In every report I’ve found I’ve only ever seen that the J21A-1 had problems with cooling on the ground, This was fixed by quote:
“The cooling during ground operation was provided by a fan in each wing, which, via a special gearbox, was powered by the aircraft engine when the landing gear was deployed.” - Stig Hertze - Arboga Elektronikhistoriska Förening
The J 21A-2 (series 2 & 3) succeeded the A-1 on the production line in Trollhättan, and around the turn of the year 1946/47, the first planes were delivered to the Air Force. They now had a more sophisticated cooling flap system, partly designed by Flygmotor. The planes also received an artificial horizon system, and the nose-mounted 20mm cannon was of type m/45 (Bofors). The sight was a K-14 type (automatic reflector sight).
The final version, A-3 (series 4 & 5), was prefixed with A (also B) and was primarily intended for attack and bombing missions. The J 21A never became successful as a pure fighter aircraft. However, the A 21A-3 performed well within the attack units. Deliveries began in the autumn of 1947, and the version remained in active service until decommissioning in the summer of 1954. Armament and equipment were the same as for the A-2, but in addition, bomb and rocket payloads could be carried. The K-14 reflector sight was supplemented with a BT 9 bombsight (SAAB). Additionally, the aircraft could be equipped with two disposable take-off rockets (type 500/14-2) mounted under the tail booms.
Fun fact
The Fastest recorded Speed in the J21 was recorded to be near 900km/h! however this was in a prototype J21 stripped of any armament. Additionally it was among one of the first aircraft to be equipped with a ejection seat.
