Fuel flow vs fuel use

[Gazzareth 808]

I've noticed that on every flight the amount of fuel used from the middle engines tanks is much more than the outer engines. By the time I'm up to altitude and have done a couple of hundred miles there is a 500lb difference on the fuel used gauges. This despite the fact that the fuel flow gauges show exactly the same usage with each engine.

On longer flights I tend to have to open up the cross flow valves, was under the impression that shouldn't be necessary. Anyone else seeing this?

 

G

[ark 1,288]

1 hour ago, Gazzareth said:

I've noticed that on every flight the amount of fuel used from the middle engines tanks is much more than the outer engines. By the time I'm up to altitude and have done a couple of hundred miles there is a 500lb difference on the fuel used gauges. This despite the fact that the fuel flow gauges show exactly the same usage with each engine.

On longer flights I tend to have to open up the cross flow valves, was under the impression that shouldn't be necessary. Anyone else seeing this?

 

G

Hi G,

Where are the fuel used gauges?  I see fuel remaining gauges for each engine, and rate of fuel used for each engine, and a total fuel used counter, but I don't fuel used gauges for each engine.

Also note with the tanks topped off, each main wing tank holds about 1000lbs more fuel than the main center tank.  However, the center feeder tank when full holds about 1056 more pounds than the each wing feeder tank. So overall, with everything topped off, the center main tank/feeder combination holds about 56 more pounds of fuel than each main wing tank/feeder combination.

Also, when the toggle switch below the fuel gauges is Up, the fuel gauges read the main tank values. When the toggle switch is Down, the fuel gauges read the feeder tank values.

Once the feeder tanks get down to about 600lbs, they are maintained at that level as long as there is fuel in the associated main tank to keep the feeder at that level.

Al

Edited January 29, 2020 by ark

[chevelle505 11]

I have noticed fuel flow in the center engine seems to be a tad higher on average, HOWEVER, i think this would be normal/correct..engine 2 is ducted..same reason it spools a little slower on throttle up would, in theory make the engine have a little more restriction of intake. I assume this would cause a very very small amount of increased fuel burn due to slightly lower efficiency from the duct. Who knows, maybe im off base here.

Edited January 29, 2020 by chevelle505

[Gazzareth 808]

43 minutes ago, ark said:

Hi G,

Where are the fuel used gauges?  I see fuel remaining gauges for each engine, and rate of fuel used for each engine, and a total fuel used counter, but I don't fuel used gauges for each engine.

Also note with the tanks topped off, each main wing tank holds about 1000lbs more fuel than the main center tank.  However, the center feeder tank when full holds about 1056 more pounds than the each wing feeder tank. So overall, with everything topped off, the center main tank/feeder combination holds about 56 more pounds of fuel than each main wing tank/feeder combination.

Also, when the toggle switch below the fuel gauges is Up, the fuel gauges read the main tank values. When the toggle switch is Down, the fuel gauges read the feeder tank values.

Once the feeder tanks get down to about 600lbs, they are maintained at that level as long as there is fuel in the associated main tank to keep the feeder at that level.

Al

You need to look harder, digital counters (not at the PC at the moment) on fuel flow gauges I think. Perhaps I'm completely wrong about what they are and it's just a coincidence that they seem to add up to total fuel used. Not reading for each engine, I think it's counting fuel from tank, as cross flowing fuel to the centre stops it.

I am aware how feeder tanks and the toggle switch work.

 

G

 

[Gazzareth 808]

42 minutes ago, chevelle505 said:

I have noticed fuel flow in the center engine seems to be a tad higher on average, HOWEVER, i think this would be normal/correct..engine 2 is ducted..same reason it spools a little slower on throttle up would, in theory make the engine have a little more restriction of intake. I assume this would cause a very very small amount of increased fuel burn due to slightly lower efficiency from the duct. Who knows, maybe im off base here.

I did wonder that, but figured fuel flow gauge would be noticeably different. 

 

G

[ark 1,288]

1 hour ago, Gazzareth said:

digital counters (not at the PC at the moment) on fuel flow gauges I think

G,

You are correct. I don't fly the Falcon and had assumed those digital displays where just digital readouts of the needle values. But then I noticed they start from zero when you start the engines, so I ran an experiment. I set the N1 for the engines at 76% and let them run just sitting on the runway. After about an hour the fuel used by engine 2 was about 7% higher than for the other two engines whose fuel used values were the same. Why this is I don't know. There may be a setting in the air file that accounts for the difference. Another possibility is the coding erroneously assumes the APU is running since the APU runs off the center feeder tank. I'll have to see if Mark knows anything about this.

Al

 

Edited January 29, 2020 by ark

[Gazzareth 808]

1 hour ago, ark said:

G,

You are correct. I don't fly the Falcon and had assumed those digital displays where just digital readouts of the needle values. But then I noticed they start from zero when you start the engines, so I ran an experiment. I set the N1 for the engines at 76% and let them run just sitting on the runway. After about an hour the fuel used by engine 2 was about 7% higher than for the other two engines whose fuel used values were the same. Why this is I don't know. There may be a setting in the air file that accounts for the difference. Another possibility is the coding erroneously assumes the APU is running since the APU runs off the center feeder tank. I'll have to see if Mark knows anything about this.

Al

 

 

You may have hit the nail on the head with the APU - that would explain why the fuel flow readings are identical but quantities different. Although 500lb of fuel for the APU seems a LOT !!!

 

G

[ark 1,288]

3 hours ago, Gazzareth said:

 

You may have hit the nail on the head with the APU - that would explain why the fuel flow readings are identical but quantities different. Although 500lb of fuel for the APU seems a LOT !!!

 

G

I ran some more experiments and figured out what is happening -- it is not the APU.

When the feeders get down to their 600lb maintenance level, that is when the fuel used counters go wrong -- they slow down. Since the side feeders are smaller than the center feeder, they reach that 600lb point sooner than the center feeder, so the center fuel used counter is still correct (until the center feeder gets to 600lbs). So I'll talk to Mark and we will try to figure out why this problem occurs when the feeders get to 600lbs,

Al

Edited January 30, 2020 by ark

[Gazzareth 808]

That would probably explain how I managed to get from Rio to Cape Town on less than 8000lb of fuel lol

 

G

[gaab 111]

On 1/30/2020 at 5:08 AM, ark said:

So I'll talk to Mark and we will try to figure out why this problem occurs when the feeders get to 600lbs,

Al

Hi Ark,

Just in case FSW would issue another update, there is a "small bug" in clipboard RECOG LIGHTS.

The recog lights are managed by the "L:SW_RECOG_LIGHTS,bool" local variable, not the "A:LIGHT RECOGNITION,bool" which are used for the Shield Lights...

Gérard

[ark 1,288]

6 hours ago, gaab said:

Hi Ark,

Just in case FSW would issue another update, there is a "small bug" in clipboard RECOG LIGHTS.

The recog lights are managed by the "L:SW_RECOG_LIGHTS,bool" local variable, not the "A:LIGHT RECOGNITION,bool" which are used for the Shield Lights...

Gérard

Thanks Gérard , I fixed the clipboard recognition lights bug and will let Mark know.

Regarding the fuel used issue, we re-wrote the code so it works better. The new code will be in the next release which I would guess will be fairly soon.

Al

Edited February 2, 2020 by ark

[Gazzareth 808]

13 minutes ago, ark said:

Thanks Gérard , I fixed the clipboard recognition lights bug and will let Mark know.

Regarding the fuel used issue, we re-wrote the code so it works better. The new code will be in the next release which I would guess will be fairly soon.

Al

Great to hear, thanks Al.

 

G

[ark 1,288]

On 2/1/2020 at 10:17 AM, gaab said:

Just in case FSW would issue another update, there is a "small bug" in clipboard RECOG LIGHTS.

The recog lights are managed by the "L:SW_RECOG_LIGHTS,bool" local variable, not the "A:LIGHT RECOGNITION,bool" which are used for the Shield Lights...

Gérard ,

It turns out the mistake is the Clipboard label is wrong -- it should say something like Shield Lights instead of Recognition Lights. That section of the Clipboard deals with the various interior lights. So the labeling will be fixed in the update.

Al

[gaab 111]

1 hour ago, ark said:

Gérard ,

It turns out the mistake is the Clipboard label is wrong -- it should say something like Shield Lights instead of Recognition Lights. That section of the Clipboard deals with the various interior lights. So the labeling will be fixed in the update.

Al

This makes sense  !

Thanks Ark for your feedback.

[gaab 111]

Ark,

I sent you a PM.

Regards