QF engine stats Vs Manufacturer stats

[The Other Half]

Just flicking through the "About Our Aircraft" section on QF's website and was wondering why the stated output of any particular engine can be up to 1,000 lbs different in thrust compared to what the engine manufacturer states for that exact variant of the engine? It can be + or - the stated figure so there's no boasting there. :confused:

Cheers :ok:

[The Other Half]

In fact there are other details that don't make sense. How can the A330 - 200/300 have the same range as each other (according to their website) Is it a company thing? What about their MTOW shouldn't they be 230T not the 202T and 212T they are quoting?
Would someone (probably from QF) enlighten me

What variation of the V2500 engine will the A320's of Jetstar be getting along with their thrust ratings?

Do QF still have the 767-200er?

What engined 767's have been transfered to Australian Airlines as well? Was it the RB211's?

Are there any RB211's being interchanged between the 747 and 767 in their fleet?

Cheers

[enicalyth]

The airline is certified to use the aircraft set out and the destinations listed in Schedule 2 and 3 of AOC (SY 216147-49). These practicalities determine what weights and ranges will actually be and not the sales figures promoted in brochures.

To prolong life and reduce cost an engine is matched into an application. It mustn't be, for the want of a better word, de-rated so far as to become inefficient but there is for every chore a set-up that is best for the current state of ops/mods/sectors/profiles. So faced with such a poser the engine manufacturer quotes for the test-bed; the operator quotes for the power match of inlet, engine, exhaust and airframe. Even a subtly different aircon package makes a difference. A good treatise is Mechanics and Thermodynamics of Propulsion by Hill and Petersen ISBN 0-201-14659-2 especially pp202-208. Although a bit dated you can get an insight into how the company managers and engineers can come up with a range of thrusts for particular applications, mod states, kit fits etc and yet it still says GE CF6-80E1 (or RR Trent 700, PW 4000) on the side. The fine detail is in the letters that follow these codes (eg E1A2 and a lot of other letters and marks after that). +/- 1000lbf is nothing and you go by the book and the beast (computer) for each particular aircraft.

Yes Airbus say the A330-200 for example can have a 230 tonne TOW. But Qantas have decided that they wish to be certified only to 202 tonnes. They run a business and have no wish to pay airport taxes and navigation fees for a weight they never intend to reach. Essentially look at the AOC, study your market and make the sensible choice. So the answer is no, no a thousand times no, 202 tonnes is fine, we're here to make profits not pay unnecessary taxes!

What variation of the V2500 engine will the A320's of Jetstar be getting along with their thrust ratings? Dunno mate!

Do QF still have the 767-200er? Nope. Twenty two B767-338ERs and seven B767-336ERs. As you seem interested in Airbus it is four A330-201s, three A330-301s and four A330-303s... I think.

Are there any RB211's being interchanged between the 747 and 767 in their fleet? Er? Can I speak to an engineer please?

Finally on range Airbus brochurespeak says of the A330... "The range shown is for a full passenger payload with baggage allowance. It takes into account fuel reserves and other typical airline operating rules as well as weather conditions, such as head and tail wind". Notice it doesn't say how fat the pax, how heavy the bags, how high, how fast, how much the reserves are, which statistical variant of wind etc, etc. I suspect that Qantas from its AOC looks at the routes that the A330 family will serve, including the alternates and just how far Qantas fuel reserves can prudently carry the aircraft and calls that total figure "Range". If it turns out that the A330-200 and -300 happen to serve the same destinations and are chosen according to predicted payload they will have the same range in practical airline terms. But for sure salesmen and pilots speak a different language and I know which definition suits me best. My own!

Once you realise engines, airframes and pilots speak different languages (though the words sound the same) the penny drops..."I know you think you understand what you thought I meant but what you heard was not what I said" [To quote Jimmy Gilmour].

[The Other Half]

Thanks enicalyth for going out of your way to make such an in depth reply, that makes a lot of sense, greatly appreciated. :ok:
Can anyone else answer the others?

Cheers :D

[DJohnsen]

Greetings “The Other Half”… As mentioned above there is never a simple answer. Let me give you another "twist" on your question regarding engine thrust. There are two primary methods of measuring thrust on a turbofan engine; One is to assume a specific thrust based on fan speed (N1), primarily used by GE engines. Another way is to measure the engine fan pressure ratio EPR. Previous low bypass turbofan models such as the JT8D used the overall engine pressure ratio (Pt2/Pt7). I’m mostly familiar with the GE engines.

When an engine is being assembled, either from new production or refurbishment, it typically has to undergo a test cell certification run. The various test cells are normally calibrated to a baseline test cell, often a manufacturers test cell, and certain parameter adjustments are applied. When we would refurbish the GE CF6-50C2 engines, we would often see a “thrust margin” in excess of 1000 lbs for a given N1 based on the test cell book value for that specific ambient condition. In other words the engine was producing more thrust for a given N1… You were never allowed to pass an engine with negative thrust margin. This excess thrust margin would also “consume” your EGT margin. This was corrected on later FADEC models such as the CF6-80C2 /-80E1 etc. where the excess thrust could be adjusted with an N1 “modifier”. A plug would be fitted to the EEC to adjust the N1 output value to better match the N1/thrust relationship. Now to make things more complicated, the core also produces a certain amount of thrust… 20 to 30% depending on the bypass ratio… and this relationship will also change as the engine deteriorates. This is primarily due to higher EGT and thus core energy or thrust. The fan/core thrust relationship also changes with static sea level conditions and during flight, which takes me to another variable. GE will typically give you a Sea Level Static Thrust on the data plate, but Boeing for example uses the “installed” thrust at a given speed. This was changed on the B777’s where GE90-90B actually produces around 94K lbs static, but only 90K “Boeing Thrust”. In other words the engine looses almost 4K lbs from static conditions to somewhere around Vr. This was again adjusted on the B767-400 CF6-80C2B8F powered aircraft, which was fitted with a thrust - lapse rate computer…Confused yet...:confused:

Dag

[enicalyth]

Hi guys!

Nice one, Dag, good stuff. And just a wee bit from me on some mathematics.

We have few controls over thrust and power except altering the fuel flow and changing the condition of the air as it passes through the engine. Things such as propeller pitch (!?) or moveable incidence compressor blades but these refinements are usually an automatic function dictated by speed, fuel flow etc etc and are not really capable of independent control by the pilot. So…, taking a gulp.

Three well chosen variables such as pressure, density and Mach No can almost completely describe the condition of the air. I suppose a Mach No, a Reynolds No, a Temperature Ratio, a Gas Constant and a Ratio of Specific Heats would be the biz but if we are interpolating smoothly between two adjacent similar states then three will do. I say “completely” but not “uniquely” because any meaningful triad such as pressure, temperature and velocity will do. If we translate everything to standard atmosphere then pressure, temperature and density become functions only of altitude. Better still.

It is tempting therefore to say that fuel flow, velocity and altitude (which encompasses pressure and temperature) are the preferred set of variables for analysing and predicting thrust/power issues. But even they are not unique and fuel flow as a variable could be replaced by shaft speed or engine pressure ratio come to that.

With three variables it is easy to think of a family of X-Y charts or look-up tables on each of which one independent variable is held constant. But of “n” variables there will be say “q” fundamental quantities meaning that expressions of mass, length, time and temperature can be reduced to (n-q) arbitrary and dimensionless groups. Of these some will be pure gold. Because...

It is then possible to test hypotheses of what is fundamentally an independent variable and what is not. For example if Thrust/Pressure ratio is plotted against Shaft speed/Sqrt Temperature ratio for a fixed altitude and a set of Mach Nos and the curves prove to be non-kinky then thrust depends solely on Mach No and N/”root theta”.

Surprisingly this is true for quite a long way up, ToC for example and well beyond. Reynolds No seems to prove to be less significant than you might think and once you are at a fixed flight level a lot of variables like specific heats etc are, er... constants.

Going on from there it can be shown that for axes of [Thrust/(ambient pressure x ingest area)] versus Flight Mach No. one can draw curves of [(fuel mass flow x heating value)/(ambient pressure x ingest area x freestream velocity)] and permissible turbine tip Mach No. twinned with ambient temperature.

Alas the curves (and especially turbine tip Mach No) are slightly curvy-kinky but as the graphical axes are dimensionless numbers any suitable line regression algorithm is valid. Even an Excel spreadsheet has the power to predict accurately what occurs across a large range of variables.

Next off, if the airframe drag polar curves of CL plotted against CD are simply transformed into curves of [Lift/(ambient pressure x wing area)] plotted against [Drag/(ambient pressure x wing area)] on the y-axis and flight Mach No on the x-axis a not so strange thing emerges - the curves are still smoothly curvy, with minima but...

Because the axes are of dimensionless number, namely Force/Force and Mach Number, the graphs in the preceding paragraphs (or look-up tables) if suitably scaled purely for convenience can be legitimately superimposed without loss of meaning or driven off a common Excel command line or Visual basic macro. So what??

We now have not only the Mach Number associated with minimum drag but also the associated engine parameters without further ado. The same holds for any Mach No. All the engine parameters fall off the graph or are delivered by the Excel spreadsheet/Java Applet. Whatever.

We can easily command the engine performance via a simple computer programme Or else calculate the optimum rated thrust of a particular engine (and its minor imperfections) under test….

It is also the key to many a thorny problem when you have sets of graphs and/or figures for two pressure altitude-temperature combinations and wish to interpolate a third.