(ArtKramr) wrote in message ...
Subject: Survivability in Combat
From: "The Enlightenment"
Date: 12/7/03 5:12 AM Pacific Standard Time
Message-id:
"ArtKramr" wrote in message
...
Let's take two planes going on low level support missions. They will
have to
fly through heavy ground fire including small arms fire. One plane
is equipped
with a radial engine,. let's say an R-2800. The other with a jet
engine. Which
plane would have a better chance of survival inder these
conditions?. Opinions?
Regards,
Arthur Kramer
344th BG 494th BS
England, France, Belgium, Holland, Germany
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer
Much of the Structure of a Gas turbine is thinner than that of the
rugged engine blocks, cylinder and heads required on piston engines
and thus penetration into a vital component by projectiles may be more
likely however gas turbines can be quite tough. The central casting
of which the shaft and combustion chambers are suspended is quite
solid and centrifugal compressors can be very rugged.
It might be possible to obtain data as to how influential compressor
type is on combat ruggedness.
I suppose that the best comparison might be to assume an aircraft such
as the B26,A26 or B29 had of been equipped with a turboprop like the
Rolls Royce Dart. (Fokker when designing the F27 (built latter by
Fairchild) resisted American Airlines's pressure to use the PW2800.)
This engine would have about 1/2rd the weight and I suspect 1/2 to
volume of the PW2800 and this in itself would reduce its chance of
being hit. The two stage centrifugal compressor was very rugged and
for the weight saved you could wrap the engine in armor.
The Allison T53 gas turbine used on the UH-1 Iroquois and many other
aircraft had a reputation for ruggedness. It kept operating with
objects like bolts ingested and stuck in the compressor. This engine
had as a first stage an axial compressor, a second stage centrifugal
stage that led to a double reverse flow combustion chamber.
The Germans seemed to have had a concern with debris ingestion
(presumably after a hit on a target) in the Jumo 004B engine of the
Me 262. For ground handling and safety reasons wire baskets had been
developed to prevent unfortunate ground crewman being ingested. The
aircraft was tested in flight with the baskets attached and apparently
suffered no reduction in performance.
The concern of 'combat ruggedness' was one reason that the RLM
technocrat Helmuth Schelp (who mapped out Germany's 15 year gas
turbine development program in 1938?) specified that the Heinkel
Hirth He S11 1300kg turbo-jet was to have a 'diagonal compressor'.
This is essentially a centrifugal compressor faired such that the air
flow exits axially (backward) instead of radialy (outward). The air
is then impinged upon a stator to get a degree of axial compression.
In the He S11 there were then 3 subsequently axial stages.
The beauty is that the ruggedness of centrifugal compressor in object
ingestion and turbulent airflow as a first stage can be combined with
subsequently more axial stages of higher efficiency. (Thus He S11
aircraft designees had very flexible air intake shapes e.g. slits in
wing leading edges )
The efficiency at the operating point for the axial unit of the Jumo
004B was 0.79. For the hybrid diagonal-axial He S11 it was 0.8. By
the time the He S11 entered production in 1945 the diagonal compressor
for the BMW 003C the HERMESO I was achieving 0.85 on the test stand
and the HERMESO II of the BMW 004D was expected to achieve 0.91. (By
this time the Germans were converting to more efficient reaction type
axial compressors over the impulse type axial seen on the Jumo 004B
and BMW 003A then in service) so they sacrificed a lot to achieve this
diagonal/compressor on the He S11.
The British style centrifugal compressors, the double sided impeller
types, must have been much more rugged than the axial types they
Germans preferred (for their low frontal area and ease of
installation)
However a shrapnel or bullet hole in the post combustion area of a
combustion chamber in either type of engine would have been fatal as a
flame would be expelled that would eventually melt or burn through
something. A holed combustion chamber or rocker cover was unlikely
to be fatal in an air cooled radial.
The answer clearly is to try and armor parts of the Jet engine, e.g.
the Chance Vought A7 used silicon carbide. Jets are free of the
oil water cooler problems of piston engines.
Lots of good info. Thanks. I woiuld love to hear the take on all this by a
pilot who flew Jugs in WW II in low level operations then flew jets
later and hear comparative opinions. Any jugheads around here?
It's not inconceivable that some US WW2 types such as the A26 might
have seen action with turbo props or suplemental jets slung on for
extra speed and power. Jets simply lacked the fuel efficinecy for
many missions. (Several types such as the B36,Neptune and others)
There is a Rolls royce Dart Restored Mustang out. (The Dart ranged in
power from 1650shp to 4000shp). I've found at least one restoration
attempt:
http://www.p51.mustangsmustangs.com/.../A68-187.shtml
I recall reading an article in the last 2-3 years in "wings" on the
development of the P47 the designer (Seversky?) discusions with his
development insiders (Probably at coffee break). Lots of interesting
stuff on why he concluded that the aircraft had to be as big as it did
to do the missions and carry the armour and armament that would be
needed. (Sorry the issue is in my dusty attic and my hay fever tells
me not to go have a look)
At one point the P47 designers get around to saying that if they are
going to have turbo-super chargers that they may as well cut out the
piston engine in between. Presumbly to get Jet thurst or to make a
turbo-prop. (Indeed converting automotive turbocharges into jets and
turbo props is a common hobby pursuit these days)
Any of the Jets of the 1940 period could be modified to turbo props
simply by putting on a gearbox and a bigger (perhaps 2 stage) turbine.
The british centrifugal types were a little more suited to conversion
as the airflow path is simpler as it need not be smooth so the ducting
needed around the intake needs less care. (The axial engines of the
Germans were so much narrower it was much easier fitting them to a
wing though)
The US was doing some good work at the time, I'm just not as familiar
with it.
Quite suprisingly Hungary had a turbo-prop in 1940 that was to go into
production.
http://tanks45.tripod.com/Jets45/Lis...ginesOther.htm
"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"
One big problem in any gas turbine was that designing the airflow in
combustion chambers needed extensive test stand experience. The
airflow has to be designed to protect direct flame impingement of
flames on metal by using films of air and a controlled flame
propagation. The Germans, Americans, British, Hungarians all faced
that. The Germans faced with horrible materials to use had the best
test stand facilities of all.
During the second world war the Arado 234 seemed to have no problem
with AA artillery even over the radar directed proximity fused guns in
the British isles. 10,000 meters at 400 knots would have meant that
the aircraft would have travelled almost 3km-5km ( 2-3 miles) before
a shell got near.
Attacking the bridges at Remagen was different and many a Arado pilot
lost his life attacking these bridges due to the super intense AAA at
low altitude. The engine once holed seemed to keep going by some
accounts) but rapidly set the whole wing on fire. (Fuel lines and
Hydraulic lines everywhere) Escaping from an Arado was very difficult
and the ejection seats intended for the awkward to egress cabin never
got fitted to the few production aircraft.
Having said that even getting near the bridges for a piston engined
aircraft must have been near to impossible.
FOI (Foreigne Object Ingestion) is an issue on jets especialy axial
types. Northrop tested the intakes of the F17 (ie F/A 18) by
sprinkling cornflakes on the floor.
The Mig 29 shutters of its intakes with a mesh and draws in airflow
via gills in the top of the intakes on the ground.
The material used probably make a difference. Using steel rather than
Aluminium.
Regards,
Arthur Kramer
344th BG 494th BS
England, France, Belgium, Holland, Germany
Visit my WW II B-26 website at:
http://www.coastcomp.com/artkramer