(20 13? A model in Jiading District hangs a red flag by helicopter and flies horizontally at a constant speed in the sky. The mass of the red flag (including the flagpole) is m, and the weight of the red flag is no problem. Solution: Taking Hongqi as the research object, the stress analysis is shown in figure 1. According to the equilibrium condition:

f′= mgtanθ

Then take the whole as the research object, and analyze the stress situation as shown in Figure 2. According to the equilibrium condition, the helicopter propeller is subjected to air force:

f =(Mg+Mg)2+(f+f′)2 =(Mg+Mg)2+(f+mgtanθ)2

So the answer is: mgtanθ, (mg+mg) 2+(f+mg tan θ) 2.