Why inverted V12

[tail end charlie]

Colin is right.
Trying to "flip" an engine to suit different airframes would require modification and testing of both the oil system and cooling systems if nothing else. And by testing you are probably looking at hundreds of test stand hours in addition to flight testing hours.
Since "flipping" the engine is going to bring no benefits in either power or longevity (if the engine was designed/developed properly to begin with) that is a lot of trouble and expense for no gain.

According to wiki there were a few pre war engines with inverted V design but all seem to be air cooled, maybe they decided to water cool it and went down that path. I suppose all engines must work "upside down" when in negative G or when flying upside down anyway.

 

[Shortround6]

According to wiki there were a few pre war engines with inverted V design but all seem to be air cooled, maybe they decided to water cool it and went down that path. I suppose all engines must work "upside down" when in negative G or when flying upside down anyway.

There is working upside down and there is working upside down. Both coolant and oil systems (and oil could remove about 15-30% of the heat from the engine) were designed to flow in certain paths in order to cool most effectively or provide lubrication and cooling. Flying upside down (negative "G") for a number of seconds or even a couple of minutes might be able to be tolerated, flying the engine upside for several hours might not be.

Take the example I gave above of the Ranger R-770 V-12. the overhead (underhead?)cam cover boxes acted as the oil sumps for the engine. Oil from the crankcase and crankshaft was routed down to the cam boxes along with what ever oil was used to lubricate the cams and valve gear. It was allowed to pool slightly in the cam covers and absorbed some of the heat from the heads/valve gear before the scavenger pumps picked it up to cycle it through the oil cooler and oil tank. Flipping the engine over to run it "Heads UP" would require not only different locations of the scavenger pumps and/or pickups (oil would now collect at the bottom of the crankcase) but might require more oil directed to the valve gear to begin with and might also require some sort of extra cooling arrangements for that part of the engine.

Please note that the Rolls Royce Merlins that merely had the radiators higher than the engine had different MK numbers than otherwise identical engines that had radiators below the engine. The so called reverse flow engines used in Mosquitoes.
In the Merlin the coolant went into the block (the cool part of the engine)and rose up into the heads (the hot part) where it exited. While you could invert the engine you would now have the coolant as it heats up in the block trying to sink down to the heads ( yes it is being pumped) while the even hooter coolant in the heads is trying to rise up into the block. The system was also designed so that at least a small part of the coolant turned to steam at times. With all the various passages in the block and heads (and an occasional steam bubble to temporarily block one) I certainly would not guarantee proper cooling in a flipped engine without a lot testing.

 

[VALENGO]

I can´t stop thinking that exhausts piping layer had something to do with he engine position. In an inverted one they are nearer the bottom. Just one more fact to contribute to the whole picture...

 

[PWR4360-59B]

Well inverted is not the easy way to go for working on it. The lower cylinders are the more difficult on a radial, for that matter any of the underside work on any engine is bad. That is why overhaul stands are made to flip the engine over so its easy to work on. And someone mentioned german cars not easy to work on. Hmmm the old Air cooled VW wasn't too bad as far as the engine and transmissio goes, the rest of the vehicle is debateable.

 

[michaelmaltby]

The early Ranger inverted six's - like on the Cornell - were AIR cooled. Is the V-770 air or liquid cooled?

MM

 

[tyrodtom]

I think they're meaning with the engine still installed. if a engine was took off, it was being replaced. It's much easier to work from the ground, than get down and move a stand ever time you have to acess a different part of the engine. Carrying a heavy tool box up the stairs wouldn't be easy either.
The older VWs may not have been too bad to work on, but about any other vehicle from Germany was not designed with ease of maintainence being a high priority.

 

[Snautzer01]

some reading on inverted V

 

[tail end charlie]

What lay behind the Germans being the only country to develope the inverted V12. The only thing I can see that the DB series and Junkers Jumo designs provide different from upright V12s is a lower thrust line. And the thrust line can be changed easier by different crank gearbox designs.
I can't see that it doesn't improve pilot vision, the crank sump is still in the way. It seems to me the inverted design introduced difficult oil scavaging problems.

Was their desire to develope motor cannons that fired thru the propelle hubr behind it ?
Why, why, why ?

I was thinking along these lines today.

The maximum load for the piston con rod and big end are on the down stroke during the combustion part of the cycle. When an aircraft is turning at maximum then these G forces will be added to the load, inverting the engine could have been a way to reduce these loads (Just a thought}

This got me to thinking about radial engines, which leads me to ask this question.

Did the radial engines popular with the US forces have heavier wear on big/little end bearings or more failures on the top cylinder compared to other cylinders.

 

[PWR4360-59B]

I was thinking along these lines today.

The maximum load for the piston con rod and big end are on the down stroke during the combustion part of the cycle. When an aircraft is turning at maximum then these G forces will be added to the load, inverting the engine could have been a way to reduce these loads (Just a thought}

This got me to thinking about radial engines, which leads me to ask this question.

Did the radial engines popular with the US forces have heavier wear on big/little end bearings or more failures on the top cylinder compared to other cylinders.

The most loaded bearing is the big master rod bearing, its loaded all the time from many different directions.

 

[Shortround6]

Did the radial engines popular with the US forces have heavier wear on big/little end bearings or more failures on the top cylinder compared to other cylinders.

I think cylinder failures had more to do with the fuel/air mixture distribution not being equal to all cylinders. while most radials were better in respect to this than most V-12s, the Wright R-3350 seemed to be the exception with the pattern of mixture distribution moving around at different throttle settings.

 

[VALENGO]

One more observation: the cross sections of 109´s was narrow at top and wide at bottom. The inverted engine repeats that pattern. Attractive idea, isn´t it?.

 

[Roland CII]

The inverted V-12 engines were the result of a request by the Air Ministry in the early 30ies for then to-be-developed Jumo 210 and DB600. The aim was better visibility. Remember that the older BMW V-12 engines, which were the only high performance engines available in Germany, were fairly large an the view was indeed restricted. It proviedes better access to the plugs for maintanance as well.

Another idea was to get the always oiling cylinder heads away from the front the pilots windows. The idea was not new, as the upcoming smaller air-cooled inverted in-line engines for sports a/c show. It was new for the 20-30 liter class. Beside maintanance and view, the layout gives better aerodynamics for a low-wing a/c.

 

[Vintageaeroengines]

some interesting comments on this thread have been posted. I have been very blessed to have worked on or restored Alisons, Merlins, Griffons, DB 601s, BMW 801s, R1300s, R1820s, R3350s R2800s, Centuarus and a few others. That said I have a few thoughts of my own. First off, everything done suring the war was a compromise of cost, time, weight, strength, relliability and performance. Take the gear ratio of the propshaft: top end speed or accerelation? Then there is the issue of gyroscoptic forces the prop generates with higher speeds and also the tip speed can go supersonic and kill thrust. Add in the time to make changes and the costs to the issue. Through in a little National pride and you sould have a good picture. Anyway,
Oil scavenging is not an issue with the lower cylinders with the proper rings. Hydraluc lock is an issue with the radials, but not so much with the inverted V-12. The end of the cylinders projects high into the case and the drainage of oil is into the rocker covers. Running any engine inverted from it original design is a real problem as every moving part gets it lube either from a pressure passage or from splash. The splash lubed parts are the issue as even the drain oil lubes parts. The oil system for the later R3350 looks like a map of the LA freeways.
Cooling is designed to cool and making changes usually dosn't work. Flow, back pressure, steam removal, corrossion, sonic cavitation and lots more are at play here.
Having the banks down does give easier access to the plugs on the 601 etc. however the plugs are on the outside with the fuel nozzels on the intake side. Of course that caused problems with the flame front over the piston. The later 601 and 605 banks had the plugs moved as wide as possible to fix this.
Why the Merlin makes more power than the Griffon at Reno: 6" bore verses 5.4" bore and the time it takes the flame front to travel over the piston. Same issue with the R3350 at 6.25" bore. RPM limits the big bore engines so more boost which then overloads the rods and bearings. That is why Strega can go 512+ at Reno.
For every question there are many answers all with more questions.
Enough for tonight.
Mike Nixon

 

[robwkamm]

I never gave it anythought as to the bore size being a issue with the flame front speed. makes sence. could you just "crank "up the boost to compensate? or is the size maxed out for gasoline fuel .

 

[Colin1]

...could you just crank up the boost to compensate?

If I read it correctly
I think so, but not in a good way

...RPM limits the big bore engines so more boost which then overloads the rods and bearings

 

[Shortround6]

Increasing RPM also increases the loads on the rods and bearings. Increase in load goes up with the square of the RPM. 10% increase in rpm is a 21% increase in rod and bearing load.
Both higher RPM and more boost put a higher load on the cooling system.
Getting these race powers and keeping them up for more than a minute or two is a very careful juggling act.

 

[Aaron Brooks Wolters]

If I read it correctly
I think so, but not in a good way

You could space two or more spark plugs around the compression chamber so that you had two or three flame fields instead of one. They did this in Top Fuel Dragster and Funny Car. They tried 3 plugs but the classes got restricted to two plugs per cylinder due to cost and to much performance.

 

[Shortround6]

You could space two or more spark plugs around the compression chamber so that you had two or three flame fields instead of one. They did this in Top Fuel Dragster and Funny Car. They tried 3 plugs but the classes got restricted to two plugs per cylinder due to cost and to much performance.

Most aircraft engines had dual plugs, as much for this very reason as much as for reliability. some engines had the plugs firing at different times to get the flame pattern they wanted.

 

[stano666]

Some reading on inverted v was very good tanks
Greetings stano666

 

[drgondog]

some interesting comments on this thread have been posted. I have been very blessed to have worked on or restored Alisons, Merlins, Griffons, DB 601s, BMW 801s, R1300s, R1820s, R3350s R2800s, Centuarus and a few others. That said I have a few thoughts of my own. First off, everything done suring the war was a compromise of cost, time, weight, strength, relliability and performance. Take the gear ratio of the propshaft: top end speed or accerelation? Then there is the issue of gyroscoptic forces the prop generates with higher speeds and also the tip speed can go supersonic and kill thrust. Add in the time to make changes and the costs to the issue. Through in a little National pride and you sould have a good picture. Anyway,
Oil scavenging is not an issue with the lower cylinders with the proper rings. Hydraluc lock is an issue with the radials, but not so much with the inverted V-12. The end of the cylinders projects high into the case and the drainage of oil is into the rocker covers. Running any engine inverted from it original design is a real problem as every moving part gets it lube either from a pressure passage or from splash. The splash lubed parts are the issue as even the drain oil lubes parts. The oil system for the later R3350 looks like a map of the LA freeways.
Cooling is designed to cool and making changes usually dosn't work. Flow, back pressure, steam removal, corrossion, sonic cavitation and lots more are at play here.
Having the banks down does give easier access to the plugs on the 601 etc. however the plugs are on the outside with the fuel nozzels on the intake side. Of course that caused problems with the flame front over the piston. The later 601 and 605 banks had the plugs moved as wide as possible to fix this.
Why the Merlin makes more power than the Griffon at Reno: 6" bore verses 5.4" bore and the time it takes the flame front to travel over the piston. Same issue with the R3350 at 6.25" bore. RPM limits the big bore engines so more boost which then overloads the rods and bearings. That is why Strega can go 512+ at Reno.
For every question there are many answers all with more questions.
Enough for tonight.
Mike Nixon

Great Post Mike - welcome!