The Blackburn C.A.15C Monoplane and Biplane were a pair of British aircraft intended to be as similar as possible apart from their wing arrangement.

[1] Unusually, they intended to offer a biplane equivalent, an option made easy by the monoplane's wing-engine configuration.

[2] These designs suggested to the Air Ministry that two otherwise identical aircraft could be built in monoplane and biplane versions to settle the constant dispute over which of these two configurations was the superior.

Because the Air Ministry envisaged the aircraft going to Imperial Airways after the trials, the cabins were fully fitted out for ten passengers, with two compartments containing six and four seats placed singly on either side of a central aisle.

[1] The two versions used the same engines, a pair of 400 hp (300 kW) Armstrong Siddeley Jaguar IVC radials driving wooden two-blade propellers.

[1] The proposed post-trial move to Imperial Airways did not happen for they were already re-equipping, so the biplane was immediately broken up.

The monoplane did do useful service at the Royal Aircraft Establishment at Farnborough in the development of automatic pilots and in wireless experiments in RAF colours as K4241.