• Crew: one, pilot (two in training version with bench seat)
• Length: 23 ft (7.01 m)
• Wingspan: 25 ft 8 in (7.82 m)
• Height: 10 ft (3.05 m)
• Wing area: 240 ft² (22.30 m²)
• Empty weight: 1,297 lb (590 kg)
• Loaded weight: 1,742 lb (792 kg)
• Powerplant: 1× Clerget rotary engine, driving a two blade wooden propeller, 130 hp 

Performance

• Maximum speed: 90 knots (103 mph, 162 km/h) at sea level
• Service ceiling: 10,000 ft (3,050 m)
• Rate of climb: to 2,000' (2 min 42 sec) to 6,500' (11 min 00 sec)
• Endurance: 2.25 hrs

Armament

• 1 × Lewis gun
• 2 × 65 lb (28 kg) bombs

In its final production evolution, the Sopwith Baby utilized a 130 HP Clerget Rotary engine. This engine produced the performance specifications as listed above. Availability, cost, and reliability issues rule out an original engine in favor of an appropriate substitute.

Therefore, it stands to reason that in order to reproduce an airworthy replica while maintaining appropriate authenticity, the goal is to replicate the above specifications for the 130 HP Clerget powered Baby as closely as practical while ensuring that design flight and thrust loads are neither exceeded, nor grossly underestimated.

  

Analysis of the Original Power Plant

Specifications (Clerget Type 9B)

General characteristics

• Type: 9 cylinder air cooled rotary
• Bore: 120mm (4.7 in)
• Stroke: 160mm (6.3 in)
• Displacement: 16.3 Liters (992 cu in)
• Dry weight: 173kg (381 lb)

Components

• Fuel system: Carburetor
• Cooling system: air

Performance

• Power output: 130 (96 kw) hp @ 1,250 RPM

To determine torque output of original engine, therefore…..

                                                     Horsepower * 5252
                              Torque  =       -----------------                = 546.2 Foot lbs
                                                RPM

To evaluate horsepower at T.O. rpm of considered replacement engine....

                                                                   Desired Torque (546.2) * RPM
           Horsepower      =      -------------------------------
                                                                   5252




The above factors will determine the basic evaluation criteria of considered engines.