Dornier's experience in developing its unique Do 335 "Pfeil" ("Arrow") fighter-bomber / very-fast-bomber led the concern to realize the relative inefficiency of a nose-mounted engine ("puller") coupled with the propulsion power of a tail-mounted engine ("pusher"). While this made for one very fast prop-driven aircraft at 474 miles-per-hour, it restricted nose installations (in terms of armament and equipment) and reduced pilot vision out-of-the-cockpit. Thought was therefore given to a similarly large fighting aircraft of modern design in which the two propeller units were seated at the rear of the aircraft, the engines themselves to be seated inline and aft of the cockpit - leaving the nose completely available for armament and radar.
Design studies for a capable, high-performance night-fighter were being undertaken by Dornier as early as August 1941 and this work resulted in a handful of promising projects. It was not until the Do 335 took shape and was flown for the first time in October of 1943 that data on the unique twin-engine configuration could be collected and digested by engineers. Introduced in 1944, the Do 335 operated for only a short time in what was left of the war (the conflict would end in 1945) and production yielded just 37 total units before the end.
There were several notable offshoots of the Do 335 and this included the jet-powered "P.256" (detailed elsewhere on this site). Another, more conventionally-powered offering, became the "P.252" project aircraft - which utilized the aforementioned "twin-pusher" prop arrangement.
The Do 335's influence could be seen in the design lines chosen for the P.252. The design was a large, heavy-class fighter seating its crew under a heavily-glazed cockpit aft of a nosecone. The dorsal fuselage line was elevated behind the pilot so this restricted vision to the rear consequently adding more internal space for fuel, life support, and avionics. The fuselage was well-streamlined, slim, and long, tapering at the tail - which seated a cruciform-style tailplane arrangement (including a shorter ventral plane). Aft of the tail were the twin propeller units. Like the Do 335, a very-modern tricycle undercarriage was fitted for ground-running.
The wing mainplanes were given sweepback, dihedral, and rounded tips and intakes were positioned at the roots (these feeding the forward engine installation). Air scoops were also positioned at the fuselage port and starboard sides (feeding both engines) while exhaust ports for each engine were found along the sides of the airframe.
Design work on the aircraft took place in 1943 but it was not until January 1945, with data in hand and a standing need for a new, highly-capable Luftwaffe night-fighter, that the P.252 gained steam. It was seen that the rear-mounted engine approach allowed the nose of the fighter to accept both heavy armament and radar (and give the pilot excellent frontal vision) to make for one complete "bomber-destroyer" ("Zerstorer") machine. Dornier drew up plans for three distinct possible in-service forms as the "P.252/I", "P.252/II", and "P.252/III".
The P.252/I was completed as a two-seater (the crew seated back-to-back) during February of 1945. The second crewman was the dedicated radar operator and helpful in reducing the mission workload. The wing mainplanes in this proposal were straight as opposed to swept back.
The P.252/II added a third crewman which forced an extension of the fuselage (and thus an increase in operating weight).Wing sweep reached 35-degrees in this entry with a wider span over that seen in the P.252/I.
Then followed the P.252/III which reduced the wing sweep, added more mainplane surface area, and increased internal fuel loads for extended operating ranges. A large air scoop was also added to the base of the dorsal tail fin. The P.252/III was drawn up with a length of 56.4 feet, wingspan of 51.9 feet, and height of 16.5 feet.
What remained consistent between the three studies was the nose-mounted armament (large caliber, cannon-centered) and radar fitting, heavily glazed ("greenhouse" style) canopy, triangular small-area dorsal/ventral tailplanes, twin rear-mounted engines with their associated propellers, and tricycle landing gear.
The primary engine of choice became the Junkers Jumo 213J series liquid-cooled 12-cylinder engine, two to be seated inline in the middle and act sections of the fuselage. Each unit offered up to 1,750 horsepower at take-off, giving the fighter exceptional power and performance for the initial climb and subsequent cruising actions. MW50 boosting was also integrated for additional, albeit limited, bursts of power in combat. The engines drove a pair of 10.5-foot diameter three-bladed propeller units at the tail in contra-rotating fashion, this motion effective cancelling out the natural effects of torque seen in a single-engine design. Extension shafts mated the propeller units to their respective engines.
Estimated performance figures included a maximum speed of 577 miles-per-hour and an operating ceiling of 41,000 feet (necessitating life support and a pressurized cockpit for the crew).
The nose section was designed as a modular assembly - meaning that the P.252 could be outfitted with various radar types as well as armament options. The standard battery focused on 2 x 30mm MK 108 autocannons in the nose, 2 x 30mm MK 213C autocannons in the lower forward fuselage, and 2 x 30mm MK 108 autocannons at midships obliquely angled to fire upwards into the vulnerable belly area of an unsuspecting bomber. Beyond this was provision for 2 x 250kg or 500kg drop bombs carried under the wings (one bomb to a wing) - giving the night-fighter a fighter-bomber quality if needed.
Mission equipment was to include the FuG 244/245 series air-search radar, FuG 280 air-search radar, an Identification Friend-or-Foe (IFF) system (FuG 25a), and landing aids required of night time operations.
One of the detrimental developments working against further development of the P.252 was the rising value of the turbojet engine - which at this point in the war were offering warplanes greater performance potential than piston-driven fighter types. The piston engine was reaching its apex in terms of design and output and airframes had also maximized their inherent capabilities as rocket and jet propulsion schemes were being integrated into more aerodynamically-refined aircraft featuring swept back wing mainplanes. Indeed, a February 1945 initiative by German authorities forced preference towards the turbojet over an piston-driven designs going forward - though this does not appear to have dissuaded Dornier engineers from continuing work on the P.252.
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AIR-TO-AIR COMBAT
General ability to actively engage other aircraft of similar form and function, typically through guns, missiles, and/or aerial rockets.
INTERCEPTION
Ability to intercept inbound aerial threats by way of high-performance, typically speed and rate-of-climb.
GROUND ATTACK
Ability to conduct aerial bombing of ground targets by way of (but not limited to) guns, bombs, missiles, rockets, and the like.
X-PLANE
Aircraft developed for the role of prototyping, technology demonstration, or research / data collection.
56.4 ft (17.20 meters) Length
51.8 ft (15.80 meters) Width/Span
16.6 ft (5.05 meters) Height
18,960 lb (8,600 kilograms) Empty Weight
27,117 lb (12,300 kilograms) Maximum Take-Off Weight
+8,157 lb (+3,700 kg) Weight Difference
2 x Junkers Jumo 213J 12-cylinder, liquid-cooled inline piston engines developing up to 1,750 horsepower each (integrated MW50 injection) seated in tandem driving 2 x Three-bladed propeller units in contra-rotating fashion. Propulsion
PROPOSED:
2 x 30mm MK 108 automatic cannons in the nose.
2 x 30mm MK 213c automatic cannons in the lower forward fuselage.
2 x 30mm MK 108 autocannons near midships, obliquely-angled to fire upwards.
OPTIONAL:
2 x 250kg or 500kg conventional drop bombs for fighter-bomber role.
2 Hardpoints
P.252 - Base Project Designation.
P.252/I - Initial night-fighter design; radar-equipped; straight wing mainplanes and crew of two seated back to back; 559mph estimated maximum speed.
P.252/II - Second night-fighter design study; radar-equipped; lengthened fuselage for third crewman; 35-degree wing sweep.
P.252/III - Third night-fighter design study; reduced wing sweep; increased internal fuel capacity.
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