Fw-190 Prototype engine changes

[davebender]

Spring 1937.
RLM request to develop a new fighter powered by the DB601 engine.

Summer 1938.
RLM change their request. The Fw-190 prototype will use the new BMW139 radial engine.

Apr 1939.
First BMW801 engine prototype.

1 June 1939.
Fw-190 prototype flying with BMW139 engine.

April 1940.
Fw-190 prototype first flight with BMW801 engine.
In addition to delaying development by 10 months, this engine change added 635kg to the aircraft weight.

March 1941.
Fw-190 A-1 limited production for operational testing. Still has teething problems caused by the switch to an air cooled radial engine.

Why did the Fw-190 prototype have so many engine changes? From what I can see it delayed development of this excellent aircraft by at least 2 years.

What I think RLM should have done.
Spring 1937.
RLM requests development of a new fighter aircraft powered by the DB601 engine. At the same time RLM orders construction of an additional factory to produce DB601 engines.

Spring 1939.
Fw-190 A-1 limited production aircraft flying. Powered by DB601 engines from the new DB601 engine factory.

Fall 1939.
Fw-190 enters mass production powered by the DB601 engine. Less engine power is at least partially compensated by the aircraft being lighter and better streamlined.

 

[KrazyKraut]

AFAIK the Fw 190 was never designed for the DB601, the requirements were changed before any prototype was ever designed let alone constructed. The overheating issues were inherent to the BMW engine and probably worsened by the initial confidence in the spinner and fan layout. I don't think they had much to do with the original specification asking for an inline fighter.

The BMW 801 had a better development potential, thus that switch is also justified.

Your proposal would most likely have been cancelled. There were already two fighters designed around the DB601. A third one would not make much sense, especially since it would've been way behind the Bf 109 in terms of learning curve, production facilities etc...

 

[Colin1]

The following is the introductory chapter on a book concerning the Fw190 and sums up Dipl Ing Kurt Tank's philosophy in designing his fighter.

It was during the spring of 1938 that the RLM in Berlin asked the Focke-Wulf company to submit design proposals for a new fighter to supplement the Bf109 which had just entered service.
My project office submitted several alternatives, all based around the idea of a fighter somewhat more rugged than the Bf109. One of these proposals was accepted and we received an order to proceed with the construction of prototypes of the Fw190.
The Bf109 and the British Spitfire, the two fastest fighters in the world at the time we began work on the Fw190, could both be summed up as a very large engine on the front of the smallest possible airframe; in each case armament had been added almost as an afterthought. These designs, both of which admittedly proved successful, could be likened to racehorses: given the right amount of pampering and an easy course, they could outrun almost anything but the moment the going got tough they were liable to falter.

During WWI I had served in the cavalry and I had seen the harsh conditions under which military equipment has to work in wartime. I felt sure that a quite different breed of fighter would also have a place in any future conflict: one that could operate from ill-prepared frontline airfields; one that could be flown and maintained by men who had received only a short training and one that could absorb a reasonable amount of battle damage and still get back.

This was the background thinking behind the Fw190; it was not to be a racehorse but a Dienstpferd, a cavalry horse.

Obviously if it was fitted with an engine developing the same power, a racehorse fighter with a lighter structure would always be able to outrun and outclimb the cavalry horse fighter, yet we could not allow this difference to become too great. The design problem centred around building a stronger airframe and one able to carry heavier weapons without sacrificing too much in the way of performance.

We chose an air-cooled radial for the new fighter for two reasons. Firstly, because such engines were far more rugged and could survive more punishment than the liquid-cooled types and secondly because BMW were bench-running prototypes of a new engine, the 1,550hp BMW 139 which developed more power than the current liquid-cooled types in use.
Some people suggested that I had to fight some sort of battle with the RLM to get them to accept the idea of a radial-engined fighter. That might make a good story but it is not history. In fact, there was a large body of official opinion in favour of such a fighter for the Luftwaffe.

Looking further afield we saw that other nations, in particular the USA, were pushing ahead with the design and development of high-powered radial engines for fighters and we in Germany had no wish to lag behind in this field.

So the air-cooled radial engine was fitted to the Fw190; I never had cause to regret the decision. When the fighter went into action the resiliance of this type of powerplant was proved again and again. There were several occasions when these fighters returned home and made normal landings having had whole cylinders shot away.

I would surmise from this that Tank and his design team didn't consider the DB 601 because they couldn't or wouldn't consider the DB 601; it was an anathema to their ideals of what constituted a good fighter.

Sources
Focke-wulf 190 at War
Alfred Price
Ian Allan
ISBN: 0 7110 0768 3
Pages 10 - 11

 

[BombTaxi]

Was it realised at the time that radials would still perform with whole cylinders shot away? I have seen that reason as an argument for radial use, particularly in American aircraft, but always thought it was a post facto justification of an unintentionally good design choice.

 

[Catch22]

I personally don't know why you'd have that opinion dave, as the Fw 190 proved to be one of the best and more versatile aircraft of the war. Why was there a need to change it? Yes, its high altitude performance would have been better, but you'd lose a lot of the ruggedness of the design.

 

[Colin1]

Was it realised at the time that radials would still perform with whole cylinders shot away? I have seen that reason as an argument for radial use, particularly in American aircraft, but always thought it was a post facto justification of an unintentionally good design choice.

I've typed it verbatim
it doesn't suggest to me that the radial was selected because it 'would still perform with whole cylinders shot away' per se, it simply says that 'such engines were far more rugged and could survive more punishment than the liquid-cooled types'; I'm pretty certain the relative merits of radial vs inline would have been largely deduced by that time, he more or less just endorses the choice of the radial with the 'cylinder shot away' example.
That's how I read it

 

[BombTaxi]

Thought so. Cheers 8)

 

[delcyros]

The Db-601 had plenty of unused developmental reserves. The design ended with the -E subversion, boost rating to 1.42 ata, delivering 1350 hp (1420 hp max). This was long before the advent of MW-50 ADI injection, which would in turn, increase the boost rating to about 1.7 ata.

With C3 fuel MW-50, the Db-601EM arguably could deliver in between 1700 and 1750 hp @ 1.7ata, while weighting only 700 kg (including MW-50 equipment). About 90-100 Kg lighter than the 50 hp more powerful Db-605AM with 1.8 ata (1800 hp).

Just as an idea, my favourite Bf-109 mod would be based on this engine. Basicallly a Bf-109F4 airframe, but with Db-601 EM instead of Db-601E. Armament changed to one through the shaft firing 20mm Mg-FF/M (100 rpg, drum or belt fed) and two wing mounted 20mm MG-FF/M (80 rpg each, belt fed). No cowling guns.

weights removed:
2 x MG 17
(= 20.4 Kg)
1000 rounds 7.9mm ammo
(= 30 Kg)
1 x MG 151/20
(=42,4 Kg)
200 rounds 20mm ammo
(= 50 Kg)
= 142.8 Kg

new armament:
3 x 20mm MG-FF/M:
(=78,9 Kg)
260 rounds 20mm ammo
(=65 Kg)
=143,9 Kg

empty weight: 2092 Kg
equipment: 282,1 Kg (including new arms)
400 l fuel: 308 Kg
36 l lubes: 33 Kg
pilot: 100 Kg
ammo: 65 Kg
MW-50: 110 Kg

max. take off weight: 2.990 Kg (with MW-50, compare Bf-109 G6 with Db-605 AM, 1 x 20mm 2 x 13mm: 3.148 Kg with MW-50)

So my Bf-109F/mod is 350 lbs lighter than a Bf-109G6 in clean configuration with MW-50 and has about 50 to 100 hp less power. It is also a bit cleaner aerodynamically, and will be a bit more responsive, better turner and climber:
Wingloads:
Bf-109F (with Db-601EM) max.: 186 Kg/m^2
Bf-109G (with Db-605AM) max.: 196 Kg/m^2
Powerloads:
Bf-109F (with ~1710 hp Db-601EM):1.749 Kg/hp
Bf-109G (with ~1800 hp Db-605AM):1.749 Kg/hp
equal acceleration for both planes.
Top speed is likely superior for the Bf-109F/mod. with an estimated 680 Km/h (422 mp/h) at about 4800m altitude as opposed to ~650 Km/h for the G6/AM at 5000 m altitude.
It would have been a deadly fighter in the intermediate band of altitudes (3000m to 6000m) with the turning abilities of the -109F and the climb / acceleration of the G-model.
A high altitude variant could be built with GM-1 injection instead of MW-50.

 

[BombTaxi]

Del,

Sorry if I'm asking a stupid question (don't know much about engines! ), but what is the definition or meaning of the term 'ata'? is it similar to the English 'lbs of boost'?

 

[delcyros]

Yes, Bombtaxi. Ata was used by the germans, lbs/inch^2 by the british. The US soviets and japanese used other boost pressure definitions.
1 ata = 98.067 kPa
1 lb(f)/sqin = 6.895 kPa

I believe but am not sure that british practice of determining boost pressures was above normal pressure while others, notably the US used absolute (zero based) figures.

 

[BombTaxi]

Cheers del 8)

 

[davebender]

Focke-Wulf Fw 190 - Wikipedia, the free encyclopedia

In autumn 1937, the Reichsluftfahrtministerium (RLM) or Reich Air Ministry asked various designers for a new fighter to fight alongside the Messerschmitt Bf 109, Germany's front line fighter. Although the Bf 109 was at that point an extremely competitive fighter, the RLM was worried that future foreign designs might outclass it and wanted to have new aircraft under development to meet these possible challenges.

Kurt Tank responded with a number of designs, most incorporating liquid-cooled inline engines. However, it was not until a design was presented using the air-cooled, 14-cylinder BMW 139 radial engine that the RLM's interest was aroused.

 

[BombTaxi]

It would imply that the inline-engined designs were not designs using the airframe that became the 190. That's how I read it anyway.

 

[Colin1]

Focke-Wulf Fw 190 - Wikipedia, the free encyclopedia

Not necessarily
the more accurate question would be CAN Wikipedia be wrong - yes.

Wikipedia's entry for the definition of Wikipedia:
No article in Wikipedia undergoes formal peer-review process and changes to articles are made available immediately. No article is owned by its creator or any other editor, or is vetted by any recognized authority. Except for a few vandalism-prone pages that can be edited only by established users, or in extreme cases only by administrators, every article may be edited anonymously or with a user account, while only registered users may create a new article

Anyone can write a Wikipedia article, just as anyone can post an opinion on a forum. What I typed was taken verbatim from an article submitted by Dipl Ing Kurt Tank himself, I was careful in its reproduction and quoted my source.

The article doesn't say he didn't look at inline engine options, it stipulates that he went with the radial pursuant to his vision of the fighter aircraft as a cavalry horse, rather than a race horse. It goes on to say he had no regrets about his decision. I got the impression from the article that once on the radial bandwagon, he didn't look back.

I'm not saying 'believe me, don't believe Wikipedia' because however carefully constructed, it's still only my opinion whatever source I derive it from but I know which I believe - and it's not just because I submitted it.

 

[delcyros]

Kurt Tank and Dr. Blaser indeed submitted two official proposals to the RLM request. One of them the radial driven Fw-190 ancestor, the other a Db-601 driven fighter. The decision against the inline engined variant was not as easy as many think, mostly owing to aerodynamic quetsions (larger frontal area) and poor visibility during take off and taxiing. Udet finally advanced the radial driven variant, which I feel was reasonale, considering that the Db-601 production was already overloaded.

This information is not basedon Wikipedia but H.J.Nowarras narrative of the Fw-190 developmental history in his: Die Deutsche Luftrüstung 1933-1945, vol. 2 (Koblenz 1993), p. 72.

However, the RLM in 1937 better had approved the Fw-187 design with Db-601 instead.

 

[Colin1]

This information is not basedon Wikipedia but H.J.Nowarras narrative of the Fw-190 developmental history in his: Die Deutsche Luftrüstung 1933-1945, vol. 2 (Koblenz 1993), p. 72.

However, the RLM in 1937 better had approved the Fw-187 design with Db-601 instead.

My statement stands
The article doesn't say he didn't look at inline engine options, it stipulates that he went with the radial pursuant to his vision of the fighter aircraft as a cavalry horse, rather than a race horse.

Heinz Nowarra himself says
in the spring of 1938 the Technisches Amt decided to invite tenders for a second fighter aircraft. It was assumed that the prototype would require 12 to 18 months development. Lead time to production was usually in the order of two years at that time so the new fighter would not be ready for service use until 1941 at the earliest and so would certainly need a more powerful engine than the Daimler-Benz DB 600 or 601 currently being used. The only more powerful engine which was at all suitable was the 14-cylinder twin-row BMW 139 which would produce 1,500 PS instead of the 1100 PS of the DB 601.

so I'm guessing there weren't that many eligible engines around to challenge the BMW unit - inline or radial.

Sources
Focke-wulf Fw190 Ta152
Heinz J Nowarra
Haynes
ISBN: 0 85429 695 6
Page 7

 

[delcyros]

The problem with the BMW-139 is that it weights up 800 Kg dry (without equipment). Note that the BMW-801C (=1.560 hp) weighted 1055 Kg dry! The corresponding weight of the Db-601A was 620 Kg. 180 to 455 Kg is a lot of difference for a single engined, single seat fighter, esspeccially considering that it means actually a mere factor of 2 with all structural weights added.
Add the larger drag and You may easily see that the Db-engine option would promise significantly better performance.

It´s not just a question of power. The relation of power to involved weights, spaces and drag is as important.

 

[Colin1]

...you may easily see that the Db-engine option would promise significantly better performance...

Sure we're not looking at this from a race horse perspective?
Because regardless of who's right or wrong here, that's not where Kurt Tank was looking at it from.

 

[davebender]

That's the way I look at it also. You are likely to get a significantly lighter Fw-190 that consequently has superior maneuverability and better endurance.

 

[Colin1]

That's the way I look at it also. You are likely to get a significantly lighter Fw-190 that consequently has superior maneuverability and better endurance.

I'm familiar with power:weight as a design factor
So was Kurt Tank and another Bf109/Spitfire isn't what he was after