Channel wing
A half-tube wing principle using a ducted propeller for enhanced lift.
The channel wing is an aircraft design where an engine sits inside a half-tube, with its propeller at the rear of that channel. Willard Ray Custer came up with the idea in the 1920s. The concept works like a ducted fan: the half-tube speeds up the airflow through it. Because the top of the tube is cut away, the fast-moving air creates lift only upward. This shares some ideas with the coleopter, a circular-duct design meant for true vertical takeoff and landing.
Aircraft using the channel wing could take off and land in very short distances, but the design had serious problems and never caught on. One major issue: as long as the engine runs, the lift can’t be turned off. On a twin-engine plane, if one engine fails, that wing produces much more lift than the other, making control extremely difficult. The design also required complex mechanical work, which usually made the aircraft heavier.
**Development** In 1925, Custer saw strong winds lift a barn roof. He realized the high wind speed created low pressure above the roof while pressure stayed high inside, blowing the roof off. This same low-pressure-above, high-pressure-below effect gives an airplane wing lift. Custer studied this and by 1928 had built the first models of a wing with a half-tube shape instead of the usual profile. He patented the idea in 1929. He kept refining the half-tube channel wing, and on November 12, 1942, the CCW-1 (Custer Channel Wing 1) made its first flight. Custer built more experimental aircraft; the last was the CCW-5, with a few made in 1964.
**Operating principle** Custer said that lift depends on the speed of the air flowing over the wing, not the speed of the plane itself: it’s the air’s speed, not the aircraft’s airspeed. A normal wing works because air above it has lower pressure than air below. A conventional plane must reach a certain minimum speed before that pressure difference is big enough to lift off. In Custer’s channel wing, the spinning propeller pushes a steady stream of air backward through the channel. A propeller on the low-pressure side would normally draw air from all directions. But because the half-tube blocks air from coming from below, the air is forced through the channel instead. This creates a low-pressure area in the channel, which generates lift.
- Developer
- Willard Ray Custer
- First model year
- 1928
- Patent year
- 1929
- First flight
- November 12, 1942
- Aircraft designations
- CCW-1, CCW-2, CCW-5
- Ccw1 takeoff distance
- 200 feet (61 m)
- Ccw2 takeoff distance
- 66 feet (20 m)
- Minimum takeoff speed
- 20 miles per hour (32 km/h)
Lore & Background
In 1925, Custer observed how strong winds had lifted the roof of a barn, realizing that high-velocity wind created lower pressure above the roof while pressure remained high inside, the same phenomenon that allows an airplane wing to provide lift. By 1928 he had made the first models of a wing with a half-tube section instead of the usual wing profile, patenting the idea in 1929. The half-tube channel wing was refined further, and on November 12, 1942, the CCW-1 airplane flew for the first time. Custer built additional experimental aircraft; the last was CCW-5, of which a few were manufactured in 1964.
Custer's summary of his invention was that lift is created by the velocity of the stream of air passing over the wing, not the velocity of the airplane itself. In the channel wing, the rotating propeller directs a stable stream of air backwards through the channel. Since the half-tube prevents air from being drawn from below, air moves through the channel instead, creating a low-pressure area that generates lift. Although Custer showed theoretically and experimentally the principle of vertical flight, his designs used conventional rudders requiring airspeed, so none were capable of vertical takeoff; they were characterized as STOL aircraft. The required runway for takeoff was remarkably short: 200 feet for the CCW-1 and 66 feet for the CCW-2, with a takeoff speed as low as 20 miles per hour.
A significant issue is that there is no way to 'turn off' the lift as long as the engine is running; in the case of a single-engine failure on a twin-engine plane, this leads to dramatically more lift on one wing than the other, making control very difficult. It also introduces a challenging mechanical design that generally leads to higher weights. At higher speeds and high propeller RPM, oscillations occurred around the propeller, causing increased noise and long-term destructive vibrations. The twin-engine layout was the most tested configuration but had a higher risk of loss of control during single-engine failure and required a high nose-up attitude for STOL flight.
Reader's Guide
The channel wing principle, though never widely adopted, represents a notable attempt to improve low-speed lift and short-field performance. Custer's designs demonstrated remarkably short takeoff distances—200 feet for the CCW-1 and 66 feet for the CCW-2—and a takeoff speed as low as 20 miles per hour. However, the concept had several drawbacks that prevented its widespread use. A critical issue was the inability to 'turn off' lift while the engine ran, making single-engine failure in twin-engine configurations extremely hazardous due to asymmetric lift. The design also incurred higher weight and mechanical complexity. Later NASA research concluded that the advantages in lift and field length did not offset deficiencies in climb and high-speed ability, and that a conventional straight wing could provide almost equivalent lift enhancement when exposed to the same slipstream-induced dynamic pressure. Despite these limitations, the channel wing has seen renewed interest in hybrid forms: from 1999–2004 a joint research project used channel wing layouts with circulation control devices leveraging the Coandă effect, and in 2017 the startup Hop Flyt Inc. was founded around eVTOL aircraft using channel wing technology for vertical flight, targeting the remote resupply market with claims of 90% lower operational cost and 50-fold CO2 reductions.
Did You Know?
- The channel wing was developed by Willard Ray Custer in the 1920s after he observed a barn roof lifted by strong winds in 1925.
- The CCW-1 had a takeoff distance of only 200 feet (61 m), and the CCW-2 required just 66 feet (20 m).
- Two of Custer's CCW aircraft survive: CCW-1 at the Smithsonian's National Air & Space Museum and CCW-5 at the Mid-Atlantic Air Museum.
- In 2017, startup Hop Flyt Inc. was founded to develop eVTOL aircraft using channel wing technology for vertical flight.
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