P.Z.L. P.46 Sum from the left
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The P.Z.L. P.23 Karas (Crucian-carp) was a reconnaissance aircraft and light bomber that performed well in the bomber role after the German invasion in 1939, before heavy losses reduced its effectiveness.
In 1931 the Polish Department of Aeronautics issued a requirement for a new armed reconnaissance and army support aircraft, to replace the mix of Potez XXVs, Potez XXVIIs and Breguet XIXs being used as ‘liniowe’ or ‘front-line type’ aircraft. The ‘liniowe’ type was a close support and reconnaissance aircraft that was expected to be able to operate largely unopposed by enemy fighters. The type had been developed after the Russo-Polish War of 1919-20, where that had indeed been the case, but only because neither side had many aircraft, so air battles were very rare.
At the time P.Z.L. has a design ready for a single-engine six-passenger transport, the P.Z.L. 13, but the Polish ‘Lot’ airline wasn’t interested it. After discussions between the aircraft’s designer Stanislaw Prauss and the Department of Aeronautics it was decided to use this design as the basis for the P.Z.L. entry into the design contest.
Late in 1931 the basic design won out over the two-seat high-wing monoplane P.W.S.19 and the Lublin R.XVII biplane, and development of the new P.Z.L. P.23 was approved in the spring of 1932. A contract for three flying prototypes and a static-test aircraft was given in the autumn of 1932.
The prototype P.23 was a low wing monoplane, powered by a Polish Skoda licence built Bristol Pegasus radial engine. It had a fixed undercarriage with streamlined spats, a enclosed cockpit for the pilot leading back to an open position for the rear gunner. Below the fuselage was a gondola which contained a ventral gun position and the bomb aimer’s position. In an attempt to produce a light but strong wing Prauss used a torsion-box wing, with front and rear spars connected by ribs. The observer also operated as the ventral gunner and bomb aimer, although they had to fold up their seat to be able to drop down into the gondola.
The static tests revealed some weaknesses in the design, and weren’t successfully passed until the end of 1933. As a result the production of the flying prototypes was delayed.
The first prototype, P.23/I, was powered by a 570-590hp Bristol Pegasus IIM2 engine, driving a two-blade wooden Szomanski aircrew. It made its maiden flight in August 1934, by which time it had already been realised that visibility for the pilot and observer was poor, and the large internal bomb bay made it difficult for the crew to reach their positions. The /I also suffered from vibration in the rear fuselage and tail flutter.
The second and third prototypes, P.23/II and P.23/ III, were modified to try and solve some of these problems. On the P.23/II the engine was moved down and given a low drag cowling. The bomb bay was removed, and the bombs carried on racks between the undercarriage legs. The pilot’s and observer’s compartments were redesigned to make them larger, and were given much more glazing. The wings were given slotted ailerons and flaps. It was powered by a Pegasus II engine, and flew in the spring of 1935. It was an improvement over the /I, but the pilot’s view was still poor. The second prototype crashed early in the summer of 1935 during airworthiness trials, and the crew were killed.
The third prototype, P.23/III, was modified once again. The engine was lowered once again, placing it well below the central axis of the fuselage, while the pilot’s seat was raised, the cockpit canopy was raised and the windscreen modified. The /III was used to complete the airworthiness and service acceptance trials, then as the development aircraft for the Karas A. It was then given a more powerful 680hp Pegasus VIII engine and was used as the development aircraft for the Karas B.
P.23 Karas A
Production of the P.23 Karas A began in the spring of 1935 at P.Z.L.’s new Okecie plant. The first airframes were ready by the end of the year, but problems with the Pegasus II delayed delivery.
The Bristol produced Pegasus engines had suffered from some problems, but these weren’t too bad. In comparison the Pegasus engines being built under licence at the former Polish Skoda Works (now owned by P.Z.L.) suffered from regular crankshaft failures and jammed reduction gears. The problem was eventually traced to faults with the plans issued by Bristol – their subcontractors had found problems with the original design which they had solved, but the Pegasus II then went out of production in the UK, so the original plans weren’t updated. Poland had been given the faulty plans. As a result the Polish engines had to be modified, and were never quite right.
The Karas A wasn’t approached for service use until June 1936, and its service ceiling was limited to 9,842ft (3,000m). Forty Karas As were built, all of which were soon withdrawn from front line units and used as trainers.
Both the Karas A and Karas B could carry up to 1,543lb of bombs on external racks. They normally carried six 220lb bombs, eight 110lb bombs of 24 27.5lb fragmentation bombs.
P.23 Karas B
The main production version was the P.23 Karas B, which was powered by a much more reliable 660-680hp Pegasus VIII radial air cooled engine.
Deliveries of the Karas B began in the autumn of 1936. By the end of 1937 200 P.23 Karas Bs had been delivered, and by early 1938 seventeen squadrons were being equipped with the type. However there weren’t quite enough aircraft to maintain so many squadoons, so in 1938 five of the squadrons were disbanded, leaving twelve full strength squadrons.
The Karas B was a three-seat low-wing monoplane, of all metal construction. The wing had a slight dihedral. The fixed main undercarriage was carried within large spats, although these could be removed for operations from rough airfields. The bombs were carried under the centre section of the wing, between the wheels. The fuselage had an oval cross section. The pilot sat in a fully enclosed glazed cockpit, complete with heating and air conditioning. The observer’s cockpit was just behind. Again it was heavily glazed, and contained detachable dual controls. The observer was also the bomb aimer and gunner, and had to fold up his seat to move down into the ventral gondola to carry out those roles. Finally the rear gunner had an open cockpit only partly screened by the back of the main cockpit cover. It had a single fin and rudder.
The Karas B was armed with three 7.7mm machine guns – one fixed forward firing gun (sometimes two), one flexibly mounted dorsal gun and one rear firing ventral gun in the gondola. Up to 1,543lb of bombs could be carried.
The P.43 was a modified version of the P.23, designed in 1936 in response to a Bulgarian order. It had a more powerful Gnome-Rhone engine and two forward firing machine guns. An initial order for 12 aircraft was followed by more for 42, not all of which had been delivered by the time the Germans invaded Poland in 1939.
The P.46 Sum was designed to be the successor to the P.23. It was closely enough related to the P.23 for some of the development work to have been carried out on Karas Bs, but it had a more powerful engine, retractable gondola and twin tail.
Combat Record
In the spring of 1939 the front line squadrons of the air force were re-grouped. Five P-23 squadrons (Nos.21, 22, 55, 64 and 65) joined five P.Z.L. P.37 Los squadrons to form the Bomber Brigade, an independent bombing force. Nos.24, 31, 32, 34, 41, 42 and 51 were each allocated to one of the seven Polish armies to serve as reconnaissance units. The intention was to equip each of these squadrons with either a bomber or reconnaissance version of the P.46 Sum once they began to enter service in 1940, so the split into two types of unit was carried out in order to allow them to train in their new roles.
The army units weren’t well used during the short September campaign, operating in small detachments and providing a limited amount of reconnaissance information but the Polish army was rarely able to make use of it.
The Bomber Brigade was more effective, at least to start with. On 2 September 18 aircraft from Nos. 64 and 65 Squadrons carried out the first large attack on a German formation, but lost 7 aircraft in combat and three in landing accidents. On 3 September 28 aircraft from Nos.21, 22 and 55 Squadrons made three attacks on German armour, again inflicting significant losses on the Germans. Between 4-8 September ten raids were made on German armour in the Radomsko-Piotrkrow area, again inflicting heavy losses on the Germans, in this case the 4th Panzer Division and the Panzer Division ‘Kempf’. However these early successes had come at heavy cost, and for the rest of the campaign the few remaining aircraft were unable to repeat them.
During the campaign the Poles committed 118 P.23Bs and 5 P.43Bs to the action, and lost 112 of them, mostly in the air. At least 15 large scale raids were carried out during the campaign. After the Russians attacked from the east the remaining 11 P.23Bs were evacuated to Romania. About 30 training aircraft had arrived in the previous few days. Ironically most of these aircraft then entered service with the Romanian Air Force, so ended up fighting for one of Germany’s allies.
P.23B
Engine: P.Z.L. Pegasus IIM2 (P.23A) or Pegasus VIII (P.23B)
Power: 570-590hp (P.23A) or 660-680hp (P.23.B)
Crew: 3
Span: 45t 9.5in
Length: 31ft 9.5in
Height: 10ft 10.25in
Empty Weight: 4,250lb
Recon Weight: 6,477-6,918lb
bombr weight: 7,704-7,773lb
Maximum Speed: 198.2mph at 11,975ft, 170.2mph at sea level
Climb rate: 4min 45sec to 6,561ft, 15min 10sec to 13,123ft
Service Ceiling: 23,949
Range:
Guns: One (P.23A) or two (P.23B) 7.7mm KM Wz 33 fixed forward firing guns, one 7.7mm Vickers F gun in rear firing dorsal position, one 7.7mm Vickers F gun in rear firing ventral position.
Bomb load: 1,543lb on racks under centre wing section