Fuel flow at ground idle (RB211)

[Andrea1]

Hi,
Happy Easter to all!
Just updated my psx to 10.4 beta 7 version
I'm preflighting with an RB211-524H8 engine version model.
Just started my engine but fuel flow indications appear very strange and abnormal:
I'm at LIMC (about 700 ft AGL) pressure QNH 1021, temperature 9°C (really cold in Northen Italy today!) but I read a fuel flow of 1,0 (1000 kg/h) per engine!
You know, it'd be about one half (0,5-0,6=500-600 kg/h) also because I've no abnormal loads (i.e. engine anti ice-wing anti ice on and so bleed air) all Others parameters appear normal: EPR=1,02, N1=23%, N2=42%, N3%=61% EGT 290-295

Best
Andrea Buono

[Hardy Heinlin]

Hi Andrea,

I can't reproduce your problem.

My FF is 0.5 under the same conditions.

Please confirm you have KGS, not LBS selected.


Cheers,

|-|ardy

[Andrea1]

Hi Hardy,
Thanks for your answer, yes I've kg...
I'll retry from a cold and dark situation after dinner...

I also had a residual thrust so strong that, w/o parking brake Iwas taxing at a groundspeed of 29 kts !!! (my weight is about 250 tons= ZFW225+25 fuel for an hop LIMC-LSZH) I've tried also a reverse and returning at ground idle but same result...
I'll try later...
Ciao
Andrea

[Hardy Heinlin]

Do you have a network? Did you update all PSX instances?


|-|ardy

(You can taxi at idle at light weights, no problem, especially on downhill slopes.)

[Andrea1]

Hi,
No..I've no network..
Now I'm going out but Tomorrow I'm going to delete and reinstall last version (10.04 beta 7) 'cause maybe something was wrong during installation..I tried again but this time I got 0,8 (800 kg/h) but it was also something strange with weather I usually use real weather updated according with flight zones but by looking at LIMC metar textbox I could see a lot of strange signs like ///??? etc. so maybe I had an upset with weather data..( I've also tried another location LIRF but Always the same result 800 kg/h of ground idle fuel flow)

Best

Andrea

[Andrea1]

Hi,
Reinstalled..now RB fuel flow is ok!...Maybe an upset with weather data Yesterday...

Thanks a lot to Hardy for his quick reply...

Best Regards

Andrea

[United744]

In Beta 4 I saw excessive fuel flow at idle (RB211, Schipol). It showed 2000 lbs/hr per engine.

In the latest Beta it appears OK.

[Andrea1]

Hi,
Now it's seems quite normal..at normal altitudes (0-1000) ft and air condition (ISA) I can read 0.7 (700 kg/h but it could be also 660 rounded to 0,7)..Others engine (PW or GE) are less (0,5-500 kg/h at the same conditions but it could be 540 kg/h)...

Ciao

Andrea

[Ivo de Colfmaker]

Hi,
Yesterday I was in PANC, Anchorage, QNH 29.89    
1°C
With The RB211 engines.
just out of curiosity  when I saved the situation at the runway I had
ZFW 211 Tons
Fuel 26.7 Tons
GRW 237.7 Tons
FF 1.0 Ton per engine
in the same conditions changing the numbers
ZFW 170
Fuel 10 Tons
GRW 180
I got a FF of 0.7 per engine
changing to
ZFW 240
Fuel 120
GRW 360
I got a FF of 1.2 per engine
Why is it that at idle  thrust there is a difference of 500 kg per hour per engine , standing still ?
running beta 6
ivo

[Hardy Heinlin]

When you have a lot of icing on the nacelle, the engine performance may be reduced and the FF increased.

Please check if the Instructor's De-ice button helps.


|-|ardy

[Andrea1]

Hi,
very strange indeed...G-CIVR model...LIMC (700 ft MSL) temp. 14°C QNH 1018 till 220 tons of ZFW I got 0,6 FF at ground idle..but if I load more than 220 tons of payload I got 0,7..(maybe more pax means more power for air conditioning and electrical power for individuals bulbs etc.)..no ice in these conditions (also I've anyway executed a de-ice..)

Best

Andrea Buono

[Andrea1]

On the other hand by starting from another model (GE or PW) and reloading G-CIVR...fuel flow at idle returns to 0,5...very puzzling situation...

Best

Andrea

[Andrea1]

Also by starting with an engine off situation (Basic003 on ground and cleared for engine start) I got normal values (0,5) so let's assume is normal...

Ciao

Andrea

[Ivo de Colfmaker]

Hi Hardy;
it helped to reduce the fuel flow!
amazing, you think of everything.

ZFW 211 Tons
Fuel 26.7 Tons
GRW 237.7 Tons
FF 1.0 Ton per engine de iced 0.6
in the same conditions changing the numbers
ZFW 170
Fuel 10 Tons
GRW 180
I got a FF of 0.7 per engine de iced 0.4
changing to
ZFW 240
Fuel 120
GRW 360
I got a FF of 1.2 per engine de iced 0.8

so, lower figures, but still 400 kg per engine more at higher weight.
It will be more complex than I think , but idle is idle, how is  the weight of the aircraft stationary affecting the fuel flow under the same atmospheric conditions if the engines do not have to move anything?

[United744]

Confirmed here - simply increasing the payload increases idle fuel flow (between 1000 lbs/hr and 1800 lbs/hr) depending on weight only.

Actual idle N1 remains constant (around 28.0-30.0%).

This would explain what I saw in Schipol - I was heavy.

[Hardy Heinlin]

Fixed in 10.0.4-beta8:

http://aerowinx.com/forum/topic.php?id=2782