What's the definition and the meaning of "soft dirt runway"? You can read that expression in the following text:

..The aircraft's rolling resistance, μ, is determined by the type of runway surface and by the type, number, inflation pressure and arrangement of the tires. A thin, high-pressure tire operated over a soft dirt runway will have so much rolling resistance that the aircraft may be unable to move. A large, low pressure tire can operate over a softer runway surface but will have more aerodynamic drag if not retracted, or will take up more room if retracted. Values of μ for different runway surfaces are provided in the detailed takeoff analysis in Chapter 17. ...

Source: Daniel P. Raymer, Aircraft design: a conceptual approach. Chapter 5 Thrust-to-weight ratio and wing loading, paragraph 5.3 Wing Loading, sub-paragraph Takeoff Distance, page 88.

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    $\begingroup$ It sounds like a description of relative hardness. I don't think a specific definition is needed, as it appears he's just trying to create an example to show how a software runway would need a different tire setup. $\endgroup$
    – Steve
    Mar 16 '16 at 16:05
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    $\begingroup$ @Steve Software runways are only found on flight sims :) $\endgroup$
    – TomMcW
    Mar 16 '16 at 17:59
  • $\begingroup$ Err... Walk out on the runway. If your shoes are leaving obvious tracks, it's soft. $\endgroup$
    – jamesqf
    Mar 16 '16 at 19:24

The are many types of runway. But the basic are paved, unpaved. Paved runway may be in form of rigid and flexible. Rigid is one which is made of concrete.Flexible runway are made of like bituminous. And the soft runway is one which is not paved. The runway may be on ice sand or water. But generally for a soft runway we can assume it as a grassy runway. I did not find anything specific about the dirty runway. But in general we can think dirty means the runway conditions which are not so good for the engine when using of reverse thrust , applying brakes or maintaining direction while on take off roll.

  • $\begingroup$ Not so. I assume by "like bituminous" you mean asphalt paving? Those are paved runways, just as concrete ones are. There is also a major difference between a grass runway and a dirt one, this difference being that one is covered with grass (usually mown short), the other is bare dirt. The OP asks specifically about "soft dirt". $\endgroup$
    – jamesqf
    Mar 16 '16 at 22:16

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