# How do the actuator loads (e.g. for the ailerons) vary between different flight phases?

Assume the hinge moment is given as

$HM = 0.5\rho v^2*C_{h\delta} \delta*S*c$

$\rho$ = air density

$v$ = air speed

$C_{h\delta}$ = Hinge moment coefficient

$S$ = Control surface area

$c$ = average surface chord

the resulting moments / actuator loads are mainly influenced by the aircraft's altitude (air density $\rho$), speed $v$ and the control surface deflections $\delta$. (AoA is neglected to keep it simple)

Can there be anything said about the actuator loads regarding different mission types or flight phases? E.g. does cruise (high altitude and speeds, small surface defelctions) cause higher actuator loads than approach (low altitude, low speed, larger surface delections).

I was planning to use X-Plane to investigate this, but as far as I know it will only output the rudder's deflections, not the hinge moment itself.

• have you tried plugging numbers in the equation and see what happens? – Federico Feb 27 '17 at 13:38
• @Frederico, thanks for your comment. Actually i didn't because i do not have any reliable data concerning the rudder deflections ($\delta$). Of course I could generate some data by simulation (X-Plane) - but I'm not sure how realistic this approach will be... – Henrik Feb 28 '17 at 14:01
• Notice that the the hinge moment is proportional to dynamic pressure ($\frac12\rho v^2$) and deflection ($\delta$) and so is the aerodynamic force on that control surface. – Jan Hudec Mar 1 '17 at 21:08
• For a passenger plane or a jet fighter? – Koyovis May 6 '17 at 22:47
• For clearification: I'm interested in the actuator loads for an uav, which will be used in different mission scenarios. However, I started to set up a simulation environment via X-Plane to investigate this further. I'll let you guys know what I'll find out once I have some data. Many thanks so far for your comments – Henrik May 8 '17 at 12:50

Indeed the hinge moment equation is (with index $$_s$$ for surface) $$H_s = C_{h_s} \cdot ½ \rho V^2 \cdot \delta_s \cdot S_s \cdot \bar{c_s}$$
The moment coefficient $$C_{h_s}$$ depends on aircraft angle of attack, surface deflection (!) and trim tab deflection, as depicted in the figure below (from this answer). It is not a simple constant linear function due to shading of horizontal tail in the flow of other bits of aircraft structure. 