This rosnode performs naive dead reckoning using the IMU (accelerometer, gyroscope). This works with RealSense data, but can be adapted to work with your tello.
cd ~/catkin_ws/src
git clone https://github.com/BWSI-UAV/localization_naive.git
cd ..
catkin_make
source ~/catkin_ws/devel/setup.bash
Download the data from here.
roscore
roslaunch localization_naive start_rqt.launch
roslaunch localization_naive dead_reckoning.launch