Back in the early 30's bombers were still crude: The were meant to take off, cruise, drop
bombs, cruise possibly fend of fighter with machine guns and land. This was
quite the same approach as in the First World War. In fact, night bombing
(which happened to small extent in WW1) was included, but not exactly popular
due to poor accuracy. This dominant bomber concept was so crude that Ju 52/3m
passenger aircraft were adaptable as auxiliary bombers.
This primitive model of a bomber was shaken
in the 30's by two new concepts; the dive bomber (for better accuracy of bomb
drops; notably the Ju 87) and the fast bomber (for avoiding
fighters; notably the early Blenheim,
early Do
17 and SB-2).
Tupolev SB-2.
Skin by Karel Chvojka, 3dz by Captain Kurt mod. by Karel C.
The machine gun defence proved to be
unsatisfactory. It was difficult to add more defensive machine guns, while
fighters increased their weaponry from two to up to eight machine guns. Armour
plating, armoured windshields and self-sealing fuel tanks plus the increasing
strength of airframes reduced the effectiveness of normal machine guns.
Fighters were able to cope by adding 20 mm autocannons, while the same calibre
was very unwieldy in movable installations for bomber defences.
Bombers needed better survivability than
armour and machine guns could afford. Four approaches promised relief; flying
higher, flying faster, flying in darkness and flying with escort fighters.
To fly higher was no good solution (for
bombers) because of the inherent accident and reliability issues (due to
freezing temperature), added aircraft cost, low payload and poor accuracy of
bombing runs.
To fly faster was a questionable solution (for bombers) because it was a time of rapid improvements of top speeds in aviation. A bomber prototype could easily fly faster than all contemporary fighters and still find itself to be much slower than hostile fighters during a war only a few years later. The Mosquito was later on successful with this approach, but only so because it faced opposing forces that were limited in their performance (especially at high altitude) in part by an inferior raw materials base. Propeller aircraft were also bound to meet the limit of their potential at about 800 km/h, and without the introduction of turbine engines we'd have seen an air war scenario in which almost all aircraft would have had a very similar top speed again (as they had already in WW1).
To fly in darkness meant high training and
avionics costs, a high accident rate and a typically poor accuracy.
To fly with escort fighters proved to be
most successful, but that wasn't about bomber design itself.
- - - - -
Reconnaissance aircraft of the late 30's looked still a lot like First World War
reconnaissance aircraft, but they had badly fallen behind fighters in both
cruise and top speed. The Hs 126 is a typical example. The poor survivability
of such recce aircraft called for new approaches.
One approach was to fly higher - this
proved less problematic for (photo) reconnaissance than for bombing, and the Ju
86P was one of the extreme examples.
Another approach was to fly faster, and
this worked for recce better than for bombing simply because air forces needed
fewer recce aircraft and the fast fighters could be adapted to photo
reconnaissance. The Spitfire PR versions are a good example, also the F-4/-5/-6
U.S.A.A.F. aircraft and the Bf 109 and Fw 190 with recce kit (a specific
"Rüstsatz"; mission module). There were also successful two-engined
reconnaissance aircraft and even some dedicated fast photo recce aircraft.
The highly successful Japanese Mitsubishi Ki-46 III
high speed photo reconnaissance aircraft
To fly in darkness proved to be a niche
escape, for both illumination/flash bombs and infrared photography were
apparently not fully satisfactory.
To fly with escort fighters - a typical WW1
approach - was unsuccessful because it was both uneconomical and because the
ground control for interceptors enabled the defenders to face such a recce
package with altitude and numerical superiority just about every time. This in
combination with the fact that a single recce aircraft suffices to make photos
while a single bomber doesn't suffice to bomb a target properly defined the
recce aircraft as unique. They were usually alone on their missions. This
influenced which survivability strategies did work and which didn't.
A unique alternative for battlefield recce
aircraft was to fly too slow. Fighter had advanced in top speed at the cost of
aerodynamics that led to a high stall speed. The Fi 156
was very successful as a short range battlefield reconnaissance aircraft in
part because even fighter aces had difficulties to get a Fi 156 into their
crosshairs if they managed to do it at all. It was just too damn slow and
agile. The same effect was observed in trial mock dogfights against Fl 282
helicopters. Very slow recce aircraft were only suitable for very short range
aerial recce and very vulnerable to anti-air weapons, though.
The next analysis is about fighters.
There were basically two directions for fighter philosophies in the 30's; the
manoeuvrability school (Italians, Japanese, Czechs) that emphasised dogfights
and even aerobatics (overall a similar philosophy as in WW1 air combat) and the
high speed school (Germany) that emphasised a superior speed. The Russians
initially followed both schools with their I-16
(fast monoplane) and I-153 (more agile biplane).
The high speed school was typically
combined with low drag liquid cooled engines that were less powerful than
radial engines (during the 30's) and did thus initially lack a superiority in
climb rate over the more agile fighter designs. Liquid-cooled engines caught up
with radials when radials grew to the limits of single radials (the solution
was the double radial engine, but that brought cooling issues) at the end of
the 30's. By 1939/1940, both liquid and air cooled engines were at about 1,000 to
1,300 hp. By this time liquid cooled engine-driven fighters had caught up with
comparable radial-driven fighters in climb rate.
The whole competition changed during WW2.
The high manoeuvrability school lost out in Europe; faster fighters were
dominant because they chose when to fight and only they were able to cope with
fast bombers. The Japanese stuck to the manoeuvrability school with few
exceptions, Italy did too (and failed for several reasons) and the British did
at least keep a better manoeuvrability than Bf 109 fighters.
The new conflict was different than the
1930's conflict between fighter philosophy schools: All fighters had to have a
similar top speed to be competitive, but they proved to have different
manoeuvrability strengths.
The vertical air combat manoeuvrability
school emphasized climbing and diving and in some cases also a high roll rate.
The horizontal air combat manoeuvrability school emphasized tight turns and a
low stall speed. The vertical school won, as evidenced by the Fw 190's success
over Spitfires and the 1943-1945 success of U.S. fighters against most Japanese
fighters. The reason was simple; the vertical school was again dominant, for it
was the key to offensive manoeuvres. The horizontal manoeuvring was only at its
premium in defensive manoeuvring and at very low altitudes.
Vertical air combat manoeuvre example: A Bf 109 expert
vs. defensive fighter ring
To fly tight turns was mostly about shaking
off a pursuing fighter (and had little chance of success if employed offensively),
while climbing and diving was mostly about attacking a fighter (often with the
deadly advantage of surprise). Defence may be stronger than offence most of the
time, but offence is decisive. The vertical air combat manoeuvrability school
was furthermore still potent in numerical inferiority situations.
Another division between fighters was
between fighters for high altitude and for low altitude. Eastern Front and
Pacific air wars were mostly about low altitudes, while Western European air
combat was mostly about high altitudes. There was a spiral for ever greater
practical flight ceilings whenever high altitude combat became dominant in a
theatre. The Allies won this race in 1942-1944 thanks to the British lead in
two-stage superchargers and the American ability to supply the necessary
heat-resistant alloys for turbochargers. The Germans trailed in both regards,
but jumped far ahead in 1944 with turbojet engines (even though they lacked
heat-resistant alloys and had a very short lifespan, poor reliability and
handling characteristics).
It's also possible to divide between short
range and long range fighters; long range was important for escort fighters and
over the vast expanses of the Pacific theatre, while short range was sufficient
for interceptors and fighters supporting ground warfare.
- - - - -
The
post-WW2 period saw competing philosophies for fighters as well:
# Short
range ("WVR") vs long range ("BVR") air combat
# Short
range fighters vs. long range fighters
# high
performance vs. huge numbers
#
pursuit of superior speed and altitude performance after the first Mach 2
generation (mostly MiG-25, later F-22)
# low
visibility to sensors ("stealth") vs. much external hardware
#
avionics with finesse vs. brute power avionics (example for the latter: MiG-25
radar)
- - - - -
It's interesting stuff (to me), but I'm not
so sure about the lessons.
Aircraft kept becoming more capable, more
refined, more oriented at their purpose.
There's an eternal development for better
survivability.
Superior offensive qualities tend to
dominate over the superior defensive qualities in air combat.
