Focke-Wulf Fw 190A poor high-altitude performance
 

The poor performance of the Fw 190A above 20,000 feet is well-known. As best I could ascertain, the reason for this limitation was ineffective superchargers for the Fw 190's BMW radial engine. The Republic P-47 Thunderbolt had excellent high-altitude performance with its radial engine, which was attributed to a large degree to its supercharger. The Germans seem to have effective superchargers for their inline Daimler-Benz and Junkers Jumo engines, so I am curious why an effective supercharger was not able to be developed for the BMW radial engine. (Searching on Google was fruitless for me.) Am I missing the real reason(s) for the poor performance of the Fw 190A at altitude?

Thanks,
Kenneth

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

The P-47 was the happy recipient of a lot of research and experiments by the USAAF with turbo-superchargers (exhaust driven) and was, therefore, ready for high-altitude combat.

The Germans, on the other hand, never anticipated the WWII high altitude combat that resulted from the USAAF’s high altitude bombing campaign. Recall, that the DB 601 engine was developed in the late 19030s when medium altitude combat was the expected norm. The DB engines were not that great over 20k feet, hence the eventual addition of GM-1 to the DB 601 and 605 for high altitude performance and eventually, the make-shift AS types. This was also true of the RR Merlin which did not have effective high-altitude performance until the Merlin 61(?) in the Spitfire IX. Superchargers for in-line liquid cooled engines were much simpler to develop than for radial engines, hence all the work by the US on the turbo superchargers—it was tedious work. The Germans never made that much effort for radials until the Fw 190 experiments which resulted in nothing for the BMW radials. It was simpler, easier and quicker to do the D-9, pending the Ta 152.

Bottom line: the need was not anticipated and money for experiments was always a big issue for the pre-war Luftwaffe. Goering and Hitler wanted a strong air force, now, not a few years down the road.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

IIRC US Navy/USMC radial engine fighters (F4F, F6F, F4U) had similar performance drop offs to the 190A at high altitude.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

It is not a function of radial engines. It is largely a matter of superchargers and the maximum compression ratio. All single-stage supercharger engines begin running out of power around 20000ft. The radial BMW 801 was no different to the inline Sabre, hence the problems with accepting the Typhoon into a Fighter Command that increasingly emphasised high-altitude performance. For performance at higher altitudes the US went to turbochargers, the UK to two-stage superchargers, the Germans to exotic fuel additives. This was partly a matter of available materials, turbochargers requiring exotic metals the Germans lacked; and available expertise, RR being particularly good with superchargers.

For additional altitude, aerodynamic advantage can be gained from larger wings, either by increased span or greater aspect ratio (span divided by mean chord, or span squared over wing area). The Fw 190 has a low aspect ratio wing, so loses out here. Consider the Ta 152H.....

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Focke Wulf and BMW planned to add the turbo charger but these developements never went beyond experimental stage. IIRC the only plane which reached more or less experimental service with the BMW turbo charged engine was the Ju 388.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

The Germans were going towards two stage mechanical superchargers as well. There were numerous such projects, the development was just slow. The Jumo 213E was the only such engine to reach the service in some degree.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

And Allison did a two-stage supercharger, which saw production in the P-63, and postwar in the F-82.

It is worth pointing out that phrases such as "poor high-altitude performance" is only meaningful comparated to those aircraft with turbochargers or two-stage superchargers. The Fw 190 was superior to the Yaks and Lavochkins it faced on the Eastern front, although curiously it does not seem to have gained the same reputation in the East that it had in the West. A supercharger design is set to a given pressure, and hence a given fixed throttle height. Witness the "cropped" LF series of Merlins, which gave the Spitfire LF Mk.V possibly the highest low-level climb rate of any WW2 service fighter, but reached its maximum power at only 5000ft.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Kenneth,

I suggest you take a look at:

Focke-Wulf Fw 190A
Die Ersten Baureihen
Dietmar Hermann, Ulrich Leverenz & Eberhard Weber
Aviatic Verlag, 2002
3-925505-72-5
Laminated, 222p

Focke-Wulf Fw 190 "Long Nose"
An illustrated history of the Fw 190 D series
Dietmar Hermann
Schiffer Publishing, 2003
0-7643-1876-4
Hard Cover, 206p

Focke-Wulf Höhenjäger
Vom ersten Höhenjäger zur Fw 190 H
Jet & Prop Typen-Chronik 6 Spezial
Dietmar Hermann
VDM, 2002
3-925480-XX-X
Softcover, 132p

The first title is also available in English as published by Schiffer (I usually by original German if I have a choice).

These three books cover your questions regarding the Fw 190 and high altitude performance.

Issues as design philosophy, impact of the RLM, engine and supercharger research are all covered. The Fw 190 was seen by Tank as a flexible frame for a work horse.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Thanks for those book recommendations Ruy, I've been looking for quality books on the Fw190 for ages. :)

Btw, what does IIRC mean?

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

"If I Recall Correctly"

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Jim,

Do you have Peter Rodeike's Focke Wulf book?
If not, that one certainly deserves a place with these three works.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

There is also:

Kurt Tank: Focke-Wulf's Designer and Test Pilot
Wolfgang Wagner
ISBN 0-7643-0644-8

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Ruy-

Thanks for the book recommendations. I have Jerry Crandall's (Focke Wulf Fw 190 Dora Vol 1" on order and I am hoping it will cover the altitude issues that led from the Fw 190A to the Fw 190D. I'll see if I can find Dietmar Hermann's Fw 190 books.

Kenneth

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Thanks to everyone who posted on this thread. I gained more insights into why the Fw 190A had poor performance above 20000 feet, why it was not initially considered a problem, and more books to read.

Kenneth

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Guys:

Say can anyone define what an 'exotic' metal is? Also, does the power drop off to an engine due to lack of oxygen at high altitudes or to another reason?
Thanks ahead of time;

nm

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

I'll take a shot at answering. However, if I am wrong, please, more knowledgeable members do not hesitate to correct me!

1. Exotic metals - I think what Graham Boak was referring to were metals for higher-strength alloys, which Germany sorely lacked. These are needed for high-compression engines and I think this is the reason the Bf 109 and Fw 190 relied on chemical boosters such as GM-1 and MW-50 to increase power output. I suspect these were needed for superchargers as well and thus a reason the Fw 190A did not have an effective supercharger for its BMW radial engine.

2. Oxygen - yes, the lower oxygen at higher altitudes results in lower piston engine (both radial and inline liquid-cooled) power output. This is the reason superchargers are needed for high-altitude performance; they compress the air and thus increase oxygen concentration, then the compressed air is injected into engines to ignite with fuel.

Kenneth

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Kenneth, one needs exotic metals in turbo superchargers because of the hot exhaust gases used to spin the turbine wheel. Mechanical superchargers sucked in 'cold' air. Even in the 2 stage superchargers, the air from the first stage was not that 'hot'.

The Jumo 004A used exotic metals but the Jumo 004B did not, which reduced its TBO from 100 hrs, in the 004A, to 25hrs.

MW-50 was used below the engine's FTH and GM-1 was used above the engine's FTH.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Regarding 1, the German engines were of typically high compression ratio engines (starting at 6.7:1 and increasing 8.5:1 during the war) against the typical Merlin/Allison 6:1.

Regarding 2, lack of oxygene that can no longer be provided by the supercharger as it runs out of air (get it?) above its rated altitude is one of the reasons for the drop of power with altitude. The other cause is the supercharger itself - unless we talk of single stage superchargers, the second high altitude speed/stage of the supercharger always takes away more power from the propeller to drive the supercharger harder.

There is some inherent handycap with the radial engines themselves, as typically radial engined fighter require more power to develop the same performance as inline ones, it also means the engine needs to develop more power - and thus it also needs more air to burn more fuel, and thus having greater need for a high capacity supercharger than an inline engine.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

You should have mentioned Kurfurst that German engines used less boost. The highest boost, except for the penny pocket of 109ks using 1.98ata, was 1.80 ata. 1.80ata being a little less than 11lb.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

The power drop is due to the drop in pressure above full throttle height, not to a shortage of oxygen in particular.

Even a single stage supercharger requires power to drive it.

A turbocharger takes energy from the exhaust that on mechanically supercharged engines can be used to provide thrust from angled and ducted exhausts, though this is less than that needed to drive the supercharger. However, a turbocharged radial would not be able to benefit from the engine/airframe integration that was so cleverly devised on the Fw 190 - which is the example under discussion. The extra power would therefore be counteracted by greater configuration drag - the precise tradeoff depending upon the actual design.

The P-47 found the turbocharger's stainless steel ducting valuable as pilot armour for the ground attack role, but I think that can be described as a fortunate result rather than a planned feature. However, all advantages count.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Graham-

I thought that basically piston engines provided power by oxygen igniting fuel and creating little explosions within the cylinder walls, the force of which pushed the pistons up and down. By this reasoning, I surmised that the lower power at altitude was due to the relatively lower oxygen concentration, which would lead to mismatched stoichoimetry in the combustion of fuel and oxygen and therefore lower power. By the same token, I thought superchargers compressed air, which therefore increased oxygen content and therefore restored power.

You mentioned the power drop was due to drop in pressure above full throttle height. Pressure of what? Could you kindly elaborate some more on this? I readily admit my ignorance here, I'm not following the reasoning here.

Thanks!
Kenneth

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Increasing the compression ratio increases the power output of the engine slightly at all altitudes, all other factors being constant; increasing the boost will increase the power output more rapidly, but only below the rated altitude of the engine (=capacity of the supercharger).

Therefore, as far as high altitude performance go, increasing the compression ratio yields power output advantages, while increasing boost doesn't, unless the supercharger is improved, too.

German engine development advanced parallel in many areas, by increasing displacement, permissable rpm and compression ratio and supercharging; Allied developments revolved around supercharging.

A comparison of the output of two-staged Allied inline engines like the Merlin and single staged German inlines with increased superchargers show that these were really two roads to similiar outputs at altitude, although I consider German powerplants more efficient overall in terms of the developments resulting in lesser bulk and more favourable fuel consumption.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Kurfurst: Allied engines also went the route of increased displacement, for example Merlin to Griffon, Taurus to Hercules to Centaurus, Twin Wasp to Double Wasp. This in itself was not specifically a German approach: indeed the step from DB601 to DB605 was not linked with any major increase in displacement. As for which detail design route is the most efficient, the RR engines managed similar output to the DB designs despite considerably smaller internal volumes: that seems one measure of efficiency to me.

Kenneth: To some exctent this is just different ways of saying the same thing. Air pressure reduces with altitude. An engine has a maximum pressure it is designed to withstand (which can vary with time, hence the time limits on different power ratings). This can be above that obtained naturally at low altitudes. The purpose of the supercharger is to provide the engine with that maximum air pressure, by forcing more in . Each supercharger is designed to provide a given maximum boost, allowing excess to bleed away at sea level, and hence as the aircraft rises in the air the supercharger is providing a greater proportion of the pressure, until it reaches its maximum - the full throttle height (or rated altitude). Above this height the engines' maximum boost cannot be maintained, and the power output falls.

So at altitudes above the full throttle height the engine is short of the ideal amount of air - you may see this as a shortage of oxygen if you wish (as I'm sure the combustion specialists would) but it is normally expressed as a pressure shortfall. Using exotic additives at altitude is a way of adding more oxygen to the mix, but this saw little use outside Germany, which had specific problems with fuel supplies.

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

I don't think it does..the best discussion of the technical issues is Dietmar's 'Focke Wulf Höhenjäger' as recommended previously (cheap & concise Jet & Prop special issue - in German)

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Kenneth:

I'll firstly state that the technical content of this discussion is well beyond what I can contribute to.

That said, Heinz Nowarra's Focke-Wulf Fw 190 & Ta 152 (ISBN 0-85429-695-6) includes a dedicated chapter The High Altitude Fighter - a Failure. The theme of this chapter is the failed efforts to develop a satisfactory turbo-supercharged engine for the Fw 190 airframe, consistent with earlier discussions in the thread

Examples: The shortage of raw materials in Germany meant it was not possible to produce a suitable heat-resistant alloy.....The problems experienced by the Germans with turbo-superchargers were not overcome before the war had ended

The Fw 190C-1 high altitude fighter version would probably have been an excellent aircraft.....but...it failed because it proved impossible to manufacture a reliable turbo-supercharger system. THe HMZ turbo-supercharger 9-2281 produced by Hirth kept burning out.

FYI

Don W

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

One best use of high-altitude fighter is the combat of the 4-mots nd their dog-guards, for the cover the Bf109 was used, but against the bomber they used Fw190 nd the heavy-ones, seems that they hv given satisfaction even at the altitudes where the fighting of the Mighty Eighth take place...

Remi

Re: Focke-Wulf Fw 190A poor high-altitude performance
 

Graham and John summed up the engine design philosophies of the three western combatants very well. I'd like to add that the two successful USAAF fighters with turbosuperchargers (P-38 and P-47) were designed around them, and were huge as fighters go. The Germans not only lacked the high-strength, high-temperature steels necessary for the most efficient superchargers, they were limited by metals shortages of all kinds to relatively small, light-weight aircraft. Turbos just "didn't compute" for the Germans. Also keep in mind that German in-line engines were less efficient on a power/weight basis than Alisons or Merlins -- they were heavier because their steel had to be thicker. Their two-stage mechanical superchargers were never suitable for mass production (IIRC) and chemical additives were a clumsy workaround.

Don