Did the Allies Just Have Better Engines?

[NevadaK]

Thinking about a number of posts in recent threads, it seems as if a critical advantage the Allies has during the crucial 1943-1944 time frame was aircraft power plants that were significantly better than those of the Axis. The inability of the Axis to develop comparable power plants was a major failing and a major factor in the outcome of the air war. Or, oversimplified:

Did the Allies just have better engines?

Your thoughts?

 

[Deleted member 68059]

Did the Allies just have better engines?
Your thoughts?

See the "events" section of the forum.

Online lecture on WW2 engine development

(The answer is "yes", but without the story of the "why" I`d say its too simplistic to be meaninful.)

 

[NevadaK]

See the "events" section of the forum.

Online lecture on WW2 engine development

(The answer is "yes", but without the story of the "why" I`d say its too simplistic to be meaninful.)

Thanks Snowygrouch!

Yes, my question is way oversimplified but not being an engine guy its about the best I could do without my morning coffee. Your presentation looks like something worth attending, and if my schedule fits I will try to attend. While you are focusing on the Western Front, my feeling is that it was a conflict wide issue with the Allies (the US and UK in particular) establishing engine superiority in all fronts in 1943.

Regards, Kevin

 

[Koopernic]

Thinking about a number of posts in recent threads, it seems as if a critical advantage the Allies has during the crucial 1943-1944 time frame was aircraft power plants that were significantly better than those of the Axis. The inability of the Axis to develop comparable power plants was a major failing and a major factor in the outcome of th[/B]e air war. Or, oversimplified:

Did the Allies just have better engines?

Your thoughts?

You can not answer this question without getting into a discussion of fuel octane and performance numbers nor the difficulties the German Coal to Synthetic fuel industry faced in producing large quantities of high octane fuel. There is a case to argue that the Germans made mistakes in developing superchargers that lead to serious problems dealing with USAAF escorts above 20,000ft and intercepting mosquitos.

The German situation was that neither Germany nor Europe had significant crude oil resources outside of limited amounts from Romania. This compelled the German industry the difficult task of not only providing the German military, population and economy with fuel but the rest of occupied Europe and Axis allies such as Italy. Coal is much harder to mine than oil is to pump out of the ground. A synthetic fuel plant needs to be much larger than a oil refinery and only 55%-60% at most of the coal comes out as fuel as opposed to 90%-95% for an oil refinery.

The increase in RON from 87 to 100 allows an increase in compression ratio of 7-8:1 to 10:1 which allows an increase in brake thermal efficiency and therefore power of 28% to 33%. This is equal to a 22% increase in power. The Merlin was able to go from 1030hp to 1260-1310hp without significant modification though this was by exploitation of another factor, the performance number of the fuel.

A quick summary:
Situation in USA. The USAAF adopted a policy of only purchasing 100 octane fuel even if it was for engines that ran well on lower octane fuel. The policy started about 1934/35 and was pushed by James Doolittle among others. This had the effect of pushing the US industry to invest in plant and new techniques for production of high octane fuels. iso-octane was generally made out of the gas iso-butylene which was obtained from cracking. The introduction of catalytic cracking seems to have greatly enhanced this.

Situation in UK. The UK experienced with US 100 octane but had long been aiming at fuels with a high rich mixture performance number. This technique of using a rich mixture had developed during the Schneider Trophy sea plane races using mixtures of methanol, tolulene benzen etc. The Fuel was eventually developed using a process called 'acid alkylation' and came on line in quantity during the BoB. As a result British fuel was 100/130 with the 130 referring to the 30% additional power possible when the engine was run rich. The US adopted the British fuel formulation.

Situation in Italy.
Situation in Japan.
Situation in Soviet Union

Situation in German. Germany began the war with a 87 octane fuel generally referred to as B4, it was dyed blue. It was rated 87 octane though British testing of German drop tanks, captured aircraft and crashed aircraft measured ratings as high as 90.5 as the war progressed. A higher grade fuel that was green dyed had an octane rating of 93/115, perhaps C2 fuel.

This fuel evolved to a rating of about 96/125 by 1942 and was probably 98/130 by the end of 1942. It is generally referred to as C3. The Germans improved it several times. Interestingly allied intelligence picked up the improved fuel but did not pick up the improvements to the BM801D2 engine which were 'increase boost' by increasing boost pressure and rich mixture injection by injecting the fuel into the supercharger to preschool and contract the air when emergency power was needed.

The production of C3 involved the addition of iso-octane (about 22%). Since Germany had no oil they manfuctured iso-butylene from iso-butanol from syngas obtained from coal. The iso-butylene was also needed for production of BUNA-S and BUNA-N synthetic rubber. This meant high octane fuel could not be produced in quantity in 1940.

A lower grade version of green dyed C2/C3 fuel about 93/115 did enter service in the dying days of the BoB on Me 109E4/N and Me 109E7/N aircraft with the early versions of the DB601N engine. Due to its low grade the engines output was barely 5% greater.

Basically during the BoB Bf 109's and Bf 110 had 1050-1100 hp whereas spitfires and hurricanes had 1260-1310. Its a big difference.

Had the Germans had quantities of American grade 100 octane they might have obtained 20% more power. It's almost certain they would have just increased the compression ratio and obtained 10% or more power at all altitudes.

The DB601N reached about 1270 metric horse power when run at 2600 rpm and probably could have gotten to 1400hp but was replaced with the enlarged DB605A instead, this engine ran on 87 octane.

The British had made advances in the fluid dynamics of their supercharger impellors and then added two stages with intercooling. High octane 100/130 fuel allowed exploitation of this.

The DB engine was not so dependant on a high performance supercharger but relied on increased swept volume made possible by not having bolts to tie down the head but using the cylinder liner instead as a giant hollow bolt.

Nevertheless the Merlin had better altitude performance and the DB605, being a new engine, had troublesome reliability for a few years which forced a reduction in boost pressure from 1.42 ata to 1.3 till late 1943 when improved spark plugs, stronger pistons and better lubrications solved the problem. It's likely the spark plugs were the Important part of the solution and that 100 octane would have avoided the need for even this.

Thus the US and UK had better fuel and better engines due to better superchargers and Turbo superchargers. In the American case turbo-superchargers.

The Germans did have high altitude superchargers under development. These engines were actually much higher performance than the Merlin or turbo charged american engines and capable of opperation 45,000 to 55,000ft but they were to radical a modification and could not be fitted to the Me 109 or Fw 190. The Germans had an extreme high altitude program called the Hubertus program that looked at all aspects such as medicin. The high altitude test chambers developed for were usefull for jet engine development.

For instance the DB627/DB628 had a two stage supercharger with impellor around the nose and a second stage on the side. Too big and ambitious for a Me 109, intended for BV.155.
The BMW801R radial had a two stage 4 speed supercharger with intercooler. It was slightly longer than the DB603/Jumo 213 and was to be fitted to the Ta 152C. Bombing destoyed the tooling and production was abandoned.
The BMW 801TJ and 801TQ was turbo charged and would have given Ju 488 operational ceilings of 48500-50000ft and Ju 388 over 46,000ft. Huge intercoolers combined with turbo chargers and the existing 2 stage superchargers gave exceptional performance. Unlike the Merlin these needed new airframes so their advances could not be exploited in a timely manner.

 

[soaringtractor]

Thinking about a number of posts in recent threads, it seems as if a critical advantage the Allies has during the crucial 1943-1944 time frame was aircraft power plants that were significantly better than those of the Axis. The inability of the Axis to develop comparable power plants was a major failing and a major factor in the outcome of the air war. Or, oversimplified:

Did the Allies just have better engines?

Your thoughts?

The Allies, especially the USA had a better atmosphere, no bombings, better higher grade fuel supply and were not under constant bombardment, so yes they were able to develop better engines !! !

 

[Milosh]

Situation in UK. Initially used US 100 octane but had long been aiming at fuels with a high rich mixture performance number. This technique of using a rich mixture had developed during the Schneider Trophy sea plane races using mixtures of methanol, tolulene benzen etc. The Fuel was eventually developed using a process called 'acid alkylation' and came on line in quantity during the BoB. As a result British fuel was 100/130 with the 130 referring to the 30% additional power possible when the engine was run rich. The US adopted the British fuel formulation.

No, the 100/130 was the PN when running rich.

 

[NevadaK]

The Allies, especially the USA had a better atmosphere, no bombings, better higher grade fuel supply and were not under constant bombardment, so yes they were able to develop better engines !! !

I wonder how much this really affected the engines that were available in 1942/43. The majority of power plants that became available then had all been in development for some time, well before the war would have had an impact on Axis factories and development centers. I do think material availability and resources like fuel quality were significant factors, but when power plants like the R2800 were becoming available, it seems that Axis engine manufacturers just couldn't get similar power plants developed.

 

[Shortround6]

You do have to be careful when reading some of the old accounts/memo's.

If you see the phrase "from the Americas" for example it can very well mean from the British owned/controlled refinery/s in Trinidad that were processing oil from the region.
It may have nothing to do with oil or oil products from the United States of America.

the 100/130 fuel specification came into being after the BoB. BoB fuel was around 100/115-120 depending on batch. The performance number scale itself was developed after the BoB.

 

[Shortround6]

I do think material availability and resources like fuel quality were significant factors, but when power plants like the R2800 were becoming available, it seems that Axis engine manufacturers just couldn't get similar power plants developed.

In part because of the fuel. The Allied engines could use more boost (cram more fuel/air into a given size engine at a given rpm) than the Axis engines could which left the axis with either trying to make larger displacement engines or run them at higher rpm, or a combination of both. However large displacement has a harder time with high rpm and both choices can mean heavier engines which means a poorer power to weight ratio.
You can "cheat" and accept a shorter engine life to help keep the weight down.

 

[NevadaK]

Thank you Koopernic and Shortround6 for the great insight on the role aviation fuel played in the air war. To be honest, I really didn't understand that aspect of war material production.

Its a good day when you learn something new.

Kk

 

[Tkdog]

In addition to the discussion of the impact of bombing mentioned above is the morale factor. The Allies were not using slave labor nor were they subjecting their citizens to the impact of a totalitarian regime.

In addition the nazi tendency to flail around looking for a super weapon fortunately held them back as well. Lots of "amazing prototypes" but no organizational acumen to be able to develop them. Being led by immoral impulsive idiots isn't a good national strategy.

 

[Jugman]

Nitpick: Aviation gasoline is measured in MON (Motor Octane Number) not RON (Research Octane Number). Technically it should be in AON (Aviation Octane Number) which is similar MON, but nobody does.

 

[Koopernic]

I wonder how much this really affected the engines that were available in 1942/43. The majority of power plants that became available then had all been in development for some time, well before the war would have had an impact on Axis factories and development centers. I do think material availability and resources like fuel quality were significant factors, but when power plants like the R2800 were becoming available, it seems that Axis engine manufacturers just couldn't get similar power plants developed.

I agree with your assessment with some caveats. The BMW 801 (2550cubic inches) had the same swept volume as the Curtiss Wright R-2600 but the 801 was a better engine because it had a much lower frontal area and in addition the gear driven fan allowed a tightly fitted cowling. The Pratt & Whitney R-2800 however also had a much lower frontal area than the R-2600 plus 8% more swept volume and better cooling and aspiration. If things had of stayed with single stage two speed superchargers for both the BMW 801 and PW R-2800 (as used on the B-26) I dont think you could argue that the R-2800 was a much better engine, Maybe slightly better (probably a little lighter, a little more drag and ,little more power) but the difference is small. However the US fighters that entered combat service in 1943 (P-47, Corsair and Hellcat) all had either turbo-superchargers or two stage, intercooled superchargers with independent drives and this is where the USAAF gained a huge jump on the Luftwaffe in performance above 20,000ft.

So how long did it take for the Luftwaffe to catch up? Almost 2 years. History shows that their first two stage intercooled engines entered service only in 1945 (Jumo 213E on the Ta 152H and Jumo 213F on Fw 190D12 and DB601LA on Ta 152C). The Turbocharged BMW 801TJ entered service also in the dying days of 1944 with some Ju 88S and in 1945 with Ju 388L.

It is not quite as clear cut as that. The DB605 and DB603 were not as reliant on supercharging for basic power because of their high compression ratios and high swept volume design. In 1944 the Germans made significant hydrodynamic improvements to their single stage two speed supercharger designs that partially closed the gap in altitude performance with allied engines eg DB605ASM(enlarged and improved impellor) and BMW 801TS (improved impellor, improved head design). The final version of the BMW801F was likely to have been producing 2600hp. The improved fuels, increased boost and rich mixture injection meant a 1943 BMW 801 had 1900hp not 1700hp.

The BMW801R with two stage supercharging, intercooling, 4 speeds (as two separate drives) was intended for the Ta 152C but bombing destroyed the tooling. There is not doubt had the German industry not been under such extreme pressure they might have rolled out these engines much earlier. The allied oil bombing campaign so reduced the production of C3 fuel that engines had to be delayed to accomodate the new fuel. The Ta 152C with DB603EM would have been in service in 1944 for instance.

The bigger problem on the Me 109G was the poor airframe tolerances and tooling problems. Had the Me 109G6 that met the P-51B/C in combat in 1944 had a retractable tail wheel, no gun bulges over the cowling and fully enclosed main wheel covers it would have been 5% faster (419mph instead of 399 mph). These were all features the Me 109G0 had (and lost due to weight growth) but and all features the P-51B/C had. When the new DB605ASM engine came into serivice in May 1944 the P-51B/C and Me 109G6 should both have been roughtly 440 mph aircraft. It was October 1944 before the Me 109K4 fixed these minor airframe issues.

 

[fastmongrel]

Spark plugs had a big effect on engine power. The UK had probably the best most advanced spark plugs early on the Germans never catching up.

 

[Milosh]

The bigger problem on the Me 109G was the poor airframe tolerances and tooling problems. Had the Me 109G6 that met the P-51B/C in combat in 1944 had a retractable tail wheel, no gun bulges over the cowling

The gun bulges never disappeared. They just became more aerodynamic. Some G-6s did get the aerodynamic bulges.

 

[swampyankee]

I'm not going to argue the relative merits of engines from different countries (although I do think the R-2800 was easily the best engine produced during WW2, with the Merlin a close second), but I will suggest that the US, followed by the UK had the best installations.

Of course, the important attributes of an aircraft engine are installed weight (including fuel for typical missions), installed drag (which was usually not significantly different for liquid-cooled, vs air-cooled engines).

 

[Shortround6]

installed drag (which was usually not significantly different for liquid-cooled, vs air-cooled engines).

This changed before/during the war.
The P-40 had significantly less drag than the P-36.
Both types got better. The air cooled engines got much closer.

 

[Milosh]

It would be nice if Koopernic would give references/links for the statements he makes.

 

[Koopernic]

Spark plugs had a big effect on engine power. The UK had probably the best most advanced spark plugs early on the Germans never catching up.

Ive heard that said but Im not sure how true it is since German advances late in the war are often over looked. I believe it comes from a book called "the vital spark"

The original spark plug on the DB605A was the Bosch DW250ET 7 and this
sometimes caused pre-ignition at 1.42ata MAP for the DB605A meaning
the Me 109G frequently had to be restricted to 1.3 ata
(atmospheres or Barr of pressure) as fuel quality was also a problem.

New spark-plugs were needed to the end of the war for each increase in
manifold pressure.
1.30ata - Bosch DW250ET 7
1.42ata - Bosch DW250ET 7/1.
1.80ata - Bosch DW250ET 7/1A and 10/1.
1.98ata - Beru F280 E43. (Driving the DB605DCM and ASCM to 2000hp)

The gun bulges never disappeared. They just became more aerodynamic. Some G-6s did get the aerodynamic bulges.

Replacing the MG81 rifle calibre guns with MG131 13.2mm reduced Me 109GG speed by 9km/h at sea level at 1.3ata boost (about 506kmh). Streamlining them would have lowered this speed reduction to only 3kmh. This stream lining was never implemented except on the variants with the enlarged superchargers that had a larger cowling anyway. The impact of 9kmh would have been much higher at higher boost levels and speeds.

Loss of the partially retractable tail wheel was at least 4kmh and loss from not having fully covered main wheel covers is 14kmh. This adds up to about 24 kmh ie 4.8%. Quite a lot.

Its odd that it seems to have been possible to design the Me 109K6 with rather large MK108 canons in the wings just inboard of the slats but not to have simply retained the rifle cable MG on the engine but installed additional MG131 in the wings, where they would have fitted neatly.

 

[Deleted member 68059]

German spark plugs (during the war) were mostly pretty terrible, and were far worse than British plugs. They had appauling problems with gas leakage
between the electrode and the insulator, together with poor longevity. This should not be confused with them not being clever enough, like most
German problems in the war usually the engineers knew perfectly well how to solve them, they just couldnt.

Remove nickel, copper, platinum & iridium from Allied plug makers warehouses and they would have done no better.