Turboprops in WW2?
David E. Powell
lower temperature and have a longer life than pure turbojets?
It would seem that if that was the case they could get better than
conventional performance with less maintenance and longer service life
of the engine components.
Didn't the Brits have a strong turboprop program after WW2, into the
late 1940s and early 1950s?
Gordon
wrote:
Jerries had a variant of the Jumo with big paddle props. Not past the
paper stage, as far as I know.
Dan
Dan, U.S. Air Force, retired
Gordon
> Jerries had a variant of the Jumo with big paddle props. Not past the
> paper stage, as far as I know.
I should amend that - THEY didn't take it past the paper stage. The
massive a m___f___ing LOUD Tu 95 Bear bomber is powered by the final
derivative of the Jumo turboprop; that design is essentially two Jumo
004s turning contra-rotating props. Quite probably the loudest
aircraft on earth.
G
Rob Arndt
powered by 2x Jendrassik Cs-1 Turboprops @1,000 h.p:
http://rareaircraf1.greyfalcon.us/picture/h6.jpg
http://tanks45.tripod.com/Jets45/Histories/Varga/Varga.htm
Jendrassik Cs-1:
http://tanks45.tripod.com/Jets45/ListOfEngines/img3/JendrassikCs-1.jpg
Designed by Gyorgy Jendrassik in 1938 the Cs-1 was the worlds first
working turboprop engine, first run in 1940 and hoped to produce 1,000
hp it never made more that 400 hp due to combustion problems. All work
on the engine was stopped in 1941 as the Daimler-Benz DB 605 engine
was to be made in Hungary. A plane was specifically made for the Cs-1
the RMI-1 X/H, which ironically was fitted with the DB 605 in 1944.
Next were the Brits with the Gloster F1Trent Meteor which flew after
VJ-Day:
http://tanks45.tripod.com/Jets45/Histories/Trent/Trent.htm
R.B. 50 "Trent"(turboprop):
http://tanks45.tripod.com/Jets45/ListOfEngines/img3/trent.jpg
http://tanks45.tripod.com/Jets45/ListOfEngines/img3/RB50_3.jpg
Based on a converted Derwent engine, the "Trent" was fitted with a
reduction gearbox and a five-blade Rotol propeller, having it's first
flight on 20/09/1945, fitted on a converted Gloster Meteor Mk-I. This
primitive turboprop engine was designated RB.50" Trent". It however
left much to be desired, but as an experimental engine it provided
much useful feedback. The "Trent" name would be used again for a more
successful turboprop engine.
Other turboprop:
Armstrong Whitworth ASX:
http://tanks45.tripod.com/Jets45/ListOfEngines/img3/ASX.jpg
Designed in 1942 and built in 1943. The AWX was a 14 stage axial-flow
engine making around 2,600 lb of thrust. Never used in any production
aircraft, how ever it was developed into a turboprop engine delivering
3760 hp, known as the ASP and given the name "Python". This engine was
fitted into the Westland "Wyvern"
Germans were last with two turboprop proposals:
A) Daimler-Benz 109-021 (turboprop):
http://tanks45.tripod.com/Jets45/ListOfEngines/img3/DB022.jpg
The development of the Heinkel He S 011,as a base for a turboprop
engine. The engine was acquired from Heinkel-Hirth (He S 021) due to
Heinkel's work overload. It was hoped to fit the engine in the Arado
Ar-234 and Me-262B-2a
B) Junkers Jumo 109-022 (turboprop):
http://tanks45.tripod.com/Jets45/ListOfEngines/img3/Jumo-022.jpg
One engine made by 1945, but it's development was continued by the
USSR under the name NK-12:
http://tanks45.tripod.com/Jets45/ListOfEngines/img3/NK-12.jpg (Tu-128)
NK-12 led to all manner of Soviet postwar turboprops that led to the
Bear's!!!
Rob
guy
David E. Powell wrote:
As Rob mentioned RR flew a Trent Meteor both with normal props and
later with the props cropped, I have not seen tne reason for this but
I suspect it was simply testing different variations of power
distribution through the prop and jet thrust. The reason for the
interest in the turboprop was much more to do with fuel economy
(=range) than service life. Service life of the Derwent was not a
problem, unlike the German engines, which had problems due to material
shortages.
Probably the best early turboprop was the RR Dart whose compressor was
apparently derived from the supercharger of the RR Griffon
Guy
David E. Powell
Thank you! I didn't know that, that' pretty cool. Very long lived
design, too. The metals and alloy improvements must have been huge in
that development, as German turbojets had short operational lives.
That is interesting.... Boeing B-29 and Junkers developments in one
plane.
Eunometic
wrote:
> Did the Germans or British work up turboprops in WW2? Would they be
> lower temperature and have a longer life than pure turbojets?
Junkers was developing a turbojet known as the 109-012 (TL), (or jumo
022) in many ways a scaled up Jumo 004 with 8 instead of six
combustion chamber cans, though due to its size a cast compressor
casing wasn't possible so a bit of trouble was expected there.
Thrust was expected to be 2780kp/6130lbs. Parts were made for a
prototype and a mock up completed but development was probably
suspended in December 1944.
A turbo prop derivative, the 109-022, was under development of this
engine: 4600shp and 1300kp/2646 thrust. It drove a big contra prop
and it is said that it and the German Junkers team that was forcibly
shipped back to the USSR more or less developed the NK-12.
The Russians tended to 'shadow' the Germans and take their best ideas.
BMW was developing the 109-018 turbojet with three turbine stages
which was expected to produce 3400kp/7500lbs thrust more or less a
scaled up BMW 003 apart from the tendancy towards multiple turbine
stages seen on German gas turbines towards the end of the war. The
109-028 (PTL) was the turboprop derivative which was to produce 4700hp
and 2200kp/4851lbs with 4 total stages. Work was started on the
compressor but it was destroyed by explosives, nevertheless much was
left and there are pictures of US personel inspecting it.
Heinkel Hirth had the 109-011 (HeS 011) turbojet under development (it
was benching 1150kp at the end of the war). When Daimler Benz was
ordered to stop development of the 109-007 turbofan they were ordered
to redirect effort into developing the 109-021 turboprop
based on this turbojet.
The HeS 011A was to have a thrust of 1300kp, the HeS 011B was to have
a thrust of 1500kp and they HeS 011C some 1700kp.
The Daimler Benz 109-021 was to have a power of 1950hp plus 500kp/
1100lbs thrust, Heinkel had its own version of this engine with a
simpler arrangment. One application of the 109-021 was to be a long
range patrol version of the Arado 234C. (a two seat pressurized
model)
A word on designation systems: the suffix 109 means gas turbine
engine, often just the manufacturers abbreviation is used.
>
> It would seem that if that was the case they could get better than
> conventional performance with less maintenance and longer service life
> of the engine components.
The turbine inlet temperature of the German engines BMW 003A-2 and
Jumo 003B-4 was about 700C to 720C.
As subsequent stages were added the temperature would drop and the
thermal stress would be less. However
the first stage would still receive full stress so I would not expect
any more reliabillity.
Gearboxes were another issue though those of around 2000hp were
probably not a challenge.
The Jumo 004B-1 used turbine blades of a krupp alloy known as tinidur,
in the more reliable Jumo 004B-4 these were hollow for the
purpose of cooling.
Tinidur was about 30% Nickel, 12% Chromium, 6% Titanium and balance
Iron. It was known that using a version of tinidur with a
Nickel content of 60% would have worked much better but the nickel
just wasn't available to Germany. This was part of the reason for
the low MTBO of the Jumo 004B-1 and Jumo 004B-4 of 25 hours (only the
hollow bladed Jumo 004b-4 got near this). Fairly early on Jumo
004B-4's started getting blades of another alloy called chromidur
(about 18% Chromium, 12% Manganese balance steel) to get rid of the
scare nickel out of the alloy. Nominally inferior chromadur blades
could however be formed by folding and welding on the trailing edge
whereas tinidur being an alloy with an austinictic grain structure
lost that structure if welded and was formed by deep drawing.
The BMW engines used a material called sicromal, sort of like tinidur
with half the nickel.
German metallurgists did continue to develop alloys: the BMW 109-018
was expected to opperate at 860C with a turbine life of 80 hours and
similar alloys should have let the Jumo 004 opperate for 150 hours
field and 500 lab.
In addition they experimented with ceramics and cermets (eg DUG an
material of alumina and iron) mainly for the turbine nozzles and
probably would have succeeded by 1946.
The material shortage was so severe that versions of the HeS 011 and
the BMW P.3307 (and engine BMW started work on that was to match the
HeS 011 which was experiencing problems) were to use turbine blades of
iron that were in effect disposable (2 hours opperation) which would
cover only 1 or 2 missions achieved by lowering inlet temperatures to
650C. (See the 2nd Anthony Kay book)
There was also work on water cooled turbine blades. These definitely
work and have been used commercially (in stationary form) but would
have needed radiators, evaporative leading edge cooling or a turbofan
style engine with heat exchangers in the bypass duct.
There was much work in gas turbines for ships, e-boats, power plants,
tanks since gas turbines were much easier to produce and could run on
fuels easily made with coal to oil technology. The Germans were
particularly keen to power tanks with these engines.
>
> Didn't the Brits have a strong turboprop program after WW2, into the
> late 1940s and early 1950s?
Like the Germans the British probably focused on jets as more
urgent.
The British had a superb alloy called Nimonic consisting of 80% nickel
and 19.8% chormium with
traces of zirconium that was developed around 1942 I think.
It was really the metallurgists that made jet propulsion possible, not
whittle or von Ohain,
Peter Stickney
> Did the Germans or British work up turboprops in WW2? Would they be
> lower temperature and have a longer life than pure turbojets?
As Gordon and Eunometic have pointed out, there were the Junkers in Germany,
with the Jumo 022, (Which almost got to the running stage) and the Rolls
Trent (A Derwent turbojet with a propeller tacked on) were early examples.
There also were the General Electric TG-100, Northrop Turbodyne, and a Pratt
& Whitney project to use a free-piston Diesel as a gas generator for a
turboprop.
Turboprops don't have any intrinsic advantage in durability over a pure jet.
Internally, pressure ratios and temperatures at the burner cans are the same
as the contemporary jets. and hot section components are under the same
stresses. While the tailpipe temperature of a turboprop will probably be
lower, this is due to the extra heat that's being extracted from the hot
gas going into the turbines to turn the propeller.
> It would seem that if that was the case they could get better than
> conventional performance with less maintenance and longer service life
> of the engine components.
Well, it doesn't actually work that way, and you have the added complication
of extension shafting and very high ratio stepdown gearboxes. As with
anything else, when the parts count goes up, the reliability goes down.
> Didn't the Brits have a strong turboprop program after WW2, into the
> late 1940s and early 1950s?
Yes, they did - although it really didn't gain them much in the long run.
When examined from the point of view of, say, the large recip powered
aircraft of the late 1940s, they appeared to offer improved speed and
altitude performance. However, as jet engines and our understanding of
transonic aerodynamics improved in the late '40s, it was realized that a
turbojet airplane capable of cruising at Mach 0.8 or above offered much
better range/payload/speed performance. The upshot of these studies was
that Boeing and Douglas skipped past turboprop airliners straight to the
Boeing 707 and DC-8, and Lockheed did not develop the turboprop
Constellation flown in prototype form as the Navy R7V-2/ USAF C-121F, and
developed the L-188 Electra for shorter stage lengths.
With a couple of thousand 707s and DC-8s built, vs. 85 Britannias and 43
Vanguards, history shows that they figured right.
--
Pete Stickney
Any plan where you lose your hat is a bad plan
LIBERATOR
> The Hungarian Varga RMI-1 X/H was the first turboprop a/c to be
>
> Jendrassik Cs-1:http://tanks45.tripod.com/Jets45/ListOfEngines/img3/JendrassikCs-1.jpg
>
> Designed by Gyorgy Jendrassik in 1938 the Cs-1 was the worlds first
> working turboprop engine, first run in 1940 and hoped to produce 1,000
> hp it never made more that 400 hp due to combustion problems. All work
> on the engine was stopped in 1941 as the Daimler-Benz DB 605 engine
> was to be made in Hungary. A plane was specifically made for the Cs-1
> the RMI-1 X/H, which ironically was fitted with the DB 605 in 1944.
>
> Next were the Brits with the Gloster F1Trent Meteor which flew after
> VJ-Day:http://tanks45.tripod.com/Jets45/Histories/Trent/Trent.htm
>
ROBBIE IS KING OF ALL KNOWLEDGE!!
Now comment on the space monsters disclosure!
Keith Willshaw
"David E. Powell" <David_Po...@msn.com> wrote in message
news:67b72984-3b80-43ac...@d70g2000hsc.googlegroups.com...
> Did the Germans or British work up turboprops in WW2?
The world's first turboprop was the Jendrassik Cs-1 designed by the
Hungarian mechanical engineer György Jendrassik. It was produced and tested
in the Ganz factory in Budapest between 1939 and 1942.
It delivered around 400hp but work on it was dropped when the factory
switched
to producing DaimlerBenz aero-engines
The first British turboprop was the Trent which flew for the first time in
Sept 1945
> Would they be
> lower temperature and have a longer life than pure turbojets?
>
Nope
> It would seem that if that was the case they could get better than
> conventional performance with less maintenance and longer service life
> of the engine components.
>
> Didn't the Brits have a strong turboprop program after WW2, into the
> late 1940s and early 1950s?
Certainly did and it was rather successful, unlike most of the British
aircraft
they were designed for.
Keith
** Posted from http://www.teranews.com **
Rob Arndt
the Varga X/H that you ignored as well.
I posted between Gordon and Euno and you ignore my contribution?
That's OK, people like you who claim you are morally superior, more
intelligent, and socially responsible are in fact Hypocrites far more
often then not.
Be nice if you gave the Hungarians some credit though instead of
historical omission ;)
Rob
p.s. Glad you support Euno- he's an Aussie Nazi who denies the
holocaust...
Peter Stickney
<snip - long list of German jet and turboprop projects, some of which ran>
> The turbine inlet temperature of the German engines BMW 003A-2 and
> Jumo 003B-4 was about 700C to 720C.
> As subsequent stages were added the temperature would drop and the
> thermal stress would be less. However
> the first stage would still receive full stress so I would not expect
> any more reliabillity.
This is incorrect, or at best poorly stated. The life and performance
limiting thermal stresses are at the entry point to the turbines.
While the work required to run the compressor and, in the case of a
turboprop, the propeller will lower the exit temperature, the lowered exit
temperature does not lower the stresses on the entry stages of the turbine,
which is the most likely failure point.
>
> Gearboxes were another issue though those of around 2000hp were
> probably not a challenge.
AS it turned out, they were more difficult than expected. Not only did the
gearboxes need to handle the power being fed into them, they also had to
handle the extreme step-down ratios (10:1 or 20:1) that were required to
get the propeller speed down to a usable level. This required small,
highly stressed gears that proved to be the most difficult part of tyboprop
development.
>
> The Jumo 004B-1 used turbine blades of a krupp alloy known as tinidur,
> in the more reliable Jumo 004B-4 these were hollow for the
> purpose of cooling.
>
> Tinidur was about 30% Nickel, 12% Chromium, 6% Titanium and balance
> Iron. It was known that using a version of tinidur with a
> Nickel content of 60% would have worked much better but the nickel
> just wasn't available to Germany. This was part of the reason for
> the low MTBO of the Jumo 004B-1 and Jumo 004B-4 of 25 hours (only the
> hollow bladed Jumo 004b-4 got near this). Fairly early on Jumo
> 004B-4's started getting blades of another alloy called chromidur
> (about 18% Chromium, 12% Manganese balance steel) to get rid of the
> scare nickel out of the alloy. Nominally inferior chromadur blades
> could however be formed by folding and welding on the trailing edge
> whereas tinidur being an alloy with an austinictic grain structure
> lost that structure if welded and was formed by deep drawing.
>
> The BMW engines used a material called sicromal, sort of like tinidur
> with half the nickel.
>
> German metallurgists did continue to develop alloys: the BMW 109-018
> was expected to opperate at 860C with a turbine life of 80 hours and
> similar alloys should have let the Jumo 004 opperate for 150 hours
> field and 500 lab.
If wishes were horses, then beggars could ride. (And if pigs had wings,
they'd be Pigeons.) By 1945, German metallurgists could expostulate in
their beer all they liked. The mines weren't being worked, and any metal
that was coming in from overseas was being dropped on them in lots ranging
from 25# to 22,000#.
>> Didn't the Brits have a strong turboprop program after WW2, into the
>> late 1940s and early 1950s?
>
> Like the Germans the British probably focused on jets as more
> urgent.
>
> The British had a superb alloy called Nimonic consisting of 80% nickel
> and 19.8% chormium with
> traces of zirconium that was developed around 1942 I think.
You've also left out Elginalloy (3% bismuth, 12% chrome, 2% moly, 80%
nickel) originally developed for watch springs, and
Hayes Stellite (Various levels of Cobalt, Chromium, and Tungsten)
Both of which existed well before the Second World War.
>
> It was really the metallurgists that made jet propulsion possible, not
> whittle or von Ohain,
Easier, perhaps, but not possible. Whittle and von Ohain were able to use
existing materials that fit their needs. While the Germans may have had
trouble making turbines that worked well and stood up to use, it should be
pointed out that the early Rolls Derwents and the Allison J33 started life
with TBOs (Time Between Overhaul) that equalled or exceeded that of the
highly stressed recips, such as the Rolls Merlin.
--
Pete Stickney
Any plan where you lose you hat is a bad plan
Eunometic
> Eunometic wrote:
>
> <snip - long list of German jet and turboprop projects, some of which ran>
>
> > The turbine inlet temperature of the German engines BMW 003A-2 and
> > Jumo 003B-4 was about 700C to 720C.
> > As subsequent stages were added the temperature would drop and the
> > thermal stress would be less. However
> > the first stage would still receive full stress so I would not expect
> > any more reliabillity.
>
> This is incorrect, or at best poorly stated.
I beg your pardon. What is incorrect about:
"However the first stage (turbine) would still receive full (thermal)
stress so I would not expect any more reliabillity."?
It just needs to be read in context. Context, rather than nit
picking. You're always welcome to add to my post or genuinely
clarify it since you are a genuine engine nut with real stuff to
contribute.
> The life and performance
> limiting thermal stresses are at the entry point to the turbines.
Let me clarify you as well. The peak stresses are at THE first stage
turbine. The thermal stress on the stationary nozzles(blades or inlet
guide vanes) of the first stage are even higher than that and despite
the lower mechanical stresses this area can be more prone to failure.
Subsequent turbine stages operate at progressively lower temperatures
and lower gas densities and therefore lower heat transfer.
> While the work required to run the compressor and, in the case of a
> turboprop, the propeller will lower the exit temperature, the lowered exit
> temperature does not lower the stresses on the entry stages of the turbine,
> which is the most likely failure point.
quite
>
> > Gearboxes were another issue though those of around 2000hp were
> > probably not a challenge.
>
> AS it turned out, they were more difficult than expected. Not only did the
> gearboxes need to handle the power being fed into them, they also had to
> handle the extreme step-down ratios (10:1 or 20:1) that were required to
> get the propeller speed down to a usable level.
The smaller German axial engines operated at jumo 004B-4 8700rpm jumo
004D 10000rpm ,
a lot less than the centrifugal types, such as the Derwent, which was
in the same
thrust category with 16500 rpm.
Turn downs of 5:1 to 6:1 are more the order there; with two stages
being an option.
It seems for the same thrust the German axial types ran at 66% the rpm
which is in effect
The far greater smoothness and lack of torque pulsations which are
carried through to
the propeller (which acts as the flywheel as well) should actually
simplify aspects of gear design and
> This required small,
> highly stressed gears that proved to be the most difficult part of turboprop
> development.
>
>
> > The Jumo 004B-1 used turbine blades of a krupp alloy known as tinidur,
> > in the more reliable Jumo 004B-4 these were hollow for the
> > purpose of cooling.
>
> > Tinidur was about 30% Nickel, 12% Chromium, 6% Titanium and balance
> > Iron. It was known that using a version of tinidur with a
> > Nickel content of 60% would have worked much better but the nickel
> > just wasn't available to Germany. This was part of the reason for
> > the low MTBO of the Jumo 004B-1 and Jumo 004B-4 of 25 hours (only the
> > hollow bladed Jumo 004B-4 got near this). Fairly early on Jumo
> > 004B-4's started getting blades of another alloy called chromidur
> > (about 18% Chromium, 12% Manganese balance steel) to get rid of the
> > scare nickel out of the alloy. Nominally inferior chromidur blades
> > could however be formed by folding and welding on the trailing edge
> > whereas tinidur being an alloy with an austinictic grain structure
> > lost that structure if welded and was formed by deep drawing.
>
> > The BMW engines used a material called sicromal, sort of like tinidur
> > with half the nickel.
>
> > German metallurgists did continue to develop alloys: the BMW 109-018
> > was expected to operate at 860C with a turbine life of 80 hours and
> > similar alloys should have let the Jumo 004 operate for 150 hours
> > field and 500 hours lab.
>
> If wishes were horses, then beggars could ride. (And if pigs had wings,
> they'd be Pigeons.) By 1945, German metallurgists could expostulate in
> their beer all they liked. The mines weren't being worked, and any metal
> that was coming in from overseas was being dropped on them in lots ranging
> from 25# to 22,000#.
Vulgarly put; I've been genuinely trying to uncover the German gas
turbine program development for years.
Perhaps you have a problem with that?
The German jet engines are sometimes dismissed by what I immagine are
triumphalists with the following statements.
1 They were unreliable therefore the technology was not as good as the
more belated allied ones.
2 That they did not influence post war developments.
In fact my researches have discovered the following:
1 It was known that alloys of tinidur with increased nickel content
from 30% to 60% would improve reliabillity of the turbines.
Increasing use of Nickel was infeasible due to the supply limitations.
2 The German engines used plain steel for hot section that need to be
made of heat resisting alloys: combustion chambers, exhaust gas ducts
and exhaust nozzles. Quite apart from the unreliability of the two
components made of heat resisting super alloys (turbine and turbine
nozzles) much of the reliability problems actually stem from the part
of the engine not made of 'stainless steel'. The variable area nozzle
'onion' could distend under heat and block the jet exhaust,
combustion chambers needed to be replaced at least every 25 hours,
injection nozzles every 5.5 hours and often these parts burned through
or failed because the cermaic coatings and heat treatments had to be
done properly or because.
3 The German researchers pioneered air cooling of turbine and turbine
nozzles to overcome their metals shortages and developed models
appropriate to predict heat fluxes to its use and the techniques were
studied by the victors post war.
4 There was a considerable program of ceramic and cermet development
to replace parts of the engine such as
disks, combustion chambers, linings. heat exchangers etc. While the
oxides were showing poor resistance to thermal shock, the carbides
were hard to fabricate the cermets were both strong and heat resistant
though their corrosion resistance was poor it was adequate for a short
running times. Again this research seeded allied research.
5 Apart from developing oxide and vitreous coatings, air cooling,
progressing ceramics to an almost usable state, water cooling basic
research on alloys was yielding success in producing alloys that both
improved on the existing alloys to provide greater life and opperating
temperature but continued to decrease dependence on scarce materials.
haraeus vacuum scmeltze and a research institute known as the DVL
(sort of a German NACA) developed some of those alloys.
>
> >> Didn't the Brits have a strong turboprop program after WW2, into the
> >> late 1940s and early 1950s?
>
> > Like the Germans the British probably focused on jets as more
> > urgent.
>
> > The British had a superb alloy called Nimonic consisting of 80% nickel
> > and 19.8% chromium with traces of zirconium that was developed around 1942 I think.
>
> You've also left out Elginalloy (3% bismuth, 12% chrome, 2% moly, 80%
> nickel) originally developed for watch springs, and
> Hayes Stellite (Various levels of Cobalt, Chromium, and Tungsten)
> Both of which existed well before the Second World War.
These alloys didn't work well for full sized gas turbines. They
worked for the turbines of turbo superchargers which are
tiny in comparison to full sized jet engines capable of powering an
airplane. BMW were for instance able to weld the roots to the disks
and produce reliable turbine blades for turbo superchargers but this
method failed when scaled up and forced them to anchor blades
mechanically. If you want to make a 1mm diameter gas turbine out of
silicon, as is being done, it would be the ideal material. If you
want to make it 5cm in diameter it wouldn't. If you want to use
satellite for a turbo supercharger for the 3 turbines on a R-3350 it
will work, if you want to use it for a J-79 or Avon it won't.
>
> > It was really the metallurgists that made jet propulsion possible, not
> > whittle or von Ohain,
>
> Easier, perhaps, but not possible. Whittle and von Ohain were able to use
> existing materials that fit their needs. While the Germans may have had
> trouble making turbines that worked well and stood up to use, it should be
> pointed out that the early Rolls Derwents and the Allison J33 started life
> with TBOs (Time Between Overhaul) that equaled or exceeded that of the
> highly stressed recips, such as the Rolls Merlin.
The reality was that the fuel proportioning control on these engines
eg Welland was poor and all but the most deftly handed throttle
opperation could lead
to over dosing of fuel and burnouts and shedding of blades. The wide
use of high temperature
alloys throughout the engine, available to the British, helped here.
BMW was able to obtain 200 hours life out of the BMW 003A-2 combustion
chamber which
was made of only mild steel. This left only the turbine which had to
be replaced (for recycling)
every 20 or so hours, something that could be done in two man hours
while the engine remained
on the wing.
Peter Stickney
> On Sep 30, 1:50 pm, Peter Stickney <p_stick...@verizon.net> wrote:
>> Eunometic wrote:
>>
>> <snip - long list of German jet and turboprop projects, some of which
>> ran>
>>
>> > The turbine inlet temperature of the German engines BMW 003A-2 and
>> > Jumo 003B-4 was about 700C to 720C.
>> > As subsequent stages were added the temperature would drop and the
>> > thermal stress would be less. However
>> > the first stage would still receive full stress so I would not expect
>> > any more reliabillity.
>>
>> This is incorrect, or at best poorly stated.
>
> I beg your pardon. What is incorrect about:
>
> "However the first stage (turbine) would still receive full (thermal)
> stress so I would not expect any more reliabillity."?
That part is correct. The preceding sentence - "As subsequent stages were
added, the temperature would drop and the thermal stress would be less."
Is, while in the strictest sense accurate, is misleading, since the stresses
that count are not at the back end of teh turbine cascade, but the front.
>
> It just needs to be read in context. Context, rather than nit
> picking. You're always welcome to add to my post or genuinely
> clarify it since you are a genuine engine nut with real stuff to
> contribute.
>
Not nit picking - just trying to add some clarity.
>> The life and performance
>> limiting thermal stresses are at the entry point to the turbines.
>
> Let me clarify you as well. The peak stresses are at THE first stage
> turbine. The thermal stress on the stationary nozzles(blades or inlet
> guide vanes) of the first stage are even higher than that and despite
> the lower mechanical stresses this area can be more prone to failure.
> Subsequent turbine stages operate at progressively lower temperatures
> and lower gas densities and therefore lower heat transfer.
Well, it would have been more accurate to state that the thermal stresses
were greatest at the entry point of the turbine assembly, which includes
(in some, but not all cases) guide vanes, and includes diaphragms and the
first rotating stage. But I was aiming at a non-technical audience - You
and I are not the only people reading this thread.
>
>> While the work required to run the compressor and, in the case of a
>> turboprop, the propeller will lower the exit temperature, the lowered
>> exit temperature does not lower the stresses on the entry stages of the
>> turbine, which is the most likely failure point.
>
> quite
>
>>
>> > Gearboxes were another issue though those of around 2000hp were
>> > probably not a challenge.
>>
>> AS it turned out, they were more difficult than expected. Not only did
>> the gearboxes need to handle the power being fed into them, they also had
>> to handle the extreme step-down ratios (10:1 or 20:1) that were required
>> to get the propeller speed down to a usable level.
>
> The smaller German axial engines operated at jumo 004B-4 8700rpm jumo
> 004D 10000rpm ,
> a lot less than the centrifugal types, such as the Derwent, which was
> in the same
> thrust category with 16500 rpm.
>
> Turn downs of 5:1 to 6:1 are more the order there; with two stages
> being an option.
> It seems for the same thrust the German axial types ran at 66% the rpm
> which is in effect
> The far greater smoothness and lack of torque pulsations which are
> carried through to
> the propeller (which acts as the flywheel as well) should actually
> simplify aspects of gear design and
Except, in practice, it didn't. Real working turboprops end up having, in
gas turbine terms, rather small mass flows, and thus, compared to pure
jets, have smaller gas generators. These end up requiring high shaft speeds
in order to run the smaller compressors hard enough to supply a proper
pressure ratio.
A GE T58 screams along at 44,600 RPM. Even the output shaft, (It's a free
turning engine) is clocking in at about 6000 RPM. In order to work in its
intended environment, you end up using a step-down ratio on the order of
50:1.
Even a fairly big turboprop like a Tyne is still cranking at about 15,000
RPM. The step-down ratio there is 15:1.
No problem whatsoever. And when you're correct (As, for example, your
statement of the projected thrust of the 109-007 at over twice that listed
by most references - examination of the engine from first principles shows
that there were translation errors in cascading sources) I'm not going to
dispute that. I do, however, find your Teutonophilia amusing, and your
tendency to Pop Smoke and Evade when pressed doesn't, as pointed out many,
many times by Geoff Sinclair, add to the weight of your argument.
Yes, the Germans had good Metallurgists. And they didn't have a lot to work
with. The thing is, After the Autumn of 1944, as German industry
re-organized yet again, and attempted to re-align itself to deal with the
reality of overwhelming forces closing on it from the East, West, and
South, with no ability to protect itself from air attack, how much of this
effort was actually going to produce results, and how much was noodling
away with the knowledge that at that point, it was busy work, keeping the
pressgangs from rounding up idlers, handing them a Panzerfaust, and
pointing them in the general direction of Poland?
Or, to be more specific - How many Jumo 004B-4s were built? How many were
accepted? How man actually made it out into the field, and got hung on
airplanes?
> The German jet engines are sometimes dismissed by what I immagine are
> triumphalists with the following statements.
>
> 1 They were unreliable therefore the technology was not as good as the
> more belated allied ones.
Belated? By early 1944, while the Germans were still trying to get anything
acceptable out of the Jomo 004 and the BMW 003, the Allies were already
running engines far in advance of the Germans, both in reliability and
performance. (GE J30, J33, and J35, Rolls Welland, Armstrong Siddely ASX,
Metrovick F2, Westinghouse J30). Rolls had gotten wind of the J33 and J35,
and launched the effort that became the Nene and the Derwent. At that
point, they were competing with the Americans, not the Germans.
I contend that the German jet engines were not as good because the
compressor and turbine aerodynamics were extremely poor, giving no surge
margin and poor efficiency.
> 2 That they did not influence post war developments.
There's no doubt that the SNECMA Atar series was a direct descendant of the
BMW engine program, or that the Junkers turboprop efforts influenced
Kuznetsov. It should be pointed out that after a brief flirtation with
transliterated German jet engines, the Soviets sought out British and
American technology.
Of the engines that I noted above as running in early 1944 (And stretching
it slightly to include the Rolls Nene and the Wastinghouse J34).
there were 4 engines that remained in production from 1945 through the
1960s. (J33, J35, J34, and the Nene(As the Soviet VK-1). These engines are
still in use.
> In fact my researches have discovered the following:
>
> 1 It was known that alloys of tinidur with increased nickel content
> from 30% to 60% would improve reliabillity of the turbines.
> Increasing use of Nickel was infeasible due to the supply limitations.
Which means what, exactly? The UK was using Nimonic from about 1943 onward,
and the U.S. was using Elginalloy and Waspaloy. Both Nickel-Chrome Moly
alloys. (With other stuff, like tungsten thrown in) High temperature
superalloys were hardly a secret.
>
I'm running out of time here. I'll address the later points tonight.