Editing Thrust-to-weight ratio (section)

==Aircraft==
The thrust-to-weight ratio and [[Lift-to-drag ratio|lift-to-drag]] ratio are the two most important parameters in determining the performance of an aircraft.

The thrust-to-weight ratio varies continually during a flight. Thrust varies with throttle setting, [[airspeed]], [[Altitude#Altitude in aviation|altitude]], air temperature, etc. Weight varies with fuel burn and payload changes. For aircraft, the quoted thrust-to-weight ratio is often the maximum static thrust at sea level divided by the [[maximum takeoff weight]].<ref>John P. Fielding, ''Introduction to Aircraft Design'', Section 3.1 (p.21)</ref> Aircraft with thrust-to-weight ratio greater than 1:1 can pitch straight up and maintain airspeed until performance decreases at higher altitude.<ref name="thedrive20160509">{{Cite web |url=https://www.thedrive.com/the-war-zone/3383/what-it-was-like-flying-and-fighting-the-f-16n-viper-topguns-legendary-hotrod |title=What it's Like to Fly the F-16N Viper, Topgun's Legendary Hotrod |last1=Nickell |first1=Paul |last2=Rogoway |first2=Tyler |date=2016-05-09 |website=The Drive |access-date=2019-10-31 |archive-date=2019-10-31 |archive-url=https://web.archive.org/web/20191031061848/https://www.thedrive.com/the-war-zone/3383/what-it-was-like-flying-and-fighting-the-f-16n-viper-topguns-legendary-hotrod |url-status=live }}</ref>

A plane can take off even if the thrust is less than its weight as, unlike a rocket, the lifting force is produced by lift from the wings, not directly by thrust from the engine. As long as the aircraft can produce enough thrust to travel at a horizontal speed above its stall speed, the wings will produce enough lift to counter the weight of the aircraft.

:<math>\left(\frac{T}{W}\right)_\text{cruise} = \left(\frac{D}{L}\right)_\text{cruise} = \frac{1}{\left(\frac{L}{D}\right)_\text{cruise}}.</math>

===Propeller-driven aircraft===
For propeller-driven aircraft, the thrust-to-weight ratio can be calculated as follows in imperial units:<ref>Daniel P. Raymer, ''Aircraft Design: A Conceptual Approach'', Equations 3.9 and 5.1</ref>
:<math>\frac{T}{W} = \frac{550\eta_\mathrm{p}}{V} \frac{\text{hp}}{W},</math>
where <math>\eta_\mathrm{p}\;</math> is [[propulsive efficiency]] (typically 0.65 for wooden propellers, 0.75 metal fixed pitch and up to 0.85 for constant-speed propellers), hp is the engine's [[shaft horsepower]], and <math>V\;</math>is [[true airspeed]] in feet per second, weight is in lbs.

The metric formula is:
:<math>\frac{T}{W}=\left(\frac{\eta_\mathrm{p}}{V}\right)\left(\frac{P}{W}\right).</math>