Corsair Turning Ability in AH

[mtnman]

Even in a chase by a spit on the deck, the hog can kill him with a very simple manev. I not gonna say what that manev is as it my secret. I sure mtnman, chrispy and saxman know what manev i talking about.

MtnMan

BTW- You've all witnessed history!  I actually figured out how to do quotes and smilies tonight!  This is the first I've ever had it work right!  

Some applause would be acceptable at this point...

[SgtPappy]

Originally posted by mtnman
That's awesome Ack-Ack! I'd never heard that bit of info...  I was just speculating.

MtnMan

Not only did they fight the Japanese and initially lose, they ran out of fuel over the ocean sometimes, on rare occasions. The Spitfire Mk.Vc's arrived in Australia in defense of Darwin early in '43 and fought many-a Zeke and Betty. They arrived with the sand-filtering Volkes air intake unit (designed to filter sand not the stuff of tropical climates) along with many MANY technical fallouts including oil line corrosion. Those of you who know how engines react to the smallest malfunction know that it can pull quite a few miles off the aircraft. The Volkes chin filter alone killed the Spitfire's ram-air performance, lessening its range, speed and climb rate. Add that to the tech. malfunctions and you got yourself one dead Spitty.

Eventually, the Spitfires used their better E fighting techniques (yeah I know, Spits aren't the greatest E fighters, but better so than the A6M) and BnZ'd the meatballs off those Zekes. In October 1943, the Aussies got their Spitfire Mk.VIII's. Boo-yah.


ANYWAY back to the topic. Crispy, when I get out of a Hog and into a Spitfire, La-7 and a Niki, it feels more like getting into a sports car .... right after getting out of a muscle car. That is a muscle car with dive breaks

Try out-vertical scissoring a Zeke in a Spitfire and see what happens.

[dtango]

There’s been a lot of discussion about the impact of flaps on turn performance.  Specifically, how does the increased drag of flaps impact the rate of turn of an aircraft?

My previous responses to this question relied on a series of calculations to explain the physics at work in a sustained turn and the resulting turn rate performance.  This explanation is harder to intuitively understand because of the stages of calculation needed.  I’ve since found a more mathematically intuitive method to explain sustained turn rate performance.

The Problem
It’s widely stated that sustained turn performance is a function of an airplane’s specific excess power.  As already discussed specific excess power is



Specific excess power is the sum of the energy usage in maneuvering the airplane.  It gives us insight into the maneuvering loads an airplane can sustain bound by it’s energy gain or loss as a function of thrust and drag.

A difficulty, however, lies in how to translate specific excess power to turn performance.  Turn performance is usually expressed as load factor, turn radius, and turn rate.  Specific excess power does not give us direct visibility to these performance variables. They must be derived from key aerodynamic coefficients embedded in Eq. (1.1) in order to make them visible.  For instance an aircraft’s rate of turn is



To arrive at a value for turn rate in Eq. (1.2) as a function of specific excess power from Eq (1.1) requires several stages of calculations.  Therefore, it is non-intuitive to arrive at an aircraft’s turn performance through specific excess power.

Is there a more intuitive way of understanding the relationship between specific excess power and turn rate without having to go through a series of calculations to gain understanding?  The answer is yes.  

An aircraft in a sustained turn neither gains or loses altitude and airspeed while holding it’s turn. This means that the aerodynamic forces are in equilibrium while in a maneuver.  In mathematical terms specific excess power equals zero (PS = 0).  Bypassing the mathematical derivation, knowing this relationship leads to the following



where n is the load factor of the aircraft in a sustained turn as a function of the basic aerodynamic variables of lift, drag, thrust, and weight.  


The Key Equation: Turn Rate as a Function of L/D, T/W, & Velocity
Substituting Eq. (1.3) for load factor in Eq. (1.2)



We now have an expression of an aircraft’s sustained turn rate in key aerodynamic ratios derived from specific excess power.  Eq. (1.4) gives us a more intuitive way to understand how key aerodynamic factors affect an airplane’s sustained turn rate.

We can now intuitively evaluate the affect of deploying flaps on turn rate as a function of the flap’s lift and drag.  From Eq. (1.4) we see that turn rate is a function of lift-to-drag ratio, thrust-to-weight ratio, and velocity.  Rate of turn is maximized when lift-to-drag and thrust-to-weight are maximized while velocity is minimized.

We know that deploying flaps reduces an aircraft’s lift-to-drag ratio.  Flaps increase the lift of aircraft but at a cost of increased drag as well.  If L/D ratio reduces with flaps, then so should turn rate right?  So what’s going on if turn rate remains the same or is actually better with flaps deployed?  

The reason is we can’t forget about velocity in Eq. (1.4).  Flaps also reduce the minimum maneuvering speed of an airplane too so while L/D decreases, so does velocity.  Secondly for piston-propeller aircraft thrust varies with velocity as well increasing as velocity decreases.

The bottom line is sustained turn rate is a function of lift-to-drag ratio, thrust-to-weight ratio, and velocity which all need to be factored in because they all vary depending on the configuration and airspeed of the airplane.

Illustration Using the Equation
Let’s put some data to this to demonstrate the dependence of turn rate on the combined ratio of lift-to-drag and thrust-to-weight divided by velocity.  For the below I used the same static variables and propeller efficiency curve from my previous calculations.  The calculations represent sustained turns at maximum lift coefficient (Clmax), or the maximum lift-limit achievable by an aircraft.

Here’s a table with variation in Cl/Cd for comparison to evaluate Eq (1.4) above.  At the point of best sustained turn rate (Ps=0) Cl/cd, V, T, and W were plugged into Eq (1.4).  These are the results for turn rate.

Plane Config Clmax Cd0 Cd cl/cd V Ps=0 T W n rate (dps)
1 clean 1.6 0.02 0.2 8 160 3949 12400 2.55 18.4
2 flaps 2.8 0.1 0.6 4.3 100 5164 12400 1.79 18.7
3 flaps 2.2 0.1 0.4 5 120 4755 12400 1.92 17.1
4 flaps 2.8 0.18 0.7 3.8 97 5281 12400 1.64 17.2

Plane #1 and #2 were the same ones in my previous calculations (same results as before).  Note that they are both approximately the same turn rate despite L/D ratio being lower for Plane #2.  The reason is the thrust is greater while the velocity where thrust=drag is also lower.  The net result is Plane #1 and #2 have approximately the same turn rate despite Plane #2 being "draggier" because of the flaps.

Plane #3 I hypothetically decreased Clmax.  This results in a better lift-to-drag ratio (remember CD includes both the parasite and induced components of drag) compared to Plane #2, yet Plane #3 has a worse turn rate.  The reason is the velocity where thrust=drag (Ps=0) has increased which also reduces the amount of thrust available. The combination of both the increase in airspeed for Ps=0 and reduction in thrust results in a lower turn rate.

Plane #4 I left Clmax the same but increased the profile drag from .1 to .18.  This results in a lower velocity where thrust=drag (Ps=0) and higher thrust but in combination with the lower lift-to-drag ratio results in a lower turn rate compared to that of Plane #1 or Plane #2.

What happens if we changed the engine BHP available for Planes #1 and #2?  It was assumed to be 2380 HP.  Let’s reduce it to 2000 HP and see what the result is.

Plane Config Clmax Cd0 Cd cl/cd V Ps=0 T W n rate (dps)
1 clean 1.6 0.02 0.2 8 151 3520 12400 2.27 17
2 flaps 2.8 0.1 0.6 4.3 96 4625 12400 1.6 16.4

We see now that Plane #2 has a lower sustained turn rate compared to Plane #1.  Changing the available horsepower changed the thrust and also the velocity where thrust=drag.  The net result is a lower turn rate for Plane #2.

All these examples demonstrate that sustained turn rate is function of the combination of lift-to-drag, thrust-to-weight, and airspeed as expressed in Eq. (1.4).  

A key learning is that we should be careful with making conclusions regarding airplane performance that rely on generalizations.  Equation (1.4) demonstrates why conclusions such as increased drag of flaps reduces sustained turn performance or extrapolating steady climb performance to turn performance are inaccurate because they oversimplify what occurs in a sustained turn.

I hope this helps to illuminate the topic.

Tango, XO
412th FS Braunco Mustangs

[Knegel]

Hi,

i  still think there is something badly wrong in that calculation.

Specialy the comparison between Plane #2 and #4 looks strange.
How shal a plane with same CLmax but more drag(less excess thrust) shal turn faster??
This would be like reducing power, this cant result into a faster sustained turn rate. With same CLmax it cant turn more tight and with more drag(less excess thrust) is must turn more slow.

With thrustline i mean the angle between flightpath and engine, while using full flaps this change much, not a bit, as faster the plane fly with flaps as more this phenomen get visible. This would count specialy for #3, where the thrustline must point far outside the flightpath. As result some parts of the thrust work against the lift and dont work into flight direction at same time.  This minimise the excess thrust and increase the needed lift at same time.

The "excess lift" also dont seems to be included in your calculation. A slower plane produce less lift, as result the needed lift to keep a level flight(1G) weights more than in a faster plane.
As slower a plane fly as more problematic gets the gravity.
So a faster plane can bank more and have a higher "excess lift".

btw, what is "T" ?

Its difficult for me to follow all your explanations without a calrification of the values. Some vary from what we use in germany, some i simply never saw. Sorry for my ignorance.

Edit: Where in the F2A test we have the climb rate listed with flaps??

Greetings,

Knegel

[dtango]

(1) Equation / calculation badly wrong?
-------------------------------------------------
I'm extremely confident in the equation (1.4).  I've crossed checked the derivation against 3 separate aerodynamics texts.  Feel free to check the math logic.



This equation gives sustained turn rate performance from the basic aerodynamic variables using the standard assumption of small thrust angle (alpha-t).

There is some rounding in the actual numbers I'm putting in but it doesn't change the outcome.


(2) Plane#2 vs. plane#4
--------------------------------
Plane #4 turns slower than Plane#2.



(3) Thrustline, thrust angle differences
-------------------------------------------------
Since you insist on including it here is the sustained turn rate equation with thrust angle factored in.



A little bit more messy but if you examine the key relationships between L/D, T/W and velocity are the same between Eq (1.4) and Eq (1.4b).  

Alpha-t represents the thrust angle.  For conventional aircraft it is usually between 2-7 degrees.  (The Hellcat of course was odd in that it had a -2 degree thrust angle.)

Let's say you're right about the thrust angle issue (which I don't think is true at all in a turn as I explained earlier).  But suppose you are right. Let's assume 7 degrees of thrust angle (very high for conventional aircraft).  Let's assume that with full flaps as you say thrust angle is reduced by -7 degrees.  Here's what we get for turn rate.

Plane Config Clmax Cd0 Cd cl/cd alpha-t V Ps=0 Thrust Weight n (g's) rate (dps)
1 clean 1.6 0.02 0.2 8 7 160 3949 12400 2.56 18.6
2 flaps 2.8 0.1 0.6 4.3 0 100 5164 12400 1.79 18.7
3 flaps 2.2 0.1 0.4 5 0 120 4755 12400 1.92 17.1
4 flaps 2.8 0.18 0.7 3.8 0 97 5281 12400 1.62 16.5

Alpha-t is the thrust angle.  T=thrust.  I've relabled the table so that you can see that.

Notice that the outcome really doesn't change at all.



(4) F2A Report:
--------------------
Regarding climb, fig 32, 33, & 34.  Re-read my post that has it spelled out.

Tango, XO
412th FS Braunco Mustangs

[evenhaim]

dam tango great stuff

[Knegel]

Hi dtango,

thanks again for your clarification.
Regarding "2." , i had a "brain fart", of course #4 turns slower than #2, so all is ok.

With the thrust angle included the result looks much more friendly to me, what i still dont understand is, where in the sustained turn formula is the lift included to overcome the 1g, to keep a level flight?
While comparing planes that fly with same or similar speed this isnt that important, but while flying at so much different speeds(160mph vs 100mph), the needed lift to overcome the gravity should have a not to smal influence to the the bank angel and so to the  "excess lift".

Although the full flap condition have a much better lift coefficient as result, the plane fly much more slow, as result the produced lift isnt in the same relation, while the needed lift to overcome the -1g (gravity) remain the same. As result the more slow flying plane suffer more by the -1g, than the faster plane.
This gets best visible when the planes fly with much reduced power. At one stage the plane without flaps start to turn more tight and much faster, than the more slow flying plane with flaps. Simply cause the plane with flaps have problems to bank, without to lose altitude. As result the "excess lift" is smaler than that of the plane without flaps. As faster the planes fly, as less important the gravity get, cause the ammount of produced lift get much higher than the needed lift to overcome the -1g.

btw, where do you got the thrust values from??

Greetings,

Knegel

[dtango]

Knegel:

It’s included in the Cl (lift coefficient) term in the equation:


By definition in a turn Cl must be greater than Cl at 1g.  Thus:



Therefore another way to represent the turn rate equation is:



This would be rather unconventional and simply redundant so we just leave Cl as....well simply Cl and not as Cl1g+delta_Cl_turn.  
 

Although the full flap condition have a much better lift coefficient as result, the plane fly much more slow, as result the produced lift isnt in the same relation, while the needed lift to overcome the -1g (gravity) remain the same. As result the more slow flying plane suffer more by the -1g, than the faster plane.
This gets best visible when the planes fly with much reduced power. At one stage the plane without flaps start to turn more tight and much faster, than the more slow flying plane with flaps. Simply cause the plane with flaps have problems to bank, without to lose altitude. As result the "excess lift" is smaler than that of the plane without flaps. As faster the planes fly, as less important the gravity get, cause the ammount of produced lift get much higher than the needed lift to overcome the -1g.

You should be careful in how you’re characterizing the physics in these statements.  There is only a portion of the flight envelope where this is true so be careful not to oversimplify this and apply it universally.  This only applies when the reduction in lift coefficient to satisfy where thrust=drag in a turn at higher velocities becomes pronounced compared to the aircraft without flaps.

2ndly remember not to confuse turn rate with load-factor.

---------------------------
Thrust…

thrust = engine BHP * prop-efficiency *550 / velocity

So if we know engine BHP, prop efficiency and velocity we can find thrust.  Engine BHP for the F4U is readily available from various sources.  The prop-efficiency curve was derived from calculations based on momentum theory.  You can find all these listed above in my previous post discussing my original calculations (page 7 of this thread).

Cheers!

Tango, XO
412th FS Braunco Mustangs

[nooblet187]

Hey, do we need all this math? lol. I'm going to try to explain this since I'm not so good at math.

While climbing thrust is the 'mostly' the limiting factor, not lift. It doesn't matter if your going max speed at max climb or 110 mph climbing fast as possible without stalling. Thrust is limiting you in both these cases. If you increased lift by adding more wing area or engaging flaps you're also increasing drag.

Increasing wing area will increase lift and drag, it will help with turning and allow for slower stalls and slow your plane down overall .  Flaps also increase lift & drag, except alot. Which isn't very usefull when there is already plenty of lift in a climb. Excess lift will only create excess drag, ALSO the thrust is unable to take advantage of all that lift!  If you increase lift and drag you must increase thrust to be able to maintain the same speeds.

Also important to point out. While climbing flaps have the tendency to push your nose upwards, which the elevators have to fight against. Which makes your wings fly in a weird angle that they dont like! If you didn't lower your nose after engaging flaps you would stall out soon. Basically you're adding much more drag to the plane when combining these factors, then you are lift. This is basically what you want though in a turn.

When doing a sustained turn at full throttle, lift and thrust are factors. Without flaps, your wings AOA and lift will max out at a certain point, and you will stall. Your wings lose lift as the AOA is too high. Flaps will increase your AOA and lift at the cost of drag and speed, allowing tighter turns to stay on that spitfires arse. Now your flaps are actually doing something useful !!

Also you keep saying something about lift is worse at slower speeds and its less efficient to fight the earths gravity. Thanks to someone(sorry I'm too lazy to go back! nice math I dont get any of it:cry) here is nearly 1G of pull saved by slowing down and going in a tighter turn:
mph   g   rate
170   2.90   20.1
110   2.02   20.1


I hope this makes sense somewhat to you, if you think I've left anything out let me know.

[rednex21]

i have no clue what you guys are talking about but i love the Corsair.  And btw...the F4U-4 turns great without flaps.

[SgtPappy]

Originally posted by nooblet187

Increasing wing area will increase lift and drag, it will help with turning and allow for slower stalls and slow your plane down overall .  

Wing area is only increased in aircraft with Fowler flaps like the P-38 or the Ki-84 'Frank'. Next the F4U's flaps help increase lift co-efficient and then you have smelly flaps on the Spitfire. IMO the otherwise awesome Spit's main fault was it's 'crap flap' which was a split flap designed ONLY to increase drag.

[nooblet187]

Ok, this should clear some things up.

When flaps are engaged in level or climb, the planes nose is at a lower angle. The wing tips(past the flaps) produce little or no lift and are causing drag and worsens at higher speeds. Also the elevator causes drag keeping the nose down. This may be more or less extreme in AH or real life though.

While turning the wings tips past the flaps is at a high enough angle to help produce lift. At 20 degrees of flaps the elevator causes alittle drag, at 40 degrees there is more drag on the elevator. As the f4u pilots stated I noticed the best results at 20 or less degrees.

I did some tests in X-plane, and frapsed them with flight model enabled, with a  f4u-1a corsair. In the video you will see in the scenes first 'no flap climb', then 'full flap climb', 'no flap turn', 'half flap turn', 'full flap turn'.

Video: http://www.mediafire.com/?4i4wdh3dtyd

[Knegel]

Originally posted by dtango
Knegel:


Therefore another way to represent the turn rate equation is:



This would be rather unconventional and simply redundant so we just leave Cl as....well simply Cl and not as Cl1g+delta_Cl_turn.  
 
Cheers!

Tango, XO
412th FS Braunco Mustangs

Hello Tango,

after a bit more reading in this article, it got clear to me that the effect i did describe is already included in your formula, but its hidden and only got visible to me while looking to the other fomulas, which at the end result in your formula.
http://flighttest.navair.navy.mil/unrestricted/FTM108/c6.pdf

But in this articel i found another agument against a that good turn at very slow speed(same weight, fuselage, wingspan etc), its the effect of a increased sideforce, which work against the lift. This sideforce effects need a higher rudder variation(or smaler bank angle)  at slower speeds, cause the Fuselage/Rudder work somewhat like a wing while a banked flight, so the slower flying plane need a higher rudder variation to overcome this sideforce and this add drag and reduce the excess thrust. This specialy count for high bank angles.

This article also confirm the influence of Alpha-t to the thrust lift(lift = wing lift + thrust lift) and of course the thrust lift also influence the turn performence(more AoA = more thrust lift).

In all this calculations is the bad influence of a higher torque(specialy at max power) at slower speeds not included, which result in the need of a higher aleron and maybe rudder deflection, what will have a higher drag and a more bad stall speed(smaler CLmax than expected) as result.

Anyway, your last calculation with alpha-t included already show what i assume and what the F2A also show. A slower turn rate with max flaps than without in a sustained turn, already at sea level and max Power(best case).
19,3 sec/360° 160mph(Radius 722ft) without flaps and 21,8sec/360°(Radius 492ft) with full flaps seems to be more credible, while the absolutly easy and stable full flap flight at stall speed seems to be a bit off(max up trim alone keep almost the most tight turn, torque effects dont disturb, while the stall edge at higher speeds is more difficult controllable, at least for me).

Only few planes in AH show a turn rate penalty due to full flaps of 2,5sec/360° at sea level, while the F4U seems to have rather outstanding flaps.
 
I still keep my opinion, the flaps in AH are overdone while turning, while they give the right penalty while climbing.

The reason for this discrepancy might be that the thrust lift got included while climbing, while it got neglected for the horizontal turning part.

[Knegel]

Originally posted by SgtPappy
......................... IMO the otherwise awesome Spit's main fault was it's 'crap flap' which was a split flap designed ONLY to increase drag.

In AH the Spit´s turn great with full flaps, it show a better radius reduction due to full flaps than the Ki84 or P38(both with fowler flaps).  

[Knegel]

Originally posted by nooblet187
Ok, this should clear some things up.

When flaps are engaged in level or climb, the planes nose is at a lower angle. The wing tips(past the flaps) produce little or no lift and are causing drag and worsens at higher speeds. Also the elevator causes drag keeping the nose down. This may be more or less extreme in AH or real life though.

While turning the wings tips past the flaps is at a high enough angle to help produce lift. At 20 degrees of flaps the elevator causes alittle drag, at 40 degrees there is more drag on the elevator. As the f4u pilots stated I noticed the best results at 20 or less degrees.

I did some tests in X-plane, and frapsed them with flight model enabled, with a  f4u-1a corsair. In the video you will see in the scenes first 'no flap climb', then 'full flap climb', 'no flap turn', 'half flap turn', 'full flap turn'.

Video: http://www.mediafire.com/?4i4wdh3dtyd

Hi,

at a climb speed of 100mph, the full flaps AH F4U-4 elevator is absolut level, so the drag is perfect regarding this and also the wingtips stand good in the "wind".  At max AoA(around 75mph), the climb is worse.
The slower climb speed with full flaps result in a rather similar drag, like the same plane without flaps at 170mph, despite the drag coefficient got increased by the flaps and at same time the effective thrust is better at slow speed than at higher speeds.

One reason for the so much worse climb with full flaps must be the smaler thrust lift due to a disadvanced angle between airfoil and engine, while flying with full flaps. The engine points relative more downward in combination with fhe "full flaps airfoil", this is wanted to provid a better sight while landing. And the max AoA is also worse with full flaps.
Roundabout like this:


While climbing and turning at max AOA the discrepancy is most big, resulting in a smaler thrust lift.

Greetings,

Knegel