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84              PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
Pmir,
v,
                               v
Fig.2.9   Power-required curves for propeller aircraft
value at some velocity, which will be denoted by Vmp and can be obtained as
follows.
 ForPR, n,
or
dPR  3
d~ = ~p V2SCDO _ (:=k~WS)
      - 0                                          (2.73)
            4k W2
Vm4p = 3p2S2~DO
Vmp .-
(2-74)
                                                 1
                                                          = ~ VR                                                 (2.75)
The lift coefficient in level flight when the power required in level flight is
nunimum is as follows.
   2W
CL.mp - .
          = p S~2p
= ,~-
= V5Cz
(2.76)
AIRCRAFT PERFORMANCE
Similarly, we can show that
T
Emp = 0.8 6 Em                                   (2.77)
Then, we get
                       8 kW2
                                                PR.min = 3 p S /.-p
                                                                  W Vmp
                      -                    (2.78)
                                             = O 866Em
Thus, we observe that both thrust- and power-required curves assume their mini-
mum values at some velocities. In view of this, we have two intersection points
between power-available and power-required curves as shown in Fig. 2.10a for the
propeller airplane and between thrust-available and thrust-requircd curves for ajet
 airplane as shown in Fig. 2.10b. These two intersection points give us two solutions
Pmin
D mln
Vmin         Vm       Vma^
        a) Propeller aircraft
　
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