Thrust to Weight Ratios

[FLS]

Going into 0G minimizes drag ...

I was keeping it simple because my earlier slightly fuller explanation created some confusion.   

[bozon]

Induced drag is a component of lift.  If lift is created at 0G, you have induced drag.  However, at zero G, wing loading is zero, so the load factor does not contribute to the amount of induced drag being created.  Only way to eliminate induced drag is to fly at an attitude that reduces the effective angle-of-attack to whatever is required to create a coefficient of lift = zero.

So really, flying at zero G really just removes weight and all of its influences...

As far as I understand the definitions, G = lift/weight. So zero G means zero lift, and zero lift means no formal induced drag. Of course that is not perfectly accurate locally since at a total of 0 lift some parts of the plane could be producing lift canceled by other parts producing negative lift.

I was keeping it simple because my earlier slightly fuller explanation created some confusion.   

I know FLS. I was expanding on this for the other readers.

[Stoney]

As far as I understand the definitions, G = lift/weight. So zero G means zero lift, and zero lift means no formal induced drag. Of course that is not perfectly accurate locally since at a total of 0 lift some parts of the plane could be producing lift canceled by other parts producing negative lift.
I know FLS. I was expanding on this for the other readers.

You may be thinking about the lift = weight or that required lift = weight X load factor (G).  From that, it would appear that at zero G, lift would = zero but that relationship is only true > 0G.  But any time the wing is at an AoA that produces lift, even at zero G, there will be induced drag being created.  So, unless the aircraft is at an attitude where the airfoil's lift coefficient is = zero, there will be induced drag present.  However, at zero G, the induced drag for that attitude will be minimized.  Remember that relative wind over the airfoil is what produces lift, and that's independent of load factor.  Flying at 0G merely reduces induced drag to the absolute minimum, for that attitude or AoA.

[hitech]

You may be thinking about the lift = weight or that required lift = weight X load factor (G).  From that, it would appear that at zero G, lift would = zero but that relationship is only true > 0G.  But any time the wing is at an AoA that produces lift, even at zero G, there will be induced drag being created.  So, unless the aircraft is at an attitude where the airfoil's lift coefficient is = zero, there will be induced drag present.  However, at zero G, the induced drag for that attitude will be minimized.  Remember that relative wind over the airfoil is what produces lift, and that's independent of load factor.  Flying at 0G merely reduces induced drag to the absolute minimum, for that attitude or AoA.

I am missing something in your post stony. Are you simply speaking about the (for lack of better summation) stability AOA generating lift I.E. sum of all torques must be 0 and sum of all forces perpendicular to the velocity vector must be 0?

Because 0g = 0 NET lift generated by the plane and hence 0 NET lift coefficient.

HiTech

[Stoney]

I am missing something in your post stony. Are you simply speaking about the (for lack of better summation) stability AOA generating lift I.E. sum of all torques must be 0 and sum of all forces perpendicular to the velocity vector must be 0?

Because 0g = 0 NET lift generated by the plane and hence 0 NET lift coefficient.

HiTech

If the airfoil in the wing is at an AoA that creates lift, there will be induced drag, regardless of load factor.  At 0G, there is still relative wind over the airfoil.  Unless the airfoil is at an angle of attack that causes the airfoil Cl to = zero, there is lift being produced, and hence, induced drag.  Since load factor = zero, the Cli will be minimized to its smallest value at that AoA, but will exist, theoretically, even if its almost negligible.

[bozon]

If the airfoil in the wing is at an AoA that creates lift, there will be induced drag, regardless of load factor.  At 0G, there is still relative wind over the airfoil.  Unless the airfoil is at an angle of attack that causes the airfoil Cl to = zero, there is lift being produced, and hence, induced drag.  Since load factor = zero, the Cli will be minimized to its smallest value at that AoA, but will exist, theoretically, even if its almost negligible.

Stoney, are you talking about a local phenomenon or an integrated one? a section of the wing can be producing lift with an associated "induced drag", while other sections produce negative lift such that the total is zero. In that case, I think it is formally considered as part of the global parasitic drag. A wing with a twist to its angle along the length of the wing will do this. Also, at 0 total lift the wings still need to produce some roll torque (one wing positive lift, the other negative) to cancel the torque from the prop.

In any case, the total (integrated) instantaneous drag at a given airspeed is lowest when the plane is practically at 0 (total) lift and hence 0 G. Perhaps one can setup some odd body where this is not perfectly accurate, but I doubt it will apply to any flying plane.

[Stoney]

Stoney, are you talking about a local phenomenon or an integrated one? a section of the wing can be producing lift with an associated "induced drag", while other sections produce negative lift such that the total is zero. In that case, I think it is formally considered as part of the global parasitic drag. A wing with a twist to its angle along the length of the wing will do this. Also, at 0 total lift the wings still need to produce some roll torque (one wing positive lift, the other negative) to cancel the torque from the prop.

In any case, the total (integrated) instantaneous drag at a given airspeed is lowest when the plane is practically at 0 (total) lift and hence 0 G. Perhaps one can setup some odd body where this is not perfectly accurate, but I doubt it will apply to any flying plane.

No, not talking about localized lift effects from the fuselage, H-stab, etc. nor twist or washout.  Induced drag is a function of lift.  Cl is a function of AoA.  Right?

Assume an unswept, constant-chord wing, with no washout.  Unless that wing is at an attitude where the lift coefficient of the wing = zero, there must be induced drag being created, regardless of load factor.

Maybe I'm wrong?

[FLS]

Stoney could you give an example of 0G flight with an AOA that creates lift? I get that the Cl comes from the AOA  but isn't the load factor also a function of lift?

[hitech]

No, not talking about localized lift effects from the fuselage, H-stab, etc. nor twist or washout.  Induced drag is a function of lift.  Cl is a function of AoA.  Right?

Assume an unswept, constant-chord wing, with no washout.  Unless that wing is at an attitude where the lift coefficient of the wing = zero, there must be induced drag being created, regardless of load factor.

Maybe I'm wrong?

Stoney.

Lift = 1/2 ro * v^2 * area * cl.

0g Means lift = 0.

Hence Cl must be zero, you are not moving ,in a vacuum or infinitely small.

Am I missing something?

HiTech

0 g

[Midway]

Stoney.

Lift = 1/2 ro * v^2 * area * cl.

0g Means lift = 0.

Hence Cl must be zero, you are not moving ,in a vacuum or infinitely small.

Am I missing something?

HiTech

0 g

  HiTech is so smart.    All I can say to that is wow... just wow!   

[Stoney]

Maybe I'm looking at this wrong.  I know that we use Lift = weight.  So, it follows that at zero G, lift = 0.  But, if the wing is at an AoA that produces any coefficient of lift, per the lift formula, and there is dynamic pressure (i.e. relative wind over the wing), there is lift being created, right?  And, if lift is being created (and I'm talking about negligible amounts here, from a theoretical perspective), there must be induced drag being created, because you can't have one without the other, unless you have a wing with infinite span.

So, the way I figure, the whole "lift = weight" can only exist when G does not equal zero.  Now, when G is equal to zero, no amount of lift is required to keep the aircraft "flying", but given that the plane has forward motion in some direction, there must be some lift being produced, unless the attitude of the aircraft in that direction is such that the Cl of the wing = 0.

[FLS]

Lift can only equal weight at 1G.

If I understand you you're saying that lift from something like the Bernoulli effect could cause some lift and induced drag at 0 AOA?  Unless you're taking about absolute vs geometric AOA isn't 0 Cl the definition of 0 AOA?

[Midway]

Maybe I'm looking at this wrong.  I know that we use Lift = weight.  So, it follows that at zero G, lift = 0.  But, if the wing is at an AoA that produces any coefficient of lift, per the lift formula, and there is dynamic pressure (i.e. relative wind over the wing), there is lift being created, right?  And, if lift is being created (and I'm talking about negligible amounts here, from a theoretical perspective), there must be induced drag being created, because you can't have one without the other, unless you have a wing with infinite span.

So, the way I figure, the whole "lift = weight" can only exist when G does not equal zero.  Now, when G is equal to zero, no amount of lift is required to keep the aircraft "flying", but given that the plane has forward motion in some direction, there must be some lift being produced, unless the attitude of the aircraft in that direction is such that the Cl of the wing = 0.

 

Lift can only equal weight at 1G.

If I understand you you're saying that lift from something like the Bernoulli effect could cause some lift and induced drag at 0 AOA?  Unless you're taking about absolute vs geometric AOA isn't 0 Cl the definition of 0 AOA?

 

 

[hitech]

Ahh I understand your disconnect Stoney.

G loading by definition is Lift / Weight.  This applies in any attitude. So  there is not any lift (BY DEFINITION) being generated at zero g. If you assume some lift, then we would not be at Zero g.

DISCLAIMER.

The above only is the basic all the minor forces going into the calcs of lift needed such as offset thurst, CG , wing twist ......


HiTech

[Charge]

I understand it so that if you e.g. push the stick forward and effectively reach a 0G state (ballistic arc), it means that only portion of lift that carries the weight of the aircraft, at that speed, is negated but it does not necessarily mean that all of the lift is negated i.e. induced drag is still created, or it is not at its minimum, unless the wing AoA is at such angle that the lift on both sides of airfoil are equal, but depending on speed that could be even a -G state of the airframe. That would also effetively mean that there is likely a certain speed where the AoA net effect is really 0 as well as the G loading of the airframe is 0 at the same time but only at that certain speed.

-C+