This is a rework of the parts of PR #766 related to railbutton aerodynamics.

Drag calculations should be reasonably accurate up to transonic speeds

core/src/net/sf/openrocket/aerodynamics/barrowman/RailButtonCalc.java

@@ -0,0 +1,50 @@
+package net.sf.openrocket.aerodynamics.barrowman;
+
+import net.sf.openrocket.aerodynamics.AerodynamicForces;
+import net.sf.openrocket.aerodynamics.FlightConditions;
+import net.sf.openrocket.aerodynamics.WarningSet;
+import net.sf.openrocket.rocketcomponent.RailButton;
+import net.sf.openrocket.rocketcomponent.RocketComponent;
+import net.sf.openrocket.util.MathUtil;
+import net.sf.openrocket.util.Transformation;
+
+public class RailButtonCalc extends RocketComponentCalc {
+	
+	private double refArea;
+
+	public RailButtonCalc(RocketComponent component) {
+		super(component);
+
+		final RailButton button = (RailButton) component;
+
+		final double outerArea = button.getTotalHeight() * button.getOuterDiameter();
+		final double notchArea = (button.getOuterDiameter() - button.getInnerDiameter()) * button.getInnerHeight();
+
+		refArea = (outerArea - notchArea) * button.getInstanceCount();
+	}
+
+	@Override
+	public double calculateFrictionCD(FlightConditions conditions, double componentCf, WarningSet warnings) {
+		// very small relative surface area, and slick
+		return 0.0;
+	}
+
+	@Override
+	public void calculateNonaxialForces(FlightConditions conditions, Transformation transform,
+			AerodynamicForces forces, WarningSet warnings) {
+		// Nothing to be done
+	}
+
+	@Override
+	public double calculatePressureCD(FlightConditions conditions,
+			double stagnationCD, double baseCD, WarningSet warnings) {
+
+		// this is reasonably close for Reynolds numbers roughly 10e4 to 2*10e5, which takes us to low supersonic speeds.
+		// see Hoerner p. 3-9 fig 12, we summarizes a bunch of sources
+		// I expect we'll have compressibility effects having an impact well below that, so this is probably good up
+		// to the transonic regime.
+		double CDmul = 1.2;
+												  
+		return CDmul*stagnationCD * refArea / conditions.getRefArea();
+	}
+}

core/src/net/sf/openrocket/rocketcomponent/RailButton.java

@@ -207,12 +207,6 @@ public class RailButton extends ExternalComponent implements AnglePositionable,
 		clearPreset();
 		fireComponentChangeEvent(ComponentChangeEvent.BOTH_CHANGE);
 	}
-
-	@Override
-	public boolean isAerodynamic(){
-		// TODO: implement aerodynamics
-		return false;
-	}
 	
 	@Override
 	public double getAngleOffset(){