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98 Rotor<br />
κ<br />
κ<br />
1.14<br />
1.12<br />
1.10<br />
1.08<br />
1.06<br />
1.04<br />
1.02<br />
Maxial = 1.176<br />
Maxial = 0.5<br />
Maxial = 2.0<br />
1.00<br />
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0<br />
4.50<br />
4.00<br />
3.50<br />
3.00<br />
2.50<br />
2.00<br />
1.50<br />
μ z /λ h<br />
Figure 11-5. Induced power factor for rotor in axial flight.<br />
CT /σ = 0.08<br />
CT /σ = 0.14<br />
(μedge , κedge )<br />
1.00<br />
0.00 0.10 0.20 0.30 0.40 0.50<br />
Figure 11-6. Induced power factor for rotor in edgewise flight.<br />
where Mdd0 is the drag divergence Mach number at zero lift, and typically κ =0.16.<br />
b) Similarity model: From transonic small-disturbance theory (refs. 11–12), the scaled wave drag must<br />
be a function only of K1 =(M 2 at − 1)/[M 2 atτ(1 + γ)] 2/3 . An approximation for the wave drag increment<br />
is<br />
Δcd =<br />
τ 5/3<br />
[M 2 at(1 + γ)] 1/3 D(K1)<br />
τ<br />
=<br />
5/3<br />
[M 2 at(1 + γ)] 1/3 1.774(K1 +1.674) 5/2<br />
(constant for K1 > −0.2). Integration of Δcd over the rotor disk gives the compressibility increment in<br />
the profile power. Following Harris, the resulting compressibility increment in the mean drag coefficient<br />
μ
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