A model this large and with only 40 pounds of thrust will fly rather slowly; I'd hazrd a guess and say less than 100 mph.
You are only thinking about the 40 pounds of static thrust.....not the 500 - 600 MPH exhaust velocity.
The jet below is 102" span with 36 pounds of thrust, weighing 52.5 pounds with fuel and flies at speeds well over 100 mph.
Nice project, Gary!
