S.82 vs. Ju.52. Which one is the better transport aircraft?

[Shortround6]

How do you define "non-strategic materials"?

Oil was about the only thing in short supply in 1941 Germany. Plus munitions manufacturing capacity which was still being built and expanded from scratch.

Most everything was in short supply in Germany in 1941 and later. Somethings were in shorter supply than others. A Plane built of steel tubing and wood with little aluminium, as long as it did the job, would be an advantage. The SM 82 could do the job. What ever it gave up in payload compared to an all aluminium plane was a small difference compared to the advantage the retractable landing gear and better aerodynamics gave it over the Ju52.

A plane that could deliver more cargo/troops faster for the same fuel consumption would save on fuel as well as aluminium

 

[davebender]

Why do you say that? Unlike Britain and the Soviet Union, 1941 Germany was not short of aluminum.

 

[Siegfried]

The 1000-1200hp Bramo 323 (as used on the FW 200) was also available and more powerfull than the BMW 132 or Alfa Romeo 128 and might have been donated by the Germans to power the SM82 since the SM.82PW could take the PW 1830 post war, also the 1500hp Piaggio P.XII RC.35 radial engine, 1,120 kW (1,500 hp) as used on the P.108 was also available as well as the Piaggio P.XI as used on Italian fighters.

 

[davebender]

A derivative of the Bristol Jupiter engine which dates all the way back to 1918. I don't see that as a winning solution for a 1940s aircraft.

IMO Italy would be further ahead to purchase Jumo211 engines since Germany had a surplus of that engine type by 1942. With three 1,350hp Jumo211 engines the Sm.82 might make a pretty good transport. As would the Ju-252.

 

[Shortround6]

A derivative of the Bristol Jupiter engine which dates all the way back to 1918. I don't see that as a winning solution for a 1940s aircraft.

Aside from both being 9 cylinder radials there was little in common between a Bristol Jupiter and a Bramo 323, different bores, different strokes, different number of valves per cylinder, different construction from even a 1927 Jupiter let alone a 1918 version.

IMO Italy would be further ahead to purchase Jumo211 engines since Germany had a surplus of that engine type by 1942. With three 1,350hp Jumo211 engines the Sm.82 might make a pretty good transport. As would the Ju-252.

A 1000hp Bramo weighed about 1250lbs. A 1350hp Jumo went about 1450lbs not including radiators and coolant. Could be a difference of about 500lbs per engine.

 

[Denniss]

The Bramo 323 was not really known for fuel economy. On the positive side it could be boosted with C3 fuel to 1100 PS and with C3+MW-50 to 1200 PS for take-off.

 

[davebender]

So could any other engine. A Jumo-211 optimized for C3 fuel would probably produce 1,500 hp.

 

[Denniss]

So could any other engine. A Jumo-211 optimized for C3 fuel would probably produce 1,500 hp.

No, only engines able to cope with the higher boost pressures would benefit from this. The 211 was not designed for higher pressures, already reached limits earlier on and had to be strengthened for 211F/J series.

 

[davebender]

211 was not designed for higher pressures, already reached limits earlier on and had to be strengthened for 211F/J series.

Strengthened in what way?

 

[tyrodtom]

Why do you say that? Unlike Britain and the Soviet Union, 1941 Germany was not short of aluminum.

Germany might had plenty of bauxite ore to make aluminum from, but short of fuel to generate the electricity to refine it.

Even today 5% of America's electricity goes to refining aluminum, the % was much higher during WW2.

 

[Siegfried]

Strengthened in what way?

There was a jump in weight with the introduction of the Jumo 211F due to a strengthened crankshaft and I immagine a few other parts of the engine, pressurisation of the cooling circuit had produced the Jumo 211E. Weight went from about 620-640 to about 720kg. An intercooler and supercharger shroud (diffuser?) seem to have added a bit of weight in the 211J as well. At this point the engine seems to have had a higher power to weight ratio than the DB605, at least till its 1.42 ata rating came in sometime in 1943. It's fall of in altitude performanc seems to have fallen of faster than the DB605s.

An outright introduction of C3 fuel with modest mods seems to have added about 10% in power over B4 eg DB603A -> DB603G (1750 to 1900hp) or Jumo 213A -> Jumo 213B (1770 to 2000hp). However more agressive mods could achieve higher power levels eg by inection the fuel into the eye of the supercharger to create the emergency boost rich mixture and a charge cooling effect rather than just directly into the cylinders. That kind of mod seems to have taken the Jumo 213A from 1770hp to 1900hp on B4 alone.

Germany had plenty of coal for coking and electricity generation, however coal is an cumbersome labour intensive form of energy and if converted to liquid fuels the situation doesn't improve.

 

[tyrodtom]

Unfortunatly coal doesn't mine or transport itself, very labor intensive in that era. Making it into coke also took labor, all of which Germany had in short supply, even with all the slaves they had no scruples about working to death.

 

[Shortround6]

very few, if any, engines gained substantial power increases without some sort of beefing up. Heavier parts, different materials, different manufacturing techniques. The Allison went through several different crankshaft specifications. Some were manufacturing, like shot peening and nitriding but the last was a 27lb increase in weight, mostly in larger counter balances that allow for higher rpm. Trying to use an early war crankshaft without shot peening or nitriding at late war power levels is going to make for a rather short lived engine.
An engine might survive a few minutes of such abuse but it's chances of reaching it's nominal overhaul life are pretty slim. While it might be rare for combat fighters to go through more than a couple of engines some transports went through over a dozen engine changes. The cost/benefit ratio of using "boosted" engines for transports is a bit different than combat aircraft and trying to 'boost' older engines by using newer fuels is probably not a good idea.

 

[davebender]

The Jumo 211 design was just as new as the DB601 and RR Merlin.

 

[Shortround6]

Even with 150 octane fuel, you don't dump it into the tank of a plane with a Merlin III engine and crank the boost to 25lbs. Or try to run a 1941 R-2800 "A" series engine at "C" series power levels even with the same fuel as the C"C series. Same with the Wright Cyclone R-1820, While it eventually hit 1525hp using 115/145 fuel in the "H" series engines you can't dump super fuel into a "G" series engine and rune the same pressures/rpm.

And so on.

 

[Siegfried]

The Jumo 211J seems to have picked up and intercooler, perhaps this is the true source of the weight increase? The Two stage Merlin was over 100kg heavier than the non intercooled versions.

 

[davebender]

Even with 150 octane fuel, you don't dump it into the tank of a plane with a Merlin III engine and crank the boost to 25lbs.

I agree.

Engines designed for high octane fuel normally have a higher compression ratio and that's what I would expect for a Jumo 211 version designed for C3 fuel.

 

[Shortround6]

I agree.

Engines designed for high octane fuel normally have a higher compression ratio and that's what I would expect for a Jumo 211 version designed for C3 fuel.

For unsupercharged cars that is the right answer, for supercharged engines it is the wrong answer. The Merlin never changed compression ratio and the Allison was lowered from 6.55:1 to 6.0:1 in the last versions to allow more boost before detonation set in.
If you have an engine running at 60in of manifold pressure and then raise it to 80in of manifold pressure at the same rpm you are putting 33% more AIR and FUEL through the engine in the same period of time. Raising the compression ratio gets you more power per unit of fuel burned but it limits the amount of fuel you can burn per firing cycle.
The 1st problem with trying to dump late war fuels into a pre war or early war engine, even if it is the same basic type as a late war engine, and run it at late war power levels is that the pressures inside the cylinder go way up. The BMEP of a Merlin X running on 87 octane fuel was 181lb/sq in. The Merlin XX went to 209-238 depending on boost limit and by the time you get to the 25LB boost limit the BMEP is over 300. BMEP is Brake mean effective pressure. That is the mean pressure acting on the pistons (and everything else inside the cylinder) to deliver the rated power to the prop. IMEP is indicated mean pressure which is the pressure needed inside the cylinder to account for friction loss, pump losses and supercharger requirements and is much higher. Neither of these is peak pressure. Later Merlins had a revised crankshaft with a different oil flow pattern for better lubrication to the bearings to help handle the loads in addition to a few other changes. The Wright R-1820 got a new crankcase, new cylinders and new cylinder heads between the "G" and "H" models including 4 more bolts per cylinder to hold the cylinder to the crankcase.
The 2nd problem is cooling. Burning that much more fuel per second or minute means that much more heat that has to be gotten rid of. You MAY be able to overload a liquid cooled engine for a short period of time but aircooled aircraft engines didn't have much give to them. They were already running on the limits. Later R-1820s, R-2600s, R-2800s, Bristol Hercules engines and others had more cooling fin area or cooling fins of different materials than earlier versions did.

 

[Siegfried]

I agree.

Engines designed for high octane fuel normally have a higher compression ratio and that's what I would expect for a Jumo 211 version designed for C3 fuel.

This is the case for the DB series, which rather uniquely ran very high compression ratios of about 7.3 for B4 (87 octane versions) and 8.4 for C3 (96/100) versions.

Most other engine Jumo, Griffon, Merlin, Allision ran ratios of around 6.3 and gain power by agressively supercharging their engines. The DB didn't need to do this, in fact was less capable of doing it.

This meant the DB supercharger could be relatively small and its efficiency was less important. It's purpose was not to overboost the engine so much as to compensate for altitude. This is why the
DB seems to have had good altitude performance on only a single stage supercharger.

 

[davebender]

DB series, which rather uniquely ran very high compression ratios of about 7.3 for B4 (87 octane versions) and 8.4 for C3 (96/100) versions.

What about the DB605D which produced 1,850hp with B4 fuel and 2,000hp with C3 fuel? As far as I'm aware it was the only WWII aircraft engine designed to work well with both low and high octane fuel.