14.11: Input additional Drag
Beside the airfoil drag and the induced drag there are additional drags. This
are the fuselage drag and the interference drag, which arise by influence
between fuselage and wings. In the following input fields one can enter these
values manually or you can select pre-set values from a table.
In general a bubble will form at the highest position when flowing an airfoil.
The length of this bubble depends on the Reynolds number. Behind this bubble
the flow turns into a turbulent (swirled) form. In this bubble arises viscous
drag.
Click the check-box 'Compute Airfoil with Bubble Drag' to include this drag
into the vortex computation.
I many applications the fuselage drag coefficient refers to the fuselage
cross-section at the thickest part of the fuselage.
In the following input field you can enter the cross-section surface in
meter^2. Near the input field are Up/Down-buttons located. They can be used to
change the cross-section surface with mouse clicks. A click on the right mouse
button pops up a menu to set the increment between 0.001m and 1m.
The fuselage drag coefficient can be entered into the input field 'Cd_fusl'.
Near the input field are Up/Down-buttons located. They can be used to change
the fuselage drag coefficient with mouse clicks.
There is a third method to change the value. Move the mouse cursor into the
input field and click the right mouse button.
A pull-down menu pops up and offers the pre-set values for different fuselage
shapes for quick selection.
The drag coefficient seems do be quit high, but one have to take in
consideration that this value is related to the fuselage cross-section, not to
the surface of the airplane.
At the transitions from fuselage to wings often arise turbulences
(interferences) which produce additional drag. This drag can be entered into
the input field 'Interference Drag Cd_int'. Near the input field are
Up/Down-buttons located. They can be used to change the interference drag with
mouse clicks.
There is a third method to change the value. Move the mouse cursor into the
input field and click the right mouse button.
A pull-down menu pops up and offers the pre-set values for different
fuselage-wing transitions for quick selection.
The interference drag is related to the total surface of the airplane so that
significant smaller values in comparison to the fuselage drag can be selected.