The Slingsby T.3 Primary (a.k.a. Dagling) was a single-seat training glider produced in the 1930s by Fred Slingsby in Kirbymoorside, Yorkshire.
During the 1920s Alexander Lippisch designed a training glider with very low performance to introduce pilots gradually to full-blown gliding. The result was a glider with a very simple structure of an open framework fuselage, with short wings attached by cables to a king post and the base of the fuselage. Lippisch's original design, the Zögling (Pupil in English) had an all-wood fuselage but Wolf Hirth instigated a redesign of the rear fuselage using steel tubes.
The plans for the modified Zögling made their way via the United States to the London Gliding Club and Reginald Foster Dagnall, whose RFD company put it into production as the RFD Primary. They built 27 in 1930-31. The type became known as the Dagling, a name formed by combining Dagnall and Zögling, which later became used informally to cover all types of primary gliders in the UK. Fred Slingsby took over construction in 1934 and production continued up to the outbreak of World War II. The Primary should not be confused with the similar T.38 Grasshopper which was produced for the Air Training Corps in the 1950s.