diff --git a/core/src/net/sf/openrocket/simulation/BasicEventSimulationEngine.java b/core/src/net/sf/openrocket/simulation/BasicEventSimulationEngine.java
index eb84e43e8..2d5d7d070 100644
--- a/core/src/net/sf/openrocket/simulation/BasicEventSimulationEngine.java
+++ b/core/src/net/sf/openrocket/simulation/BasicEventSimulationEngine.java
@@ -194,13 +194,17 @@ public class BasicEventSimulationEngine implements SimulationEngine {
 				}
 				
 				// Check for Tumbling
-				// FIXME - need to test things like no longer stable.
+				// Conditions for transision are:
+				//  apogee reached
+				// and is not already tumbling
+				// and not stable (cg > cp)
+				// and aoa > 30
 
 				if (status.isApogeeReached() && !status.isTumbling() ) {
-					int last_data_index = status.getFlightData().getLength() -1;
-					double cp = status.getFlightData().get(FlightDataType.TYPE_CP_LOCATION).get(last_data_index);
-					double cg = status.getFlightData().get(FlightDataType.TYPE_CG_LOCATION).get(last_data_index);
-					if( cg > cp ) {
+					double cp = status.getFlightData().getLast(FlightDataType.TYPE_CP_LOCATION);
+					double cg = status.getFlightData().getLast(FlightDataType.TYPE_CG_LOCATION);
+					double aoa = status.getFlightData().getLast(FlightDataType.TYPE_AOA);
+					if( cg > cp && aoa > 30 ) {
 						addEvent( new FlightEvent(FlightEvent.Type.TUMBLE,status.getSimulationTime()));
 					}
 					status.setTumbling(true);
diff --git a/core/src/net/sf/openrocket/simulation/BasicTumbleStatus.java b/core/src/net/sf/openrocket/simulation/BasicTumbleStatus.java
index 5e391a176..db2d97469 100644
--- a/core/src/net/sf/openrocket/simulation/BasicTumbleStatus.java
+++ b/core/src/net/sf/openrocket/simulation/BasicTumbleStatus.java
@@ -1,42 +1,77 @@
 package net.sf.openrocket.simulation;
 
+import java.util.Iterator;
+
 import net.sf.openrocket.aerodynamics.AerodynamicForces;
 import net.sf.openrocket.aerodynamics.FlightConditions;
 import net.sf.openrocket.aerodynamics.WarningSet;
 import net.sf.openrocket.motor.MotorInstanceConfiguration;
 import net.sf.openrocket.rocketcomponent.Configuration;
+import net.sf.openrocket.rocketcomponent.FinSet;
+import net.sf.openrocket.rocketcomponent.Rocket;
+import net.sf.openrocket.rocketcomponent.RocketComponent;
+import net.sf.openrocket.rocketcomponent.SymmetricComponent;
 
 public class BasicTumbleStatus extends SimulationStatus {
 
-	private double tumbleCd;
+	// Magic constants from techdoc.pdf
+	private final static double cDFin = 1.42;
+	private final static double cDBt = 0.56;
+	// Fin efficiency.  Index is number of fins.  The 0th entry is arbitrary and used to
+	// offset the indexes so finEff[1] is the coefficient for one fin from the table in techdoc.pdf
+	private final static double[] finEff = { 0.0, 0.5, 1.0, 1.41, 1.81, 1.73, 1.90, 1.85 };
+
+	private double drag;
 	
 	public BasicTumbleStatus(Configuration configuration,
 			MotorInstanceConfiguration motorConfiguration,
 			SimulationConditions simulationConditions) {
 		super(configuration, motorConfiguration, simulationConditions);
-		computeTumbleCd();
+		computeTumbleDrag();
 	}
 
 	public BasicTumbleStatus(SimulationStatus orig) {
 		super(orig);
 		if ( orig instanceof BasicTumbleStatus ) {
-			this.tumbleCd = ((BasicTumbleStatus) orig).tumbleCd;
+			this.drag = ((BasicTumbleStatus) orig).drag;
 		}
 	}
 
-	public double getTumbleCd( ) {
-		return tumbleCd;
+	public double getTumbleDrag( ) {
+		return drag;
 	}
 	
 	
-	public void computeTumbleCd() {
-		// FIXME - probably want to compute the overall CD more accurately.  Perhaps average
-		// CD over three AoA: 0, 90, 180.  In any case, using barrowman to compute this Cd is
-		// completely wrong.
-		WarningSet warnings = new WarningSet();
-		FlightConditions cond = new FlightConditions(this.getConfiguration());
-		cond.setAOA(Math.PI);
-		AerodynamicForces forces = this.getSimulationConditions().getAerodynamicCalculator().getAerodynamicForces(this.getConfiguration(), cond, warnings);
-		tumbleCd = forces.getCD();
+	public void computeTumbleDrag() {
+
+		// Computed based on Sampo's experimentation as documented in the pdf.
+		
+		// compute the fin and body tube projected areas
+		double aFins = 0.0;
+		double aBt = 0.0;
+		Rocket r = this.getConfiguration().getRocket();
+		Iterator<RocketComponent> componentIterator = r.iterator();
+		while ( componentIterator.hasNext() ) {
+			RocketComponent component = componentIterator.next();
+			if ( ! component.isAerodynamic() ) {
+				continue;
+			}
+			if ( component instanceof FinSet ) {
+				
+				double finComponent = ((FinSet)component).getFinArea();
+				int finCount = ((FinSet)component).getFinCount();
+				// check bounds on finCount.
+				if ( finCount >= finEff.length ) {
+					finCount = finEff.length-1;
+				}
+				
+				aFins += finComponent * finEff[finCount];
+				
+			} else if (component instanceof SymmetricComponent ){
+				aBt += ((SymmetricComponent) component) .getComponentPlanformArea();
+			}
+		}
+		
+		drag = ( cDFin * aFins + cDBt * aBt );
 	}
 }
diff --git a/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java b/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java
index 0d5ac5c4a..d0ec8da67 100644
--- a/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java
+++ b/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java
@@ -18,7 +18,6 @@ public class BasicTumbleStepper extends AbstractSimulationStepper {
 	
 	@Override
 	public void step(SimulationStatus status, double maxTimeStep) throws SimulationException {
-		double refArea = status.getConfiguration().getReferenceArea();
 		
 		// Get the atmospheric conditions
 		AtmosphericConditions atmosphere = modelAtmosphericConditions(status);
@@ -30,11 +29,11 @@ public class BasicTumbleStepper extends AbstractSimulationStepper {
 		// Get total CD
 		double mach = airSpeed.length() / atmosphere.getMachSpeed();
 
-		double totalCD = ((BasicTumbleStatus)status).getTumbleCd();
+		double tumbleDrag = ((BasicTumbleStatus)status).getTumbleDrag();
 				
 		// Compute drag force
 		double dynP = (0.5 * atmosphere.getDensity() * airSpeed.length2());
-		double dragForce = totalCD * dynP * refArea;
+		double dragForce = tumbleDrag * dynP;
 		MassData massData = calculateMassData(status);
 		double mass = massData.getCG().weight;