classic g-break

[punkalouver]

Concerning an accident report I am reading on a Searey......

"Wings level, the aircraft typically stalls with a classical g-break at all flap settings."


What is a g-break?

thanks

[Mad (Flt) Scientist]

A sudden loss of lift at/near the stall, caused by a breakdown in attached flow over an area of the wing large enough and happening fast enough to register as a discontinuous jump on the 'g' trace if plotted against time.

One alternative would be a slow and/or localised flow breakdown, which might result in a mathematical CLmax being attained, but without the pronounced indication of the g'break.

If you were to plot a CL-versus-alpha plot, an aircraft with a g-break is more likely to have a very sharp spike at CLmax and a marked drop in CL just above that, whereas a non-g-break aircraft may have a more 'rounded' lift-curve.

[punkalouver]

So from a pilots point of view, a classic g-break means a sudden pitch down as opposed a "mushing" stall?

[alf5071h]

… a sudden pitch down as opposed a "mushing" stall?
IIRC this is not what it implies. Any change in pitch depends on the pitching moment characteristics with CL and alpha; so depending on aircraft type the ‘stall’ might be ‘mushing’, a nose down (self recovery), or even nose up.

From the original question / quote, it might be assumed that there is little pitch changed, thus the stall identification is predominated by the ‘g’ break.

[Mad (Flt) Scientist]

alf5071h is basically correct - g-break really refers to the lift behaviour, not the pitching behaviour.

Where there may be some overlap in the two (and where pilots and engineers may disagree) is that you're sat sometimes a long way forward of the cg. As a result an aircraft with a pronounced pitch-down at the stall may feel like there's a distinct loss of lift associated with it, due to the pitch rate/acceleration effects when sat forward of the cg. But there may in fact be no real g-break in the data measured at the cg, which is what us graph-plotters care about.