How does the F4U-1A beat the Spit 16

[FLS]

not quite, a plane needs to roll before it can explore its turn rate...

Why do you need to roll before you can turn?

I'm thinking that " The state of flight is the crux of the maneuver fight" would be a good signature for you thorsim.

[thorsim]

so the ability to speed up slow down and dive (unless you mean lift as a negative value as well) have no place in conversations about maneuverability?

 

maneuverability: Ability to change the direction of its velocity vector.

The only force that is perpendicular to the Velocity vector , simply by definition, is lift. Until you accept this very simple premise, there is no use in any discussion, because turning, and changing vel vector are 100% the same term.

HiTech

yea we were posting at the same time.

Wow. No.

A rigid object's position is defined by 6 degrees of freedom - [X, Y, Z] (translational freedom) and [roll, pitch, yaw] (rotational freedom).

Each of these has a corresponding velocity component and an acceleration component.

A pilot/airplane traveling horizontally along the X axis (which we assume for simplicity) has direct control over his acceleration in the X direction and indirect control of his acceleration in the other translational directions.

The direct acceleration control comes from throttle and drag. The pilot has indirect control over the acceleration in other translational directions via the use of roll and pitch to orient the lift vector and increase/decrease it. Alternatively the pilot could use roll and yaw to do the same, but it is generally less efficient because the lift provided by yaw is much less than the lift provided by pitch.

Of course this does not contradict your point that roll is important. But BnZs has already covered that.

well since the accepted limits on maneuverability in this discussion are limited to steady states of flight, and only one direction i will just leave all you experts at it and go into the arena and kill some more guys with my wild notions ...

+S+

t

[boomerlu]

Sorry boomerlu, I miss read you post as not agreeing with change in roll rate, yes I agree with a basic idea that drag (if you think of it that way) increases with the ^2 of the length, and roll force increases linearly with the length.  In Aerodynamics, I tend to think of everything in AOA's when any force is applied as a lifting force, and not a drag slowing the roll.

Hey no problem. I'm used to thinking about forces, you're used to thinking about AoAs. I just wanted to figure this thing out and see if I understood what was going on underneath the surface. Good to hear my basic premise is correct.

[boomerlu]

well since the accepted limits on maneuverability in this discussion are limited to steady states of flight, and only one direction i will just leave all you experts at it and go into the arena and kill some more guys with my wild notions ...

This clearly shows me you don't understand what I was getting at, which may be partially my fault. I was primarily trying to correct your notion that there are 8 degrees of freedom.

There are 3 positional degrees of freedom which define where the aircraft is (XYZ) and 3 angular degrees of freedom which define how it is oriented (roll pitch yaw). Each of these DoF also has a corresponding velocity and acceleration.

The pilot has no direct control over the 3 translational degrees of freedom. He approximately has direct control over pitch and yaw angles. The pitch angle in turn indirectly controls the size of the lift vector and thus acceleration in the direction of the lift vector. The yaw angle indirectly controls a yaw-force vector as well, but we generally don't use it to maneuver. The pilot also has approximately direct control over roll velocity (in other words roll rate) which allows him to orient the lift vector. He also has direct control over acceleration in the direction the aircraft is pointed in via throttle.

In total there are actually 18 degrees of freedom! The pilot has direct control over 4.

P.S. I already addressed your "steady-state" fallacy earlier.

[thorsim]

it wasn't you i was referring to boomer

i just think i am on a different level of thought right or wrong, or people here like to over complicate or over simplify things to advance their agenda.

simply stated if you are going in one place heading in one direction and then you apply forces and you are in another place heading in another direction how big and heavy you are will make some notable difference in how long it takes you to get to your new place and direction.

i am sorry if that concept is not well received, but nobody here has convinced me otherwise.

t 

[boomerlu]

simply stated if you are going in one place heading in one direction and then you apply forces and you are in another place heading in another direction how big and heavy you are will make some notable difference in how long it takes you to get to your new place and direction.

What you're missing here is the following...
F = m a

Since we're talking about aero and maneuvering, F = Lift so
L = m a

Rearranging we get
L/m = a

What's L/m? Lift loading.

Alternatively, F = Thrust
T = m a
T/m = a

What is T/m? Thrust to weight ratio.

Or if we're trying to decelerate, F = Drag
D = m a
D/m = a

In other words, roll rate aside, the ability of a plane to change its velocity vector is defined by its Lift/Weight, Thrust/Weight, and Drag/Weight ratios.

Oh and just to be extra clear...
a = dv/dt

in other words, the acceleration a is equal to the change in velocity over one unit of time.

[thorsim]

well ok does the application of force via the controls translates into direction/velocity changes instantly and fully?

if not do you think that the mass that is required to be moved may have an effect on how quickly the force applied results in the desired changes?

?

t

[boomerlu]

well ok does the application of force via the controls translates into direction/velocity changes instantly and fully?

No, because, acceleration, velocity, and position are all continuous rather than discrete. You cannot instantly go from 10 mph to 20 mph, nor can you instantly go from 10 mph south to 10 mph east.

if not do you think that the mass that is required to be moved may have an effect on how quickly the force applied results in the desired changes?

Yes it does, but again, if you look at the equations above (which are the SIMPLEST forms in which I can show the math), acceleration depends only on the RATIO between lift, drag, and thrust to mass.

To move a bigger mass with the same acceleration, you must have a correspondingly bigger force. The capacity of the plane to generate that extra force for the purposes of turning is directly proportional to the wing area as per the Lift equation (which I will not write down, but I invite you to Google it to see for yourself).

So as with all our "scaling" thought experiments, if you double the mass of a plane but also double the wing area , double the thrust, and double the drag it will perform exactly the same in all regards except roll rate as per the equations of motion I've written down for you.

Notice the lift equation works at all AoA, not just steady state. The AoA effects are captured by CL the coefficient of lift which also incorporates the effects of wing shape (and we assume wing shape does not change).

We also have not considered the effects of control forces and other practical engineering constraints. We ignore them because they are irrelevant to the thought experiment which merely involves comparing two hypothetical aircraft, the second of which has double the thrust, drag, weight, and wing area of the first.

[Saxman]

Wow, 12 pages later does anyone remember that this thread essentially started as a question on how the 1A can beat the Spixteen in a fight?

[thorsim]

yes provided your control surfaces are as relatively efficient and that you have enough extra power to counter the drag of those control surfaces and of course the weight of those control surfaces and the weight of the extra power and the extra wing for the wing and lift loading and the extra fuel the extra power requires ...

i don't intend to be snide but i suspect you can see what i am getting at.  scaling up is easy on paper, the engineering realities, not so much.

EDIT : and since we are talking WW2 does the pilot have the strength to be able to deflect that much more force required to make the desired changes, if not how much will the system to assist the pilot weigh and once again you get into the scaling problem.

t

No, because, acceleration, velocity, and position are all continuous rather than discrete. You cannot instantly go from 10 mph to 20 mph, nor can you instantly go from 10 mph south to 10 mph east.
Yes it does, but again, if you look at the equations above (which are the SIMPLEST forms in which I can show the math), acceleration depends only on the RATIO between lift, drag, and thrust to mass.

To move a bigger mass with the same acceleration, you must have a correspondingly bigger force. The capacity of the plane to generate that extra force is directly proportional to the wing area as per the Lift equation (which I will not write down, but I invite you to Google it to see for yourself).

So as with all our "scaling" thought experiments, if you double the mass of a plane but also double the wing area, it will perform exactly the same with regards to changing direction using its lift vector.

[boomerlu]

i don't intend to be snide but i suspect you can see what i am getting at.  scaling up is easy on paper, the engineering realities, not so much.

The point was never to highlight engineering realities, but to do a thought experiment to see what the most important variables are.

And again, they are lift/mass, weight/mass, drag/mass, with lift being proportional to wing area.

The RATIOS are important. Mass in and of itself is not.

[thorsim]

well we will need to agree to disagree about the importance of size and weight as it seems very difficult to isolate them for discussion. 

i am sorry i am unable to express my ideas better. 

+S+

t

The point was never to highlight engineering realities, but to do a thought experiment to see what the most important variables are.

And again, they are lift/mass, weight/mass, drag/mass, with lift being proportional to wing area.

The RATIOS are important. Mass in and of itself is not.

[thorsim]

and maybe that is where the core of the disagreement lies ...

in theory some say we can double all the values and achieve the same result.

practically i say that is impossible for a lot of reasons that tend to stack the deck against that result.

and i am sorry but i always saw this as a practical discussion not a theoretical one.

and even if roll rate alone is the only change that would be enough to make my case ...

imo

+S+

t

The point was never to highlight engineering realities, but to do a thought experiment to see what the most important variables are.

And again, they are lift/mass, weight/mass, drag/mass, with lift being proportional to wing area.

The RATIOS are important. Mass in and of itself is not.

[boomerlu]

 

Then you should have said "extra size and mass from the AIRFRAME cause engineering constraints such as extra control surface forces etc etc and these constraints will factor in as disadvantages to larger and heavier AIRFRAMES."

You have basically been trying to run a debate over the wrong topic the whole time. Your inability to come out with your point earlier is absolutely astounding.

Also note in the F104 vs F15 example, the engineering improved so dramatically for the F15 that it was able to overcome its inherent weakness of a larger and heavier airframe and is thus a better maneuvering fighter. Once again showing that a larger and heavier airframe alone will not make a worse fighter.

And finally, you only mentioned roll rate after 80% of the debate had already occurred despite repeated requests for you to completely define what you mean by maneuverability. Also, BnZ covered roll rate's non-correlation with mass.

[FLS]

Boomerlu I think what you're noticing is that thorsim isn't arguing any particular point, he's just arguing that he's right.