enzo011 wrote:lightsaber wrote:Just to be clear, hot is defined as 30C/86F when engines start to produce less thrust. As JNB isn't over 86F, engines produce full thrust and thus it is not hot. There is actually a technical threshold for hot. Yes, some engines that were Marginal on thust, such as initial CF6 on A330 (later PiP'd to 30C) had a 55F definition as hot, but that isn't the industry standard 30C/86F. High is any drop in barometric pressure reduces engine thrust and wing lift.
However, the A359 and 77L will both do fine at JNB as did RR powered A330s and many other Aircraft. JNB isn't a really tough spot. DXB with 114F and 600ft barrometric conditions is tougher (EK's infamous operating point for purchase decisions, which is pretty typical in the hot months).
So what is the engine performance like for the 77W out of DXB on a 114F day compared to the same 77W out of JNB at 77F but at its 5 558ft altitude? Is that even a valid comparison?
Have you looked at aircraft performance with altitude and temperature? Both Boeing and Airbus have extensive outlines:
http://www.boeing.com/commercial/airpor ... nuals.page
For the 777-200LR:
http://www.boeing.com/resources/boeingd ... 2lr3er.pdf
See slide 44 for altitude of 6,000 ft, the maximum takeoff weight of the 777-200LR is 705,000 lb or so (I'm eyeballing). So there is a reason DL did a morning takeoff as slide 45 shows us a hot day at JNB is way down at 685,000 lb (or so, again, I'm graph reading and there is some error).
If you look at slide 47, the hot day at sea level, at 114F, is about 730,000 lb, at 2000 ft only 685,000 lb, so I had it backward, the JNB takeoff means an allowed takeoff weight about 25,000 lb less than a hot day at Dubai (I find it telling Boeing now just publishes an easy way to interpolate the EK conditions). So a 777-200LR is taking off from JNB heavier in the morning than during EK's hot season.
So the GE-90-110 has enough spare margin to overcome.
It is a valid comparison as both impact takeoff performance.
Note: 766,000 lb MTOW just isn't going to be achieved under these conditions at either airport. .
A reduction of 55,000 lb in MTOW reduces the 777-200LR payload at range a little. Looking at slide 41 and knowing the OEW is about 320,000 lb (give or take) we see a non-fuel takeoff for 8500nm of 395,000 lb or so (again, eyeballing charts) or 75,000 lb of payload. At 105kg/pax (about 69,300lb) plus catering, crew, leaves about 4,000 lb for cargo above full pax on the 777.
Doing the same chart reading for the A359:
https://www.airbus.com/aircraft/support ... -data.html
https://www.airbus.com/aircraft/support ... stics.html
Looking at slide 158, we see at 6,000 ft, the A359 Maximum takeoff weight is 600,000 lb or so.
Slide 155 shows for 617,000 lb takeoff weight max pax could be taken out to 7,800nm. In other words, for JNB-ATL (or JFK), the flight must stop for fuel.
Airbus provides less information to non-paying customers (but far more in a bid, I've been amazed at the spreadsheets generated by airlines where they model every existing route cost and a bunch of future possible routes and buy aircraft on which has the least cost). They even model breaking down fleets (replace with 2 sizes instead of one, or cost of subfleets).
I even looked at the 789. From 6,000 ft, max takeoff of 458,000 lb. Oh... Not a great pick from JNB...
Delta needs an A359 with more thrust at altitude. A lot more thrust. More than any project I'm aware of. Cest la vie. They'll make it work with a refueling stop at lower altitude.