- In May 1944, the RLM commissioned Daimler Benz to develop the turboprop DB 109-021 Pollux, based on the Heinkel HeS 011 turbojet.
The engines of this type allowed to regulate the fuel flow with adjustments in the airscrew pitch, which, together with its low specific fuel consumption of 0.45 kg/eshp/hr made them very suitable to propel long-range airplanes. Turboprops were lighter and more powerful than the conventional piston engines and could work with heavy kerosene.
Version Sk.021.50-0008.10 (August 2, 1944) was designed to propel a future variant aufklärer (reconnaissance) of Arado Ar 234. It consisted of a HeS 011A turbojet to which had been added an extra third turbine stage and a 2.5 m diameter variable pitch six-bladed airscrew that could be driven through reduction gearing of the epicyclic planetary type, giving an airscrew speed ratio of 1 to 5.82 (1,800 rpm). The whole assembly had a length of 3.7 m and was suitable for installation under the wings of Arado Ar 234. At least 50 per cent of the turbojet power was diverted to airscrew thrust.
Version Zeich.Nr.109-021.6008 (17 October 1944) was designed to propel the Messerschmitt Me 262 B-2 nachtjäger (night fighter). It had a length of 4.1 m and was based on the HeS 011 A-0 turbojet. Compared with pure jet fighters, the PTL airplanes were superior in take-off, climb, acceleration and endurance, but the power of the turboprops rapidly declined with height and were not adequate to propel high-altitude interceptors.
In general, the jet versions were 107 per cent faster and 87 per cent lighter, with the service ceiling 130 per cent higher and a 34 per cent longer range compared with the turboprops versions. When the future performances of the 109-021 turboprop were known in July of 1944, Kurt Tank decided to use it to propel a Flitzer schlacht version (ground attack), called Projekt VII, capable of taking off using smallest forward landing strips with heavy loads.
The adaptation of the turboprop to the airframe of a single engine fighter, required the use of a long power shaft to connect the airscrew, in the extreme nose, with the turbojet installed in the rear section of the fuselage. On 2 August 1944, modification Zeich.Nr.0310 226-114, described in the dossier Baubeschreibung Nr.226, was proposed to the OKL. The power plant would be a version of the 109-021 named Sk.021.50-0008, with a power shaft of 3 m and an airscrew built with wide wooden Holzblättern blades from the VDM 9-12157 H-3 used by the Fw 190 D-9.
To compensate for the loss of power in the shaft, the diameter of the propeller increased to 2.7 m. The complete turboprop averaged 6.8 m in length and produced 2,400 hp shaft power, at 800 kph and sea level, with a residual jet thrust of 585 kp. The planned armament for this version consisted of two Mauser MG 151/20 cannons (synchronized variant) under the cockpit floor and two Mauser MG 151/15 heavy machine guns in the wings.
The dimensions were the same as those of the Flitzer III (20 July1944) except the overall length which was reduced to 9.9 m. The internal fuel capacity was 1,354 litres of heavy kerosene K1, enough to fly 1,460 km. Each wing panel housed one 210 litres fuel tank; the fuselage housed one tank with 597 litres of capacity and another with 337 litres. Take-off weight amounted to 5,000 kg, the maximum speed was estimated at 845 kph and the initial rate of climb at 40 m/sec.
On September 8, the OKL received a proposal to construct the zerstörer (bomber destroyer) version, described in document Zeich.Nr.0310 226-113a, which was named Peterle, derived from the acronym PTL. The power plant consisted of a HeS 011 A-0, a power shaft of 4.6 m and a conventional reduction gear box that allowed the installation of a Rheinmetall-Borsig Mk 103/30 heavy cannon in the nose that fired through the propeller hub. The shaft power, at 800 kph and sea level, was 3,300 hp with a residual jet thrust of 770 kp.
The main modifications made in the design of the Peterle consisted of the adoption of a single fuselage fuel tank of 720 litres, an asymmetric nose leg that did not interfere in the operation of the shaft when retracting and an armament consisting of a MK 103/30 heavy cannon in the nose. Two Mauser MK 213/20 (synchronized variant) rapid-fire cannons were positioned under the cockpit floor and two MG 151/15 machine guns in the wings. The Revi 16 C gunsight was replaced by a ZFR 4a telescopic gunsight and the overall length increased to 10.5 m.
According to some authors, the Peterle had a reverse thrust system for short landing run consisting of constant speed airscrew control with a quick blade pitch reverse mechanism.
Continuing its strategy of combining different types of airframes with all available power plants, on 14 November 1944 Kurt Tank proposed to the OKL the construction of a kampfjäger (strike fighter) turboprop based on the airframe of the P.011.037a. The new project weighed less than the Peterle and eliminating the tail-boom improved the roll rate and reduced the drag. It was expected that these changes would allow to achieve a maximum speed of 900 kph, an initial rate of climb of 39 m/sec and a ceiling of 13,800 m
Described in dossier Baubeschreibung Nr.281 as P.0310 226-127 and in the specialized literature as Projekt VIII, the Kampjäger would be propelled by a turboprop Daimler Benz Sk.021.50-0008, with a power shaft of 6.7 m and a variable-pitch six-bladed airscrew with 2.7 m diameter. The proposed armament consisted of a Rheinmetall-Borsig MK 108/30 cannon, firing through the propeller hub, and two Mauser MG 213/20 (synchronized) cannons under the cockpit floor. A bomb rack with capacity for a SC 250 bomb would be installed under the fuselage belly. Each wing panel, with 35 degrees swept and 10 per cent thickness ratio, housed one fuel tank with 280 litres of K1 heavy kerosene, one main undercarriage leg and one air-intake/air duct ensemble. The wing span was 8.2 m and the wing surface 17.5 sq. m. The fuselage, with 10.8 m of length, housed the turboprop, the armament and ammunition, the pressurised cockpit, with armour protection, the ejector seat and reflector gunsight, the electronic equipment, four fuel tanks with 880 litres of K1 and the asymmetric nose leg. With 1,440 litres of fuel, its range would be 1,020 km, with an endurance of 1.17 hours and a maximum take-off weight of 4,900 kg.
In August 1950, the North American company McDonnell decided to modify the prototype of the XF-88 installing an Allison XT-38 A-5 turboprop, to study the performance of this type of engines at high speeds. The modification was completed in early 1952 and the first flight was made on 14 March 1953 under the designation XF-88B. First flying tests revealed that the weight of the power shaft /gearbox/propellers ensemble did not compensate for the fuel savings and that this type of power plants could not be used successfully in long-range escort fighters. Between 1954 and 1957 the XF-88B was used by NACA-Langley to test up to 27 types of supersonic propellers in flight.
In 1951 the Republic Aviation Corporation started two research programmes using the Allison XT-40 A-1 turboprop. The first programme consisted of the design of a research aircraft to test supersonic propellers. The second was a study of the possibilities of turboprop to propel a strike fighter for the USAF and one high-performance carrier fighter for the US NAVY. The decision to construct two prototypes XF-84H based on the airframe of an F-84 fighter was taken in December1952. The first flight took place on 22 July 1955. During the flying test program, it was discovered that the sonic waves generated by the propeller produced physical damage to the ground crews within several hundred feet of the aircraft. This unexpected circumstance, along with numerous problems experienced with the hydraulic system and gearbox malfunction, led to the cancellation of the programme in October 1956.
(Img. 59, 63 and 64 Speculative drawings)
The engines of this type allowed to regulate the fuel flow with adjustments in the airscrew pitch, which, together with its low specific fuel consumption of 0.45 kg/eshp/hr made them very suitable to propel long-range airplanes. Turboprops were lighter and more powerful than the conventional piston engines and could work with heavy kerosene.
Version Sk.021.50-0008.10 (August 2, 1944) was designed to propel a future variant aufklärer (reconnaissance) of Arado Ar 234. It consisted of a HeS 011A turbojet to which had been added an extra third turbine stage and a 2.5 m diameter variable pitch six-bladed airscrew that could be driven through reduction gearing of the epicyclic planetary type, giving an airscrew speed ratio of 1 to 5.82 (1,800 rpm). The whole assembly had a length of 3.7 m and was suitable for installation under the wings of Arado Ar 234. At least 50 per cent of the turbojet power was diverted to airscrew thrust.
Version Zeich.Nr.109-021.6008 (17 October 1944) was designed to propel the Messerschmitt Me 262 B-2 nachtjäger (night fighter). It had a length of 4.1 m and was based on the HeS 011 A-0 turbojet. Compared with pure jet fighters, the PTL airplanes were superior in take-off, climb, acceleration and endurance, but the power of the turboprops rapidly declined with height and were not adequate to propel high-altitude interceptors.
In general, the jet versions were 107 per cent faster and 87 per cent lighter, with the service ceiling 130 per cent higher and a 34 per cent longer range compared with the turboprops versions. When the future performances of the 109-021 turboprop were known in July of 1944, Kurt Tank decided to use it to propel a Flitzer schlacht version (ground attack), called Projekt VII, capable of taking off using smallest forward landing strips with heavy loads.
The adaptation of the turboprop to the airframe of a single engine fighter, required the use of a long power shaft to connect the airscrew, in the extreme nose, with the turbojet installed in the rear section of the fuselage. On 2 August 1944, modification Zeich.Nr.0310 226-114, described in the dossier Baubeschreibung Nr.226, was proposed to the OKL. The power plant would be a version of the 109-021 named Sk.021.50-0008, with a power shaft of 3 m and an airscrew built with wide wooden Holzblättern blades from the VDM 9-12157 H-3 used by the Fw 190 D-9.
To compensate for the loss of power in the shaft, the diameter of the propeller increased to 2.7 m. The complete turboprop averaged 6.8 m in length and produced 2,400 hp shaft power, at 800 kph and sea level, with a residual jet thrust of 585 kp. The planned armament for this version consisted of two Mauser MG 151/20 cannons (synchronized variant) under the cockpit floor and two Mauser MG 151/15 heavy machine guns in the wings.
The dimensions were the same as those of the Flitzer III (20 July1944) except the overall length which was reduced to 9.9 m. The internal fuel capacity was 1,354 litres of heavy kerosene K1, enough to fly 1,460 km. Each wing panel housed one 210 litres fuel tank; the fuselage housed one tank with 597 litres of capacity and another with 337 litres. Take-off weight amounted to 5,000 kg, the maximum speed was estimated at 845 kph and the initial rate of climb at 40 m/sec.
On September 8, the OKL received a proposal to construct the zerstörer (bomber destroyer) version, described in document Zeich.Nr.0310 226-113a, which was named Peterle, derived from the acronym PTL. The power plant consisted of a HeS 011 A-0, a power shaft of 4.6 m and a conventional reduction gear box that allowed the installation of a Rheinmetall-Borsig Mk 103/30 heavy cannon in the nose that fired through the propeller hub. The shaft power, at 800 kph and sea level, was 3,300 hp with a residual jet thrust of 770 kp.
The main modifications made in the design of the Peterle consisted of the adoption of a single fuselage fuel tank of 720 litres, an asymmetric nose leg that did not interfere in the operation of the shaft when retracting and an armament consisting of a MK 103/30 heavy cannon in the nose. Two Mauser MK 213/20 (synchronized variant) rapid-fire cannons were positioned under the cockpit floor and two MG 151/15 machine guns in the wings. The Revi 16 C gunsight was replaced by a ZFR 4a telescopic gunsight and the overall length increased to 10.5 m.
According to some authors, the Peterle had a reverse thrust system for short landing run consisting of constant speed airscrew control with a quick blade pitch reverse mechanism.
Continuing its strategy of combining different types of airframes with all available power plants, on 14 November 1944 Kurt Tank proposed to the OKL the construction of a kampfjäger (strike fighter) turboprop based on the airframe of the P.011.037a. The new project weighed less than the Peterle and eliminating the tail-boom improved the roll rate and reduced the drag. It was expected that these changes would allow to achieve a maximum speed of 900 kph, an initial rate of climb of 39 m/sec and a ceiling of 13,800 m
Described in dossier Baubeschreibung Nr.281 as P.0310 226-127 and in the specialized literature as Projekt VIII, the Kampjäger would be propelled by a turboprop Daimler Benz Sk.021.50-0008, with a power shaft of 6.7 m and a variable-pitch six-bladed airscrew with 2.7 m diameter. The proposed armament consisted of a Rheinmetall-Borsig MK 108/30 cannon, firing through the propeller hub, and two Mauser MG 213/20 (synchronized) cannons under the cockpit floor. A bomb rack with capacity for a SC 250 bomb would be installed under the fuselage belly. Each wing panel, with 35 degrees swept and 10 per cent thickness ratio, housed one fuel tank with 280 litres of K1 heavy kerosene, one main undercarriage leg and one air-intake/air duct ensemble. The wing span was 8.2 m and the wing surface 17.5 sq. m. The fuselage, with 10.8 m of length, housed the turboprop, the armament and ammunition, the pressurised cockpit, with armour protection, the ejector seat and reflector gunsight, the electronic equipment, four fuel tanks with 880 litres of K1 and the asymmetric nose leg. With 1,440 litres of fuel, its range would be 1,020 km, with an endurance of 1.17 hours and a maximum take-off weight of 4,900 kg.
In August 1950, the North American company McDonnell decided to modify the prototype of the XF-88 installing an Allison XT-38 A-5 turboprop, to study the performance of this type of engines at high speeds. The modification was completed in early 1952 and the first flight was made on 14 March 1953 under the designation XF-88B. First flying tests revealed that the weight of the power shaft /gearbox/propellers ensemble did not compensate for the fuel savings and that this type of power plants could not be used successfully in long-range escort fighters. Between 1954 and 1957 the XF-88B was used by NACA-Langley to test up to 27 types of supersonic propellers in flight.
In 1951 the Republic Aviation Corporation started two research programmes using the Allison XT-40 A-1 turboprop. The first programme consisted of the design of a research aircraft to test supersonic propellers. The second was a study of the possibilities of turboprop to propel a strike fighter for the USAF and one high-performance carrier fighter for the US NAVY. The decision to construct two prototypes XF-84H based on the airframe of an F-84 fighter was taken in December1952. The first flight took place on 22 July 1955. During the flying test program, it was discovered that the sonic waves generated by the propeller produced physical damage to the ground crews within several hundred feet of the aircraft. This unexpected circumstance, along with numerous problems experienced with the hydraulic system and gearbox malfunction, led to the cancellation of the programme in October 1956.
(Img. 59, 63 and 64 Speculative drawings)
Attachments
Last edited:
