P51D/K vs Me109K-14 (1 Viewer)

[Milosh]

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

What is this flettner he mentions?

There was a Flettner tab on the rudder of late production 109s but this was not cockpit adjustable.

 

[FLYBOYJ]

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, you have not factored in bank angle and reduction of thrust will not diminish that quickly, especially in an aircraft with a basically aerodynamically clean airframe, like a WW2 fighter.

"When airspeed is held constant a larger angle of bank will result in a smaller turn radius and a greater rate of turn."

"When angle of bank is held constant, a slower airspeed will result in a smaller turn radius and a great rate of turn."

The point here Soren is there's a lot that could of been gained from a captured -109 that was not developing full power and all one had to do is ensure the aircraft had enough power to perform in Va(as anything outside of that could technically damage the aircraft) and you could probably capture 80% of the performance data needed to give a good analysis of the aircraft, and I believe that was accomplished in some cases.

 

[drgondog]

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

SR - all (er, many) of the airfoil lift and drag profiles for WWII era wings can be found in Theory of Wing Sections by Abbott and Von Doenoff - 1949. My copy was $4.00 in 1965.

Most of the airfoil section charts include CL vs AoA as well as Moment Coefficients and many have comparisons for smooth to rough airfoil effects. There are many airfoils plotted out as function of chord as well showing the pressure distribution as a function of Chord.

The 1.7 CL IIRC was around 16 degrees for the 109 slat deployment at CLmax - but Soren and Kurfurst (and probably Altea) would know for sure.

The 51 wing under optimal conditions would 'break' around 14-15 degrees.

Predicting how drag would change as function of AoA - in the context of manueveing AoA - needs wind tunnel data to develop the Drag Polar throughout the velocity range... and even then it is less precise for high bank angle drag as 99% of all wind tunnel drag is set with airframe symmetrical to the stream tube (i.e 'heading directly into the wind')

When an a/c turns in curvilinear flight the Parasite drag must include control deflections (aileron, rudder and elevator) trim drag as well as attempt some fudge factor for the increase in span wise flow properties over the wing.

When many of the computer gamers engage in these performance discussions they a.) calculate the Induced drag (easily) because the may pick a velocity, look up the wing dimensions, pick a gross weight, assume a wing geomerty efficiency factor, use the appropriate density for the altitude of interest ----> Out pops INDUCED DRAG for high speed level flight.

b.) At the top speed of that a/c for a specific altitude, they pick the Hp denoted for that run and convert to Thrust with the key assumption being the propeller efficiency. There is a component of Propeller Disk Drag embedded in Parasite/Form Drag but often discounted as too difficult to find data for it in Wind Tunnel tests.

c.) Using the Thrust calculated in b.) and the Induced Drag calculated in a.) then the Force Equation of Thrust = Induced Drag + Parasite/Form Drag can be solved for that velocity to obtain Total Parasite Drag (all Drag components other than Induced Drag due to lift).

NOTE: This result is 'true' for level flight at the velocity and Hp and altitude at MAX speed - in which there is no excess thrust to accelerate the airframe any faster.

All this (Induced and Parasite/Form Drag for Total Drag is valid at the extreme 'right' of the Drag Polar chart I presented - at max velocity. For all velocities less than max the Total Drag of the system is less and less until that point where Induced Drag and Parasite Drag 'cross over' near the middle of the Velocity range.

At the instant of time that the airplane rolls into a turn, all the initial Drag information goes out the window.

As the bank angle increases, the CL increases as a function of Bank angle, the CD of the wing changes with the 'new AoA' required for the higher CL and All the Parasite Drag components change (friction Drag reduces, form drag could increase due to major flow separation, form drag due to aileron and elevator and rudeer control gaps decrease, parasite drag of radio mast, etc devrease as velocity decreases) and Trim Drag increases due to the control deflections required to sustain Bank and turn and angle of attack.

At some point in time the limits of Bank Angle, Lift required for the Weight of the A/C, and the Velocity will reach equilibrium in the turn.

ALL the initial values calculated from Max Speed have degraded. At this moment in time the aircraft is operating at the velocity and AoA just short of stall, the power available is equal to power supplied.

At this point an assumption may be made that Induced Drag for this velocity in calculable by assuming that spanwise flow contributions for banked flight are negligible (not necessarity true). Thrust may also be calculated if Hp available in this flight config is reliable (probably true).

But remember - Parasite Drag/Form Drag is NOT what was used at the beginning of this exercise as the velocities are significantly less in the max turn than they were at top velocity, same altitude, and ALL of the Parasite/Form Drag components(friction,radio mast, radiator cowling, separation form drag at high AoA, etc) are 'tweaked', particularly the Form and Trim Drag at high AoA.

Looking at the Drag Polar Chart the Total Drag of the system has been lowered (moved to 'left on the curve') as a result of lower velocity but without the Drag Polar OR the engineering estimates for Form Drag/Parasite drag components you have no way to accurately re-calculate these components of drag in this new 'high trim' (elevator, aileron and rudder deflection) state.

The CD0 of the wing at minimum drag or the airframe at top speed are not useful for any condition of high AoA banked flight.

For the same reasons the CLmax at stall is less useful for banked flight as all these data are collected for level flight conditions with a singe set of control positions that are not likely to be the same as a high speed highly banked turn.

I hope some of this makes sense.

 

[Shortround6]

Thank you for your explaination and the book recommendation, I see they are available on Amazon in the 12.00 range used.

I have seen a few charts (in addition to the the Altea provided) that show CL's of 1.6-1.8 not being reached until AoA exceeded 20 degrees but since the exact airfoil/wing was not specified I would not claim that the 109 couldn't reach that CL at a lower AoA, less than 20 degrees.

Every thing you have said makes sense to me and again I thank you for the time and trouble you went to to post it.

 

[drgondog]

Thank you for your explaination and the book recommendation, I see they are available on Amazon in the 12.00 range used.

I have seen a few charts (in addition to the the Altea provided) that show CL's of 1.6-1.8 not being reached until AoA exceeded 20 degrees but since the exact airfoil/wing was not specified I would not claim that the 109 couldn't reach that CL at a lower AoA, less than 20 degrees.

Every thing you have said makes sense to me and again I thank you for the time and trouble you went to to post it.

SR - Remember that all of the airfoil data given are for 2-D (infinite span/AR) airfoils.

Aspect Ratio, Plan form (elliptical/rectangular) tip geometry/artio to root chord, etc need to be applied - and that all wings of even same exact plan form design have slightly different characteristics based on aileron, twist, mfr tolerances/roughness, flap, boundary layer control fences, slats, etc.

All of these factors can be considered but airflow is NOT really laminar and does funny things at High AoA and sideways motions - particularly imbedded in propeller thrust turbulence.

While Aero design is a science - it is the physics of assumptions in the preliminary design phase and gets 'fined tuned' based on empirical results and data for the next design.

Regards,

Bill

 

[Shortround6]

Thank you again.

I do remember seeing a study over on the NASA site about a comparison of 8 (at least) aircraft/wing shapes with airflow patterns and stall air flow both with propelleers and without. Single engine and multi engine but I can't seem to find it now.

"While Aero design is a science - it is the physics of assumptions in the preliminary design phase and gets 'fined tuned' based on empirical results and data for the next design."

Very true, if airplanes could be designed on therory and wind tunnel tests alone there wouldn't be any need for test flights or modifications after test flights

 

[Soren]

Bill,

IIRC the Clmax of the 109 was reached at around 17 to 18 degrees AoA.

 

[Altea]

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

Well, i'm not the Bf-109 specialist.

Some sources (AFDU...) quoted it's wing profile at NACA 2312. But RC builders plotting the 109E profile saying 2412, since 70'ies. Maybe german 2R1 profile is 100% similar to the NACA one?
And what about the pressure field distribution towards the 109 wing to estimate slats rule?

Anyway freeflow values may be very different from propeller blowed ones, with Karman fairing, + whole fuselage fin, elevators influence...

It' why it would be very kind of Kurfurst to send other sustainted values for the sustainted 18.92s turn...
Radius, speed, bank angle for a plane in good condition.

Unfortunatly, Kurfurst's link :
http://kurfurst.org/Tactical_trials/109E_Kurvenwendigkeit/Me109turntimes.pdf
doesn't work...

Is someone here can help us with that document ?

Regards

 

[Soren]

The 109 used the NACA 2R1 airfoil, a modified Clark Y airfoil with increased lift and reduced drag characteristics. It is listed in MTT documents.

 

[Kurfürst]

Is someone here can help us with that document ?

Regards

Here it is!

 

[Altea]

Here it is!

Thank you very much Kurfurst, sorry for disturbing you...

I will try to study it in german , it can takes a while...

Well to resume 18,92s for 203m radius at 2 540 kg weight, no ?

 

[Kurfürst]

Thank you very much Kurfurst, sorry for disturbing you...

I will try to study it in german , it can takes a while...

Well to resume 18,92s for 203m radius at 2 540 kg weight, no ?

Yes it is, as well using 990 PS output, 0 m altitude (ie. 5 minute emergency, though the DB 601A-1 had a special 1-min takeoff rating with 1100 PS).

There is another figure below the 18.92 sec figure, but that is assuming a -50 m/sec diving turn with altitude loss.

 

[Altea]

Yes it is, as well using 990 PS output, 0 m altitude (ie. 5 minute emergency, though the DB 601A-1 had a special 1-min takeoff rating with 1100 PS).

There is another figure below the 18.92 sec figure, but that is assuming a -50 m/sec diving turn with altitude loss.

-50 m/s loss from 0 m altitude turn?

But seriously now, thanks for that valuable information....even if i wasn't enough advanced in my translation to be on that point yet.

And what about ca and cw values, were they constructor estimated or tunnel measured ones, please? And so for the propeller output?

Regards

 

[Gaston]

Since 109 had always a better rate of climb than 190, and some lower WL, that seems logical.


But AFAIK, TsAGI made virtually no comparative trials between planes. Never... -It was either NII- VVS, or LII-NKAP jobs.- Only real conditions flights to validate T-103 and T-101 giant wind tunnels results.
Of course both 109 and P-51 complete airframes went in TsAGI windtunnels, but full test results were never published AFAIK, even if they were partially used by soviet designers (from Arlazarov, Surgenko memors...).

NII had only ex british Mustang mk I, with some wear in rather bad condition. Turning tests were made at 1000m hight. With new Packard engined P-51 B/C/D at 7000-9000m and full-laminar wings (new condition), results should have been different.

Moreover, the soviet P-51 (23-25s) was turning ALLOT better than the soviet Bf 109E-3 (26.5-29.3s).

Regards

Can anyone contact Altea or tell me what he means by "But AFAIK, TsAGI made virtually no comparative trials between planes. Never..." ?

Does that mean none of the 360 degree turn times of different aircraft types were made the same day?

These TsAGI tests contradict the British comparative tests in respect to sustained turns. Are there original documents of these tests and, more importantly, where can I see them?

If there are original documents, what does Altea mean by " full test results were never published AFAIK" ?

I would just like to know as much as possible about these TsAGI tests, and especially the 360 degree turn times portion of these tests and their relevance to make comparisons.

Thanks.

Gaston

 

[Gaston]

Since 109 had always a better rate of climb than 190, and some lower WL, that seems logical.


But AFAIK, TsAGI made virtually no comparative trials between planes. Never... -It was either NII- VVS, or LII-NKAP jobs.- Only real conditions flights to validate T-103 and T-101 giant wind tunnels results.
Of course both 109 and P-51 complete airframes went in TsAGI windtunnels, but full test results were never published AFAIK, even if they were partially used by soviet designers (from Arlazarov, Surgenko memors...).

NII had only ex british Mustang mk I, with some wear in rather bad condition. Turning tests were made at 1000m hight. With new Packard engined P-51 B/C/D at 7000-9000m and full-laminar wings (new condition), results should have been different.

Moreover, the soviet P-51 (23-25s) was turning ALLOT better than the soviet Bf 109E-3 (26.5-29.3s).

Regards

Hello, sorry for reviving such an old thread...

-Can anyone contact Altea or tell me what he means by "But AFAIK, TsAGI made virtually no comparative trials between planes. Never..." ?

Does that mean none of the 360 degree turn times of different aircraft types were made the same day?

These TsAGI tests contradict the British comparative tests in respect to sustained turns. Are there original documents of these tests and, more importantly, where can I see them?

If there are original documents, what does Altea mean by " full test results were never published AFAIK" ?

I would just like to know as much as possible about these TsAGI tests, and especially the 360 degree turn times portion of these tests and their relevance to make comparisons.

Thanks.

Gaston

 

[bobbysocks]

best you can do is send him a PM. in his profile he doesnt furnish an email address.

 

[MaximusGR]

1945 average US pilot vs 1945 average LW pilot my pick would be the P-51.
1945 experienced US pilot vs 1945 experienced LW pilot ...Me109

 

[Sagittario64]

I thought the K-14 model was armed with only 30mm cannons. It would be a bomber destroyer if so, not an anti-fighter fighter. performance maybe, but trading in the mk108s for 151/20s seems to me to be the only way they can truly have at each other