main spar attachment point and carry-through structure. In 1954 Wocke returned to the German Democratic Republic, moving to West Germany shortly afterwards and joining Hamburger Flugzeugbau (HFB) as their chief designer. In Hamburg, Wocke completed work on the HFB 320 Hansa Jet business jet which flew in 1964. The forward sweep enabled the main spar to be moved aft behind the cabin so that the spar did not need to project into the cabin. Moderate forward sweep has been used for similar reasons in many designs, mainly sailplanes and light aircraft. Many high-wing training gliders with two seats in tandem have slightly forward-swept wings in order to enable the wing root to be located further aft to prevent the wing from obscuring the rear occupant's lateral visibility. Typical examples are the Schleicher ASK 13 and the Let Kunovice LET L-13 Blaník. Other examples include: Cessna NGP, a prototype single-engine aircraft intended to eventually replace the Cessna 172 and Cessna 182. CZAW Parrot Saab Safari, Bölkow Junior & ARV Super2 all have shoulder wings for increased visibility, necessitating forward-swept wings to maintain correct CofG. Scaled Composites Boomerang, a prototype piston twin design which would allow for safe handling in the event of a single engine failure. SZD-9 Bocian and PZL Bielsko SZD-50 Puchacz, multi-purpose two-seat sailplanes designed and built in Poland. Fast jet The large angles of sweep necessary for high-speed flight remained impractical for many years. In the late 1970s, DARPA began investigating the use of newer composite materials to avoid the problem of reduced divergence speed through aeroelastic tailoring. Fly-by-wire technology allowed for the design to be dynamically unstable and improved maneuverability. Grumman built two X-29 technology demonstrators, first flying in 1984, with forward swept wings and canards. Maneuverable at high angles of attack, the X-29 remained controllable at a 67° angle of attack. Advances in thrust vectoring technology and a shift in air combat tactics toward medium range missile engagements decreased the relevance of a highly agile fighter aircraft. In 1997, Sukhoi introduced the Su-47 fighter prototype at the Paris Air Show. It did not enter production, although it underwent a series of flight tests and performed at several air shows. The KB SAT SR-10 is a prototype Russian single-engine jet trainer aircraft, fitted with forward-swept wings. It first flew in 2015. In biology Large-headed pterosaurs had forward swept wings in order to better balance in flight. See