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Thursday, May 19, 2011

Blind confusion, improper terminolgy, and the on-going 3D RC debate

It strikes me that more than other hobbies, RC enthusiasts tend to make a lot of crap up.  From amateur hour motor testers, creating huge databases of statical noise derived from unsound methods and their subsequent outer space conclusions, to vocal rank amateurs produced by our "there-is-no-wrong-answer" "school" systems, the shear volume of wrong stuff posted on the usual-suspect message boards is quite impressive.  Yes, there is no shortage of posts and blogs and RC forums universally aspiring to make us all dumber.

One on-going cyber debate is what "3D" aerobatics really means.  It's such a waste of time, I thought I would do the world a favor by wasting a few minutes of my own time to save the minutes of billions.  Here is the proper, aerodynamically sound definition of 3D as it applies to the unscrupulous world of the big RC forum crazies:

3D maneuvering, as commonly used to describe a class of radio control airplanes, simply denotes predictable control at AOAs above critical.  Simple as that.

To underpin a useless term with a few useful definitions and assumptions, we have:

  • AOA = the angle between the wing chord line and relative wind resulting primarily from the aircraft's flight path.  I say "primarily" because the high speed air column created by the motor is often used to create blown wing lift or to enhance control surface effectiveness, this effectively creates a different AOA near the wing root than the rest of the wing experiences from flight path alone.
  • Critical AOA = the AOA above which the wing stalls, thereby producing less lift than at a lower AOA, at positive or negative angles of attack.
  • Predictable control = repeatable.
  • Since the wing is stalled for all or part of 3D maneuvering, any true 3D aircraft must have a T:W greater than 1:1 (or achieve it at some point during the flight).
  • "Wing" refers to the main wing(s), not the prop blades.
  • Prop-driven aircraft with greater than 1:1 Thrust:Weight are technically a rotary-wing aircraft, as well as a fixed-wing aircraft.
  • All helicopters fit the proper definition of 3D, since carrying a stalled fixed wing is not technically different than having no fixed wing.  Some helicopters are advertised as 3D helis, but such a distinction  from other helis is not proper since it boils down to a matter of degree.  Any craft that can hover is performing a staple 3D maneuver.

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