diff --git a/core/src/main/java/info/openrocket/core/simulation/AbstractSimulationStepper.java b/core/src/main/java/info/openrocket/core/simulation/AbstractSimulationStepper.java
index dcd152768..94810fb8e 100644
--- a/core/src/main/java/info/openrocket/core/simulation/AbstractSimulationStepper.java
+++ b/core/src/main/java/info/openrocket/core/simulation/AbstractSimulationStepper.java
@@ -163,14 +163,12 @@ public abstract class AbstractSimulationStepper implements SimulationStepper {
 	 *  
 	 * @param status					the current simulation status.
 	 * @param timestep					the time step of the current iteration.
-	 * @param acceleration				the current (approximate) acceleration
-	 * @param atmosphericConditions		the current atmospheric conditions
+	 * @param store                     the simulation calculation DataStore (contains acceleration, atmosphere)
 	 * @param stepMotors				whether to step the motors forward or work on a clone object
 	 * @return							the average thrust during the time step.
 	 */
-	protected double calculateThrust(SimulationStatus status,
-			double acceleration, AtmosphericConditions atmosphericConditions,
-			boolean stepMotors) throws SimulationException {
+	protected double calculateThrust(SimulationStatus status, DataStore store,
+									 boolean stepMotors) throws SimulationException {
 		double thrust;
 
 		// Pre-listeners
@@ -240,8 +238,6 @@ public abstract class AbstractSimulationStepper implements SimulationStepper {
 		
 		public FlightConditions flightConditions;
 		
-		public double longitudinalAcceleration = Double.NaN;
-		
 		public RigidBody rocketMass;
 		
 		public RigidBody motorMass;
diff --git a/core/src/main/java/info/openrocket/core/simulation/RK4SimulationStepper.java b/core/src/main/java/info/openrocket/core/simulation/RK4SimulationStepper.java
index 91b76d28d..f235da572 100644
--- a/core/src/main/java/info/openrocket/core/simulation/RK4SimulationStepper.java
+++ b/core/src/main/java/info/openrocket/core/simulation/RK4SimulationStepper.java
@@ -325,7 +325,7 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
 		double fN = store.forces.getCN() * dynP * refArea;
 		double fSide = store.forces.getCside() * dynP * refArea;
 
-		store.thrustForce = calculateThrust(status, store.longitudinalAcceleration, store.flightConditions.getAtmosphericConditions(), false);
+		store.thrustForce = calculateThrust(status, store, false);
 		double forceZ =  store.thrustForce - store.dragForce;
 		
 		store.linearAcceleration = new Coordinate(-fN / store.rocketMass.getMass(),