Kent Walters


Most scale modelers have considered speed on frequent occasions and how it affects many other forms of maneuver realism that are observed in flight. This was also a question to scale modelers for many years since ambiguous terms were earlier used in competition for judging maneuvering speed and overall flight realism.

This article will briefly look back in the history or "epilog of scale speed" and then provide a detailed review of the many other observed speed-sensitive features in flight affecting maneuver realism. These include correct flying attitudes such as realistic bank angles in scale-size turns, energy management to permit realistic vertical maneuvers, realistic flight stability, realistic g-factor loading appearances on airframe or passengers, and others. All of these realistic features are influenced by speed if models are to perform like full-size aircraft. However it is not in the manner some had expected by attempting to fly at scale speed. The primary physical reason is simply because the accelerating pull of gravity cannot be scaled to smaller values similar to the smaller sizes of our models. This subtle consideration of the fixed-gravity environment we fly our miniature aircraft produces a notable conflict in scale speed with all the other forms of maneuver-flight realism. In other words "you canít have your cake and eat it too" with scale speed if we are to fly realistically for all the other maneuver realism features we often take for granted. The basic physics for understanding this are also presented in this article.

These considerations have provided another well-defined speed relation used by NASA and others in optimizing model speeds for maneuver realism. This has historically been known as Dynamic Similitude Speed (DSS) by the aircraft industry when using RC scale models (much like those we fly) when studying prototypical flight characteristics. Despite this sophisticated name, most modelers would likely better recognize this simply by the descriptive terms of "Maneuver Realism Speed." Further examples of this DSS feature using tables and graphs are also provided in the latter section of this article for a broad range of scale-size models.

Recognition of these physical relations and the latest changes in competition guidelines also helps achieve a level-playing field for small and large-scale models of different vintages. This is particularly important after giant-scale models were included in Sport Scale competition in 1992 by the Academy of Model Aeronautics (AMA). For example, most modelers had recognized that scale speeds favored larger models better approaching full-size dimensions. However, it was also apparent there were significant added costs in trying to follow this path. Some had further argued this was also taking its toll in new participants in a hobby intended for a variety of "miniature size" scale models.

The earlier ambiguous requirements of "scale like speeds" also invited inconsistent judging, particularly since judges often did not know the scale of the model or the maneuvering speeds of the full-size aircraft from which to scale. There was also difficulty in judging speed itself despite any "gifted mental ability" to make all these calculations while judging. Examples of typical full-size aircraft maneuvering speeds at air shows will also be discussed later in this article.

All the notable RC Sport, Expert, Designer, and Team Scale events in the USA have wisely elected not to mention the words of scale speed or the ambiguous words of "scale like speed." Any words that implied scale speeds were also likely removed when considering the precarious or dangerous levels at or below model stall speeds it may have encouraged despite weight saving efforts by modelers. Rather than risk this possibility with ambiguous rules, the notable scale events in the USA took another look at this and started making changes.

The US Scale Masters began describing maneuver realism speed or DSS in 1994 and deleted ambiguous scale like speeds. The AMA also deleted these words in 1999 and began emphasizing the frequently observed speed-sensitive turns that should be flown with realistic bank-angle attitudes before, during, or after maneuvers as also implemented by the USSMA. This provided "speed limits" as recognized by excessive bank angles in scale-size turns when models were flown too fast. An effective judging paraphrase became, "if it looks right, it is right for speed as well." Top Gun simply does not mention any requirement to fly at scale or scale like speeds.

The following pages will give a comprehensive background for those scale modelers wanting further details.



scalaro2.gif (2313 bytes)

Hit Counter