## 3 Results
### Aircraft Design  
The results at aircraft level are presented in the following section. In total, there are five major concepts. First, the reference aircraft D261 based on the Boeing 767-300 with conventional combustion chambers and fossil Jet A-1. Second, there is the new design D261+, which is an evolutionary advancement of the D261 based on the entry into service (EIS) of 2040. This incorporates an advanced high-bypass-ratio turbofan engine and high aspect ratio carbon fibre reinforced wings. Furthermore, this concept and all further hydrocarbon fuel based ones are evaluated twice, first equipped with an conventional combustion chamber and second with new low-NOx and low-soot technology. Figure 8 shows the increased span and the reduced wing and horizontal tailplane area. The next two concepts D261+DropIn and D261+SAF incorporate the same technology bricks but are operated and designed for the drop-in capable fuel and the synthetic one, respectively. The differences in mass, geometry, and performance are rather small. Last, the liquid hydrogen powered aircraft D261+H2 is designed with the same technology assumptions. The big LH2 tanks are integrated in front and behind the cabin, see Figure 9. The access of the pilots to the cabin is not considered, as this would penalize the aircraft's performance and there is no official regulation. However, the drawback is the additional laboratory and galley inside the cockpit, which adds weight and needs to be serviced. Furthermore, two additional exits or one exit and one top hatch are needed, as the first two doors of the cabin, which are considered to be in the flight crew area, are not accessible, see CS 25.807 [61]. However, having a long tunnel between cockpit and cabin should result in the same problem. To better maintain a reasonable fines ratio of the fuselage, the diameter has been increased to accommodate an eight-abreast cabin arrangement. The insulation architecture of the cryogenic tanks is foam with a carbon fibre load carrying inner wall and an kevlar outer wall for protection. This reduces the maximum tank volume and the total vented gaseous hydrogen. The maximum operational pressure is set to 0.25 MPa and additional 5% inner tank volume is required for safety aspects. The delivery of the fuel to the consumer is conducted in the liquid state. The high pressure pumps and the heat exchanger for evaporation are installed near the engines. The total mass of the tank structure, delivery lines, and tank subsystems is roughly 9 tonnes, which leads to a total gravimetric index of about 50%. In addition, the maximum operating altitude and the cruise Mach number are traded for the D261+SAF and D261+H2 concepts to reduce the climate \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Unit** & **D261+SAF** & **D261+H2** \\ \hline BPR & - & 16.2 & 17.3 \\ OPR & - & 51.0 & 50.9 \\ TET max & K & 1850 & 1731 \\ TET mid. cruise & K & 1613 & 1613 \\ Thrust mid. cruise & kN & 29.3 & 31.7 \\ Thrust SL static & kN & 189.5 & 168.6 \\ TSEC & W/N & 579 & 540 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Turbofan Performance Characteristics. Figure 8: Generic top view of all concepts. impact of the altitude dependent non-CO\({}_{2}\) contributions. The maximum altitude constraint is varied between flight level 290 and 410 whereas the cruise Mach number varies between 0.75 and 0.8. For each of these points, a new design is conducted incorporating new sweep angles and high-lift performance. Figure 8 shows the generic top view of all concepts. All new concepts have an increased wing span of 52 m compared with the reference D261. The fuselage width and length of the LH2 aircraft design is increased due to the integration of the big storage tanks which is also visible in Figure 8.  
The masses of all concepts for the MTOM and maximum payload case are shown in Figure 10. The masses of all new kerosene based concepts are strongly reduced compared to the reference D261.