# Why $\frac{\Delta p}{\overline q}$ is depending by weight, flap deflection and other parameters? Which are other parameters?

As you can see in this link (Roskam, Airplane Aerodynamics and Performance, Chapter 2.5.3 Airspeed corrections) ...

... in the first and second line of page 30 Roskam tells that, in hypothesis of incompressible flow $$\frac{\Delta p}{\overline q}=\frac {\frac{1}{2}\rho_0V_c^2-\frac{1}{2}\rho_0V_I^2}{\frac{1}{2}\rho_0V_c^2}$$ " depends on factor such as weight, flap deflection and other airplane parameters ". Why does it depend on weight, flap deflection?

Which "other airplane parameters" do affect $\frac{\Delta p}{\overline q}$ ?

Note: for completeness of definitions, above in the same link, page 27 Roskam is defining:

"[...] $V_I$ (IAS) is the indicated airspeed corrected for instrument error, $\Delta V_i$, only:

$V_I=V_i+\Delta V_i$ ________________$(2.54)$

$V_c$ (CAS) is the calibrated airspeed. It is equal to the indicator reading corrected for position error due to incorrect static port location $(\Delta V_p)$ and also corrected for instrument error:

$V_C=V_I+\Delta V_p$ ________________$(2.55)$ [...]"

• Sorry, but the linked page will only show by chance - in my case, "La pagina non è disponibile". Without that context I would need to guess what the question is about. Commented Jun 4, 2017 at 7:01