I'm not surprised at all. This was always going to take a while. Its not simply a case of reading the boxes and that's it, problem solved. Initial findings for these things don't usually come within a week...
Air India Crash
- Thread starter Grim5
- Start date
A pattern I've started to notice with all of the theories people have come up with is that they are all saying "This issue could have happened and it would have crashed the plane" or "The pilots could have made this error and it would have crashed the plane".
And in almost every single instance it's always pointed out that "of course it couldn't happen in an A350 due to the extra protection/failsafes".
I guess this is what happens when one manufacturer becomes the biggest in the world via cost cutting and bribes.
Are you insinuating that Airbus have been bribing and cost cutting in recent years, as they are the biggest producer of civil airliners.
No, hence why nobody else read it like that.
The mention of the Airbus A350 (the 787s main competitor) was in relation to the fact that of all the theories put out so far as to how it could have happened almost all have included the caveat that they wouldn't affect an A350. In example the flight computer on the A350 wouldn't let the pilots accidentally retract the flaps instead of the gear during takeoff, this is due to differing safety approaches between Airbus (who think pilots should be prevented from killing themselves by the computers) and Boeing (who think pilots should have ultimate control over the aircraft).
The mention of cost cutting and bribes was in relation to Boeing (historically the worlds largest producer and seller of passenger aircraft) historically being able to outsell and outproduce all of their competitors over the years due to cutting corners to under-price the competition and in many cases straight up bribing airlines (there is also the fact that for the majority of their existence there was a belief in America that US airlines should buy American planes which cut out SUD, BAE, Tupolev, etc from a lot of the US market).
Last edited:
I know I replied to these earlier and it was over a week ago but I've investigated and can confirm that this is all correctly modelled in the sim. I hadn't specifically noticed when I was testing at the time but I did have reduced thrust, down from a possible 107% N1 at full throttle to about 95%, which is enough to take off and maintain flight.
I just wanted to return and add closure to that part.
How do you know that it's *correctly* modelled?
Associate
- Joined
- 19 May 2010
- Posts
- 1,810
- Location
- Cheltenham
Is that a natural consequence of the suction feed reaching a limit or the engine sensing that lower supply pressure and protecting itself? Probably impossible to tell without going into the code itself to be fair! Need some GenX engine manual notes…
The manual describes it, the sole developer has confirmed it and practically, you can see and feel the lower thrust. It's not rocket science, it's jet engine science
So the engines basically suck the fuel right out of the tanks anyway, and the pumps are mostly used for startup / or maintaining fuel pressure?
Yes most aircraft you turn off the fuel pumps once the engine is running.
Probably to ensure fuel pressure/delivery especially if the fuel is low in a tank and you're not flying straight and level.
Sounds a bit like petrol strimmers and mowers, where you must remember to pump the little red button the right number of times to start the engine purring. Too little and it doesn't, too much and you flood it.
Associate
- Joined
- 19 May 2010
- Posts
- 1,810
- Location
- Cheltenham
Not in an airliner. The tank pumps are centrifugal impeller types that provide a head pressure down to the engine like your car tank pump, but won’t go over a certain pressure and will just sit there spinning if there’s no demand. You start them prior to engine start and they’ll just be left there till the engine is shutdown at destination.
The engine itself has at least one gearbox driven pump but usually two - on the old RB211 they were built as one unit powered from the main gearbox. The low pressure would take the fuel from the tank pumps and feed it through to the high pressure pump where it would be dramatically increased in pressure and fed to the fuel nozzles for burning.
If the tank pumps failed then mavity would allow the fuel to flow straight through them down to the engine, where it would suctioned through by the low pressure pump. There was usually a limit of flying hours you could run the engine for like this as it increased the internal wear on the pump, but as the tank pumps are usually mounted in pairs it’s not a common problem.
Essentially, the fuel systems these days are so automated that they look after themselves, with just the one switch to turn on the fuel at the engine and begin ignition - apart from that it’s all just monitoring by the pilots. I recommend reading about Air Transat 236 to see what CAN go wrong though:
Air Transat Flight 236 - Wikipedia
The manual describes it, the sole developer has confirmed it and practically, you can see and feel the lower thrust. It's not rocket science, it's jet engine science
If you can't do jet engine science you turn your hands to rockets.
There's a reason why there are only 4 (well 5 if you count Russia) major jet engine makers in the civil world.Just look at India, they have a successful rocket programme but still haven't built a viable jet engine. Everything is in partnership with Western companies. Or China, the Comac C919 uses CFM Leap-1Cs.
Associate
- Joined
- 19 May 2010
- Posts
- 1,810
- Location
- Cheltenham
If you can't do jet engine science you turn your hands to rockets.
Just look at India, they have a successful rocket programme but still haven't built a viable jet engine. Everything is in partnership with Western companies. Or China, the Comac C919 uses CFM Leap-1Cs.
Don’t forget Boom Supersonic.
/s
Interesting bit of information, our equipment is on the C919 and ARJ21.If you can't do jet engine science you turn your hands to rockets.
Just look at India, they have a successful rocket programme but still haven't built a viable jet engine. Everything is in partnership with Western companies. Or China, the Comac C919 uses CFM Leap-1Cs.
I remain respectfully unconvinced.
What exactly is the sim modelling?
Just because the developer has put in a line of code that effectively says reduce N1 by 12% if fuel pumps off does not mean that the sim is correctly modelling a takeoff with no fuel pumps. (Are the fuel flow and EGT parameters different as well? - In this case compared to 95% N1 with fuel pumps on)
In order to be able to model this, the developer would have to have access to real world flight test data showing the behavior of those particular engines at take-off thrust with no ancillary fuel pumps. I doubt very much if he has access to this as I imagine it's proprietary and not widely available. (If it even exists)
There will be failure modes associated with low or abnormal fuel pressure, the ones I can think of would possibly be abnormal EGT, low idle, possible engine surge, abnormal thrust lever response. I'm sure there are others I'm not aware of. Possibly some of these failure modes are not well understood. And unless the sim is correctly modelling possible failure modes, it's not correctly modelling the engine performance under these conditions. I assume the sim has selectable failures - what are they with regards to the engines?
I personally doubt that even a level D full flight sim would correctly model this.
So, I think we'll have to agree to disagree on this one.
(I'm currently spec'ing out a new PC to run flight sim as I want to get back into it, and to teach my son to fly - start em young. So will probably try to have a play around with some of the pro add-ons and report back but I think there's a different thread for that)
Edit: Just to add, I don't doubt that the your sim is a very good representation of an actual 747 but that you are using it to support conclusions that are not warranted, from what is a rather niche area of aircraft performance, where actual performance data is not available.
Last edited:
I'm with the above. Just because something is modelled does not necessarily mean it's accurate, even if based on the best available data.
The Aerowinx manual states (with my emphasis):
"Main boost pumps are installed in all four main tanks. Each main boost pump is AC motor driven and provides sufficient fuel pressure to one engine during takeoff, or to two engines in cruise. If there is no pressure in the manifold, check valves automatically open, allowing fuel to bypass the inactive pumps so that the engines can suction the fuel from the tanks directly. However, suctioning alone cannot produce the same high fuel flow as the tank pumps can, hence thrust in the takeoff range is then no longer available."
This seems to contradict what actually happens in the sim.
The Aerowinx manual states (with my emphasis):
"Main boost pumps are installed in all four main tanks. Each main boost pump is AC motor driven and provides sufficient fuel pressure to one engine during takeoff, or to two engines in cruise. If there is no pressure in the manifold, check valves automatically open, allowing fuel to bypass the inactive pumps so that the engines can suction the fuel from the tanks directly. However, suctioning alone cannot produce the same high fuel flow as the tank pumps can, hence thrust in the takeoff range is then no longer available."
This seems to contradict what actually happens in the sim.
I used to work in a research lab. We had just spent an hour in a meeting discussing whether to build it or simulate it. One of the old guys who had sat in silence all meeting when asked for his opinion simply said "Simulation is a bit like masturbation, the more you do it, the more you think it's better than the real thing".