I'm asking if I'm doing this correctly. I've estimated the thrust of a ducted-fan model aircraft neglecting pressure changes across the duct as follows:
$$F = Q * \rho * (V_e - V_0)$$
$$= Q * rho * (Q/A_e - Q/A_0)$$
$$ = 131 [cu. ft. / sec] * 0.00237 [slug/cu. ft] * (131/0.74 -131/0.92)$$ $$ = 0.31 * (177.03 - 142.4)$$ $$= 0.31 * 34.6$$ $$= 10.7 lbf$$
where
- F = Thrust,
- Q = volume flow rate of air = 131 [cu. ft. / sec],
- $\rho$ = density of air = 0.00237 [slug / cu. ft],
- $A_0$ = an circular inlet area = 0.92 [sq. ft],
- $A_e$ = an exit area = 0.0.74 [sq. ft].
That seems an awfully high value for thrust to me. Am I missing something?
