diff --git a/libraries/SITL/SIM_ADSB.cpp b/libraries/SITL/SIM_ADSB.cpp
index ba6e916116..3b4a46bd6c 100644
--- a/libraries/SITL/SIM_ADSB.cpp
+++ b/libraries/SITL/SIM_ADSB.cpp
@@ -27,8 +27,7 @@ namespace SITL {
 
 SITL *_sitl;
 
-ADSB::ADSB(const struct sitl_fdm &_fdm, const char *_home_str) :
-    fdm(_fdm)
+ADSB::ADSB(const struct sitl_fdm &_fdm, const char *_home_str)
 {
     float yaw_degrees;
     Aircraft::parse_home(_home_str, home, yaw_degrees);
diff --git a/libraries/SITL/SIM_ADSB.h b/libraries/SITL/SIM_ADSB.h
index 6dc3627ad6..f324a17791 100644
--- a/libraries/SITL/SIM_ADSB.h
+++ b/libraries/SITL/SIM_ADSB.h
@@ -46,7 +46,6 @@ public:
     void update(void);
 
 private:
-    const struct sitl_fdm &fdm;
     const char *target_address = "127.0.0.1";
     const uint16_t target_port = 5762;
 
diff --git a/libraries/SITL/SIM_Gripper_Servo.h b/libraries/SITL/SIM_Gripper_Servo.h
index c255baf879..5d991eb659 100644
--- a/libraries/SITL/SIM_Gripper_Servo.h
+++ b/libraries/SITL/SIM_Gripper_Servo.h
@@ -53,7 +53,6 @@ private:
     uint64_t last_update_us;
 
     bool should_report();
-    bool zero_report_done = false;
 
     // dangle load from a string:
     const float string_length = 2.0f; // metres
diff --git a/libraries/SITL/SIM_Sprayer.h b/libraries/SITL/SIM_Sprayer.h
index e6f3043311..3db3ccc8a1 100644
--- a/libraries/SITL/SIM_Sprayer.h
+++ b/libraries/SITL/SIM_Sprayer.h
@@ -52,7 +52,6 @@ private:
 
     double capacity = 0.25; // litres
 
-    uint64_t start_time_us;
     uint64_t last_update_us;
 
     bool should_report();
diff --git a/libraries/SITL/SIM_last_letter.cpp b/libraries/SITL/SIM_last_letter.cpp
index 31f2b2b337..ab6547f5ac 100644
--- a/libraries/SITL/SIM_last_letter.cpp
+++ b/libraries/SITL/SIM_last_letter.cpp
@@ -32,8 +32,7 @@ namespace SITL {
 last_letter::last_letter(const char *home_str, const char *_frame_str) :
     Aircraft(home_str, _frame_str),
     last_timestamp_us(0),
-    sock(true),
-    frame_str(_frame_str)
+    sock(true)
 {
     // try to bind to a specific port so that if we restart ArduPilot
     // last_letter keeps sending us packets. Not strictly necessary but
diff --git a/libraries/SITL/SIM_last_letter.h b/libraries/SITL/SIM_last_letter.h
index 3a956a050f..65df3b2a9e 100644
--- a/libraries/SITL/SIM_last_letter.h
+++ b/libraries/SITL/SIM_last_letter.h
@@ -70,8 +70,6 @@ private:
 
     uint64_t last_timestamp_us;
     SocketAPM sock;
-
-    const char *frame_str;
 };
 
 } // namespace SITL