Thrust to Weight Ratios

[Baumer]

[morfiend]

(Image removed from quote.)

  Vomit comet???


  BTW good to see ya back,come yak at me in the TA when you have the time!




   

[FLS]

Bell curve.  

Dude where's my lift?

[Stoney]

Bell curve.  

Dude where's my lift?

If you pushover at 350kts, achieving 0 g for a few seconds, while the wing is at an angle of attack that produces lift...that would be an example...kind of like Baumer's illustration.

[FLS]

If you pushover at 350kts, achieving 0 g for a few seconds, while the wing is at an angle of attack that produces lift...that would be an example...kind of like Baumer's illustration.

Hence my question. When during the 25 second 0 G maneuver is the wing producing lift?

[hitech]

So what you're saying is that if there is relative wind over the wing, and the wing is at an AoA that creates lift, the plane cannot be at 0 G, and vice versa?

Correct.

But obviously this is the NET  lift, I.E. the H stab could be producing lift in the opposite the wing. The net lifting force would be zero but wing would not be at zero lift angle. But as we agreed earlier, this was not what we were speaking of.


HiTech

[Stoney]

Hence my question. When during the 25 second 0 G maneuver is the wing producing lift?

If there's 350kts of relative wind over the wing, its making lift, unless the attitude of the plane gives the wing an AoA that results in a Cl of zero.  

[Stoney]

Correct.

But obviously this is the NET  lift, I.E. the H stab could be producing lift in the opposite the wing. The net lifting force would be zero but wing would not be at zero lift angle. But as we agreed earlier, this was not what we were speaking of.


HiTech

Got it...

[FLS]

If there's 350kts of relative wind over the wing, its making lift, unless the attitude of the plane gives the wing an AoA that results in a Cl of zero.  

I doubt it's going 350 over the top but I understand what you're saying about airspeed.  However, in order to have 25 seconds of 0 G it has to have a 0 lift AOA. You can posit If you pushover at 350kts, achieving 0 g for a few seconds, while the wing is at an angle of attack that produces lift but then you're assuming your conclusion in order to prove your conclusion. I think it's just the word "lift" that's creating a problem.

Airflow over the wing creates pressure differences which when in opposition to gravity or radial acceleration we consider "lift". Sometimes the airflow is not creating lift. The difference is the vector of the net forces. It's only lift, by definition,  in opposition to acceleration. So airflow over a wing creates pressure differences which increase up to a point with AOA and minimize at 0 AOA (absolute) and exist at 0G but since there is no opposition to acceleration at 0 G there is nothing we can call "lift". So yes I agree that the relative wind over the wing is still creating pressure differences but the 0 G tells us that there is no lift.

[Stoney]

I doubt it's going 350 over the top but I understand what you're saying about airspeed.  However, in order to have 25 seconds of 0 G it has to have a 0 lift AOA. You can posit If you pushover at 350kts, achieving 0 g for a few seconds, while the wing is at an angle of attack that produces lift but then you're assuming your conclusion in order to prove your conclusion. I think it's just the word "lift" that's creating a problem.

Airflow over the wing creates pressure differences which when in opposition to gravity or radial acceleration we consider "lift". Sometimes the airflow is not creating lift. The difference is the vector of the net forces. It's only lift, by definition,  in opposition to acceleration. So airflow over a wing creates pressure differences which increase up to a point with AOA and minimize at 0 AOA (absolute) and exist at 0G but since there is no opposition to acceleration at 0 G there is nothing we can call "lift". So yes I agree that the relative wind over the wing is still creating pressure differences but the 0 G tells us that there is no lift.

Ok, I capitulate...I think we've beat this one long enough...  I don't understand the physics of flight nearly as well as the aerodynamics, so I'll just push the "I believe" button on this one...  I just can't see, dynamically, how a wing could stop producing lift when it still has relative wind hitting it at an angle that otherwise, at any other condition, would cause it to produce lift.

[Baumer]

This is from Wikipedia and is consistent with what I was taught in school.

"A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction. If the fluid is air, the force is called an aerodynamic force.

Lift is commonly associated with the wing of a fixed-wing aircraft, although lift is also generated by propellers; kites; helicopter rotors; rudders, sails and keels on sailboats; hydrofoils; wings on auto racing cars; wind turbines and other streamlined objects. While the common meaning of the word "lift" assumes that lift opposes gravity, lift in its technical sense can be in any direction since it is defined with respect to the direction of flow rather than to the direction of gravity. When an aircraft is flying straight and level most of the lift opposes gravity. However, when an aircraft is climbing, descending, or banking in a turn, for example, the lift is tilted with respect to the vertical. Lift may also be entirely downwards in some aerobatic maneuvers, or on the wing on a racing car. In this last case, the term downforce is often used. Lift may also be horizontal, for instance on a sail on a sailboat."

[FLS]

Ok, I capitulate...I think we've beat this one long enough...  I don't understand the physics of flight nearly as well as the aerodynamics, so I'll just push the "I believe" button on this one...  I just can't see, dynamically, how a wing could stop producing lift when it still has relative wind hitting it at an angle that otherwise, at any other condition, would cause it to produce lift.

I usually learn something from these discussions. 

When does the wing stop producing lift when it still has relative wind hitting it at an angle that otherwise, at any other condition, would cause it to produce lift. I'll bite, when does it? If it is at an angle to produce lift then it will. If it isn't producing lift it's not at that angle. The conditions you propose to coexist contradict each other.

Baumer the acceleration tilts along with the lift.

[hitech]

Baumer: It is also 100% consistent with my diagrams and equations.

HiTech

[nrshida]

So building on HiTech's previous illustration, are these diagrams a fair representation of the forces that have been discussed? Note the length of the vectors are not meant to imply any meaning, just the orientation.

So in a ideal Zero G zoom climb, the situation would be this, with (essentially) no net lift and no lift induced drag:-



Thus if we altered the above situation slightly with your accelerometer was reading 1 G (acting on the normal to your thrust line) you would get a lift vector at 90 degrees to the wing and eventually loop round inverted because the weight (the effect of gravity on your mass) would still be straight down?


Then would this be the situation in a steady 45 degree 1 G climb:-



I really have guessed about the orientation of the lift induced drag vector, it just feels about right that it would act in that direction? Obviously the speed would degrade without sufficient thrust (0.707 to maintain this climb angle, is that right?).

You can keep discussing this with equations, just some people can't reason with mathematics and have to resolve it pictorially.

[hitech]

ALL drag is opposite the velocity vector . I.E the definition of lift induced drag is in the same direction as parasitic drag.

The arrow you have labeled as parasitic drag should be labeled simply drag on both diagrams.

And drag = parasitic + induced.

Thrust is the strange one with it's definition. Because the force from the prop can be lift and thrust at the same time.

These exact definitions become meaningful when you start trying to do the calculations per lift and drag curves which used these conventions when being charted.

HiTech