Aircraft thrust calculation I had a question regarding thrust calculation for an aircraft during cruise. For an aircraft flying at a constant cruise altitude and a constant Mach number (level unaccelerated flight), what exactly is the weight we use in the equation T = W/(L/D) while calculating the thrust?
What I understand is that since the mass of the aircraft is continually reducing due to constant fuel consumption, therefore the lift requirement will change. Assuming a constant L/D ratio, that implies the drag will change leading to a constant change in the thrust. Therefore the cruise thrust is not a constant value. So how can we apply the above equation for a calculation of the thrust anyway? Is it a thrust at some specific point during the cruise?
The equation refers to instantaneous thrust in unaccelerated flight. The weight in this equation is instantaneous weight.
Indeed, this weight changes over time. This is for example the reason we have to use the  Breguet range equation instead of just divide thrust by thrust specific fuel consumption to calculate the range of an aircraft.