Shawn, Re #7 ‘energy’. A long time ago, I had several informal meetings with Dr Pinsker (RAE Bedford) to discuss landing. One aspect, which I think I understood from his expert views (Aero D and landing), was that the landing maneuver is about the distribution of energy.
In the short term, wing generated lift can be considered as energy, this energy is ‘distributed’ by the elevator.
Important parameters, apart from the total energy, are the rate of distribution and rate of loss of energy; both related to Cl / alpha and elevator power (the ability to access the energy).
For a conventional aircraft, the approach speed must provide sufficient energy to counter the expected energy loss during the landing flare. Thus, the flare time is proportional to Cl / alpha, which in most aircraft is about 7 sec. The duration of the maneuver is sufficient for reasonable iterations in the closed loop control.
STOL aircraft probably have greater capability to access the energy quickly (higher Cl / alpha), thus, they should be able to flare later – shorter flare time. However, this may be at the expense of landing finesse as there may be less iteration judging the flight path. There may even be a point at which the landing becomes open loop; the nearest to this might be landing performance testing.
During a steep approach, a conventional aircraft would have to flare earlier (longer flare), but in a timescale to achieve a shallow flight path before the energy available is used up; if not then a higher approach speed would be required (more energy). A STOL aircraft may be able to use the shorter flare time as the wing characteristics and shorter flare time enable a flight path change with lower loss of energy, but again there is a control loop limit.
There are deviations from this, e.g. blown flap effects (C17) and direct lift control. The latter was demonstrated by RAE (BAC 1-11) where a conventional flare from 6 deg required 100ft, but wing spoiler DLC enabled 35 ft. The tradeoff was a higher approach speed due to the spoiler-out reduced stall margin (not a need for energy), which enabled a very precise touchdown, but unfortunately without commercial advantage of a reduced landing length. STOL aircraft generally need a STOL wing.
Re 1.3 VS, this appears to be an empirical value which provides capability for landing or GA, and to counter gusts and windshear during the approach. The energy for landing is probably met at Vref – 5 kts as indicated by certification requirements. However, I suspect that -5 kts is an approximation for a 5% safety margin, thus a safe min approach speed at 3 deg could be 1.25Vs.
A GA during the flare (as energy is reducing) will require additional energy, which in this case must come from thrust. The maneuver is quite safe if considered as being more like a landing touchdown (which might occur) and subsequent take off. A hazard is touching down before the runway (which is where I believe #18 comes from).
The skill is to is to achieve level, flight, accelerate, and then clean up before attempting to climb. Sufficient thrust will available in 8 sec as required by certification.