B737-300 FFS. 61 tonnes Flap One. Sea Level 15C. Stab trim correct at 5.2 units. Engine failure arranged at V1 with a VR 15 knots later. In other words a spread of 15 knots between V1 and VR.
In this simulator the stick force at VR on one engine is very heavy indeed and the control column is two thirds of the way back to rotate. It is common to see pilots struggling to reach iniitial climb attitude. If they relax momentarily during pull back, the main wheels hit the runway a couple of times before the pilot manages to drag the aircraft into the air. Stab trim is correctly set as part of the before takeoff checks. Once airborne and well clear of the ground, at least 3 units of back stab trim from original takeoff setting is needed for comfortable trim for single engine climb out..
I believe it is because instead of two upward vectors of thrust as happens with normal two engine takeoff, only one engine has its upwards vector meaning the stab trim setting is such that the aircraft is significantly nose heavy when rotating after the engine had failed at V1. But the VR does not occur until a few seconds later on reaching VR. By then the stab trim is incorrect at VR.
Most simulator exercises have a spread of maybe five knots between V1 and VR in the 737 Classic and by the time the engine fails the VR has already passed. Thus there is no chance of the very nose heavy trim manifesting itself. But throw in a case where there is a large spread between V1 and VR meaning a relatively long time on the runway accelerating on one engine, then this is a game changer.
. This nose heavy phenomenon only manifests itself if an engine fails while the aircraft is still on the runway. Apologies for rather scratchy description of this event in this simulator. Which brings up the question of takeoff stab trim setting. Does that setting mean the aircraft should be in trim at V2+15 all engines; but is invalid for single engine VR?
Last edited by Centaurus; 25th September 2019 at 12:28.