Colin1
Senior Master Sergeant
Kansas City, Missouri
R2800 vs R3350
- Thread starter krieghund
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syscom3
Pacific Historian
The R3350 used magnesium. There are lots of accounts of B29 being completley destroyed from an engine fire igniting the casings and being impossible to extinguish.
The R2800's didnt have that problem.
The R2800's didnt have that problem.
Colin1
Senior Master Sergeant
Why does that prove the presence of magnesium?
Wright engineers looked long and hard at the overheating/cooling issues of the R-3350 and found several reasons for its occurrence:
Cowl flaps were set for highest cylinder head temps allowable 260C for take-off and 232C for auto-lean cruise. This didn't allow for discrepancies in thermocouples or instruments. Inspections thereafter often found thermocouples out of calibration.
Damaged baffling would cause overheating of the affected cylinders.
The top three cylinders in a row (1, 3 and 5) were very susceptible to exhaust seat erosion with subsequent erosion on the valve guide boss. This seemed to be occurring after 175hrs. Policy thereon was to inspect at 150hrs and every 15hrs thereafter; any evidence of port erosion and the 'plant was swapped out.
A very serious problem was the leaking of the exhaust ball joint for the front cylinders. A leak would allow white-hot exhaust gases to be blown over the cylinder head, contributing considerably to overheating. Improved design remedied the situation.
Ground cooling was improved with cuffs at the root of the prop blades. Cowl flaps were shortened and additional cowl flaps incorporated on top of the nacelle. Baffling was constantly updated and seals were improved. Valve stems were flooded with rocker box lube lines, helping to carry away some of the combustion heat.
Wright's decision to stick with cast heads cost them dear, the R-3350's performance far exceeded what could reasonably be expected with a cast head design. Pratt Witney realised this and incorporated forged head design in their dash C.
By the end of the war, R-3350 mean overhaul time had grown to 400hrs, about on the money for a WWII combat powerplant.
The R-2800 had its share of overheating/cooling problems, these weren't fully eliminated until the dash C, which in fact over-compensated to the point where overcooling could exist under certain conditions eg cold climates in N Europe.
syscom3
Pacific Historian
The issue of R3350's catching fire and burning itself to a slab of metal was a serious issue and was one of the reasons the engine took so long to develope.
The R2800 would not burn like that. It was already a "mature" engine when it first entered into production.
The R2800 would not burn like that. It was already a "mature" engine when it first entered into production.
Shortround6
Major General
I guess that is why they did thousands of hours of bench testing on the "C" series engines (the 2100hp ones ) before they first flew one several years after the "A" series (1850hp) engines were in production. Total waste of time right?
Read a book in the 80's or early 90's about the XX Bomber Command.
I can't remember the name of the book or the author, so this makes this a lame reference...sorry.
But, the book frequently and clearly mentioned the R-3350 engine fires that couldn't be extinguished due to burning magnesium.
The book mentioned that reducing bomb loads and/or flying at lower altitudes reduced these fires from starting.
I can't remember the name of the book or the author, so this makes this a lame reference...sorry.
But, the book frequently and clearly mentioned the R-3350 engine fires that couldn't be extinguished due to burning magnesium.
The book mentioned that reducing bomb loads and/or flying at lower altitudes reduced these fires from starting.
syscom3
Pacific Historian
I guess that is why they did thousands of hours of bench testing on the "C" series engines (the 2100hp ones ) before they first flew one several years after the "A" series (1850hp) engines were in production. Total waste of time right?
The fact it was a peacetime engine design (when funds were scarce) and was ready for production by 1940 is testament to its basic design, in that it was an incremental improvement and not an evolutionary advance.
The R3350 pushed engine design considerably and it showed that in 1942 and 1943, with LOTS of money being thrown at it, it still really wasn't ready for combat use.
The B29 ground crew veterans at the B29 website have told many stories just how much maintenance they had to perform on it to get them to work, with the problems not really solved until late in the war.
The R2800's were not selected for the last generation of piston aircraft for a reason. They were at the end of the line for improvement and the R3350 and R4360 were better engines.
Colin1
Senior Master Sergeant
Peacetime engine design?
You mean like design work for the R-2800 coming straight off the back of the decision to up-displace an R-2600 design (that's an R-2600, not the R-2600) to 2804cu in March 1937?
R-3350 design work kicked off in January 1936, so who was the US at war with in either of those years?
The Truman Committee uncovered alot of reasons as to why Curtiss-Wright were falling short of the mark and under the Curtiss-Wright umbrella, you'll find the R-3350. Some engineering design decisions (sticking with cast heads) and some QC shortfalls served to hamstring the progress of the powerplant.
The problems with the R-3350 however, need to be carefully bifurcated from the problems with the XB-29 program which was probably two orders of magnitude more complex than any bomber program prior to it; hundreds of novel systems and thousands of sub-contractors trying to get a program into operations within a deadline dictated by the necessities of war. I'm willing to bet there were one or two program managers and senior engineering staff aged before their time at the program's completion.
R-2800-32Ws were turning out 2800hp @ 2800rpm which was at least as good as the most powerful R-3350s (dash 47, 49 and 51) none of which were procured.
In my own opinion, I think an ironed-out, bug-free R-3350 would have come to fruition alot quicker under Pratt Witney.
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Shortround6
Major General
The R-3350 was an evolutionary advance? a two more EXISTING R-2600 cylinders to each row isn't an incremental improvement?
Just how did it push engine design?
an 18 cylinder radial?
Lots of people working on those. At least 10 different projects around the world not including the US.
2 valves per cylinder? not exactly a big advance
Use of magnesium for non stressed cover plates? that had been many times by many people.
It wasn't at the forefront in hp to weight, or in hp/cu in or in bemp or in piston speed.
So again, what boundaries was it pushing?
No argument there but that doesn't show that the engine was advanced, only troublesome.
The R2800's were not selected for the last generation of piston aircraft for a reason. They were at the end of the line for improvement and the R3350 and R4360 were better engines.
They were more powerful (as they should be given their larger displacement) and so you could design a bigger airplane using 4 larger engines than 4 smaller ones. Nothing strange there.
Better engines might be debatable though. Last production plane in the West to use large radials used a pair of R-2800s.
Shortround6
Major General
Maybe if Wright hadn't been spending a lot of time/money on the R-2160 Tornado engine??
Maybe if Wright hadn't been spending a lot of time/money on the R-2160 Tornado engine??
OMG, I was about to pose the query if a liquid cooled radial would be feasible. Thanks for mentioning the R-2160.
- Thread starter
- #32
Colin1
Senior Master Sergeant
So much for the 'fundamental differences' between the R-3350 and an R-2800 that used 'traditional metals'; both used magnesium and in practically identical applications.
The R-3350 didn't 'push' engine design any more than the R-4360 did, it simply increased displacement in search of more power.
PWR4360-59B
Senior Airman
- 379
- May 27, 2008
One of the biggest problems with the early 3350's were the forward facing exhaust stacks and front collector ring, for the front row, that not only had leaking problems but all the heat was piped out front, to help heat the engine behind, leading to out of tolerance cylinder HEAD (was heat, made edit) temperatures and the resulting destruction. And there is lots of info about the high magnesium content of the castings for and aft not being a good thing when the fires started, even stories about DC-7 s having intense fires due to rain showers during the engine fire event.
Even into the 1960's there were problems with TC-18s, it seems the engine impeller intermediate drive gear, would fatique and fracture, causing metal to be dispersed through the lube system which caused the governor pilot valve to seize in the "on speed" position, making feathering not possible.
Even into the 1960's there were problems with TC-18s, it seems the engine impeller intermediate drive gear, would fatique and fracture, causing metal to be dispersed through the lube system which caused the governor pilot valve to seize in the "on speed" position, making feathering not possible.
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RktSci
Recruit
I worked on 3350 engines as used on the C-119G (and subsequent variations) while in the USAF ('56-'59). These were -89A Turbo-Compound engines. The nose housing was made of a magnesium alloy and they were capable of burning. (By the way, they did not use fuel injection on these engines.) I saw the result of the combustibility on an engine which failed due to lack of lubrication to the front bearing in the nose casting. The flight crew did an excellent job in that they feathered the prop and activated the on-board fire suppression system before the prop departed the aircraft, and before the fire spread to the rest of the aircraft. When I first saw the bird on a pad at Bitburg AB, Germany. the prop was at an angle which may only be described as extremely out of tolerance - 30 to 45 degrees (it's been a long time) as compared to the normal position. Normally, to remove the engine, we would remove the prop, install an adapter collar which bolted to the aforementioned casting, attach an application specific lifting sling, and, using a portable hoist, remove the engine. So, as the Marines (our good brothers) say, we improvised and adapted. We used tie-down straps from the cargo compartment wrapped around the engine, called for a C-2 wrecker (a big tow truck) and dropped the unit to a standard engine stand. Where, again, we had to lash it in place because the collar was normally used as part of the stand. We mounted the new engine without a problem, and, with a new crew, motored on back to Dreux.
Why the oil starvation occurred (if indeed that was the problem), I do not know. I suppose that a report was written later describing the failure, but who knows.
I never got to talk to the flight crew, but I can guess there was a lot of puckering going on when that prop went crazy.
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Are you sure of that? AKAIK all the turbo compound R3350's were fuel injected and the -89A being a later high output (3500 hp) version would certainly have been injected.
Flew both engines: The 3350 in the AD-1, 4B, 5, 6 and 7 and the 2800 in the M-404 extensively. Both engines were extremely reliable and that becomes very important when flying from a carrier deck in a single engine a/c as in the AD. Had one impeller shaft failure on the 2800 in over 10 years of flying the Martin
max m will
Recruit
The biggest factor for the problems with the 3350 was the PRT. The PRT turbine wheels had a bad habit of destroying themselves at the worst moment. When I attended Spartan, one of my classmates told me about his experiences in a Connie squadron(EC121). What the mechanics used to do was to disconnect the wheels(there were three per engine), and the engines would operate just fine. Even though it was something like 150hp scavenged out of the exhaust back to each engine, the pilots and mechanics didn't feel that it was a big enough advantage when it meant the engine most likely would fail in flight
jellydonut
Recruit
- 3
- Mar 10, 2011
Does anyone know why the PRTs were such an unreliable design? The metallurgy of the day not being up to the challenge.. or something else?
I'm curious about compound turbine designs today and this is one of the more prominent designs. Detroit Diesel uses a compound turbine on their DD15, it seems to work there, so it's not something fundamentally flawed in the idea.. I think, anyway.
