The PZL P.23 Karas was a light bomber used by Poland during the German invasion of September 1939.
History[]
Early in the ’thirties, the Polish Lotnictwo Wojskowe (Military Aviation) requested a replacement for its ageing Potez 25 and 27 light bomber/reconnaissance biplanes. Panstwowe Zaklady Lomicze (PZL — State Aviation Works) responded to the 1931 specification, which requested an all-metal light bomber powered by a Bristol Pegasus air-cooled radial engine able to carry a 600kg (1330lb) bomb load. It was required to attain a minimum speed of 300km/hr (186mph) and to operate from improvised airfields. PZL decided that it could develop the new bomber from its earlier R13, a high performance six-passenger light transport monoplane powered by a 420hp Pratt 8t Whitney Wasp. Designed by Stanislaw Prauss, this lightplane had been abandoned when at an advanced stage of detail design.
Apart from extensive redesign to the fuselage, other changes were centred around the addition of wing flaps and provision for the mounting of both offensive and defensive weapons. The wing was designed by Franciszek Misztal, based on an original stressed-skin concept which had been tested earlier on the PZL19 high performance touring aircraft. This wing, tested on a static airframe in 1933, presented serious problems and caused delays in the construction of the first prototype which, powered by a 570/590hp Bristol Pegasus II M2, made its maiden flight in the third week of August 1934. Flight tests revealed rear fuselage vibration and tail flutter, while crew accommodation and visibility from the cockpit left much to be desired.
Extensive modifications were incorporated into the second prototype (P.23/II) which flew early in 1935. The fuselage was redesigned, the internal bomb bay which made crew access extremely difficult was removed while the engine, now installed in a close-fitting low-drag cowling, was lowered to improve visibility. Improvements were also introduced into the design of the wings which received more effective slotted ailerons and improved flaps. Automatic slats were added to the leading edges of the wings while the root fairings were enlarged. This prototype, which proved highly superior to its predecessor, was lost during a bad weather landing accident and had to be substituted in the test programme by the third Karas which was completed in the middle of 1935.
Having reached a satisfactory standard, an order for Z00 P.23s was received by PZL. Production started with a series of problems, mainly centred around the Pegasus I1 M2 engines built under licence by the Polish Skoda works: frequent jamming of reduction gear, and fractures in the crankshaft were the major causes. After producing 40 examples of what had by then become known as the P.23A ‘Karas’, production switched to the P.23B; its wing leading edge slats were removed and it was re-engined with the much more reliable 660/ 68Ohp Pegasus VIII which had become available as from the summer of 1936. All P.23As were relegated to training duties, being passed on to training schools as soon as the ‘B’s became available.
By February of 1937, production of the Kams had reached the rate of 20 aircraft per month. Thus the initial order of 200 examples was completed by September and an additional order of 50 P.23Bs was placed in February, 1938. Meanwhile, the P.23B entered service with the lst Air_ Regiment in Warsaw and a total of 14 combat squadrons, each equipped with ten Karas, were to be formed. Of these only twelve had been completely equipped when war broke out in September 1939, as the other two were equipped with the newer P.27 Los.[2]
Technical Desciption[]
The Karas B was an all-metal cantilever monoplane powered by one Skoda Bristol Pegasus VIII engine rated at 670 hp driving a wooden two-bladed Szomanski propeller. Of note was the wing structure which was one of the earliest metal sandwich structures attempted on a production aircraft. Misztal’s wing (Patent N° 16,585, June 20 1932), was built around a wide central box-girder of two light duralumin spars and corrugated duralumin sheet to which a smooth duralumin skin was added externally. A duralumin ‘D’ leading edge and a stressed-skin multi-cell trailing edge were attached, forming a wing structure which became the hallmark of PZL on the Karas and most of their subsequent designs.[2] Fuel was contained in two 230lt tanks fitted between the wing spars in the centre section and two 5Olt tanks fitted aft of the rear spar. An additional 25lt tank was housed in the front fuselage, ahead of the windscreen. The tail unit was structurally very similar to the wing. The fixed landing gear consisted of two main PZL oleo legs enclosed in streamlined fairings fitted with Dunlop 775x240mm wheels, and a sprung tailskid.
The oval-section fuselage was similarly strengthened internally by corrugated sheeting under its stressed-skin construction. The pilot sat in the front within an enclosed cockpit while the observer, provided with removable dual controls, sat behind. This second crew member doubled as bomb aimer/gunner, descending into the ventral gondola which was equipped with bomb-release gear and camera in the forward section and a Vickers ‘F’ Type 7.7mm machine gun at the rear firing downward. Another Vickers gun was provided for a third crew member who sat in an open cockpit; the Vickers were sometimes substituted by indigenous 7.9mm Km W237 Szczeniak machine guns. The pilot could use a ‘fixed 7.9mm Km Wz 33 fitted to the starboard side of the fuselage, firing through the engine cylinders’ banks and propeller arc. Up to a maximum of eight 100kg bombs could be carried attached to racks under the wing centre-section although the bomb load was usually restricted to 700kg.[3]
An Export Model[]
Bulgaria showed great interest in the R23 Karas and placed a order for 12 machines early in 1936 specifying the need for a more powerful engine and a second forward firing gun. To offset the centre of gravity movement resulting from the heavier Gnome-Rhone l4N~0l engine, the main cabin had to be redesigned and the rear fuselage lengthened by 27cm. The original third prototype (R23/III, by then registered SP-BMI-1) served as test bed for the new engine. The first aircraft, which had been designated PZL.43 ‘Tchaika’ (Seagull), to be delivered to Bulgaria were fitted with the Gnome-Rhone l4Kfs engine due to delays of shipments from France until the 14N-Ols became available. These aircraft gained an excellent reputation and a second order for 42 machines was placed with PZL.
Some thirty of this second order had been delivered by August 1939, while eight were awaiting delivery and a ninth ready to leave Airframe Plant N“ 1 at Warsaw-Okecie. Crews from N“ 41 Squadron, Polish Air Force, were ordered to pick these P.43Bs on the second day of the war to replace losses of P.23 Karas. Of these, only five could be retrieved as the others had been destroyed on the ground in a German attack against the Okecie airfield.
As early as 1936, Prauss had begun work on a Karas replacement to be powered by a 1200hp radial under the designation of PA6 ‘Sum’. A twin fin and rudder tail was dcviscd to provide the rear gunner with a better field of fire while the gunner’s ventral gondola could be retracted. A production P.23B was taken off the line for conversion, designated R42. A true prototype, the R46/I, flew in October 1938 and a second was available by spring of the following year. Results were so encouraging that 300 Sum As powered by a 25hp PZL-built Pegasus XX radial were ordered for the Polish Air Force while a Gnome-Rhone powered version was being considered by Bulgaria. Deliveries to the squadrons had been scheduled for early 1940 but production had hardly got underway at the time of the German invasion.[3]
In Combat[]
114 P.23s were flown by first-line units during the September Luftwafle onslaught, and an additional ll machines (including the five PZL. 43s) were received as replacements. In spite of the numerical and technical inferiority of the Polish aircraft, they managed to put up a brave defence. As soon as hostilities began N" 21, 22, 55,64 and 65 equipped with Karas, together with the four Lus Squadrons, were formed into the Bomber Brigade under the direct command of the Polish Armed Forces. Karas of N" 24, 31, 32, 34, 41, 42 and 51 Squadrons were attached to one each of the seven land army units in the reconnaissance role and put under their complete command. The latter were completely wasted when they could have been put to better use in the.bomber role, notwithstanding that by the time of the German invasion they were already obsolescent.
On September 2 1939, 18 Karas from N" 64 and 65 squadrons performed their first successful bombing of German targets though at a great cost, as five aircraft failed to return and a further three were damaged. On the following day, 28 Karas from 21, 22 and 55 Squadrons hit enemy armour near Radomsko where they claimed to have put 30% of German vehicles out of action. Sorties continued between September 4-8 by Karas units in conjunction with the four Los squadrons concentrating on enemy armour in the Radomsko-Piotrkow region and around Pultusk, inflicting heavy losses to the German 10th Army Group’s 4th Armoured Division and the Kempf Armoured Division. However the losses were such that by the middle of September the operational capability of Karas units had become insignificant. With the Russian intervention of September 17, surviving P.23s were flown to Rumania — some twelve aircraft reaching that country — and were impressed into service into the Rumanian Air Force.
Though not a brilliant fighting machine, the PZL.23 Karas has found its niche in history as one of the first aircraft to oppose the mighty Luftwafle during World War II. It's limited capabilities in the face of an opponent of gigantic proportions could only be partially offset by the tremendous valour which its crews displayed in the defence of their homeland. Most of them lost the battle, but not the war, as they fled their country to continue the fight with whoever could hit back, helping in no small way in the Allied war effort.[3]