Reply To: Trim in the PMDG NGX

[jackz]

and here’s the complement (ACJ) of the JAR 25.143 Load factor for large aircrafts

ACJ No. 2 to JAR 25.143(f)
Controllability and Manoeuvrability (Interpretative Material)
See JAR 25.143(f)
See Orange Paper Amendment 96/1
1 The aircraft will be considered to have been overstressed if limit strength has been exceeded in any critical component. For the purpose of this ACJ, limit strength is defined as the minimum demonstrated strength against the relevant manoeuvre load condition divided by 1·5.
2 Minimum Stick Force to Reach Limit Strength
2.1 The stick force necessary to reach limit strength in steady manoeuvre or wind up turns should not be less than 50 pounds, except that if severe buffeting occurs before the limit strength condition is reached a somewhat lower stick force may be acceptable. This minimum stick force applies in the en-route configuration with the aeroplane trimmed for straight flight, at all speeds from the minimum speed at which the limit strength condition can be achieved without stalling. No minimum stick force is specified for other configurations, but the requirements of JAR 25.143(f) are applicable in these conditions.
2.2 The acceptability of a stick force of less than 50 pounds at the limit strength condition will depend upon the intensity of the buffet, the adequacy of the warning margin (i.e. the load factor increment between buffet onset and the limit strength condition) and also on the acceptability of any associated non-linearities of the stick force characteristics.
3 Stick Force Characteristics
3.1 At all points within the buffet onset boundary determined in accordance with JAR 25.251 (e), but not including speeds above VMO/MMO (see JAR 25.253(a)(3)), the stick force should increase progressively with increasing load factor. Any reduction in stick force gradient with change of load factor should not be so large or abrupt as to impair significantly the ability of the pilot to maintain precise control over the load factor and pitch attitude of the aeroplane.
3.2 Beyond the buffet onset boundary hazardous stick force characteristics should not be encountered within the permitted manoeuvring envelope without adequate prior warning being given by severe buffeting or high stick forces. It should at all times be possible, by use of the primary longitudinal control alone, to pitch the aeroplane rapidly nose down so as to regain the initial trimmed conditions. The stick force characteristics demonstrated should comply with the following:
a. For normal acceleration increments of up to 0·3 g beyond buffet onset, where these can be achieved, the ability to control pitch attitude and load factor with precision should be retained. Local reversal of the stick force gradient within this range of load factor will be acceptable provided that any tendency to pitch up is mild and easily controllable.
b. For normal acceleration increments of more than 0·3 g beyond buffet onset, where these can be achieved, more marked reversals of the stick force gradient may be acceptable. It should be possible for any tendency to pitch up to be contained within the allowable manoeuvring limits without applying push forces to the control column and without making large and rapid forward movement of the control column.
[ 3.3 In flight tests to satisfy paragraph 3.1 and 3.2 the load factor should be increased until either – ]
a. The level of buffet becomes sufficient to provide an obvious warning to the pilot which is a strong deterrent to further application of load factor; or
b. Further increase of load factor requires a stick force in excess of 150 pounds (or in excess of 100 pounds when beyond the buffet onset boundary) or is impossible because of the limitations of the control system; or
c. The positive limit manoeuvring load factor established in compliance with JAR 25.337(b) is achieved.

hope this helps
Jacques