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The Boulton & Paul P.25 Bugle was a further development of the P.7 Bourges and all-metal P.15 Bolton twin engined bombers, and was produced in small numbers as part of the Air Ministries attempt to keep as many aircraft companies working as possible with limited funds.
The P.7 Bourges was a twin engined three-man fighter bomber that was almost as manoeuvrable as the fighter aircraft of 1918, but that didn't enter production before the end of the First World War. The P.15 Bolton was a similar aircraft, but with an all metal structure, and was the first all-metal aircraft to be delivered to the RAF.
The first two prototypes of the P.25 Bugle were ordered under Specification 30/22 in 1922. Like the Bourges and the Bolton it was a twin engined three man aircraft, now considered to be a medium bomber. Most of the structure used Boulton & Paul's locked joint system of steel tube construction, but the Air Ministry also allowed the use of some light alloys, so features such as the outer wing struts were made of the lighter duralumin. The Bugle was a three bay biplane. On the Bugle I the engines was mounted between the wings, on the same line as the inner wing spars. On the Bugle II the engines were mounted on the lower wings. On the Bugle I the fuel tanks were carried below the upper wings, as the Air Ministry had imposed a ban on fuel tanks within the fuselage.
The wings had the standard Boulton & Paul square ends, as did the tail surfaces. The horizontal tail surfaces were rectangular, with a cut out at the back to allow the rudder to move. The vertical tail had an inverted 'L' shaped rudder at the back, and an overall rectangular profile. In level flight the bottom of the tail was just above the level of the lower wing.
The fuselage had flat sides on the bottom half, and taped up to a point at the top, to allow the rear gunner a good field of fire downwards. The nose was changed from the Bourges/ Bolton model, where the pilot and nose gunner had been on about the same level. On the Bugle the nose gunner's position was lowered, to a position half way between the wings, and his gun ring was tilted slightly forward to improve his field of fire down. The pilot was above and behind, closer to the level of the upper wing, and with a better forward view. The bombs were carried externally, with two bomb rails under the fuselage and two under the inner wings. The nose gunner was also the bomb aimer, and had limited flight controls for use on the bomb run.
The first two prototypes were powered by 400hp Bristol Jupiter engines. The first (J6984) made its maiden flight on 30 June 1923 with Frank Courtney at the controls, and the second (J6985) made its maiden flight later in the year.
In 1924 a third prototype (J7235) was built. This was powered by Jupiter IV engines and carrying a crew of four. The wing span was reduced to 62ft 6in. This aircraft became the first Boulton & Paul design to reach a front line squadron, spending some time with No.58 Squadron in 1925. The squadron leader flew the aircraft at the 1925 Hendon Display, where he held his own in a mock dogfight with two Gloster Glebe fighters, showing that the basic Boulton & Paul design was still impressively manoeuvrable.
Another two Jupiter powered Bugle Is were ordered in January 1924 (J7259 and J7260). These were similar to J7235, with the reduced wingspan.
In 1925 two prototypes of the Bugle II were ordered (J7266 and J7267). These were powered by Napier Lion engines, which were mounted on the lower wings and the fuel tanks were moved from the upper wings to reduce drag (after the Air Ministry lifted its ban). The bomb carriers were given fairings to improve streamlining.
The Bugle was just as manoeuvrable as the earlier Bourges and Bolton, but in the mid 1920s the RAF had no real interest in medium bombers, and so very few were purchased. The two Bugle IIs were probably ordered to keep Boulton & Paul in the aircraft industry, at a time when funds were limited but their expertise in metal construction was seen as valuable. The company's hard work was soon to pay off, when the Boulton & Paul P.29 Sidestrand was ordered into production.
Bugle I (first two prototypes)
Engine: Two Bristol Jupiter II or III
Power: 400hp each
Crew: 3
Span: 65ft 0.5in
Length: 39ft 9in
Height: 15ft 8in
Empty weight: 5,079lb
Loaded weight: 8,110lb
Maximum take-off weight:
Max speed: 120mph at sea level
Climb Rate: 15min 30sec to 10,000ft
Armament: Two Lewis guns, one in nose, one in dorsal position
Bomb load: External bombs
Bugle I (modified prototypes)
Engine: Two Bristol Jupiter IV
Power: 434hp each
Crew: 4
Span: 62ft 6in
Length: 39ft 9in
Height: 15ft 8in
Loaded weight: 8,670lb
Maximum take-off weight:
Armament: Two Lewis guns, one in nose, one in dorsal position
Bomb load: External bombs
Bugle II
Engine: Two Napier Lions
Power: 450hp each
Span: 62ft 6in
Length: 39ft 9in
Height: 15ft 8in
Loaded weight: 8,914lb
Maximum take-off weight:
Max speed: 112mph at sea level
Armament: Two Lewis guns, one in nose, one in dorsal position
Bomb load: External bombs