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HeronVA

Fuel Scalar in T7 CFG

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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

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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

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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?

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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

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

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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. 

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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?

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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

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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?

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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.

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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.

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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,

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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 :)

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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

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Ehm,

 

WHAT is wrong with adjusting something for my own reasons?

 

Nothing. But the problem you're facing is akin to solving a difficult equation, and your solution is to simply ignore the bits you can't solve to get an 'answer'. We simply want to help you get to the bottom of the problem, rather than you using a fudge factor.

 

I've flown multiple PFPX flights and always ended up within a few hundred kgs of what was predicted, and I'm not the only one. If something isn't adding up for you there could be a multitude of reasons why. Do weights definitely match between PFPX and 777? Is the weather source you're using the same, both in terms of source and time frame?

 

Basically i know that a 777 burns almost 8000 kg per hour per engine, and i had something like  7000kg, no realistic.

 

At what altitude? Fuel flow will decrease as you climb; less air, less fuel required to maintain the same RPM. You can't use figures like that as absolutes as they'll change with respect to environmental conditions.

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Thanks for the update!

 

Does anyone knows what PMDG says about fuel burn of the aircraft? Is it near to the actual factory figures?


 

 


I've flown multiple PFPX flights and always ended up within a few hundred kgs of what was predicted, and I'm not the only one. If something isn't adding up for you there could be a multitude of reasons why. Do weights definitely match between PFPX and 777?

 

So you are saying that PFPX and 777 calculations are correct, so i need to check the weight in pfpx. I need to tell that iam useing one of the templates stored in the PFPX program.?!

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So you are saying that PFPX and 777 calculations are correct, so i need to check the weight in pfpx. I need to tell that iam useing one of the templates stored in the PFPX program.?!

 

I'm simply saying that you should check the basics first. For example: ZFW. You have to enter it correctly in 3 places: PFPX, the FMC, and lastly in the payload menu, and make sure they all match. It's easy to make a mistake with data entry.

 

Also, weather. What's the weather source for PFPX, and does it match FSX? Again, one slight mistake here and you'll end up with predictions being out.

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Thanks Jordan for your input. I am a 6500 hour MD80 captain and been doodling in FS since FS5 ;-)  I still have an original "Precision Manual" from Mr. Randazzo lying around. The original product and explanation of the company name. I'm not trying to appear better than anybody else or anything. Just that I know already about all the things concerning planning. Step Climbs, Actual vs Forecast Winds, Landing Weight effects on trip fuel, approach fuel, increase or decrease of CI as compared to plan etc etc. Believe me I get it. What I'm trying to let everyone know is that what I have is not a "problem". It's just being aware that the FSX atmosphere is sometimes simplistic/unrealistic and adjusting the sim to meet my personal preference. 

As far as the variations in planning, there are indeed. And that is why you would expect extra fuel upon landing on some flights, and others where you have eaten slightly into you international reserves. It's why they're there. I haven't seen posts regarding landing with less than planned fuel. Constant extra fuel on all flights indicates a discrepancy between PMDG and PFPX. Since the PMDG is more frugal (Not the case usually on used airplanes as compared to factory figures) I decided to try out something. If it doesn't work I can always revert. 

 

Hope everyone understands what I'm trying to say without feeling offended. I'm just saying that for me.....it is more believable to (try to) match PMDG to PFPX than the other way around in this given scenario.

 

 

Cheers,

 

EDIT: Just want to let you guys know also that I'm not making a decision based on trip fuel etc., but by validating the actual flight parameters at any given point in time to the PFPX Database (Evaluation Tool). The extra remaining fuel on all my flights is just a confirmation of what the Evaluation Tool is telling me.

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The weather source as i read in forum is noaa the same as opusfsx uses! so as far as weather concerne we are covered!!! :excl:

As for data input in fmc i use the exact fugures used in pfpx.... so we are done with that too!!!

if the above are correct then i have to check pfpx parameters over the choosen template i try to much the pmdgs . How i will do that any ideas?

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HeronVA,

 

I find that my PMDG 777 templates were set at 104% BIAS originally. I don't know if yours are set there too.

What you can do (For the PMDG 777 at least) is set Climb, Cruise and Descent BIAS for all the 777's you have added to your database to 100%. Do not change the template yet as you don't know if you like that setting. Say for example you fly N855FD FedEx 777 in your aircraft database. Go to your aircraft database and change all the 104% biases to 100% for this airplane. Then plan your flight with that same airplane. See if you like it better like that.

 

 

Cheers,

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i will try to do what you told me and i will post the results!

 

If anyone else has i new or better idea kindly post it over and lets hope that something will come up!

 

Thanks

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If your performance isn't matching the PFPX planning, you're not doing something right.

 

My initial thought is that you're using a Cost Index in the plane, while PFPX is planning based on a constant speed (it defaults to this when you create a 777 profile).

 

In order to have the sim accurately follow PFPX, what you do in the sim has to match what PFPX was planned using exactly.  If PFPX used a M.83 cruise, you have to use a M.83 cruise.  If you planned the flight well before departure, you should replan it closer to departure to ensure the winds will match up.  Your weights should match closely.  You should plan to execute step climbs that closely follow the PFPX plan (the STEP SIZE should be updated accordingly in the plane).

 

People should really stop blaming the programming first and look to themselves, instead.  Most of the time, it's user error.  If you don't believe me, call your local help desk and ask them for their stats.  Look for discrepancies in your own actions, and if you can rule yourself out entirely, then it might be an issue.  Until that point, though, it's probably you.

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Hi Dear 777 Pilots,

 

A lot have been said about the 777 fuel consumption. A lot of assumptions, opinion, feelings, remarks, mixing up terms like wind effect, CI, etc.

I think all of this boil down to one question: are the fuel flow figures of the PMDG 777 correct or not? PMDG advertises this product that it is 5% within real world (factory)figures.

I'm sure the only valid test is a test flight, recording the data and compare them to real performance figures.

I have a 777-200LR GE90-110B1L FPPM (performance manual) with all the detailed data reqired.

I will go out for a test flight, (Mid Weight, optiomum cruise altitude, etc, and will report back my findings in detail.  We'll see the result.

 

 

Cheers,

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I'm consistently getting to each waypoint on time and on fuel with no tweaks, when compared to PFPX predictions and FSX actuals. 

 

As Kyle and I have said, if you're not, something's wrong.

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