No screenshots tonight – just a confirmation of what I have known all along and question as to wither other people have the same problem or it is just my installation.

This is the situation. Payload 31850, fuel 20000 lbs., GTOW 182726, flaps 5, CG 30%, wind calm, OAT +15C, thrust at derate 2, assumed temp 60, stabilizer trim 3.17, VR 145, and V2 151. Plane liftsoff runway at 100 knots and flys LNAV/VNAV departure even through VR is 145 knots. Stabilizer trim needs to be about –4.0 to keep the plane on the ground until VR at 145 kts. How can a 752 become airborne at 100 kts and fly, accelerate and climb with the thrust significantly reduced?

Michael Cubine

Exact conditions as previoius takeoff. FMC computed VR at 139 kts not 145 kts but it makes no difference since the 752 will liftoff and fly at a 100 kts. A trim of -4.0 made the plane stay planted on the runway until I rotated at 139 kts.

Michael Cubine

I think I understand now what I have been doing wrong in regards to the stabilizer trim. When I load the 752 for flight the trim is at 4 on the indicator or 0.0% on Tool Tips. It is neutral - neither APNU or APND. Once the CDU/FMC takeoff page is completed it might show a trim of 2.8. I believed that this was added to the default trim of 4.0 giving me a trim of 6.8 APNU. Since the trim was not a -2.8 I believed it was positive and set the trim to +2.8 using Tool Tips/ This in fact gave me a setting on the horizonatal trim indicator of 6.8 The indicator needs to be set at 2.8 which is in APND range. Now the 752 stays on the ground until I rotate and the trim indicator and Tool Tips agree. See attached image.

Michael Cubine

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I was never using the cockpit ToolTips for the trim settings on the 752. I always left it at 4 on the Stab Trim Indicator UNTIL v4.6, then I would put it as close as possible to the setting shown in the Takeoff page of the CDU.

I see that the ToolTip is showing -2.8 over the Trim Indicator in the VC (in the image), but I have only ever seen the ToolTips there in the 2D Throttle panel. Now I'll have to go and check to see if I can get it to display in the VC like yours. :o ;D

[edit]Just finished checking and the cockpit ToolTip does show. ;D[/edit]

DAL191 wrote on Jul 14^th, 2013 at 2:48pm:

the trim indicator and Tool Tips agree. Michael Cubine

After about 10 more flights and setting the trim indicator to what is shown on the CDU Takeoff page the 752 stays on the ground. However it appears that the agreement between the trim indicator and Tool Tips was just a coincidence of 2.8. At any other setting they do not agree.

Michael Cubine

thank you for that info i was always using the tooltip to set trim.  now using the actual reading on the indicator my responce is much more fluid and no more lifting off the ground @ 100 kias,