A question about aero diesel engine in WWII (1 Viewer)

[Shortround6]

But what was the actual technical reason for not liking rapid throttle changes? Frankly I find those usual remarks in general literature dubious until someone produces a credible technical reason for such problems. I wonder if the experience with the Leyland engine (of 2-stroke opposed piston design) in the Chieftain tank would be of use...

My impression is that it had more to do with maintenance issues than actual response "times" in combat. Perhaps ring problems or oil consumption? The engines may have given adequate service in airline use but had shorter overhaul times when used for combat?

 

[davebender]

Why would a diesel powered heavy bomber have shorter overhaul times? Normally they cruise to and from the target at a slow and steady speed. Not much different then a Do-18 hauling mail to South America.

 

[Trilisser]

In general all engines in military servive have shorter overhaul lives than their civilian counterparts. Even in the case of bomber the handling of the throttles will be more violent than in a commercial plane and the time limits for particular power settings may be exceeded which rarely happens in commercial service.

 

[Shortround6]

Why would a diesel powered heavy bomber have shorter overhaul times? Normally they cruise to and from the target at a slow and steady speed. Not much different then a Do-18 hauling mail to South America.

As noted by Trilisser, bomber engines had a shorter overhaul life the same engine used in transports. Fighters were even shorter. There is no reason to suppose that diesel engines would follow a different pattern.

Only the Germans and Russians tried to use diesels in combat aircraft. While they did complete combat missions neither country found them satisfactory for combat use.

 

[davebender]

Pratt Whitney JT3D turbofan engine.

Pratt Whitney JT3D - Wikipedia, the free encyclopedia
Major applications.
B-52H heavy bomber.
Boeing 707 passenger liner. Douglas DC-8 passenger liner.
C-141 cargo aircraft.
KC-135 tanker aircraft.

The same engine. Four different aircraft types. 8,600 engines have been built and they have been in service since 1959. So there must be all sorts of real world data for engine life.

What is the average engine life for each aircraft type?

 

[tyrodtom]

World war 2 bombers flew usually in close formations, for mutual support. That required a lot of throttle changes, that's not good for any engine.

Even when used in Vietnam, the B-52's formations were not in anyway what anyone would call close. The only time a B-52 would require any sudden throttle changes would be during aerial refueling.

Comparing modern jet overhaul times military versus civilian isn't valid when comparing the same for WW2 bombers verses civilian.

 

[davebender]

This engine was produced in massive numbers and used to power all sorts of aircraft. What was the average engine life for each aircraft type?

B-17 and B-24 heavy bombers.
F4F and P-36 fighter aircraft.
TBD Devastator torpedo bomber.
DC3 passenger liner.
C-47 cargo aircraft.
PBY Catalina naval amphibious aircraft.

 

[Shortround6]

The B-17 didn't use R-1830s.

The R-1830 was built in a variety of models over a number of years with improvements in materials and manufacturing techniques as time went on.

This also applies to the jet engines. It is also worth noting that the JT3D is a development of the earlier JT3C with many common parts. Service life increased drastically over the years in all aircraft types.

There are a few figures for the Merlin available from "The Merlin in Perspective-the combat years", Alec Harvey-Bailey, Rolls-Royce Heritage Trust. Make of them what you will.

In 1939 they are saying the life of a fighter engine was 240 hours and a bomber engine was 300 hours. For 1944/45 they are saying that the life of a fighter engine was 300/360 hours, bomber engine was 360/420 hours and transport engines 480/500 hours.

Please note the increased life rating (not always achieved) even with much increased max power ratings.

 

[NVSMITH]

-This link: http://www.oldengine.org/members/diesel/Duxford/avrange.htm will take you to some pages with technical information on early diesel aero engines.
-Both supercharging and turbocharging were tested but one has to remember the state of super/turbo charging before and during the war. The turbocharged Allison V-1710 only went to the P-38. That is one of the reasons the supercharged Merlin was such a popular replacement for the Allison.
-Naturally I can't find the information now, but there was at least one annual publication on diesel aircraft engines before WW2.
-This is off WW2 topic but there have been a number of recent experiments in producing small aircraft diesel engines. With modern technology the engine weights have come down considerably and the specific fuel consumption figures are still good.

 

[GrauGeist]

Simple mistake regarding the P&W R-1830...it was used in the B-24 while the Wright R-1820 was used in the B-17

 

[Shortround6]

I don't know about an Annual but Paul Wilkinson who did do the "Aircraft Engines of the World " series of annuals did publish 3 books on aircraft diesels between 1936 and 1942. I have not seen one so I don't know how different they are from his other books.

Edit> a few chapters of his 1940 book are on www.enginehistory.org

 

[krieghund]

I posted a few of his diesel engines from the 1941 edition.

 

[JetA4GA]

They were heavy. Because of the high cylinder pressures a diesel operates at they require heavier construction than a gas engine. The better fuel economy doesn't equal the combined engine+fuel weight of the gas engine until long flights are required. There was a lot of interest in diesels during the 20s and 30s but gasoline kept getting better allowing higher compression to be used in gas engines for better economy so the goal post kept moving. The diesels that were built needed careful maintenance and didn't like the frequent throttle changes that combat required.

We are in 2012, not in the 1920-1930s; Think of the 24 hr LeMans compression ignition (diesel) racing at 700-800+ [SHP] for 550 [lb] 5.5 liter (335 cu in) installed (0.7 [lb/SHP]) using lightweight materials/manufacturing technologies, common rail injection (chamber pressure control, startability, SFC, etc.), liquid cooled (i.e. higher power densities, stability, TBO reliability) dual channel FADEC, Jet A/A-1 fuels, etc.. For 2500+ hr TBO with this technology think of ~1.25/1.50 [lb/SHP] installed which favorably compares with the current AVGAS installations that are at equal or higher figures. Think also of the installed weight + total mission fuel advantage that is most of the time positive.

 

[swampyankee]

Do-18
Do-26
Bv-138
Bv-139
Bv-222

Blohm Voss and Dornier built quite a few seaplanes powered by Jumo 205 diesel engines.

1930s Dornier was probably the most experienced seaplane builder in the world. They must have had good reason to power the state of the art Do-26 with 4 Jumo 205 diesel engines rather then 2 Jumo 211 V12s.

One would be single-engine out performance. Say you need to maintain X rate of climb (I do not know what the German certification standards were). If you need a total of 1,500 hp to get the mandated climb performance with one engine inoperative, you can start with two engines, each 1,500 hp or four of 500 hp. The former may result in an airplane which is uneconomically overpowered, an important consideration for anything except short-ranged military aircraft. A second could be reliability: aircraft piston engines were (and are) much less reliable than turbines (they would not have had that comparison), so there was always a significant chance of engine failure in a long flight. Losing a quarter of the aircraft's required power is not quite so bad as losing half. Do note that the many long-ranged aircraft of the time had four engines, even if they could have been adequately powered with two (although, again, you can't replace four 500 hp engines by two 1,000 hp engines; you'd need to replace them with two engines of something like 1,500 hp), the designers, many of whom were very experienced in that most challenging of markets, commercial aviation, used four engines for long-ranged aircraft. Dornier may have been very experienced in designing seaplanes, but so were Boeing, Martin, Consolidated, Latécoère, Short, Sikorsky, and many of them converged, along with Dornier, to four-engines for aircraft designed for routine long-range, over-water operations.

 

[msxyz]

Had it been available in time, with all the issues resolved, the Jumo 223 would have been the ideal engine for any long range bomber.

More than 50 HP/liter and a very good SFC.

 

[R Pope]

Another factor may be the limited RPM range of a diesel. Not familiar with aero diesels, but a 3406 Cat, for instance, has a power band from 1500-2100 RPM. A similar power gas engine will have a band much wider, like up to 3300 RPM for a Griffon-like engine. That's one reason why gas engines remained common in tanks, the wider power band required less gear shifting. A diesel aero engine would require a much more sensitive CSU (governor) to adapt to throttle settings.

 

[razor1uk]

We are in 2012, not in the 1920-1930s; Think of the 24 hr LeMans compression ignition (diesel) racing at 700-800+ [SHP] for 550 [lb] 5.5 liter (335 cu in) installed (0.7 [lb/SHP]) using lightweight materials/manufacturing technologies, common rail injection (chamber pressure control, startability, SFC, etc.), liquid cooled (i.e. higher power densities, stability, TBO reliability) dual channel FADEC, Jet A/A-1 fuels, etc.. For 2500+ hr TBO with this technology think of ~1.25/1.50 [lb/SHP] installed which favorably compares with the current AVGAS installations that are at equal or higher figures. Think also of the installed weight + total mission fuel advantage that is most of the time positive.

Fair enough, but that are todays more developed diesels, back in WW2 however, where this thread is based upon, they didn't have all that accumulated tech, materials and design knowledge we have gained since then.

 

[Dogwalker]

We are in 2012, not in the 1920-1930s;

In this respect, it could be interesting to note that two Isotta Fraschini gasoline-fed aero engines of the '30s are still wit us, under the form of diesel marine engine. The W18 Isotta Fraschini Asso 1000 / L.181 became the CRM W18 (same bore, stroke, crankshaft assembly, ignition sequence, connecting rods, even the details of the valve train), probably establishing a record of an engine in production since 1927. The V12 Asso XI / L121 became the CRM Asso 1500 / Asso 2000 (bore and stroke are now those of the Asso 1000, but the rest remained pratically the same).
The max power is now of 2400hp at 2300 rpm for the W18 and 2000hp at 2300 rpm for the V12. However also the mass increased. Being marine engines, the weight considerations are less important than in aero engines.
crm spa motori marini

 

[swampyankee]

Another factor may be the limited RPM range of a diesel. Not familiar with aero diesels, but a 3406 Cat, for instance, has a power band from 1500-2100 RPM. A similar power gas engine will have a band much wider, like up to 3300 RPM for a Griffon-like engine. That's one reason why gas engines remained common in tanks, the wider power band required less gear shifting. A diesel aero engine would require a much more sensitive CSU (governor) to adapt to throttle settings.

This is probably moot; by the late 1930s, constant speed props were pretty much de rigueur for long-range, multi-engine aircraft. VDM, Hamilton Standard, and Curtiss all had them for sale in the mid-1930s.

 

[davebender]

I doubt the twin engine Do-18 would fly well with 1 engine out. Maybe on the way home with most fuel burned off but not immediately after catapult launch.