Thursday, November 21, 2013

First, some terminology

It's important to note that since we are working with monocoque designs (and will start with lifting bodies and flying wings), it's a good idea to know the technical vocabulary I will be using here.  The next post will cover (extremely) basic aerodynamics for hobbyists.  Before trying any of these designs it is a good idea to familiarize yourself with these terms.

Chord and Camber (airfoil cross-section)

  • Chord length is the length of the cord line (below).  It is, essentially, the width of the wing.
  • Chord line is the line from the foremost leading edge straight to the trailing edge.
  • Camber line is the line or curve which passes through all points half-way between the top edge and bottom edge of the wing.  if the airfoil is perfectly symmetrical (or "uncambered") the camber line will be the same as the chord line.  Otherwise the camber line will curve, usually above, the chord line.
  • Camber ratio is the ratio of the maximum distance between the camber line and the chord line, against the length of the chord line.  For example an 8 inch wide wing where the mid-point rises 1/8 inch above the chord line, that leads to about a 1.5% camber (not a bad ratio).

Wing Planform (top-down geometry)

  •  Aspect is the ratio to wing length to chord length.  High aspect wings are very long and thin.  Low aspect wings are short and stubby.

Other related devices 

These become increasingly important as we get into more advanced designs.
  • Chines are sudden corners lengthwise on the fuselage.  These generate vortices. 
  • Wingtip Devices are extensions of the wing tip designed to reduce wingtip vortices.
  • Leading Edge Root Extensions are extensions of the wing root up the fuselage.  These have the effect of generating vortices. 
These three devices in particular are involved in managing aerodynamic vortices involved in lift and the drag that lift induces.  They create important tradeoffs, that future blog entries will discuss in detail.   Paper airplanes often have additional keels which generate vortices in reaction to yaw changes (and thus stabilize the airplane yaw-wise).  Some designs here will have such keels.  Keels are not common on commercial airplanes, and the empenage (tail assembly) takes over that role.