Question about RoC of Spitifire IX, XIV vs late BF 109's.

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Milosh said:
Tomo, Griffons were restricted to 21lb boost. Merlins had 25lb boost.
Click to expand...

I will not trumpet that Griffons were routinely operating at +25 psi, however there is a number of tables & charts that show the Griffon being tested for +25 psi.
OTOH, not all Merlins were running on +25 psi either.
 
tomo pauk said:
I will not trumpet that Griffons were routinely operating at +25 psi, however there is a number of tables & charts that show the Griffon being tested for +25 psi.
OTOH, not all Merlins were running on +25 psi either.
Click to expand...

Fwiw, Griffon 64 and 69 engines were approved to operate at +25 lbs./sq.in.. See also Griffon 64 - Operating Limitations and Griffon 69 - Operating Limitations.
Presumably most folks know that ADBG and 2nd TAF operated the Griffon 65s in Spitfire XIVs at +21 lbs/sq.in.
 


1 the data for Me 109K4 empty weight is incorrect. The weight is about 6400lbs.

2 the spitfire had a large wing area compared to most other fighters including the Me 109. The spitfire external wing shape may have been complex but its internal structure was simple and efficient so the Spitfire did not suffer a weight disadvantage. To generate the same overall lift from its smaller wing a Me 109 would need to operate at a higher angle of attack to obtain higher coefficients of lift. This comes with the penalty of a proportionately higher lift induced drag which slows the Me 109 down. The slats don't help here. This is because slats increase lift by allowing a higher angle of attack before stall. This again comes with a penalty of a reduced L/D ratio.

The advantage of the smaller wing is lower drag in level flight. The spitfire compensated by having about 8% more power. The Me 109G6 surrendered its drag advantaged by having engine gun bulges, a non retractable tail wheel and no main wheel covers. The Merlin generally had better fuel but also two stage supercharger and intercooler..

2 The Me 109K4 was faster than the Spitfire IX and about the same in climb (so long as no gondola guns carried)

3 The Griffon spitfire XIV was due to its more powerful engine and big wing superior to the Me 109K4 in climb. Adolf Galland said best thing about the Spitfire XIV was how rare it was.

4 Comparing engine horse power is almost useless without a power versus altitude chart.

Is the power quoted at sea level or is it quoted at rated altitude (usually about 6000ft) where power is more due to the supercharger not being throttled. What is the power at high altitude?

Both the Spitfire XIV and IX had two stage superchargers with an intercooler and these tended to maintain power at altitude a little better. The Me 109K4s engine was often DB605DB/DC and lacked these features. Admittedly the DB605 (which had LESS frontal area than the Merlin and had 30% more swept volume needed less boost. Remember that 25psig is 2.8 ata compared to the 1.8 of the Messerschmitt.

A DB605L with two stage supercharger was becoming available for the Me 109K14.

Remember that the Me 109 is an older design of hawker Hurricane vintage and had reached its limits and was not being upgraded. The upgraded version of the Me 109 was the Me 209-II with DB603 engine lost out a competition to the Fw 190D-12 and Ta 152 which were derivatives of Fw 190A.

5 Finally the spitfire is supplied with 110/150 fuel. To match this the Germans need an equal fuel to allow reliable operation at 2.0 ata.
 
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Back to the topic:
I think I've found the answer

Data is based on sea level

Spitfire XIV (18psi)
HP 1850
Takeoff 8494
Climb 4700ft/m
Powerloading 4,591

Spitfire IX (25)psi
HP 1980
Takeoff 7400
Climb 5400
Powerloading 3,737

Tempest V (9psi)
HP 2420
Takeoff 11480
Climb 4400
Powerloading 4,743

BF 109 K4 (1,8 ata)
HP 1850
Takeoff 7495
Climb 4300
Powerloading 4,051

KI 84 (?)
HP 1970
Takeoff 7940
Climb 4300
Powerloading 4,030

J2M (?)
HP 1870
Takeoff 7080
Climb 4600
Powerloading 3,386

P51D (67hg)
HP 1680
Takeoff 9611
Climb 3400
Powerloading 5,720

*All my sources are from ww2aircraftperformance.org

Here's the interesting part:
Let's calculate RoC based on powerloading:

Example:

Mustang vs Frank
5,720 100%
4,030 70,45% = 29,54%

100 3400
129,54 4400

4400-3400=900
4400-900=3500

Documents: KI 84 4300ft/m, P51 3400ft/m
My calculation: KI 84 4400ft/m, P51 3500
That's a difference of ~100ft/m

Another one:
K4 vs J2M
4,051 100%
3,786 93,54% = 6,54%

100 4300
106,54 4600

4600-4300=300
4600-300=4300

Documents: BF 109 4300ft/m, J2M 4600ft/m
My calculation: BF 109 4300ft/m, J2M 4600ft/m
Difference: None


Now it's getting funny:
Tempest vs J2M
4,743 100%
3,786 79,82% = 20,17

100 4400
120,17 5300

5300-4400=900
5300-900=4400

Documents: Tempest 4400ft/m, J2M 4600
My calcualtion: Tempest 4400ft/m, 5300ft/m
Difference: +700ftM

And again:
K4 vs XIV
4,591 100%
4,051 88,23% =11,76%

100 4,591
111,76 5,130

4,591 4700
5,130 5200

5200-4700=500
4300-500=3800

Documents: K4 4300ft/m, XIV 4700ft/m
My calculation: K4 5200ft/m, XIV 4700ft/m
Difference: +900ft/m

When comparing Japanese, German and U.S against each other these calculated numbers are very close to official documents. However when British planes are involved there's something really strange going on, in fact the numbers don't make any sense at all.

However if we take German, Japanese and U.S as reference:

Spitfire XIV 3900ft/m
Spitfire IX 4600-4700 ft/m
Tempest ???
BF 109 4300ft/m
KI 84 4300ft/m
J2M 4600ft/m
P51 3500ft/m

There's something wrong with British performance charts.

What's the powerloading for the Mustang with 75hg at sea level? 1940 hp? Is that correct? Which takeoff weight?
 
I put your data into a spreadsheet and plotted it (of course!) and got this graph:
R^2 is the correlation coefficient; 0.59 is better than chance (which would be zero), but it's low enough to show that there's definitely something other than power loading that needs to be considered.
 
...or there's something wrong with the way somebody's data were reduced, which I suspect is the most likely answer. There is not enough data to determine whether there was "something wrong with the British" data. There may have been something wrong with correction to standard conditions, or they were correcting to different standard conditions
 
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The data is obviously selective. RoC is one value there were many other values that were considered in the compromise of the finished article.
 
Thank you, Calum

It has just crossed my mind: British were often testing, at RAE and other places, the climb rates of their fighters at max power and made the RoC tables/graphs based on that. For German aircraft, the official LW charts often used data for RoC with engine in 'Steig & Kampfleistung' power setting; manufacturer's charts often used RoC figures that were result of engine in more aggressive setting, like 'Notleistung' etc.
So we need to find out whether the data for 109K-4 (or any other A/C compared) is a result of max possible power, or a more conservative power setting.
 
Different countries measured things differently and direct comparison is not simply X + y =z. All the figures discussed are official figures used in engine and airframe development and I think it would be wrong to say one set of figures is flawed because it doesn't match up with our preconceived notions. No one was doing the tests with the 21st century internet in mind.
 

For 109 K4 operating at 1.8 ata please see Steiggeschwindigkeiten, DB 605 DB/ASB Sondernotleistung mit MW..., Oberammergau, 19.1.45
 

Apart from "powerloading" you need to consider "wing loading". There are other factors. Propellers can be ootimised for either high speed or for low speed pulling force. A propellor good for high speed may not be good for climbing or hauling bombs of a runway.. For instance one of the Me 109K4s experimental thin blade props increased speed the 457 mph but at the expense of climb.

The Mk XIV 21psig spitfire looks unremarkable compared to the Mk IX 25psig until you realize that the Merlin could not sustain 25 psig except at low altitude. Above 20,000ft the Griffin spitfire is superior and above 25,000ft it's no contest.

The very high pressure British engines also had enormous jet thrust worth about 300lbs thrust in a Merlin or about 400hp.
 
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Hi,

Some people already have pointed out that powerloading is not the only measurment for climb performance. There's also wing loading and drag to consider.

To my knowledge:
Wingloading: low wingloading increases lift but also drag, high wingloading reduces lift but also drag.
Drag: Increase in drag will reduce speed, the rate and angle of climb.

These things are undoubtely important but their impact on RoC isn't really worth taking into consideration.
And I think here's why:

Let's ignore everything but powerloading:
We take the BfF109 and KI84 as reference:

BF 109 K4 (1,8 ata)
HP 1850
Takeoff 7495
Climb 4300
Powerloading 4,051

KI 84 (?)
HP 1970
Takeoff 7940
Climb 4300
Powerloading 4,030

KI 84 is less streamlined, has lower wingloading and has an advantage in powerloading of 0,021 = 0,5%
4,051=4300
4,072=?
4,072x4300:4,051=4322=4300
According to official documents KI84 climbs at 4300ft/m at sea level. 0,5% is basically nothing. The BF 109
has an advantage in drag, right? Impact in climb performance: None
My calculation matches with official documents.


BF 109 K4 (1,8 ata)
HP 1850
Takeoff 7495
Climb 4300
Powerloading 4,051

J2M (?)
HP 1870
Takeoff 7080
Climb 4600
Powerloading 3,786

J2M is less streamlined, has lower wingloading and has an advantage in powerloading of 0,265=6,5%
4,051=4300
4,316=?
4,316x4300:4,051=4581=4600
According to official documents J2M climbs at 4600ft/m at sea level. 6,5% is ~300ft/m. The BF 109
has an advantage in drag, right? Impact in climb performance: None
My calculation matches with official documents.

As I've stated previously all my calculation matches 90-100% with official documents. Unfortunately it doesn't work with British planes
because their powerloading is way off for achieving such astronomically high climb performance given in offical documents.

Raiden (-17,5%) can't outclimb Spitfire? Why?
Tempest (+20%) is close to Raiden? Why?

There's simply no logical explanation for this.
 
MaxPower said:
There's simply no logical explanation for this.
Click to expand...
There is a very simple and very logical explanation. It is more complicated than you think. The P-51s wings were thicker than a Spitfires but produced less drag. The P-51 was bigger in all dimensions than a Bf109 but produced less drag. The Tempest was powerful and fast at low altitude, at higher altitude it wasnt, it didnt need to be.
 
???
I'm aware that the Tempest was fast at low altitudes, no one is going to dispute that. The Tempest however has a worse powerloading at sea level in comparision to the BF 109 (+14,9%) or the Raiden (+20%). That's ~ 650ft/m and ~950ft/m. The Tempest with a powerloading of 4,743 is not capable to climb at 4400ft/m. Perhaps you were talking about zoom climbing, that's very different though...
 
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