A question on 737 simulator stab trim fidelity re engine failure V1/Go on runway
In the back of my mind was the understanding that the correct setting of the CG/Stab Trim from the load-sheet meant the aircraft was designed to be in-trim at V2+15 with both engines operating. A former inspector qualified to conduct simulator fidelity checks on the Boeing 767 told me that the stab trim setting from the load sheet on the 767 is based upon an engine failure at V1 - accelerate to VR on one engine - and be in trim at V2 +15.
The discussion arose over stick forces in one particular 737 simulator following an engine failure at V1 - accelerating to VR - and rotating. Experience with this simulator is that with the V1 and Go situation allowing say a 10 knot spread between V1 and VR, the back stick force to achieve rotation to around 12 degrees initially on one engine, is very heavy requiring a determined pull and by the time the aircraft has reached gear selected up height of about 100 fet agl, it is necessary to use considerable back stab trim to the order of at least seven units indicated. The stab trim was initially set to 5.2 Units for take off. The take off weight was 50 tonnes with flap 5 sea level standard temp.
On a normal two-engine take off the stab trim of 5.2 Units poses no problems as far as I recall. If the airworthiness certification of the simulator stab trim forces means in-trim at V2+15 with two engines then I can understand that following a engine cut at V1 and the decision is made to continue, the absence of the failed engine to provide a vertical component of thrust as the nose rises, will give the effect of a nose heavy aircraft that requires significant stab trim aft to get back into trim. This is what we experience on the engine failure on the runway case (V1) with continued acceleration on the live engine. It is not uncommon for pilots in the simulator to sink back onto the runway as they are caught by surprise by the significant pull needed to rotate on one engine and get the climb going from VR.
The question therefore relates to the simulator airworthiness meaning of the normal take off stab trim setting. Is it designed to be in trim for V2+15 on two engines? Or does the stab trim setting from the load sheet assume engine failure at V1 and continue? Once that fact is known then it becomes a simulator fidelity discussion re stick forces on VR.
Last edited by Centaurus; 27th Jan 2013 at 10:07.