mpvincent From New Zealand, joined May 2011, 10 posts, RR: 0 Posted (3 years 5 months 1 week 4 days 18 hours ago) and read 4525 times:
Does anyone have a rough equation I could use to estimate the improvement in takeoff payload of a b777 200er off a runway that is descending and ascending by a certain gradient? I was thinking if I used the Boeing curves from airport manual to work out max tow and then used some relationship between gradient acceleration and velocity to work out how much more speed I would have with a gradient and then back calc to give implied payload?
Unless someone has some take off curves for the 200er varying by gradient?
mandala499 From Indonesia, joined Aug 2001, 7016 posts, RR: 77
Reply 1, posted (3 years 5 months 1 week 3 days 5 hours ago) and read 4233 times:
Quoting mpvincent (Thread starter): I was thinking if I used the Boeing curves from airport manual to work out max tow and then used some relationship between gradient acceleration and velocity to work out how much more speed I would have with a gradient and then back calc to give implied payload?
Hmmm... that would be a bit more difficult than just looking at some dispatch tables from the FCOM.
Get the runway length, then put in gradient correction and wind correction to get the "corrected runway length", pull that runway length onto a take off vs TOW table and get the max number for that corrected length.
When we're talking about runway length, the TOW is primary weight limit... then, you can calculate the payload from that (if you know how much fuel is on board).
You're in luck in that it's a sunday today and I just did this for fun ( ), so take it as is and no implications that it is correct (but I did take the numbers from a 777-200ER FCOM performance dispatch section).
Gradients are in percent... + means upslope, - means downslope.
When losing situational awareness, pray Cumulus Granitus isn't nearby !