RB.108

RB.108
Name	RB.108
Type	Experimental lift jet
Manufacturer	Rolls-Royce
First flight	1960s (testbeds)
Primary user	United Kingdom
Status	Retired

RB.108 The RB.108 was an experimental vertical lift turbojet developed in the late 1950s and early 1960s for short takeoff and vertical landing (VTOL) applications. It served as a small, lift-only engine used in flight test programs that examined VTOL concepts and integration with manned aircraft. The program influenced subsequent lift-jet designs and informed development decisions for both military and civil VTOL projects.

Introduction

The RB.108 emerged from mid-20th century interest in vertical flight that involved collaboration among British aerospace firms and research establishments such as Rolls-Royce Limited, Royal Aircraft Establishment, Short Brothers, and Hawker Siddeley Aviation. Program objectives aligned with requirements set by organizations including Ministry of Supply (United Kingdom), United Kingdom Ministry of Defence, and procurement directives influenced by aircraft projects like the Hawker Siddeley Harrier and experimental efforts tied to V/STOL Research. Engineers referenced advances from contemporaries such as Pegasus (engine), Bristol Siddeley programs, and research at institutions like Imperial College London and Cranfield University.

Development and Design

Design work for the RB.108 was led by teams at Rolls-Royce Limited under senior engineers formerly associated with projects like Welland and Derwent. The engine was conceived as a compact, lightweight lift jet to provide vertical thrust without cruise capability, complementing thrust-vectoring designs seen in engines for aircraft such as the British Aerospace Harrier II family. Testbeds included conversions of aircraft from manufacturers such as Short Brothers and Hawker Siddeley Aviation, with flight trials overseen by pilots and test establishments from Royal Air Force test squadrons and civil test pilots from British Aircraft Corporation. Development drew on aerodynamic and control research performed at Aerospace Research Laboratories and data from trials at facilities like Boscombe Down and RAF Boscombe Down.

Technical Specifications

The RB.108 featured a centrifugal-compressor and axial-flow hybrid architecture similar in scale to small turbojets of the period. It delivered vertical lift in the order of magnitude necessary for light VTOL aircraft and lift sections of larger prototypes; its thrust-to-weight ratio was optimized for hover performance more than forward flight. Components were manufactured by precision workshops experienced from projects for Rolls-Royce Conway and Rolls-Royce Avon, and materials selection took cues from high-temperature alloys used in engines such as the Rolls-Royce Spey and Rolls-Royce Nene. Control integration used mechanical and early electro-hydraulic systems developed alongside avionics from firms like Ferranti and Marconi plc.

Operational History

Flight testing of the RB.108 occurred in the early 1960s on multiple aircraft testbeds and in ground-rig evaluations conducted by establishments including Royal Aircraft Establishment and Aviation Experimental Establishment. Trials provided data that fed into VTOL decision-making for projects evaluated by procurement bodies such as Ministry of Defence (United Kingdom) committees and influenced proposals submitted to companies like Hawker Siddeley Aviation and British Aircraft Corporation. While not adopted for widespread operational service, the RB.108’s test program informed government assessments during competitions and reviews involving aircraft like the Hawker Siddeley P.1127 and influenced later adoption decisions regarding engines used in service aircraft tested by Royal Navy and Royal Air Force.

Variants and Modifications

Variants of the RB.108 included versions with differing intake arrangements, exhaust deflectors, and mounting interfaces to accommodate various airframe installations. Modifications addressed challenges revealed in trials, such as heat shielding, lubrication systems, and control response; engineering changes were implemented drawing on lessons from projects at Rolls-Royce Limited and partner contractors like Dowty Rotol for thrust-vector hardware and Sundstrand-type auxiliary systems. Some experimental iterations were adapted for integration tests alongside vectored-thrust engines similar to those developed for the Pegasus (engine) program.

Applications and Aircraft Integration

The RB.108 was integrated as a lift module into several prototype and demonstrator aircraft from manufacturers including Short Brothers, Hawker Siddeley Aviation, and smaller experimental programs run by university teams at Imperial College London and Cranfield University. Installations explored multi-engine lift arrangements and combinations with conventional propulsion units; test aircraft were flown by pilots seconded from Royal Air Force test units and civilian test organizations such as British Steel Corporation’s aviation affiliates. Insights from integration trials informed designs considered by contractors bidding for contracts from agencies like the Ministry of Supply (United Kingdom) and influenced avionics and flight-control approaches used later in operational VTOL types evaluated by NATO partners including United States Navy and United States Air Force liaison teams.

Legacy and Impact on VTOL Technology

Although the RB.108 itself did not enter production, its test program contributed empirical data on lift-jet behavior, thermal management, and installation effects that impacted later lift and vectored-thrust engines. Lessons influenced engineering practices at Rolls-Royce Limited and design choices for engines that powered aircraft such as the Hawker Siddeley Harrier, and informed standardization efforts by organizations like British Standards Institution for aerospace subsystems. The RB.108’s heritage persists in academic literature and museum collections documenting the evolution of VTOL technology and in the engineering lineage of subsequent short takeoff and vertical landing systems evaluated by defense establishments across Europe and North America.

Category:Experimental aircraft engines