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Guest nightbird

Trim setting - looks wrong

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Guest nightbird

I'm probably being a bit thick here but here goes anyway............I have been trying out the load editor and as a result for the first time I have been using different CoG's and trim settings for take off. The aircraft I am using is the B777-200LR and for this flight I had a ZFW of 375203lbs and 210000lbs of fuel on board, the load editor gave me a CoG of 27%. In the aircraft I entered all the data into the FMC as normal which then suggested the trim setting of 5.75.After setting the trim to 5.75 I took a look outside and noticed that the horizontal stabiliser was actually deflected down a little. I thought that looks strange for a take off setting but decided to try the take off anyway and see what happens (not quite standard procedure I know). Just as I would of expected the aircraft didn't want to get off the ground at the VR speed, if fact it was doing well over 170knots before I could rotate.I have attached a picture showing what the trim setting of 5.75 looks like on my aircraft. Is this the way it's meant to look? I'm not sure if this is a problem with way the external model reacts to the trim setting on the panal or if I am doing something else wrong, any ideas?Philhttp://forums.avsim.net/user_files/136937.jpg

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Guest NormanB

Phil,I just set my aircraft with similar settings and a trim of 6 (mine gave 6 - possibly my maths as I converted your values to KG). Departure (derated) from Seattle was uneventful. The stab was showing up, as expected.Can you check by starting things from a default flight and reporting back please?

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Guest nightbird

Hi NormanFirst off my default flight is the bog standard MS cessna default flight at Seatac.I tried another flight with a slightly different setup but got similar results. This time I selected a 2/3 full aircraft which gave a ZFW of 373191 lbs and 210000 lbs of fuel (and yes I am changing the fuel load within the aircraft!). My CoG was shown as 26% and this gave me a trim setting of 6.For take off I used flaps 15 and had vref speeds of V1=143, VR=147 & V2=153. I didn't use a de-rated take off (not my fuel bill).This time I did manage to get the aircraft to rotate at about 155kts but I had to really pull back hard on the yoke (thought I was going to rip the yoke off the table there for a while), and had to maintain a lot of back pressure to keep the nose up on climb out.I tried the same take off again but this time left the trim setting at it's default position 7.5 and the aircraft rotated perfectly on VR speed with a 'normal' amount of back pressure on the yoke.Interestingly in both instances when I was airborn and the autopilot was activated the trim setting went to a setting of at least 8.Phil

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Guest gat12

Interesting, I have too been having to pull back really hard on my yoke the full way to get this bird airborn. Now maybe I know why LOL will have to try with normal CoG setting.Brian

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I never set the trim setting as it is computed by the FMC. I have it set between 7 and 9 (full TOW) and I rotate easily right on the numbers. Essentially I still use the trim settings from the FS2000 PSS 777 - which I have memorized.I think this is a bug. But that is just me. Is anybody setting the FMC-computed trim and getting an easy rotation ?Thanks

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Guest DaveI

Using the Load Editor the trim settings are much different (furthur forward) than using the spreadsheet.On a flight to West Coast USA with 110 tonnes fuel load the takeoff proved difficult with a real pull on the yoke required to keep the 777LR climbing.Doing a VNAV step climb from FL310 to FL 350 on the same flight as soon as FMC commanded I had a sharp pitch occillation,which looked as if it was instigated by the Flight Director. The only way I could stop it was to cancel VNAV and set up a Vertical speed controlled Climb at a much lower VS than VNAV set up.I wonder if there is a Weight/balance/ C of G issue here.Hmmmm....

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