3.5.2. Masses and Center of Gravity

Compared to the reference aircraft, HAIQU has a higher MTOM due to the additional weight of the system masses of the hybrid powertrain. The resulting individual masses are listed in Table 12. Regarding lightweight construction, HAIQU has a composite vs. total structure volume ratio of 54% leading to four-times higher [43] usage of composite material in comparison with the reference aircraft. In case of the typical 400 km mission, the aircraft masses are listed in Table 13.

**Table 12.** Summary of the component masses.


Considering the tank position in the tail, the center of gravity (CoG) shift during the refueling process is important. The CoG is located at 23.8% mean aerodynamic chord (MAC) at the operating mass empty (OME) as shown in Figure 8. Considering the ferry case as the most critical loading case, the CoG is located at 33% MAC.

**Table 13.** Aircraft masses.


#### 3.5.3. Wing and Empennage

For the wing design, the classical configuration of high wing and T-tail was chosen. The shape of the main wing resulting from the design code is a two-shape design with a rectangular shape from the centerline towards the inboard motor and a trapezoid shape from there until the outboard motor as shown in Figure 8. The wing features single segment Fowler flaps [43] that stretch for 60% of the wingspan with a depth of 17%. As the wing profile, the proven parameters of the reference aircraft were selected leading to a NACA 43018 at the root and a NACA 43013 at the tip [75]. The sizing resulted in an increased wingspan of 28.5 m and an aspect ratio of 15.

Retractable struts on the lower side of the wing are necessary for takeoff and landing in strong side winds to protect the WTPs. During the flight they are retracted and fully enclosed and covered inside the wing, so that no drag is added. In case of an emergency, the struts brake before the wing would be overstressed. The T-shaped empennage was chosen to reduce the wing-and propeller-wake interaction with the tail plane. Furthermore, the volume coefficient of the vertical tail area was set to a larger value than the reference aircraft to provide enough yawing moment during wingtip engine failure.
