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777 Climbing  
User currently offlineRendezvous From New Zealand, joined May 2001, 516 posts, RR: 0
Posted (10 years 8 months 3 days 23 hours ago) and read 4584 times:

Just a question out of interest. At MTOW how long does the 777 take to reach cruise altitude (distance/time) for optimum altitude (how high's that?).

Let's assume ISA / no wind and standard speed restrictions.

16 replies: All unread, jump to last
 
User currently offlineLugonza_2001 From Spain, joined Oct 2001, 315 posts, RR: 1
Reply 1, posted (10 years 8 months 3 days 3 hours ago) and read 4429 times:

Hi!

I am not sure, but, altough noise restrictions have to be respected, i do not think any aircraft "goes up" as fast as it is capable of, due to fuel savings specially.


 Smile/happy/getting dizzy


User currently offlineFoxBravo From United States of America, joined Nov 2003, 2996 posts, RR: 4
Reply 2, posted (10 years 8 months 3 days 2 hours ago) and read 4392 times:

Another factor to take into account is ATC. Planes are frequently unable to climb as quickly as possible due to traffic.

As for "optimum" altitude, it would depend on a variety of factors including winds and weather. Although you mentioned no wind for purposes of calculating the fastest climb, many flights--particularly east-west routes--are planned to take advantage of tailwinds or to avoid headwinds, so that might determine the "optimum" altitude.



Common sense is not so common. -Voltaire
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 3, posted (10 years 8 months 3 days ago) and read 4344 times:

Lugonza,
they try to get to cruise as fast as possible to save fuel. No use loitering about at lower altitudes. Thrust is reduced from take-off to climb to save engine wear - which means slightly worse fuel economy.

Wind won't affect the time to cruise.

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineThrust From United States of America, joined Sep 2003, 2688 posts, RR: 10
Reply 4, posted (10 years 7 months 2 weeks 5 days 22 hours ago) and read 3926 times:

The 777 takes a while to get off the ground, and its climb is gradual probably because of its gigantic size and heaviness, however, it is not incredibly slow. I will say this, the cruising speed can vary, Fred T. They don't try to cruise as fast as possible necessarily all the time. My flight from BOS-LHR had a speed set for 575 mph, and eventually we were cruising at 630 mph. On the way from LHR-JFK, we cruised much more slowly, at 535 mph. That is 20 mph below the typical cruising speed of a 777, 555 mph. Fox Bravo's statement about "optimum altitude" ties into these factors. The speed an airplane cruises at is influenced by weather and wind.


Fly one thing; Fly it well
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 5, posted (10 years 7 months 2 weeks 5 days 22 hours ago) and read 3926 times:

"I will say this, the cruising speed can vary, Fred T. They don't try to cruise as fast as possible necessarily all the time. My flight from BOS-LHR had a speed set for 575 mph, and eventually we were cruising at 630 mph. On the way from LHR-JFK, we cruised much more slowly, at 535 mph.

The speed an airplane cruises at is influenced by weather and wind."


Ground speed will change becuase of wind. I'm pretty certain that if you had been in the cockpit during the flight, you would have seen on the instruments that airspeed would have been pretty much the same on both the flights.

Staffan


User currently offlineCx flyboy From Hong Kong, joined Dec 1999, 6597 posts, RR: 55
Reply 6, posted (10 years 7 months 2 weeks 4 days 21 hours ago) and read 3723 times:

On Approach into Narita the other day we had a ground speed of 102kts!!

Time taken to climb to cruise obviously depends on weight, and what your cruise altitude is. Also, the way the pilot programmes the FMC with regard to climb speed will affect this, so it is very hard to give you an answer.


User currently offlineAJ From Australia, joined Nov 1999, 2389 posts, RR: 24
Reply 7, posted (10 years 7 months 2 weeks 4 days 19 hours ago) and read 3685 times:

The FMC Cost Index takes wind into account, as well as temperature, altitude, weight and so on. The cost index can be varied, or a constant mach cruise can be used.

Cx_flyboy, were you flying in these winds: http://www.jetphotos.net/viewphoto.php?id=212294?
Very impressive!


User currently offlineCx flyboy From Hong Kong, joined Dec 1999, 6597 posts, RR: 55
Reply 8, posted (10 years 7 months 2 weeks 4 days 14 hours ago) and read 3595 times:

Indeed I was, AJ, but fortunately we didn't have 190kt winds on approach into Narita (We would have been going backwards!) , although it was bumpy with a bit of shear.

Interesting to see your clock there has a decimal point! Our certainly don't. It would be interesting, but is it distracting with that end number always changing? Do you see it out the corner of your eyes?


User currently offlineAJ From Australia, joined Nov 1999, 2389 posts, RR: 24
Reply 9, posted (10 years 7 months 2 weeks 4 days 13 hours ago) and read 3586 times:

I've never been distracted, it changes every 6 seconds, but then again so does the speed so the green trend arrow catches the eye more!

User currently offlineCx flyboy From Hong Kong, joined Dec 1999, 6597 posts, RR: 55
Reply 10, posted (10 years 7 months 2 weeks 4 days 11 hours ago) and read 3569 times:

Come to think of it, I think the 744 might have had it. In cruise the green arrow wouldn't appear much unless it was turbulent, in which case it would catch my eyes and force me to put away my magazine!....whoops, did I say that? I meant flight manual! Big grin

User currently offlineMr.BA From Singapore, joined Sep 2000, 3423 posts, RR: 22
Reply 11, posted (10 years 7 months 2 weeks 4 days 7 hours ago) and read 3499 times:

Hi AJ,

Just wondering why does the speed green trend arrow fluctuates now and then?

Thanks!



Boeing747 万岁!
User currently offlineAJ From Australia, joined Nov 1999, 2389 posts, RR: 24
Reply 12, posted (10 years 7 months 1 week 6 days 15 hours ago) and read 2965 times:

Hi Alvin, the 767 is not a very speed stable aircraft, related to the supercritical wing. In turbulence the green arrow fires off all over the place. On a 747-400 you can fly the aircraft based on trend vector information, not on the 767 though!

User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 13, posted (10 years 7 months 1 week 6 days 14 hours ago) and read 2949 times:

Fred T. They don't try to cruise as fast as possible necessarily all the time.

Nor did I say they do. Read again.  Big grin

Cheers,
Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineMr.BA From Singapore, joined Sep 2000, 3423 posts, RR: 22
Reply 14, posted (10 years 7 months 1 week 5 days 18 hours ago) and read 2718 times:

Thanks AJ! Sorry for another question.. what do you mean by flying the aircraft based on trend vector information?

Thanks!



Boeing747 万岁!
User currently offlineAJ From Australia, joined Nov 1999, 2389 posts, RR: 24
Reply 15, posted (10 years 7 months 1 week 5 days 17 hours ago) and read 2702 times:

Alvin, when targetting a speed the green trend arrow can be used by placing the tip next to the required speed on the airspeed tape and using power or attitude to reduce the size of the trend arrow to keep the tip on that speed. Very hard to explain!

The VSI needle can be used in the same way on the altitude tape; as long as it points to the required altitude a smooth level off can be achieved.


User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 25
Reply 16, posted (10 years 7 months 1 week 5 days 1 hour ago) and read 2534 times:

To answer the original question:

If you look at the equation for R/C, you see that among other things, weight and excess thrust (and in turn total drag, because excess thrust is approximately equal to total thrust minus total drag) play a part. Given that we're talking about a 777 at MTOW, weight obviously remains a constant (if you want to disregard the use of fuel and resulting slight decrease in weight during climb). Thus, the main variable is total drag (or excess thrust). Less drag, better R/C.

Now, the drag depends on many lift-related and atmospheric variables, which can easily change. Drag is also indirectly affected by the various speed restrictions, etc., that you mentioned. Because of the many changing conditions, you can't really calculate R/C with the information you've set out as givens -- total drag depends on a lot! Even the optimum cruise altitude you talked about depends on a multitude of changing figures!

Again, R/C really depends on a lot!!!

Also, all that is the purely aerodynamic stuff. "Real-life" conditions come into play, such as a more economic climb, airline policies, etc.

Alright, I've rambled on enough. Sorry,
qantasA332


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