Discussed the old charts with djpil. Like me, he is a bit removed from the cut and thrust these days .. but thought that LeadSled's view was correct. For my own interest I'll touch base with some CASA buddies when convenient and check out the current story from the horse's mouth.
it will be impossible to even achieve the factored filed lengths in day to day operations
takeoff shouldn't be too much of a problem but landing is a whole different ball game.
Think about it, do you know how the base figures were established?
Generally, you won't have any way of knowing the detailed history. However, the AFM should give you a story, especially for the heavies.
As an overview, though ..
(a) the base data will be determined from the standard mathematical modelling for takeoff and landing with flight test confirmation of particular test card points to derive fudge factors to make the theory better fit the reality.
(b) OEM flight test will be flown as critically as the OEM can get away with .. you only really have the Regulator's oversight to safeguard against things getting a bit too optimistic.
Having said that, TPs of integrity will be doing a pretty good job. However, it would be foolish to think that the TP has much interest in addressing the typical sort of flying one might see at the aero club or on the line. Performance take off and landing trials set out to get "good" data for the OEM's marketing effort.
The military TP programs probably are a bit more interested both in the optimum data as well as addressing line problems and concerns.
In the case of, say, the old DCA charts, several techniques were represented ..
(i) the more serious work would involve an experienced experimental TP with cinetheodolite recording for read out of test data.
(ii) as we moved down the dollar scale, one used simple still camera records to figure the 50ft point and liftoff/touch down points. Very crude but, nonetheless pretty effective. The pilot could be a TP or even a moderately experienced CPL type of chap/chapess.
(iii) sometimes, Industry would talk DCA into permitting the use of test points from FAA approved POH data and then the expansion would follow the usual DCA techniques.
In the good old days, expansion of test points would have been via slide rule, later machines such as the HP calculators ... and finally microprocessor devices/PCs. The equations used were fairly basic derivations from kinematics although as we moved into the larger OEMs, the resources permitted very elegant modelling to get the data to agree with FT as close as could reasonably be achieved. The number crunching devices became much bigger and faster as well.
One of the problems between the FT/aerodynamicist work and the aero club real world is that the former were out to get the best data they could. In addition, the TP would discard runs he/she didn't like. Then, during analysis, the aerodynamicists would discard a few more of the poorer quality runs. End result was that the data presented to the certificating Regulator was skewed to the good side.
I suggest that, in general, any pilot without an FT background who talks him/herself into believing he/she can replicate unfactored AFM data .. especially for landing .. is just having him/herself on. A fool's errand. The TP is going to be doing well to replicate the published unfactored data !!
Landing technique generally is along the lines of
(a) steady approach angle
(b) weather conditions perfect and nil wind
(c) approach speed as scheduled plus/minus nil
(d) 50ft is not critical as the data capture and analysis shifts the exercise to suit .. ie the test work is done on long runways where it doesn't matter an iota where the actual touch down point is. The only real constraint is that it be within a reasonable range for the data capture setup
(e) throttle closure generally will be at 50ft
(f) the flare generally will be somewhat more aggressive than that used by Joe Bloggs, aero club pilot
(g) maximum braking means just that .. until the aircraft has really stopped.