Select the back bottom polygon and extrude it. Next, slice the newly extruded part, twice.

Now, select all of the polygons as in the picture (polygons where the upper tail part will attach to the body) and click on the Bridge button.

Next, we will be adding some more details to the nose of the airplane, so just follow the pictures.

To create the nose cone, create a sphere and set its Hemisphere value to around 0.5. Then, from the top view, scale it along the Y axis to elongate it.

Next, cut the whole model right down the middle, delete all of the polygons right of the cut (top view) and mirror it. Then attach the mirror part to the original one. Select all of the vertices and click on the Weld button. You should get something like this.

Only thing left is to add the Mesh Smooth modifier and adjust the Smooth Groups for the cock pit.