Fig. 1. Geometric model of small rotorcraft

Fig. 2. Surface meshing

Fig. 3. Far-infrared thermal images of rotorcraft under different working conditions. (a) Static and no load; (b) 10-minute flight and no load; (c) 10-minute flight and load 100 g

Fig. 4. Gridded spherical receiving surface

Fig. 5. Flow chart of calculating infrared radiation by Monte Carlo method

Fig. 6. Spatial distribution of far-infrared radiation intensity of rotorcraft under different working conditions. (a) Static and no load; (b) 10-minute flight and no load

Fig. 7. Curve of radiation intensity with zenith angle θ while \begin{document}$\varphi {\text{ = 90}}{\text{.}}{{\text{9}}^{\text{o}}}$\end{document}

Fig. 8. Curve of radiation intensity with circumferential angle φ while θ = 78.3°