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Tobin69

77-300 Altitude wing issues...

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Was working a 77-300 departure today and a pilot told me the 300 has wing issues at Altitude that it can't fly high altitudes until fuel load is burned down. I didn't low this and thought with the GE90 engines that this thing was a power house but he said power isn't the issue its the wing...

 

Any real 300 pilots care to alleviate?

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I'm pretty sure that's how all jet aircraft behave at altitude.. If the weight is too much for the wing to support in the thin air at altitude, it cannot climb until it's fuel is alleviated. 

 

In other words, I'm pretty sure this "problem" is not exclusive to the 777-3

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The reason some flights start out at lower cruise altitudes is because with the fuel amount still high after departure the plane is to heavy to continue climbing at a steady rate and speed, until later on when enough fuel is burned and the aircraft is able "step climb" to higher altitudes. Technically, any  type of aircraft really can have this problem, more so in a heavy jet like the 747, 777, or A380 because of the enormous amounts of fuel they usually depart with. 


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So with step climbs you request a raise in altitude of 2000ft when the planes efficient cruise altitude is 2000ft higher then your current cruise altitude?


Oliver Cooksey

Owner of the PMDG 737, 747 and Majestic Q400.

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So with step climbs you request a raise in altitude of 2000ft when the planes efficient cruise altitude is 2000ft higher then your current cruise altitude?

Usual rule of thumb is soon as OPT ALT indicates 1000ft above your current altitude, you step climb to an altitude 1000ft above the optimum. Unfortunately you can't always be directly on your optimum altitude due to RVSM rules (direction of flight etc.)

 

For example, you are crusing at F360. When OPT ALT in FMC shows reaches F370 (and if MAX ALT is also above F380), you would climb to F380. Across the atlantic, usually flight levels are available every 1000ft, so it may be possible to cruise at your exact OPT ALT (or within 1000ft of) depending on the traffic in the area.


Regards,
James White

 

Aerosoft (Airbus X Extended/Twin Otter Extended/PFPX) & Majestic Q400 Beta Team
blueaerosofta320extbeta.png

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Was working a 77-300 departure today and a pilot told me the 300 has wing issues at Altitude that it can't fly high altitudes until fuel load is burned down. I didn't low this and thought with the GE90 engines that this thing was a power house but he said power isn't the issue its the wing...

 

Any real 300 pilots care to alleviate?

The 767-300ER has a better power to weight ratio than the 777, even the NG 777s with the GE90s.

 

The wing of the original 200 (and 300) is different to the NG. And, I would say that the 200's wing can handle the lighter loads than the 300s which are heavier at empty and with loads.

 

Ill give you an example:

 

So, if you bought a Ferrari but hooked it up to a caravan of 4500lb (2000kg) do you think it will perform as what it was supposed to? Being very light I wonder if it would have any traction to 'lift' the caravan. But the thing is the Ferrari now has to pull something far heavier than its own weight. And you may have noticed, when you load a car up with weight it doesn't accelerate as quick? It may have the same power, which is all very nice, but extra weight will affect performance. Also the air affects performance. If it is hot the performance, just like an aircraft, will be lesser, because there is less molecules of O2 in the same given volume.

 

Reading and studying a physics book would certainly be helpful. It will help address questions like this.

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I get you guys points.. My thinking was with the new technology available ( wing designs, powerful GE90 Engines) I thought you could take a big tank to cruise Altitude ( in a timely manner) save fuel and live happily ever after. Instead your step climbing and burning fuel that could be saved IF you could get to Cruise.

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are you guys at PMDG going to incorporate this issue into the 77-300?

 

Ehm. That is one of the principle characteristics of the 300(ER) - being heavier than 200. I don't see how could they not incorporate it.


--Peter Fabian 
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I get you guys points.. My thinking was with the new technology available ( wing designs, powerful GE90 Engines) I thought you could take a big tank to cruise Altitude ( in a timely manner) save fuel and live happily ever after. Instead your step climbing and burning fuel that could be saved IF you could get to Cruise

 

You would be mistaken about saving fuel.  Recall in our discussion here we mention the "Optimum" cruise altitude. It isn't as simple as "higher is better", the optimum altitude for fuel burn is lower than the maximum altitude you can reach, and increases as you get lighter.  When you fly above the optimum altitude, the increased AoA required to maintain altitude results in an increase in induced drag and thus increased fuel burn.

 

So in actuality, step climbing saves you MORE fuel than simply climbing as high as you can as soon as you can.

 

To be fair, it sounds like you might be misinterpreting what the pilot said and might be mixing a few different concepts together. Step climbs aren't forced by any wing issues or lack of power, but are a natural result of pursusing an optimum altitude as it changes with your aircraft's weight.


Brandon Hathaway

UAL-1298

United Virtual Airlines

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You would be mistaken about saving fuel.  Recall in our discussion here we mention the "Optimum" cruise altitude. It isn't as simple as "higher is better", the optimum altitude for fuel burn is lower than the maximum altitude you can reach, and increases as you get lighter.  When you fly above the optimum altitude, the increased AoA required to maintain altitude results in an increase in induced drag and thus increased fuel burn.

 

So in actuality, step climbing saves you MORE fuel than simply climbing as high as you can as soon as you can.

 

To be fair, it sounds like you might be misinterpreting what the pilot said and might be mixing a few different concepts together. Step climbs aren't forced by any wing issues or lack of power, but are a natural result of pursusing an optimum altitude as it changes with your aircraft's weight.

 

That's another way of looking at it.

 

From the design point of view, the wing is designed to take a certain loading. It's very shape and angle can make it a high speed wing or a slower one like an Airbus. But economically you wouldn't achieve long distance flights if you had to reach 41000ft as soon as you completed gear up. 

 

Fuel is a large component of weight and 200,000kg of fuel (440,000lbs) is a huge chunk of an aircraft's load. Considering that it is about half of the entire weight that can be carried, let us put it into perspective. With passenger and cargo loading being about half the weight and fuel the other half, it only makes sense that when a higher altitude is reached it has to go faster to maintain lift and even faster to carry more weight. Air is thin up there and that is where over 85% of the entire flight is operated. So designers take this into account. 

 

Flight is about flying and staying in the air. It isn't about the highest, the fastest and greatest. Look at the Concorde, it was a great Ferrari of the skies and very nostalgic for many spotters and aviation enthusiasts. But it isn't flying today, even though it can fly faster, higher and is greater. Just like the rabbit and the tortoise (turtle).

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But it isn't flying today, even though it can fly faster, higher and is greater. Just like the rabbit and the tortoise (turtle).

The reasons for that were entirely political (they were talking rubbish when they said it was no longer profitable).

 

The airframes were good for at least another 20 years of service (Concorde had pretty low utilization despite its speed, compared to other long haul aircraft - it flew IIRC 1/3 as often as a typical 747, so if the 747 did three flights, Concorde would only complete one).

 

Best regards,

Robin.

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So with step climbs you request a raise in altitude of 2000ft when the planes efficient cruise altitude is 2000ft higher then your current cruise altitude?

 

 

 


Across the atlantic, usually flight levels are available every 1000ft, so it may be possible to cruise at your exact OPT ALT (or within 1000ft of) depending on the traffic in the area.

 

To add a little detail to what James wrote about the OPT ALT, it's every 2000 feet (in RVSM - reduced vertical separation minima - airspace) up to FL410.  After FL410 it's every 4000 feet.

 

To clarify one point, though, I have to point out that getting an altitude change on the NATs is pretty rare if you're flying at peak times.  Since there is no radar coverage out there, non-radar separation is applied, which means separation minima are vastly increased (laterally).  While it's true that all altitudes are opened to the direction of the NAT, you will likely want to hit the NAT at your max altitude as you will not be able to change altitude upon entering the non-radar environment, until you are back in radar coverage on the other side.  Climbing to the max alt just prior to NAT entry means that you're essentially hitting you opt alt at about halfway (in theory), which means your overall profile has a better burn than hitting the NAT at your opt alt, and then being below the opt alt for the rest of the crossing.

 

Ever wonder where all of those cool mid-air shots of heavies come from on A.net?  The NATs.  With all altitudes open, vertical separation is 1000' for same direction traffic, and there are a ton of planes on the crossing.  The frequency of those photos just goes to show how busy those tracks are, and how unlikely it is that you'll get an altitude change approved.


Kyle Rodgers

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