# Longitudinal Wind Tunnel Tests of the PROSIB 19-Pax Airplane
## 1 Introduction
The effects of external storage were investigated by several authors, especially on high-speed fighter aircraft [31; 32; 33]. The experiments were focused on the best position of an external pylon-mounted pod on either the wing or the fuselage. Apparently, there are few data available on the effects of pods integrated within the fuselage belly. Such arrangements are emerging in new hybrid-electric aircraft concepts, like the Heart Aerospace ES-30 [34] or the Ampaire Eco Caravan [35]. A patent related to a removable cargo pod for light aircraft, invented by [PERSON] [36], is also available. Among the claims, there is an easy installation and removal of the pod, eliminating unnecessary weight and drag when not needed, but no useful data on the impact of the aircraft performance, stability, and control are presented. The research study conducted by [PERSON] [37] focused on the analysis of the belly-mounted storage for the NASA's MAPIR (Marshall Airborne Polarimetric Imaging Radiometer) project, installed below a Piper Navio aircraft. However, the preliminary predictions made with potential flow theory and simplified CFD analyses were invalid because flight tests provided totally different data--thus, the necessity of the experimental investigation of complex aerodynamic systems. This paper presents the first experimental test campaign on the PROSIB 19-passengers aircraft model to evaluate its power-off longitudinal stability and control characteristics. A rendering of the model is shown in Figure 1. A pod-simulating battery and system storage was conceived to be installed below the fuselage. The pod of the full-scale model would have a useful volume of about 4 m\({}^{3}\), with the battery occupying about 1.6 m\({}^{3}\) and weighing about 1500 kg, including battery casing, cables, and internal electronics. The remainder of the volume would be shared by the thermal and power management systems, with their own masses and cables. The airplane would have about 55% less block fuel consumption with a battery-specific energy of 270 Wh/kg on a typical 200 nmi mission, with an entry into service forecasted between years 2025 and 2030. Beyond obtaining the usual aerodynamic coefficients and their derivatives, the project consortium required an investigation of the effects of the integrated battery pod and asked for an experimental comparison between a body-mounted empennage vs. a T-tail configuration. The geometry and sizing of the components were fixed by the preliminary design team and a detailed description of the design process is out of the scope of this work. The experimental data presented in this paper, with the evaluation of the impact of the belly-mounted pod and empennage layout, will be useful to aircraft designers working on the same airplane class. The remainder of this work is organized as follows. Section 2 presents the experimental setup, along with wind tunnel characteristics, the data acquisition system, the geometry of the test article, and the test matrix. Section 3 discusses the results with a focus on the stability and control derivatives at several flap and elevator deflections. Conclusions are drawn in Section 4.