good grief dude, the Van Allen belt doesn't have ANYTHING to do with asteroids and asteroids don't live there! Are you getting your science from Comic books? That is truly the dumbest discussion of asteroids I have ever heard.

Here are the points I made to correct the "wrong" physics.

Two asteroids passing the Earth at the same distance from the Earth will accelerate towards the Earth at the same rate. Their mass doesn't matter, only the distance from the Earth.

The speed of an asteroid does not affect the pull of gravity. The speed does, obviously, affect the trajectory.

This is the line which is throwing everything off. Terminal velocity can vary based on drag, and drag depends upon surface area and resistance.

I think you meant to say "accelerate", not "fall"....a word you used previously within the post explaining the same idea from a different example.

I missed this little gaff on my first reading....though I read it rather carefully. I was satisfied and agreed with Metalwing's post based on my own understanding. In fact, I was typing my own explanation of Bernoulli's as applied to the feathers and lead, but I deleted it because it was much too wordy.

I used fall and accelerate interchangeably to try to explain the concept better.

If you drop a stone near the Earth it will fall to the Earth.

If you drop a stone near the Earth it will accelerate at 32 ft/second squared towards the Earth.

Both statements mean exactly the same thing and describe the same event.

Yes, but "fall" and "rate" imply they will have the same velocity, which is not necessarily true. Granted, once within the atmosphere, it is more likely to become true at some point (objects tend to disintegrate during descent), but when talking about asteroids and distance, we are also discussing forces within the vacuum of space.

Anyway, it's not a big deal because I got your point in my first reading. I was just hoping to maybe resolve a point of confusion.

As far as Bernoulli's always being present, I also agree. Just because lift is insufficient or zero doesn't mean that it doesn't apply. Bernoulli's Principle is used for more than just flight. It's used in auto design and marine design as well. In 1983, Australia II experimented with a winged keel design to increase maneuverability during The America's Cup. While we may not be talking about generating lift, it is still a matter of the interplay of forces (specifically pressure) as an object moves through a fluid medium, creating increased maneuverability through enhanced stability.

The word "rate" applies to speed, velocity, and acceleration.

The Bernoulli Effect applies to anything in an ideal fluid and it can be positive pressure, negative, or zero, as you said. It is used to calculate pressures on buildings and other structures that have nothing to do with airfoils. An airfoil is simply a structure used to provide lift.

where am i wrong as regards bernoulli?



i went into great detalail explaining aerodynamic effect on a bullet? i don't recall mentioning any details whatsoever in that regard. seems i asked a question about rifling and bullet spin but made no mention of it's effect did i?



ah, so when you said that bernoulli is in effect on all objects one hundred percent of the time in an ideal fluid you meant to say all objects with wings. so let's stick with things with wings if you'd like. i'll ask again rephrasing. if bernoulli's principle involves accelerating a fluid and in doing so decreasing the pressure within that fluid, which is precisely what it does say; and if the means of accelerating air, the fluid in question as regards aerodynamics, is to employ a more curved upper surface of a wing relative to the lower surface requiring the air above the wing to accelerate to a higher velocity than the air below; and it's adhesion to the upper surface makes it travel a longer distance and still meet the lower air at the same time at the trailing edge of the wing; what happens when a wing stalls and the adhesion of the boundary layer departs the upper surface no longer accelerating the fluid thereby no longer lowering the pressure within the fluid? now the pressure above the wing is again equal to the pressure below the wing. no fluid is being accelerated so new drop in pressure. either bernoulii is in effect one hundred percent of the time on all objects or it is not? so forget bullets, coke machines, feathers. let's just talk about your assertion that bernoulli is in affect on airplane wings one hundred percent of the time. or pick a helicopter rotor blade if you'd rather. flew those several thousand hours too. then whe could get into even more issues that have nothing to do with theories of the solar system; issues like why is a stall in an airplane wing most often associated with low speed flight and a blade stall in a helicopter is associated with high speed flight. bring your hangar flying buddies, we'll have a great and humorous time i'll wager.



hey, me too.




yeah, i too get a laugh out of pilots who hang out at hangars explaining aerodynamics. but as none seem to be here, it's just you and me, huh?



ah, but two asteroids can travel on identical trajectories at different speeds no? speed AND trajectory effects, not the pull of gravity, but the effect of gravity on the two astroids.

so you agree with him then that once the boundary layer, or laminar flow, over the uppersurface of a wing is disrupted and no longer adhering to the upper surface bernoulli is STILL in effect? how is the fluid, air in this case, being accelerated over the upper surface if not by the adhesion of air causing the air to travel a longer distance over the upper surface thereby causing it to accelerate if it's going to meet the air below the wing at the trailing edge in the same time span.

when the leading edge of the wing impacted air at whatever airspeed, the air separated some flowing above the wing and some flowing below. that separated air will again meet at the same time at the trailing edge and since the distance the air above must travel over the curved upper surface is longer then to meet at the trailing edge the air must accelerate. that is the essence of bernoulli in a nutshell as regards airfoil aerodynamics. it's the adhesion of air that allows the fluid to accelerate thereby reducing it's pressure. so if you agree that bernoulli is in effect all the time, what makes the air accelerate after the point of separation during a stall?

we could take it even further aerodynamically. thus far we've been discussing asymetrical airfoil shapes. but not all airplane wings and no rotory wings have asymetrical designs. the best aerobatic aircraft often employ symetrical foils as to helicopters. that is precisely why a helicopter does not always fly when the blades are turning. at flat pitch on the ground no lift is being produced because the distance air has to travel from leading edge to trailing edge is the same over the top and bottom of the blade. does bernoulli say that two fluids excelerating equally will cause the pressure in one fluid to drop relative to the pressure in the other? no, of course it doesn't. so how is bernoulli in effect on a rotor blade at flat pitch or zero angle of attack?

Your posts just get goofier and goofier. You could at least look some of this stuff up so you could pretend that you know the material.

The post above is bazaar!

"thus far we've been discussing asymetrical airfoil shapes"

No we haven't. We have been discussing bullets and chunks of rock falling out of the sky. You brought up airfoils as some kind of proof that it (Bernoulli Effects) only applies to airfoils which it most certainly does not. It applies 100% of the time to any object in an ideal fluid. You stated flatly and repeatedly that is only applies to laminar flow which it does not and we certainly have not been discussing asymmetrical airfoil shapes, or any airfoil shapes for that matter.

Then you go off on this weird tangent about helicopter airfoils.
"and no rotory wings have asymetrical designs" That isn't true. Where are you coming up with this crap. I don't need a website to know this but here is a website for you and the other people who don't know.



http://www.pilotfriend.com/training/flight_training/aero/rot_foil.htm

And then you come up with this junk!

"does bernoulli say that two fluids excelerating equally will cause the pressure in one fluid to drop relative to the pressure in the other? no, of course it doesn't."

Bernoulli doesn't deal with two fluids, it deals with any object in an ideal fluid. It doesn't only deal with airfoils. It deals with ANY OBJECT IN AN IDEAL FLUID 100% OF THE TIME! With no motion the pressures are zero. With motion it gives the pressures.

Then you crown your comments with this jewel ...

"so how is bernoulli in effect on a rotor blade at flat pitch or zero angle of attack?"

If an airfoil is at flat pitch the lift (negative pressures) are equalized between the upper and lower surfaces!!!!!! So the net lift is zero.

Duh!

When you present yourself as knowledgeable in science and then post repeated foolish and incorrect remarks in a public forum you are truly doing a disservice. Some people might actually think you know what you are talking about and repeat it.

And BTW, the reason helicopters are not always flying if their blades are turning is because the blades are not providing enough lift to raise the aircraft.

i don't recall my presenting myself as knowledgeable in science, physics, aerodynamics or any other discipline but i won't even bother with the inane personal attacks. i've simply been trying to to participate in a respectful discussion.

you of course have chosen not to participate in the entire discussion as i've not heard your replies to my queries about stalls, lift dump devices, etc. so here's another question that you sparked with your latest post. are the helicpter blades in flat pitch providing any lift whatsoever???? wink backatcha. and if you say bernoulli does not deal with two fluids, how then is the pressure above the wing reduced relative to the pressure below the wing in the asymetrical airfoil you depicted??? are there not two airmasses involved, one above the wing and one below???????????

nice pic btw, used to draw almost the exact same thing while teaching aerodynamics. but a plan view might be helpfull too depicting ALL the airflow over a wing, spanwise flow as well as cordwise flow.

Okay...

The Bernoulli Effect influences drag. Rotation influences drag. The shape and rotation of a bullet reduces air resistance (drag) without necessarily generating lift. The bullet will fly farther, faster, and more accurately than a lead musket ball, given the same powder charge. So, Bernoulli's Principle is actually present in the case of a bullet because Bernoulli states a fluid's pressure will decrease simultaneously with a rise in the fluid's velocity.

Furthermore, with a bullet's oblong shape and tapered tip, the twist rate of the rifling must be precisely calculated for the bullet's size. This is because the twist rate creates a balance of stability and instability of air pressures which allow the bullet to be more accurate (stability) while keep the tip pointed towards the target (instability) rather than up. This means modern bullets must take Bernoulli's Principle into account to prevent tumble (an oblique impact present more initial surface area, and thereby has less penetrating power).

Another example: the dimples on a golf ball.

They change the airflow around the ball to reduce drag, allowing the ball to travel farther and faster. What happens is, the dimples allow turbulent flow to be achieved behind the ball at a lower velocity. Once achieved, the flow is narrower than on a smooth ball, thereby reducing drag. As a further benefit, as the dimpled ball increases velocity, the turbulent flow changes very little meaning drag increases only slightly.

This is just if the golf ball wasn't spinning, but Bernoulli's Law still applies here. The spin of the ball actually does generate lift, bringing a second application of Bernoulli's Principle into play.

Finally, if velocity is zero, fluid pressure remains constant. If velocity rises, fluid pressure will drop accordingly (like a hurricane....low pressure, high winds). If velocity drops, pressure rises (the dog days of summer....Bermuda High, heavy stagnant air). This is all Bernoulli's Law states, but it veritably has a thousand uses and derivations.

all true. but is the bernoulli effect happening aft of the point of separation of laminar flow on an aircraft wing? if the fluid, air in this case, is no longer being accelerated, which it's not as the boundary layer has separated and no longer adheres to the upper surface of the wing, does not airpressure above the wing equalize to the air pressure below the wing? the wing is stalled and still in motion but without the acceleration of air over the upper surface. how is bernoulli in effect without accelerating the fluid?

Nice post.

Because Bernoulli's Law is still affecting air pressures even though lift is not being generated. Flight is only one application that is derived from Bernoulli's Law. Even when movement is zero, Bernoulli's still governs pressure.

Any change in velocity (not acceleration) will cause a change in pressure. So from your wording, the air over the upper surface normally moves faster than the wing's velocity, hence the lower pressure on top. But Bernoulli's also tells us that the deceleration of air flow must cause air pressure to begin rising again, even if to create equilibrium between two air flows. Bernoulli's is not all about lift.

When I am running, Bernoulli's applies to me as well. It's why I hear wind in my ears when I run, and that only happens once I reach a certain speed. It never happened when I was a child because I couldn't run fast enough. When I grew 8 inches in one year, the longer stride allowed me to achieve a faster speed....and that's when I could hear the wind in my ears. It's the lower air pressure from the increased velocity that creates the wind noise, just like the whoosh of a swinging bat.