Hi Induced Drag,
I'm trying to think up another way of explaining the condition. Not sure where I'll be leading myself even!
Our dear friend Isaac Newton tells us that every body in a 'uniform state of motion' continues in that uniform motion until acted upon by an external force. That, as we all know, is inertia, ie movement or lack of movement relative to space. Much the same as the pendulum of a clock swings relative to space, not the clock it sits in. Ditto a gyroscope. In the case of the pendulum it has a name. Cycloidal error. (Sinsinoidal)
So to try and relate this to our aircraft - its inertia is relative to space, which in its simplest term is relative to the bit of ground sitting underneath.
So let's say I am at the top of a wingover, ASI showing 15 knots in a fifteen knot wind. My position relative to space/earth underneath is static, and the inertia I possess is zero. The only energy I possess is the potential to fall to earth under the influence of 1G. ie ... 'Potential Energy.'
Now to achieve some speed I need an external force applied to accelerate me. Well in the instance I have given, I only have the wind and gravity.
Yes, as I reciprocate 180 degrees, the 15 knot wind is applied to my airframe, but I am not going to accelerate in a micro second to 15 knots in the opposite direction, and depending on the aerodynamic drag of my hull, that may take a few seconds. It is interesting here that the more streamlined my airframe, the slower the acceleration. A nice big draggy helicopter will speed up more quickly! (until it equals 15 knots groundspeed, therafter it becomes less efficient)
I hope I am making some progress here!
So we have a situation where, my airframe is at zero or low inertia for a short period and the only external force now affecting me is the 1G towards mother earth!
Now IF the time period before striking the ground is sufficient to allow the 15 knot wind to take full effect, and give me translational lift, I'm home and dry. But IF NOT, the 1G acceleration to earth takes precedent and you can see what happens. So we are talking here about extra height and extra speed for a safe wing-over manoeuvre ... something we all know.
All this of course assumes I don't increase power at some early stage, but since I am performing a low entry speed 'wing-over' manoeuvre followed by a steep descent, I wasn't planning on doing this until I need to level off close to the ground.
So in summary, I believe it is that short period of zero inertia when the aircraft is at risk. Plenty of height (ie time) to convert to speed is good. A streamlined and heavier ship has a corresponding higher period at low inertia and is correspondingly more at risk.
I can tell you that in display flying, the transition effect in a steep descent is as noticeable as the extra lift we all feel on a standard take off profile. The same thing happening in a steep descent takes some getting used to until one works out what is going on.
I haven't used any technical jargon or lift/gravity formulae here, since there are others better versed in those areas than me. But here's a plea. Nick if you are reading this, we'd all like your pennorth!
Best wishes,
Dennis Kenyon.