The first of two prototype R.E.8s (Reconnaissance Experimental 8) flew on 17 June 1916. Design of the new type had begun in late 1915, so that it was conceptually at least almost contemporary with the B.E.12 and the B.E.2e.
The installation of the 150 hp (112 kW) Royal Aircraft Factory 4a air-cooled V12 engine closely resembled that of the B.E.12, with the same large air scoop and similar vertically mounted exhausts protruding over the upper wing to carry the fumes clear of the crew. The only real difference was that the engine was slightly raked back, to improve take off and landing characteristics.
The single bay, unequal span wings were identical to those of the B.E.2e, although the span (and thus the wing area) was increased slightly by the use of a wider upper centre section, and lower stub wings to match. The tailplane was also the same as the B.E.2e. The entirely new parts of the design were confined to the fuselage aft of the engine firewall, and the vertical fin and rudder.
The new type was intended from the beginning to replace the B.E.2, which was already attracting widespread criticism, and an attempt was made to address each of the earlier type’s main failings. The more powerful motor was intended to improve the feeble speed and climb of the B.E.2, and in particular to allow a better payload. This permitted the type to operate as a true two-seater – since the observer no longer had to be left at home when bombs or a full fuel load were carried, there was no need for his seat to be at the centre of gravity – as a result he could now be seated behind the pilot, in the proper position to operate a defensive machine gun. It was also possible to allow for a pilot’s gun. The new wings had already proved themselves on the B.E.2e – maintaining the stability of the B.E.2c while providing rather better manoeuvrability, although the long extensions on the upper wing looked as if they might collapse if the aircraft was dived too sharply, which did not improve the trust in which they were held by some pilots. The new tail, as originally fitted, had a much smaller fin, which it was hoped would improve rudder control and allow the new type to turn more easily without seriously affecting stability.
In July the second of two prototypes was sent to France for service trials, which were successful, aircrew being generally quite favourably impressed, and by September production was well underway. The Vickers-Challenger interrupter gear and the Scarff ring were both still in short supply, being required for the Sopwith 1½ Strutter and other types, and a few early R.E.8s were built with a pillar mounting for the observer’s gun as an interim measure. An alternative to the pilot’s synchronised Vickers had been designed, consisting of a fixed Lewis gun with deflector plates fitted to the propeller, although this was never actually used – a Vickers gun for the pilot being mounted on the port side of the fuselage in a similar position to that on the B.E.12, at first synchronised by the Vickers-Challenger gear - and then by the improved Constantinesco hydraulic gear. Photographs of this armament installation make it clear that the cocking handle of the Vickers gun was in easy reach of the pilot, and that a normal Aldis sight was mounted in the pilot's windscreen, giving the lie to statements that the forward firing gun could not be sighted properly due to its position.
To make the R.E.8 less tiring to fly the pilot’s controls included a wheel to adjust the tailplane incidence in flight, and a form of primitive rudder trim (applied to the rudder bar itself!) was provided to alleviate the constant pressure necessary to counteract the torque of the propeller. Very basic flight controls were installed in the observer's cockpit – these folded out of the way when not in use. They were connected to the elevators, rudder, and throttle, but not to the ailerons, and were plainly intended to give observers a chance to make a forced landing if the pilot was killed or incapacitated rather than to offer true dual control.
Although much better than the B.E.2 in this regard, the R.E.8 was still underpowered; and a model re-engined with the Hispano-Suiza engine was projected from quite an early stage, being officially designated the R.E.8a. The cowling designed for the liquid-cooled engine closely resembled that of the B.E.12b and the S.E.5a. Supplies of Hispano-Suiza engines, more urgently required for other types, never permitted production of the R.E.8a, although a prototype was built and tested in December 1916. Plans to mount Rolls-Royce aero engines, such as the Falcon, never eventuated for similar reasons. These power plants were in chronically short supply, and were reserved for other types such as the D.H.4 and the Bristol Fighter.
A total of 4,077 R.E.8s were produced with a further 353 on order cancelled at the end of the war. As well as the Royal Aircraft Factory, several private companies built R.E.8s, including Austin Motors, Daimler, Standard Motors, Siddeley-Deasy, and the Coventry Ordnance Works.
- R.E.8 : Standard general purpose aircraft, powered by 140 hp (104 kW) RAF 4a engine.
- R.E.8a : Conversion of one R.E.8 with 200 hp (149 kW) Hispano-Suiza engine in a square, S.E.5 (or B.E.12b) type cowling. No production due to shortage of Hispano engines. At least some of the R.E.8s supplied to Belgium were also re-engined with Hispanos - in this case in a cowling resembling that of the later SPADs.
- R.E.9 : R.E.8 modified with equal-span wings similar to those of the B.E.2c/d and the larger fin and rudder fitted to some R.E.8s at training units. Two were converted in 1917, but they showed no advantage over the standard R.E.8 (climb and manoeuvrability were worse) and no production followed.