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737-800 Stab Trim

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5 replies to this topic

#1 Inactive Member_mruane_***

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Posted 27 April 2004 - 02:20 AM

OK now it begins to make sense. I have just reset the flight and retried the same takeoff. I left the fuel tanks fully loaded and reprogrammed the takeoff. This time I had the same Trim setting of 4.9 but the predicted VR was 154KTS (which is within 1 knot of the actual VR speed last flight with empty centre tanks). As I offload the fuel in the centre tank, I get the reduced VR of 140KTS but the aircraft still thinks it has full tanks during the take off roll.So I suspect that the reason I cannot rotate at the predicted speed is that the actual liftoff is being determined by what the fuel was when the aircraft is selected and not by what is actually in the tanks during the take off roll.Perhaps someone might be able to confirm this.
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#2 Inactive Member_mruane_***

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Posted 27 April 2004 - 02:08 AM

Thanks KrisI found the Trim advise on the FMC Take Off page. It advised 4.9 with a predicted VR of 140KTS. I set the trim accordingly but VR actually occured at 155KTS. There was no way I could get the -800 up at 140KTS. So I wondered if there was something I am missing (flat tyres perhaps :-) )
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#3 Inactive Member_boxjockey99_***

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Posted 27 April 2004 - 01:35 AM

Set it somewhere in the green band usually around 4 to 5 units and this should give you enough trim to get airborne. I thought there were figures there, but I must confess to not looking very hard! RegardsKris
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#4 Inactive Member_mruane_***

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Posted 27 April 2004 - 12:53 AM

HiWhat should the Stab Trim be for the B737-800 with a ZFW of 130K lbs and Fuel of 42K lbs. The manual provides Stab Trim figures for the -600/700 but not the -800/900. I am having some trouble pulling the -800 of the ground at VR speed and the stab trim is currently the default of 5 (or thereabouts). The Load Manager has 157 in Coach (Single Class) and 4,990lbs in the Forward locker and 5,656lbs in the aft locker. So the CG should be pretty near where it needs to be.
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#5 Inactive Member_bigun_***

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Posted 27 April 2004 - 06:20 AM

Also, pause the sim when changing fuel loads. The FMC will then pick it up and everything should work just fine.
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#6 Inactive Member_boxjockey99_***

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Posted 27 April 2004 - 05:22 AM

Erm not quite sure where you are going with this, this is what I think you did:I think what you are saying is that you loaded the fuel but didn't go back to the take off page and reselect the V speeds in order to get the new Vspeeds for the heavier fuel load. Bear in mind for your fuel planning that full centre tank is not always needed. The 3/4/500 series have a rule that you must not land with fuel in the centre tank unless you have a bloody good reason so the centre tank should always be used up prior to landing. consider that you perhaps are taking way too much fuel with you unless you are doing particualrly long routes. A route of 2hrs or so should be more than satisfied with full main wing tanks and an empty centre,You must understand that the V speeds are a function of weight so the higher the weight the higher the V speeds. Also make sure you aren't going clean! normally the B737 goes with flap 5 for take off so make sure you set the flap.Just some words of wisdom, I hope they don't sound too much like I'm trying to teach you to suck eggs or anything like that! happy trailsKris
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