Dornier 217 hypothetical

[wiking85]

What if this aircraft had the DB603 as a power plant, having not been cancelled in 1937, available in 1941 with about 1650hp and the reliability it achieved in late 1943, and never had dive bombing as part of its mission/design profile? Would it have had better performance without the dive requirement and available earlier without the dive testing and redesigns? What about with the DB603 being unreliable, but in production in 1940?
How soon could it have been available and what would it have replaced? I imagine it would have the performance of the Do217M in 1942 when the DB603 historically produced 1750hp, but in 1941 would have had somewhat reduced performance.
http://en.wikipedia.org/wiki/Dornier_Do_217#Specifications_.28Do_217_M-1.29

Specifications (Do 217 M-1)

General characteristics
Crew: 4
Length: 17.00 m (55 ft 9 in)
Wingspan: 19.00 m (62 ft 4 in)
Height: 4.96 m (16 ft 3 1⁄2 in)
Wing area: 57.00 m2 (613.54 ft2)
Empty weight: 9,100 kg (20,062 lb)
Max. takeoff weight: 16,700 kg (36,817 lb)
Powerplant: 2 × DB 603A 12-cylinder inverted-vee engine, 1,750 PS (1,726 hp, 1,287 kW) each

Performance
Maximum speed: 557 km/h at 5,700 m (347 mph at 18,700 ft)
Cruise speed: 400 km/h (248 mph)
Range: 2,145 km (1,332 mi)
Service ceiling: 7,370 m (24,180 ft (with max bombload))
Rate of climb: 210 m/min (688 ft/min)

Armament
4 × 7.92 mm (.312 in) MG 81 machine guns in nose and lateral positions
2 × 13 mm (.51 in) MG 131 machine guns in dorsal and ventral positions
Max Load 4,000 kilograms (8,800 lb) internally externally.
Max Internal Load 2,517 kilograms (5,550 lb).[129]

 

[Denniss]

A DB 603 that early would be impossible as DB had more than enough problems with their DB 601, both in development and production. Invest more money and manpower into DB 601 and German a/c manufacturers may have been flooded with DB 601 engines and DB 605/603 may have been available a little bit earlier.

But yes, the dumb dive bombing requirement for both Do 217 and He 177 increased cost and development time a lot while negatively affecting a/c performance.

 

[davebender]

Late 1930s Jumo 211 had three engine factories (Dessau, Magdeburg, Kothen). Two more relatively large Jumo engine plants opened in 1942 at Leipzig and Stettin.

DB601 had a single modest size factory at Genshagen prior to 1940.

Give Daimler-Benz engine program resources similiar to Jumo engine program and I'll hazard a guess Daimler-Benz engine development would be considerably faster then historical.

 

[wiking85]

Late 1930s Jumo 211 had three engine factories (Dessau, Magdeburg, Kothen). Two more relatively large Jumo engine plants opened in 1942 at Leipzig and Stettin.

DB601 had a single modest size factory at Genshagen prior to 1940.

Give Daimler-Benz engine program resources similiar to Jumo engine program and I'll hazard a guess Daimler-Benz engine development would be considerably faster then historical.

Any idea when the Jumo factories were built? I thought it was in the late thirties and prior Daimler and Jumo were not much different in size until the RLM decided to bult extra factories for Jumo, but not Daimler.

 

[davebender]

Junkers Engines - Jumo 211
Dessau 1086 prototypes, test engines
Magdeburg 24267 July 1937 to Aug. 1944
Kothen 20911 1938 to Feb. 1944
Leipzig 17032 1942 to Aug. 1944
Stettin 4714 only 1942
Strassburg 238 1943 to Feb. 1944

The large Stettin factory (about 400 engines per month) produced Jumo 211s only during 1942 because Germany had more Jumo 211 engines then they could use.

IMO the Stettin factory should have been producing 400 DB603 engines per month from 1941 or 1942 until the end of the war.

 

[davebender]

Let's use historical RLM standard for BMW801 engine.
BMW 801 - Wikipedia, the free encyclopedia
1,539hp.
Engine service life of 30 to 40 hours.

Our early model DB603 engine will enter mass production when it can pass a 50 hour endurance test @ 1,540hp while running on B4 fuel.

Next version of DB603 engine will enter mass production when it can pass a 100 hour endurance test @ 1,680hp while running on C3 fuel.

 

[wiking85]

I think that late 1940 for the first benchmark is not unreasonable. The engine historically was started in 1936 and cancelled in 1937; it restarted in 1940 and was able to complete the 100 hour test in late 1943. Altogether that is about 5 years of development, as very little was done in the years 1937-1940 with the engine other than adapt it to a short landspeed record in a race care that never took place.
Assuming funding isn't interrupted in 1937 and in fact increases, then the unit by mid-1940 will have five years under development; that time period would correspond with the historical 1942 version, which was in service and IIRC passed the 50 hour test.
Perhaps late 1940 is too ambitious, though that would have been over 4 years of development by then. By mid-1941 though that would have been 5 years of development, which was the historical amount of time it took to make the DB603 reach 100 hours endurance. By 1942 in this scenario it would have have 6 years of development, so would be fully reliable by then and broken in.

 

[davebender]

That would change a lot more then just Do-217 program. Focke Wulf and Messerschmitt aircraft designs would take advantage of DB603 engine. Junkers would be running scared that their Ju-88 would get Daimler-Benz engines rather then Jumo engines.

 

[wiking85]

That would change a lot more then just Do-217 program. Focke Wulf and Messerschmitt aircraft designs would take advantage of DB603 engine. Junkers would be running scared that their Ju-88 would get Daimler-Benz engines rather then Jumo engines.

Of course, but the Ju88 would need to be adapted to handle the larger engine, while the Do-217 would offer better payload and range than the Ju88/188 with a Db603. Plus initially it would mean the Db603 would be relatively scarce, so in late 1940 (October or so) it would go to testing for the Do-217, Ju-188, and Fw190C rather than operational units. As it gets more production and becomes more reliable in mid-1941 then we would see operational Do-217Ms (the E-series with the BMW 801 would enter service in March 1941 historically, maybe earlier here if the airframe is ready sooner because of the lack of the dive requirement).

The Fw190C is IMHO not likely before some time in mid-1942.

The Ju-288 could see operational status with the DB603 perhaps in 1943 when the Jumo 222 is cancelled.

Is it possible that that Db603 has greater horsepower than historical versions in 1943-44? The greater development time seems to make it more likely IMHO.
Perhaps the Do-217 here, thanks to taking both the Db603 and BMW 801 and having greater range, speed, and payload than the Ju88 might start to over take it deeper in the war?

 

[davebender]

That depends on when the engine starts to look promising.

It's my understanding DB603 prototype #1 was producing 1,500 or 1,550hp during 1937 when program funding was cancelled. Construction of a Genshagen size factory (220 engines per month) could start in 1939 with production beginning early 1941.

Stettin factory begins producing 400 engines per month during 1942 just as it did historically. Except in this scenerio they are DB603 engines rather then Jumo211. By mid 1942 Germany would be producing 600 DB603 engines per month.

 

[Shortround6]

Is it possible that that Db603 has greater horsepower than historical versions in 1943-44? The greater development time seems to make it more likely IMHO.

Not likely without some other changes. Development can only do so much. Power is limited by the rpm, the pressure in the cylinders and the size of the cylinders. The size of the cylinders is pretty much fixed or you are dealing with a new engine with new vibration patterns/problems. Cylinder bore is pretty much already at the maximum without going to triple ignition. Length of stroke is already on the high side for a WW II aircraft engine which helps limit RPM. Big cylinders are harder to cool than small ones, more volume for fuel/air per unit of area of cylinder wall/piston crown and cylinder head. This leaves pretty much increasing the pressure in the cylinders through higher boost. Pressure in the cylinders is limited by the available fuel. MW 50 can only do so much. Germans could have lowered the compression and used more boost for more power but that cuts fuel economy.

Please note that while a certain few engines did post very large increases in power over their history they usually started in the mid to late 30s with 87 octane fuel and went on to use 100/130 or above, some with major modifications. Engines that started in the very late 30s or 1940/41 showed a much smaller increase in power due to starting with 100 octane fuel to begin with. The P&W R-2800 was air cooled ( which may have helped limit it's power ) but it started at 1850hp, went to 200ohp very quickly and despite a total redesign that kept only the bore and stroke ( aircraft engine designers were very loath the change those numbers) only a couple of models went over 2500hp even by the time of the Korean war and using 115/145 fuel or 130/100 and ADI.

Please also note that the Jumo 213 was in a lot of ways a "developed" 211. But look at the amount of weight it gained while being developed.

They might have been able to get more power from the 603 but some "development paths" are going to come with costs; worse fuel consumption or higher weight ( or both?) Maybe they are worth it, maybe not.

 

[Denniss]

Junkers was state-owned while DB was a private company, quite natural that Junkers got more money especially as the big fat man wanted bombers.
An early 1940 DB 603 would most probably lack many of the advanced features developed for the DB 601N and E such as pressurized water cooling, the redesigned cylinders, etc. Power with B4 would hardly exceed 1600PS and it would require large radiators for cooling.

 

[tomo pauk]

Since the DB-603 of early 1941 would be offering notably less power than the DB-603 of late 1942, it will offer no advantage over the BMW-801A? Let alone when we account for greater weight of the 603.

 

[wiking85]

Junkers was state-owned while DB was a private company, quite natural that Junkers got more money especially as the big fat man wanted bombers.
An early 1940 DB 603 would most probably lack many of the advanced features developed for the DB 601N and E such as pressurized water cooling, the redesigned cylinders, etc. Power with B4 would hardly exceed 1600PS and it would require large radiators for cooling.

Jumo was a separate company from Junkers at some point, so I'm not sure if Jumo was owned by the state when they took over Junkers.
As to the 1940 Db603, you're right that it wouldn't have those features in the A-series, but in the 1941 it would.

Since the DB-603 of early 1941 would be offering notably less power than the DB-603 of late 1942, it will offer no advantage over the BMW-801A? Let alone when we account for greater weight of the 603.

http://en.wikipedia.org/wiki/BMW_801

Dry weight: 1,012 kg (2,226 lb)

http://en.wikipedia.org/wiki/Daimler-Benz_DB_603

Dry weight: 920 kg (2,030 lb)

It seems the 603 weighed nearly 100kg less than the BMW 801. Also the 1940 version of the DB603 would likely not be as heavy because of the lack of features mentioned by Denniss, making it even lighter. The 1941 version would be as heavy as the weight I have listed here, but it would also have the extra features AND more horsepower, offsetting the weight.
Not only that, but as a liquid cooled engine it would have better altitude performance, as the BMW 801 air cooled engine's horsepower dropped off significantly above 20,000 feet.

 

[tomo pauk]

It seems the 603 weighed nearly 100kg less than the BMW 801. Also the 1940 version of the DB603 would likely not be as heavy because of the lack of features mentioned by Denniss, making it even lighter. The 1941 version would be as heavy as the weight I have listed here, but it would also have the extra features AND more horsepower, offsetting the weight.

The weight of cooling system need to be added to the DB-603, and then we can compare. For the P-40, for example, the weight of cooling system was circa 300 lbs, maybe up to 350 lbs for the DB-603? I agree that a pre-603 would be lighter than the 603 of ~1943, so maybe a whole powerplant would be of the same weight when either pre-603 or early 1941.
Shouldn't the non-pressurrised cooling system weight more than a pressurrised?

Not only that, but as a liquid cooled engine it would have better altitude performance, as the BMW 801 air cooled engine's horsepower dropped off significantly above 20,000 feet.

Whether the engine is liquid cooled, or air cooled, has nothing to do with altitude performance. That's a prerogative of supercharger system, ability of the engine to make high RPM, and it's about the displacement. The liquid cooled engine without pressurised cooling system will suffer at altitude.

 

[wiking85]

The weight of cooling system need to be added to the DB-603, and then we can compare. For the P-40, for example, the weight of cooling system was circa 300 lbs, maybe up to 350 lbs for the DB-603? I agree that a pre-603 would be lighter than the 603 of ~1943, so maybe a whole powerplant would be of the same weight when either pre-603 or early 1941.
Shouldn't the non-pressurrised cooling system weight more than a pressurrised?

Why does the cooling system weight have to added? Why wouldn't it be included in the weight of the unit? Are you talking then about the fuel that would be part of the engine, the 'wet weight'?
What about the BMW 801's cooling system?

 

[tomo pauk]

It needs to be added to the dry weight:

Dry weight: 920 kg (2,030 lb)

quote from Wikipedia.

Since without the cooling system the liquid-cooled engine is worth nothing, it would be a god idea to add it
Fuel system was not the part of 'dry weight' too, neither was lubrication system, those two would vary from airplane to airplane. The cooling system of the air cooled engine is, well, dry (fins and that, plus fan), that makes it included into dry weight.

 

[davebender]

Junkers was state-owned while DB was a private company, quite natural that Junkers got more money

The dispute concerned what Daimler-Benz was to manufacture.

RLM wanted Daimler-Benz to quit manufacturing automobiles and concentrate almost entirely on aircraft engine production.

Daimler-Benz wanted to remain diversified to improve chances for long term survivability and profitability. Daimler-Benz management were especially determined to keep manufacturing automobiles.

Personally I think RLM handled this matter foolishly. WWII era German armed forces needed all the 3 ton trucks they could obtain. Giving Daimler-Benz a long term contract for 500 or 1,000 diesel powered 3 ton 4WD trucks per month would have bought peace and helped the Wehrmacht too.

 

[davebender]

More to it then that.

Aircraft which employ large air cooled engines require a larger then normal engine compartment to facilitate air flow. Fw-190 is a good example of this. Engine compartment had to be enlarged to solve cooling problems. I'd hazzard a guess fuselage size increase adds as much or more aircraft weight as a liquid cooling system.

 

[tomo pauk]

It depends what engines are compared with, in this case, BMW-801. Ie. the DB-603 was a big engine on it's own, far bigger than the DB-601/605.