MOST UNDERRATED AIRCRAFT OF WWII?

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A proper SOHC set up should not have any problems with valve guide wear. However if short cuts were made either through cost cutting or trying to reduce the volume of the valve cover (or short/light rockers) then problems may arise.
 
Shortround6 said:
A proper SOHC set up should not have any problems with valve guide wear. However if short cuts were made either through cost cutting or trying to reduce the volume of the valve cover (or short/light rockers) then problems may arise.
Click to expand...

Allison provided a durable roller-rocker arrangement, but direct DOHC still puts less load on the valve & spring,
inertia-wise, & sleeve-valves avoid all that nasty recip' chattering, wear-prone, adjustment hungry gubbins - altogether..
 
J.A.W. said:
@ SR6, a possibly useful parameter point for comparison between Bristol & US radials might be..
found in permissable CHT figures - perhaps?
Click to expand...

Well, cylinder head temperatures sort of depend on the location of the thermocouple don't they?
Often under the spark plug (or between the spark plug and the head?)

car CHT sensor


Since the allowable CHT was much more of indication of engine operating limits of a particular engine and not direct measurement of temperatures inside the cylinder I am not sure how well it compares different engines.

I really don't care if engine A has a limit of 260 degrees C and engine B has a limit of 285 degrees C. What I care about (as a pilot, if I was one, or designer) would be power to weight/power to volume of the installation and fuel economy.
The War time almost never exceeded 8.75lbs of boost (many versions were lower) and used a 7.0 compression ratio. The American radial used compression ratios of 6.7 to 7.0 so no real advantage (not even the 10-11% difference of the Merlins and Allison) and some of the Americans radials used used higher manifold pressure.
The R-1830 which did use smaller/easier to cool cylinders used 6.7 compression and 9lb of boost and could do that on 100 octane (NOT 100/130) fuel.
 

To the best of my knowledge, Cosworth did no such thing.

They built the DFV (Double Four Valve), which was based on the 4 cylinder FVA.

It remained in F1 until 1985.

Keith Duckworth was not a fan of the turbo engines. He believed them to contravene the rule about only one power source. But since they were dominating F1, Ford asked him to build a turbo engine.

Duckworth's response was to design a turbo-compound. Going to the extent of building a single cylinder test engine.

The FIA told him that it would be banned immediately after it won its first race. So it did not proceed.

Instead, Cosworth developed the Ford TEC/Cosworth GBA twin turbo 1.5l v6, which raced in 1986 and 1987.

Ilmor developed a rotary valve engine in the 1990s, but this was banned. But this was also not a sleeve valve.
 
Yeah SR6, some Bristol fighter engines did get higher boost ( 1944: Centaurus @ + 12lbs), &/or ADI,
but earlier, ( see post 339) I did pose a power/economy comparison question.
 
 
Hairog said:
The Lightning defeated both the Japanese and the Luftwaffe before the more publisized cleanup crew showed up.
Click to expand...

Not to ridicule or limit the achievements of the brave men who flew the Lightning in combat, but this type of inflammatory rhetoric is commonplace when your favorite aircraft doesn't have the stats to back up your wild claims. But I guess it's a far easier task to minimize the officially recognized victory record of both the Mustang and Hellcat than to actually bring real statistics to support your claims. That the Lightning some how singlehandedly cleared the sky of all seasoned German and Japanese pilots, only to leave the "dregs" to the two highest scoring American fighter aircraft of the war, sounds like sour grapes to me.....
 
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How about someone splits all the engine comments into a separate thread - it is definitely a topic worth discussing, and in detail but is leading this discussion astray.

For my 2 cents worth the most underrated aircraft of ww2 is the Douglas DC-3 and all its many military derivatives produced in the US, Japan and Russia. The US Army alone operated the C-41, C-47, C-47A, RC-47A, SC-47A, VC-47A, C-47B, VC-47B, XC-47C, C-47D, NC-47D, RC-47D, SC-47D, VC-47D, C-47E, C-47F, C-48, C-48A, C-48B, C-48C, C-49, C-49A, C-49B, C-49C, C-49D, C-49E, C-49F, C-49G, C-49H, C-49J, C-49K, C-50, C-50A, C-50B, C-50C and C-50D, C-51, C-52, C-52A, C-52B, C-52C, C-52D, C-53, C-53B, C-53C, C-53D,C-68, C-84, C-117A, VC-117A, SC-117A, C-117D, LC-117D, TC-117D, VC-117D, YC-129, XCG-17 - and that is without getting into the Vietnam derivatives.

Did you know that as a cargo glider (XCG-17) it had a far better glide ratio than any of the gliders that were designed from the ground up?

To quote wiki
Trials conducted using a conventional, powered C-47, first conducting ordinary deadstick landings, then being towed by another C-47, indicated that the scheme was feasible.[2] Therefore, a C-47-DL was taken in hand for conversion into a glider, which was given the designation XCG-17.[4][5][N 2] The aircraft, formerly a Northwest Airlines DC-3 that had been impressed into military service at the start of World War II,[7][N 3] was modified by the removal of the aircraft's engines; the nacelles, containing the landing gear, remained in place, covered with aerodynamically profiled hemispherical domes for streamlining, containing fixed weight to compensate for the removal of the engines.[3][7][9] Other equipment, no longer necessary with the conversion to an unpowered configuration, was also removed to save weight;[3] items removed included the aircraft's wiring and bulkheads, along with the navigator's and radio operator's positions.[1][7]

The C-54 was the preferred tow aircraft for the XCG-17

The conversion, carried out at Clinton County Army Air Field, was completed on June 12, 1944, with the aircraft undergoing its initial flight test shortly thereafter.[7] The flight testing of the XCG-17 proved that the aircraft was satisfactory; compared with conventional gliders in service, the aircraft possessed lower stalling and higher towing speeds than conventional gliders, as well as gliding at a significantly shallower angle.[4][10] Tow tests were conducted using a variety of aircraft; the most commonly used configuration was a tandem tow by two C-47s, with the towing aircraft coupled one in front of the other and the leading aircraft detaching following takeoff.[3] This configuration was dangerous for the "middle" C-47, however,[7] and it was determined that a single C-54 was the optimal tug aircraft.[2][7]


The XCG-17's cargo hold had a capacity of 15,000 pounds (6,800 kg);[1][7][9] alternatively, up to 40 fully equipped troops could be transported, these figures being significantly larger than conventional gliders' capacity.[3] The XCG-17 was also capable of carrying three jeeps in a single load, or alternatively two 105-millimetre (4.1 in) howitzers.[7] Regardless of the aircraft's load, no ballast was required to maintain the aircraft's center of gravity,[3] a trait unique among American assault gliders.[7]


Despite the satisfactory results in testing, however, the aircraft failed the Army's requirement that it be capable of landing on unimproved fields;[7] in addition, by the time the evaluation of the XCG-17 was completed the need for such a large assault glider had passed.[1][9] The primary role for the glider had been intended to increase the amount of supplies that could be carried to China over "The Hump"; the war situation had, however, become more favorable and the added capacity an oversized glider would provide was no longer required.[11] No further examples of the type were produced; the prototype, its trials complete, was placed in storage, being ferried to Davis-Monthan Air Force Base for disposal in August 1946.[7]


In August 1949, the aircraft was sold to Advance Industries, its engines being reinstalled to return the aircraft to powered status in DC-3C configuration.[7] Some sources, however, indicate that the XCG-17 was reconverted to C-47 configuration in 1946.[9] Following its restoration to powered status, the aircraft was transferred to Mexico,[7] where it remained in civilian service until 1980.[12]
 
Shortround6 said:
Well, cylinder head temperatures sort of depend on the location of the thermocouple don't they?
Often under the spark plug (or between the spark plug and the head?)

car CHT sensor
View attachment 489812
Click to expand...

Your car CHT sensor is similar to the aircraft ones used on ww2 aircraft like the B-24 and C-47 and almost identical to those used on many modern Continental and Lycoming engines.
The sensor replaces the spark plug gasket.
 

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Poppet valve radial cylinder heads had to contend with supporting one cool (relatively)
& one hot ( incandescent exhaust ), valve - plus the ports flowing gas to-&-from them,
along with the oil lubricating/cooling - the valve gear itself.

Overheated exhaust valve seats could be hammered out of the Al castings supporting them,
& valve heads may drop off..
(any members here experience having a hard-run, heat-soaked, air-cooled VW mill..
- drop a valve head?.. it was invariably from No 3 cyl, the hottest running one,
due to it being blanketed by the oil-cooler..)

Bristol sleeve valve heads had zero moving parts above the piston,
& nothing needing copious oil - to be damaged by heat, or leak, or fly apart, & burn..
 
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The main trouble with the Sleeve valve was that it almost always was one step behind the poppet valve.

You use as an example the troubles with one poppet valve engine in one installation. Yes the troubles of the R-3350 as used in B-29s are well known. However if we step back and look at the bigger picture there were somewhere around 2500-2800 Bristol Centaurus engines built in total?
over how many years and in 34 different versions (some minor)?
Production of the R-3350 hit 2500 total sometime in April of 1944. By the end of 1944 they were making almost 1900 a month.
The engine was rushed into service before being thoroughly sorted out.
Anybody want to tell us how many Bristol Centaurus engines saw combat in WW II?

Contributing to the R-3350s woes in early models was the poor supercharger inlet which resulted in poor mixture distribution. This meant not all cylinders got the same mixture and some were running a lot leaner than others, including the infamous No 3.
Before the war ended new R-3350 engines were being fitted with direct fuel injection which solved the mixture distribution problem. There were a number of other problems including one that had nothing to do with the valve action. They had problems with exhaust leaks from the ball joint
in the exhaust system on some of the front cylinders. Having hot exhaust gases blowing on your cylinder heads certainly doesn't help cooling.
By the end of the war against Japan the R-3350s were being rated for 400 hours between overhauls. It took a lot of hard work and many modifications to get there but it did. Post war saw many more improvements and higher times between overhauls.

As too the CHT thing. That was also part of the R-3350s woes. Some of them were out of calibration and not giving accurate readings.
Most service engines only had or two(?) per engine and the crew hoped it was placed on the hottest cylinder on their engines.
 
@ SR 6, there is no doubt the US aero-engine manufacturing system was much more efficiently
organised & directed than any other.. FDR's 'New Deal' federal overseers were cranked up for
war, with skilled men such as JK Galbraith able to cut through many 'vested interest' issues.

& capable engineers in US automotive corporations put their considerable talents to work.
Chrysler in fact, while building R-3350s showed Wright how to effectively sort out a number
of problems, since the Mopar team's mills were increasing durability/TBO quicker than CW.

But it is important not to conflate design merit with production numbers, a Model A Ford
aint no blower-Bentley.

@ pbehn, it is important not to conflate muliplicity with complexity, & sleeve valve engines
had advantages in fewer moving/wearing parts, improved access to items like spark-plugs,
& no need for valve adjustments between overhauls.

@SY, the author of those articles apparently has little actual 'hands on' experience with engines,
as he makes some assumptions from a basis lacking a grasp of engine architecture & function.
IMO, this also applies to his thesis supervisor, who ought to referred him to an engineer with a
proper working understanding of the tech - to check his work, & advise corrections.

Also, he needs to do a more diligent literature review, many primary sources are available.
(several members here, for example - could have guided him in the right direction).
& even a quick search brings up stuff like: http://www.flightglobal.com/pdfarchive.com/view/1944/1944 - 2008.html
 
In the late war years Rolls Royce developed a sleeve valve H format 24 cylinder engine, the Eagle. It was used in the prototypes for the Westland Wyvern a carrier based strike plane. Given the free choice they chose sleeve valves but almost all their wartime experience was with water cooled V 12s. The H format is two water cooled flat 12s fastened together. As far as I understand the discussion it is not so much that sleeve valves had greater volumetric efficiency but that they could have higher boost on the same fuel without detonation, the downside being the scraping of pistons and rings against open ports.

The needs of poppet engines gave rise to new alloys like Brightray and Nimonic , while sleeve valves facing the same operating environment needed advanced nitrided austenitic spun forged steel.

To increase performance from two row 18 cylinder, radial air cooled engines or V12s was not easy. Based on a maximum bore and stroke of 6inch the radial has the advantage because of 18cylinders but water cooling a radial is almost impossible.

By 1944 Rolls Royce could no more come up with a ready made air cooled radial design any more than Wright could produce a water cooled H or V format engine.
 

I think you are rather missing the point. If you are going to build hundreds if not thousands of engines per month you had better have at least tried to finalize the basic design. In fact this was a major problem with the R-3350. Dodge actually outproduced Wright by large margin despite thousands of engineering changes.
However there was one problem that Dodge could not solve, or took longer than it should have.
When tooling up the factory in 1943 they had to decide between using cast heads or forged heads in order to get the appropriate equipment. The Forged heads were still in the developmental stage at the time so they went with the cast heads as an expediency to get the factory going sooner. This bit them in ass big time as the stronger forged heads would have been less prone to dropping valve seats.

We are back to comparing the oh so wonderful sleeve valve engines of 1945-46 with the poppet valve engines of 1943-44, not comparing model As and blower Bentleys. Two years was long time in WW II in terms of metallurgy (alloys and heat treat).

Why were several hundred Vickers Warwicks built with P & W R-2800s............Oh yeah, the Centaurus engine wasn't ready yet, the Vulture had been dropped form production and the Sabre was not being built in large enough numbers to swipe any from Typhoon production. I will admit that the R-2800 Warwick was more than a bit of of a dud but then that is what happens when you stick a pair of 1850hp engines in a 45,000lb plane. I doubt anybody else's 1800-1900hp engine would have done any better.

From Wiki so.....
"The first major problem experienced during the first few flights was serious engine vibrations, which were cured by replacing the rigid, eight-point engine mountings with six-point rubber-packed shock mounts. In a further attempt to alleviate engine vibration, the four blade propeller was replaced with a five blade unit; eventually, a finely balanced four bladed unit was settled on.[35][36]Problems were also experienced with engine overheating, poor crankshaft lubrication, exhaust malfunctions and reduction-gear seizures. Because of these problems, and because of the decision to "tropicalise" all Tempest IIs for service in the South-East Asian theatre, production was delayed"

Now this was right about the time the The R-3350 was going into full scale production in two major factories, flawed as it was.

How long did it take for the Hercules, a 2360 cu in engine to really exceed the Wright R-2600 in power per cubic in?? I mean by more than a few hundredths of a hp per cu in?
Or when was the Hercules first flown in service??? or issued to to a service squadron??
The R-2600 first flew the Atlantic on June 24, 1939 and this was not a stunt as they had started the first San Francisco to Hong Kong flight on February 23, 1939

I don't really care about first runs on a test bench or even first flights in a test hack aircraft. The Sleeve valve engines were trailing the poppet valve engines in service/squadron use.
 
Shortround6 said:
Two years was long time in WW II in terms of metallurgy (alloys and heat treat).

.
Click to expand...
A long and informative post S/R but this is the most important part, discussing "valves" and "sleeves" without discussing what they were made from ignores a major part of the technical battlefield, much of it about boring details about metal manufacture and properties.
 
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