Fuel Scalar in T7 CFG

[HeronVA 0]

Hi,

 

I was wondering if the fuel scalar in aircrafts cfg is accurate or needs to be modified, thus i have grate differences between PFPX landing fuel and the aircraft itshelf.

 

Regards

Giorgos

[Yosm 19]

I know the biggest operator of the T7 uses between 14-10 tons as landing fuel. This differs per airport because of alternates and weather offcourse

[HeronVA 0]

Ok i understand that but what is going on with PMDG! fuel scalar is based on a real operator (DELTA) or the manufacturer (BOEING).

Did they modified and burn less thun it should?

[xkoote 57]

Hello,

 

I was also getting an extra 2 tons arrival fuel on all my long hauls. I only just yesterday asked about this on the PFPX forum. Phil told me that their reference for 777 performance comes from a pretty complex tool. As it was, the PMDG 777 was too frugal on fuel.

I increased my value to 0.87103. If you want you can try it out. For personal use at your own risk ;-)

 

Currently flying EGLL-CYVR to test out the change.

 

Regards,

 

 

Xander

[Airbusman330 300]

Are the winds uploaded into the fmc or are you using accurate weather? I land within a couple of tons of my planned fuel.

[willywonka 36]

There's a whole lot of variables that can affect fuel burn. The winds you plan a flight with will not necessarily be the same as the wind you fly. Some differences are unavoidable. 

[HeronVA 0]

Hi,

 

Yesterday i finished a 5536nm flight and the difference between PFPX and actual fuel burn was almost 6.5 tones less so i found my shelf limited by landing weight at least 4 tones. I use the OPUSFSX for wx and i load the wind aloft that this engine produces. still can figure out what is going on. How can i match PFPX with PMDG777. Currently i flying a 6350nm flight following the re-dispatch procedure  to see what is going on.

 

Does anyone figured out what must be done?

[xkoote 57]

Winds can have an effect indeed. But always check my fuel against plan fuel AND plan time. I landed all my flights within 5 minutes of flightplan time but with 2 to 3 tons extra. That is why I modified my .cfg.

 

 

Xander

[Flamin_Squirrel 71]

Winds can have an effect indeed. But always check my fuel against plan fuel AND plan time. I landed all my flights within 5 minutes of flightplan time but with 2 to 3 tons extra. That is why I modified my .cfg.

 

 

Xander

Are you flying real time or accelerated?

[http404 22]

I usePFPX, I always fly heavy. I always arrive within 1 tonne of landing fuel difference, usually on the plus side which is a good thing, the difference isn't really big in most cases. Even when deciding to go with a reasonably higher Cost Index to save a few minutes, I am still within reasonable limits. All in all, a few hundred KGs plus is the usual for me with proper planning prior to departure.

 

I'm currently trying a 17+ hour, 8226nm route from Toronto to Kuala Lumpur in Malaysia over the NPole.

 

Runway roll started with 142.6 tonnes or so, planned arrival is 13.3 for a good diversion to Southern Malaysia or Singapore if required. Flying east with strong tailwind was another option for arrival within the 17hour frame.

 

Will post the landing fuel today after 1315 GMT.

[Fabo 213]

Ehm.

 

WHY are you going around modifying PMDG, with who-knows-what consequences?

 

Instead of using fuel bias option in the PFPX? The option was put there because it is used even in RW, differences between two different airframes can be as much as 10% in some situations...

 

Just use a small minus bias and you will be fine. And more realistic.

[xkoote 57]

Ehm,

 

WHAT is wrong with adjusting something for my own reasons? I fly strictly non-accelerated, always. I have not posted this because it was my own personal choice just as it is yours to adjust PFPX to match PMDG. My only reason behind it was that when validating PFPX I saw that the 777 was using less fuel than "book". It is not common (realistic) for a used line aircraft to be more economical than factory values. So I posted in PFPX. I was informed that PFPX use a complex tool to determine 777 data. And I believe them. You can plan flights even on cost index, and for that you must have some pretty accurate factory data. And this is why I adjusted my scalar instead of the PFPX bias. The result is that my flights are now much more accurate. You are allowed to have differences between actual and planned fuel.....of course. But personally I found the difference too much. That is why I adjusted my scalar. I'm not saying it's a fix, I'm not saying this is something PMDG should check. I'm saying I did it for me, and it might be something somebody else is interested in.

 

 

Cheers,

[http404 22]

Cool down gents.

 

Right, I found myself arriving ahead of schedule due to the wind change. I did some offsets and eventually one hold loop at destination, WMKK, which caused a +3 minute arrival than scheduled... awesome!

 

Planned trip time was 17:20

Estimated Arrival Fuel 13.37.

F/O clock: 17:24 the minute i vacated rwy and was slow enough to go and fiddle with the clock to stop it.

Runway vacated fuel: 13.3 Tonnes!

Looks like the plane performed better for the reason you stated above (Factory Figures), and add to that, My step climbs were more efficient than proposed by PFPX. PFPX sometimes tends to  give you a much lower cruise altitude due to an airway constraint midway, which i do not follow, resulting in saving the climb burn back to the normal cruise altitude.

 

All-in-all, it's way better than arriving with 1 tonne of fuel for each engine on ultra-long haulers like I used to get with the PMDG747

[HeronVA 0]

Gents,

 

Thank you all for your interest to solve once again advance and complicated issue with our so called favor addon. Still even with my last flight i arrived with far more fuel than i should. Basically i know that a 777 burns almost 8000 kg per hour per engine, and i had something like  7000kg, no realistic. If the pfpx calculates fuel at list with 90 - 95% realism why the number cant much? 
 
I am searching the net for a solution! Even with my 9350mn flight i end up with more fuel than i should.

 

If let say that PMDG is more accurate than PFPX, what i am missing and i end up with wrong calculations over fuel!

 

Can someone help me out and solve that mind trapping issue?

 

Giorgos

[DescendDescend 25]

You may well find that the PMDG engine and fuel system do not even use the FS fuel flow scalar.