Longitudinal stability

This section performs longitudinal stability and trim analysis for the example airplane. This includes estimation of neutral point and static margin, along with estimation of elevator deflection for trimming the airplane in cruise conditions. Note that trim analysis should be performed for takeoff rotation and landing conditions as well. Refer to lecture notes and Section 16.3 in Raymer for further details. Following topics are covered:

1. Static margin

2. Cruise trim analysis

Before proceeding to above topics, it is important to define the size of the elevator. The elevator chord ratio (\(c_e/c\)) is set to 40% based on the historical data in Table 8.3a in Roskam Part 2. For the analysis, it assumed that the elevator extends along the entire span. The elevator size can be later updated, if dictated by the stability and trim requirement. Note that elevator is essentially a plain flap, so the lift change in horizontal tail due to elevator deflection can be computed using a similar analysis demonstrated in HL devices section.