Service, Overhaul intervals for WW2 aircraft engines question.

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bdefen

Senior Airman
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527
Nov 26, 2019
Boise, Idaho USA
If not damaged in combat or other use, what were the typical hours operation of P&W, Bristol, and BMW radial engines, as well as D-B 600 series, Jumo 200 series, Allison, and R-R Merlin engines before certain maintenance was required?

Fuel (presumably), oil, coolant, hydraulic fluids checked and added for each sortie?

How many hours before "tune ups" like carburetor or FI adjustments, timing, ignition, valve adjustments, spark plugs, etc?

And how many hours before major overhauls, like valves, valve seats, rings, pistons, bearings, re-boring, etc.?

At what point was an engine considered worn out and not rebuildable, and therefore scrapped?

Was the "power egg" system used by most air forces?

If this has been covered by other threads, please direct me there.

Thanks!
 
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People have written books on the subject, just for one engine. Just on one issue spark plugs, some spark plugs were better than others, so using better spark plugs changed things. Some fuels caused fouling so the issue is the fuel not the engine. If you have unlimited time and resources almost any engine can be rebuilt, the issue is the effort involved. If you take a ball park of 250-500 hours for a Merlin engine before a rebuild is needed, after 500 hours a Spitfire air frame is also very tired and 500 hours would be about the hours a squadron did before they changed type anyway.
 
Manuals for all of those engines are available, which detail all the service intervals.

The difficult bit is understanding that in wartime, many of those were not realised.

By the end of WW2, in reality, Germany aero engines were lasting about 50hours before total overhaul. This bore little to do with
the contents of the manuals.

Also, I`d recommend not putting so many questions in one opener, you are asking for a gigantic volume of information.

For example the manual below is available from Udo Hafner.

Luftfahrt-Archiv Hafner

 
Guess I asked too many questions. Never mind.
 
bdefen said:
Guess I asked too many questions. Never mind.
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Many of the individual questions have books written about them for each engine, and each one is a history. "Merlin engine" is just a general term, it was changed in all sorts of ways continuously during the time it was in service.
 
bdefen said:
Guess I asked too many questions. Never mind.
Click to expand...
Don't take it that way - they're all relevant questions, but the same info could be gained from one or two questions. For someone reading the thread, a wall of questions is pretty hard to get through.
The P-40 Maintenance Manual (there's a copy on the forum somewhere) has the info, and includes, pre-flight, daily, 25, 50, and 100 hour periods, daily and pre-flight are visual checks to make sure there's nothing obvious (broken, dirty, etc) to be done. The other checks involve more in-depth checking and adjustment as necessary.
 
Thanks.
 
I think its also remembering the type of use the engine was being used for. In the 8th Airforce there was a considerable difference in the wear of the B17/24 engines. Those in Heavy Bomber units found they didn't last nearly as long when formation flying as the settings were continually changing to maintain their position. An experienced crew often had improved wear and tear on their engines
 
I found an interesting paragraph in an SAE paper.
A History of Aircraft Piston Engine Lubricants. Robert V. Kerley page 2613
SAE Transactions Vol. 90, Section 3: 810614––811014 (1981), pp. 2601-2628 (28 pages)

A History of Aircraft Piston Engine Lubricants on JSTOR

Robert V. Kerley, A History of Aircraft Piston Engine Lubricants, SAE Transactions, Vol. 90, Section 3: 810614––811014 (1981), pp. 2601-2628
www.jstor.org
 
I think the author is very mistaken.


From the 01-25CJ-2 P-40E-1 E&M (42-08-15- r44-01-15) 50 hour inspection includes


From an earlier undated (preliminary TO??) for the P-40D & E.

Given this manual has no TO number and lots of pages saying Will be furnished when available I would strongly suspect this is the preliminary first edition P-40 D/E manual issued when the first D/E models were on the production line so was written somewhere around April/May 1941.

 
gumbyk said:
Don't take it that way - they're all relevant questions, but the same info could be gained from one or two questions.
Click to expand...
I agree - good questions but make them more specific rather than using a shotgun


Some early engine manuals will contain the information you want but since early WW2 (or even earlier) the oil change and other maintenance periods were more often set by the airframe manufacturer as they know how hard the component is working, how much oil is carried, how hot it will be getting and all the other variables that the engine manufacturer has no control over and so the airframe maker can set the times that suit the application.

Think of it this way - an engine in a passenger aircraft that is doing very long flights is running at high power for maybe 5% of its life. It is spending probably over 80% of its life operating at its designed best operating rpm/boost/temperature/mixture/etc

The same engine in an interceptor is running at high power for close to 50% of its life, overboosted, overtemped, running at full rich (because at high power settings the carb adds fuel to act as a coolant) and so obviously is going to need overhaul much much sooner. When the carb automatically adds fuel for cooling that also removes oil from the cylinder walls resulting in increased wear.

In each case the aircraft manufacturer knows what the engine will be doing so can estimate the internal wear on the engine and components so they will set recommended overhaul periods accordingly. On the airliner the mags may need changing between engine overhauls - on the interceptor the mags and starter etc will last through multiple engines.

Throw in operating in dust, or worse still fine dust, and overhaul lives drop dramatically.

Obviously from the above there is no one size fits all overhaul period for any military engine - it is very dependent on type of operation and where you are operating.
 
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Simon Thomas said:
This is an interesting article regarding wartime maintenance at Coastal Command : https://blog.aopa.org/aopa/2014/01/14/the-waddington-effect/
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That is an interesting article and quite possibly in part reflects the difference between operating the B-24 as a heavy bomber and as a maritime patrol aircraft

As a bomber it takes off and climbs to one altitude then throttles back below cruise power for formation form up and during "cruise" is being continuously adjusted to maintain formation etc. All these power changes cause differing wear patterns (many of the ww2 engines have rpm ranges that must be avoided and cannot be operated under certain rpm/boost combinations). Some of the power settings will result in the carb automatically adding fuel for cooling which removes oil from the cylinder walls resulting in increased wear.

As a patrol aircraft it is mainly operating alone at one power setting for long periods, never approaching the critical rev/boost combinations etc. The cylinders and oil will seldom overheat, it will be running full rich far less often, etc etc etc.

As such it needed less maintenance.

Add to that a crew that is less stressed because of formation flying, AA and fighters, and able to learn the "feel" of the particular aircraft and they will be more objective in their defect reporting.
 
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pbehn said:
Many of the individual questions have books written about them for each engine, and each one is a history. "Merlin engine" is just a general term, it was changed in all sorts of ways continuously during the time it was in service.
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As did all the other engines. Like the Merlin the Wright R-1820 more than doubled in horsepower during it's life. The oldest I worked on was just under 700 horsepower and un-geared. The latest I worked on was in the Grumman tracker and produced 1500+hp. If my memory is correct there were some less powerful versions as well.

With most/all manufacturers some models produced no more power than their predecessors but had considerably better operating reliability.
 
August 2019 BC (Before Covid), I attended an air show in Nampa, ID. One of the stars was Dottie Mae, a P-47D recovered from an Austrian lake, and restored in nearby Caldwell, ID. See photo and article. After watching Dottie Mae start up, which produced a whole lot of oil smoke, I asked one of the ground crew how often they change the oil. He said we don't change the oil in normal maintenance, we just add more.

This link describing Dottie Mae is from an air show in Chino, CA:

Living History Flying Day - P-47D Thunderbolt | Planes of Fame Air Museum

planesoffame.org
 

Attachments

  • P-47.jpg
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MiTasol said:
Throw in operating in dust, or worse still fine dust, and overhaul lives drop dramatically.
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An example of this is the Typhoon operating in summer over Normandy. The air filter system had to be changed as the fine dust over the
battlefield was wrecking the engines.
 
Most of those engines used oil at of rate of several gallons an hour (per engine for multi engine aircraft).
Even using a 52-75 US gal drop tank called for several gallons more oil in the oil tank.
It might be possible for a few ounces (or a few pints?) to last dozens of hours as the oil tank is refilled 10-20 times with fresh oil but old dirt oil wasn't a problem like cars even the 1930s cars.
 
I wonder what he considered "normal maintenance?"

MiTasol makes great points on his post #13)

With that said I would wonder what the manufacturer's original guidelines were for oil changes on a P-47D, I'd guess the traditional 50 hour increment. The reason why I ask is because to gain an airworthiness certificate for that aircraft, the owner/operator would have to present a maintenance program to the FAA and if the owner/ operator wanted to deviate from what the manufacturer specified in the original maintenance manuals, they would have to put up a very rational and convincing argument. I know on many turbine engines running synthetics, there are no oil change intervals, you just add oil as the engine consumes it providing it is not at an excessive level specified in the maintenance manual.
 

Gateway Aviation in Canada in the late 60s and early 70's when I worked for them had a strict policy of doubling oil changes (so every 25 hours instead of 50 on the Pratt's) and part of their oil change procedure was and oil dilution and to fill the oil tank with fuel and leave sit while doing other work (even if that was only cleaning the aircraft). When the tank was drained the first gallon or so was thick sludge. Same with the oil cooler.

We bought a "new" Otter with some 200 hours on its engine and on its post delivery oil change I had to change oil half a dozen times before the oil filter was clean enough for me to consider letting it fly. Most of those oil changes the oil cooler drain ran like tar. After five hours we did another oil change and the filter was loaded with carbon deposits and oil cooler still did not drain as clean as other aircraft in the fleet that were coming close to overhaul.

Just because there is no dust around does not stop the inside of the engines and oil system filling with combustion byproducts, varnish and other undesirable shit.

At the time Gateway were approved to run their 985, 1340 and 1830 radial engines 50% longer between overhauls than other operators and they had a lower overhaul cost than other operators because there was little or no baked on sludge inside the engine.
 
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