I can't really comment on the Typhoon as I am not familiar enough with the history of that design, but did the Thunderbolt really fail as an interceptor? More than anything the sort of fighters the USAAF and RAF required shifted over to designs able to perform as long-range escorts. The finely tuned engine variant used by the P-47M was a source of constant trouble, but I think it was quite capable at intercepting V-1s and other high-speed threats. I don't think the Soviets received a particularly large number of lend-lease Thunderbolts, but didn't they hold them in reserve particularly for use as high-altitude interceptors?
Were there any high-performance wartime prop fighters that didn't face big problems with compressibility in a high-altitude dive? It was a huge problem for the P-38 too which in many respects had very fine aerodynamics. Was it a slightly less of an issue on the P-51 due to the wing?
- In 1937, during a series of diving-flight tests conducted in the Rechlin test centre, one Messerschmitt Bf 109 B-0 pulled into the lake Müritz on 17 July. The Messerschmitt test pilot Dr. Kurt Jodlbauer was killed becoming in the first victim of the compressibility.
The odd aerodynamic phenomenon, usually defined under the term
compressibility buffeting was suffered by different type of aircraft diving between 25,000 ft and 18,000 ft, at different speeds and manifested itself in different ways.
The aircraft were suddenly out of control, the ailerons did not respond properly, the tail plane suffered a violent flutter and the control column jumped in the pilot hands as if alive. The whole airframe was under a high frequency vibration that sometimes caused catastrophic structural failures.
The cause of all this was an odd physical phenomenon known by aerodynamicists as
Coanda effect. It stated that any fluid running above a curve surface tends to adhere to it and increase its speed proportionally to its curvature.
On 4 November 1941 the Lockheed test pilot Ralph Virden was killed when his YP-38 broke up during a dive recovery test.
The problem with the
Lightning manifested itself at 0.675 Mach as a turbulence generated in the junction between the pilot nacelle and the wing. At 0.73 Mach, the disturbance reached the tail plane, pressing down the control surface that could not be operated by the pilot, to get the airplane out from the diving.
A number of P-38’s lost empennages and the aircraft earned a reputation as a pilot killer.
In the
Thunderbolt, the disturbance was generated by the cowling of the engine and tended to jam the tail plane at 0.805 Mach, with loss of control or even loss of the tail assembly.
On 26 March 1942 a structural failure on the rear fuselage of the P-47B caused the separation of the empennage and the test pilot George W. Burrell was killed.
The Mach critical number of the Grumman F6F was 0.75, in the Pacific theatre many
Hellcat pilots dived to their deaths because of compressibility.
In the P-51 D structural damage occurred at 0.85 Mach.
In the P-38 and P-47, dive-recovery flaps were the eventual solution. Both airplanes were equipped with an electrically driven dive flap that opened up to 35 degrees in less than one second. Its purpose was not to act as an airbrake, given that at 25,000 ft. it would not have produced a significant loss of speed. However, the turbulence generated when opening the dive flap, raised the nose of the machine and effectively took it off from the diving.
It is an accepted fact nowadays that the Allies designers never understood the true causes behind the compressibility phenomenon. At the end of the war, when they had access to the research conducted by the Germans on the areas of swept wings, the transonic flux, the Mach critical number of the air intakes with an air-flow separator for the boundary layer.
The cultural shock was similar to that one produced in the Newtonian world with the introduction of the relativistic physics.
The difficulty to understand these problems during the forties was due to the lack of tunnels for testing aerodynamic designs with supersonic capabilities.
The only way to study the supersonic performance of a scale model was to install it over the wing of a fast airplane and film it during a high speed dive. At that moment, the air reaches local supersonic speed over the wing, but the airplane has not yet got into the uncontrolled phase of the flight.
This type of research was dangerous and difficult to perform, rendering results that were either distorted by the vibrations of the carrier plane of by unclear films, due to the loss of transparency of the air caused by the turbulence.
In the spring of 1942 it became clear that Eighth Air Force bombers were suffering too many casualties during their daytime missions over Europe and had to be escorted by fighters.
On June 1942 the 31st Fighter Group was equipped with
Spitfires Mk.V, but its reduced range only allowed them to escort the bombers to Amsterdam, located just 175 thousand (280 km) from their bases.
In September, the P-38Fs of the 14th F.G. carried out some escort missions before being transferred to Algeria.
In December 1942 the P-47Cs began operating with the Eighth Air Force, these aircraft had an internal fuel capacity of 1,154 liters and could offer protection up to Paris.
At the time the
Luftwaffe had only 100 fighters in the Occidental Front and used to remain inactive until the
Thunderbolts began to retreat when they were 230 thousand (370 km) from their bases.
The P-47s participated in numerous combats over Ruhr during the spring of 1943, the heavy fighter could successfully face the Fw 190A above 14,800 ft (4,500 m) but was outperformed in climb rate by the German fighters.
At 10,000 ft (3,000 m) and 400 kph the roll rate of the P-47C was 84 degrees/sec and the Fw 190A was 160 degrees/sec. At heights below 3,000 m the
Thunderbolt could only survive thanks to its extraordinary structural robustness.
The P-47C could reach Frankfurt fitted with a drop tank of 409 liters, but this equipment was not available until September 1943.
During the fall the
Thunderbolts began using a new type of 625 liters ventral drop tank, but even this was not enough to prevent the bombers from paying a high price to reach Berlin by being attacked with impunity by the German fighters.
Between January and November 1943 the
Jagdwaffe had increased the number of aircraft on the Western Front from 670 to 1,660.
The
Mustang was considerably cheaper ($58,698) than the P-47 ($104,258), had an escort range of 748 thousand (1,200 km) and could protect bombers over Berlin and even Prague. It was also faster than the P-47 and surpassed the Fw 190 and Bf 109 G in dog fight at any altitude. In mid-1944 the USAAF decided to equip with P-47 thirteen Fighter Groups of the 9th Tactical Air Force considering that strong airframe and powerful armament of the
Thunderbolt would be very useful in strafing missions.
Acting as fighter-bombers, the P-47s managed to destroy 3,315 airplanes (in the ground), 9,000 locomotives, 86,000 wagons, 6,000 armoured vehicles and 68,000 trucks, after the
Mustangs achieved the air superiority over the Reich.
In November 1941, a number of
Luftwaffe fighter-bombers Messerschmitt Bf 109 F-4/B from the 10.(Jabo)/JG2 and 10.(Jabo)/JG26, based in Caen/Carpiquet, started operating on the Channel Front attacking shipping and port towns, with SC 250 bombs, around the south-east coast of England.
To meet the menace the
Typhoon was prematurely pressed into service while still so unprepared.
The massive
Tiffie proved to be 40 mph faster than the
Spitfire Mk.VB (below 20,000 ft) and the Air Staff hoped that it could successfully face the Fw 190, despite their disappointing climb rate, lack of performance in altitude and unreliable power plant.
The morning of 6 September 1942, the British radar positioned along the Eastern coast of the island, detected several airplanes coming from Southeast.
They were six Messerschmitt Me 210 A-1
Zerstörer of the 16./KG6 that had taken off an hour before in a
Frei Jagd mission from the Dutch base of Soesterburg. The Me 210 was the most modern of the
Luftwaffe fighters. Their crews, coming from units of Bf 110, had just one month experience with the new model and were in their first operational sortie.
Several Hawker
Typhoon Mk.IB of the RAF No. 1 Squadron (code JX) went out to intercept them. The unit, based in Acklington, had exchanged their
Hurricanes by the
Typhoons in July and this was also their first combat with the new Hawker model. The Zerstörer was very fast - 350 mph at 17,820 ft. - and the
Typhoons flew at 412 mph at the same altitude.
It was a difficult interception with the British starting a steep dive at 30,000 ft. to gain speed. In the rarefied air the 7 tons machines accelerated violently and when reaching 25,000 ft, with the instruments reading 450 mph, the aircrafts were actually flying at 675 mph. (Mach 0.64). At this point, the
Typhoons were suddenly out of control. The ailerons did not respond properly, the horizontal tail plane suffered a violent flutter and the control column jumped in the pilot hands as if alive.
The whole structure was under a high frequency vibration, transferring to the pilot a feeling similar to an electric current, and the air that circulated through the radiator went in the opposite direction than usual!
At Mach 0.75, a shock wave was formed above the wings and the air around the cockpit went white. At 20,000 ft, the denser air started to restrain the airplanes, but when reaching 18,000 ft. in a most puzzling way, the controls were again working fine.
Even after such a terrifying experience, the British pilots still had the courage to reach two
Zerstörers (2H + HA and 2N + CA) and shot them down over Yorkshire.
Back in Acklington, they reported the deficiencies and the pilot notes had to be rewritten.
Designed for structural strength, the wing of the
Typhoon was very thick (18% thickness/chord ratio) and in the superior curvature the air flux made itself locally supersonic at 0.64 Mach, producing a shockwave and, therefore, huge structural charges in the tail and in the rear section of the fuselage.
During the air battles with the Fw 190, some
Typhoons suffered structural failures in the tail assembly and others failed to pull out of their dives, or simply vanished while flying over sea.
No less of 155 such failures occurring and evidence was slowly accumulating on the transport joint just forward of the tailfin.
To strengthen this point, engineers made a wreath of 20 fishplates bolted around the suspect joint, but the problem was not completely solved after 26 deadly accidents, the decision was made to abandoning the primary task for which the
Typhoon has actually been designed.
On the second half of 1942 their role was changed from low-level interceptor to a fighter-bomber and night intruder, during full-moon periods.
The I-200 high-altitude Soviet interceptor was designed in 1939 by the Polikarpov Design Bureau, inheriting all the deficiencies of its lineage and thus proving the correctness of the Latin sentence
Errare humanum est, sed perseverare, diabolicum. (To err is human, but to persist is diabolical).
The extremely short fuselage had originally been designed for the I-185 fighter (powered by one radial engine) and was totally inadequate to compensate for the long and heavy AM-35A V-12 engine, with 1,350 hp.
During the flight tests performed on August 29, 1940, the prototype showed longitudinal instability, heavy control, and a dangerous tendency to flat spin.
It was difficult to fly and deadly in combat for an inexperienced pilot. Its instability at high speeds could make aerial gunnery difficult and requiring constant pilot intervention to remain on target.
A feature common to all Polikarpov fighters was the ‘snaking effect’ that affected weapon accuracy during combat maneuvers.
The triangular wing planform, with leading and trailing edge sweep and larger roots that tapered to the tips, were the cheapest compromise between performance, strength and drag. It was strong at the root, light at the tips and easy to build, and could be lethal, because the strongly tapered wings had a dangerous tendency to low-speed stall.
In combat, the I-200 was prone to spinning out of a steep banking turn. Despite the seriousness of the shortcomings displayed by the prototype, it was ordered into immediate mass production, as OKO MiG-1, in September 1940.
Some aircraft from GAZ-1 were delivered to the VVS-RKKA (Soviet Air Force) and PVO (Soviet Air Defense Force) in April 1941, but little is known of their performance in combat because more than half of all Soviet fighters were destroyed on the ground or in the air within 48 hours of the
Luftwaffe assault.
Meanwhile the Mikoyan-Gurevich Design Bureau (OKO-Kiev) worked feverishly to correct the MiG-1 deficiencies.
The MiG-3 was ordered into production in December 1940, but the improvements added nearly 500 lb. to the take-off weight and exacerbated its instability at high speeds. Its poor climb performance was caused by the excessive weight (1,830 lb.) of the AM-35A engine (Soviet version of Fiat A.20 V.12 with single-stage gear-driven supercharger) and the steel wing spar.
The aircraft was originally designed as a high-altitude interceptor with 37,700 ft. (11,500 m) service ceiling, but in practice few MiG-3 managed to reach that altitude due to the poor design of the fuel and oil pumps and the M-100's supercharger malfunction, as the impeller alloy AK-1 was prone to material fatigue.
In real combat conditions some planes entered irrecoverable spins flying at 30,000 ft. (9,150 m).
The MiG-3 had a take-off weight of 7,395 lb. (3,350 kg) at a time when the Yak-1 weighed 6,309 lb. (2,858 kg) and the Messerschmitt Bf 109 F-1 4,943 lb. (2,239 kg).
Designers were forced to reduce the armament to just three machine guns so as not to further degrade its climb performance.
On the Eastern Front most air-to-air combats were at altitudes below 16,400 ft. (5,000 m). The Yak-1 and LaGG-3 fighters powered by M-105 P (Hispano-Suiza 12 Y) engines attacked the German Henschel Hs 126 reconnaissance planes and the Junkers Ju 87 dive bombers as they tried to escape the Messerschmitt Bf 109 F fighters.
Attempts to use the MiG-3 as ground attack airplane and frontal low altitude fighter were a bloody failure.
The aircrafts used by the PVO in Moscow's defense failed to reach the high-flying Ju 86 P-2s during the day and, at night, their inaccurate PAK-1 gunsights, the low optical quality of the Plexiglas windscreen and the poor firepower, proved inadequate to destroy the Heinkel He-111 H bombers fitted with 270 kg armor.
Production of the MiG-3 was stopped in December 1941 and six fighter regiments in charge of the defense of Moscow were equipped with Lend-Lease Hawker
Hurricanes Mk.II A and Mk.IIB.
