Talk:Supercritical airfoil

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Critical

I came here to understand one thing, namely in what regard these things are critical or even supercritical .. and did not find an answer. So if I have not overlooked it (in which case I would suggest to place that information more visibly and closer to the top) I would believe that adding that information would be highly educational since an explanation for the very name of the beast surely includes further information about its physical nature. JB. --92.193.245.36 (talk) 09:56, 24 September 2024 (UTC)[reply]

To maybe answer my own question, it seems that the thing that gets critical is the Reynolds number in regard to laminar flow. Somebody familiar with the topic hopefully might be able to express this in a useful. JB. --92.193.245.36 (talk) 10:11, 24 September 2024 (UTC)[reply]

The speed at which an aerofoil begins to encounter locally supersonic flow (e.g. develop small shockwaves on typically the upper surface) is referred to as the critical Mach number since at those speeds it makes a lot more sense to express speed as a Mach number. At this critical speed, bad things tend to happen on a traditional aerofoil due to the shock-wave occurring a relatively short distance downstream (e.g. 1/3 the chord), which can cause quite large upsets to the normal centre of pressure, and/or rendering control surfaces less effective or not effective at all (e.g. P-38 "Mach tuck").

The different design of a supercritical aerofoil with the flatter upper surface means that the flow acceleration over the upper surface is less, so the critical Mach number occurs at a higher overall speed, and the location of the shockwave also occurs further downstream, which reduces the effect of the locally supersonic flow on the centre of pressure. This means it's possible to operate the aerofoil a little bit beyond the critical Mach number, i.e. "supercritical". 89.243.113.98 (talk) 22:28, 13 November 2024 (UTC)[reply]