The Saunders-Roe SR.177 was developed by British aero-industry during the early-Cold War period as an extension of the SR.53 (detailed elsewhere on this site). The SR.177 was a further evolution of the earlier form and intended to improve upon endurance (and therefore mission range) while also incorporating an onboard radar system for self-direction and attack to aerial targets (through missile weaponry). Like the SR.53 before it, the SR-177 would feature a hybrid, "combination" propulsion scheme incorporating a conventional air-breathing, afterburning turbojet engine with a rocket booster to extend performance. As an interceptor, the aircraft would be called upon to go airborne in short order and reach engagement altitudes quickly - hence the design decision to incorporate two different propulsion systems.
The enemy of the day was the Soviet Union and this vast military power was keen to use bombers and high-speed interdiction aircraft to assault key positions across Europe in the event of Total War. As such, interceptors were in high demand for the West and much experimentation was had across Britain, France, and the United States during the Cold War period (1947-1991). Despite efforts, many designs simply fell by the wayside with few making it to production-quality, in-service forms. In the case of the SR.177, and as with other promising, impressive British aero-projects of the 1950s, the SR.177 was cancelled after the 1957 defense review (the infamous "Defence White Paper" review) - primarily due to the perceived notion of a future battlefield ruled entirely by missiles and the understanding that Soviet air defenses would grow technically to advanced stages beyond the scope of Western interceptor capabilities (as such flying "high-and-fast" would no longer be suitable qualities).
The SR.177 was born from a 1955 authorized design study meant to advance the SR.53 form - in this way the aircraft would retain the form-and-function of its predecessor and similarly utilize a mixed-propulsion scheme. Key features included blown flaps and a completely revised (ventrally-positioned) intake approach for improved efficiency. A first-flight was, rather optimistically, expected for 1957 with service entry following in 1960. The platform was expected to serve as an airspace protector, a supersonic high-altitude fighter countering Soviet air incursions head-on.
Beyond its impending adoption by the British Royal Air Force (RAF) (to succeed a line of Hawker Hunter jet fighters), the SR.177 - or rather its production-quality, in-service form - would also be used to satisfy a standing Royal Navy Fleet Air Arm (FAA) requirement. In time, the West German Air Force and Navy services also took a deep interest in this British work.
On paper, the design proved promising enough to warrant an early commitment to twenty-seven aircraft. The series would be broken down into batches set to cover various aspects of development - flight-testing for the first five airframes, weapons development of the following three airframes, specialized forms of the subsequent five, evolution models of the next six, and service trials platforms of the final eight examples.
As in the SR.53, the SR.177 was to feature its mixed-powerplant in an "over-under" arrangement which, in turn, generated a deep appearance of the fuselage when viewed in its side profile. The chosen power systems were 1 x de Havilland PS.50 "Gyron Junior" afterburning turbojet of 14,000lb thrust output and 1 x de Havilland "Spectre" Model 5A liquid-fueled rocket engines offering an additional 10,000lb of thrust (if only for a limited time).
The turbojet would be seated along the ventral line of the fuselage, aspirated by an intake mounted under the nose section, and exhausted through a conventional circular port under the tail. This left the rocket booster to be seated over the turbojet and, as it did not require air-breathing for its proper function, the unit simply exhausted from under the tail - above the turbojet's exhaust.
With this mixed-powerplant arrangement, the SR.177 was estimated with a maximum speed reaching Mach 2.35 and could fly to altitudes of 67,000 feet with a 60,000 feet-per-minute rate-of-climb. The rocket booster could supply up to seven minutes of total burn time (and therefore seven minutes of additional thrust) before it would be completely expended.
The wing mainplanes were positioned at midships and were mid-mounted with each member showcasing slight anhedral (downward angle). At each wingtip was planned a missile hardpoint with the initial weapon to be carried being 2 x de Havilland "Firestreak" Air-to-Air Missiles (AAMs). Later, this was evolved to become 2 x Hawker Siddeley "Red Top" AAMs. Up to 1,000lb of ordnance would be supported in this fashion.
The cockpit was seated towards the front of the fuselage in the usual way, positioned just aft of the radar-housing (A.I 23 Airborne Interception Radar) nosecone assembly. The position was heavily framed yet offered useable views out over the nose and to the sides of the aircraft. Since the onboard equipment would be doing most of the mission work when search, tracking, and attacking, this was an acceptable design approach for the time.
The undercarriage comprised a conventional tricycle arrangement. Under the nose was a single-wheeled leg retracting forwards under the cockpit floor. Under each wing member were single-wheeled main legs retracting inwards. This would provide the needed support for ground-running actions for the interceptor.
The tail unit was given a Multhopp "T-style" arrangement in which the horizontal planes were seated at the extreme top edge of the single vertical tail fin. This elevated the planes considerably away from the fuselage and is a common feature in many of today's civilian marketplace aircraft.
Finalized dimensions of the aircraft included a wingspan of 30.2 feet with a height of 14.3 feet. Empty weight totaled 14,535lb with a Maximum Take-Off Weight (MTOW) registered at 28,175lb.
Despite its promising features and expected performance, projects like the SR.177 were easily given up by the British government of the time. With the cancellation of the SR.177, the SR.53 was retained for testing purposes and went on to record its first-flight on May 16th, 1957. Afterwards, it provided British engineers an active platform for data-collecting of a supersonic performer and two flyable prototypes eventually completed the series (though the second example was ultimately lost to a crash in June of 1958). The first prototype managed to survive its time in the air and was preserved for future generations at the Royal Air Force Museum at RAF Cosford, Shropshire.
The SR.187 became a short-lived, related design study born from the SR.177 work. Dimensionally larger, it was intended to satisfy the requirements of O.R. F155. With the first prototype almost nearly complete, this project, too, was axed because of the 1957 defense review and its completed contents scrapped some years later.