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rennman

TO Config

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What is the proper way to compute Flap setting, Trim, an V-Speeds?

 

 

Mike Ryder.

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You need something like TOPCAT to do this very accurately but for flight sim entering the weights, flap settings and assumed temp in the fmc will generate v speeds on the takeoff page.

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I'm using FS2 crew, which has flap 20 by default...The FMC has V speeds computed in the 130's...but she doesnt like to get up until 180...as for the trim, im just guessing...the chances of me being right on my own are not good...id like to become more accurate...

 

 

Mike Ryder

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The trim will be displayed in the FMC after you have input your parameters.

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Is flaps 20 for TO typical?...The V Speeds in the FMC are much lower than what it takes to get her lifted...

 

Mike Ryder

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Is flaps 20 for TO typical?

 

Depends on airline, but for the Big Airline flap 20 is standard for takeoff on the 744.

 

Remember that the B747 has a very wide range of operating weights -- anything from about 200 tonnes to 397 tonnes -- and so speeds can vary significantly depending on weight, runway length etc - I've seen rotation speeds from below 120kt empty up to over 170kt at MTOW. Unlike overpowered big twins, there is often a significant split between V1 (the latest point at which the takeoff may be rejected) and Vr (rotation speed), especially at higher weights.

 

I don't think the current version of the 747 comes with performance tables in order to do the calculations manually, so as mentioned above you will either need software such as TOPCAT which will calculate the derate and V speeds for you, or else use the FMC which will give you as basic (but usable) calculation.

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Is flaps 20 for TO typical?...The V Speeds in the FMC are much lower than what it takes to get her lifted...

 

Mike Ryder

As Simon said TO flap setting varies with the airline SOP, aircraft weight, thrust derate, ambient conditions and the runway in use. Often either 10 or 20 can be used safely and then it depends on the airline SOP or even the Captain's preference. Generally speaking Flap 20 means you need less runway but you have less climb gradient if there is a terrain clearance issue.

 

Regardless of the flap setting, I have always found that the FMC gives reliable V speeds. I use TOPCAT to calculate thrust derates, but I always use those FMC V speeds rather than enter TOPCAT's numbers. So if your V speeds are too low the data you entered may be incorrect. Have you checked the weight units selected in the sim match the units you are entering in the FMC CDU? To make sure, try accepting the Gross Weight that the FMC offers you on the INIT REF page. That way the FMC will use the same weight that the sim has loaded.

 

If you are still having problems, please post the weights you are using and the V speeds you get. Ideally as a screenshot.

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