View Full Version : IAE vs. CFM

1st Mar 2001, 01:42
Hoping the collective brains and regular contributors can help me out here...

Relates to the subject of IAE vs. CFM on the A320 with respect to airline economics.
Yawn !!
As i understand it, the CFM's burn more fuel, but have lower maintenance costs.

This would suggest to me that airlines based in the Middle East would be best suited to CFM's. (fuel being nearly as cheap as water). Yet most airlines down there use IAE.

I heard a while ago that IAE operate better than CFM's at higher temperatures, but cant for the life of me remember why that was.

Some stats
Tref ISA+15
Tmax ISA+40
Tflex ISA+45

A320231 (V2500-A1)
Tref ISA+15
Tmax ISA+40
Tflex ISA+46

Tref ISA+29
Tmax ISA+40
Tflex ISA+53

A320232 (V2527-A5)
Tref ISA+31
Tmax ISA+40
Tflex ISA+55

Clearly the Tref, Tmax and Tflex aren't determining factors. What other differences are there ??

Many thanks

1st Mar 2001, 03:22
The choice of engine is more than just a fuel consideration, the difference between the engine types could be 0-5% depending on the operation.

The CFM engine is lighter, burns less fuel lower (SFC of 0.2 lb/hr/lb lower), produces slightly more thrust in climb, however has a higher SFC 0.15 lb/hr/lb in cruise.

Depending on how the operator has their cost index set, this will effect the overall fuel burn for the flight.

Other considerations used by operators include technical support both from the manufacturer and line maintenance, existing fleet installations (i.e. CFM engines on A340 or 737), and flight crew (the IAE and CFM have different cockpit presentations).

The engine may also be owned, leased separately from the airframe, or leased with the airframe, the economics of these lease methods can blow any fuel saving, and may in mean a level of compensation to the operator is delays in schedule are caused by engine related delays.

Last I looked all the lease A320 aircraft that were available presently on the market are all V2500 powered, i.e. no CFM powered airframes are without a home. This may an indication of customer preference.

Engine type CFMI CFM 56 IAE V2500
Engine model 5A1 A1

Thrust (lb) 25000 25000
Flat rating (C) 30.0 30.0
Bypass ratio 6.00 5.40
Pressure ratio 26.50 29.40
Mass flow (lb/s) 852 781
SFC (lb/hr/lb) 0.33 0.35

Max. thrust (lb) 5670 5620

Altitude (ft) 35000 35000
Sfc lb/hr/lb 0.596 0.581
Basic eng. wt. (lb) 4860 5210

Number of shafts 2 2
Compressor 1+3LP 9HP 1+4LP 10HP
Turbine 1HP 4LP 2HP 5LP

IAE has further information on their web site www.v2500.com (http://www.v2500.com)



1st Mar 2001, 13:24
Cheers for the info.
food for thought


6th Mar 2001, 17:44
I think a CFM-engined A320 looks better & neater than a V2500-engined A320!!!!!

Any input from Marketing types???

6th Mar 2001, 17:55
I fly Airbus's with both IAE and CFM.
Nothing between them really, the IAE's start sequence takes ages compared to the CFM.

IAE's operate on EPR as the main power instrument, but I find most crews still use N1 (as on the CFM).

They both burn roughly the same, both seem very reliable.
The IAE's have a 5 minute warm time (start up to takeoff) restriction that can be a 'gotcha' at small airfields.

We have different on ground ice shedding procedures for the CFM and IAE.

Given a choice I prefer the IAE's, they seem to give a better performance at higher levels (bigger bypass ???).

8th Mar 2001, 09:26

Your line of thinking is correct regarding the IAE engine at altitude.

The CFM 56-5A1 has a fan diameter of 1.830 m, bypass ratio of 6, and pressure ratio of 25.6.

The IAE V2500-A1 has a fan diameter of 1.681 m, bypass ratio of 5.4, and pressure ratio of 29.4.

At low altitude where the air is thick the fan is producing most of the performance for the aircraft, up high with thin air, the engine core is producing most of the performance. As the IAE engine has a lower bypass ratio and higher pressure ratio it is “closer” to a turbojet design (more pure jet thrust) hence the better performance at altitude.



8th Mar 2001, 15:20
T+T Agree 100%.

Zeke Interesting, that helps explain the fuel burn differences. In the ground our V2500's burn 400Kg/hr/engine as opposed to just over 300Kg/hr/engine at idle.