Harmonization FTT
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Harmonization FTT
Hello All,
If you would have to perform specific exercises to check harmonization of forces (between pitch and roll), what type(s) of exercises would you perform?: entry into turns in level flight, entry in descent, in climb ?
Thanks a lot for your always valuable inputs !
Leonard
If you would have to perform specific exercises to check harmonization of forces (between pitch and roll), what type(s) of exercises would you perform?: entry into turns in level flight, entry in descent, in climb ?
Thanks a lot for your always valuable inputs !
Leonard
Join Date: Dec 2001
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You'd want to do maneuvers that exercise both axis at the same time. If it's a reversible control system, make sure to do the tests at the extremes of longitudinal CG. I'm reminded that a 90 pound person flying solo trying to land a Cessna 172 in a crosswind is going to have incredible disharmony between very heavy pitch forces and very light roll forces.
Join Date: Sep 2002
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Definitely good advice regarding longitudinal CG position - it can have a very large effect on stick forces in pitch, particularly for reversible controls.
To really pin down control harmonisations I would suggest you need to perform separate evaluations for the pitch and roll axes, then perform role-related manoeuvres such as crosswind landings and side-step manoeuvres during final approach. For the pitch axis, classic test techniques such as stabilised points, level accelerations and steady pulls should be used to quantify and characterise the stick free apparent longitudinal static stability and manoeuvre stability. For the roll axis you are only really interested in the roll mode response, so rolls with different magnitude stick deflections would be sufficient. Provided the roll and pitch manouvres were flown at the same test conditions to permit comparison of the stick forces involved, this would give you a good idea of whether pitch and roll stick forces were well matched. I seem to recall that a ratio of 2:1 is considered ideal, although I cannot remember if that is pitch to roll or roll to pitch; anyone care to elaborate further?
Regarding loaded rolling manoeuvres, approach with care! If you do not have a means of monitoring sideslip, you could easily take the aircraft outside its cleared side-slip limits without realising it, which could have fatal consequences. Also, when approaching longitudinal G limits with high roll rates or sudden roll onset it is not uncommon to encounter nasty effects such as sideslip divergence and inertial coupling, and before you know it you could be into spin territory, with some very uncomfortable departures from normal controlled flight
. If your aircraft has a spin clearance you would probably be ok provided flight conditions were suitable (i.e. VMC, clear horizon and plenty of height for recovery), but if not then you really do not want to be messing about in this flight regime. Either way, a careful incremental approach is key, and a means of monitoring slideslip is essential. I would not advise anyone to devise or undertake flight test in this part of the flight envelope unless they are a trained flight test professional, or have consulted closely with one.
Hope this is helpful, feel free to PM if you have any questions!
Regards,
WF
To really pin down control harmonisations I would suggest you need to perform separate evaluations for the pitch and roll axes, then perform role-related manoeuvres such as crosswind landings and side-step manoeuvres during final approach. For the pitch axis, classic test techniques such as stabilised points, level accelerations and steady pulls should be used to quantify and characterise the stick free apparent longitudinal static stability and manoeuvre stability. For the roll axis you are only really interested in the roll mode response, so rolls with different magnitude stick deflections would be sufficient. Provided the roll and pitch manouvres were flown at the same test conditions to permit comparison of the stick forces involved, this would give you a good idea of whether pitch and roll stick forces were well matched. I seem to recall that a ratio of 2:1 is considered ideal, although I cannot remember if that is pitch to roll or roll to pitch; anyone care to elaborate further?
Regarding loaded rolling manoeuvres, approach with care! If you do not have a means of monitoring sideslip, you could easily take the aircraft outside its cleared side-slip limits without realising it, which could have fatal consequences. Also, when approaching longitudinal G limits with high roll rates or sudden roll onset it is not uncommon to encounter nasty effects such as sideslip divergence and inertial coupling, and before you know it you could be into spin territory, with some very uncomfortable departures from normal controlled flight
. If your aircraft has a spin clearance you would probably be ok provided flight conditions were suitable (i.e. VMC, clear horizon and plenty of height for recovery), but if not then you really do not want to be messing about in this flight regime. Either way, a careful incremental approach is key, and a means of monitoring slideslip is essential. I would not advise anyone to devise or undertake flight test in this part of the flight envelope unless they are a trained flight test professional, or have consulted closely with one.Hope this is helpful, feel free to PM if you have any questions!
Regards,
WF
