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.

Wednesday, September 4, 2013

Launching this Blog

For a couple of years I have been into building advanced paper airplanes.  One of my long-term goals is to build an airplane where the structure is entirely built out of conventional (probably 24lb) office paper, capable of carrying sufficient weight as to be capable of powered flight.  This is an extremely difficult task and I have not yet succeeded.  As this blog goes on we will discuss the problems of doing so, what I have tried so far, and possible avenues for future efforts.

In the mean time, I will be discussing my current existing designs.  These designs are built for the express purpose of exploring aerodynamics regarding lifting bodies and airfoils.

I expect by the third post or so to get into actual designs.  This post is just an introduction.  The next post will be an overview of how airfoils work for the hobbyist (with some notes as to where to go to find more advanced explanations).  Most of what many of us have been taught in school regarding airfoils is overly simplistic at best and downright wrong at worst.

I have settled on monocoque designs (meaning designs where the skin bears the entire load without any extra frame components) almost entirely.  These designs (which I have never seen elsewhere) are very difficult to make and take significant practice, but they also allow very fine control over shape, providing unparalleled learning opportunities.  They are also light, and when properly made quite aerodynamically stable even at high speeds.  in general when trying my designs you can expect several failures before achieving success and it will take quite a number of tries before you get feeling really good at it.

In general when we get into the plane building phases of the blog, you will need the following materials minimally to build a paper airplane:

  • Office paper, preferably reasonably heavy and sturdy, US letter or A4 will both work though the specifics will be slightly different for either (giving you a chance to play with things)
  • A pencil or pen
  • Scissors
  • Cellophane tape or similar.
So come join us, have fun, and maybe you will learn something!