Why was the BF109 so slow compared with the P51?

[Deleted member 68059]

Because North American had better aerodynamicists than did the Messerschmidt company, and those NA engineers also had access to better resources. After all, look at how many Luftwaffe aircraft used NACA airfoils.

There is no doubt the Mustangs aerodyanamics were superlative. However, it is too simple to start saying this was due to the chaps at Me just not knowing how to do it. In fact they did know perfectly well what Laminar flow wings were (although there are many other nice aero bits it has too).

A very important thing to note is that the Germans could NOT impliment Laminar flow wings because they discovered through testing that they were only effective if the fit and finish of the aircraft was absolutely spot - on. Knowing perfectly well that such a fit and finish was impossible to imagine in the manufacturing environment that existed in Germany in wartime, they didnt bother, as they actual advantage would have been negligable. A second point being that this requirement for fit and finish made it impossible to retain the
leading edge slats. Eliminating those on an existing aircraft would have been a total rework of the plane (thats not something I`ve "read" into it, thats a direct statement in the
original report as well). (Ref#1)

There are about 20 other things one could talk about on this subject but thats one to keep in mind before assuming incompetance of the aerodyamics staff, who had actually designed one for the 109. It was never implimented. They do seem to have waited longer to try it than the USA did, but that can probably be attributed to the fact that nobody in Germany
had been seriously planning for them to even be at war after about 1942, so they really slacked off with development until it became evident that things were a bit stickier than hoped for. So this seems to have been a case of bungled direction of research from above, rather than technical inability. (Ref#2)

=============
ARCHIVAL SOURCES
=============

1) "Me.109 Laminar Profile wing" - Pieckert, TB No.128/44 - Messershmitt A.G. Windtunnel Report

2) "A Scientists Analysis of the German Defeat" - Professor Dr. Walter Georgii; being interrogated on 19th Nov 1945 (Georgii had been in charge of the glider development aerodyamics
centre in Germany through much of ww2.

Some bio info on him here:
Walter Georgii (Meteorologe) – Wikipedia

 

[nuuumannn]

So this seems to have been a case of bungled direction of research from above, rather than technical inability.

Oh yes, the downfall of the whole Third Reich, really.

Nice bio, Calum; looking forward to nabbing a copy of the book.

 

[tomo pauk]

I believe the main answer is that the U.S. and Britain had far better fuel. The powerplants of the two A/C in question had different compression ratios. The Merlin engine specified higher octane than the DB because they could.

Because who could?
There was a DB engine that used hi-oct fuel, it was called DB 601N. Due to many inter-related things (one of them being, indeed, much higher compression ratio), that engine never took advantage of the C3 fuel, and barely attained 1.40 ata (around +5.25 psi). We can compare speeds of Bf 109F1 or F2, the aircraft with 601N engine, and see that they lag behind P-51A on military power (= slightly less altitude power than 601N) by some 30 mph.

There is no doubt the Mustangs aerodyanamics were superlative. However, it is too simple to start saying this was due to the chaps at Me just not knowing how to do it. In fact they did know perfectly well what Laminar flow wings were (although there are many other nice aero bits it has too).

Against already thin and small wing of Bf 109, the P-51s wing probably offers just small advantage for over-all speed; that 'transplantation' of P-51s wing would've improved other things - like usable internal volume, better U/C layout and lower wing loading (= no need for slats?) - is probably not in the scope of this thread.
All of what brings us to a part two of the answer to The Question - streamlining.
On the Bf 109E-G, there was a number of things that add the 'delta Cd', the drag increments. In no particular order:
- ram air scoop was not blended in fuselage shape
- coolant radiators will be 'struck' by turbulent air, two of them, vs. one on P-51 that went improving 4 times between P-51 and P-51H
- no cover for wheen wells
- separate oil cooler
- questionable use of Meredith effect
- fixed tailwheel on many produced examples
- HMG 'bumps' at cowling on many later Bf 109Gs
- possible imperfections at slat/wing joint
- wing bumps for wheels on late 109Gs and 109Ks

All of these, along with many more, are listed at the Hoerner's analysis of drag of the Bf 109G. He states that wing contributed to drag by more than 1/3rd, and engine-related drag being at almost 1/4th of whole drag.

 

[Schweik]

Is there some systematic standard by which they measure drag across different aircraft types? Like a number?

 

[swampyankee]

Is there some systematic standard by which they measure drag across different aircraft types? Like a number?

Well, at least two: zero-lift drag coefficient and lift/drag ratio.

 

[gliding]

IIRC the Allies called the C3 as '96 oct fuel', while Germans called it '100 oct fuel'. Both values being lean rating, while rich rating going steadily up towards 140+ as war progressed. Used mostly by DB 601N and BMW 801D. The fuel used by most Bf 109s was B4 - 87 oct.

The comparison of fuels and their knock resistance is not possible over "the" octane number. Then and now different methods of measurement are used.
For the comparison, one needs a test engine, which is operated with Isooctane. Depending on this test engine, there are different "octane" numbers.
(An early German C3 fuel (95 german-octane) was roughly comparable to a 100 US-octane fuel.)
The production of high-octane gasoline was complex and expensive and could not be realized in the required extent by Germany in the last years of the war.

Reports from Daimler show that higher performance was possible even without GM or MW50. The required fuel was not sufficiently available.

 

[drgondog]

I will devote a lot of time in the Apendices of my new book on this very subject:

Start with Power Available vs Power Required as the fundamental set of calculations once the drag parameters are derived (wind tunnel testing);

'The Wing is The Thing' to begin the discussion.
The achievement of (Close to) net zero drag for the internal cooling system is an assumption based on the composers (Horkey and Ashkenas) of the Performance Calculations contained in NA-5534 on the P-51B-1-NA airplane - for high speed Cooling Drag. In this assumption the Pressure and internal friction Drag compared to Thrust generated by the design often referred to as the Meredith Effect is specifically stated as "0 for high speed cruising at Critical Altitude" BUT the Delta CDp for 35,000 feet = .0004 and at 40,000 feet = .0010. In other words Net Zero Internal CDp for only a region at high speed in a narrow altitude envelope.

The Delta CDp for CLIMB condition = .0064 at ALL altitudes independent of Reynold Number.

The INITIAL base CDp for RN =1.8x10^^ for the Wing = .0074 (note: the same initial value for same wing at 2.0x10^^6 for the P-51D wing =.0070). This is a value that considers the profile drag of the wing immersed in a flow - INDEPENDENT of the friction drag.

This value is far below that of the same relative thickness wings of the Fw 190/F6F/F4U/P-47/Bf 109 using NACA 230xx airfoils at same RN.

The second significant base Delta CDp values for comparison, but less than the wing in importance, are the form drag totals for Fuselage, empennage, carb duct, cockpit enclosure build ups. If you wish to ask why, consider that the entire airframe Lines were developed using Descriptive geometry for which the contour from nose through cockpit enclosure was essentially an ascending shape area of low gradient change aft of the card intake duct (including Allison).

(Note that ALL Mustang variants placed the 'disruptor' (scoop, ducting for radiator/oil cooler, intercooler, and exhaust exit) aft of the CP of the wing and aft of the boundary layer separation from fuselage and wing.)



The next significant CDp factor was the Friction Drag Delta CD = .0008 + 'Gap' Drag Delta CD = .0004 = .0012 which is Constant for All RN - a Very low value speaking to the following: 1.) Extremely good production design co-ordinated with factory processes to achieve extremely good sheet butting, flush riveting, excellent jigs and fixture design, priming/sanding/painting of upper and lower wing surfaces through ~ 40% wing chord, and placement of important panels at or aft of that region.

These values for CDp were the very best in comparison with all the values I have seen presented for other aircraft.

Looking to Hoerner 14-4 (b.) Drag of the Wing ------------> the comparable Friction drag for paint irregularities, gaps, bumps, sheet edge and rivet losses @ RN=1.1X10^^7 (For ONLY the wing) ----------> .0035 (skin friction) plus .010 (gap/surface imperfections). Compare to .0008 plus .0004 for the P-51 values above. More than 10x Bf 109G total skin friction and surface imperfection components for the wing drag over P-51B drag.

Hoerner does not present the individual components of parasite drag as a function of RN like NAA. That said, the clues for his Parasite Drag as function of RN @ 4x10^^6 (Wind tunnel at Chalais-Meudon for either Bf 109E or F in 1941) = CDp .030 Without momentum drag of engine air intake of that of the tail wheel.

The comparable CDp for RN=4x10^^6 for the P-51B = .0190 -----------> ~ 63% of the Bf 109E

Comparing CDp for his calculation of .028 @RN=2^^7, the comparable P-51B CDp = .0155 ----------> 55% of the Bf 109E

In Chapter 14 he 'reverse calculated total drag based on T=D;
For his Calculated Total Drag (CDt) at Vmax (= 380mph at 22,000 feet) = 0.036 [includes base parasite/form drag, vortex drag + high speed cooling drag) multiplied by Mach No. correction +Induced drag. For the P-51B, the same CDt = 0.24 ------------> 66% of the Bf 109G

Last note - the High Speed/Low Drag 45-100 wing while loosely described as Laminar (not so much), was extremely low drag in two areas of discussion. First, the low velocity gradient from LE to max T/c at 37.2 % was much lower than equivalent thickness 23016 airfoil which delayed Mach drag rise and major CP shift, and second - the form drag of the wing was simply lower.

I HAVE not spent a lot of time looking at the Hoerner discussion, but the P-51B drag values for CDp and CDp1(combined gun ports, radio mast, gaps/leaks, friction, etc) are extracted from the P-51B Report, compared to P-51D and P-51H to check for unexplainable variances (none other than P-51H had lower wing parasite drag)

Postscript. The Cooling drag build up for climb (worst case) was .0064 for a combination of internal pressure drag/flow losses of the scoop/plenum/oil cooler/radiator/exit plenum and open exit gate. So, if we take Horkey and Ashkenas at their technical competency, then for Net Zero high speed Cooling drag, the CD to be recovered by incremental Meredith Effect jet thrust = .0064. Thus, if Jet THRUST = 0 and all internal drag components are not neutralized, the the total drag build up for RN=2x10^^7 = 0.31 --------> 86% of the Bf 109G-6 calculated total by Hoerner.

Take what you want, leave the rest.

 

[Shortround6]

In the west (American and Britain) the Performance Number scale was developed. While this could be applied to any octane number of fuel it was rarely applied to under 100 octane. 100PN does equal 100 octane so any numbers over 100 are PN numbers. PN numbers under 100 explain a lot but get discouraging rather quickly.
OCt=PN
100=100
96=87.5
91=75.7
87=68.3
80=58.3
70=48.3

The octane scale was NOT linear and was really screwed up between 90 and 100. One can also see the huge improvement between 87 oct and 100 oct, what one cannot see is that the British never published a rich rating for their 87 octane fuel.


The Germans may have shot themselves in the foot with their fuel injection system. I am open to correction on this, by my thinking goes along like this.

The allied fuel was rated at lean (low number) and rich condition (high number) and difference was that under rich conditions the fuel system was providing 30-40% more fuel per HP (or per pound of air) than it was at lean condition. I don't know if the German fuel injection system could reach this level of "richness". Now it might not have necessary to quite go that far as the Germans did have better fuel distribution (less difference between rich and lean cylinders) but the Germans may not have been using excess fuel as an internal coolant either.

German fuel when tested by the allies often did have a good (and sometimes excellent) rich rating, but if the engine is not set up to take advantage of it where are you?
The next problem is that unless the purchasing dept specifies a particular rich response it can vary from batch to batch even at the same refinery let alone between refineries, Just because batch A was 96/135 doesn't mean batch B is any better than 96/120 for instance.

 

[Shortround6]

I will devote a lot of time in the Apendices of my new book on this very subject:
.

Welcome back

 

[tomo pauk]

The comparison of fuels and their knock resistance is not possible over "the" octane number. Then and now different methods of measurement are used.
For the comparison, one needs a test engine, which is operated with Isooctane. Depending on this test engine, there are different "octane" numbers.
(An early German C3 fuel (95 german-octane) was roughly comparable to a 100 US-octane fuel.)

No problems with this.

The production of high-octane gasoline was complex and expensive and could not be realized in the required extent by Germany in the last years of the war.

Agree pretty much.
On the other hand, crediting just the fuel quality for performance gap existing between Mustangs and Bf 109s would've mean a discreditation of engineers at NACA, NAA, RR etc. Again - we know that Bf 109F1 or F2, fighters whose engines used hi-octane fuel, were slower by large margin than P-51A (Mustang II) on when on similar engine powers vs. altitude.

Reports from Daimler show that higher performance was possible even without GM or MW50. The required fuel was not sufficiently available.

Higher performance was certainly possible with higher octane fuel. However, when we have both Bf 109 and P-51 with hi-oct fuel and no anti-detonant injection, Bf 109 will come as second best, speed wise.

 

[Deleted member 68059]

I`m not following why we are discussing octane, the title of the thread is why the PLANE was slower, in that respect it is a simple matter to write down the horsepower outputs of each engine (which are all known very well).

Getting into a mess about octane numbers and engine development is a new thread, and WHY the engines were making less power is not the same question.

Just my opinion, I think the thread would be better served concentrating on the aero-features, whilst acknowledging the thrust power available to each plane.

Its very clear from Archival records that the big factor here is airframe, as is evident from the utter shock at the British air ministry at the performance of the Mustang over the Spitfire with essentially an identical engine. Of course the 109 shares neither the airframe NOR the engine, but all I`m saying is that in my view - I`d be far more interested in discussing the aero than octane stuff - I`m not very convinced another DB vs RR thread will help the original post ? - maybe the original poster can clarify whats wanted !

 

[gliding]

My post was a comment on #19. The engine technology (performance) would certainly have led to similar results for the Germans, if the same materials (fuel, metals, ..) would have been available.

A comparison of Bf 109 to P-51 is in my view without sense. The Bf 109 was developed when biplanes still served in many air forces. The first flight was in 1935.
The P-51 had its maiden, as already the 5th generation of the Bf 109 was produced. The experience from the war led to the specification.

A better comparison would be P-51 and Me 262. Both come from the same generation.

 

[jetcal1]

My post was a comment on #19. The engine technology (performance) would certainly have led to similar results for the Germans, if the same materials (fuel, metals, ..) would have been available.

A comparison of Bf 109 to P-51 is in my view without sense. The Bf 109 was developed when biplanes still served in many air forces. The first flight was in 1935.
The P-51 had its maiden, as already the 5th generation of the Bf 109 was produced. The experience from the war led to the specification.

A better comparison would be P-51 and Me 262. Both come from the same generation.

Better yet, P-36 versus Bf-109.

 

[Schweik]

My post was a comment on #19. The engine technology (performance) would certainly have led to similar results for the Germans, if the same materials (fuel, metals, ..) would have been available.

A comparison of Bf 109 to P-51 is in my view without sense. The Bf 109 was developed when biplanes still served in many air forces. The first flight was in 1935.
The P-51 had its maiden, as already the 5th generation of the Bf 109 was produced. The experience from the war led to the specification.

A better comparison would be P-51 and Me 262. Both come from the same generation.

Lol

 

[tomo pauk]

My post was a comment on #19. The engine technology (performance) would certainly have led to similar results for the Germans, if the same materials (fuel, metals, ..) would have been available.

I'll disagree as before.
For aerodynamical reasons of why Bf 109 was slower than P-51, please see post #27 by Bill, who is a) one of prominent scholars on P-51 and b) engineer that worked in industry, including Lockheed for example.
For 'power' reasons*, Germans missed opportunity to design & produce a V12 engine with 2-stage supercharger until it was too late. Jumo engineers designed the Jumo 213E, a 3-speed 2-stage supercharged engine that used 87 oct fuel. No fancy metals are needed for a 2-stage S/C, people at RR designed a service-worthy 2-stage S/C engine in 1941-42, at Jumo and DB in late 1944. The Bf 109 was slated for DB-605L for spring of 1945.
Mentioning the quality of fuel and metals are worn-off excuses for lacklustre performance of German fighters in 1944.

* the author of the video devoted a few minutes to this

A comparison of Bf 109 to P-51 is in my view without sense. The Bf 109 was developed when biplanes still served in many air forces. The first flight was in 1935.
The P-51 had its maiden, as already the 5th generation of the Bf 109 was produced. The experience from the war led to the specification.

5th generation of Bf 109 in October of 1940? That's something new.
What particular experience from the war had to do with any crucial technology P-51 used to a good cause, ditto with specification?

A better comparison would be P-51 and Me 262. Both come from the same generation.

I disagree, but you are certainly entitled to your opinion.

 

[Shortround6]

The 109 is a mish-mash.

The Bf 109 was developed when biplanes still served in many air forces. The first flight was in 1935.

Not exactly the best radiator set up, strut braced tail plain, no ejector exhaust.

Carb (or air) intake not the best. Spinner and forward cowl looks a bit suspect.

By the 109F

Better radiators under the wings (with bounder splitters?)Better even if not great air intake., Better spinner, front of cowl. (canopy still sucks). ejector exhausts, wing tips have gone from square to round (????) changes in ailerons, and slats form early models (? asking, not telling?)struts for the tail plain have gone away. The 109 got a redo in 1940 and not a minor one.

 

[GrauGeist]

A comparison of Bf 109 to P-51 is in my view without sense. The Bf 109 was developed when biplanes still served in many air forces. The first flight was in 1935.
The P-51 had its maiden, as already the 5th generation of the Bf 109 was produced. The experience from the war led to the specification.

The Bf109 had it's first flight in 1935 BUT it was accepted into service in 1937.
It should be also pointed out that the Hurricane first flew in 1935 and entered service in 1937, and the same for the P-36, first flight in 1935, though it entered service in 1938. All of which were world class fighters for their time.

The P-51 had it's first flight in 1940 and entered service in 1942. By 1942, the Bf109 had matured considerably, by way of engine, aerodynamics and firepower.

A better comparison would be P-51 and Me 262. Both come from the same generation.

This is not even a consideration - the technology and design between the both are night and day.

Why not compare the P-51 to the He280? The He280 was the world's first combat jet and designed as a true fighter. It also shared a development timeline comparable to the P-51.

 

[parsifal]

Can anyone extrapolate or guess what the performance increase in bf109g might have been had been provided with 130 or 150 octane fuel like the P-51?

 

[gliding]

I think I did not express myself correctly. The P-51 was a wonderful aircraft and also superior to the Bf-109. No doubt. It is also a great airplane for me. But in my view, it's not fair to compare a development started > 5 years earlier.

What particular experience from the war had to do with any crucial technology P-51 used to a good cause, ditto with specification?

The order for a fighter-development received Messerschmitt in February 1934. It should be fast with short range and low altitude. It should only carry 2 MG17 (7.9 mm) and the undercarriage must be attached to the fuselage. Maybe the wrong demands, but the order to Messerschmitt. The solutions of the engineers were in my opinion (1935!) more than good. Airplanes of the same time (Spitfire development starting from 1935, Hurrican development starting from 1933) were on similar level.

The P-51 should be a long-range hunter. Great heights were required. The Mk I wore 4 machine cannon and 4 machine rifle. Demands from the current war.

For aerodynamical reasons of why Bf 109 was slower than P-51, please see post #27 ....

The results are undoubted. Dr. Hoerner also wrote (14-7): "If rebuilding the ME-109 in a manner that would reach 100%, the maximum speed would be 610 to some 800 km / h, if using the same power plant." Even in the ideal case, the speed of the P-51 could only be achieved with a larger engine. A larger engine did not fit in the Bf-109. The diagram of Dr. Hoerner shows the development of the parasite drag coefficient. It also shows the difference of 5 years. European scientific sources say degreasing drag coefficient reduction of 1920 (100%) -> 1932 (88%) -> 1936 (51%) -> 1940 (42%). However, it should also be mentioned here that these results were determined many years later (Dr. Hoerner, 1957).

Messerschmitt had also recognized that the Bf-109 was outdated. The planned replacement "Bf-209" with DB603 could be possible compared with the P-51. It also has similar performance data. However, the policy was afraid that a change of the series production could mean a loss of quantity. In addition, Messerschmitt (also Focke-Wulf, according to Kurt Tank) was in this time no more interested in piston aircraft, because he saw the jet aircraft as future.

5th generation of Bf 109 in October of 1940? That's something new.

Not really new. B - C - D - E - F. Until the end (K), the adjustments were always small. The biggest change was E -> F, not a priority for performance but in more production-efficiency. (Blueprints for F are dated from mid-1940)

I disagree, but you are certainly entitled to your opinion.

The comparison P-51 - Me-262 should be fun. Nevertheless, they were designed at the same time. If you want to make a "real" comparison, maybe P-51 and Do335 would be suitable. Again, different requirements and solutions, but also here you can see that about the same time comparable benefits were achieved.

Yes, that's my opinion and thank you for allowing me to. I think a forum lives from different opinions. I do not want to convince anyone.

 

[tomo pauk]

I think I did not express myself correctly. The P-51 was a wonderful aircraft and also superior to the Bf-109. No doubt. It is also a great airplane for me. But in my view, it's not fair to compare a development started > 5 years earlier.

Probably it is not fair.

The order for a fighter-development received Messerschmitt in February 1934. It should be fast with short range and low altitude. It should only carry 2 MG17 (7.9 mm) and the undercarriage must be attached to the fuselage. Maybe the wrong demands, but the order to Messerschmitt. The solutions of the engineers were in my opinion (1935!) more than good. Airplanes of the same time (Spitfire development starting from 1935, Hurrican development starting from 1933) were on similar level.

The P-51 should be a long-range hunter. Great heights were required. The Mk I wore 4 machine cannon and 4 machine rifle. Demands from the current war.

British, the people that aproached NAA to make P-40s didn't asked for anything like. NAA offered them a 'better fighter than P-40'. Long range was not specified, Mustang I was even without drop tanks facility. Neither were the great heights specified, the Mustang was featuring 1-stage supercharged V-1710 that had lower altitude-power than the old Merlin III.
Mustang I didn't wore cannons until well into 1942. Look at the armament from British perspective - their pre-war Hurricanes and Spitfires were outfitted with 8 LMGs, the cannon-armed fighters were in the design phase in 1938/39, so Mk.I with 4 HMGs and 8 LMGs is nothing awe inspiring to them.

added: RLM didn't asked for undercarriage to be attached to fuselage - MTT used the known tech from BF 108, while the He 112 was not disqualified because of the place the U/C legs were attached. I agree that MTT did a good, if not a great job with Bf 109.

The results are undoubted. Dr. Hoerner also wrote (14-7): "If rebuilding the ME-109 in a manner that would reach 100%, the maximum speed would be 610 to some 800 km / h, if using the same power plant." Even in the ideal case, the speed of the P-51 could only be achieved with a larger engine. A larger engine did not fit in the Bf-109. The diagram of Dr. Hoerner shows the development of the parasite drag coefficient. It also shows the difference of 5 years. European scientific sources say degreasing drag coefficient reduction of 1920 (100%) -> 1932 (88%) -> 1936 (51%) -> 1940 (42%). However, it should also be mentioned here that these results were determined many years later (Dr. Hoerner, 1957).

That drag reduction was not applied to any design from those years, some designers/companies did a better job, other failed. Hurricane was much draggier than Bf 109, Me 210 and Welkin were much draggier than Mosquito, Typhoon was much draggier than Mustang.
Bf 109 was certainly able to accept DB 605L, a 2-stage superchaged engine from 1945. The DB 605AS/ASM engines were also fitted, bringing the altitude powers to levels of 2-stage Merlins. Problem with those engines is their late introduction.
Then we have aerodynamics improvements - all the time use retractable tailwheel, cover the Wheel wells, avoid the draggy HMG installation, introduce better radiators (whether in leading edge extensions like on Mosquito, or take a page from Italian or Soviet fighters, or from D.520, or go with annular radiator), blended ram air intake like on He 100. Some of these improvements were fitted on the K series.

Not really new. B - C - D - E - F. Until the end (K), the adjustments were always small. The biggest change was E -> F, not a priority for performance but in more production-efficiency. (Blueprints for F are dated from mid-1940)

I see the B/C/D as one generation, E as another, F as another. The F series represented a major improvement of aerodynamics vs. E.

The comparison P-51 - Me-262 should be fun. Nevertheless, they were designed at the same time. If you want to make a "real" comparison, maybe P-51 and Do335 would be suitable. Again, different requirements and solutions, but also here you can see that about the same time comparable benefits were achieved.

Yes, that's my opinion and thank you for allowing me to. I think a forum lives from different opinions. I do not want to convince anyone.

1940 and 1942 are not same time.
As for the P-51 vs. Do 335, I'd pick P-51H - on just one engine, it is no worse a fighter than Do 335 that needed two.

added: without different opinons, we would never have meaningful discussion, whether in forums or otherwise. I am certailnly not the one allowing/disallowing people from expressing their opinions.

*edited due to the typos/grammar and additions*