The units of lift in the lift equation can be confusing because the English unit of pound represents force when representing weight, while kilogram is the metric unit of mass (newton is the unit of force).
The conversion factor of 1 kilgram = 2.2 pounds, therefore converts the units of mass to force.
The lift equation is L = ½ ρ S V 2 CL where L is lift, S is area, V is airspeed, and CL is the lift coefficient. After unit analysis, lift is in units of kg·m/s2 = newtons, or slug·ft/s2 = pounds-force.
The 4th edition of Martin Simons', Model Aircraft Aerodynamics, pg 212, has a simple example in both systems of units:
| Units | Density | Area | Airspeed | Cl | Lift (F=MG) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Force | Gravity | Mass | |||||||||||
| Metric | 1.225 | kg/m3 | 0.2 | m2 | 20 | m/s | 0.4 | 19.6 | N | 9.81 | m/s2 | 2.0 | kg |
| English | 0.00238 | slugs/ft3 | 2.16 | ft2 | 65.7 | ft/s | 0.4 | 4.4 | lb | ||||