Pratt & Whitney R-2800 Double Wasp

Overview

Look at a Double Wasp from the propeller end and the cylinders form a circle. Look along its side and a second row becomes apparent. Eighteen cylinders supply a single shaft, giving aircraft designers a large displacement in a comparatively short engine. [S1]

The cylinders stay fixed to the aircraft while the crankshaft turns. That makes this a radial, unlike early rotary aircraft engines whose cylinder assembly spun around a stationary shaft. Circular appearance does not establish the operating principle. [S5]

Historical Background

Pratt & Whitney developed the engine in the late 1930s and showed it publicly at New York's 1939 World's Fair. Wartime requirements expanded production, but the design also continued into commercial aviation. The manufacturer's retrospective gives 1939–1960 and more than 125,000 engines, including licensed manufacture. [S1, S3]

Ford participated in that manufacturing effort: the USAF museum preserves an R-2800-21 built at Dearborn in 1943. Engineering work continued alongside output. Archival accounts of the crankshaft describe extensive investigation of vibration, counterweights and absorbers. The production engine was the result of repeated development. [S4, S6]

Why It Was Developed

New aircraft asked for more power without an engine of proportionately greater diameter. A second cylinder row added displacement behind the first. That choice brought a problem with it: rear cylinders needed an adequate share of cooling air. [S8, S6]

Powerplant and airframe had to be developed together. The Navy's high-speed fighter requirement helped shape the Double Wasp-powered Corsair; clearance for its large propeller contributed to the inverted gull wing. Cooling-fin and valve-timing investigations likewise show that useful power depended on more than fitting additional pistons. [S7, S8]

Where It Was Used

Thunderbolt, Hellcat and Corsair fighters are familiar applications, but the engine also served multi-engine aircraft such as B-26 Marauder variants and the Curtiss C-46. Aircraft versions require their own engine identifications. [S1]

The civil CB16 carried the design into airline service in DC-6A/B aircraft, Martin 202A/404 aircraft and the Convair 340. An engine family could therefore outlast its original wartime role without every installation sharing the same hardware. [S2]

Key Mechanical Features

• Cam rings: multi-lobed, geared rings distribute valve timing around each cylinder row. Followers, pushrods and rockers open one inlet and one exhaust valve per cylinder; springs close them. [S9, S8]
• Cooling fins and baffles: surface area and directed flow work together to remove heat. [S1, S10]
• Two plugs per cylinder: ignition arrangements vary. A dual system does not necessarily have two separate external magneto housings. [S11, S12]
• Reduction gearing: the propeller runs more slowly than the crankshaft; the ratio belongs to the named variant. [S9, S11]
• Vibration control: counterweights and absorbers address loads from combustion and moving masses. [S6]

Typical Specifications

This table describes the CB16, using Federal Aviation Agency specification E-264, revision 9, dated 6 June 1962. The hero photograph is identified as CB17. [S11]

That rating requires low blower, anti-detonant injection, 59.5 inHg manifold pressure and at least 100/130 aviation gasoline. Omitting these conditions would misrepresent the figure. It is neither continuous output nor a specification for the whole R-2800 family. [S11]

Advantages and Limitations

Two radial rows offered many cylinders and a short crankshaft. Air cooling removed the liquid-coolant circuit, but it demanded careful control of air through the engine. The complete installation could still be large: the P-47's distant turbo needed substantial ducts. [S9, S10]

Heat and vibration constrained increased output. NACA tests compared cooling fins and valve timing, finding tradeoffs between operating conditions. Some ratings also depended on anti-detonant fluid injection to permit higher boost for limited periods. That additional equipment controlled abnormal combustion; it did not replace basic cylinder cooling. [S8, S6, S12]

Why It Was Replaced or Discontinued

Pratt & Whitney gives 1960 as the end of new production. Aircraft already in service did not all stop flying then. [S3]

Jets and turboprops changed new-aircraft choices as airlines sought different combinations of speed and operating capability. A turboprop retained a propeller but used a gas turbine in place of the reciprocating engine. Adoption proceeded by mission and operator, leaving useful work for existing piston aircraft. [S13]

Modern Use and Surviving Examples

Collections preserve different versions and teaching cutaways. The Ford-built USAF specimen and Smithsonian CB16 record document specific objects; the latter was listed as not on display in Dora's 2 October 2026 check. Museum ownership does not establish running condition. [S4, S2]

Operator evidence is more specific. The Flying Bulls identifies R-2800 power in its DC-6B and documented a summer 2026 U.S. tour. Everts Air's fleet page, checked on 2 October 2026, listed DC-6 aircraft with CB17 engines. These dated records support those examples, not a blanket claim about every surviving engine's airworthiness. [S14, S15, S16]