Jet fighter inlet duct
Space shuttle fuselage lofts
LOFTING FUNDAMENTALS
In the aerospace industry, conic equations are used to describe the curves that are swept through space to generate surfaces.
Conics are the curve of choice since they form smooth surfaces that are capable of creating laminar flow across surfaces. The military has used conics since they are a reproducible curves due to their mathematical equations. In addition, almost all existing aircraft used books full of conic equations to describe the lofts. these "Master Dimension Books (MDB)" or "loft books" are the only road map's available to obtain the true definition of aero surfaces. Bayden Engineering Groups team of seasoned loftsmen are highly skilled at the interpretation of these conic equations and then recreating the matching surface in today's high end CAD systems.
The advent of 3D surface definition has created surface "Hackers” (No concept of tangency, parameterization, patch count, etc.) who create surfaces that may appear to be fine but the underlying equations for that surface are bad. Surfaces are the root geometry for all downstream CAD applications (solid modeling, NC programming, etc.). Some companies have attempted to convert point maps back into 3D surfaces which result in:

4th order approximations

Gaps between adjacent surfaces

Curvature discontinuities

Unusable surfaces for downstream applications

Curves made up from individual arcs
True lofting is more than just sweeping curves through space to genreate surfaces. The proper use of curves creates proper surfaces. Once the surface has been generated, you need to go back and massage the surfaces to maintain critical specifications such as:

Curvature Control

Tangency Control

Dimensional Accuracy

Patch Count

Polygon Arrangement

Correspondence Control Parameterization
CURVATURE CONTROL
Curvature control is controlling the radius of each arc used to generate a surface. Curve Analysis should result in a Bell Curve. A negative radius is unacceptable for an air foil as it indicates an inverse or crease in the surface.
Curvature Analysis
Lofting curvature control
TANGENCY CONTROL
Tangency Control is the angle between two surface boundaries The lack of tangency results in surfaces that cannot be concatenated or joined to an adjacent surface. This leads to poor modeling practices.
Tangency control along green edges
Lack of Tangency control
POLYGON ARRANGMENT
Polygon arrangement is the placement of control points on a patch. Poor polygon arrangement results in:

Increases patch count

Decreases dimensional accuracy of the surface

Limits downstream use, example: unable to generate NC cutter paths

CAD file is very susceptible to failure (System Crash)
Example of poor polygon management
Example of poor polygon management
POINT CORRESPONDANCE
Correspondence of points is the alignment and organization of adjacent patches. Lack of correspondence control will create a data explosion when surfaces are concatenated
Example of good point correspondance
Example of poor correspondance
PARAMETERIZATION
Parameterization is the manual control of polygonal alignment and tangency of adjacent patches. Misaligned patches will cause operations such as surface offsets and fillets to fail. Parameterization is required for downstream usability.
Non parameterized patches
Parameterizd patches