Why did the Germans use inverted V-12 engines in WWII? Why not a traditional ‘right-side-up’ design?
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Lower center of gravity and less interference with field of vision.
I did look at Wiki. Of course I searched on DB 601.
That may be true, but I’m not entirely convinced. I’m not sure the moment is great enough to make a difference in the CG. And when you consider that the vast majority of successful types used upright V-12s or large radials, a rather marginal increase in visibility seems an unlikely reason to build an engine upside-down. Since fluids tend to flow down, isn’t there a risk of getting cylinders full of oil? If so, do the stated advantages outweigh the (possible) extra trouble at start-up?
I’m not an engine expert. Far from it, actually. But ISTM that if inverted engines were superior to upright ones, then most engines would be inverted.
yes. when the engine starts, the oil’s flying around the crankcase anyway. Besides, radial engines were used for a long time and they had the same “problem.” For a military plane, the important thing was that they were as robust and reliable as possible.
you have to account for the engine itself and its application. you can’t separate the two. in that application it was felt that an inverted vee engine was superior. It wouldn’t work in, say, a car because it would make it difficult to package the engine between the subframe/frame rails. there simply isn’t “one true engine configuration to rule the world.”
It was common for ground crew to turn radial engines by hand in order to get the oil out of the bottom cylinders (and for other reasons – I’ve seen in-lines being hand-turned as well). The argument that military engines must be robust (which is true) carries the implication that the inverted design was, in the Germans’ opinion, more robust than the upright design. Again, if that’s true then there should have been more inverted engines.
I completely agree that the powerplant must be suited to its purpose. But why did the Germans feel that the inverted engine was superior, and the rest of the world didn’t?
The usual reason for inverting an engine is to get the crank higher - since this sets the height of the centre of the propeller. For smaller planes this can be a rather critical dimension. The concomitant design issues with the engine may be considered rather less important than the design viability of the aircraft as a whole. Once you have an engine designed and working, using it, as is, in other aircraft, even if they don’t need the same dimensional clearances, is going to be easier, and less prone to problems, than re-engineering the engine into a new variant.
Clearly in cars you want the crank low. Horizontally opposed engines have it both ways, or neither, depending upon your viewpoint.
There are a great number of inverted aircraft engines, they are not peculiar to the Germans.
no, it doesn’t! you’re jumping to that conclusion. They felt it was robust enough to put up with any initial oiling difficulties.
at any rate, you’ve already been told why they used it. It’s not our problem if you’re “not convinced.”
That makes sense, and the Bf-109 (for example) was a small aircraft. The closest Allied aircraft I can think of is the Spitfire. Both aircraft were of similar size, both aircraft used under-wing radiators, and both aircraft used outwardly-retracting landing gear and thin wings, so their layouts were similar. (The Hurricane and the P-51 Mustang used belly radiators and had inwardly-retracting undercarriages, and the P-40 Kittyhawk used a chin radiator and used aft-retracting gear.) Given the similarity in airframe designs, was lowering the crankshaft really necessary, even given that the lower thrust line may have been advantageous?
The Bf-109 was designed to use the Junkers Jumo 210 engine, which was, like the Daimler-Benz DB 601, inverted. IIRC, aircraft at the time tended to be designed around available engines – or at lease engines that were expected to be available. And of course commonality is a great logistical advantage. Since the Germans had inverted V-12s, it makes sense that they’d design airplanes to use them and to use the engines in many types.
But what I’m really getting at is this: Someone is designing an engine. All (or virtually all – again, my knowledge of ever engine ever built is lacking) other in-line engines were upright. So why did the designer turn it upside-down? Was it a case of there being a need for an inverted engine in the first war, and they just kept building them that way? Or was there a significant real or perceived advantage to the inverted design?
You provided a link to an uncited statement. Given only that, one may conclude that the only reasons for building engines upside down is because they CG is lower and they provide better visibility. I’d like to see some evidence.
Somewhat inspired to have a look, I notice a couple of things that contradict what I wrote. Both the British and German V12’s use reduction gears. This means they place the propeller centre away from the crank axis - and with little surprise, the British engines raise the axis and the Germans lower it.
What I do note is that the German engines were commissioned by the German Defence Ministry, who provided the guidelines for the required design. So the answer to your question probably lies within the ministry. History has shown that on many occasions the such issues can be sheeted home to rest with the prejudices or whim of a single civil servant.
FWIW, in the Wikipedia article on the Me 109, it says “Fighters with liquid cooled engines were vulnerable to hits to their coolant system”, and quotes a Russian mechanic who inspected a 109, saying
“The Messer was a very well designed plane. First, it had an engine of an inverted type, so it could not be knocked out from below. […]”
Agreed, but: The Bf109 engine had a reduction gear between the crank and the propeller, which actually lowered the placement of the propeller axle. ETA: And I see on posting that you’ve made that point already.
No cites or anything of the sort, but two reasons do come to mind:
The field-serviceable bits of the engine - spark plugs, valves etc. - are easier to reach in improvised settings. And the dual machine-gun armament has a nice place in its traditional WWI spot, shooting along the crankcase. (Before anyone comes to say that such matters couldn’t possibly have been part of the design, think about Goering’s background as a WWI ace. It took arguing before he accepted closed cockpits.)
Somewhat, but the German V-12s were dry sump engines. Almost all of the oil stayed in a separate reservior.
Looking at several pictures, the Bf 109 may have been narrower at the top of the nose than a Spitfire or a P-51 Mustang. It looks like the pilot would have had a much better view below.
There were a number of other inverted inline engines around, for example the de Havilland Gipsy Major. I acknowledge that it is an older design in a different league to the V12s but the idea wasn’t new. As noted above, the typical reason to invert an engine was to lift the crank higher off the ground allowing for better clearance for the prop. As also noted above, the prop reduction gearbox on the V12s placed the prop opposite the crankshaft so the inverted engines on the German aircraft actually allowed less clearance. Given that a lower prop requires longer undercarriage legs, and the undercarriage legs have to be retracted into the wing which have limited space, it’s reasonable to assume they had a very good reason or reasons for doing it that way. I think it was probably a number of things. I don’t know anything about the gun design on the fighters but that may have been a factor as the guns were sometimes positioned on top of the engine, e.g., the BF109. Forward visibility may have been a factor, the BF109 has a downward slope to its nose which is not possible with an upright V12 so vis on the ground may have been a little better. Ease of servicing has already been mentioned.
Another example was the Continental I-1430 ‘hyper’ engine developed pre war for the USAAF.
The DB 601 and 605 were designed to accommodate a cannon between cylinder banks and firing through the propeller hub. It is really hard to find detail drawings of how exactly this worked, but there is no way that the crank shaft was inline with the propeller. The soviet Klimov 105 & 107 v12’s also had cylinder bank cannons and reduction gear driven props but were not inverted.
I doubt robustness had much to do with the design choices. The war era DB 60X engines had short operational life spans. Fighter engines were rarely very durable, the lives of most were measured in tens of hours. The need to eek every bit of performance was primary. Most had combat emergency power settings where pilots could push the throttle past a safe operating limit reducing engine life even further to gain a few horsepower. The counter example would be the Packard Merlin, needed for long range Mustangs and british bombers; its durability was achieved through dramatic refinements in the manufacturing process rather than initial design considerations - the Rolls Royce Merlins did not have the same engine life.
Air cooled radial engines were the generally the answer for robustness.