Consolidated Vultee XP-81

Consolidated‑Vultee XP‑81

Origins and Strategic Context

The Consolidated‑Vultee XP‑81 was conceived during the closing phase of the Second World War, when the U.S. Army Air Forces sought fighters with both long‑range endurance and high‑speed combat capability.

Early turbojets offered speed but suffered from short range, while turboprops promised excellent fuel economy but lacked high‑altitude performance.

The XP‑81 was designed as a mixed‑power fighter, combining a turboprop for cruise with a turbojet for combat, reflecting the transitional moment between piston‑engine fighters and the emerging jet age.

Development History

Concept Phase (1944)

Convair proposed a single‑seat fighter powered by:

A General Electric TG‑100 turboprop in the nose

An Allison J33 turbojet in the rear fuselage

This hybrid arrangement aimed to deliver long‑range escort capability for Pacific operations and anticipated postwar strategic missions.

Engine Delays and the Merlin Substitution

The TG‑100 turboprop was still in early development and suffered repeated delays.

To avoid halting the airframe test programme, Convair installed a Rolls‑Royce Merlin V‑1650‑7, the American‑built Packard version of the famous British engine.

This was the same engine family powering the P‑51 Mustang, and its reliability made it ideal for initial flight trials.

First Flights (1945)

The XP‑81 first flew on 7 February 1945 with the Merlin engine driving a four‑blade propeller.

These flights focused on:

Airframe handling

Aerodynamic behaviour

Systems integration

Jet‑engine airflow testing

The Merlin‑powered prototype demonstrated stable handling and validated the basic airframe design.

Transition to Turboprop Testing (1946)

Once the TG‑100 became available, the Merlin was removed and the turboprop installed.

The aircraft resumed testing in 1946, now operating with its intended hybrid propulsion system.

However, the turboprop suffered from the following:

Gearbox vibration

Power delivery inconsistencies

Maintenance complexity

These issues slowed progress and prevented full performance validation.

Cancellation (1947)

By 1947, pure jet fighters such as the P‑80 Shooting Star and emerging designs like the F‑86 Sabre rendered mixed‑power concepts obsolete.

The XP‑81 programme was cancelled, and the second prototype was never completed.

Design and Technical Characteristics

Airframe

The XP‑81 featured:

A streamlined, mid‑wing monoplane layout

All‑metal construction

Tricycle landing gear

A bubble canopy for excellent visibility

Laminar‑flow wing profiles inspired by late‑war fighter research

Propulsion System

The XP‑81’s defining feature was its hybrid propulsion arrangement.

Rolls‑Royce Merlin V‑1650‑7 (Prototype Only)

Used for initial flight testing

Approx. 1,700 hp

Liquid‑cooled V‑12 piston engine

Provided reliable, predictable thrust for early airframe evaluation

Allowed Convair to begin flight testing months before the turboprop was ready

The Merlin never represented the intended operational configuration, but it was essential to keeping the programme on schedule.

General Electric TG‑100 (XT31) Turboprop

Approx. 2,300–2,500 shp

Drove a large four‑blade propeller

Intended for long‑range cruise efficiency

Suffered from early‑generation turbine reliability issues

Allison J33 Turbojet

Approx. 4,000 lbf thrust

Side‑mounted intakes

Tail exhaust nozzle

Provided high‑speed dash capability for combat

Performance (Projected)

Because the turboprop‑jet combination was never fully refined, performance figures remain estimates:

Max speed: ~540 mph

Cruise: 300–350 mph

Range: ~1,200 miles

Ceiling: ~40,000 ft

Armament (planned): Six .50‑cal machine guns

Variants

XP‑81 Prototype 1

Flew with Merlin engine initially

Later converted to turboprop configuration

Only prototype to fly

XP‑81 Prototype 2

Never completed

Intended to incorporate improvements from early testing

Operational and Historical Significance

The XP‑81 represents a technological crossroads:

One of the earliest American attempts at hybrid turbine propulsion

A reflection of wartime urgency and postwar technological acceleration

A demonstration of how rapidly pure jet fighters overtook mixed‑power concepts

Its brief life highlights the speed at which aviation technology evolved between 1944 and 1947.

Legacy

Although it never entered production, the XP‑81 contributed to:

Early turboprop development

Mixed‑propulsion research

The broader transition from piston fighters to jets

Digital Artworks by Peter Coletti.