Most you have heard that the first aircraft to do the ‘Cobra’ maneuver was the SAAB J-35 Draken. But the truth is that, what the Draken did is not a Cobra at all ! It is an example of a serious drawback to the high aspect ratio, high sweep compound delta, i.e. its tendency to go into an uncontrollable deep stall/ superstall if the airflow was sufficiently disturbed. All it took was a quick jolt in the roll axis at a moderate AoA and the entire aircraft would pitch up violently and eventually enter an irrecoverable spin toward the ground if the pilot did not react quickly enough with precisely the right control input before the machine passed the spin threshold. This inherent design issue was well known, but it was kept largely under wraps for the time being due to the negative publicity it would have caused. Being a highly novel design, the developers knew that they took some serious risks and they had to persuade the government and the public opinion that taking such risks were worth it to stay in the game and produce a competitive aircraft. At the end of the 1960s the Swedish Air Force decided to address it by commissioning four trainer Drakens (Sk 35C) modified with anti-spin chutes and additional wing fences in the role of letting pilots familiarize themselves with this problem and learn how to recover from it should it occur. Typically the modified Sk 35C would be piloted by the student, with an experienced test pilot in the 2nd seat. Even with the spin recovery chutes and airframe modifications, it was a bit sweaty and the exercises were carried out at 35-38,000 feet or more for additional safety as you still needed quite a margin for recovery should things go even a tiny bit wrong. With enough training, the pilot could however recover from it fairly swiftly. But do keep in mind that it was a dangerous and essentially uncontrollable maneuver, and it led to quite a few disasters over Drakens service years. Foreign Draken operators were also keen on putting their pilots through this ‘superstall familiarization programme’, which was carried out at the former Swedish AF base in Ängelholm (F-10, Scania Air Force Wing). As far as the engine airflow goes, they had to be kept at idle over the course of the stall and recovery, or another heap of problems would arise.
Posted on: Thu, 25 Dec 2014 18:34:05 +0000
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