anton k asked 3 months ago
I’m trying to analyze a fairly standard plane, and I’m seeing high discrepancies after making small tweaks to the planform
The 3 planes have the same wing area and the same tail, very similar NURBS fuse. The differences are:
- Black – Tapered wing and high wing, i.e. the wing is above the fuse (but attached to it)
- Blue – Tapered and the wing goes through the center of the fuselage
- Green – The wing is straight, and goes through the center of the fuse.
The analysis is T2, linear tri panels, thick sufaces, includes wing tip forces, everything else is standard.
anton k answered 3 months ago
I just realized that fuselage drag was no enabled in #2 and #1. After enabling it the high wing configuration still stands out considerably. The analysis shows that induced drag is much lower around the fuse with the high wing configuration. Is this realistic?
It’s difficult to say just by looking at the images. Fuselage wing connections are a dfiifficulty in these analyses because of numerical interations between the panels. The things I usually do and check:
– Switch to tri-uniform which is the recommended method. Trilinear improves accuracy only marginally, but creates all sorts of numerical issues.
– Make sure that the vortex core size (Analysis/3d Analysis settings) is one order of magnitude less than the smallest element
– Make sure that wing and elevator do not lie in the same horizontal plane
– Display the wake panels at alpha = 0 and see if those shedded by the wing interact with either the fuse or the tail surfaces
– It there is any concern with the last two points, switch to the VPW. This wake model is specifically intended to solve the problems of panel interactions.