The reference below has a table that seems to show optimum climb is at m0.8, when that mach speed corresponds to 300kts. Below or above 300kts increasingly consumes more fuel than the ideal case.
Does my interpretation make sense?
So that might be a good target for climb, to climb using the above numbers until your climb rate is unreasonably low, maybe <500fpm.
When you can’t climb at least 500pm that determines a good optimum cruise altitude for the current step in the step climb (for your current weight)?
I’ll have a full topic about this coming tomorrow morning but for now I can tell you that the A330 is bad at climbing but cruises like any other widebody twin jet. Very much benefits from step climbing.
Hi! Before I got to this target question I was reading about trade off between fast and slow climb for fuel economy.
Engines are of course more efficient at high altitudes - want to climb fast. But there is also more fuel economy the closer you are to cruise speed. So there’s a balancing act between maximising your vertical vs horizontal speed.
I was wondering if there’s maybe some design meaning in that, related to why Airbus tends to climb at lower rates than Boeing?
idk the optimal climb/cruise but i can tell you its a slow climber and simbrief gave me a cruise of 40,000 ft at about 45% load. needing 96% N1 to maintain M .82 cruise but fuel is looking good for brussels so simbrief must have expected this
40,000 sounds reasonable at first reading, given your 45% load. I was testing at MTOW, taking off from a high airfield. Used all the runway and was obviously limited. I learned to apply pitch gently in such conditions!
Interesting your cruise is .82, given the fuel efficient climb listed of .80 Not a whole lot of difference. That’s going to be a shallow climb if it were followed.
A good ballpark is to not exceed 91% N1 in cruise. If you’re exceeding 91% you’re either too high for your given weight or requesting a speed that is too fast or a combination of both. Try pulling back on the speed and a lower altitude. Drop down 2000ft to the next lowest altitude for that direction of flight and you’ll extend your fuel endurance by quite a bit. 🙂
It is advised to maintain IAS rather than aiming for VS to reach cruise faster in the A330. The following about cruise thrust for M0,8 at ISA temp is interesting :
Yes, that’s very interesting. Showing the trade-offs between N1 setting, fuel consumption in time vs distance, and IAS vs TAS, for different weights and altitudes!
Still trying to wrap my head around it a bit. It says “Max. Cruise Thrust Limits.” By Limit, does it mean these are the Max N1 settings for each entry condition, and the other numbers are what you get for that max setting?
So these are engine limit effects on flight?
Actually it’s fascinating if I understand correctly. You can ask, I want the best range for my fuel? And it shows you what you have to give up. Or ask for highest load, or best time to destination etc.
I think the word limit concerns only the bottom part, which basically fixes the max altitude you may cruise at given your weight. Anywhere else, it shows the thrust needed for the set speed. So if more thrust, you will accelerate.
