Cheppali 117

Cheppali Cp 117
Role	Fighter
National origin	Tennai
Manufacturer	Cheppali
Designer	Lathusa Prithiyanga
First flight	February 1935
Introduction	December 1936
Retired	1948
Status	Retired
Primary user	Royal Tennaiite Air Force
Produced	1936-1947
Number built	35,955
Developed from	Cp 75
Developed into	Cp 218

The Cheppali Cp 117 is a Tennaiite Siduri War fighter aircraft that was the backbone of the RTA’s fighter force. The Cp 117 first saw operational service in early 1937 during the offensive to push the Inner Sphere from Tennai and was still in service at the dawn of the jet age 1945. It was one of the most advanced fighters when it first appeared, with an all-metal monocoque construction, a closed canopy, and retractable landing gear. It was powered by a liquid-cooled, inverted-V12 aero engine. From the end of 1941, the Cp 117 was steadily supplemented by the Nikita AN.157.

It was designed by Lathusa Prithiyanga who worked at Cheppali during the early to mid-1930s. It was conceived as an interceptor, although later models were developed to fulfill multiple tasks, serving as bomber escort, fighter-bomber, day-, night-, all-weather fighter, ground-attack aircraft, and reconnaissance aircraft. It was supplied to several states during Siduri War, and served with several countries for many years after the war.

Design and development

In October 1933, Air Marshall Vihari Jakkala sent out a letter requesting aircraft companies consider the design of a fast, modern fighter. Each company was asked to build three prototypes for run-off testing. By spring 1935, both the Devati and Nikita aircraft were ready and the Cp 117 in March.

The Air Ministry outlined specifications, for the supply of a new fighter aircraft, that submissions for the competition had to meet certain characteristics, including; a) have an all metal construction, b) have a monoplane configuration, c) have retractable landing gear, d) be capable of achieving a top speed of at least 400 km/h (250 mph) at an altitude of 6,000 m (20,000 ft), e) endure ninety minutes at full throttle at 6,000 m (20,000 ft) f) reach an altitude of 6,000 m (20,000 ft) in seven minutes and have a service ceiling of 10,000 m (33,000 ft) g) be able to be fitted with a Sinhatta Darva 210 engine h) be armed with either two 7.92mm fixed machine guns or one 20mm cannon and i) have a wing loading of less than 100 kg/m^2.

In February 1934 the three companies, Devati, Nikita and Cheppali, were awarded contracts to develop prototypes for the competition. The prototypes that were eventually submitted for the competition were the Devati Dv 112, Nikita AN.143, and the Cheppali 117. Cheppali had begun development of their submission in late 1933 in anticipation of the announcement. At the helm of their design project was Lathusa Prithiyanga, designer of the Cp 116, who weas then working on the design for the Cp 117. The first prototype had its first flight in September 1935.

Cheppali’s design was created primarily by Lathusa Prithiyanga, whose designs would dominate most of Cheppali’s work. They started work on Cp 117 in late 1933 based around the Manepalli XV inline engine. Work was already under way when the official request went out on 2 May, and on 5 May the design was named the Cp 117.

The primary source of inspiration for the Cp 117 was their earlier Cp 75 design. The Cp 75 was a single-engine, four-passenger aircraft originally designed for use by Royal Tennai Airlines. Like many civilian designs of the time, the aircraft was pressed into military service and was used as a two-seat bomber (although mostly for reconnaissance). The Cp 75 introduced a number of new construction techniques to the Cheppali company; it was their first low-wing monoplane, their first with retractable landing gear, their first all-metal monocoque design, and its elliptical, reverse-gull wing would be seen on a number of later projects. The Cp 75 could almost meet the new fighter requirements itself, so it is not surprising that Prithiyanga would choose to work with the existing design as much as possible.

Cheppali’s Cp 117 submission was a scaled-down version of the Cp 75, a fast mail-plane, sharing numerous features with it including; an all-metal construction – including its oval cross-section fuselage and two-spar monoplane wings which were covered with flush-head rivets and stressed metal skin-, similar inverted semi-elliptical gullwings and retractable landing gear. The wide-track of the undercarriage, a result of having outward retraction from the low point of the wing's gull-bend, granted the aircraft excellent ground handling for take-off and landing. The open cockpit and fuselage spine behind the headrest mounted into the deep-section fuselage offered the pilot a good view when taxiing and were included to provide excellent vision and make the biplane-trained pilots feel more comfortable.

Prototypes

The first prototype, V1, was completed on 1 September 1935. Specifications of the Air Ministry required that the competing aircraft be fitted with the Gomathi Parvahtta 210, however, as the engine was unavailable, a 518 kW (695 hp) O’Connol-Fundy GyrfalconV was fitted instead. The V1 prototype of the Cheppali had comparatively large wings and was heavier than its contemporaries, however, due to the wing size, the mass was more evenly spread out resulting in lower wing-loading. The upshot of this was that the aircraft had better turn performance; the downshot was that it generated more drag than expected and had a slowed roll rate.

The second prototype, V2, was completed in November. It was powered by a 480 kW (640 hp) Parvahtta 210C engine and fitted with a three-blade propeller, but was otherwise identical to the V1. Meanwhile, the data from the V1 factory flights was studied to discover where the unexpected drag was coming from. Lathusa Prithiyanga identified the large, thick wing as the main culprit, and designed an entirely new smaller and thinner wing with an elliptical planform. As a stop-gap measure, the V2 had its wings clipped by 1.010 m (3 ft 3.8 in) to allow it to compete with the Dv 112. This made the Cp 117 creep over the wing loading requirements in the specifications, but with the Dv 112 way over the limit, this was not seen as a problem, and the V2 was sent off for testing. The V2, like its predecessor, had problems with spin stability and eventually crashed and was destroyed when test pilot Vani Vedantham bailed from the aircraft after losing control during a set of spin tests.

The V3 took to the air in January. Largely similar to the V2 and powered with the same engine, the V3 had minor changes including having a larger radiator, fuselage spine and vertical stabilizer, having a single cover over the exhaust ports instead of the more common "stack", and it also included modifications to allow armament to be installed in the cowling. The V3 was the first prototype fitted with armament in the form of two 7.92 mm (0.312 in) Basu HV 80 machine guns.

The first of these new versions, V4, was completed in April 1936 and was almost an entirely new design. It featured a new single spar fully elliptical wing, a more powerful 210D engine with a two-speed supercharger that brought the power to 510 kW (680 hp) for takeoff and a smaller tailplane. The redesign also had a redesigned and cut-down rear fuselage, a new fin and rudder and a completely enclosed cockpit with a bubble-style canopy. The canopy was somewhat more complex than later bubble designs; instead of having two pieces with the majority sliding to the rear, the Cp 117 V4 canopy was in three pieces, the middle sliding back over a fixed rear section. Even with additional framing, the Cp 117 had excellent visibility for its day. Armament was standardized on the V4 with two 7.93 mm (.312 in) Basu HV 80 machine guns in the sides of the cowling with 500 rpg and two 20 mm Basu FG 20-20 cannons in the wings with 60 rpg. For aiming, the cockpit included the new Singh 3B reflector gunsight.

The performance of the V4 was deemed excellent and work continued on the design through July 1936. In the middle of July 1936, the V5 prototype was completed. It featured several small refinements in the design, but was otherwise identical to V4. The V5 was accepted as the production model of the Cp 117 with the new 1,000 PS (986 hp, 735 kW) Devati S-P251-112 engine, but the initial A-series aircraft were equipped with the 210D engine as the Devati design was not readily available at the time.

Design Competition

At the competing aircraft's demonstration flight for the Air Ministry in October 1935, the thick high-lift aerofoil and open cockpit of the Cp 117 generated more drag than its contemporary opponent, the Dv 112, causing its performance to suffer despite being equipped with an identical engine. Whereas the Dv 112 prototype was able to clock in a top speed of 467 km/h (290 mph), the Cp 117 could only manage 440 km/h (273 mph). The other competing aircraft, the Nikita An.143, had been plagued with problems from the outset and was outclassed by both the Dv 112 and the Cp 117 resulting in it being eliminated from any serious consideration. At the end of the demonstrations, Devati and Cheppali were awarded contracts to produce ten prototypes for further testing and competitive trials.

At this point, the Cp 117 was the favorite over the "unknown" Dv 112, but opinions changed when the Dv 112 V2 arrived on 21 March. All the competitor aircraft had initially been equipped with the O’Connol-Fundy Gyrfalcon engine, but the Dv 112 V2 had the Parvatta. From that point on, it started to outperform the Cp 117 in almost every way, and even the arrival of the Pavatta-engined Cp 117 V2 on 15 April did little to address this imbalance.

The Cp 117 had better turn performance due to its larger wing, but the Dv 112 was faster at all altitudes and had considerably better agility and aerobatic abilities. During spin tests on 2 March, the Dv 112 V2 showed no problems while the Cp 117 V2 crashed. Repairs were made to the aircraft and it was returned in April, but it crashed again and was written off. The V1 was then returned to Heinkel on 17 April and fitted with the V2's clipped wings.

Meanwhile, the Siduri War was ongoing. The front in Tennai was bogged down and the Inner Sphere was showing few indications that they would withdraw. Time now took on as much importance as any quality of the winning aircraft itself, and the Air Ministry was ready to put any reasonable design into production. Devati and Cheppali were given another month to build and test another prototype. Lathusa Prithiyanga drastically redesigned the Cp 117, essentially creating a new aircraft. The redesign proved successful and the Cp 117 was selected as the winner of the competition. On 12 April the Air Ministry produced a document called Cp 117 Priority Procurement which indicated which aircraft was now preferred. There were some within the Air Ministry who still favored the Devati design, and as a result the Air Ministry then sent out contracts for 10 "zero series" aircraft from both companies. Testing continued until October, at which point some of the additional zero series aircraft had arrived. At the end of September, there were four Cp 117s being tested, and appeared equal to the Dv 112. From October on, the Cp 117 appears to have been selected as the winner of the contest.

Production

Mass production of the Cp 117 began in November of 1936 and the first operational units began operation in February of 1937. By the time production ceased, nearly 36,000 aircraft had be produced.

Specifications (Cp 117 B2-L2)

|prime units?=met |crew=1 |length m= |length note= |span m= |span note= |height m= |height note= |wing area sqm= |wing area note= |aspect ratio= |airfoil=NACA 2R1 14.2; tip: NACA 2R1 11.35 |empty weight kg= |empty weight note= |gross weight kg= |gross weight note= |max takeoff weight kg= |max takeoff weight note= |fuel capacity= |more general= |eng1 number=1 |eng1 name= |eng1 type=V-12 inverted liquid-cooled piston engine |eng1 kw= |eng1 hp= |eng1 shp= |eng1 kn= |eng1 lbf= |eng1 note=2,000 PS (2,000 hp; 1,500 kW)

|prop blade number=3 |prop name= |prop dia m= |prop dia note=light-alloy constant-speed propeller |max speed kmh= |max speed note=

1 km/h (0.62 mph; 0.54 kn) at 4,000 m (13,123 ft)

1 km/h (0.62 mph; 0.54 kn) at 6,300 m (20,669 ft)

1 km/h (0.62 mph; 0.54 kn) at 8,000 m (26,247 ft)

|cruise speed note=at 6,000 m (19,685 ft) |stall speed kmh= |stall speed note= |never exceed speed kmh= |never exceed speed note= |range km= |range note= |combat range km= |combat range note= |ferry range km= |ferry range note= |endurance= |ceiling m= |ceiling note= |g limits= |roll rate= |climb rate ms= |climb rate note= |time to altitude= |wing loading kg/m2= |wing loading note= |fuel consumption kg/km= |power/mass=0.344 kW/kg (0.209 hp/lb) |more performance= |guns=

• • 2 × 12.7 mm (.51 in) synchronized MG 131 machine guns with 300 rpg or
  • 2 × 20 mm MG 151/20 underwing cannon pods with 200 rpg
  • 2 × 20 mm (.78 in) MG 151/20 cannon in wings with 200 rpg

|bombs=1 × 250 kg (551 lb) bomb or 4 × 50 kg (110 lb) bombs or 1 × 300-litre (79 US gal) drop tank |rockets=2 × 21 cm (8 in) Wfr. Gr. 21 rockets (G-6 with BR21) |avionics=FuG 16Z radio }}