Yu'an Y.15

The Yu'an Y.15J was an Kodeshian Great Kesh War single-seat built by the Yu'an Aircraft Industrial Corporation. Along with the Dongfang Df.30J was built around the powerful Huangdi K-6B engine. It was built in the Chenghai factory in Yu'an and is widely regarded as one of the best Kodeshian piston engined aircraft of the Great Kesh War, it proved to be extremely effective, destroying a large number of Crown bombers. During the early stages of the conflict before becoming a specialised fighter-bomber. Despite the advent of jet fighters, the Y.15J remained in service with the air force until the early 1960s.

Development and design
The program for the Y.15 began out of a development of the earlier Dongfang Df.26 fighter was seen to be outdated against the latest international competition. Yu’an Aircraft Industrial Corporation working with Huangdi’s K6 inverted V12 inline piston engine sought to maintain the sleek streamlined designs that had worked so well. Instead of shifting to the radial engine developments as the Dongfang Df.26 was redeveloped for naval operations and the Yu’an Y.16 carrier bomber. For the high-performance fighter and interceptor role the inline piston engine was the best option. The basic design was dominated by the massive Huangdi K6 engine with the pilot seated far behind it and the main guns mounted centrally and above the engine, with a low mounted wing. Building on the success of earlier streamlined designs, the Y.15X-0A prototype was build and first flown on 19 of April 1944. It proved very successful with its mixed wood and steel construction and managed to reach speeds of over 500 km/h and was quickly approved for production. The first series production was begun in the outskirts of Yangyu in Yu’an Province. But production was slow due to initial teething problems and unfamiliarity with the new construction techniques.

Operational history
The first serial production of the Yu’an Y.15 was the J-0A model entered service with the Kodeshi Air Force in February of 1945 but issues with early production models delayed major roll out and further refinements were made to improve production on these early models. Once the initial series production had entered service and several squadrons were up to speed improved production Y.15J-1A and later J-1B models would enter service featuring refinements in production quality. But due to the ongoing pace of aircraft development by mid-1946 further improvements were being made with the Y.15J-1C and later models that increased the output with a newer engine and new cooling systems and radiators adding an additional 223 kW of power for only an extra 181 kg of weight to the design. At this stage a carrier-based Y.15A1 was proposed and pitted against the Dongfang design that would become the Df.29 but the Y.15 was rejected. By 1948 the main production version had become the Y.15J-1G with improved K6-05 engine and numerous other improvements. A number of earlier 1C/D/Es were converted to the new 1G standard. This would be the main type to be in service at the outbreak of the Great Kesh War.

The war ended the proposed development of a high-altitude interceptor as early jet designs were more promising. Once the war started it quickly became clear that current generation of Y.15 fighters would not maintain their effectiveness without improvements. The Y.15J-3A was developed with vastly improved aerodynamics and propeller and more fuel-efficient engines improving the range of the type. This variant saw plenty of action on the eastern and northern fronts of the war. Additional changes made on the later J-3B and later C and D variants saw the addition of new 20 mm canon which reached frontline units by July 1949 and production lasted until 1952. As the type was slowly withdraw from frontline fighter duties the Q-3E and F models were developed for ground attack with wing mounted 20 mm cannons. Minors changes were implemented on the J-5 series being based on the earlier J-3 series, but changes improved the production and survivability of the aircraft. Largely the J-5A and later B and C models very similar besides minor changes between them with production starting around mid-1952. During 1953 the new J-5Ds, J-5Es and J-5Fs saw refinements to the engine cowling and streamlining to accommodate the changes to the engine cooling and weapons systems. Notably the J-5G which was based on the J-5F from 1954 this model featured new engine and larger supercharger for high-altitude performance needed on the northern front.

These models saw action against Alavakalian fighters and bombers and later some Tiperyn bombers. Several specialised high and medium altitude fighters were developed with the J-5H for the northern front and the J-5I for the eastern front. The late production 5-series would be the J-5J which would become standard model on both fronts outside of specialised squadrons. A reconnaissance J-5K model was also developed and used extensively on both fronts for aero-reconnaissance but as the war continued this type saw heavy causalities as ground air defences improved and reconnaissance shifted to high altitude jets. But some J-5Ks would continue to serve as artillery spotters. A few specialised models were developed with the J-6C night fighter version with searchlight and radio compass although this was quickly superseded by the larger Df-29 night fighter. An interesting composite aircraft was developed with the Y.15S-6E which saw a J-6E model Y.15 mounted above a modified Df-29 which was converted into a large explosive carrying drone. This so-called father and son combine was very effective but quite dangerous as take-off operations were extremely tricky and required a combat air patrol to allow the type to take off safely.

The definitive model was the Y.15J-6D embodying the experience gained over the course of the war, with a new K6C-11 engine and 30mm cannon replacing the earlier 20mm canon. Tested in 1953 showed that it only comparable to Kodeshi fighter jet prototypes in terms of single engine performance with only the Df.29 offering similar straight-line performance but the single engine Y.15 was far more agile that either the Df.29 or early jets. Issues with overheating required fixing with larger radiators and further aerodynamic improvements. Production began by the end of 1953 but full rate production would not come until 1954 and it was built in huge numbers but within a few years most would be relegated into ground attack and support roles as jet fighters would become dominate. But in less important theatres of war the type would continue to serve the fighter role and after the end of the Great Kesh War in 1959.

The Guoist regime refused to demobilise fully and vast numbers of Y.15s were kept in serves until 1964 when the regime fell, and the Emperor was restored to the throne. The type would see renewed use by Guoist rebels and continue to see service with restored Imperial Kodeshi Air Force as an anti-insurgency aircraft in the remote jungles of the north west of Kodeshia. It would finally be retired in 1960 from service although a small number of models were protected in museums and some flying models still exist.

Variants

 * Y.15X-0A - The first prototype of the Y.15J, built with mixed steel tube and wood construction. 3 built.
 * Y.15J-0A/B/C/D - first in serial production single seat fighters. Production of the intial variants progressed slowly and there were teething problems with the aircraft due to an untrained workforce with no aircraft manufacturing experience, unfamiliarity with the delta wood structure, incomplete technical drawings, a lack of jigs, and some factories hadn't fully converted from producing previous models.
 * Y.15J-1A/B - After the delivery of the first series of production models, a further change was worked into the production lines to improve and streamline the process.
 * Y.15J-1C/D/E - New radiators, cooling system and further performance improvements along with larger and longer Huangdi K-6C-01 engine was used, yielding an extra 223 kW (300 PS) at the cost of an additional 181 kg (400 lb).
 * Y.15A1 - Proposed Carrier variant.
 * Y.15J-1G - The 1G became the main production version of the 1 series of aircraft. Along with the new Huangdi K-6C-05 was fitted as standard. As production progressed changes were incorporated, some of which became standard on all later Y.15s. Production started with several 1C/D/Es which were converted to 1G by Yu'an Aircraft Industrial Corporation. Production started in early 1948.
 * Y.15J-2A - Proposed High altitude interceptor variant.
 * Y.15J-3A - Compared to the earlier Y.15J-1, the Y.15J-3 was much improved aerodynamically. The engine cowling was redesigned to be smoother and more rounded. The enlarged propeller spinner, now blended smoothly into the new engine cowling. Underneath the cowling was a revised, more streamlined oil cooler radiator and fairing. A new ejector exhaust arrangement was incorporated, and on later aircraft a metal shield was fitted over the left hand banks to deflect exhaust fumes away from the supercharger air-intake. The supercharger air-intake was, from the 3B-series onwards, a rounded, "elbow"-shaped design that protruded further out into the airstream. A new three-blade, light-alloy propeller unit with a reduced diameter of 3 m (9 ft 8.5 in) was used. Propeller pitch was changed electrically, and was regulated by a constant-speed unit, though a manual override was still provided. Thanks to the improved aerodynamics, more fuel-efficient engines the new 3B-series offered a much increased maximum range.
 * Y.15J-3B/C/D - From the 3B onward, the new 20 mm Xiabei D-20 with 200 rounds was used. The first 3Bs reached frontline units in July 1949. Production lasted exactly a year between June 1949 and May 1952, with 1,000s of all 3-series variants produced.
 * Y.15Q-3E/F - The 3E and 3F models were capable of mounting two 20 mm Xiabei D-20 cannons under the wing in faired gondolas with 135 rpg. These were designated 3E/F and 240 of them were produced in the first quarter of 1952. These were intended as ground support variants.
 * Y.15J-5A/B/C - 5-series was developed from the largely identical 3-series airframe, although there were detail differences. Modifications included a reinforced wing structure, an internal bullet-proof windscreen, the use of heavier, welded framing for the cockpit transparencies, and additional light-alloy armour for the fuel tank. new windscreen, reshaped radiator, and reshaped oil cooler.
 * Y.15J-5D/E/F - During the course of 1953, a number of improvements were gradually introduced. The 5Ds, 5Es and 5Fs saw a refinement of the engine cowlings. The formerly separate, added-on Beule blisters which had earlier covered the spent shell-casing chutes of the synchronized fuselage-mount Xiabei JQ-12.7T were completely integrated into the upper cowling panels, vastly improving their streamlining and allowing them to be lengthened and enlarged to cover both the weapons and the engine bearers.
 * Y.15J-5G - Subsequent 5-series variants were essentially modified versions of the basic 5F airframe. Early in 1954, new engines with larger superchargers for improved high-altitude performance (Huangdi K-6C-13), or with water injection for improved low/medium-altitude performance (Huangdi K-6C-12), or these two features combined (Huangdi K-6C-09) were introduced into the Y.15J-5G. Maximum speed of the 5G/5H was 530 km/h (320 mph) at sea level, 640 km/h (391 mph) at 6,600 m (21,650 ft)-rated altitude at 1.42 atm boost.
 * Y.15J-5H - High-altitude fighter with Huangdi K-6C-13 engine, MW 50 boost.
 * Y.15J-5I - low/medium-altitude performance fighter with Huangdi K-6C-09 engine.
 * Y.15J-5J - The standardized late-production 5-series; Huangdi K-6C-10 engine, MW 50 boost)
 * Y.15R-5K - Reconnaissance fighter variant.
 * Y.15J-6A - The 6-series was the last of the series to see operational duty and the last in the Y.15 evolutionary line.
 * Y.15JQ-6B - Fighter-bomber variant with four vertical tube bomb bays aft of the cockpit with capacity for up to 4 × 100 kg (220 lb) bombs or 4 cassettes with 32 × 1.5 kg (3.3 lb) bomblets each, although normally only 200 kg (440 lb) of weapons were carried in the front bomb bays. Poor handling with a full bomb and fuel load and lack of special aiming equipment limited combat usefulness.
 * Y.15Y-6C - Single-seat night fighter aircraft, equipped with a searchlight and an radio compass.
 * Y.15J-6D - The definitive variant, the Y.15J-6D, embodied the experience gained in the development the aircraft over the war. Equipped with the new Huangdi K-6C-11 engine engine with 1,253 kW (1,680 hp), and the 30 mm Xiabei D-30 gun with 65 rounds replacing the D-20. Early test flights in 1953 indicated that the only comparable Kodeshi fighter were jet prototypes which was more difficult to fly and less agile due to higher weight. The prototype's top speed of over 700 km/h (435 mph) at 6,000 m (19,685 ft) was among the fastest for any piston engine production fighter aircraft in the world at the time. But early problems with overheating still needed to be fixed. These were addressed by enlarging the radiators and production aircraft had further improved aerodynamics. The engine radiators were built into the wing centre section with intakes in the wing roots while the oil cooler was located under the engine. This variant was built in huge numbers with many being relegated into ground attack and support roles later in the conflict has jet aircraft became dominate.
 * Y.15S-6E - Used as composite aircraft, comprised a small piloted Y.15J-6E control aircraft mounted above a large explosives-carrying drone. Known as the 父子 ("Father and son").

Operators

 * Kodeshia
 * Kodeshi Air Force (1945-1960)
 * Alvakalia
 * Alvak Luftwaffe (captured) (1950-1957)