CFM VS IAE A320

[vilas]

CFM VS IAE Engines A320
I find the following different characteristics between the two engine types.
IAE engine takes longer to start than CFM.
IAE engine as you open thrust for take off appears bit noisier than CFM.
IAE has fan flutter that is why there is KEEP OUT ZONE between certain RPM when applying take off thrust while there is no such thing in CFM.
IAE engine for circling approach OEI and flap3 is seven tons more weight restricted than CFM for circling.
IAE engine aircraft have Flap full with flaps at 40 while CFM engine aircraft have flap full with flaps at 35. I don't know is it because engines size or shape.
The question is with all this why would anybody want an IAE engine? Fuel efficiency may come to mind but these days nobody will buy fuel inefficient engine so they must be evenly matched. Is it price or any other advantage which overrides all this?

[pattern_is_full]

Well, you list characteristics important to pilots - but airlines choose engines based on other factors as well. Up-front cost, fuel efficiency, maintenance costs, commonality with other engines in their fleet.

The IAEs are (or at least were - competition means this is always a horse-race) slightly more fuel efficient (5% or so). But apparently that only becomes significant on longer cruise segments. So airlines with mostly short routes may prefer the CFM, while the V2500 may be preferred by airlines with mostly longer routes.

The IAE option is preferred in Asia - and surprise, surprise - the IAE consortium includes Japanese manufacturers. Never discount the role of national or regional pride (and jobs), when other factors are minor. BA goes with the engine with Rolls-Royce content, but the rest of Europe seems to prefer the CFM (US/French manufacture).

AFAIK, purchase costs slightly favor the IAE - but in any given deal, there is always some wiggle-room in price to close a deal.

AFAIK, the IAE requires more complex overhauls, but less frequent ones. So again, a particular customer's operational pattern may have an influence.

[Coldbear]

Hi Vilas,

Would you mind elaborating on this part:

"IAE engine aircraft have Flap full with flaps at 40 while CFM engine aircraft have flap full with flaps at 35. I don't know is it because engines size or shape."

[vilas]

Coldbear and pattern_is_full
It is as I said, in FCOM it is written that in IAE fitted aircraft the flaps are extended to 40 in full position while in CFM they are extended to 35 it is not written as degrees.
OEI circling seven Tons handicap is big. It should be the extra drag when flaps are lowered. Are flaps of different design required in IAE aircraft?

[tubby linton]

What figures are you coming up with for the OEI circling ?
For a standard A320 cfm I am coming up with 77t at 15c seal level (Sharklet A320- 78t).
An IAE powered 321 gives 76t but we also have some newer A321 which give 80t

IAE powered A320-70t

Is the greater flap setting because the IAE has greater residual thrust than the CFM?

[oldchina]

I have a very old and admittedly vague memory of this.
A320 initial (=CFM) flight testing showed up a vibration (can't remember where) at 40 flap that wasn't there at flap 35.
That didn't bother anyone so it was certified to 35.
The IAE flight testing followed the original CFM pattern and, guess, no vibration at 40. Bingo!

[G.Green]

I find the CFM very touchy when taxiing to stay within the 40% N2 limit whereas the IAE is very easy. I believe some airlines choose the latter engine for economic and local engineering reasons.