tail end charlie
Senior Airman
- 615
- Aug 24, 2010
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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.
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.
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.
If I read it correctly...could you just crank up the boost to compensate?
...RPM limits the big bore engines so more boost which then overloads the rods and bearings
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.
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