public void SendAck()
{
mavlink_command_ack_t ack = new mavlink_command_ack_t();
ack.command = (byte) MAV_CMD.PREFLIGHT_CALIBRATION;
ack.result = 0;
// send twice
generatePacket((byte) MAVLINK_MSG_ID.COMMAND_ACK, ack);
System.Threading.Thread.Sleep(20);
generatePacket((byte) MAVLINK_MSG_ID.COMMAND_ACK, ack);
}