Airspeed Envoy / Oxford

1st Flight 1934

Military Users-

Air Force of the Independent State of Croatia, Finnish Air Force, Luftwaffe, South African Air Force, Spanish Republican Air Force, Spanish Air Force, Royal Air Force.

Airspeed Oxford

The Airspeed Envoy was a twin-engined low-wing cabin monoplane of all-wood construction apart from fabric covered control surfaces.

It had a rearward retracting main undercarriage with a fixed tail wheel.

Airspeed Oxford

Having been designed from the onset as a twin-engined development of the company’s earlier Courier, numerous commonalities were shared between the two aircraft, including near-identical wooden construction, the same outer wing panels and the main undercarriage.

The airframe had a plywood exterior while the structure was composed of wood as well and was considered to be conventional for the era.

In a typical configuration, the cabin could accommodate eight passengers along with a single pilot, while the Envoy’s normal fuel capacity was 78 gallons, accommodated within a pair of aluminium tanks in the centre section.

Oxford

A separate aft compartment was normally used to store baggage, accessible via an exterior door on the starboard side of the aircraft.

If the optional lavatory was installed, a reduced maximum capacity of six passengers was necessary.

Passenger access to the cabin was via a single door on the port side of the aircraft.

Oxford

The wing of Envoy changed between models, with early-built aircraft not featuring flaps unlike later production models.

It also featured outboard extension wings, which could optionally accommodate a pair of additional 30 galloon fuel tanks to extend the aircraft’s range.

The wing’s centre section was integral with the aircraft’s semi-monocoque fuselage, possessing an aspect radio of 8.16, a mean dihedral of 5 degrees, and an incidence of 2 degrees at the fuselage.

Oxfords

The Envoy was powered by a range of engines across its various models.

While initial aircraft were furnished with a pair of Wolseley Aries engines, other models were equipped with power plants such as the Armstrong Siddeley Cheetah V and Armstrong Siddeley Lynx IVC radial engines.

Regardless of the engine used, each was accommodated within an appropriate cowling, typically a short chord Townsend ring, but also wider chord cowlings with and without blisters for cylinder heads.

Airspeed Oxfords

The Oxford was normally powered by a pair of Armstrong Siddeley Cheetah X air-cooled radial engines, capable of generating 340 hp.

These were initially outfitted with wooden fixed-position de Havilland-built propellers, but had been designed from the onset to accommodate variable-pitch propellers when these became available.

The starboard engine drives a hydraulic pump and air compressor, the former being used to actuate the undercarriage and flaps while the latter is used for the braking system; a vacuum pump is also present for the gyroscopic instrumentations.

Airspeed Oxford

The port engine drives a 500-watt electrical generator.

The engine cowling features an inlet that draws cooling air into a tank; a pair of tinned steel oil tanks are also contained within the cowling. 

Welded steel construction was used for the nacelles, which attach to the centre section of the wing at four separate rubber-insulated joints.

Airspeed Oxford

The retractable undercarriage of the Oxford was internally designed, featuring broken-braced twin oleo legs that retract rearward into each engine nacelle.

Although actuation of the retraction mechanism is normally achieved via an engine-driven pump, a manual fall-back mechanism is provided to force the wheels down in the event of an in-flight engine failure.

The undercarriage wheels are equipped with pneumatically-operated brakes, controlled by a lever set on each control column.

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For inspection purposes, access panels are located beneath the pilot’s cockpit for internal access to the flight controls, hydraulics and electrical components; inspection panels are also present in the outer wing sections.

The semi-monocoque fuselage of Oxford uses an arrangement of spruce longerons and stiffeners underneath a plywood exterior. 

It is constructed in two sections on separate jigs, divided between the front and rear, these are joined together at the rear bulkhead.

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The forward bulkhead is deliberately reinforced so that the structure is capable of withstanding the impact of the aircraft turning over during landing in the hands of an unfortunate trainee pilot.

Both the elevator and fin of the tail unit used a wooden spar and rib structure covered by fabric.

The fuselage can be partially dismantled, the wing dividing into three separate sections, so that it can be road-transported.

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The wing uses a stressed-skin ply-covered structure using spruce flanges and ply webs.

The spars are assembled upon a single jig, while others are used for the elements of the leading edge and trailing edge.

Similar construction to the centre section is also used in the outer panels.

The wings are outfitted with hydraulically-operated split flaps, which extend between the ailerons.

Oxford

Specifications-

Crew: 1 pilot

Capacity: 6 passengers

Length: 34 ft 6 in (10.52 m)

Wingspan: 52 ft 4 in (15.95 m)

Height: 9 ft 6 in (2.90 m)

Wing area: 339 sq ft (31.5 m2)

Empty weight: 4,057 lb (1,840 kg)

Gross weight: 6,300 lb (2,858 kg)

Oxford

Power plant: 2 × Armstrong Siddeley Cheetah IX seven-cylinder radial engine, 345 hp (257 kW) each

Performance

Maximum speed: 210 mph (340 km/h, 180 kn) at 7,300 ft (2,230 m)

Cruise speed: 192 mph (309 km/h, 167 kn) at 75% power and 7,300 ft (2,230 m)

Range: 650 mi (1,050 km, 560 nmi) at 62.5% power and 10,000 ft (3,050 m)

Service ceiling: 22,500 ft (6,900 m) service

Time to altitude: to 10,000 ft (3,050 m), 8 min

Wing loading: 18.6 lb/sq ft (91 kg/m2)

Power/mass: 0.11 hp/lb (0.18 kW/kg)

Oxford

Credits-

Airspeed Aircraft since 1931-H.A. Taylor.

Aircraft of the Royal Air Force 1918-58-Owen Thetford.

Wikipedia.

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