The Bristol Fighter was powered by a Vee form liquid cooled Rolls Royce engine (Falcon as I recall ), a forerunner of the Merlin.
(There is an example in the Rolls Royce Heritage collection at the Sinfin site in Derby )
The "Brisfit" was distinguishable by the gap between the fuselage and the lower wing.
Air cooled Rotary engines (such as the Gnome, Le Rhone, Clerget, Bentley BR2 and their German counterparts ), were used in aircraft like the Vickers Gun Bus, De Havilland DH2, (Both "pushers" ) various Sopwiths, and the Avro 504, as well, of course, in the various Fokkers.
The Gnome Monosoupape (="Singlevalve" ) was unusual in that the the Inlet valve was within the Piston, so the only external valve needing to be operated was the Exhaust.
Initially, the advantage was the better power to weight ratio compared to the in line engines of the time, but development saw that overtaken.
Being lubricated by Castor oil, on a total loss system, the pilots emerged dirty after a flight, and never suffered from constipation!
Having no throttle, power was reduced for landing by using the "blip switch" which shorted out the magneto for as long as it was held down, so that the engine "windmilled" rather than producing power.
The son of the British Airports chief, (Masefield ) used to have a replica Vickers Gun Bus at Shoreham by Sea airport. On a Sunday morning it could be seen and heard, particularly during landing.
Because of the torque reaction the aircraft would roll more quickly in one direction than the other, which was valued by the fighter pilots of the time.
Howard