WojtekSz

No. Not "fluid" drive in the sense of "Hydraulic", where the medium is contained. The Gas Path does have open ends at either end, so technically it does not qualify. In addressing this problem, the "Rigid Coupling", it isn't relevant, imo. The Vibration (causatuve of rupture) had alot of time to act on the weak portion of the design, even at that both Disc fractures occurred on climbout, and one of the Powerplants was a TRENT 700. The identified problem was not embraced by RR at any time, whether inadvertent or some thing more diabolical. They have the benefit of the doubt, as far as I am concerned. That covers the Design, Test, and Certification modes. What the firm did after the Burst/Explosion is inexcusable, keeping a client (QANTAS) in total darkness, while they casually (and cynically) completed newer Airframes for delivery. They allowed the Engines to "Time In" because they had duped EASA into relaxing the Inspex. Even in that, they almost made it.

They will correct, and move on. Hopefully, the fallout from their self sabotage will hurt deeply, suffiicient to caution themselves and others against playing Roulette with the lives of paying innocents.

Derg:
using the finite element method scientist/engineers can predict mechanical beahviour of any part in known conditions. Actually they can model it according to known and proven cases. Problem starts when we try to predict/calculate mechanical behaviour in the unknown/unpredictable/non-linear situations like worn bearing where actual 'worn' may have very different meanings including radial and/or axial play with different dampening properties. This calculation comes even worse if we get closer to loose spline coupling - i would bet a pint of guiness that there are no actual models for calculating behavoiur of loose spline couplings - simply because these couplings are designed to STAY and not to get LOOSE.

Once i heard a story of an experienced machine-tool designer who used to say: ok, so we have built it. Let's start it and see why it doesn't work.
;)

Bearfoil:
do i get you right: technically they could have made a mistake but instead of making it clear they kept on selling the stuff hoping to get away with it?
Do you believe RR have already identified the real cause and having it fixed even before the first engine exploded, just wanted the market to stay in the dark for PR or just any other business reason.? The Greed in action?

WojtekSz

IMO Rolls had identified the problem prior to the AD. They negotiated a schedule of inspections meant to monitor the wear on the Splines at Abutment Face. Clearly the AD took into account the actual cause of the problem, for goodness' sake, they approved the Fix!! The "C" modification was to have mooted all concern, for the Engines under the AD's demands were to have been pulled from service so the Power was "Exonerated". The Explosive Burst put everything into limbo. It became clear Rolls was furnishing the new engine to Airbus for facilitation of delivery of new aircraft, whilst the 972 was on wing, subjecting each flight to hazards at clearly, (Demonstrably) unacceptable levels.

How could RR not have known the source of the trouble and then claimed the "C" mod was sufficient?? Magic?? Guesswork?? Chicken Guts??

The relaxation of the inspection regimen is on the EASA's shoulders solely. They put their faith in RR and their bluff, as RR cynically advantaged the gullibility of the regulator, and their Prime client for the TRENT 972. (QANTAS).

It turns out the C mod is under the gun, and QANTAS is taking their sweet time approving LAX SYD flights at max thrust (max TOW) Where does this put the TRENT 900?? Do-Overs?? How about, 'once burned, twice shy'.......

We could all do with a pint of guiness right now I think .. but as yet it is somewhat premature - there is still much to be resolved.

But was there ever a pprune reunion? There's a long way to go yet, but it's a cool thought.

Not only counterfeit parts from bogus suppliers, but substandard parts from "approved" suppliers.

There's been a recurring problem - going back decades - with fasteners that look OK, dimensionally OK, static strength OK, but they don't meet the fatigue strength spec. It's affected all the engine mfrs. and tinknockers at one time or another. It results from cost-reduction shortcuts at the suppliers' shops. :ugh:

FAA has cracked down - even the FBI was involved - and the problem has quieted down from its worst days.

DERG

Oil Consumption
For engines that use labyrinth seals, oil consumption is largely dependent on vent air-flows and oil temperatures. As the seals wear, oil consumption rates go up. Depending on the engine design, typical consumption rates would be in the range of 0.05 to 0.30 gallons (0.19 to 1.14 liters) per hour.

SFC - Trent verses GP

One of the things that strikes me on the SFC situation is the difference between a well designed two spool engine verses a three spool design. IMO, a bare two spool engine in a test cell will have better SFC than a three spool RR engine every time. The reason has to do with the more efficent HPT of a two spool engine. It is a different story on wing. The shorter three spool engine in a shorter nacelle makes up the difference of SFC shortfall in the test cell. The reason is less aircraft drag. However, looking at the Trent 900 & the GP7200 on the A-380 wing, a longer nacelle is used for both engines and the shorter engine advantage of a three spool engine is lost. I do believe, at this moment, the GP7200 does have a SFC advantage over the Trent 900 and RR is working the issue. This may also be an issue on the Trent 1000 verses the GEnx on the B787.

Just some thoughts,,,

DERG:
I honestly do not recall any oil consumption figures, other than it might be comparable to a Continental A-65 in my old Taylorcraft.

The vent system design has a lot to do with overboard oil loss. A good centrifugal air-oil separator (sometimes built right into the main shafts) can make a big difference. :)

Certainly excess oil consumption can indicate internal problems that need addressing, and not neglected! But do we know for sure the sequence of events in the present case?

It reached a peak about two-three years ago.
I personally watched the FBI raid an aircraft repair station, haul away many records, two helicopters...and three persons...in cuffs.
The FAA and FBI appeared to mean business, as in...lock 'em up.

Oil consumption is a maintenance issue and rarely a safety issue beyond being an indicator needing other parameters to be considered (vibration, Oil temp, EGT)

Oil leakage can be a flight safety issue if you don't know where the oil is going. I've seen some operators who added quarts of oil at every major turn, figuring that next week they could get the engine changed out. Only they never made it to next week before they blew a turbine out the side of the engine. On the other hand when I was aboard one of these operators on a long haul over water, the pilot got a low oil light and turned back. Sure enough the ground crew pushed a stand up to the engine as we, the passengers watched, and there on top of the stairs was a full case of oil.

Ah but it was good news, they poured in the oil and motored the engine and presto out came the oil from a blown CSD gasket (external from the engine). That confirmed where the oil had gone! So they replaced the gasket and we were off again for our flight. Had they simply replaced the oil, I would have gotten off (I did chat with the capt about this :)

Most of the oil consumption is in fumes out the breather and thankfully the pressure balances do a good job of keeping the oil out of rotor-disk cavities. The problem is when wet oil finds it's way into a rotor disk cavity where it is often hot enough to light it off.

barit1 DERG

The Centrifugal Breather is located in the external gearbox. It is on the rear face of the gearbox between the oil pump and the Fuel Pump (HP). Aerated Oil, returning from the bearing boxes via the vent pipes and scavenge system, enters the oil tank, where it de-aerates (partially). The oil is sent then to the Centrifugal Breather where it attempts to pass through the rotating retimet, but is centrifuged out, to return to the Oil Tank. The air is dumped overboard. The Oil returns through the Oil Scavenge Pump Elements.

There is one piece of evidence to what is the root cause of the oil pipe cracking which has not been debated here. In the court filing that Qantas filed there is the following statement (from flightglobal http://www.flightglobal.com/blogs/wings-down-under/2010/12/fixing-rolls-royces-disposable-a380-engines.html)

This seems to indicate that the pressure causes movement of the structure where the stub oil pressure pipe enters into the bearing box. My conclusion is that on the A and B engines the support structure between HPT and IPT is simply not strong enough to stop the bearing box from moving at max thrust to such a level that it affects the pipes fatigue life. The solution is a strenghtend support structure. It is a big operation and explains why in the A version the problem was dectected but to late to fix it for production of the engine, the B mod is a reinforcement of the original structure and the C mod is a redesigned support structure that fixes the problem (but had to be extensively tested before applying it). The flight blogger concludes that the oil pipe needed strengthening, this is an easy fix and should not have required 3 different versions of the engine therefore I don't think this is the fix in the C mod. Further the crack is where the stub oil pipe meets the bearing box, if the box is moving a stronger pipe is not the fix, you need a more flexible and durable pipe but primarly a box that is not moving.

So what is the communities thought about this piece of evidence;)?

Well, I am glad to see that after that excursion into oil related items we have come back to technical questions. Oil supply, that is my strongest believe, has never been a problem in this engine failure. The monitoring readings published by ATSB clearly show that there was sufficient / normal oil pressure on the feeds untill the very last seconds of the usable life of that engine.
So now the question should concentrate on what has, respectively what will RR change to make these Trents as healthy as planned ?? A lot of approaches to the problems identified in this thread are thinkable, to start from cheap to expensive:
usage of sturdier oil feed tubes? re-desighn of bearingchamber and use of stronger bearings ? re-desighn of supporting structures ? re-desighn of shafts ? or the finite decision, a re- desighn of the entire core engine ?
Would be interesting to read if anywhere a leak has opened in that wall of silence RR is hiding behind ?
I think the basics of that engine are delicate and the craftsmenship with which the modules are assembled and put together are out of doubts. So what is left ?? A real engineering fault ? Or just a too early stop in development and testing, ordered by the beanscounters ?? Anyway, as it looks something very substantial must have slipped through the controlling systems! Probably just an internal communications break / interruption ?? Probably a set of wrong priorities ?? Looking foreward to more and substantial information!!
Jo

This is off the main line direction in this thread as to the whys and wherefores this engine seems to be suffering from some "built-in" shortcoming(s), but I was wondering if one of you could address a few questions as to the failure mode of the LPT disk itself. As a non-engineer, I've been musing about the "normal" operating speed of these turbines vis-a-vis the rotational speed necessary for self-destruction. (I'm retired... and I can afford to play golf and muse)

My questions start with a very basic one, which is, in the quest for efficiency and low mass, are these units designed to spin in a near supersonic regime, or do they experience tip velocity excursions approaching SS, say at the highest power settings, like N1 does?

Its moot to the cause of this engines demise, but, regardless of whether the LPT may or may not ever operate near the "shock" regime, at some point after the output shaft separation, and prior to disk impingement with the stators, could the free wheeling disk (blades) have been almost instantly accelerated past Mach 1 prior to the disk burst point? If so, could the blades have failed first from "swallowed shock," their sequential departure thus initiating intolerable out of balance, and, therefor, premature disk rupture?

If management of near supersonic blade tip velocity is, in fact, a parameter in this engines software, its actions in this regime and any harmonic issues impinging on the bearing box would have been completely addressed... No surprises there, right?

My, oh, My! You all have an extremely interesting discussion on-going here.

Ferpe

Good post!:ok:

You may possibly hit the "Mods" (nail) on the head.

Re DERG's post # 296 Spline Fretting and stuff
 

Hopefully some of you gentlemen can advise me, re, on page 3 of the PDF file

http://workspace.imperial.ac.uk/medy...ng_Trb2008.pdf

the illustration shows an " External spline run-out " on the external component. Is this the " 2.65 mm spline crown " dimension as mentioned in the original AWD, re the spline wear problem and is this a result of uncontrolled/unexpected wear of the thrust washers from vibration/harmonics ? Is the disintegrated turbine disc the equivalent of the " Internal component " ? I appreciate that this drawing is not type specific, but I have been confused as to what the 2.65 mm referred and there were no mentions of which axial faces were wearing.

Also, is the helix on the splines designed to continually apply the thrust loading towards the thrust washers ? Thank you..

The "Tube" is not the problem :ugh:. It is the result. No matter the cause of the damage to the "Stub". Misbore or Vibration, Box movement (!), etc. The Support Structure is insufficient. In other words, the Core has mass issues, as DERG points out (as have I).

The Splines too, are not the problem. They are also a result.Oil problem? Certainly, but again, not the cause.

If the Splines were the only issue, There would be no AD, there would have been a revocation of the certificate. "Inspections only" certify that both Rolls and EASA were cognizant of the procuring cause. Again, Simply Certifying the "C" Mod as curative means that the source of the problem was KNOWN, and from the beginning. We do not know if the "C" is the complete answer, simply because QANTAS is not flying it, nor have the EASA certified the Engine as yet, UNDER THE ORIGINAL CERTIFICATE. Inspections are still required.

Think about that. This Engine has had two rebuilds since approval, and still the Engine is not released for its predicted service life. The Engine is still in TEST, can one see it any other way?? Either the engine itself with the C is complete, and needs no re-cert, or it is not, and its reliability is subject to doubt.

10 hours over water. That's the "good news". The bad? Ditch, Crash, loss of life.

Vibration, Resonance, lack of sufficient mass, destructive rapid wear. This engine had an oil fire on the stand, Remember? What happens when the Stub (IP) shaft is severed next time? At some point, the word Burst will have to be retired. It is insufficient to describe what may as yet prove out.

radken

\

Happy to see that you are at least prone to asking questions before forming ill advised opinions:ok:

You questions about speed have two parts imbedded in them. One part has to do with aerodynamics which of course has something to do with shock waves. The secoind part is a structural question which has a great deal to do with stress and strain.

Talking about speed of sound at the largest diameter (of a rotor) in the fan is easier to comprehend since it operates at a more familiar ambient temperature and pressure. On the other hand deep inside the engine the pressures and temperatures are quite extreme so the speed of sound would be far different. Simplistically the engine revolves around a defined cycle and as such the designer goes for the most effeciency per pound of thrust per pound of fuel. Thus one designs the compressor to operate at the highest pressure that can be obtained without tip stall or any other perturbation you might want to call it, including shock waves etc. The turbine driving the compressor had about the same tip diameter so its surface speed at its tips are about the same.

The bottom line after this is to ensure that centrifugal stresses are kept within an acceptable envelop with substantial margins against combinations of overspeeds and vibratory modes that might combine and produce rapid fatigue cracking. This is basic regulatory stuff and codified in the design regulations.

The problem comes in when the operation of the engine is outside of the certifcated conditions. Either from mis-operation of the engine (including maintainence) or mis-manufacturerd parts.

Vibratory modes are predictable and calibrated via experience including the hundreds of hours in development testing before the engine is certified. So obviously no mis-designed or undertested severe failure conditions are expected in service before any recommended maintainence cycles. assuming of course no mis-operation or mis-manufacturerd parts.

I've tried to keep this brief and cover some nuggets of your questions.

Just one editorial comment; don't confuse low mass with low cost or low safety margins. Margins of safety are regulated and it's stiffness and dampening that make it possible to design for light weight and still meet safety margins, else all the plumbing visible around the outside of engines wouldn't be called tubing but would be made out of thick steel pipe

lomapaseo

"Vibratory modes are predictable and calibrated via experience including the hundreds of hours in development testing before the engine is certified. So obviously no mis-designed or undertested severe failure conditions are expected in service before any recommended maintainence cycles. assuming of course no mis-operation or mis-manufacturerd parts."

Problem. That is not ill-informed, but it is wrong. It is the casual expectation of results that gets engineers into trouble. Most vibratory modes are known, especially when building a "replica" of a known model (TRENT). The 900 is quite different from the others, in RPM, discrepant RPM, and bearings. I predict it is exactly what you casually discard that is the problem, just as you have predicted that all vibratory modes are predictable.

Trent rpm limits
 

MAX PERMISSIBLE ENGINE ROTOR SPEEDS
(Based on the limits stated in FAA TCDS for RB211 TRENT 500-series and 900-series, % converted to RPM)

.........Trent 500 ... Trent 900
HP ...... 12954 ....... 11932
IP ......... 9045 ......... 8117
LP ........ 3608 ......... 2787

Are these the differences you are referring to?

Yes, just those. Keep in mind, the QF32 #2 IPT failed at a Thrust value of 72,000 POT. This power is commanded by the added Data Entry Plug, (DEP). The Max RPMS are limits that pertain to the base engine; by claim, the 900 can produce 80,000 POT. Where is the extra Power derived? The failure of the EEC to control the first bump of Added Thrust either in not sampling the "Oil Fire's" production of wavering power, high temps and Oil Pressure anomalies, or over "limit" RPM shows us that the engine is not dependable at this very first Power increase (72). This engine is a different "TRENT". The discrepant RPM limits are evidence of this.

lomapaeso

To add to your explanation to radken: Assuming the disc began to stretch, because of overspeed and presence of higher than designed for temperatures in the bore area, the turbine blades could have started to unlatch at the tip shrouds. Since the tip shrouds provide blade dampening, it would have been the beginning of the end for the turbine blades very quickly, even without any contact with other adjacent components. The extreme unbalance created would be catastrophic to the disc already operating beyond its design capability.

Turbine D

It is an assumption that there was Stretch due excess Heat. Would not the Disc fail instantly even at in limit RPM once the Drive Arm fractured? Also, Contact of any description IPT/NGV Platform would be exactly simultaneous with aft movement of Shaft??

Given the AD's, and their warning of Metal/Metal with aftward drift, isn't the better assumption that the Disc Fractured after contact with Stationery Parts, melted, Disintegrated, and caused burst?? I see no need to entertain Fire, or Blade shear to explain this Engine Explosion. The simpler explanation is generally assumed to be the more likely cause, No?

Applying Occam, then, we can simplify the assumed failure to include no fire, no overspeed (save after fracture), and no need to index the Failure with cockpit data (displayed), at least insofar as it is not immediate in nature, and relies on the EEC, which failed to control the engine in the first place? This demands on actual events in the IPT locale, and taken in sum, they argue against a failure due to Fire.

In this way: Any fire would need time to act on the IPT bore. The more logical assumption is that the bearings (balls) wore beyond their ability to prevent axial (aft) movement, and the Drive Arm was pushed into the Stator Ring. The ten Radial Struts here, were under suspicion via AD targeting their Bolts on the case. They were to be inspected during Strip or borescope. The Splines, oddly enough, at this point, though worn, may not have actually caused the failure. The Splines were subject to inspection, but were just canaries in the mine; What caused the Spline wear also caused the Bearing wear, also caused the Oil Problem, etc.

So we take serious note of the AD's in the Burst, or we rely on The Manufacturer's claim that the Burst was caused by Oil Fire. It is more or less that simple, IMO.

Good grief

Thanks DERG. It looks like a good read. I notice the paper releases the TRENT for Flight. Let us hope they mean TEST Flight. When modelling, it is precisely the novelty that Cannot be seen. Modelling relies on abstract Thought, it does not think, nor does it conclude. IMO. It is generally the "novelty" that kills when it strikes, having no follow on Fail safer. again, IMO.

bearfoil:How true.

There's a T-shirt somewhere that says " G*d laughs at numbers ". Not only in turbomachinery, but in AGW.

DERG

A good find and good read !

Here is something that the FADEC/ECU didn't do on QF32's Trent 900 engine #2 six years after this study:

A three-speed model of normality was able to identify as novel an event which gave rise to diverging speeds prior to automatic shutdown of the engine on the test bed.

Humm, what happened?

Bearfoil
My Quote:
In this post I was responding to another quote on how the IPT blades could have failed without physical contact with other neighboring components. It was not an attempt to explain the total failure, where it started and how it progressed.

But, in that you brought up the subject of the disc:
Take a look at the photos of the recovered section of the IPT disc in the ASTB report. In the fracture surface photo, note the structure close to the bore on the forward side and the shape of the bore surface forward to aft.. In the photo of the rear face of the disc, note how one turbine blade root seems firmly in place, but another has a significant gap present in the corresponding disc slot and there is no indication of metal to metal contact at the disc rim or blade slot area. Also note the ductile bend of the power arm drive where it is present.

Now think about something, what are the two elements required to permanently form or deform metal where the normal material ductility is less than 10%?

Just tried to look at the photo in the ATSB report in this topic when it was in Rumours and News.
Couldn't.

Only 2 pages available in R & N .

Am I missing something?:confused:

Flapping Madly

Try this link, then click on the link to download the full report.

Investigation: AO-2010-089 - Inflight engine failure - Qantas, Airbus A380, VH-OQA, overhead Batam Island, Indonesia, 4 November 2010

flapping madly

I'll send along a pdf in a moment.

Turbine D

I doubt there was fusing of the Metallic bits at the Rim (IPT). First, the speed at which they travel, and the relatively low mass they contain (relative to the Drive Arm) don't allow for time on station to effect a puddle. The Stator Vanes Platform describes a cylinder (barrel) with only its rim effacing the IPT Rim/Blades' roots. The Rim(s) are closer to one another than the Drive Arm/Stator Ring. Thus the Blades would leave, concurrently with the disintegration of the Platform (and its aft fixed Vanes), prior to DA melt. I feature the Drive Arm slipping aftward until the IP Rim contacts the NGV Platform. This conflict shatters the platform as the Blades unroot. The Drive Arm continues aft into the Stator Ring, where melting and Fracture occur simultaneously. Once fractured, the Wheel itself splits in threes, and blows out the case. Loss of Blades cause Stall (HPT)(Bang 1), and the blow out of the case causes the second "bang".

The metal deposition at the flaring Bore, comes from the melted remnants of the Drive Arm Join with the bearing sleeve. The "Foldback" ( of portions of the edges of the Drive Arm) have to do with your poser re: insufficiently ductile metal permanently deformed??

I'd have to say two elements needed would be "Heat, and Hammer".

We need to remember that the supports that mount the Stator Ring to the Case were a constant problem, vis a vis the fastening bolts. The bolts were chronically coming loose..A guess at their looseness would be dramatic vibration in this area.

Agreed
 

Yup..the thing tore itself apart. Maybe the fire lasted a second or a few, the dark stains on the wing structure could be oil mist or carbon soot from a fire. Unless we could get in there and smell it we don't know. But the tear on the drive arm looks like a plain tear. Amazing the thing did not continue to burn, against the odds I would guess.

What I wanted you to look at in the photo, Figure 15, Page 21, was the fracture surface near the forward face of the disc (golden color) very close to the bore. enlarge it. Look at the stepped lines that have been created in that area and the directional orientation. It could be these lines represent plastic deformation (slips). You answered the question correctly, Heat and stress (rpm's) combined. It is the only way the drive arm could bend that much without snapping. Also, there is no sign of rubbing on the IPT disc rim, meaning this portion of the disk, at least did not contact the stator ID band behind it. My thought is the disk tore out of its fastening mechanism, at the 580 power drive arm bolt holes because of plastic deformation (stretching). Also, it seems there were 4 fractured pieces of the disc. The three that were not found went out over or under the fuselage to the right according to the exit trajectory sketch in the report. The found disc piece came out of the engine to the left based on where it was found according to the labeled map.

Turbine D

Hi. From the larger (135 degree) piece of Turbine Wheel recovered, I note the lack of flange, (bolt area). Instead, there is what EASA called a circumferential Fracture in Edelweiss, Miami. So I conclude the Drive Arm remained intact forward of the Wheel bore where it fastens to the L shaped Bearing sleeve. The Shaft flange makes up the aft portion of the bolted together assembly. It resembles a sandwich, in section.

We have made note of the molten metal "plated" to the flaring portion of the Wheel bore, so melted metal is known, and the folded over remnant of bore indicates your sub-ductile peening of this area. Also, there is Metal "Spatter" mentioned in the ATSB report, located on the aft face of the Turbine wheel. Your note of the lack of heat rub at the rim demonstrates the lack of effacement with the Stator Platform, as the Platform effaces the Blade roots, not the rim of the IPT. Here we are again at "Push and Shove" of the IPT Blades out in the forward direction from their fir tree roots, as the Wheel slips backwards into the Plane of the Stator Platform. If we find a Blade from the IP Wheel, I think the effacement Blade to Platform will show, and may even show molten metal.

I've yet to look at the Steps in the Wheel. Am I looking for "Spiral" or "Radial" stepping?? While we are at it, please look at #16. The segment of NGV Platform facing the aft Rim of IPT shows clearly the tracks of circumferential contact at the effacement IPT Wheel Rim/NGV Platform. It has characteristics of patent wear, not critical failure. The outer surface of the NGV Platform and the edge of the Platform itself show where chaotic contact Blade/Platform may have separated all the Blades. Note the missing metal where the Blade roots contacted the Platform??

This may sound farfetched, but so is IPT Burst. In looking at the fracture face of the recovered wheel piece, I note a layered area sub surface, with the surface seemingly uniform above it. This obviously degraded area looks like patent damage to me. To You??

The trajectory of the found piece was obviously eastward. I have a problem with the "drawing" of the location of the missing pieces in the core, then out the case and "up". The origin of the pieces are shown above or below the longitudinal axis of the engine. If the piece, for instance, shown above the L/A was a part of the Wheel, it would not have exited to starboard. At this point in the core, its rotation is clockwise, and therefore it would have exited to port. Now this may be picky, but it is misleading. Also, no one knows for how long the pieces remained inside their circular prison, (case). They could have rolled around its perimeter and exited anywhere.

Hazelnuts39

Sorry for taking so long. By "baseline" I mean common rated thrust, in this instance Maximum Continuous Thrust for the 900. Upgrades are for thrust that is available short term? So here, at burst, the 972 was not performing any different than a 900 would be. Maximum continuous thrust in the climb, or some lesser value?? What is different? The DEP makes available for short periods augmented thrust from the same core. The restriction on this excess thrust is the crux of the discussion, imo. Either it is a proven design, or it is not, and if not, it has no place bolted to a wing, only to a stand. So my question is as before? Where does this rather substantial thrust come from? The same Core? At the same RPMs?? This implies a merely "derated" 900, and an "augmented" 972?? There is to me a discrepancy.

The engine is certified right up to 84 so the 72 version should have been "a walk in the park" The thrust comes from the fuel and that depends on the central processor.

"Either it is a proven design, or it is not, and if not, it has no place bolted to a wing, only to a stand."

This 900 engine was designed to be experimental in service: whole raft of documentation tells us just that. Of course it had no place on a civil aircraft. No probs in military applics: see here

http://www.robots.ox.ac.uk/~davidc/p...eaerospace.pdf

Hell of a lot of work to do by RR and Airbus. Flight Aware has not published any flight times on the QFA12 service, probably cause they are only using minimum throttle and carry less payload. Not all the flights are A388s either, my guess is they send the B74s when they need to carry a real load. No wonder the Qantas B74s are munching engines, the are working hard!

From post#317:

"The focus of ACARE was to set a strategic research agenda aimed at meeting the environmental challenges set out in the European Aeronautics Vision for 2020. As a result, Rolls Royce (RR) and other companies in the aeronautical industry were faced with challenges including reducing fuel consumption and CO2 emissions by 50%, reducing external noise by 50%, reducing NOX emissions by 80% and reducing the environmental impact of manufacture, maintenance and disposal of aircraft-related products. At the forefront of responding to ACAREs pan-European research challenge is the ability of companies such as RR to investigate, through high-performance computing (HPC)-based simulations, innovative methods of design and operability of aircraft products."

A roundup flyer sheet:

Systems Analysis, Modelling and Prediction Group

Thats the design goal. Therein lies the clue to the T900 and its woes.

TURBINE D Yes I see the part. That looks like it was in a plastic state when it parted. Yes a fire.

When I was trawling through the internet I came across a very few references fom the USA to "modelling", I mean design modelling as applied to aerosapce engine.

The few that I did find were mainly published by NASA.
They were VERY conservative and made it clear that "a model" was just that "a model".

Would I be correct in thinking that the USA prefers the known to the unkown when it comes to aerospace turbofans?

I would think that the 'baseline' is the variant with the highest thrust rating, i.e. the RB211-Trent 980-84, sealevel static TO thrust rating 84,098 lbs, flat-rated to ISA+15C. The thrust levels of that rating must be achieved without exceeding operating limits of RPM and TGT. The manufacturer selects rating(s) so that they they have some margin relative to the operating limits. The lesser ratings are 'derates' and have greater margins than the highest rating. In TO ratings Trent 900 the various ratings are shown at the flat-rated temperature. The dashed line shows schematically the thrust corresponding to the operating limits, whichever is most limiting. The line is drawn arbitrarily, because the documents don't tell us where it lies. It's actual location will be different from engine to engine, and the margin will reduce as the engine deteriorates during its service life.

Prior to certification, proof of integrity of the engine operating at the declared operating limits must be provided by analysis, component testing and, finally, by a 150 hr endurance test which represents an accelerated life cycle of the engine. 'Modelling' is a design tool, not proof of compliance with airworthiness standards.

Another NOVELTY
 

The engine with a 70 cycle lifespan. Bettya that was not in the sales presentation to Quantas! Thats the life RR gives the 972 in Qantas operations.

Some of you may think that a bird strike is a "novelty event"..

Well this author does too...been waiting for this! :rolleyes:

http://www.eng.ox.ac.uk/samp/pubs/clifton_transfer.pdf

Sleep Well!:ok:

HazelNuts39

Nomenclature. It is important I understand your description. A "Baseline" machine to me is its original "Design". One seldom starts with the nephew and progresses toward the Grand Uncle. So it seems to me counterintuitive in the least.

I note your numbers and explanations, and I believe your representation of the 900 family. So I would ask, if the most powerful powerplant has the same construction, core, wheels and limits (Temperature and RPM), as the least powerful, then this appears rather strange. Airbus "found" 6k lbs. of extra weight on the whale, necessitating more thrust available at Take-off at MGW. The result was the 972, I believe, a hurried iteration with a new Data Entry Plug. Why on Earth develop an engine with X Thrust, then derate (make unavailable) its Power??

Can you help me out with a more basic explanation, then?

thanks

bear

Bear
 

Howdy!:cool:

Airbus found 6 metric tonnes of over design mass on the airframe which is closer to 13 000lbs

Greets!

Hey take a look at this about half way through you can play with the cross section of the shafts...amazing torsion these are under...amzn.

http://www.eng.ox.ac.uk/thermofluids...453,18,Heating from Seals

Perhaps you should ask RR plc. I suspect it's just marketing strategy. The market is willing to pay a certain price per pound of thrust, so the lower rated versions probably have a lower price tag, as well as lower maintenance costs. The higher rated versions provide 'growth potential'.

EDIT:: Any proof of that? It is not the first engine that RR has developed, nor the first application in a new airframe. Ever heard of a completely new airplane that didn't turn out heavier than planned?

regards,
HN39