# Thrust in Newtons (aviation)

1. Nov 7, 2014

### simurq

Given that an engine's rated power is 160 HP (~119kW), how can I express thrust (T) in newtons, if aerodynamic drag (D) requires weight expressed in newtons as well to ensure consistency when calculating power available (Pa) and power required (Pr)?:

$D = (\frac{1}{2}\rho SC_{D})V^{2}+\frac{2W^2}{\rho S\pi AV^2}$

where:

$\rho$ = density at given altitude, $\frac{kg}{m^3}$
$S$ = wing area, $m^2$
$C_{D}$ = zero-lift coefficient of drag
$V$ = true airspeed, $\frac{m}{s}$
$A$ = wing aspect ratio

I want to solve the equation for excess power: $P_{ex} = P_{a} - P_{r} = TV - DV$

Thank you!

Rustam

2. Nov 8, 2014

### OldEngr63

Power is expressed by the relation
P = F * V
where
P is power,
F is force (thrust, drag, etc)
V is velocity (speed)

3. Nov 10, 2014

### cjl

Rather than changing the thrust to newtons, why don't you convert the drag force to a power required value? You can do that with the equation mentioned by OldEngr63 above - knowing the drag force at any given speed, you can calculate the power required for level flight. Power available won't be the engine power though, which will complicate things - if you want an accurate result, you should also account for propeller efficiency.