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.