The Doak 16, which received the Army designation VZ-4, was built in 1957. It was 32 ft long, had a gross weight of 3,200 lb, a tandem two-seat cockpit, and a 16 ft wingspan. Each wing ended in eight-bladed 4 ft wide propellers within tilting ducts; they were powered by a single 860 bhp Lycoming YT53 engine.

The first flight was made on 25 February 1958. Transition from hover to 200 kt could be made in less than 20 seconds. Variable inlet guide vanes controlled roll in hover, and engine exhaust gases were deflected at the rear of the fuselage for pitch and yaw control. Deceleration and descent had to be carefully controlled in order to prevent the lip of the duct from stalling, as well as to manage a large upward pitching moment from the ducts acting as a wing at a high angle of attack. The Doak 16 suffered from a lack of control power, but completed over 50 hours of testing and proved the feasibility of the tilt duct concept.

The only example of the Type can be seen in the US Army Transportation Museum at Fort Eustis.

Source: AHS V/STOL Wheel


Data on design, manufacture and status

Design authority: Doak Aircraft Company, Inc.

Primary manufacturer: Doak Aircraft Company, Inc.

Parent type: No type defined

Aircraft status: No longer flying


Primary flight and mechanical characteristics

VTOL type: Convertiplane

Compound type: N/A

Lift configuration: Tilt rotor/prop/duct (x2)

Dedicated control device: Other

Crew required: 1-2

Crew seating: Tandem

Landing gear: Wheels (non-retractable)

Layout and Dimensions

Data on aircraft size

Overall Dimensions
Overall Height:  
Overall Length:  
Overall Width:  
Airframe Dimensions
Airframe Length:  
Airframe Width:  
Airframe Height:  
Landing Gear Dimensions
Landing Gear Base:  
Landing Gear Track:  
Cabin Dimensions
Cabin Internal Height:  
Cabin Internal Length:  
Cabin Internal Width:  

Weights and Performance

Data on aircraft weight and flight characteristics

Max Gross Weight (ground): 1,452 kg 3,200 lb
Max Gross Weight (airborne):  
Max Take-off Weight: 1,452 kg 3,200 lb
Empty Weight:  
Useful Load:  
Empty Weight Fraction:  
Climb Performance
Max Rate of Climb:  
Hover Performance
Hover Ceiling IGE:  
Hover Ceiling OGE:  
Max Level Flight Speed:  
Never Exceed Speed:  
Service Ceiling:  
Range and Endurance
Max Range:  
Max Endurance:  

Engine Details

Aircraft powerplant (lift and/or propulsion)

Provided powerplant data is for uninstalled, sea level, static operations.

Number of engines: 1
Designation: Lycoming YT53 turbine
Manufacturer: Lycoming Engines
Normal Ratings
Max continuous:  
Take-off / rated:  
OEI Ratings
OEI contingency:  
OEI continuous:  
OEI 30-second:  
OEI intermediate:  

Primary Lift Device

Data on primary lift devices such as main rotors

Ducted fans

Main Rotor Characteristics
Diameter: 1.22 m 4.00 ft
RPM: 4800.0 rpm 4800.0 rpm
Direction of Rotation: Counter-rotating
Hub Type:
Main Rotor Blade Characteristics
Blade Construction:
Blade Chord:  
Blade Tip Geometry:
Blade Twist:  
Number of Blades: 8
Main Rotor Derived Characteristics
Disc Area: 1.17 m² 12.6 ft²
Disc Loading: 621.65 kg/m² 127.324 lb/ft²
Main Rotor Blade Derived Characteristics
Blade area per blade:  
Tip Speed: 306.42 m/s 1005.3 fps

Primary Control Device

Data on primary control devices such as tail rotors

Tail Rotor Characteristics
Configuration: Unknown
Direction of Rotation: Unknown
Tail Rotor Blade Characteristics
Number of Blades:  
Blade Construction: N/A
Blade Chord:  
Blade Twist:  
Tail Rotor Derived Characteristics
Disc Area:  
Tail Rotor Blade Derived Characteristics
Tip Speed:  
Blade Area (per blade):  

Related VFS Resources

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Related Public Resources

Resources related to the 16/VZ-4 , provided by public sources across the internet.