Why did Germany use inverted engines?

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JD
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Why did Germany use inverted engines?

Post by JD » 12 Nov 2008 10:33

All their major engines were inverted vee configuration: DB601, 605, 603, Jumo 210, 211 and 213. Apart from the dry sump, what was the advantage and is there a connection between this and their predilection for mounting canon between the cylinder banks?

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Sitzkrieg
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Re: Why did Germany use inverted engines?

Post by Sitzkrieg » 12 Nov 2008 15:39

Not necessarily for cannon installation. If you take into account that both the Russians and the French used Vee engines with cannon (in fact the Russian Klimov engines were derived from the French Hispano-Suiza series), it doesn't make any difference. What matters is the positioning of the cylinders, the crankshaft and the configuration of the reduction gears and other accessories so as to make room for a weapon between the cylinder banks.

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Re: Why did Germany use inverted engines?

Post by jbaum » 13 Nov 2008 00:45

Also in this manner (inverted V), the visibility for the pilot was better because the bulk of the motor was lower in the fuselage.
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Michael Emrys
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Re: Why did Germany use inverted engines?

Post by Michael Emrys » 13 Nov 2008 02:22

jbaum wrote:Also in this manner (inverted V), the visibility for the pilot was better because the bulk of the motor was lower in the fuselage.


I thought of this too, but I am not sure is this was a design criterion or a happy side effect.

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JD
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Re: Why did Germany use inverted engines?

Post by JD » 13 Nov 2008 07:32

Yeah, I always wondered if that wasn't just a happy coincidence.

Would inverting the engine have made it any easier to work on?

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Re: Why did Germany use inverted engines?

Post by Mangrove » 13 Nov 2008 08:41

Was the oil tank on top of the engine block? Then there was no need for an oil pump.

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Visionist
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Re: Why did Germany use inverted engines?

Post by Visionist » 13 Nov 2008 14:11

Martti Kujansuu wrote:Was the oil tank on top of the engine block? Then there was no need for an oil pump.


In a civilian aircraft maybe. But these were engines designed for a combat role. Surely they would need pumps to keep the parts lubed under all conditions of flight?
I have heard that German engineers who got their hands on British Merlins were impressed with the effective simplicity of the non-inverse design.

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Re: Why did Germany use inverted engines?

Post by phylo_roadking » 13 Nov 2008 17:15

One factor that must have played an important part in the configuration and development of German aero engines is - their stifled development through the 1920s and early 1930's See Hooton's Phoenix Triumphant for details. Post-Versailles strictures on German manufacturers kept German aero engines down to very limted outputs for a decade, and any "high performance" engines fitted to German aircraft in the 20s and early 30s were purchased abroad, and production wasn't licenced. So, once the inverted vee was fastened up and development begun...they only had a few years before the war to make up a missed decade of development and testing. With years to make up, there were no alternative paths that could be explored in the time.

Regarding the configuration making German aircraft easIER to taxi - definitely not in the case of the Me109. Galland and Rall both confirmed it was actually worse to see out of than a Spitfire...coupling them with the 109's titchy-tiny straightsided and side hinging cockpit certainly didn't assist either!

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Re: Why did Germany use inverted engines?

Post by Topspeed » 14 Nov 2008 07:39

JD wrote:All their major engines were inverted vee configuration: DB601, 605, 603, Jumo 210, 211 and 213. Apart from the dry sump, what was the advantage and is there a connection between this and their predilection for mounting canon between the cylinder banks?



The weight, weight the weight and CG of it.

It was kept down..lower that is.

Down side was there was no change to make large dia props without making really long legged gears.

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Juha Tompuri
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Re: Why did Germany use inverted engines?

Post by Juha Tompuri » 14 Nov 2008 08:10

Easier maintenance

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JD
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Re: Why did Germany use inverted engines?

Post by JD » 14 Nov 2008 11:21

Topspeed wrote:The weight, weight the weight and CG of it.

It was kept down..lower that is.


I'm a little unsure as to why a lower centre of gravity would be particularly important, except for ground handling. MAybe it was easier to position the engine's C of G along the roll axis in flight if an inverted engine is used.

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Michael Emrys
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Re: Why did Germany use inverted engines?

Post by Michael Emrys » 15 Nov 2008 10:19

I guess a lower CG would tend to give it more lateral stability in level flight. Not sure if that is so desirable in a fighter though. Probably depends on the individual airframe. In any event, I would agree that keeping as much mass located as close to the roll axis as possible would be a good thing.

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Re: Why did Germany use inverted engines?

Post by jbaum » 15 Nov 2008 19:17

Having a lower center of gravity in a fighter would be very important. The inherent stability of an airplane which has sustained damage in battle might make the difference whether the aircraft could return home or crash.

Designing a stable aircraft has always been a problem with any fighter, because often the traits which provide quick maneuverability detract from stability. The Sopwith Camel biplane of WW1 was said to have had more losses during landing and take-off than in combat.

The ability of an airplane to be easy (stable) to fly, by a pilot who often had limited experience, during the most difficult of maneuvers, in a life and death situation, and return home to land with damaged control surfaces (and possibly wounded himself), would certainly rank as one of the top considerations during design of the aircraft. If something as simple as inverting the engine would help, or using a gull-wing design for the wings (as in the F4U Corsair and the Stuka Dive Bomber) to effectively raise the roll axis and thus provide a lower center of gravity (adding to stability), then the results would always be worth the effort.

Affection for an airplane which is easy to fly is always one of the things mentioned in interviews of the surviving pilots after the war.
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phylo_roadking
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Re: Why did Germany use inverted engines?

Post by phylo_roadking » 15 Nov 2008 20:40

I found the original performance specs for the DB600 family buried in Hooton's Phoenix triumphant...but no indication that any specific layout was laid down in 1930.

However - something comes to mind...in an inverted Vee configuration, is the c-of-g not ABOVE the midline, given that the crankshaft is the heaviest part of ANY engine??? Most engines I've "handled"....or dropped on my toes...including across-the-frame fours, inline fours, V-twins, and parallel twins - have been heavier in the "bottom end" the crankcase containing the crankshaft and the main weight of the conrods. An inverted cylinder bank - or two of them - may LOOK heavy - but remember they're hollow, ditto pistons in alloy, and camboxes containing lots of empty space and camshafts....

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Re: Why did Germany use inverted engines?

Post by jbaum » 15 Nov 2008 22:50

I wouldn't think that the weight of the engine block, cylinders, pistons, heads, camshaft(s), valves, valve train, induction system, and fuel and oil systems would be more than the single crankshaft.

Also, some of the propellers had a gun shooting through the hub, and having the engine in the inverted configuration would allow the gun to be more in line with the pilot's view. In this configuration, the propeller would need a gear drive of some sort, which would lower the center of gravity still more, since the motor would sit even lower in the fuselage.

The only disadvantage I can think of is that the inverted system is more prone to hydraulic lock. This happens when oil leaks past the piston rings and accumulates in the cylinders when the motor is not running. This is one of the reasons you see the propellers of the rotary motors of US aircraft (bombers especially) being pushed around by hand for a few turns before the motor is started in the old movies. It ensures that a hydraulic lock will not damage the motor. If the prop wouldn't spin by hand, a spark plug was quickly removed and the engine turned through by hand until the oil was forced out through the spark plug hole.

As far as maintenance, the routinely serviced parts of the motor would be closer to the ground. The crankshaft rarely requires service, but if it did, I would think having it able to be removed from the top without pulling out the entire motor would be an advantage.
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