At the end of 1925 at the Martens gliding school on the Wasserkuppe into Rhön-Rossitten Gesellschaft (RRG), Martens chief instructor Fritz Stamer and Alexander Lippisch were brought together to produce two such gliders and within a few days the Zögling (English: Pupil) and the Prufling designs were complete. Some parts, for example the wings and to a lesser extent the horizontal tails, of the two aircraft were similar.

Both had almost rectangular, two-spar, wooden structured, two piece wings with fabric covering everywhere except the leading edges, which were plywood covered. The Prüfling’s wing tips were more rounded and its span 500 mm (19.7 in) greater. They both had simple ailerons reaching to the tips, where they were cropped, though the Prüfling’s were a little longer. Both had triangular tailplanes, carrying elevators that were rectangular apart for a cut-out for rudder movement, though the Prüfling’s tailplane was more strongly swept and was broader in chord.

The major differences between the two were in the fuselages. The Zögling had a very simple open frame girder fuselage, the Prüfling a more conventional hexagonal cross section, wood-framed structure, ply covered forward from under the wing and fabric covered aft. The wing was supported over the fuselage with a pair of parallel lift struts on each side, bracing it at almost mid-span at the spars to the lower fuselage longerons. The open cockpit was below the wing centre section which was supported by two pairs of cabane struts to the upper fuselage longerons. The forward pair, placed just in front of the cockpit were single, upright struts but the rear ones, just behind, were each an inverted V-pair. At the centre there was a noticeable gap between the wings, bridged by a short chord wooden link. The horizontal tail was positioned on the upper longerons. with a triangular fin carrying an upright, straight edged balanced rudder which was slightly angled below the heel and extended down to the keel. The Prüfling landed on a rubber sprung skid below the whole forward, ply skinned fuselage, assisted by a very small tailskid.

It first flew in 1926 and was soon in use with the RRG related Rhön and Rossitten gliding clubs. Plans were sold and many were built inside and outside Germany.[ As examples, one was flying with the Lancashire Aero Club and another with the London Gliding Club in the early 1930s. Despite such success, the Prüfling was something of a disappointment as a secondary training aircraft, for its performance was not much better than typical primaries. Its handling was also not good, with a lack of inherent stability. Lippisch returned to the design of secondary gliders four years later, after exploring tailless types, resulting in the RRG Falke.

A Prüfling was the first glider used by the United States Navy. A single German-made aircraft was purchased from a U.S. civil glider school, assigned serial number A8546, and used for airship launch tests; the first such launch was made from USS Los Angeles (ZR-3) on 31 January 1930. The Prüfling was never assigned a formal U.S. military aircraft designation.

Wingspan: 10.50 m (34 ft 5 in)
Wing area: 15.24 sq.m (164.0 sq ft)
Length: 5.484 m (18 ft 0 in)
Aspect ratio: 7.23
Empty weight: 105 kg (231 lb)
Gross weight: 195 kg (430 lb)
Wing loading: 12.8 kg/m2 (2.6 lb/sq ft)
Capacity: One

1938 Proefling
Wingspan: 42 ft
Length: 19.5 ft
Wing area: 230 sq.ft
Aspect ratio: 7.7
Empty weight: 320 lb
Gross weight: 500 lb
Mn sink: 3 ft/sec
Glide ratio: 15-1

Built by RRG following research by Lippisch and Stamer. The fuselage was a polygonal section rather than monocoque, and the central part of the braced wing was completely straight, which was unusual for circa 1922.

Named for design lead Reginald Foster Dagnall, the all-wood R.F.D. 2’s unusual dual span cantilever wing had outer sections with constant chord, slight sweep, blunt tips and full width ailerons, joined by a choice of two rectangular centre sections. The sailplane centre section was about 15 ft (4.57 m) long, reduced to about 5 ft (1.52 m) for the secondary trainer role. The wing was not fitted with flaps or airbrakes.

The fuselage of the R.F.D. 2 was a flat-sided monocoque with the wing mounted directly on top of it. The single seat open cockpit was immediately ahead of the wing leading edge. The main landing skid ran from the nose to about mid-chord and there was a small tail skid. The triangular tailplane, mounted on top of the fuselage, and curved fin were both small but carried generous, curved edged control surfaces. The rudder extended to the bottom of the fuselage, moving between the elevators.

The R.F.D. 2 first flew in February 1931 but seems not to have received certification or registration. Only one had been built when, in January 1932, the R.F.D. company announced it was selling its glider interests to the British Aircraft Company and would concentrate on its products for the Air Ministry.

Wingspan: 48 ft 0 in (14.63 m) long span; short span 38 ft 0 in (11.58 m)
Wing area: 210.0 sq ft (19.51 m2) long span; short span 165 sq ft (15.33 sq m)
Aspect ratio: Long span 11.0; short span 8.45
Length: 26 ft 3 in (8.00 m)
Empty weight: 250 lb (113 kg) long span; short span 215 lb (97.5 kg)
Gross weight: 410 lb (186 kg) long span
Rate of sink: 120 ft/min (0.61 m/s) maximum, long span; short span 150 ft/min (0.76 m/s)
Lift-to-drag: Minimum, long span 23.4 at 32 mph (51 km/h); short span 20.4 at 34.7 mph (55 km/h)
Wing loading: 1.85 lb/sq ft (9.0 kg/m2) long span

Primary training gliders evolved as very simple, even crude, airframes sufficiently basic and strong to withstand the rough handling of inexperienced beginner pilots while having just enough flying ability (and vices) to give the trainee pilot the feel of the controls and enable him to grasp the basic skill of controlling an aircraft in flight. The best known British prewar example in this category was the Dagling, a primary glider the prototype of which was built in 1930 by R. F. Dagnall, founder of the R.F.D. Co Ltd, for the London Gliding Club using plans acquired through America; this was a version of the German Zogling primary, and the combination of ‘Dagnall’ and ‘Zogling’ resulted in the name Dagling, which was often later applied to all primary gliders regardless of their true identity.

The Dagling had a low aspect ratio constant chord wing from which a rudimentary wooden A-frame fuselage framework was suspended housing the pilot, the tail unit being carried on four steel tubular members – these had
been wooden members in the Zogling, but were changed to metal to give a stronger support for the tail. Simple wood and fabric construction was employed, with wire-braced wings and only a main skid on the bottom fuselage member for the landing gear. Some Daglings had a nacelle fitted to give the pilot some protection from the elements, while others had rounded instead of squared-off wing tips, and at least one had a nacelle with two seats in it.

Although pretty basic, the Dagling was successful enough to go into production and the R.F.D. Co built at least 27 but in January 1932 announced the cessation of its glider making activities to concentrate on its Air Ministry contracts.

Dagling production was taken up by several other British firms, the foremost of which was Slingsby, which started building the type at Scarborough in 1933 as the T3 Primary, and eventually built 67; Slingsby’s 1933 price for a complete Dagling was £45, and this had risen to £57 15s (£57.75) by 1939, or £66 with a nacelle. For amateur constructors, the British Gliding Association offered a complete set of Dagling plans in 1933 for only £2. Dagling production was also undertaken by Hawkridge Aircraft Ltd, who built five after the war, by Dart Aircraft Ltd, by the Dunstable Sailplane Co, who built one, and Abbott Baynes Sailplanes Ltd; the type’s simplicity also enabled it to be built by students at technical schools and colleges such as the College of Aeronautical Engineering, who built one at Redhill.

The Dagnell-Brewsher Primary was allocated C. of A. No. BGA 171.

The Dart Zogling was built from the same plans as the RFD Dagling.

Several other nations produced single-seater primary types in the 1930s basically similar in appearance and performance to the Dagling, such as the Italian Allievo Pavullo, also available with or without a nacelle, the US-designed Denver Primary and the German Schulgleiter SG 38 (the 108-14) and the Grunau Ei.

Slingsby T3 Primary
Span: 33 ft 0 in
Span: 33 ft 11.5 in (with rounded tips)
Wing area: 15.06 sq.m / 162 sq.ft
Aspect ratio: 7.1
Length: 17 ft 10.5 in
Empty Weight: 82 kg / 180 lb
Payload: 91 kg / 200 lb
Gross Weight: 173 kg / 380 lb
Wing Load: 11.5 kg/sq.m / 2.35 lb/sq.ft
Stalling speed: 25 mph
No. of Seats: 1