Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Actually a lot of the oil comes out of the crankcase oil breather. Other leaks may develop at the bottom of the cylinder heads (Jugs) where they attach to the crank case (Radial Engines). There is also leakage from the rocker arm covers
It depends - some manufacturers actually state in their manuals that "minor" leaks are acceptable. Others may give provisions on how much oil loss per hour is acceptable. The most common cause of oil around radial engines is oil getting blown out of the crankcase breather and there's not much one could do for that. Many manufacturers will not allow any leakage from the prop btw...Acceptable loss? or an indication that its time for maintenance? Gaskets/seals/O-rings/bearings?
It depends - some manufacturers actually state in their manuals that "minor" leaks are acceptable. Others may give provisions on how much oil loss per hour is acceptable. The most common cause of oil around radial engines is oil getting blown out of the crankcase breather and there's not much one could do for that. Many manufacturers will not allow any leakage from the prop btw...
Most of the leaks could be fixed with new gaskets and seals. Altitude changes, heat, cold and vibration play hell on seals and gaskets....
For some reason most of the engines I've seen just vent the breather oil overboard. I'm guessing that there is no return due to pressures that might build up in the crank case.Joe, some cars producers use the system where the oil gases going out from the crankcase go back to the engine inlet and in fact are burnt out. Do some a/c engine producers use the same or similar system or not? Or is the oil leak volume so high that it is impossible to send it back and burnt it out?
One thing I've wondered about in the B-29's case is why not use R-2800 engines? The smaller diameter, size, and better airflow characteristics would have eliminated the overheating problems, weight was somewhat less, with the R-3350s of the B-29 rated for just 2,200 hp, even earlier R-2800s weresn't much less powerful (2000-2100 hp rated) and by the time B-29s were entering production the R-2800-59 with 2,300 hp rating (and 2,500+ hp WEP) was being used on the latest production P-47Ds and the P-47M/N's 2800 hp R-2800-57C was availiable as well.
And just look at the B-29's nacelles, its just begging for R-2800 Double Wasps. (ie it apears to have stollen the noses of 4 P-47s)
The only reason I can think of is that the R-2800 was in too high of a demand, but seeing the priorety of the B-29 this shouldn't have been a major issue. (licence production could be set up if necessary)
The engineers responsible for propulsion could of had a number of reasons why they changed their minds. Weight, size, reduction gearing, and accessory accommodation could of all been a factor, as well as availability, producibility and last but not least - costs!Still I don't see why they didn't considder the R-2800s as an alternative in the 345 model, especially considdering that the power outputs of the R-2800 were better than those of early R-3350s of the same time, pluss the 2800 had reliabillity and prooven design on its side.
Seeing as 2100 hp Allison V-3420s as well as the more powerful R-4360s were both chosen and tested as alternate powerplants for the basic 345 design, I don't see why the R-2800 wasn't considdered: except the 2800 was nearing the end of its development for power output while the V-3420, R-3350, and R-4360 all had far more development for increase in power output and performance. Still, the 2800 should have been considdered as an intrim powerplant, and still outperformed (at least in the 2800-57C,and 59) most R-3350 models used on the B-29, and certainly those used durring the war.
The R-2800 was more expensive than the R-3350?! Either in maintenence costs or production costs I'd think the 2800 would be cheaper due to the large number produced, and the realitive reliabillity and serviceabillity.
I don't see how it would be heavier and streamline more poorly, all the info I've seen on the 2800 shows it to be ~300 lbs lighter and only ~52 in in diameter compared to the 3350's ~55 in. I don't see why the R-3350 could use a larger prop though...
Availabillity would be a factor certainly, but I don't think the early carborated versions of the 3350 had SFC any better than the 2800, though the direct injection later used likely would have. Judging by the performance of the P-47's layout and the accesories it carried it would seem to have adaquate performance for the intended long-range high-altitude role. The smaller R-2800 shouldn't have had as much of a problem with oil leaks either.
Still though, the R-4360 is the ultimate engine for the design, with excelent reliabillity in the air (compared to the R-3350, and no real fire issues), though a maintenence mess on the ground.
Overall: 1.) Weight and size is better if anything in the 2800, 2.) reduction gearing may have been an issue, 3.) accessory accommodation maby though it had alot of versitility in this area(seen in the variety of areas it was used, with turbos, 2-stage superchargers, water-injection, use in low-alt and high-alt, and long-range applications; used in fiighters, night-fighters, bombers and transports for a few), 4.) availability definitly would have been a factor due to the high demand for a number of uses, 5.) producibility I'm not sure of but shouldn't have been a big problem (licenced production if necessary), 6.) and costs shouldn't have been an issue.