WIG pitch and height stability (moving centre of pressure) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/wig-pitch-height-stability/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
Catalog version: 2026-10-20

Sizes: see table below
- In ground effect the centre of pressure moves with both pitch and height, so a craft can be stable in one and not the other. The Irodov criterion requires the aerodynamic centre in height to lie upstream of the centre in pitch (Rozhdestvensky).
- Remedies: a large tail kept out of ground effect (KM up to 50% of wing area), a reverse-delta planform that limits c.p. shift, or for flying wings, profiling and automatic damping, which have a small stable range (Rozhdestvensky).
- NASA found ground-effect wings had height stability at positive and instability at negative angles of attack, favouring positive-AoA cruise (NASA TN D-926); over waves, ram pressure raised lift at the cost of pitch stability (Frontiers 2022).
- Used on: KM (Caspian Sea Monster), Lippisch X-113.
- The file is a reference example built by Xem Studio from the numbers above. Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

parameter  value or range  source
Irodov criterion  centre in height upstream of centre in pitch  Rozhdestvensky 2006
Height stability sign  stable at +AoA, unstable at -AoA  NASA TN D-926
Tail size for stability (KM)  up to 50% of wing area  Rozhdestvensky 2006
Reference build  reverse delta 700 x 400, anhedral 15  computed

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Progress in Aerospace Sciences (K.V. Rozhdestvensky, 2006): Wing-in-ground effect vehicles (review) — web — Publisher's page; dimensions are facts — https://www.hassanhameed.com/wp-content/uploads/2016/01/wingingroundeffectvehicles-130120003005-phpapp01.pdf
- NASA Langley (Fink & Lastinger): Aerodynamic Characteristics of Low-Aspect-Ratio Wings in Close Proximity to the Ground, NASA TN D-926 (1961) — web — Publisher's page; dimensions are facts — https://ntrs.nasa.gov/api/citations/19980231058/downloads/19980231058.pdf
- Frontiers in Aerospace Engineering (2022): Review of ground-effect experiments on rectangular, reverse-delta and delta wings — web — Publisher's page; dimensions are facts — https://www.frontiersin.org/journals/aerospace-engineering/articles/10.3389/fpace.2022.975158/pdf

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/wig-pitch-height-stability/index.json
API: https://xemstudio.com/api/geometry?object=wig-pitch-height-stability