Following their experience with the Działowski D.K.D.3 at the first National Lightplane Contest in 1927, the Działowski brothers, Stanisław and Mieczysław, set about designing and funding their entrant to the following year's competition. Several established Polish aircraft companies offered both easy terms for purchase of material and free assembly. The costs of materials were covered by LOPP, while the engine was purchased thanks to the collection of money. The materials were purchased at PZL, PWS and Plage and Laśkiewicz.

 

Both the Kraków branch of LOPP and the Kraków Aeroclub agreed to buy an example. LOPP decided to use a 34 kW (45 hp) Anzani 6 six-cylinder radial engine, the Działowskis' original choice, but the Aeroclub selected a 41 kW (55 hp), five cylinder Siemens-Halske Sh 4 radial. The latter was initially designated D.K.D.5, soon revised to DKD.4bis.

 

The D.K.D.4 was a two-seat parasol monoplane with a three part, wooden, two spar, fabric covered wing which was trapezoidal in plan. The central section was mounted on two outward-leaning pairs of steel cabane struts from the upper fuselage, one to each spar and each outer panel was braced to the lower fuselage longerons with a pair of steel struts to the spars. Its wingtip ailerons were short and broad. There was a large semi-circular cut-out in the central trailing edge to ease cockpit access and enhance the upward field of view.

 

 

 

Its fuselage was similar to that of the D.K.D.3, which had a welded steel tube girder structure with wooden frames, stringers and fabric covering, producing an oval cross-section apart from a flat underside. The radial engines of both versions were mounted with their cylinders exposed but otherwise under a duralumin cowling.

 

The D.K.D.4's empennage was conventional and tidier than that of its predecessor. Its trapezoidal horizontal tail was mounted on top of the fuselage and its similarly shaped fin mounted a rectangular, unbalanced rudder which reached down to the keel, working in a cut-out between the elevators. Their steel tube structure was fabric covered. Larger area, balanced rudders area were added to both examples in late 1929, together with larger ailerons.

 

 

The prototypes had simple, single axle, fixed landing gear with two V-struts with a bracing crossbar between their vertices, though the sole production example dispensed with the crossbar.

 

The two copies of the DKD-IV aircraft were built: one (factory number 1) with Siemens engine, designated DKD-IV bis, and initially named DKD-V, for LOPP, and the second (factory number 2), named DKD-IV for the Academic Aeroclub in Krakow. DKD-IV bis also differed from DKD-IV with cut ends of ailerons. Both copies were built in Park 2 of the Air Regiment in Krakow and flown in September 1928.

 

The D.K.D.4 and the 4bis both made their first flights in September 1928. This gave time for trials and development before the second National Lightplane Contest, which started on 29 October with twelve contestants. Both took part in the 2nd National Competition of Light Ships. J. Bargiel (the winner) and Iwaszkiewiczówna took part in the DKD-IV, and DKD-IV bis, piloted by Kaczmarczyk 9 came 5^th) and M. Działowski. The D.K.D.3, flown by its designer, came third.

 

During the flight from Krakow to Warsaw for the Competition, both planes were damaged, but thanks to the help of the employees of the Polish Aeronautics Company, they were repaired in time. In the DKD-IV Competition he was 1st, and DKD-IV as 3rd.

 

In the autumn of 1928 the commander of the 2nd Air Regiment wanted to order 25 DKD-IV for military aviation, but the Aeronautics Department did not accept the order. The first plane in the series for the army was already under construction. At the turn of 1928 and 1929, S. Działowski completed the construction of this copy (factory number 3), with the Anzani engine for the Academic Aeroclub of Krakow. In 1929 aircraft received new registration marks: DKD-IV bis factory No. 1- SP-ABA, later changed to SP-ABX, DKD-IV factory number 2- SP-ABL and factory number 3 SP-ABY.

 

In 1929, SP-ABA was exhibited at the Universal National Exhibition in Poznań. In May 1930, K. Piotrowski made a flight to Olomouc and Brno in DKD-IV. Airplanes were used for training and promotion flights (eg during ski competitions in Zakopane). In addition, they took part in the South-Western Polish Flight in 1929 (Działowski at SP-ABY won the 3rd prize) and in Podhalańskie Złot Awionetka in Nowy Targ on October 3, 1930. In the Third National Competition of Light Ships in 1930. DKD-IV bis took 11th place. DKD-IV No. 2 SP-ABL was renovated in 1934 and converted into a single-seater, and the fuselage was covered with cloth directly, resulting in its sides becoming flat. The aircraft, after renovation, was used by the Kraków Aeroclub from May 1934 to July 1935.

 

On 28th January 1930 pilot J.Soltykowski flew the DKD.4bis SP-ABL under the Debnin bridge at Krakov three times.

 

 

The later D.K.D.5 was a fully aerobatic and final development of the D.K.D.4 design. It was powered by a 63 kW (85 hp) Cirrus III four cylinder upright air-cooled inline engine mounted exposed. An aerodynamic clean-up included a divided undercarriage with cranked axles and a long oleo strut from the outer axle to the upper longeron on each side. Its wings were foldable and their span and area were 11% greater than the D.K.D.4. It first flew in July 1930, piloted by its designer. Despite a slight increase in weight over the D.K.D.4bis, the large increase of power and the clean-up raised its maximum speed to 175 km/h (109 mph), gave it a ceiling of 4,500 m (14,800 ft) and enabled it to reach 1,000 m (3,300 ft) in six minutes.

 

 

Engine: Anzani 6, 34 kW (45 hp)

Speed ​​max: 135 km / h

Cruising speed: 126 km / h

Stall: 75 km / h

Rate of climb: 1.5 m / s

Ceiling: 2270 m

 

Engine: Siemens-Halske Sh 4, 41 kW (55 hp)

Propeller: 2-bladed

Wing span: 9.0 m (29 ft 6 in)

Length: 5.6 m (18 ft 4 in)

Height: 2.2 m (7 ft 6 in)

Wing area: 13.5 sq.m (145 sq ft)
Empty weight: 345 kg (761 lb)

MAUW: 638 kg (1,407 lb)
Speed ​​max: 140 kph / 87 mph / 76 kn at sea level

Cruising speed: 125 kph / 78 mph / 67 kn

Time to 2,000 m (6,600 ft): 23 min

Service ceiling: 3,000 m (9,800 ft)

Seats: 2

 

Engine: Cirrus III, 63 kW (85 hp)

DKD-IV

 

DKD-V