A continuously variable transmission for helicopters was designed in this thesis. The transmission is based on two compound split structures which are connected in series. The compound splits share a common variator strand. The concept was analyzed kinematically. There the power of the variator machines were calculated and a switching concept was created. With the help of the software KissSYS the calculated epicyclic gears were modeled including the required shafts and bearings. Furthermore, a switching element was designed, which allows the common use of one variator strand. The aim of this development is the mass reduction for a continuous variable transmission for helicopters. To achieve this aim, it is necessary to minimize the mass of the gears, as well as the variator machines. Previous research has shown that a part of the transmission concepts mass results in the required variator machines. Their mass is proportional to the spread of the compound splits. The developed concept reduces the spread of a single compound split by 50 %, still, the overall spread remains unchanged. This results in a decrease of the mass of the variator machines by half. Moreover, the engineered transmission integrates a maximum gear ratio of i = 9,5. As a consequence, prior gear stages will not be necessary anymore which could present a chance for additional mass reduction. The comparison between the developed concept and a simple compound-split, which requires only two epicyclic gears, showed that also the mass of the gears could be reduced. This reduction is caused by the even distribution of the total transmission ratio on the single epicyclic gears. The developed transmission concept has a total mass of about 540 kg and integrates a maximum base gear ratio of i = 9,5 by a spread of = 1,75. The input torque has a value of 10100 Nm by 1900 rpm. The development process has demonstrated that the theoretical advantages of a very small stance ratio, such as a high number of planet gears to enable a high internal power split, does not fulfill the expected mass reduction. This is caused by the required space for the bearing of the planet gears which increases the diameter of the planet gears. Therefore, the diameter of the sun and ring gear increase as well. Due to the larger diameters the masses of the shafts rise clearly. The masses of the carrier shafts could be significantly reduced through a corresponding arrangement of the planetary bearings and a skeletonization of the planet carrier. The first adopted models have resulted in a total mass in the range of 330 kg. Investigations, which are part of the international research project VARI-SPEED, have shown that a speed-variable drive system can increase the efficiency of a helicopter. However, the rise in efficiency is reduced by the additional unladen mass of the helicopter, due to the necessary variable transmission. Therefore, it is essential to keep the additional mass of the variable transmission as low as possible.