The Zero's Maneuverability (4 Viewers)

[GregP]

Since P-51B vs. Bf 109G was mentioned, here is my comparison. The P-51B totally dominates the Bf 109G
View attachment 798811

A P-51 and Bf 109G-6 have almost exactly the same stall speed .... around 95 mph IAS. Unless the sources I used are incorrect.

Nice chart.

 

[Aeroweanie]

A P-51 and Bf 109G-6 have almost exactly the same stall speed .... around 95 mph IAS. Unless the sources I used are incorrect.

Nice chart.

Stall speed is not the important part, as it varies with weight. CLmax is the important parameter. Here is what I have estimated from the data I have uncovered. I have Bf 109G-6 fighting at 6,700 lbs, while the P-51B is at 8,167 lbs.

 

[Aeroweanie]

Hi,
Please can you be specific on the Power and detail of the types? I can give you a huge range of "Bf 109 G" differences in power and weight. The "P-51B" probably also.

Eng

I have done everything at mil power, or its equivalent. These are the curves I have developed

 

[tomo pauk]

I have done everything at mil power, or its equivalent. These are the curves I have developed

My eyes are not young anymore. So I'd ask for clarifications:
- What engine's line is at 2000+ HP at 8000 ft, and 1700 HP at 23000 ft?
- Merlin 45 and Sakae make better power above 34000 ft than V-1650-7?
- 1650-3 makes 400 HP more at 30000 ft than 1650-7?
- What engine's line is just some 10 HP worse than that of the Jumno 213A's at 25000 ft?

Plus: are the lines with or without the ram effect?

 

[Aeroweanie]

My eyes are not young anymore. So I'd ask for clarifications:
- What engine's line is at 2000+ HP at 8000 ft, and 1700 HP at 23000 ft?
- Merlin 45 and Sakae make better power above 34000 ft than V-1650-7?
- 1650-3 makes 400 HP more at 30000 ft than 1650-7?
- What engine's line is just some 10 HP worse than that of the Jumno 213A's at 25000 ft?

My eyes aren't young either - hence the wide lines, but I do appreciate the difficulties in reading this jumble of data.
1 That is the data I have for the BMW 801D-2
2 Below is a plot of just those three. I tend to agree with you skepticism, but its the data I have found.
3 Another plot follows below. Again, its the published data
4 That line is the V-1650-7 (see plot below)

 

[SaparotRob]

That was way easier for my ancient eyes.

 

[tomo pauk]

My eyes aren't young either - hence the wide lines, but I do appreciate the difficulties in reading this jumble of data.

1 That is the data I have for the BMW 801D-2

I'm afraid that these lines are way too optimistic. Even with overboost (i.e. at some 1.58-1.65 ata), the power was about 1900 PS (minus 1.4% to arrive at HP) down low. 'Book' value for Notleistung of a fully rated engine (2700 rpm, 1.42 ata) were 1440 PS at 5.7 km (~18500 ft). Perhaps these few posts might be of interest: link.
Here is, among other lines, a line (top of the graph) denoting the total engine power, ie. power to the prop "Ne" (or "Nc"?) + power to the fan "Nluft", with minimum ram and overboost where applicable.

2 Below is a plot of just those three. I tend to agree with you skepticism, but its the data I have found.

Merlin 45 data should mimic the Merlin 20 series data above 10000 ft? Here is the graph for the Merlin 20 series: link
Max power of the 20s is at 25000 ft is some 860 HP, where the V-1650-7 is good for ~1220 HP, and 980 HP at 30000 ft (see graph), ie.
Expecting that the 1-stage supercharged Sakae can even remotely compete with the 2-stage Merlins is, I'm afraid, not going to happen. Even against the Merlin 45 it is a long shot.

3 Another plot follows below. Again, its the published data

See again here (dashed blue line for the -7, full blue line for the -3) - the difference between hi-alt power values of the two Packard Merlins was minor.
Also please see here, total of 100 HP difference between the different 2-stage Merlins at 30000 ft (that is despite the -3 having a big 1-stage impeller, unlike the Merlin 61).

4 That line is the V-1650-7 (see plot below)

Please count to about 860 HP for the -3 at 33000 ft (~10 km), and about 840 for the 213A there (the best non-ram line).
Also please note that 2-stage Merlin on the P-51 was getting heaps of power via the ram effect (~300 HP extra above 25000 ft), while the Jumo 213A was gaining perhaps 150 HP at 6-8 km? The power figures with ram effect calculated in when doing speed, lift and drag calculations might be much more valuable when making calculations than the 'static' values.

 

[Engineman]

I have done everything at mil power, or its equivalent. These are the curves I have developed
View attachment 798896

Thanks for posting these power graphs. On first look the "DB 605" curve is very low and the V1650-5 and -7 look different to my references.
However, the DB 605 went through restrictions and upgrades so, I will have to concentrate on this with a clear head!

Eng

 

[Aeroweanie]

Here is the BMW 801D-2 data I used. My interpretation of the notation might be off. Assistance would be appreciated...

On another note, I am using uninstalled engine performance and bookkeeping installation effects as drag.

 

[GregP]

Stall speed is not the important part, as it varies with weight. CLmax is the important parameter. Here is what I have estimated from the data I have uncovered. I have Bf 109G-6 fighting at 6,700 lbs, while the P-51B is at 8,167 lbs.
View attachment 798888
View attachment 798889

The Bf 109G-6 will have CL max of about 1.6 for 0.4 of the entire span include the fuselage width. The taper ratio at the edge of the tapered wing just when the rounded tip starts is 0.519.

I calculate that means 14% of the wing area has CL max = 1.6 and the other 86% of the wing area has CL max = 1.4. This area calculation includes the aileron area.

So, of the assumed 16.1 sq m of wing area, 13.846 has CL max = 1.4 and 2.245 sq m has CL max = 1.6.

Perhaps an update on the turning calcs? Perhaps not. Just curious, not nitpicking.

 

[Greg Boeser]

I have done everything at mil power, or its equivalent. These are the curves I have developed
View attachment 798896

Mmmm. Rainbow spaghetti.

 

[Aeroweanie]

The Bf 109G-6 will have CL max of about 1.6 for 0.4 of the entire span include the fuselage width. The taper ratio at the edge of the tapered wing just when the rounded tip starts is 0.519.

I calculate that means 14% of the wing area has CL max = 1.6 and the other 86% of the wing area has CL max = 1.4. This area calculation includes the aileron area.

So, of the assumed 16.1 sq m of wing area, 13.846 has CL max = 1.4 and 2.245 sq m has CL max = 1.6.

Perhaps an update on the turning calcs? Perhaps not. Just curious, not nitpicking.

I tend to rely on test data for stall, as airfoil-based estimates often don't produce accurate results. You need to consider wing twist, tip effects, fuselage upwash, etc. And then, there is the question as to how much of the wing needs to be stalled before you get a real stall break.

ARC R&M-2361 gives a value of 1.4 for a Bf 109E, as does the Ackroyd and Lamont paper. I also found the value of 1.4 in a Finnish document concerning the Bf 109G-2.

This data for Bf 109 V24 (a 109F prototype) indicates 1.45

 

[tomo pauk]

Here is the BMW 801D-2 data I used. My interpretation of the notation might be off. Assistance would be appreciated...

On another note, I am using uninstalled engine performance and bookkeeping installation effects as drag.

Title of the graph says that it denotes power available to the prop + power to turn the cooling fan ( 'Wellen- + Luefterleistung').
The thick lines are for 'Mit Stau' condition, ie 'with ram effect' - that means engine is not just installed, but the aircraft is moving at a very high horizontal speed. Another note says 'Stauausneutzung 70%', ie. engine uses 70% of ram effect out of 100% that is theoretically possible.

Thin lines are for the case without ram effect - 'Ohne Stau'. For the fully rated engine, and without overboost (= 2700 rpm, 1.42 ata), the best value in 2nd gear, total power plotted at ~18500 ft as 1560 PS. The fan required, at least on the BMW 801S, some 70 PS at 2700 rpm, so the actual power available to the prop is a bit under 1500 PS at that altitude. A bit more generous than the values from the manual, but we can probably live with it.

Graph denoted as 'mit Alkoholzusatz' - basically if MW50 is used - gives far better power values, however the MW 50 was not used operationally on the BMW 801.

Please note that German equivalent of 'military power' for the BMW 801 is the case of 2700 and 1.42 ata. The 'dry' overboost, as it was the case with allowing up to 1.65 ata operation on the fully-rated engine would've been called 'WER' on US terminology; water-alcohol use on US engine was called also WER, and sometimes 'WER wet'.

The line for the DB 605A on your graph is for the restricted engine - 2600 rpm, 1.30 ata max - that was good for 1250 PS at 5.7 km (1300 PS at S/L). For the fully rated engine, making 2800 rpm and 1.42 ata max, usually dated from October 1943 on, power was 1350 PS at 5.7 km, and 1475 PS at S/L.

Fellow members and yours truly have posted a number of graphs in this thread, FWIW.