Are there any principle differences between turbochargers & turboprops?

[Aurum]

I can not get for a long time how it could happen that Germans built hundreds & even thousands of turbojet engins JuMo 004 & BMW 003 but did not have reliable turbochargers for their DB, JuMo & BMW piston engines to be mount on?



I guess that there are no principle differences & turbocharger is obviously less powerful then turbojet. But what was real cause of that situation I do not know.

[Crimea_River]

I think technically you are speaking of a jet turbine engine, not a turboprop. The engines you noted are not turboprops as there was no propeller attached.

[Aurum]

I think technically you are speaking of a jet turbine engine, not a turboprop. The engines you noted are not turboprops as there was no propeller attached.

Sorry. yes of course. I'll try to correct

[Aurum]

Its a pitty that nobody has any ideas of such situation...

May be somebody has spacs of General Electric turbochargers? I was unsuccessful to find them

[engguy]

Maybe the more exotic metals went to the jets, and the recips got what was left over.
What kind of specs are you looking for? It is more of a material type spec your looking for I think.
If you want specs on turbine engines that is easy to get. Just order an overhaul manual, and same for a turbo charger.
Its not going to give manufacturing specs, as some of that sort of thing is proprietary and not disclosed.

[Aurum]

What kind of specs are you looking for? It is more of a material type spec your looking for I think.

First of all I look for general tech specs. such as dimensions, rotation, boost, temp. before turbine, ets. It would be good of course to get info about materials. Materials used in german turbojets are well known.
I have such specs of japan turbochargers of several mod. but regarding US turbochargers - info now is absent!

[Denniss]

Turbochargers for high alt combat had a very low priority in germany although they did some experiments with aircraft like Fw 190C. Problem was not only the additional space and weight but also the rare metals to withstand the hight temperatures. LW high command did not expect to fight an attrition war at high alts and believed the mechanical superchargers were good enough. The superchargers were good indeed but LW failed to ask manufacturers for multispeed/multistage superchargers with good high alt performance.

The Jumo 004A jet engine was built using those rare metals but had to be redesigned into the 004B to use available but lower quality metals. The 004B was not known for it's great reliability or long service life.

[MIflyer]

The Germans had a huge problem with building either turbosuperchargers or turbojet engines. They lacked suitable quantities of nickel alloys that were required. While nickel is one of the most common metals in the Earth's crust, mineable deposits are fairly rare. The only one that came close to being under German control was in very northern Finland, and hard to get to under the best of circumstances. Even today, nickel is a relatively rare and valuable metal; in the 1990's the Russians even considered converting one of their Typhoon subs into an ore carrier to get nickel from arctic sources by going under the icepack.

In order to build jet engines in quantity with inadequate alloys the Germans had to sacrifice sevice life. The typical Me-262 or Ar-234 jet engine had a life of around 25 hours, and keeping track of how many hours an engine had was vital - so much so that when the Americans captured German jets after the war they often found the Germans had destroyed the engine records so to keep us from figuring out which engines were usable. Thus, even under non-combat conditions, flying captured German jets was like riding a time bomb. In combat it was even worse.

The Germans admired American turbochargers but did have the alloys to build them. They tried with the FW-190 and found you needed the alloys for not only the turbochargers but also the exhaust pipes leading to them. They tried substituting steel pipes with an aluminum coating (a method still used today) with less than stellar results.

This problem carried over to other weapons as well. The fabulous V-2 rocket engine used a cold gas reaction to drive the turbopump, using H2O2 in order to avoid the need for a high temperature gas generator. So did the Me-163 for its rocket engine.

And at first their need for high altitude performance was minimal. The FW-190 was noted for running out of power quite noticeably at around 25,000 ft and when Kurt Tank kept telling the Luftwaffe about his plans to fix that problem they replied, "Why should we care?" The RAF did not use much in the way of high altitude aircraft at that point (note that they had the turbosuperchargers yanked from the Lightning Mk.1). Then the USAAF 8th Air Force showed up in the summer of 1942 and it was a different story!

The Me-262 was never a real threat to the Allies because the Germans could never build enough of them or build them reliable enough to create a real threat. Hitler's famous "Build them as bombers" order never was a factor in the Me-262 attaining operational status, and probably was the correct use of the airplane in the summer of 1944, given its very limited numbers and limited service life. The USAAF alone shot down something like 175 Me-262's, far more kills than the German jets ever got.

As for info on US WWII turbos, I have some illustrated breakdown parts drawings.

[basil]

MIflyer, totally correct. In the first years of the war the RLM (Reichsluftfahrtministerium) didn´t lay much focus on high altitude performance, but this changed with the increased bomb raids by turbocharged B-17s and B-24s. Besides it was expected that it wouldn´t take too long to see B-29s over Germany which really would have stretched the high altitude performance of non-turbocharged fighters to the limit. As fighter (not bomber) engines were needed from 1944 onwards, calculations and trials showed that at high speeds (and high altitudes) the exhaust thrust from the piston engines in combination with high performance variable speed superchargers and charge coolers generated higher flight speeds for fighters than turbocharger installations.

Nevertheless there were some pretty advanced engine-integrated turbocharger and turbo compound designs by Daimler Benz (DB 621, DB 622, DB 623, DB 624, DB 625, DB 629 - most of them using the exhaust pulse engergy and not only exhaust pressure), by BMW (BMW 801 TJ - which used rather advanced hollow tubine blades for cooling, several BMW 802 versions with variable valve timing and turbocharging and turbocompounding) and by Junkers (Jumo 222 and Jumo 225 versions). But as mentioned by you, all work had to be laid on turbojet development during the last months of the war.

[N4521U]

You guys make for interesting and easy to understand reading... clears up a lot of the hocus pocus of the German jets.

[basil]

N4521U, if you are interested in a well written in-depth analysis of all German turbojet and turboprop projects until 1945 you should purchase "German Jet Engine and Gas Turbine Development 1930-1945" by Antony L. Kay. It´s the best book available regarding this topic.

[N4521U]

Well, I think you guys have given me a good overview. Not sure I need to get too in depth about it. I appreciate the source tho.
You've just made sense out of wondering why the 262 didn't make the impact it could have. Didn't know about the lack of resources that could have led to successful production of the plane.

Bill

[msxyz]

Heinkel Hirth engineerd a few turbochargers, at least one was employed operationally in the BMW801T (T stands for turbolader).

Their greatest contribution to turbine design was a viable method of keeping the blades cool enough not to incur in creep. As others said, Germany faced a severe shortage of Nickel. Nickel is the main constituent of heat resistant alloys (50-75%). Germany recognized this weakness and tried to develop alternative alloys. In the end, they came up with something called Chromadur, which was nickel steel (nickel accounting only for a few % of the total weight) alloyed with Chrome and Manganese (I think the percentage was 18% Cr and 15% Mn plus some % of silicon and titanium...) This material was heat resistant but creep resistance was not as good as high content Nickel alloys.

One big advantage of Chromadur was the ability to be cold rolled: this ability was used to create hollow blades: air bled from the compressor was then pumped through to keep them cooler. The solution was found to be satisfying for turbochargers and it was also adopted in the BMW003. One big problem encountered during early testing were harmonic vibration of the turbine... This problem was eventually solved by adopting an odd number of blades and redesigning their cross section.

At Deutsches Museum in Muenchen there is a complete BMW 801T still in its nacelle (the "Power egg") cut open. Visitors can have a good look at the Hirth turbochargers and their hollow-blade turbines.

I suspect Jumo 004 short service life has more to do with the more primitive nature of this engine and poor quality of the alloys available later in the war (Bramo/BMW and Hirth designs were more advanced although they suffered from teething problem such as the frequent flameouts). It should be also noted that a turbocharger recovery turbine is subject to less intense heat than that of a jet engine: all jet engines redirect some fresh air around the bearings and to the walls of the combustion / expansion chamber to prevent melting of the metal; a turbocharger can survive without.

[MiTasol]

Going back to the original question

A turbo charger uses the piston engine to heat the air from the compressor. The turbine then extracts as much as possible of the heat as energy and uses that energy to drive a compressor.
A turbo jet uses combustion chamber(s) to heat the air from the compressor and then extracts only the bare minimum energy and uses the balance of the energy to produce thrust