Hi.
if the elevator control moves full deflection without developing a pitch rate, the likelihood is the aircraft is out of trim, by either an erroneous stabiliser setting, or an incorrect load. For the first case, the aircraft is designed to have adequate elevator authority to override the stabiliser setting. For the erroneous cg, in most cases there is adequate elevator and stabiliser available to fly the aircraft, but rotation will be at a higher speed due to the delay in response.
The cg error can be either excessively forward or aft:
for the aft cg, the aircraft will have a noticeable poor nosewheel steering response at almost all speeds, with a fair bit of scuffing occurring. If that doesn't trigger some concern, on power application on most aircraft (not the MD11/DC10) the nose will pitch up, extreme cases. In all cases the pitch attitude will increase on the roll without command. On one case evaluated,
the pitch up occurred on thrust application, and the nose wheel was off the ground before 60 KIAS, and the aircraft lifted off without control input about 5 kts before V1. The aircraft was dynamically unstable, but only mildly so, and the crew engaged the autopilot at low altitude which coped with the instability. In that case the crew then cleaned up.... and continued to destination... and the cg got worse along the way. on landing the aircraft pitched up after touchdown and went off the side of the runway at low speed. That aircraft had a cg 12%MAC aft of the normal envelope, and 2% further aft than ever tested by the manufacturer. The data showed that the AP was responding to the instability constantly during the cruise, and the possibility existed that a disengagement in cruise would have resulted in structural overload through a PIO. Don't recommend flying an out of trim aircraft at speed or high mach, altitude....
On another aft cg case,
the aircraft pitched up on thrust application and the tail hit the ground, below 50KIAS. the crew rejected the takeoff, but were able to taxi back...
For the forward cg case, it is only going to be apparent at rotate; on one case evaluated, t
he elevators moved correctly to their commanded position, but there was no pitch rate initially, with increasing pitch at about Vr+20KIAS with full elevator application. The aircraft cleanup was delayed until the crew confirmed the trim error, and evaluated that the configuration change would not adversely affect the trim case. Normal fuel burn placed the cg shift beneficially, on landing the aircraft used limited flap and full manual trim, and was still out of trim but controllable in pitch.
A jammed elevator is indicated by restricted movement of the elevator control on a conventional control system, and may be either in the control runs or the actuator/surface. Most mechanical systems have a control system split available, where override will disconnect the L & R control channels to allow freedom of movement. FBW systems introduce alternative failure modes, but for the B777 are basically conventional, the Airbus is different....
On a 4 engine aircraft at heavy/limiting weights, a jam noted at Vr is going to be bad news. The time available for evaluation and response is probably less than that available before crossing the golf course.
On a 2 engine aircraft, the situation is a little better, and there may be adequate time to apply nose up trim sufficient to fly the aircraft off the ground. I would think your ball park figure is going to be in the order of 3-4 units of additional ANU trim to get the plane to respond, and that will take some time to run, probably 8-10 seconds. From that time, the aircraft will start to pitch After liftoff, the aircraft will have excessive ANU trim and will continue to pitch up, and will need a return to near the original TO trim position. If the speed gets out of sorts, roll may be advantageous in maintaining speed until the stab trim has been set correctly.
If you have proceeded with a takeoff, and get airborne, then limiting configuration changes may be wise. The aircraft AP system particularly ones with CWS functionality may have the ability to bypass the control run if that is the cause of the jam, and act directly to the elevator hydraulic control servo (at least one type does that).
time wise, the
4 engine aircraft at balance field limit high weights is going off the end of the runway about 12 seconds after Vr... so if it takes some time for the trim to reset (say 8 secs), and then some time to rotate (say 5 secs), it is going to be close... really close (yes attitude will start to change at some point as the trim is being run...). The reject is also going off the end, at around 80-100Kts... dealers choice. The light twins are going to be in better shape for both stop and go cases. Individual case will depend on runway available, weight/thrust etc.
Best place to have this is in a sim, and probably not as an unbriefed event. Before placing any faith in the go case on a 4 engine aircraft, would really want to practice that is a sim to assess runway used. While the sim is not necessarily certified for that evolution, the trim response "should" be close to representative.
The above is some background on the issue, and should not be construed to be a procedure. At the end of the day, the buck stops in the LHS.
Good luck!
