Survivability in Combat

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?

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