wing = Polygon[{{-18,-2.2},{-14,-3},{-9,-2.5},{0,-1},{12,1},{18,1.5},{11,2},{6,2.2},{-2,2.2},{-11,1},{-17,-1},{-18,-2.2}}];
rectangle = Rectangle[{-30,-15},{30,15}];
reg = RegionDifference[rectangle,wing];
Needs["NDSolve`FEM`"]
mesh=ToElementMesh[DiscretizeRegion[reg],MaxCellMeasure->3,"MeshOrder"-> 1];
mesh["Wireframe"]
(*Remove semicolon for more detailed mesh*)
Show[mesh["Wireframe"["MeshElementIDStyle"->Red]],mesh["Wireframe"["MeshElement"->"PointElements","MeshElementIDStyle"->Blue]]];
nodes = mesh["Coordinates"];
elements = mesh["MeshElements"][[1,1]];
boundary =Flatten[mesh["BoundaryElements"][[1,1]]];
boundary=DeleteDuplicates[boundary];
(Subscript[Γ, els])=N[{{-18,-2.2},{-14,-3},{-9,-2.5},{0,-1},{12,1},{18,1.5},{11,2},{6,2.2},{-2,2.2},{-11,1},{-17,-1},{-18,-2.2}}];
upp = Cases[nodes[[boundary]],{_,y_}/;y== 15.];
low = Cases[nodes[[boundary]],{_,y_}/;y== -15.];
For[i=1,i≤ Length[low],i++,
(Subscript[Γ, els]) = Append[(Subscript[Γ, els]),low[[i]]]; 
];
For[i=1,i≤ Length[upp],i++,
(Subscript[Γ, els]) = Append[(Subscript[Γ, els]),upp[[i]]]; 
];
(Subscript[Γ, in])=Cases[nodes[[boundary]],{x_,_}/;x== -30.];
(Subscript[Γ, out])=Cases[nodes[[boundary]],{x_,_}/;x== 30.];inElems={{11, 10},{10, 402},{402, 9},{9, 8},{8, 463},{463, 7},{7, 6},{6, 453},{453, 5},{5, 4},{4, 3},{3, 451},{451, 2},{2, 1}};
outNodes = Table[Position[nodes, (Subscript[Γ, out])[[i]]][[1,1]],{i,1,Length[(Subscript[Γ, out])]}];