initial propeller efficiency model

gpkitmodels/GP/aircraft/prop/prop_test.py

@@ -0,0 +1,19 @@
+from propeller import Propeller
+from gpkitmodels.GP.aircraft.wing.wing_test import FlightState
+
+def eta_test():
+
+    fs = FlightState()
+    p = Propeller(fs)
+    p.substitutions[p.T] = 100
+    p.cost = 1/p.eta
+    sol = p.solve()
+    print sol.table()
+
+def test():
+    "tests"
+    eta_test()
+
+if __name__ == "__main__":
+    test()
+

gpkitmodels/GP/aircraft/prop/propeller.py

@@ -0,0 +1,34 @@
+" propeller model "
+from numpy import pi
+from gpkit import Model, parse_variables
+
+class Propeller(Model):
+    """ Propeller Model
+
+    Variables
+    ---------
+    T                       [N]         thrust
+    Tc                      [-]         coefficient of thrust
+    R          0.3          [m]         prop radius
+    etaadd     0.7          [-]         swirl and nonuniformity losses
+    etav       0.85         [-]         viscous losses
+    etai                    [-]         inviscid losses
+    eta                     [-]         overall efficiency
+    z1         self.helper  [-]         efficiency helper 1
+    z2                      [-]         efficiency helper 2
+
+    """
+
+    def helper(self, c):
+        return 2. - 1./c[self.etaadd]
+
+    def setup(self, state):
+        exec parse_variables(Propeller.__doc__)
+
+        V = state.V
+        rho = state.rho
+
+        return [eta <= etav*etai,
+                Tc == T/(0.5*rho*V**2*pi*R**2),
+                z2 >= 1 + Tc,
+                etai*(z1 + z2**0.5/etaadd) <= 2]