4 Basics

Jaybird180

Jaybird180

Final Approach
Joined
Dec 28, 2010
Messages
9,036
Location
Near DC
Display Name
Display name:
Jaybird180
As a plane goes through the air, its thrust offsets or overpowers the drag, hence forward movement. The wing, based on the speed of the airflow at a certain angle of attack generates lift which offsets or overcomes weight.

So as an airplane's wing generates lift, does it weigh less?
 
Are you asking if the wing reduces the earth's gravitational pull?
 
Jaybird180 said:
As a plane goes through the air, its thrust offsets or overpowers the drag, hence forward movement. The wing, based on the speed of the airflow at a certain angle of attack generates lift which offsets or overcomes weight.

So as an airplane's wing generates lift, does it weigh less?
Click to expand...

Yes... Just as if you had a pull up bar over your bathroom scale. If you don't touch the bar and stand on the scale, you will weigh at maximum. But, if you pull in the bar (providing yourself some lift) you will "weigh" less, even though your mass stays the same.

Furthermore, as the plane gets higher and higher (i.e. further from the center of the earth) it will "weigh" less and less.
 
No. There are two forces. They may oppose each other, but they are still there. It makes a difference to your wing roots.
 
Those generic definitions of lift are incorrect (NASA admits it). The only reason that they haven't been changed is the fact that most pilots won't be able to comprehend it, so they leave it as is.

http://www.grc.nasa.gov/WWW/k-12/airplane/wrong1.html

Lift occurs as a result of the change in air direction, or how much the air is "turned." This can be accomplished many different ways if you care to look up the various aircraft/airfoil designs throughout the years.

:popcorn:
 
A plane carrying hundreds of birds in cages takes off. In flight the door to the cages opens somehow and all of the birds escape and are flying around the cabin. Does the weight of the plane go down?
 
Cpt_Kirk said:
Those generic definitions of lift are incorrect (NASA admits it). The only reason that they haven't been changed is the fact that most pilots won't be able to comprehend it, so they leave it as is.

http://www.grc.nasa.gov/WWW/k-12/airplane/wrong1.html

Lift occurs as a result of the change in air direction, or how much the air is "turned." This can be accomplished many different ways if you care to look up the various aircraft/airfoil designs throughout the years.

:popcorn:
Click to expand...


When I was 15 and flying RC, I got my first symmetrical airfoil plane
and gave up on Bernoulli principal being the primary source of lift at that time.

Newton for the win.
 
I really dislike the "sum must be zero" idea, it's either wrong or a tremendous oversimplification.
 
Jaybird180 said:
As a plane goes through the air, its thrust offsets or overpowers the drag, hence forward movement. The wing, based on the speed of the airflow at a certain angle of attack generates lift which offsets or overcomes weight.

So as an airplane's wing generates lift, does it weigh less?
Click to expand...


Lift counteracts gravity (not weight). Thrust counteracts drag, not weight. Thrust also generates drag (parasitic).

But, as velocity increases so does mass (due to kinetic energy), according to Einstein. If you consider mass to be weight, then the entire aircraft and you gain mass as you increase velocity. But the ratio of a prop aircraft mass to velocity is so small the amount of mass gain is likewise infinitesimally small.
[FONT=Arial, Helvetica, sans-serif]
Back to lift and gravity. What you really want to say is lift increases load factor. Newtons F=Ma is the reason. Force = Mass x Acceleration. Gravity is a force of acceleration. The G force of the aircraft increases as you product lift and counteract the force of gravity. That is not an increase in weight, it's an increase in load factor.

So in fact, as you fly you never get lighter, to do that you have to escape the force of gravity entirely.
[/FONT]
 
Jaybird180 said:
As a plane goes through the air, its thrust offsets or overpowers the drag, hence forward movement. The wing, based on the speed of the airflow at a certain angle of attack generates lift which offsets or overcomes weight.

So as an airplane's wing generates lift, does it weigh less?
Click to expand...

No, it weighs the same. Jack Thelander who was the Chief Aerodynamics Engineer for Douglas and a CFI of mine proved it one day in a really cool method. He set a recording Barograph on the ground and we flew over it. He then took the area of the pick up against the area of the wing and the actual weight of the plane with us in it and guess what, they matched. He did this to prove that Bernoulli's equations were a result of Newtonian physics. The first time I met him, we started in aerodynamics and he said, "Everything you have learned about aerodynamics to this point, just forget it, it's wrong.":rofl:
 
Henning said:
The first time I met him, we started in aerodynamics and he said, "Everything you have learned about aerodynamics to this point, just forget it, it's wrong.":rofl:
Click to expand...

I'd like to learn from someone like him. He knows he's right and he knows how to prove it.
 
Define "Weight". Then you have the answer to the original question.

SixPapaCharlie said:
When I was 15 and flying RC, I got my first symmetrical airfoil plane
and gave up on Bernoulli principal being the primary source of lift at that time.

Newton for the win.
Click to expand...
Bernoulli's equation is just a special case of Newtons laws applied to an ideal fluid in a streamline.

They both work.

Note: Bernoulli never said **** about curved and flat surfaces and/or differences in lengths or anything else that the some people blame him for.
 
How much do you weigh in English units?

How much do you weigh in metric units?

(I'm asking these two questions for a reason.)
 
Much ado about nothing, all pilots know what makes an airplane fly!!

MONEY :rofl::rofl::rofl:
 
Henning said:
180lbs, 82kg, do your magic.
Click to expand...

Okay, now I know YOU know what's wrong with that answer...

We speak of kg as a "weight" but it's a mass. If the discussion was centered around the plane's mass and not weight, the issue would go away.
 
Okay now what's the English unit of mass?
 
CTLSi said:
So in fact, as you fly you never get lighter, to do that you have to escape the force of gravity entirely.
Click to expand...

I've found that to be true. After 35 years of flying, not only am I not any lighter, I'm actually a bit heavier!
 
Oh, ok, you want to make a semantic point, no worries. Since the point is irrelevant until you change gravity's effect, no big deal.
 
Henning said:
Oh, ok, you want to make a semantic point, no worries. Since the point is irrelevant until you change gravity's effect, no big deal.
Click to expand...

Or you introduce acceleration other than gravity in to play.
 
Sac Arrow said:
Or you introduce acceleration other than gravity in to play.
Click to expand...

Yep, however we still reference those accelerations in units of gravity. My point is it doesn't apply to this thread in any meaningful form. In our general society here on earth, kilograms are used, correctly or incorrectly, as a unit of weight. Find me a bathroom scale calibrated in Newtons rather than kilograms if you would like to refute that.
 
Sac Arrow said:
Okay now what's the English unit of mass?
Click to expand...


slug_1627430c.jpg
 
Henning said:
Yep, however we still reference those accelerations in units of gravity. My point is it doesn't apply to this thread in any meaningful form. In our general society here on earth, kilograms are used, correctly or incorrectly, as a unit of weight. Find me a bathroom scale calibrated in Newtons rather than kilograms if you would like to refute that.
Click to expand...

I don't disagree with you on that, but I do think it's on topic. The OP asked the question if the plane's weight would change with aerodynamic loading. The answer is no. But, the plane's weight will change during the transient accelerations in to a climb, or a decent, or in a banked turn. The mass will of course not change.

By the way, your spring bathroom scale measures weight. Your balance beam scale measures mass. The balance beam scale calibrated in pounds is a derived measurement. Same with the spring scale in kilograms.
 
Last edited:
jpower said:
slug_1627430c.jpg
Click to expand...

Very good. There is also a secondary unit of mass called the pound-mass (LBM) which is numerically equal to a pound-force (LBF) at standard gravity.
 
Man, you guys really know how to get off topic.
 
Jaybird180 said:
As a plane goes through the air, its thrust offsets or overpowers the drag, hence forward movement. The wing, based on the speed of the airflow at a certain angle of attack generates lift which offsets or overcomes weight.

So as an airplane's wing generates lift, does it weigh less?
Click to expand...

Yes. Usually measured by the hour
 
Cpt_Kirk said:
Man, you guys really know how to get off topic.
Click to expand...

That's what happens when there's no topic to begin with. A pointless thread, given no follow up from the OP, and how inarticulate the original post was. Maybe he was just bored and trolling. :)
 
We've known that our understanding of lift has been wrong for a long time. The book "Stick and Rudder" explained how it really worked back in 1944.
 
Sac Arrow said:
I don't disagree with you on that, but I do think it's on topic. The OP asked the question if the plane's weight would change with aerodynamic loading. The answer is no. But, the plane's weight will change during the transient accelerations in to a climb, or a decent, or in a banked turn. The mass will of course not change.

By the way, your spring bathroom scale measures weight. Your balance beam scale measures mass. The balance beam scale calibrated in pounds is a derived measurement. Same with the spring scale in kilograms.
Click to expand...

Its all a matter of interpreting the OP question. You are correct above except the answer is yes, if you interpret the OP question literally. He asks "So as an airplane's wing generates lift, does it weigh less?" A scale measures "weight" or "force on an object due to gravity". If you were able to place a scale under the wheels of an airplane and keep it there through the takeoff roll (to measure the "weight" relative to the ground), as it traveled down the runway, it would measure less and less as the wing generates lift.

Now, once it leaves the ground, there is no weight (to measure the force relative to.) But, if you measure the weight at a sea level field and then measure it at a 5,000 ft field at the same latitude, it will "weigh" less simply because the "force on an object due to gravity" will be less. This is because the object if further away from the center of the earth.

With highly sensitive instruments, I have measured weights of objects that differ when measured on the floor as compared to the weight on a table 4 ft higher, all due the increased radius from the center of the earth.
 
Last edited:
You must log in or register to reply here.
Back
Top