Hello,

 

I looked into specifications of 772LR and 777F.

 

The max Range of 777F is 4.900nm and of 772LR 9.395nm.

 

As I understand both airplanes are more or less the same in weights, engines

etc.

 

Why is the max. Range so significant different.

 

Thanks in advance

 

Regards

 

Andreas Hövel

Might have to do with loadable weight. It can carry max more weight in cargo. This then pushes on the max range

Might have to do with loadable weight. It can carry max more weight in cargo. This then pushes on the max range

The 77L has the option of 3 aux fuel tanks whereas the 77F doesn't. I would imagine that's one reason.

The figures you are citing are skewed.

If you look at the documents Boeing provides on their Technical site (free to access), you'll see the ranges are very, very similar.

 

SOURCE: http://www.boeing.com/boeing/commercial/airports/777.page

(Chapter 3)

The Maximum Zero Fuel Weight on the 77F is 248115 kgs, about 547000 pounds whereas the 77L has a MZFW of only 209106 kgs or 461000 pounds. The range figures you gave are for range at maximum payload. The Fuel capacity on both is the same (when no AUX tanks installed), so when a 77F has max payload, thus a ZFW of 248,115 kgs, the 77L at max payload has a ZFW of 209106 kgs which is almost 40 tons lighter. Therefore at max payload the 77L can carry about 40 tons more fuel than the 77F (MTOW is for both variants about the same, only differs 800 pounds). I think this is the main reason for the range difference. 40 tons with an average cruise fuel burn of roughly 7 tons per hour, that is almost 6 hours of extra flighttime compared to the fully loaded freighter.

The Maximum Zero Fuel Weight on the 77F is 248115 kgs, about 547000 pounds whereas the 77L has a MZFW of only 209106 kgs or 461000 pounds. The range figures you gave are for range at maximum payload. The Fuel capacity on both is the same (when no AUX tanks installed), so when a 77F has max payload, thus a ZFW of 248,115 kgs, the 77L at max payload has a ZFW of 209106 kgs which is almost 40 tons lighter. Therefore at max payload the 77L can carry about 40 tons more fuel than the 77F (MTOW is for both variants about the same, only differs 800 pounds). I think this is the main reason for the range difference. 40 tons with an average cruise fuel burn of roughly 7 tons per hour, that is almost 6 hours of extra flighttime compared to the fully loaded freighter.

Basically, all the support for passengers (windows, toilets, seats, galleys, oxygen tanks, wiring for all the entertainment systems, etc etc...) weigh about 40 tons on the 77L.

Not necessarily, they are already included in the MZFW figure.

Also, please sign your names and read the rules.

Basically, all the support for passengers (windows, toilets, seats, galleys, oxygen tanks, wiring for all the entertainment systems, etc etc...) weigh about 40 tons on the 77L.

 

The items you name are already taken into account in the Dry Operating Weight, This is the weight of the aircraft ready for operation without payload and without fuel (so including seats, windows, or items like spare parts, etc. etc.). Dry Operating Weight + Payload = Zero Fuel Weight. 

A buddy of mine flies the 777 for FedEx and he has done Taipei and Hong Kong to Memphis many times. Both of those flights are 7,000+ nautical miles so the freighter version can go a good but further than 4,900nm.

A buddy of mine flies the 777 for FedEx and he has done Taipei and Hong Kong to Memphis many times. Both of those flights are 7,000+ nautical miles so the freighter version can go a good but further than 4,900nm.

True, but not at full payload. Of course you can fly further but you have to sacrifice payload in order to be able to take more fuel with you to cover that distance. The 77F can carry a good 100 tons of cargo, so sacrifice f.e. 30 tons cargo to take 30 tons more of fuel and you will be able to fly way further than 4,900nm with still 70 tons of cargo on board. 

I still don't understand why people even look at range values.  Range is going to vary based on how loaded the plane is, enroute wind, and several other factors.

 

They're notional, at best, so trying to dissect them isn't going to do much good.

A buddy of mine flies the 777 for FedEx and he has done Taipei and Hong Kong to Memphis many times. Both of those flights are 7,000+ nautical miles so the freighter version can go a good but further than 4,900nm.

That's really quite cool. I like the "real world" examples. I myself have toyed with the idea of doing the VHHH or RCTP to KMEM in the sim, but gosh, that's 14+ hours.

 

Just out of curiosity, what does your buddy do on a freighter on a 14+ hour flight? I mean, I'm assuming there has to be a relief crew, but it must be a pretty boring ride. Is there any sort of cabin crew that is there to serve meals, socialize with, etc? What about meals? Do they have the same rules as passenger flights, i.e. they can't all eat the same meal?

 

EDIT...sorry, I just realized I just attempted to hijack the thread....

Yeah I haven't done any figuring at max payload. On one of my friend's Taipei-Memphis flights they had 172,000lbs of payload and 277,200lbs of fuel. It was scheduled for 13:49. I actually flew my MD-11 along with him in real time (PMDG 777 wasn't out yet) taking off at max weight and max fuel. I still only had 2,500lbs of fuel when I landed. I guess that's why they don't use MD-11s on that route.

 

He never really said what he does to occupy his time in cruise. I assume he sleeps some. They have the bunks and all. The flight takes off at 9AM Memphis time so the whole thing takes place during normal waking hours. It is 10PM in Taipei at departure. They have food but the pilots are the ones who heat it up. I guess the junior guy on the crew gets to do it.

 

 

I mean, I'm assuming there has to be a relief crew, but it must be a pretty boring ride. Is there any sort of cabin crew that is there to serve meals, socialize with, etc? What about meals? Do they have the same rules as passenger flights, i.e. they can't all eat the same meal?

 

Open the FCOMs and search for Supernumerary and you'll get a nice idea.

Yeah I haven't done any figuring at max payload. On one of my friend's Taipei-Memphis flights they had 172,000lbs of payload and 277,200lbs of fuel. It was scheduled for 13:49. I actually flew my MD-11 along with him in real time (PMDG 777 wasn't out yet) taking off at max weight and max fuel. I still only had 2,500lbs of fuel when I landed. I guess that's why they don't use MD-11s on that route.

It's really amazing when you think about the capability of the 777LR/F series and how it is perfectly suited for package cargo. According to *ahem* Wikipedia, the 77F can carry more total volume of cargo a longer distance than the MD11, all while doing it on two engines instead of three. Granted, the GE90's are a generation newer than the CF6/PW4460 and a heck of a lot more powerful. The fact that a 77F can carry 170000+ lbs of payload on a sector of roughly 14 hours all while burning less fuel than it's replacement is a testament to the design.