Inconsistancy with the Vinf field in 3.48.0

[Brendan Kelly]

While I have seen the Vinf field should not affect the lift and drag coefficients, I have noticed a large variation in the lift/drag ratio when I change it from its default of 100 to 10 (the planned speed for my aircraft in m/s), the lift/drag ratio fell from the 150-100 range to 0.  I made an OpenFOAM case of an older verion of the aircraft without the propellers and with some additional equipment that was removed in later design renditions.  The lift/drag ratio was 10.  When I made a new OpenVSP case, this time with the most recent design, I got a lift/drag ratio of 28 before the propellers were added (not too unheard of, especially with my high aspect ratio).  I am having difficulty seeing which Vinf I should use when my propellers are included.  Attached is my most recent design.

[Rob McDonald]

The change you are seeing is due to the parasite drag model and its dependence on Reynolds number.

In addition to specifying alpha and beta, you also specify Recref -- a reference Reynolds number.  That is used in conjunction with the reference chord and reference velocity to figure out the local Reynolds number (based on local chord and local velocity) across the model.  That Re contributes to the parasite drag contribution.

Make sure all of your inputs are self-consistent.

Rob

[Brendan Kelly]

Thank you.  With this new information, I am getting a realistic lift coefficient.  My total drag coefficient is negative, and it appears that it is taking into account the thrust produced by the propellers.  Is that what is happening?  If so, is there a way to get the drag coefficient without the thrust from the propellers?