BMW keeps making only the liquid-cooling engines?

[tomo pauk]

For whatever plausible cause(s), like no Hornet deal with P&W and subsequent BMW 132, no merge with Bramo (Bramo and Argus merger happens instead?) etc.
Anyway - BMW decides that their future is with liquid cooled engines. What might be the best approach? Buy licence abroad (RR, Fiat, HS, Curtiss?), morph the big VI into an en-bloc engine* while introducing a V8 or L6 version of it to cover the lower end of demand. Go with an all-new engine like the 117 was? 'Just' make a supercharged version of the VI for the starters? Short-stroke the basic VI down to perhaps 170mm stroke and work from there?

* kinda the German counterpart to the Mikulin engines

 

[swampyankee]

Give up on the VI; it's a 1920s design. The likely path wold be continued development of the BMW116 and BMW117. I suspect that development stopped because the RLM felt that they had enough V-12 aircraft engines, with Jumo and Daimler-Benz both producing them.

 

[tomo pauk]

Give up on the VI; it's a 1920s design. The likely path wold be continued development of the BMW116 and BMW117.

Certainly, the VI was outdated by late 1920s, hence my suggestions for engines that have en-bloc cylinders etc.; a supercharged VI is just an insurance against the delays of such engine (engines?). The valve gear will also need to move to 4 valves per cylinder.

I suspect that development stopped because the RLM felt that they had enough V-12 aircraft engines, with Jumo and Daimler-Benz both producing them.

That is also my understanding. To the best of my knowledge, the BMW-Bramo merge and subsequent cancellation of the 116 and 117 and resulted with 14 cyl BMW 139 and 801 were very much under RLM influence, if not outright under their 'command'.

 

[tomo pauk]

I'd suggest to BMW to buy license for either D12 at Curtiss or the Kestrel at Rolls Royce, and with the knowledge gained, embark on a 35-40L V12 engine as next generation.

 

[pbehn]

I'd suggest to BMW to buy license for either D12 at Curtiss or the Kestrel at Rolls Royce, and with the knowledge gained, embark on a 35-40L V12 engine as next generation.

The Bf-109 first flew with a Kestrel engine so Germany had it. Rolls Royce obviously knew all about the Kestrel but the move to the Merlin and Griffon took a lot of work.

 

[tomo pauk]

The Bf-109 first flew with a Kestrel engine so Germany had it. Rolls Royce obviously knew all about the Kestrel but the move to the Merlin and Griffon took a lot of work.

Germans didn't have Kestrel by the time BMW was making the 1st Hornets under licence - 1933 vs. 1935. Let alone when BMW made the deal with P&W (early 1928).

 

[nuuumannn]

I'd suggest to BMW to buy license for either D12 at Curtiss or the Kestrel at Rolls Royce, and with the knowledge gained, embark on a 35-40L V12 engine as next generation.

Certainly makes sense Tomo and the Curtiss D-12 had considerable influence on engine design in the inter-war period, including the private venture engine that became the Kestrel, if not to directly copy it but to learn from it and do things differently (Fairey imported the D-12 as the Felix and fitted it to the Fox day bomber). The Kestrel was a crucial engine for RR and led to the Merlin and Griffon, so who knows what the BMW engineers could have gained from the design? At the very least, the Germans wouldn't have had to rely on RR supplied engines for the 1930s prototypes that were powered by them, as you mentioned the Bf 109, Ju 87 and He 112.

 

[Shortround6]

I am not sure what BMW brings to the table?

The 116 was a Kestrel/Jumo 210 sized engine and the 117 was a DB 600/Jumo 211 sized engine. Unless BMW knows something (or several somethings) than DB and Junkers don't I don't see why their engine would be any more powerful or have any advantage over the two engines that did exist.

Engine RPM was limited by materials, including valve springs, bearings, lubrication and such. Manifold pressure is limited by available fuel. It is not a question of having a different idea, it is being able to implement the idea and actually build a useable engine (service life of dozens of hours in the late 1920s)

The 1928 to early 30s period as one where the air cooled engine made a very good showing against the liquid cooled engines. Liquid cooled meant water and problems with freezing, It meant a lot of weight, it meant leaks, it meant a lot of drag, Liquid cooled radiators of the time were pretty terrible.
AIr cooled engines had a lighter installed weight (even if the bare engines were comparable) one less system to go wrong and in the mostly biplane, fixed landing gear world the added drag of the engine itself wasn't that big a deal (and the Townend ring wa a major step forward).

By 1935 100% glycol was all the rage but by 1939-40 many engine designers were back to water with 30-50% Glycol as an antifreeze/higher boiling point agent. Who knew what and when can really complicate some of these stories

 

[tomo pauk]

I am not sure what BMW brings to the table?

The 116 was a Kestrel/Jumo 210 sized engine and the 117 was a DB 600/Jumo 211 sized engine. Unless BMW knows something (or several somethings) than DB and Junkers don't I don't see why their engine would be any more powerful or have any advantage over the two engines that did exist.

Herein is the problem - BMW didn't design an actual liquid-cooled engine for a decade. By mid-1930s, they probably know less about V12s than DB or Jumo knows. Thus my suggestion to buy licence for an en-bloc V12 by late 1920s, so they can gain experience and design their own V12 (I'd like something of 40 liters).

Engine RPM was limited by materials, including valve springs, bearings, lubrication and such. Manifold pressure is limited by available fuel. It is not a question of having a different idea, it is being able to implement the idea and actually build a useable engine (service life of dozens of hours in the late 1920s)

All good.

The 1928 to early 30s period as one where the air cooled engine made a very good showing against the liquid cooled engines. Liquid cooled meant water and problems with freezing, It meant a lot of weight, it meant leaks, it meant a lot of drag, Liquid cooled radiators of the time were pretty terrible.
AIr cooled engines had a lighter installed weight (even if the bare engines were comparable) one less system to go wrong and in the mostly biplane, fixed landing gear world the added drag of the engine itself wasn't that big a deal (and the Townend ring wa a major step forward).

By 1935 100% glycol was all the rage but by 1939-40 many engine designers were back to water with 30-50% Glycol as an antifreeze/higher boiling point agent. Who knew what and when can really complicate some of these stories

A lot of good points. However, in Germany monoplanes were common already in 1920s; methinks that Junkers was monoplanes-only, for example.

 

[Shortround6]

Thus my suggestion to buy licence for an en-bloc V12 by late 1920s, so they can gain experience and design their own V12 (I'd like something of 40 liters).

Well, the D-12 was 1145 cu in, 18.8 liters (rounding up) used a 4 1/2 in bore and a 6 in stroke and ran at 2300rpm. (version for sale in 1930?) it also weighed 680lbs direct drive.
Yes it was a lot better than the Liberty engine. But in the late 20s it is too small (430hp) still not supercharged.
The larger Conqueror was available in the late 20s 1570 cu in (25.7 L)
5 1/8 X 6 1/4 with 600hp at 2400rpm. weight 845lbs with reduction gear. not supercharged.

The Kestrel was 5.0 X 5.5, 1296 cu in (21.2 L) and later versions went around 600 to 700hp (lots of versions) and ran at 2750-2900 rpm, they also went over 950lbs for a supercharged version with reduction gear.

Point is that while the Curtiss engines were mono blocks their bore to stroke ratio wasn't good (more the D-12) and they were too light for high power. Part of the problem was the gasoline. The D-12 ran 5.3 compression and no supercharger for the extremely low octane fuel of the time. when better fuel becomes available the engine can't make good use of it (higher compression and supercharging) because the the engine isn't strong enough.

discuss Packard engines tonight.

 

[Shortround6]

Sorry for the delay.

Packard had two V-12 engines in the 1920s. a 600hp 1530 cu in engine and the big A-2500. A 2540 cu in (41.6 liter) engine that was rated at 825hp at 2100rpm. It also weighed around 1100-1200 lbs (sources vary) in ungeared form and 1385lbs in geared but unsupercharged form.
This was the engine that formed the basis for the Torpedo boat engines. Which eventually got up to 1350hp or more using 100/130 fuel, a supercharger and perhaps an intercooler. Marine engine weights are NOT comparable because they include a fly wheel, a clutch and gear box with one forward gear and one reverse gear. The weight might also include the water cooled exhaust manifolds.

You have the size engine you are looking for but it doesn't matter who makes it. It has a few problems that need sorting out. One is the 162mm bore and the other is the 165mm stroke (which is actually rather short for such a large engine). Can you keep the center of the large pistons cool and not have them melt down like the DB 605 (or even the Hornet B) Such a light of it's size engine is unlikely to stand up to high BMEP. Even though the short stroke allows for low piston speed and high rpm for an engine of it's size the big bore has another problem.
Engine designers like to have the flame front/s cross the piston top by the time the piston is about 20 degrees past top dead center. Combustion is not complete but this rate of flame travel and position offers good power and also good economy in cruising given the fixed ignition timing used in aircraft engines of the time. It also meant most of the fuel was burned by the time the exhaust valves opened before the piston reached bottom dead center. The longer the flame fronts take to get across the piston, the higher the pressure in the cylinder when the exhaust valves open and the more "power" just goes out the exhaust. Many of these very large diameter cylinders were operating on the edge of needing triple ignition. The Jumo 211 and DB 601 weighed about as much as the A-2500 but they were operating at BMEP about 35-40% higher.

If you want to end up with a 40 liter engine of around 1750hp you might as well start with a clean sheet of paper as apposed to trying to use a 1920s or early 30s engine. You have to change an awful lot of the engine anyway and you spend a lot of time trying to save bits and pieces, some of which do wind up needing to be replaced.

A RR Griffon VI with single stage, two speed supercharger weighed about 150lbs more than the 1939 R racing engine. At 15lbs of boost it was operating at around 236lb sq in BMEP compared to the Packard's 135-140 sq in BMEP (un-supercharged).

This is a big problem in trying to develop engines too early. Nobody really cared about the displacement of the engine. They did care about the power to weight ratio. With crappy gas you can build a large displacement/ low rpm engine with light weight and compete against smaller/ high rpm engines that need stronger parts. Once fuel improves and cylinder pressures go up you need stronger/heavier parts in both engines. It is then a race as both types of engine improve strength and power and both engines also increase rpm. However other limits to increased rpm are the available metal alloys and the bearings/lubrication.

Throw in expected service life of the engine (time between overhauls and price of overhaul) in wartime some countries accepted shorter service life than in peace time for improved performance.

Russia had some unique problems of their own. They tended to tool up for large production runs of engines and they bought an awful lot of their tooling from the west. This means they had an awful lot invested in sets of tooling (M-17, Hispano, Gnome-Rhone and Wright Cyclone) and not a lot of ways to get tooling for completely new engines. They had to try to adapt existing engines or design engines that could be built using at least some of the existing tooling. They showed a great deal of talent at this but it was a limitation that most other nations did not have.

 

[tomo pauk]

Thank you for the informative post.

...
If you want to end up with a 40 liter engine of around 1750hp you might as well start with a clean sheet of paper as apposed to trying to use a 1920s or early 30s engine. You have to change an awful lot of the engine anyway and you spend a lot of time trying to save bits and pieces, some of which do wind up needing to be replaced.
...

Yes, a clean sheet of paper design for the 40 liter V12 engine.
It will take a while to get it to do 1750 HP or more, though; 1500 HP in a 2-speed supercharged version and 87 oct fuel is more likely for a 1940-ish version.

 

[nuuumannn]

Point is that while the Curtiss engines were mono blocks their bore to stroke ratio wasn't good (more the D-12) and they were too light for high power. Part of the problem was the gasoline. The D-12 ran 5.3 compression and no supercharger for the extremely low octane fuel of the time. when better fuel becomes available the engine can't make good use of it (higher compression and supercharging) because the the engine isn't strong enough.

Interesting to note that RR didn't think it was that great either, RR had already begun ground work on the private venture F and they saw the D-12 as an example of how not to do a new engine, after the Air Ministry had asked them to produce an equivalent. Or at least the F was how RR could get better performance from a similar engine/airframe combination - the Fox day bomber powered by the Felix was an impressive performer for the time but the Hart powered by the Kestrel was faster when it came to replacing the Fox, and the same with the Firefly single-seat fighter compared to the Fury. Ultimately the Kestrel proved it was a superior engine.

 

[Shortround6]

Ultimately the Kestrel proved it was a superior engine.

There is little doubt about that.

It was bigger (13%) it could run at higher RPM and it could run at higher BMEP.
In fact the Kestrel was better than the Curtiss Conqueror V-1570 once fuel of around 73 octane or higher showed up. The V-1570 topped out at 700hp at sea level at 2450rpm.
It used 91 octane fuel and a 7.25 compression ratio but no supercharger, it also tipped the scales at 1040lbs.
This is at the end of 31 different versions or models used by the USAAC.