Report of the Second Piloted Aircraft Flight Control System - Acgsc.org

Since pilqt effort and s*face force may become independent variables
in a centaring problem, it is desirable to expees each other variable as^ a
function of these two. One soUd link in the boost package serves as a
foIlow-up loop and also measurhs the error signal. The four forces acting
upon this link are the first four variables mentioned above. Taking e\moration
of momnts on this Unk about the piston rod bearing and solving for FV
ilPdicates thnt valve forces am a direct function of control force and
surface fome only as dotenninod by the goomtry of the control mechanlsn at
neutral and as expressed by
Taking summation of moments about the valve rod bearing which eUminata~
Ptf Md eoloiag for FA indicates tht actuator forces are olso a meet
goometrical function of control force and .surface force only M eqwosmd by
To aid vimallsation of this problem, a graphical llrsthod has boen
oployed. (9.0 Fig. 2.) Tho independsnt variables are control fomw
plotted as ordinates, and aurface forces plotted as absairsa on rscturgulrr
ooo~ates, By substitution of various constant valuer for Pg in the
second equation at the top of FQ. 2, valve faroos in pounds are plottoti a8
a family of prrallrl lines with scales along the sides of the chart. By
substitution of various co~tant values of FA in the first .quation, aokuhr
forces in pounds are plotted as a fPrnily of parallel Unes xLth a rcalo .low
the top of the chart.
Since ourfaoe position ir appro;ldkately a linear function of surfaao
load8 it 8bo asy be measured Jong the 8bscissa by using a scale factor (K)
a h is detded from the oir speed in a given problem, 6 = C v2.
If q v two variables are known8 a aystsla condition is establlrrhui oo 8
pod& on this chart. A value for each other &able om then bo obtPined
A.om the cbut.
Surface rate and direction of motion nay be detenalned by applying
the valve load8 obtained irOll Figure 2, to the characteristic8 of. tho valve.
To proceed further with the analysis, reliable dab must be obtained
concerning the operating friction and loads for each eloment of the ayatAP.
Figure 3 b a plot of laboratory test data obtained from a mica bnlrnned
piston boost cylindar. During frequent intelnittent duty, the stall ond
atarbing friction piston fome in pounds, indicated by the lower solid Ila6
on Fig. 3, can be exp~esaed arr
FA ' 12 + .OU x internal pressure (psi)