Can someone explain this graph to me please?

[matta757]

Hey guys,

I am having some trouble deciphering some parts of the takeoff requirement graphs for the 757 provided on the Boeing website. My main confusion comes from the fact that I do not understand how to read the part about flaps. I understand that you take the weight on the X-axis, find the elevation of your departure airport and then follow the Y-axis to figure out the required runway, but how do those markings for flaps play into the equation?

http://i210.photobucket.com/albums/bb257/matta757/takeoff.jpg


If someone could PLEASE explain this graph to me, I would really, really appreciate it. Some of you seem much more knowledgeable about this stuff than I am. Thanks in advance!

Regards,

Matt

[Boeing Skunk Works]

The less flap you use the longer the runway requirement for a given weight and density altitude.

[saabpilot]

"Normal" T/O Flaps = 20
But with a combination of high runway altitude and heavy aicraft you have to reduce the flap setting in accordance with the markings on the graf.     
Example:  250000 LBS at a 2000 feet runway altitude = use Flap 15

Additional limiting factors are the fitted tyres which have their max tyre speeds limits and finally also max available break energy.

[matta757]

"Normal" T/O Flaps = 20
But with a combination of high runway altitude and heavy aicraft you have to reduce the flap setting in accordance with the markings on the graf.     
Example:  250000 LBS at a 2000 feet runway altitude = use Flap 15

Additional limiting factors are the fitted tyres which have their max tyre speeds limits and finally also max available break energy.

OK, but how did you deduce that flaps 15 should be used? What on the graph indicates which flaps to use? Not all of the lines are labeled with flaps, and I guess that's where my confusion is coming from.


Matt

[Boeing Skunk Works]

Each bump on each of the lines of the graph are for the flap settings. They only print the fact on one line. I find it much easier to use tables for performance data rather than graphs.

What flap setting you use will likely be determined by the FMC.