P51D/K vs Me109K-14

[FLYBOYJ]

You can read the other reports on my site, too. I was not there the 1940s, I can't tell you if there was a strange humming noise coming out of the reduction gear - I can only read the reports written on the events, and I am sure they are already a concentrated, selected reflection on the reality..

And that's fair enough. At least when you read the report it gives some inkling of what was going on with the aircraft. To say that an airplane is "worn out" paints a very broad picture in determining why noted performance figures were attained.

 

[Altea]

Would the Mustang tested by the Soviets be one of the 10 Allison Mustangs received from the British?

Yes, but they were only 4 from russian archives. Might be 6 if the pair used for operationnal trials at Kalinin Front were not the same, that was previously tested in TsAGI or LII or NII.

 

[Soren]

Additionally I have often wondered about the intangible of stick forces at high speed as well as the slat effects and true change to CL at high AoA for the 109.. I'm agnostic regarding actual increased delta CL for the 109 or more contribution to stall retardation as AoA/Airspeed reaches critical points? One, Both? and how does one prove it?

Bill,

Yes we have indeed had quite a few discussions regarding this before, but we have also drawn and uncovered some reliable conclusions from these, you must have forgotten that? I am also quite sure we came to agreement in our last discussion on the subject. You were also to make an analysis with the figures we obtained, but you've apparently been busy with other projects, for which you have my full understanding btw (Haven't had much time lately myself).

The Clmax of the Bf-109F series and onwards with slats deployed and flaps gear up was 1.70, as listed in MTT documents, that is a fact that we know by now. This is also very close to NACA's own std. which states that the handley page type automatic slats provide a minium increase of 25 to 30% in critical AoA Clmax of the covered area, should there be any doubt.

V24, a Bf-109F with no slats and a slightly shortened wing span was also measured to have a Clmax of 1.48 flaps gear up at Charlais Meudon. The shortened wing span and thereby slight decrease in wing AR probably reduced the Clmax of this wing compared to the normal F, G K wing by factor of 0.05 to 0.10 in the Cl range. Which means that the slats increased the overall Clmax of the 109F,G K's wing by approx 12.5 to 14%.

Furthermore NACA provided the Clmax for the P-51D in Report nr.829, as 1.35.

So we have the Clmax for both the Bf-109 the P-51, and additionally we also have the Cd0 for both a/c:
Bf-109: 0.0023
P-51: 0.00167

Just stating the facts.

Last but not least, both the 109 -51 suffered from heavy elevator forces at high speeds, but according to what I've rad about both a/c a simple two hands on the stick took care of the that problem.

 

[Soren]

What was worn and what was damaged???????????

I have made that clear a number of times on this forum before, but somehow people here forget very quickly. Also there is no need to get aggressive FLYBOYJ, I am merely telling it the way it is in a polite and controlled manner.

Anyway seeing as how Kurfurst already took care of this issue and don't feel the need to elaborate on what I wrote.

 

[Altea]

What are your thoughts on this?[/QUOTE]

Hello DrGong

Altea - I have never seen a 'full set' of full scale wind tunnel tests for any of these birds and certainly not for a fully functioning B/C/D Mustang with Radiator in operation generating potential thrust - and certainly not a full range of both Parasite drag and trim drag at various Reynolds Numbers and angles of attack.

B/C/D Mustang never went to TsAGI tunnels. It's a pity. But partial data are circulating in soviet/russian litterature. So the Mustang's wing Cd is quoted either 0.0077, or 0.0075. How equivalent it-is to NACA values, i don't now? We have to use soviet Langley-Field/T-103 wind tunnels equivalence curves published in some RDK (constructor files) mid thirties to convert values . From rich NACA-TsAGI exchanges. Only i can say that Yak-1 so called Clark YH Profile (in fact a TsAGI R-II-14 with different shape) had a Cd 0.015 value at lambda =5

If you go back and check the various threads, we have been down many a manueverability rathole and the required data to model these birds through a full range of asymmetrical, various altitude, different inital airspeed, for different flight regimes has not been available for good modelling.

Well if we have reliable* power request and available power curves, it should make the deal.
Assymetrical, you now...turning at 300 m radius the outer wing is not so far away from the inner one to complicate our life. So for the flow curvature from the Leading Edge to the BE of the wing in turn. (Curvature rate exists, but it's small...)

* measured, not extrapolated

Additionally I have often wondered about the intangible of stick forces at high speed as well as the slat effects and true change to CL at high AoA for the 109.. I'm agnostic regarding actual increased delta CL for the 109 or more contribution to stall retardation as AoA/Airspeed reaches critical points? One, Both? and how does one prove it?

Difficult to say. A lot of soviet fighters were tested with slats fixed closed, then free-opened. For Me-109's you should ask to Kurfurst if such experiments were made. There was a positive effect of course on the turn rate, but at the other side assymetrical and intempestive jumps around rated AoA and so in turbulent conditions. I suppose that Me-109 suffered from those drawback too, like all planes of that kind without dashpots for slats.

From NII trials, there was no huge difference at landing with opened slats and without them (Cl~ 0.05 +) for the 109E3; but it was no at max AoA (~ 15,5°) and rather around 12°.

What else? Hope makes live. Maybe TsAGI test results would be published someday...

 

[Soren]

What we do know:

Bf-109 Clmax: 1.70
P-51 Clmax: 1.35
Bf-109 Cd0: 0.023
P-51 Cd0: 0.0167

What can we use this for? Short answer: To get an idea of how well the two a/c stack up against each other in the horizontal with power/thrust being equal. And we do that by using the equations below:

Methods for calculating drag lift, all of which can be used to determine G loads, L/D ratios stalling speeds etc etc:

Lift (L) = Cl * A * .5 * r * V^2

Coefficient of lift (Cl) = Established in windtunnel tests

Drag (D) = Cd * A * .5 * r * V^2

Drag Coefficient (Cd) = Cd0 + Cdi

Induced drag coefficient (Cdi) = (Cl^2) / (pi * AR * e)

Coefficient of drag at zero lift (Cd0) = Established in windtunnel tests

Note: End results are in Newtons (N), so you'll have to convert into Kilogram force (Kgf).

1 Newton = 0.1019716213 Kgf

Methods for calculating turn radius:

Radius = (V^2) / (g * √[n^2 - 1])

Radius(min) = (Vstall^2 / g) * (n / √[n^2 - 1])

Vstall = Aerodynamic stall speed for the aircraft in question.
g = gravitational constant (i.e. 9.82 m/sec^2)
n = steady-state maneuver load factor (i.e. maximum amount of g's you can pull)

Methods for calculating 360 degree turning time and the turn rate

360 deg turn time = 2 * pi * r / V

360 deg turn time = 2 * pi * radius / velocity

The turn rate in degrees per second is then found by dividing 360 by the time:

Rate of Turn = 360 / time

__________________________________________

Plugging in the 109 51's figures and it becomes quite clear that the Bf-109 holds a very clear edge when it comes to horizontal maneuvers, while the P-51 definitely holds the edge in straight out speed (Depending on which 109 we compare it to ofcourse, in this case I picked the G-10).

 

[Altea]

Hello,

The Bf 109F-2 captured and tested in Soviet-Russia was indeed in poor condition, whatever you claim on the contrary;

Just by luck, ....
. The experienced engineer noticed that the aircraft had undergone major repair at least four times and was completely worn out. .....

This sounds doubtfull since this sentence is not written nor in the guenine russian text, neither in quoted sources. Maybe a translater deviation from accuracy, i don't know...
But, for sure it wasn't a new plane, don't need to precise that!

The same holds true to the tested Bf 109E - I believe this one was sold to the Russians before the war,arriving in crates and they assembled it themselves - the engine seems to have some problem

You mean all five of them, baught by russians ?

This - lack of power output at low altitudes would explain why the Soviets measured such absymal turn times such as ~29 secs at 1000 m, whereas the German specs for the 109E was 18.92 secs for a sustained 360 degree turn at 0 m... and much more in line with the 18-19-20 secs measured on the F/G models.

There might be another explanation for this, the E-3 was just tested a "nominal" power, just as for soviet planes, not at "forced" one.

BTW, congratulation for your site. Can you give us more datas about 109E/F/G turns, please? I mean radius, bank angle, speed...

Regards

 

[FLYBOYJ]

I have made that clear a number of times on this forum before, but somehow people here forget very quickly. Also there is no need to get aggressive FLYBOYJ, I am merely telling it the way it is in a polite and controlled manner.

I was not getting aggressive, please develop some thick skin, the only thing you have stated was vague information as you did on your original post

Anyway seeing as how Kurfurst already took care of this issue and don't feel the need to elaborate on what I wrote.

Kurfurst did provide information on the captured aircraft and it shows specifics for each aircraft. With that said there was enough information attained to come up with some performance conclusions based on the tests and the operating condition of each aircraft. For example - full power was not needed to place some of the aircraft in maneuvering speed so performance data could be achieved at Va airspeeds. Slow flight and stall speeds were achieved, so you see, unless you could come up with specifics on why one of the captured birds revealed the performance data at hand, you're painting the whole thing with a very broad brush. And as I repeated earlier, I'm sure Gunter Rall few the 109 a lot better than Brown.

 

[Soren]

The engine wasn't performing well FLYBOYJ, and that will affect the turn rate nomatter the entrance speed.

 

[FLYBOYJ]

The engine wasn't performing well FLYBOYJ, and that will affect the turn rate nomatter the entrance speed.

No it won't - you could achieve Va speeds by a dive and come up with the same amount of energy/ airspeed needed to perform the specified maneuver, and for the most part you won't need full power to attain data at Va. If you're testing an aircraft that is not developing full power then you will not be able to gain sustained performance data and data relating to performance (top speed, Vx, etc). Again it depends on the example being tested and at least one of them had a fully functional engine.

The point here is I've seen many "worn out" aircraft still perform exactly to what the flight manual states.

 

[Soren]

FLYBOYJ,

Yes you can get enough speed to perform the maneuver, but that's the not the point, the point is the time in which you complete the maneuver. A 360 degree turn will take longer the more power you take away from the aircraft. Why ? Cause you'll be taking away thrust otherwise used to keep up the energy turn rate in the turn.

 

[Shortround6]

I think I am missing something here so I would ask that somebody please point it out to me.

As I understand it ( and I am not an engineer or pilot) any wing increases it's lift coefficient as it's angle of attack increases.

As the angle of attack increases the drag coeffecient of the wing changes.

Slats/slots change the airflow over the wing and prevent stalling at high angles of attack.

Slats/slots do little or nothing to improve coeffecient of lift until an angle of attack just below stall is reached.

Increasing the angle of attack further means the unslatted/slotted wing stalls and the coeffecient of lift drops.

On the slatted wing the angle of attack can be increased a number of degrees more, thereby increasing lift, before stall occurs.

But hasn't the drag been going up as well? The wing at these higher angles of attack ( over 13-15^) having an even higher coeffecient of drag than it did at 10-12^ angle of attack?

If this has been gone over before or if I missed it, my appoligies, but could someone point it out to me.

 

[Soren]

Shortround,

Lift drag are directly related. So the higher the lift, the higher the drag.

The Cl determines how much lift the wing produces, which in turn determines how much drag is produced as-well.

Mathematically it is explained like so:
(Cl^2) / (pi * AR * e) = Cdi [induced drag]

The Cdi makes up for around 95% of the total drag, so it's pretty significant.

What an a/c in essence is trying to do when executing a tight turn is reducing the forward speed of the original path you started out traveling towards, whilst at the same time speeding you in another direction. In other words the wings are acting kinda like giant airbrakes, and so the larger a surface area you can present towards the direction your going (i.e. the higher the AoA you can pull), the faster you're going to loose progression speed in that direction whilst adding speed to a new one. And what the slats allow you to do is just that: to present a larger surface area in the direction your a/c is going without it stalling out.

 

[FLYBOYJ]

FLYBOYJ,

Yes you can get enough speed to perform the maneuver, but that's the not the point, the point is the time in which you complete the maneuver. A 360 degree turn will take longer the more power you take away from the aircraft. Why ? Cause you'll be taking away thrust otherwise used to keep up the energy turn rate in the turn.

Only if you're doing full power maneuvers - remember, Va will be at a lower power setting and airspeed and will determine your maximum maneuverability. As long as you're maintaining the required Va airspeeds you can and will determine the maximum performance parameter for the aircraft and again you're not going to operate the aircraft in Va at max power, and goes for any aircraft.

 

[drgondog]

Shortround,

Lift drag are directly related. So the higher the lift, the higher the drag.

The Cl determines how much lift the wing produces, which in turn determines how much drag is produced as-well.

Mathematically it is explained like so:
(Cl^2) / (pi * AR * e) = Cdi [induced drag]

The Cdi makes up for around 95% of the total drag, so it's pretty significant.

What an a/c in essence is trying to do when executing a tight turn is reducing the forward speed of the original path you started out traveling towards, whilst at the same time speeding you in another direction. In other words the wings are acting kinda like giant airbrakes, and so the larger a surface area you can present towards the direction your going (i.e. the higher the AoA you can pull), the faster you're going to loose progression speed in that direction whilst adding speed to a new one. And what the slats allow you to do is just that: to present a larger surface area in the direction your a/c is going without it stalling out.

Soren - I'll try to sum up responses in this one post.

First - you are right about 1.70 being posted by you as a Max CL for fully deployed slats for the 109

What I was getting to is that in the crafting of a sophisticated model of a 109 in a turn you need a.) a Polar Drag set of data specific to the 109, b.) you need the airspeed/AoA data for deployment of slats - and c.) as Altea says a *reliable* set of Hp curves for the altitudes you wish to model.

CD0 is an interesting drag datum but it is solely related to the Wing in question.

Parasite Drag is a function of everything other than Induced Drag (Form drag, Friction Drag, etc) and, as you can see from the attached Drag Polar, it varies non linearly with velocity. The values are extrapolated from various charts in Preliminary design but only 'finalized' in flight tests and wind tunnel tests.

Induced Drag is as you note above and pretty accurately calculated with the equation you posted.

Back to CD0 - it is good for one angle of attack and represents the minimum drag of the airfoil, but equally it is Always at a very low angle of attack for the airfoil in question and not very useful in high AoA profiles that would be needed in turning manuevers.

As to stick forces - I only know what I believe to be true from other pilots that flew the 109 but the 51, while not as 'friendly' at high speed as a boosted P-38L, is easily a one hand capable stick. The rudder was tougher at high speeds but the reason the reverse boost rudder modification was made to the Mustang was to stiffen it up at high speeds to discourage yanking the tail off while turning in a high speed diving chase - the elevator stiffened up but not to point where two hands were required.

Admittedly I never came close to maxing out any manuever in the Mustang but I was both in the 400 mph range and 5+ G turn range so I have a sense of the control forces and can say they aren't near as bad as you seem to imply.

Anyway I found a good representation of a typical Drag Polar to help explain my point

 

[Soren]

FLYBOYJ,

For the best 360 degree turn time you need all the power you can get, taking any of it away and you're going to take longer performing that 360 deg turn, that's a fact. Sure you can easily reach the highest possible split second turn rate even without engine power at all, all you need to do is just reach the Va as you mentioned, BUT, it will only be for a fraction of a second before you burn away all your energy, and its going to go A LOT faster with any reduction in thrust.

So in short, if you loose engine power you're also going to hurt your 360 deg turn time.

 

[Soren]

Soren - I'll try to sum up responses in this one post.

First - you are right about 1.70 being posted by you as a Max CL for fully deployed slats for the 109

What I was getting to is that in the crafting of a sophisticated model of a 109 in a turn you need a.) a Polar Drag set of data specific to the 109, b.) you need the airspeed/AoA data for deployment of slats - and c.) as Altea says a *reliable* set of Hp curves for the altitudes you wish to model.

CD0 is an interesting drag datum but it is solely related to the Wing in question.

Parasite Drag is a function of everything other than Induced Drag (Form drag, Friction Drag, etc) and, as you can see from the attached Drag Polar, it varies non linearly with velocity. The values are extrapolated from various charts in Preliminary design but only 'finalized' in flight tests and wind tunnel tests.

Induced Drag is as you note above and pretty accurately calculated with the equation you posted.

Back to CD0 - it is good for one angle of attack and represents the minimum drag of the airfoil, but equally it is Always at a very low angle of attack for the airfoil in question and not very useful in high AoA profiles that would be needed in turning manuevers.

As to stick forces - I only know what I believe to be true from other pilots that flew the 109 but the 51, while not as 'friendly' at high speed as a boosted P-38L, is easily a one hand capable stick. The rudder was tougher at high speeds but the reason the reverse boost rudder modification was made to the Mustang was to stiffen it up at high speeds to discourage yanking the tail off while turning in a high speed diving chase - the elevator stiffened up but not to point where two hands were required.

Admittedly I never came close to maxing out any manuever in the Mustang but I was both in the 400 mph range and 5+ G turn range so I have a sense of the control forces and can say they aren't near as bad as you seem to imply.

Anyway I found a good representation of a typical Drag Polar to help explain my point

Bill,

The Clmax of 1.70 is the official gear flaps up figure of the Bf-109F, G K series from Messerschmitt, it's listed in several MTT documents, the Cd0 being listed alongside as-well. (I've posted these docs on here many times before) Furthermore the P-51's Clmax Cd0 are listed by NACA as-well. So these figures we do have and can also be 100% confident in.

As for the control forces of both a/c, I agree with you, and I wasn't trying to make the P-51 sound bad, I was just pointing out that elevator forces are mentioned to be similar in that a/c compared to the 109 at high speeds. In short the same is said about the 109, modern pilots mentioning that 5+ G maneuvers are quite easily achieved with one hand on the stick at moderately high speeds. Exceeding 700 km/h and the 109's elevators becom very stiff however, but two hands on the stick will solve that according the pilots. Above 750 km/h and it becomes very hard even with two hands and trimming is needed.

 

[Altea]

I think I am missing something here so I would ask that somebody please point it out to me.

As I understand it ( and I am not an engineer or pilot) any wing increases it's lift coefficient as it's angle of attack increases.

As the angle of attack increases the drag coeffecient of the wing changes.

Slats/slots change the airflow over the wing and prevent stalling at high angles of attack.

Slats/slots do little or nothing to improve coeffecient of lift until an angle of attack just below stall is reached.

Increasing the angle of attack further means the unslatted/slotted wing stalls and the coeffecient of lift drops.

On the slatted wing the angle of attack can be increased a number of degrees more, thereby increasing lift, before stall occurs.

But hasn't the drag been going up as well? The wing at these higher angles of attack ( over 13-15^) having an even higher coeffecient of drag than it did at 10-12^ angle of attack?

If this has been gone over before or if I missed it, my appoligies, but could someone point it out to me.

Obviously you have understood everything

link: http://i92.servimg.com/u/f92/13/42/66/40/fs_bmp10.jpg

But all i wanted to say previously it's there is too much different slats, profiles, sizes, shapes, relative positions and so different results to extrapolate from a plane to another with minimal accuracy.

 

[Glider]

Bill,


As for the control forces of both a/c, I agree with you, and I wasn't trying to make the P-51 sound bad, I was just pointing out that elevator forces are mentioned to be similar in that a/c compared to the 109 at high speeds. In short the same is said about the 109, modern pilots mentioning that 5+ G maneuvers are quite easily achieved with one hand on the stick at moderately high speeds. Exceeding 700 km/h and the 109's elevators becom very stiff however, but two hands on the stick will solve that according the pilots. Above 750 km/h and it becomes very hard even with two hands and trimming is needed.

My understanding was that 700 km/h was the practical limit in the 109 from Kurfursts site:-

Me 109 G:
- How difficult was it to control the 109 in high velocities, 600 kmh and above?
The Messerschmitt became stiff to steer not until the speed exceeded 700kmh. The control column was as stiff as it had been fastened with tape, you could not use the ailerons. Yet you could control the plane."
- Kyösti Karhila, Finnish fighter ace. 32 victories

"-Many claim that the MT becomes stiff as hell in a dive, difficult to bring up in high speed, the controls lock up?
Nnnooo, they don't lock up.
It was usually because you exceeded diving speed limits. Guys didn't remember you shouldn't let it go over.
The controls don't lock up, they become stiffer of course but don't lock. And of course you couldn't straighten up (shows a 'straightening' from a dive directly up) like an arrow."
- Väinö Pokela, Finnish fighter ace and Me 109 trainer. 5 victories

How heavy did the Me controls get at different speeds?
"It got heavy, but you could use the flettner. It was nothing special, but a big help.
Once in '43, there was a Boston III above the Gulf of Finland. I went after it, and we went to clouds at 500 meters. Climbing, climbing, climbing and climbing, all the way to seven kilometers, and it was just more and more clouds. It got so dark that I lost sight. I turned back down, and saw the Russkie diving too. Speed climbed to 700 km/h. I wondered how it'd turn out. I pulled with all my strength when emerging from the clouds, then used the flettner. I was 50 meters above sea when I got it to straighten out

Me109 was almost a dream come true for a pilot. Good controllability, enough speed, excelent rate of climb. The feel of the controls were normal except when flying over 600km/h - some strength was needed then.
- Erkki O. Pakarinen, Finnish fighter pilot, Finnish Air Force trainer

Its also worth remembering that the 109G was red lined at 700 km/h unless you were below 3 KM and considerably slower than that at altitude.

 

[Shortround6]

Thank you Altea.

What would be interesting would be chart showing the increase in drag as the angle of attack changes.

Also what would be interesting is the angle of attack the 109 needed to get the 1.7 CL