Re: Combat Aircraft of the Indian Air Force Following up on dialogue in the last few posts this post is meant to cover some of the specialness of Sweden's Saab fighters and the way some or all were path breaking in their own unique way. The post does not cover details or history of each. I have kept it to a narrative style and content (and not technical) so that it can be enjoyed by all readers. The aviation community may find it simplistic - apologies.
The Saab J21 a pusher propeller piston powered started the Saab jet fighter story. The J21 entered service just as WW2 was ending and the lure of the centrifugal turbojet peeped over the threshold. To save time to service and avoid a long development phase SAAB replaced the rear facing piston with a British de Havilland Goblin turbojet of 1400 kgf thrust. Thus Sweden became the 5th country to commission its own jet fighter after Nazi Germany, UK, USA, USSR (in that order). With this the J21R became the only aircraft to enter squadron service having carried a piston in one avtar and a jet in the next. Others tried it but only the Swedes succeeded.
In 1945 Saab started the concept study of a clean sheet of paper design for a jet fighter. At that time it was realized that a rearward thrusting turbojet by definition meant that the order in which the parts of an aircraft are arranged needs to be changed. Many configurations were tried - cigar ie one behind the other (MiG-15, Dassault Ouragan), central jet with divided exhaust efflux (Hawker Seahawk), twin boom (de Havilland Vampire) and a few others more off beat. Saab after trying many combinations came out with an almost unique arrangement with the aircraft on top and engine with a straight through intake beneath. Interestingly & suprisingly wind tunnel tests revealed this gave lower drag and greater lateral stability than a cigar shaped design. Thus was born the J29 Tunnan. Tunnan was actually a nickname meaning 'barrel' a joke on its shape. Research on swept wings and thin wings was in its infancy relative to what we know today but the Swedes were a few years ahead of their time by building a thin swept wing for speed (575 knots) and primitive (what are now called) leading edge root extensions which improve airflow and stability at high angles of attack. Why this happened was not quite understood in 1950 but the Swedes were the first to venture here and took it further later with the Draken and its double delta wing. Interestingly the J29 set the world speed with endurance record flying a 1000kms closed circuit at an average of 900 kmph in 1955.
Next came the Saab 32 Lansen. This was an early example of an aircraft being designed at the very start for 4 differing roles and built in those 4 different configurations to best suit the role. The roles were - Attack, Fighter, Recce & Electronic Warfare. Today multi-role combat aircraft are the norm mainly due to advanced & flexible avionics and multi-role radars. In 1948 when the design concept started this was futuristic thinking to say the least. At that time aircraft had one primary role and some had a secondary role at which they were much less capable. Given the early stage of avionics in the 1940s and 50s Saab built a two seater. The large nose (with ample volume for avionics) and two-seater configuration lent itself to several avionic upgrades that kept this machine in front line service till 1997, 45 years after the prototype flew in 1952.
Then in 1955 flew the futuristic looking Draken. It introduced the concept of the double delta wing which improved stability at high angles of attack and lowered take off/landing speeds enough to enable routine off runway operations from highways and packed mud & gravel runways. It was also an early attempt at a blended wing/body to the extent possible with metal. Later blended bodies like that of the F-16 used carbon fibre for those smooth curves.
And finally in 1967 flew the Saab Viggen with its delta wing+foreplane combination called the canard configuration. Today this is the norm seen in the Sukhoi Su-30, Dassault Rafale, Eurofighter Typhoon but none of these was even on the drawing board when the Viggen first put skylight beneath its wings. In all fairness the value of canards has been known since 1903 but the Viggen, from a small country with less people than Hyderabad, was the first to solve the mechanical and aerodynamic and simultaneous control issues. The last mentioned is the most complex and Sweden was the first to solve it for a production aircraft i.e. how to ensure the airflow over the foreplane does not disturb the airflow over the main lift generating wing; how to figure out the co-ordination of the exact movements of the foreplane with the flaps and ailerons of the main wing. This delta canard gave greater lift for the same thrust, greater maneuverability, lower landing speeds and operations at higher angles of attack. The foreplanes of the Viggen understandably were not as advanced as those on the Rafale or Su-30, which are all flying surfaces, but it came 2 and more decades earlier. And like the Lansen they built it in 4 different versions -Fighter, Attack, Recce, Maritime Attack.
Hope you enjoyed reading this.
Last edited by V.Narayan : 23rd August 2017 at 21:38.
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