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

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M

MaxPower

Airman
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Oct 30, 2020
Hi,

According to some performance charts I've found on the internet it seems late Spitfire variants could outclimb Bf 109's.

A quick look at powerloading shows something interesting though:
Weight (empty) HP Powerloading
Spitifre IX 25psi 150 Octane 5634 lbs 2000 2,817
Spitifre XIV 18 psi 150 Octane 6376 2030 3,140
BF 109 K4 1,8 ata 87 Octane 4343 2000 2,171

Are those numbers correct?
How is the Spitifre with such a huge disadvantage in powerloading able to outclimb its opponent? Did the RAF used different methods for measuring climbing performance in comparision to the Luftwaffe? There's something fishy going on... It doesn't make any sense to me.

I have to apologize for my bad english. It's not my first language.

Greetings from Germany
 
Well, there's more to rate of climb than power loading. Wing area loading and span loading are also important, as is Cd0.
 
well for one thing, weight empty has got nothing to do with the power loading while flying.

No gas or oil or pilot makes for a very poor climbing airplane.


so get a flying weight.

then try to figure how much power is needed to fly straight and level at around 160-180mph (or perhaps a bit more.

Subtract that from the total power available

then figure your power loading using the net power figure vs the flying weight.

Of course this also ignores actual thrust or propeller efficiency.
 

Empty weight won't help us here, the take-off weight might. The wing loading figures can also help.
On 87 oct the K4 will not get 2000 HP. Typically it will be using lower power settings for climb (unless the combat was imminent).
Spitfire 14 have had far more power as altitude went up; it will not need 150 grade fuel to do +18 psi. On +25 psi, Spit 14 will past 2400 HP mark down low.
 
???
I thought 1,8 ata and 18psi were the most common in WW2? Why not comparing them? I don't really care about some super powered 1,98 or 25 psi boost or something of the sort. I don't care about prototypes either. Wasn't B4 fuel the German equivalent to 87 octane?

Powerloading based on takeoff weight:
XIV 4,186
K4 3,748

That's a huge advantage for the BF 109. How important is wing loading and drag compared to powerloading in terms of climbing performance? According to performance charts the BF 109 was faster at sea level using rougly the same hp output as the Spitifre? Is this an indicator that the BF 109 was more aerodynamic?
 
MaxPower said:
???
I thought 1,8 ata and 18psi were the most common in WW2? Why not comparing them?
Click to expand...

There is really no point in comparing boost levels, unless we speak about the same engines (say, Merlin xyz vs. Merlin abc). There was no such thing as most common boost either. Moreso since the boost varied with altitude.

I don't really care about some super powered 1,98 or 25 psi boost or something of the sort. I don't care about prototypes either. Wasn't B4 fuel the German equivalent to 87 octane?
Click to expand...

I don't really care whether you care about boost levels or not. I care about posting the proper numbers.
The DB 605D on 1.8 ata will not produce 2000 HP. A 2-stage Griffon will be capable for much more than +18 psi already on 130 grade fuel, let alone on 150 oct fuel, with power levels of 2200-2400 HP down low.
Yes, B4 was German 87 oct fuel.

Powerloading based on takeoff weight:
XIV 4,186
K4 3,748
Click to expand...

At what altitude? With or without ram? What power, what weight?


Spitfires with 2-stage engine was certainly not a very streamlined machine. The K-4 was more streamlined than late Gustavs, and it needed less HP to fly as fast as Spitfire 14. OTOH, Spitfire 14 (yes, I hate Roman numerals past number V) have had more power, especially at high altitudes.

10 % difference is not 'huge'.
 
Wing loading actually has little, if anything, to do with climb.

Once you have the plane flying level at the lowest combined drag what matters is the power to weight ratio.

A big wing plane may have a lower wing loading but it may also have a higher drag (need more power at climb speed) than the smaller wing plane.

You may need to add 10-30 mph over the lowest drag speed in order to ensure good stability in flight, this varies with plane and the tail surfaces/effectiveness.

Spitfire 14

also has that 5 blade prop to turn horsepower into thrust.

At low speeds (climbing) a prop with a lot of blade area might be better than a prop with less blade area.
However for high speed the reverse may be true. The smaller blade area might mean less drag on the prop.
Germans experimented with thin and thick props on the 109K, other countries experimented with different props too, Like on the P-47.

the power (thrust) to weight ratio governs the angle of the climb once you are at climbing speed. all the wing lift does is set up the angle of incidence or angle of attack of the wing for the speed the wing is flying. This angle of attack has nothing to do with angle the plane is climbing at (actual path of the plane)
 
Climb is measured in feet/minute or meters/minute, taking the measured performance and dividing it by random numbers is a strange and quite new science that seems to always favour objects with black crosses on them
 
An aircraft's total drag is , where is total aircraft drag, is the aircraft's drag at zero lift, is coefficient of lift, and e is Oswald's efficiency factor (for monoplanes, this is usually about 0.8. For an ideal wing with an elliptical wing coefficient, this is 1.0), and A is aspect ratio.

After doing some algebra and calculus (always fun ), one gets for the lift coefficient for best L/D. An aircraft with a higher with a wing loading will have its best rate of climb airspeed at a higher speed. If I remember (I don't feel like looking it up), the Spitfire had a lower wing loading that the Bf109, so it's not unlikely that there would be a speed range where the Spitfire would outclimb the Bf109. Also, the Bf109 was not particularly notable as a paragon of aerodynamic cleanliness.

Sorry for all the very large equations; I copy and pasted from Google Docs & Auto Latex.
 
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You also get strange real world results. Some Spitfires climbed at a higher rate than the equivalent 109 (at the time) but actually needed a higher airspeed to do it so the angle of the climb was less than than 109 which made it appear that the 109 was climbing better. It needed less distance to reach the same height even if it needed a few seconds more. Or the 109 needed a higher angle of attack?

Now all of this is for straight climbs with level wings. Throw in a bit of curve (turning while climbing) and now the wing loading starts to come into play more.
 
Hmmm...

Griffon 61, 65 (18psi 150oct) sea level: 1850 hp (4,591) 19700ft: 1650 hp (5,147) 21300ft 1700hp (4,996)
DB 605 DB (1,8 ata MW50 87oct) sea level: 1850 hp (4,051) -11,7% 19700ft: 1600 hp (4,684) -9% 21300ft 1600hp (4,684) -6,2
DB 605 DC (1,8 ata MW50 87oct) sea level: 2000 hp (3,747) 19700ft: ??? 21300ft ???

BF 109 K4 is arguably more streamlined (superior top speed at sea level with same engine output) and has an advantage in powerloading all the way up to 6500m (21300ft).
How common was the DB 605 DC? Any production numbers?

Spitfire XIV
take off 8494lbs
HP @ sea level 1850
RoC @ sea level 4700ftm
Powerloading 4,591

BF 109 K4
take off 7495lbs
HP @ sea level 1850
RoC @ sea level 4300fpm
Powerloading 4,051
-11,7 %

Let's take a look at the other side of the horizon:

KI 84
take off 7940lbs
HP @ sea level 1970
RoC @ sea level 4300fpm
Powerloading 4,030
-12,2%


J2M Raiden Model 11
take off 7080lbs
HP @ sea level 1870
RoC @ sea level 4600fpm
Powerloading 3,786
-17,5%

KI 84 vs BF 109 K4: similar powerloading
RoC is almost identical
seems logical

KI 84, BF 109 K4 vs J2M: The Raiden has an advantage of -5,3% and -5,8%
RoC +300
well that makes sense

KI 84, BF 109, J2M vs MK XIV: Err +12,2 +11,7 +17,5
RoC +300 +100
???

My sources:
http://www.spitfireperformance.com/griffonhp_b.jpg
Kurfürst - DB 601, 603, 605 datasheets - DB 605 DB/DC
Kurfürst - DB 601, 603, 605 datasheets - DB 605 DB/DC
Spitfire Mk XIV versus Me 109 G/K
http://www.wwiiaircraftperformance.org/japan/T-2_Report_on_Frank_I_Ki-84.pdf
http://www.wwiiaircraftperformance.org/japan/Jack-11-105A.pdf

????????????????
 

Griffon 61, 65 etc was doing +18 psi on 130 grade, no need for 150 grade. The chart you've posted is with ram effect (aircraft flying at 400 mph). Ram effect adds ~4000 ft to the power values there. Without ram, it was 1870 HP at 21000 ft, 2050 HP at 8000 ft (and probably 1900+ HP at SL).
Max boost for take off was +12 psi for the war-time Griffons.

6000 m = 19685 ft, not 21300 ft. Will the pilot of Bf 109 use MW 50 for taking off? If not, the take-off power will be 1430 PS.
MW 50 for climb all the way from SL?
In order to make 2000 HP at SL (= needs boost of close to 2 ata), the DB 605 will use C3 + MW 50.

BF 109 K4 is arguably more streamlined (superior top speed at sea level with same engine output) and has an advantage in powerloading all the way up to 6500m (21300ft).
Click to expand...

Yes, the 109K4 was more streamlined.

How common was the DB 605 DC? Any production numbers?
Click to expand...

Getting accurate data for that might be problematic. Hopefully D Deleted member 68059 can help.
 
Hi,

1)The chart I've posted shows the usage of 150 octane...
2)I quess ram effect values can be applied to the DB as well or any other engine for that matter?
3)According to Kurfürst's site the DB 605 DC had a power output of 2000hp @ 1,8 ata.
4)How long could the Griffon 61, 65 be flown at maximum power compared to the Daimler Benz? Most sources claim MW50 could be used for 20 - 25 minutes.
 

1 - It does, the max boost being +25 psi in that case.
2 - Of course. Since ram effect varies, at least, with speed and quality of air intake, the no-ram values give us a more level playing field.
3 - Where exactly?
4 - Not sure. 5 min probably (the war-time manual for the Spit XIV gives 5 min for +18 psi operation)? What are the sources for 20-25 min MW 50 non-stop operating? Granted, use of water/alcohol injection helps with duration of overboost since it is sorta 'internal cooling'; IIRC at least 10 min duration was for US-made engines for 'wet WER' vs. 5 min for 'dry WER' (plus side being that 'wet WER' gave much more power).
 
1) oh ok
2) How to calculate non-ram values for the DB?
3) My bad sorry. It states "kann nicht gewählt werden" which means can't be used
4) The German Wikipedia states:
"Der Vorrat des Wasser-Methanol-Gemisches von (beispielsweise beim DB 605 D der Bf 109 K-4) 70 Litern war für 26 Flugminuten mit Sondernotleistung ausreichend.
Allerdings durfte die Maschine nicht mehr als zehn Minuten ununterbrochen auf dieser höchsten Leistungsstufe betrieben werden, sonst drohten Motorschäden."
Rough translation:
The total amount of MW 50 (for example DB 605 K4) was limited to 70l for a total duration of 26 minutes. The engine shouldn't be used for more than 10 minutes nonstop though, otherwise there's a risk of engine damage.

What was the total duration for the Griffon engine?
 

2 - no need to calculate them, non-ram values are the ones stated in data tables (western, actually American tables & graphs often clearly state ram/no ram conditions in some tables, sometimes mispriniting them)
4 - my translation of the crucial part: The engine should not be run at such high power settings for more than 10 min uninterrupted, because of risk of engine damage.

There was no 'total duration' for the Griffon engine, pilot's job was to observe the coolant and oil temperature before trying to push engine to it's limits again. In other words, cool the engine a bit down from 135/105°C (coolant/oil) to 125/90 (1 hour limit) and then have another go to +18 psi.
 
Getting accurate data for that might be problematic. Hopefully [USER=68059 said:
@Snowygrouch[/USER] can help.
Click to expand...

Difficult on very late model-sub-types. The 605D in particular has very little documentation due to the rather poor situation the war
was in during its inception. The 605D itself was only at Nr. V3 in Jan 1944 (i.e. prototype #3) at Werk #60, Unterturkheim.

Sadly I have virtually no archive documents on the DC other than a modification instruction for the MW50 modifications to the
fuel pump dated 14th March 1945.

This gives Sondernotleistung as = 2800rpm, 1.8ata, 1800 PS - but does only list that for 605DB, 605AB and 605ASM, these figures
are valid only with MW50 + C3.

On 10th Jan 1945 a DB memo Nr. 6642 states (quote)

".... nach Rechlin..

1x Motor dur kolbenbrenner nach 1/2 stunde sondernotleistung
2x Motoren durch Nebelpleuelbrüche nach 7 bis 12 Minuten Sondernotleistung
1x Motor durch Laderschaden nach 8 minuten Sondernotleistung

Aus diesem Gründe hätte Herr Fl. Ob.Stabsing Cuno die Sondernotleistung DC (1.98 ata Ladedruck) für die Truppe nicht
freigegeben."

(basically at this point 1.98 ata for the DB605DC isn't approved because of piston erosion, con-rod failures and supercharger failures under emergency power)

Test results of the K4 with MW50 show max speed of about 441mph at 6km with the 605DCM - Dated 11th Dec 1944 with 1800 PS available (this is special test flights,
not the manufacturers released data-cards for the real service planes, which due to appauling surface finish were probably around 20mph slower from
interrogations I have read with German engineers in 1946). Info on the test report seems to say that the speed figures themselves may have been actually
measured on 13th August 1944.

On 24th Jan 1945, DB Niederschrift Nr. 6730, 1.98 ata for the DB605 is discussed, basically saying releaseing 1.98 ata (for 2000PS) was a bad idea to before proper testing had been carried out, basically says Galland said "just do it" and DB went along with it, and lots of problems occured.

Later 2.3ata is discussed, and its about this date when documentation really starts to run dry, however anecdotally I think it likely that by this point...say... Feb 45, they probably managed to push many to 1.98 and even 2.3 ata as basically they had no choice but engine life would have been possibly just minuites at these ratings.
 
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That presented the RAF with a practical problem in 1940, MkI Spitfires and Hurricanes couldn't climb together despite having the same engine and prop. The spitfires best rate of climb was at a much higher forward speed.
 
Tomo, Griffons were restricted to 21lb boost. Merlins had 25lb boost.

Snowygrouch, how much C3 was available for the 109s as the BMW801 required C3? How available was methanol?
 
Milosh said:
Tomo, Griffons were restricted to 21lb boost. Merlins had 25lb boost.

Snowygrouch, how much C3 was available for the 109s as the BMW801 required C3? How available was methanol?
Click to expand...

I couldnt get a complete list because the relevant archive in Germany was closed early this year, and although its now "open", in actual fact under these
new circumstances the service for getting an appointment is so laborious it might as well still be closed. Consiquently I only have the B4/C3 ratios for a couple of snapshots in time.

03/06/1942 _ C3 = 7.4% (NB this is from the complete Luftwaffe stocks in Holland and so may not be representative of the whole picture)
31/07/1943 _ C3 = 19.3% (This is from all Grossraumtanklagern in Germany, so is probably a very good real view of the picture)
03/10/1944 _ C3 = 39.2% (This is from the main fuel stores in Germany used for fighter supply, so for C3 is probably an accurate assessment)

The vague statement which everyone always copies from "The Manufacture of Aviation Gasoline in Germany" of "about 2/3" is usually taken
out of context, the report states when it was written they had no figures at all on the ratios, and that this "about 2/3" was really just
the best guess of the persons interrogated as to the position in the last section of the war. I think this fits reasonably well with
the data I got from late 1944 of about 40%. This figure was probably increased and may have been well over half by the end, hence
how much B4 and C3 was available depends entirely over which segment of time you look.

I will revise this statement if I manage to get to the 20 files in Germany which I think will provide more data, this graph should NOT
be taken as gospel, and is based on a few small snapshots of data and some guesses. However it will not be too far out...if its wrong
anywhere it may be in the first 2 years, where I`d say it could have been up to 15%, (to be confirmed by further research.) I would also say
That the 60% at the end is a guess, and even if its "true" I think it can only be 60% if you included "equivalent to C3" which was probably
B4 with various other bits hastily added to try to make the best of things. My info on that is sketchy and just comes from snippets
of interrogations of various Germans in 1945/46 about the sort of things that went on near the end, I have no proper data on it, but
for example may have been B4 with some Iso-Octane dumped into it, and an overdose of T.E.L. because they probably judged the
reduced spark plug & valve life that would cause as being a bit of a moot-point at that stage.

You also need to keep in mind that this is the percentage of the total, and from late 1944 the totals plummeted. Graphs are in my book.

 
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