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Correct way to set trim on takeoff

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Could someone please tell me, or point me in the way of a chart, to help me set the elevator trim correctly for takeoff? I'm not sure of the exact settings to use, and I know real airline pilots have charts available to use. Thanks in advance.-twilky

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If there was a way to set a trim according to some 'charts' I imagine the center of gravity would be the key input parameter here (and not the weight). I never heard of pilots setting trim on takeoff based on exact position of the CG. Maybe they do but I am just not aware of that.Michael J.


Michael J.

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Guest

Michael,Flight crew ALWAYS sets the trim for take-off based on the loadsheet. In fact, the main purpose of the loadsheet is to provide flight crew with information on where the CoG is. Based on the CoG (Or MAC% for Boeings, R/C % for Airbusses) and the flap setting, a table printed on the loadsheet will give the correct stab trim setting for take-off.

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Guest

>Michael, >>Flight crew ALWAYS sets the trim for take-off based on the >loadsheet. In fact, the main purpose of the loadsheet is to >provide flight crew with information on where the CoG is. >Based on the CoG (Or MAC% for Boeings, R/C % for Airbusses) >and the flap setting, a table printed on the loadsheet will >give the correct stab trim setting for take-off. That sounds a lot easier than the chart that was suggested here..still trying to figure that out. If anyone does, please let me know!

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Guest Stephan Haas

OK,as I understand the sheet it goes as follows:ZFW = zero fuel weight (the standard for PIC is indeed 111230(remeber everything in kilo's !)add take off fuel, subtract the fuel burnt during taxi. The result is the total weight, including fuel right before take off.adjust the TOI (take off index) for the take off weightdraw a vertical line at the index (= TOI) at the bottom of the graphdraw a horizontal line at the gross mass = LOMthe two lines will cross each otherthis crossing point is between 2 MAC's (the numbers in circles)now look at the top of the graph (in the right row for your weight) and you've found your trim position.FORZFW = 111230, fuel = 19077, burn off = 500 you'll get a TOI of 45if you draw the lines at the correct places you'll end up between MAC 20 - 22. This will give you a trimm setting of 3Kind regards,Stephan Haas

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What bothers me about this procedure is that it seemingly does not use the position of the CG. Therefore I am having difficulty justifing it in my mind.Michael J.


Michael J.

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Guest Stephan Haas

Michael,I see your point and went back to the chart. It seems that the COG is determined by the Fuel index. It assumes that first the wings are loaded with fuel and then the centre tanks. Probably also assuming that passengers are evenly spread (although they will influence the COG also via the index).I did not invent this chart, only downloaded it. For me it works.Perhaps one of the IRL pilots (or Ian, he knows everything!) would like to comment.Kind regards,Stephan Haas

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Guest

>OK, >>as I understand the sheet it goes as follows: >Kind regards, >>Stephan Haas Thanks a lot. I think I understand it now.-twilky

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Guest

Right, I teach Mass & Balance so should presumeably know a thing or two about this :)Let's go through some definitions first:BW - Basic Weight : The weight of an empty a/c.DOW - Dry Operating Weight : BW + operating crewOW - Operating Weight : DOW + Take-off FuelZFW - Zero Fuel Weight : DOW + PayloadTOW - Take-off weight : ZFW + Take-off Fuel, or OW + Payload.LAW - Landing Weight : TOW - Trip FuelMAC - Mean Aerodynamic Chord : The reference chord on the wings where the CoG is calculated.There are more, but these will do for now.When a loadcontroller trims an aircraft, by loading freight, bags and pax as required, the ultimate goal is to get the aircraft within the forward and aft balance limits for zero fuel, take-off and landing.Initially, you will trim a LIZFW, the Laden Index Zero Fuel Weight. Obviously the difference between a ZFW balance and TOW/LAW is the fuel index's. Let me give you an example:B757-200SF.ZFW MAC 14.9%, based on the actual distribution of the load on the aircraft.Take-off Fuel: 17.050 kg, index effect +2.12Trip-Fuel: 12800Landing fuel (t/o - trip): 4.250 kg, index effect + 0.58 %You insert these value on a trim sheet, and read the corresponding MAC %'s in the balance envelope. For this example, the ZFW is 72.431, TOW is 89481 and LAW is 76681. The corresponding MAC %'s are:TOW: 18.5, LAW 16.0. On the loadsheet there are two boxes with A/C weight on the x-line, and MAC % on the y-line, one for flaps 1 & 5, the other for flaps 15 & 20. By tracking the TOW and TOW MAC, the pilot will read a Horizontal Stab Setting for Take-off. In the example above, the settings for flaps 15 & 20 will be 4.8.In other words, the stab trim settings for take-off is dependent on the distribution of payload, the fuel onboard and the TOW.Trust this is of help. If any of you are interested in a PP presentation on the principles of balance, aircraft performance, runway performance and much more, drop me a line. The presentations are from 1.5 to 6.5MB and cannot be zip compressed.

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Guest Stephan Haas

Thanks for your explanation, you're better in it than I am.Apparently the trimsheet of a 757 is different than a 767's (which makes sense). Did you have a look at the trimsheet I mentioned before? Do you have a better one (for a 767) (always in for improvement)?Kind regards,Stephan Haas

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Guest

Stephan,The information I gave you is from a real life loadsheet. The airline I work for does not operate 767s, and quite honestly it's been something like 8 years since the last time I trimmed a 767 (Delta 767-300ER to be precise). Every airline have their own design for manual loadsheets, using one of the four major principles which are: Dropdown box, Christmas Tree, Circular Computer and Index Numbers. The airline I work for, European Air Transport, has moved from christmas tree to drop down box. However, we also perform loadcontrol duties for other airlines operating on behalf of DHL. One of the types we see every day is the Gemini MD11F, which is trimmed by index numbers. Then there's the DHL Airways DC8-73F which are trimmed using the christmas tree. About the only system we don't regularly use is the circular computer.The principles I've outlined in the previous post is valid for all transport category aircraft, from a Convair 580 to a B747-400.BTW, I'm certified on almost anything from Cessna Caravans up to and including the B747-400, both pax, combi and freighter, by airlines such including KLM, Air France, Delta, United, British Airways, SAS, Maersk Air, Premiair and of course DHL. I'm sure I've forgotten to mention a few :)

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Guest Ian_Riddell

" I'm certified on almost anything from Cessna Caravans up to and including the B747-400,"(Off-Topic for a moment here). The 747-400 FMC has its own inbuilt trim calculator (all that is needed is GW and CG as far as I can tell... and this can be provided by a Weight & Balance computer... if one is fitted). However, something I have never been quite sure of is why a Thrust Rating entry is also required for computing the greenbands on the trim indicator.Top Heavy, do you think thrust would also affect trim/CG? Perhaps the thrust would have the tendency to lift the nose, making trim (or at least trim limits) an issue?Any/all comments welcome.Thanks.CheersIan.

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Guest Stephan Haas

Well, we can trust Ian to make a complex problem even more complex. ;-)It's interesting however to read about all these real life complicatians. I surely appreciate input form the professionals like Ian and Topheavy.Kind regards,Stephan Haas

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Guest bob

StephanI would like a copy of the trim sheet, however, the site you suggest is suspended. Is there another site?thanksBob (EGHD)

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