Friday the 13th of June 1953 a Swedish military aeroplane, the TP 79 a DC 3 plane, disappeared in the Baltic Sea. The Swedish air force and navy started the search for the plane immediately. During three weeks the only sign of the plane was its rubber rescue-boat, that was found floating in the water. It later showed that the DC 3 had been attacked and shot down by the Soviet air force.

The DC 3 was said to be on an educational navigation mission. But many years later the truth was revealed, the real purpose of the flight was signal reconnaissance. There were no signs of the eight crew-members onboard the plane and their families had to wait over fifty years until the plane was found in 2003. Some of the crew members were found, but sadly not all.

When the Royal Institute of Technology (KTH) found the Swedish passenger shipwreck s/s Hansa at 108 metres depth seven kilometres from the original calculated position, KTH decided 1989 to begin the search for the DC 3. Since July 1951 nothing had been done in the attempt to find the DC 3.

For many years the research vessel Altair under the flag of KTH went to sea at several different occasions trying to locate the plane. The Swedish media, private persons with no compensation and the owners of the vessel were all engaged in the search.

The question is; why did it take such a long time before the DC 3 was found? International it has been shown that with the right up to date equipment it was possible in the 1950s to find planes and u-boats that had been wrecked. The r/v Altair was at the right place in 1989, but the cable to the side scan sonar was too short in relation to the depth to register the plane. The documents from the Soviet concerning the shot-down were first released when the Soviet Union fell after 1990.

In this report Bengt Grisell with the radar-expert Gunno Gunnwall and the engineer and sciencejournalist Roger Bengtsson will further relate to the circumstances in “The DC 3 – a KTH project”.

Friday the 13th of June 1953 a Swedish military aeroplane, the TP 79 a DC 3 plane, disappeared in the Baltic Sea. The Swedish air force and navy started the search for the plane immediately. During three weeks the only sign of the plane was its rubber rescue-boat, that was found floating in the water. It later showed that the DC 3 had been attacked and shot down by the Soviet air force.

The DC 3 was said to be on an educational navigation mission. But many years later the truth was revealed, the real purpose of the flight was signal reconnaissance. There were no signs of the eight crew-members onboard the plane and their families had to wait over fifty years until the plane was found in 2003. Some of the crew members were found, but sadly not all.

When the Royal Institute of Technology (KTH) found the Swedish passenger shipwreck s/s Hansa at 108 metres depth seven kilometres from the original calculated position, KTH decided 1989 to begin the search for the DC 3. Since July 1951 nothing had been done in the attempt to find the DC 3.

For many years the research vessel Altair under the flag of KTH went to sea at several different occasions trying to locate the plane. The Swedish media, private persons with no compensation and the owners of the vessel were all engaged in the search.

The question is; why did it take such a long time before the DC 3 was found? International it has been shown that with the right up to date equipment it was possible in the 1950s to find planes and u-boats that had been wrecked. The r/v Altair was at the right place in 1989, but the cable to the side scan sonar was too short in relation to the depth to register the plane. The documents from the Soviet concerning the shot-down were first released when the Soviet Union fell after 1990.

In this report Bengt Grisell with the radar-expert Gunno Gunnwall and the engineer and sciencejournalist Roger Bengtsson will further relate to the circumstances in “The DC 3 – a KTH project”.

This report is a master thesis performed at The Royal Institute of Technology divisions of Lightweight Structures and Naval Architecture in collaboration with the Swedish defence material administration, FMV. There are several naval submarines used by the Swedish navy and more to be built. The existing submarines have stability problems due to a high centre of gravity. Most parts on the existing vessels are made of steel, despite a position far above the vertical centre of gravity. By replacing the current steel casing covering the top part of the submarines pressure hull and the rudders placed on the tower, to a lighter composite structure it is possible to lower the centre of gravity. In this report the composite structure of the rudder and the casing has been weight optimized to achieve a structure as light as possible, but still able to withstand the forces applied to the structure. An analysis of the applied loads shows that the dimensioning loads vary between 50 and 90 kPa depending on the specified part. The results show that it is possible to decrease the weight of the rudder and casing with over 80 %. This would also give the submarine an increase in initial stability with over 40 % compared to the existing steel construction.