Corsair Turning Ability in AH

[Knegel]

Originally posted by dtango
Knegel:

The chart above shows you that at higher Cl's there's a part of the envelope that the drag between having flaps vs. not is the same.  So essentially it's the same power required.  
The key is at for the same amount of drag you get a higher Cl with flaps.

Tango, XO
412th FS Braunco Mustangs

And exactly here you have a misunderstanding, cause you "say the drag between having flaps vs. not is the same", but to compare you use the drag of the stall speed without flaps, but at turning speed without flaps the drag is much smaler(point "A" in your graphic).

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Edit: Now i mixed up the points!
While a turn without flaps the plane turn at point "D", but while a turn with flaps the plane also turn on its stall speed, therefor the Ca is higher than at point "D".
----------------------------------------------------


And just to make it clear: I understand that the min turn radius is smaler with flaps, i wrote this plenty of times now, as long as the plane have enough thrust to fly with max CL.

But is this so in a sustained turn??

The F2A test show that this is not the case(for this plane) in 27000ft, while its not clear if this is still the case in 13000ft, where the power load is better.

And while climbing the higher CD of course can be handycap, but since the plane fly much more slow(less zero drag) and cause the flaps provide more lift the discrepancy between the climbratio with/without flaps and turnratio with/without flaps seems to be to big to me.


I will test if the AH planes behave like the F2A with reduced power, this will show, if the flaps work ok.

Greetings,

Knegel

[Knegel]

suprise suprise, even with much reduced power the sustained turnratio remain the same with/without full flaps.

This stands in a big contrast to what at least the F2A test show.

[dtango]

Originally posted by Knegel
Your formula is for a constant turn(with altitude lost or with very much power), but i talk about a sustained turn.

Nope , the turn performance equations posted are for any kind of level turn, sustained included.

Originally posted by Knegel
...I cant understand why the climb with 110mph and full flaps is so much worse than the climb at 180mph without flaps, while the turn rate remain the same..
...To have a MUCH smaler turn radius but a MUCH worse climb ratio is what i cant understand...
...So the question remain, why do we have a so big performence lost while climbing, but not while turning?

It's pretty straightforward.  I tried communicating this with the diagram.  Let's try it this way using your 110mph & 180mph example.  What's happening is:

In a steady climb (constant velocity):
==========================
110mph full flaps (1-G) drag > 180mph no flaps (1-G) drag.  

The power required at 110mph full flaps 1-G is GREATER than that of the power required at 180mph no flaps 1-G therefore you climb better without flaps.

In a sustained turn (no airspeed or alt gain/loss):
===================================
110mph full flaps (x-Gload) drag = 180mph no flaps (y-Gload) drag.

The power required at 110mph full flaps x-G's is EQUAL to that of the power required at 180mph no flaps y-G's therefore sustained turn rate is about the same (while at 110mph turn radius is better).

[EDIT: this is an inaccurate statement.  Drag may not be the same, but power required is the same]


The chart I posted shows this charateristic in the drag polars between flaps and no flaps with changing Cl.  Why is the drag polar different at 1-g but the same at a higher g-load?[/i]  Because at higher lift coefficients the drag polar ceases to be parabolic.  The reason is lift-dependent drag due to angle of attack is strongly affected by viscous separation.  (Some folks call this variation delta-CDp, or increase in profile drag with increasing aoa.)

The end result, in a sustained turn you have the same amount of power available from your engine, and the same amount of power required due to drag between 110mph full flaps and 180mph no flaps at some gload/lift coefficient.

Let's be clear here.  This relationship is dynamic.  Here's another chart Badboy has posted in the past to illustrate this concept:



Note how this plays out in sustained turn performance between flaps and no flaps.

Hope this helps!

Tango, XO
412th FS Braunco Mustangs

[dtango]

And exactly here you have a misunderstanding, cause you "say the drag between having flaps vs. not is the same", but to compare you use the drag of the stall speed without flaps, but at turning speed without flaps the drag is much smaler(point "A" in your graphic).

----------------------------------------------
Edit: Now i mixed up the points!
While a turn without flaps the plane turn at point "D", but while a turn with flaps the plane also turn on its stall speed, therefor the Ca is higher than at point "D".
----------------------------------------------------

LOL .  Sorry, knegel you'll have to restate what you're trying to say here because you totally lost me with this statement.  

I thought I was clear about what I said:  Drag at points A & B are different.  Drag at points C & D are the same.  I think this is what you're referring to?

Tango, XO
412th FS Braunco Mustangs

[Knegel]

Hi,

whats about the much more big CL while climbing(actually i understand that the climb must be worse with full flaps)??

And whats about the real tested F2A, why do it not behave like that??

And why do you think the drag while a sustained turn with and without flaps is the same??



And your graphic isnt universal, it could be a graphic for fowler flaps, which show the CL/Cd relation in a to good light for the "with flaps" setting.

At least the F2A test make me believe this.

The F2A has a increased turn radius while a sustained turn in 27000ft, even with the "good" 22° flap setting, with full flaps the disadvantage was more big.

Greetings,

Knegel

[dtango]

And why do you think the drag while a sustained turn with and without flaps is the same??

Ah, I made an error in my statement.  Power required is the same.  Drag isn't the same.  So...

in a sustained turn in your example:
=========================
D*V (110mph full flaps) = D*V (180mph no flaps)

++++++
The graphic is of a split flap (for which airfoil I don't know) and not a fowler.  It's from the famous Perkins & Hague aero textbook.  However I have plenty of other drag polars for various other types of flaps that show the similar relationship.

++++++
You can fly a sustained turn at Clmax at a certain part of the envelope.  On Badboy's EM chart the region you can do this in is along the lift limit portion of the curve, from the bottom and up to where the Ps=0 line intersects it.  Here's another plot that has things labeled if you're unfamiliar with the EM charts.



I really must get to bed now!  

Tango, XO
412th FS Braunco Mustangs

[gripen]

Originally posted by dtango

The graphic is of a split flap (for which airfoil I don't know) and not a fowler.  It's from the famous Perkins & Hague aero textbook.  However I have plenty of other drag polars for various other types of flaps that show the similar relationship.
[/B]

There is Figure 5. in the F2A-3 turning performance report showing pretty much the same phenomena.

[Knegel]

Hi,

the results of the F2A turn tests make me believe its rather like this:



And in this case the turn ratio should decrease in a sustained turn, while the radius can be smaler, but dont have to(depending to the available thrust).

At least for the F2A this is the case and i dont know why it shouldnt be the same regarding the F4U and the other planes, which had a rather similar flap system.
Fowler flaps may vary here, cause they increase the wingarea, so they dont create the more lift only by using a higher AoA.

btw, maybe we have a different understanding of a "sustained turn"? For me thats a turn in level flight, without altitude and speed lost or gain.

Maybe there are more turn performence tests around, similar to the F2A??

Sleep well!

Greetings,

Knegel

[Knegel]

Hi,

some more testresults to proof my assumption right:

AH F4U-4, 100% fuel, WEP, climb from sea level upward.

Climb at 100mph without flaps:  2800ft/min  (thats very close to stall speed, stall horn is always enabled)

Climb at 100mph with full flaps: 1900ft/min

100mph should be roundabout at point "C" + "D" in your graphic.

If your assumtion would be right, the CD would be the same there, while full flaps would provide more lift, therefor the climbratio would increase with full flaps. (same thrust, same drag but more lift = better climb).

But, as we see, while a slow speed climb the AH F4U-4 (probably other planes do it similar in AH) have much worse climb rate with full flaps, this would fit much better to my red line in your graphic, i posted above.

So if this is the case also the turn ratio with full flaps must decrease in a sustained turn, but this dont happen in AH and there i see a rather big discrepancy to what it should be or at least to the climb results.

We cant have one without the other.

If the drag is the same, the climb must be the same as well(rather better due to the more lift).

If the drag with full flaps is so high to decrease the climbratio by 30%, also the turn ratio must decrease and the radius cant be that much better, cause the less available effective thrust dont allow a that high bank angle anymore(wihtout alt lost, cause we still need to overcome the -1G to keep a level flight).


Greetings,

Knegel

[Saxman]

I've gotten completely lost in this argument, but hasn't it ALREADY BEEN STATED that rate of climb does NOT relate/equate to turning capability and is instead a completely different animal?

[dtango]

Knegel:  

In your 100mph example two key points to make:
CD is not the same at the same velocity, 100mph in your case with and without flaps.  As others have stated lift has nothing to do with climb.  The reason is that drag at 1-g is not the same as drag at n-g's in a sustained turn.

When you're in a steady climb you're at 1-g.  When you're in a sustained turn your g-load is > 1g.

I'm off to church right now so I'll post the math to demonstrate this when I get back in the afternoon.

Tango, XO
412th FS Braunco Mustangs

[Knegel]

Hi,

lift has nothing to do with climb?? So we can retake the wings while climbing?? I would say this only work if the thrust is big enough to provite
a vertical climb.  .
A climb is exact the same like a constant 1G turn without gravity, the gravity only hinder the plane to make a turn, if the gravity would stop, the climbing plane would perform a nice turn. If a higher CL decrease the turnrate while a 1G turn, it also must increase the climb ratio.

In my 100mph example the F4U fly at stall speed, therefor it is very close to its max CD, while the same plane with full flaps fly a bit above its stall speed, therefor both must be rather close to "C" and "D" in your graphic(stall speed with full flaps is around 75mph).

If it would be like you say, the F4U with full flaps would have at least at one speed a higher lift AND a smaler drag than the same plane without flaps, but max AoA.  But you can try what you want, the F4U dont will performe a better sustained climb than 1900ft/min with full flaps, therefor the AH F4U NEVER have a smaler CD with full flaps, than the same plane without flaps at max AoA.

The F2A test also confirm my thoughts. The plane can turn more tight in 13000ft, but not without altitude lost, so with more thrust. If you look to the testdatas, you will see that the radius while a sustained turn with full flaps decrease by just 20%, while the turn rate increase.
F2A, at 13000ft, 900HP:
Radius no flaps: 825ft , 114mph, 9°/sec
Radius 22° flaps: 730ft, 90mph, 7,2°/sec,  13% radius gain, 20% turnrate lost.
Radius 54° flaps: 660ft, 85mph, 6,4°/sec, 20% radius gain, 30% turn rate lost.

If i compare this with the AH F4U-4 results, the AH F4U, but also the other planes must have magic flaps, cause they dont realy decrease the turn rate, while they decrease the radis by almost 40%.

Even with much reduced power the F4U-4 keep the same turn rate with/without full flaps.

I remeber a time when the AH flaps of most planes did work like the F2A flaps in the test, at that time many did complain the incredible f4U flaps, now all have this behaviour, although its not as extreme, at least its a bit more even.

Greetings,

Knegel

[Brooke]

OK, I said I'd post math and here it is -- The Math of Turning:

http://www.electraforge.com/brooke/flightsims/aces_high/stallSpeedMath/turningMath.html

I have also added Appendices to talk about how stall speed and climbing performance relate to turning performance.  As I summarized before, stall speed has a lot to do with turning performance -- the math shows why.  As Hitech has summarized before, stall speed and lift by itself has little to do with climb rate -- again, the math shows why.  It will also show that dropping flaps is going to decrease your maximum steady-state climb rate and why.

This is a lot of (tedious) math.  If by some miracle someone actually goes through the math of it, if you find errors, please let me know.

[mtnman]

Well, I just got back from Chicago.  Going through all these posts I can safley (very safely) say I don't have anything worthwhile to add.  You guys have taken this discussion well above my level, hehe.

I enjoyed reading the math explanations, etc, and feel I'm getting the basics...

Brooke-  Hats off to you for that math and a write-up I can follow!  

MtnMan

[dtango]

Great post Brooke.  Thanks for taking the effort to putting together the write up.

Mtnman – I just got back from Chicago myself !  Was there for the 4th and just returned Saturday evening.

+++++++
Knegel where do I start ?  Let’s try making a single statement at a time here to get on the same page.  

Why isn’t a sustained turn and a steady climb the same thing?  Because a turn means there is a net force creating acceleration normal (90 degrees) to the flight path.  In a steady climb (climb at constant velocity) however, there is 0 normal acceleration to the flight path because the net force normal to the flight path is zero.  

What does this mean?  Let’s say the airplane is wings level with the horizon.  If there was no gravity (like your example you gave) and you had a 1g lift force, then you would end up with a vertical turn, NOT a steady climb at constant velocity.  A turn means you’re going around in basically a circular path either oriented vertically or horizontally.  If you had a sustained turn in the vertical you would end up in a loop, not a steady climb.  

On the other hand a steady climb means you’re going up an inclined straight path.  The flight path is straight because there is no normal acceleration to the flight path to cause it to curve.  

Circular vs. straight.  Normal acceleration > 0 vs. normal acceleration = 0.  Turn vs. climb.  Not the same thing.

Let’s start here. We have to agree on this topic before we discuss anything else.  This is fundamental to the discussion.  Do you agree with the above concept?

Tango, XO
412th FS Braunco Mustangs