Bf-109 K-4 Air Combat Performance

[Crumpp]

The ingame K-4 does not even feature a CLmax of 1.48, that is for sure.

 

1.4 is the CLmax used by Mtt and the same value was derived by the RAE.

 

I based an analysis off of that and the Clmax of 1.48.

 

CLmax 1.4:

 

 

 

CLmax 1.48

 

 

 

The bottom line is it does not make that much of a difference. It will not change the balance.

 

The Bf-109K4 best rate of turn speed is still higher than the Mustangs. The Mustang can still turn at a slower speed with a higher rate than the Bf-109K4.

 

A P-51D Mustang simply is not able to outturn a Bf-109K4 unless the Bf-109K4 pilot tries to follow the P-51 around the turning circle at the slower speeds the P-51 can attain.

 

That being said....

 

It is not the machine that the Mustang needs to outmaneuver, it is the man in it.

 

 

For our universal pilot:

 

98.4mmHG = Arterial blood pressure

 

13.6 Kg/M^3 = Specific density of Blood (Do not be confused by the units...it is really dimensionless)

 

385mm = Distance from the eyes to the aortic valve

 

In a 90 degree upright seat:

 

G = 98.4mmHG*(13.6/385mm) = 3.47G

 

In a 14 degree seat:

 

The effect of seat angle is to directly reduce the distance from the eyes to the heart at the inverse cosine of the angle from horizontal or sine of the angle from vertical.

 

90 degrees - 14 = 76 degrees

Sin(76) = .970

 

385mm * .970 = 373

 

G = 98.4mmHG*(13.6/373mm) = 3.58G

 

In a 25 degree seat:

 

90 degrees - 25 = 65 degrees

Sin(65) = .90

 

385mm * .90 = 347mm

 

G = 98.4mmHG*(13.6/347mm) = 3.85G

 

http://forums.eagle.ru/showpost.php?p=2491319&postcount=86

 

The Bf-109K4 pilot is able to skirt the physiological edge of the blackout threshold. Depending the specific maneuvers and load factors used to get into that turning circle, his G-tolerance and G-endurance will change.

 

The seat angle of the Bf-109K4 increases G-Endurance but does nothing for the pilots G-tolerance.

 

The P-51 pilot on the other hand has a G-suit which increases his G-tolerance but does nothing for his G-Endurance. The P-51 pilot can pull a higher load factor at high speeds. He cannot sustain multiple G exposures for as long as the Bf-109K4 pilot though.

 

The P-51 pilot can withstand a higher single exposure limit which means he can take advantage of the Mustangs corner speed. That is why the USAAF published variable load factor limits for the P-51 based on weight. Their pilots equipped with a G suit could take advantage of that G-tolerance.

 

That means a Mustang that keeps it speed up and maneuvers is a rough customer for either German fighter. His time period to use that advantage is limited though by his shorter G-endurance. The mean is ~2minutes and 40 seconds. If he hits the G-endurance maximum exposure time, then his ability to handle load factor exposure is severely curtailed.

 

It seems there has been some welcome changes to the physiology model. I know I have blacked out twice and lawn darted because I pushed the load factor limits too hard. How much load factor I am pulling is correctly a part of my "air combat" thinking.

 

These aircraft were pretty well balanced combat platforms in reality. That is because in real life, things are three dimensional. That is why the P-47 shot down the majority of the Luftwaffe. It wasn't because of its aerodynamic performance on a piece of paper.

 

In DCS we have a study simulator that is making three dimensional representations of these aircraft for the first time, I believe.

 

The specific advantages and disadvantages are not equal, when you sum up the aerodynamics, stability and control, and pilot physiology technology the playing field is pretty much equal for the World War II fighters in terms of dogfighting.

 

That is what makes it such an interesting time period and so much fun!

 

Sorry for the long winded post! :)

[Crumpp]

No, I didnt confirm anything, it was stated it could be calculated in the sim, Crumpp sent me the formula, I talk with Yo-Yo all the time, so if I need to know if its correct I ask him, its easier than math.

 

That is all you need to do really. :thumbup:

[Anatoli-Kagari9]

Crumpp,

 

excellent contribution!

 

Those graphs are a must have - just saved them for the future, and while I try to learn dogfighting techniques in the K4...

 

She's a beech when you let it bleed off speed....

[Crumpp]

Thank you Jcomm!

[jester_]

I think you can already adjust them for single player by editing the weapons file.

 

god dammit.

[Anatoli-Kagari9]

Thank you Jcomm!

 

Crumpp,

 

tried only in 1.5.1, because I can't set the Fw190 in Nevada tonight ( no spare time...), but in 1.5.1, trying to fly with the same loads in SP and MP, I couldn't notice any difference in the stick behavior .

 

The only thing I did notice is that it has neutral stability for pitch up inputs, and positive stability for pitch down perturbations from trimmed flight states.

[Hummingbird]

I find a 1.4 Clmax for the 109 very hard to believe, esp. considering the 1.48 result at the Charles Meudon wind tunnels without slats and a reduced wing span and thus aspect ratio. I'd expect 1.6 at least.

 

The landing speed of the K-4 is afterall some 25 km/h slower than for the P-51D. (150 vs 175 km/h)

 

NACA tests with copied MTT slat mechanism (right)

 

 

Same results as at MTT:

 

 

Edited December 3, 2015 by Hummingbird

[Echo38]

I find a 1.4 Clmax for the 109 very hard to believe [...]

 

The landing speed of the K-4 is afterall some 25 km/h slower than for the P-51D.

 

Help me understand. Hypothetically, let's say you're correct, and that the K4 is supposed to have a 1.6 CLmax. Okay, so:

 

If the K4 is supposed to have 25kph slower landing speed than P-51, and it does;

If the K4 is supposed to have 1.6 CLmax, but it doesn't;

 

Then, if the K4's CLmax is raised to 1.6, what happens to the landing speed being 25kph slower than P-51? Does it get even slower? In which case, wouldn't it end up lower than it should be? And what would be the cause of this, if the CLmax is right? Means something else is wrong, yes?

 

And if the landing speed doesn't end up slower, when CLmax is increased--i.e., if CLmax doesn't affect landing speed--then why do you use the lower landing speed as evidence of higher CLmax? I just don't understand how the two points of your hypothesis work together. Unless you're saying that the CLmax is too low, but something else is too high, causing the landing speed to be at the correct figure, even though the CLmax is too low?

[HeadHunter52]

Yes, you can adjust the ammo type load-out in SP. Not sure of a MP server can make changes to its files available to aircraft logging in.

[Crumpp]

NACA tests with copied MTT slat mechanism (right)

 

It is the airfoil that determines our Clmax.

 

This is V24 and AFAIK, it did have slats as well as other configurations.

 

http://www.messerschmitt-bf109.de/display.php?lang=de&auth=e&name=version_display&fotonummer=1027

 

The slats on the Bf-109 did not do much for raising the Clmax. They kept the ailerons effective at the stall, mitigated the stall behaviors, and prevented spin entry.

 

Here is the polar. Now the 1.4 used by the RAF and Mtt simply may have been just a significant digit value. I get 1.41 in my calculations based on the 15 degrees radiator position.

 

You can see the dependance of Clmax on the split flap cooling position:

 

 

If you look at where the coolers are located, it is right at the root where flow separation occurs first.

 

 

It was a wing designed to squeeze every bit of performance out of the airfoil and still maintain good stall characteristics.

 

You have a split flap system placed at the point of flow separation with LE slats over the outboard section on a wing with no twist. It is not surprising radiator flap position has such an effect.

 

Mitchell did the same thing in the Spitfire.

Edited December 3, 2015 by Crumpp
"They kept the ailerons effective" not "They kept the ailerons effect"

[Echo38]

I find a 1.4 Clmax for the 109 very hard to believe, esp. considering the 1.48 result at the Charles Meudon wind tunnels without slats

 

When you say "without slats," do you mean that the slats were missing, or merely prevented from opening?

[Hummingbird]

Crumpp,

 

V24 featured no slats, and the wing span was significantly reduced as well, decreasing the wing AR.

 

Bf-109 V24:

 

Furthermore the slats helped increase the CLmax by keeping the outboard part of the wing from stalling before the inboard part by raising the critical AoA & Clmax by approx. 25%, and since the inboard part always stalls at a higher AoA and CLmax (usually ~15% higher) this thereby increases the overall CLmax of the wing by ~10-15%. This becomes esp. true with power on as the inboard part is then energized by the prop stream further raising the CLmax.

 

As a result I'd expect at least a 1.6 CLmax for the 109, and the big difference in landing speeds between the K-4 and P-51D only serves to underline this.

 

In short the K-4 ought to feature both a lower lift to weight and power to weight ratio than the P-51.

Edited December 3, 2015 by Hummingbird

[Hummingbird]

When you say "without slats," do you mean that the slats were missing, or merely prevented from opening?

 

They simply weren't incorporated in the wing. V24 was a test bed for a wing without the elliptical wing tips and outboard slats.

[Crumpp]

It was fitted with both slats, as well as without slats and fences. V24 was the test bed for the Bf-109F series and the airframe used to research the airframe changes brought about in that series. It is the airframe they tinkered with to confirm design assumptions later incorporated into the Bf-109F series

 

Aspect Ratio effects our Drag due to lift and not our CLmax. CLmax is purely a function of the 2D airfoil and the Bf-109 series has the same airfoil.

 

Messerschmitt Bf 109B NACA 2R1 14.2 NACA 2R1 11

Messerschmitt Bf 109C NACA 2R1 14.2 NACA 2R1 11

Messerschmitt Bf 109D Dora NACA 2R1 14.2 NACA 2R1 11

Messerschmitt Bf 109E Emil NACA 2R1 14.2 NACA 2R1 11

Messerschmitt Bf 109F Fredrich NACA 2R1 14.2 NACA 2R1 11.35

Messerschmitt Bf 109G Gustav NACA 2R1 14.2 NACA 2R1 11.35

Messerschmitt Bf 109K NACA 2R1 14.2 NACA 2R1 11.35

 

http://m-selig.ae.illinois.edu/ads/aircraft.html

 

The root airfoil remains unchanged throughout the Bf-109 series. The tip airfoil was changed in the Bf-109F series and remained untouched for the rest of the designs life.

 

That is why i posted the G series polar and it is more representative. The V24 is good for trend information only and not specifics.

 

Clmax of 1.6 is not appropriate IMHO. It is not reflected on any polar and most damning is not used by Mtt.

 

Again, they use 1.4 only out to a single decimal place for the Bf-109E series. I used 1.41 based on radiator flap position of 15 degrees. CLmax will change based on radiator flap position.

[Hummingbird]

It was fitted with both slats, as well as without slats and fences. V24 was the test bed for the Bf-109F series and the airframe used to research the airframe changes brought about in that series. It is the airframe they tinkered with to confirm design assumptions later incorporated into the Bf-109F series

 

Aspect Ratio effects our Drag due to lift and not our CLmax. CLmax is purely a function of the 2D airfoil and the Bf-109 series has the same airfoil.

 

 

 

http://m-selig.ae.illinois.edu/ads/aircraft.html

 

The root airfoil remains unchanged throughout the Bf-109 series. The tip airfoil was changed in the Bf-109F series and remained untouched for the rest of the designs life.

 

That is why i posted the G series polar and it is more representative. The V24 is good for trend information only and not specifics.

 

Clmax of 1.6 is not appropriate IMHO. It is not reflected on any polar and most damning is not used by Mtt.

 

Again, they use 1.4 only out to a single decimal place for the Bf-109E series. I used 1.41 based on radiator flap position of 15 degrees. CLmax will change based on radiator flap position.

 

Wing AR does affect the CLmax as well as the slope of the lift curve. An increase in AR also leads to an increase in Clmax, albeit it is relatively small.

 

However if the increase in AR is large the difference is quite noticable, as with the Ta-152H which enjoyed an increase of +0.12 from the 1.58 of the Fw190 to 1.7 using the same NACA 23xxx airfoil.

 

Also I'd be very vary of using Bf-109E data to determine 109F+ wing CLmax considering the signficant change in wing design. From the F series onwards there was less of a taper in wing thickness and the planform design was noticably changed with the incoperation of elliptical wing tips. Slat design was also altered.

[Crumpp]

Wing AR does affect the CLmax

]

 

Not for World War II fighters.....

 

Only for very very low aspect ratio designs like the F-104 Starfighter. It is not a factor or a contributor for the Aspect Ratio range we are talking about.

[Crumpp]

Also I'd be very vary of using Bf-109E data to determine 109F+ wing CLmax considering the signficant change in wing design. From the F series onwards there was less of a taper in wing thickness and the planform design was noticably changed with the incoperation of elliptical wing tips. Slat design was also altered.

 

Bf-109G series data is posted in this thread. I used 1.41 based on radiator flap position of 15 degrees.

[Hummingbird]

]

 

Not for World War II fighters.....

 

Only for very very low aspect ratio designs like the F-104 Starfighter. It is not a factor or a contributor for the Aspect Ratio range we are talking about.

 

 

Well it did do so for the Ta-152, and quite noticably.

[Hummingbird]

Bf-109G series data is posted in this thread. I used 1.41 based on radiator flap position of 15 degrees.

 

I am not quite sure what said chart is really concerning though considering the cooling flaps operated according to engine temperature. Furthermore at 0 deg is indicated 1.27, which is an odd figure.

 

Anyway 2R1 12 CLmax is 1.53, which pretty much is exactly the same as the uppermost curve on the document you posted which lists 1.55 (fits well for a 14.2% airfoil):

[Crumpp]

The chart is labeled,

 

Coefficient of Lift vs Angle of Attack

 

Lift to Drag Ratio

 

Coefficient of Lift vs Coefficient of Moment

[Hummingbird]

The chart is labeled,

 

Coefficient of Lift vs Angle of Attack

 

Lift to Drag Ratio

 

Coefficient of Lift vs Coefficient of Moment

 

Yes, but again the cooling flap position varied automatically according to engine temp. Also the 1.27 makes no sense, thus I am suspecting that the chart is part of a more detailed report.

[Crumpp]

Well it did do so for the Ta-152, and quite noticably.

 

It is not due to the aspect ratio increase.

 

AR allows a reduction in the 3Dimensional wing drag due to lift which means the wing can climb higher on the 2D airfoil polar.

 

AR ratio will not increase the 2D polar Clmax.

[Crumpp]

I am not quite sure what said chart is really concerning though considering the cooling flaps operated according to engine temperature. Furthermore at 0 deg is indicated 1.27, which is an odd figure.

 

Anyway 2R1 12 CLmax is 1.53, which pretty much is exactly the same as the uppermost curve on the document you posted which lists 1.55 (fits well for a 14.2% airfoil):

 

 

I agree and further proof it is the polar...beside being labeled that!

 

:P

[Hummingbird]

It is not due to the aspect ratio increase.

 

AR allows a reduction in the 3Dimensional wing drag due to lift which means the wing can climb higher on the 2D airfoil polar.

 

AR ratio will not increase the 2D polar Clmax.

 

The increase in AR from ~6 to almost 9 is what caused the increase in Clmax from 1.58 to 1.70.

 

An increase in AR will constitute an increase in the Clmax, as well as how steep the lift curve is. i.e. CLmax is reached at a lower AoA. It is however by a relatively low amount, hence why a gain of only 0.12 was reached with an increase in AR of almost 50%.

 

 

Edited December 3, 2015 by Hummingbird

[Crumpp]

Of the wing Hummingbird...NOT THE AIRFOIL POLAR.