Some Questions

[Macgyver]

Got a couple tech questions and I hope I can get some clarification.

Someone posted this one in the fragrant harbour forum and I figured I'd try it out here. The RR engines on CX 744 are RB211-524G/H-T. What exactly does each identifier represent (i.e. what does RB mean? 211? 524? G/H? T?). In relation to this, the 340 engines had a desginator CFM... does anyone know what this represents too?

Also, I was reading how the 777 does not need winglets because their wings are very efficient; however, the article didn't explain what makes the wings more efficient. Someone told me that they use supercritical airfoils, but this didn't make much sense since I didn't think airliners used supercrit wings. The article mentionned something about "triple bogey" wings, but again, it did not explain what triple bogey means.

Finally, the question about EPR vs thrust (if 1.8 EPR gives XXX lbs of thrust when the engine is new, will 1.8 EPR still give the same XXX lbs of thrust 10 years from today?). I have heard conflicting answers on this one.

Anyways, hopefully someone can shed some light here.

Thanks.

[longarm]

Rolls Royce engines are called "RB" after Rolls Barnoldswick the original factory site. CFM refers to the CFM56 an engine built by CFM international, a joint venture between GE Aviation of the United States, and Snecma of France. The CFM56 is used on A340's, A320 series and 737 amongst others.

[rmm]

I stand to be corrected on any or all of these.
CFM = The CF (commercial fan) is taken from the GE CF6 series engines, the M-56 is a Snecma project number used during the design stage. The first dashes are model numbers and are fitted to the following aircraft types -2 DC8/707 (military) -3 737 -5 A320/A340 -7 B737NG. Dash numbers after these are usually thrust ratings and sometimes aircraft manufacturer.
With the rollers I think the G & H are thrust ratings and the T means the engine has been refitted with the Trent core engine.
Hope this helps.

[extreme P]

Here's an explanation of supercritical wings.

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-044-DFRC.html

Triple bogey refers to the gear.

1.8 EPR is 1.8 EPR. Relates to "...will the same N1 produce the same EPR in ten years?" No.

[sudden Winds]

One way of looking at the EPR issue is ....what´s the EGT at that thrust setting, other conditions unchanged..for a brand new engine and for a 10 year old one......chances are the oldest engine will require more EGT to produce the same pressure ratios, thus, same amount of thrust...if we´re talking about identical engines, 10 years apart, then I think if 1.8 epr is achieved, thrust output will be the same.but the engine will need more fuel, more temperature to produce it....
but...I could be wrong...it´s been known to happen...

[Old Smokey]

Macgyver,

No-one seems to have addressed your third paragraph -

"Also, I was reading how the 777 does not need winglets because their wings are very efficient; however, the article didn't explain what makes the wings more efficient. Someone told me that they use supercritical airfoils, but this didn't make much sense since I didn't think airliners used supercrit wings. The article mentionned something about "triple bogey" wings, but again, it did not explain what triple bogey means."

Most modern airliners have supercritical wings, I think that the A300 might have been the first, and that's getting old now.

I suspect that your informant was referring to "triple bogey" undercarriage, the B777 has 3 pair of wheels on each bogey, not all that common on other contemporary aircraft.

Regards,

Old Smokey

[DownloadDog]

777 Wing

As I understand, the B777 was Boeing's first aircraft designed with computers. As such, they believe they created a wing with an eliptical lift distribution (which produces the least induced drag) using varying cross-section and washout, and hence no need to use winglets (which reduce induced drag).

All airliners use supercritcal wings nowadays to give low drag in the transonic region by keeping the shockwave as far back as possible on the upper surface. This is done by keeping the upper surface relativelyt flat so that the air is not accelerated. As a result, the coefficient of lift is reduced (due to not much camber). To overcome this, the rear part of the wing has a cusp to regain some of the lift lost.

EPR

EPR or Engine Pressure Ratio is defined as the Jet Pipe Exhaust Pressure / Compressor Inlet Pressure. As the area over which the 2 pressures act is unlikely to change with engine life (Thrust = Pressure x Area), the same EPR should give the same thrust despite age. The older engine is likely to need more fuel and will run at a higher EGT as it will be less efficient.

[LoadMan]

As I understand, the B777 was Boeing's first aircraft designed with computers. As such, they believe they created a wing with an eliptical lift distribution (which produces the least induced drag) using varying cross-section and washout, and hence no need to use winglets (which reduce induced drag).

I assume Boeing had the ability to make an elliptical lift distribution before everybody got a computer. But a new wing normally doesn't need winglets. It is interesting when the weight increases and the wing has to fly at higher lift coefficients (thus higher induced drag).
The tendency by some manufacturers to fit everything with winglets is questioned sometimes. After all, the normal operational benefit is quite small.

[Flap Track 6]

Someone posted this one in the fragrant harbour forum and I figured I'd try it out here. The RR engines on CX 744 are RB211-524G/H-T. What exactly does each identifier represent (i.e. what does RB mean? 211? 524? G/H? T?). In relation to this, the 340 engines had a desginator CFM... does anyone know what this represents too?

RB means Rover Barnoldswick

211 is the RR engine number

524 is the model number

G/H is the model revision (G and H are physically identical)

-T means the engine has been subject to the optional upgrade to fit the Trent HP system in place of the original to provide superior performance retention.

All RR engines have an RBXXX engine number. they may not be known generally by that designation, but they will have one.

CFM is a company owned by GE and Snecma. The name 'CFM' doesn't mean anything.

Finally, the question about EPR vs thrust (if 1.8 EPR gives XXX lbs of thrust when the engine is new, will 1.8 EPR still give the same XXX lbs of thrust 10 years from today?).

Yes.
When the engine is in service, its performance will degrade and you have to run it hotter and faster to maintain the desired output. This continues until you run out of temperature margin and the engine will need to be overhauled.

[barit1]

re EPR - the P&W engines use a single EPR based on core tailpipe pressure. This is a holdover from the pure turbojet days, when it made good sense - EPR and thrust were truly analogues of each other.

On big fans, however, the bulk of the thrust comes from fan airflow, and with deterioration over time, core EPR is no longer the best measure of thrust. RR recognized this and introduced Integrated EPR (IEPR), sort of a weighted average between fan exhaust and core exhaust pressure ratios.

GE & CFMI (BTW, rmm has the etymology of CFM right) use N1 for thrust setting, and most operators seem to find it superior for both operational and maintenance reasons.

[GlueBall]

The CFMs can also be found on the DC8-70 series and KC135s [707s].