Table of Contents
What Is Thrust-to-Weight Ratio?
TWR is thrust divided by weight. TWR > 1 means vertical takeoff capability. TWR = 1 means hovering. TWR < 1 requires wings for flight. Rockets need TWR > 1 at liftoff (typically 1.3-2.0). Fighter jets achieve 0.8-1.3; airliners only 0.2-0.3.
TWR changes during flight as fuel burns. The Saturn V went from 1.19 at liftoff to over 4 at first-stage burnout. Too high wastes fuel on drag; too low means sluggish acceleration and high gravity losses.
Formula
TWR = T / (m × g)
Vertical accel = g(TWR - 1)
Famous Vehicles
| Vehicle | TWR |
|---|---|
| Saturn V | 1.19 |
| Space Shuttle | 1.50 |
| Falcon 9 | 1.40 |
| F-22 Raptor | 1.09 |
| Boeing 747 | 0.27 |
FAQ
Why not maximize TWR?
Heavier engines reduce payload fraction. Optimal TWR balances gravity losses against drag losses and structural mass penalties.