A320 IAE V2500 powered VS A320 CFM powered?

[Vulcan607]

Hi,

I was wondering if any pilots/engineers who have experience with the above mentioned could answer a few questions for me?

From a pilots point of view, for those who have experience of both engine types on the A320 family, which engine performs better?

For the engineers, when I've seen the V25's and the CFM's being kitted with the powerplant material before returning to their respective airline, the CFM looks a far easier engine to work on - so.....can anyone give a broad outline as to which engine is more reliable through personal experiences

And finally, if anyone can answer this - operationally, which is the preferred engine type to those who have access to both of them?

Any feedback on this is greatly appreciated!!!!

:ok:

[electricdeathjet]

CFM's look cooler! :ok:

Also quicker start up times
Proper N1 gauges

[LanFranc]

7500 on A320 family, 75% CFM, 25% V2500
No preference really, both have their advantages/disadvantages.
CFM, quicker starting, lower idle thrust,higher reliability BUT, higher fuel and oil consumption.
V2500, more fuel/oil efficient, more effective reverse thrust BUT slow starting, high idle (more braking during taxi) and seemingly more problematical.

At least in MY experience.

[Dani]

IAE is undershooting speed when levelling off from above, generally reacts very slow compared to CFM. The thrust indication is sometimes very hard to recognize, because the EPR number between idle and TOGA thrust isn't much different. A lot of pilots use still N1 or even fuel flow to cross check.

[mutt]

We looked at both, from a route/payload/fuel burn perspective, the IAE was better, but historically we have had big problems with the V2500 on another fleet type, so we picked the CFM.

[Mäx Reverse]

We operate A319s/A320s with the CFM-Engine and A321s with the IAE-Engine.

As a driver, I'd prefer the CFM any day. The problems have already been named, the greatest disadvantage ist the mickey-mouse-style thrust indication on the IAE.

If you have a grossweight (landing weight) of lets say 58 tonns on a CFM-A/C, you would set N1 to GW-3 as a thrust target xx% N1 during approach, in this case some 55% N1.

On the IAE your target ist 1.0xx EPR and already by looking sharply at the trust levers you change EPR easily by > 0,01-0,02. So good luck in a heavy A321 (greetings from the slow reacting engines) on a windy day.

Also the EPR display on the IAE-A/C is a good bit smaller behind the decimal (compared to the N1-Display on the CFM-A/C), so looking at it to read the EPR takes always just this 'microsecond' longer, in which you should have been looking at the intruments/outside.

[Dani]

Sorry, Mäx, what is GW-3?

[Cough]

Dani,

I guess what max is talking about is a datum power setting on approach. Take the gross weight of the aircraft (58T) and subtract 3 (GW-3!) and that would be your reference N1 on approach (i.e. 55%).

Cough, a man who knows little about airbus, yet!

[Chris Scott]

Did about 10 years on CFMs, then 4 years mixed, before retiring 7 years ago. Agree with all I've read here. Have never liked EPR as a means of power indication – except perhaps for take-off – for the reasons others have highlighted. In the 'Seventies, we had similar problems on the BAC OneEleven when converting from early Speys, which used N2 as the main thrust indicator (except for take-off, when P7 was also checked), to the later Speys.

Fuel flow indication should be a useful tool but, if memory serves, is almost useless when the throttle is moving, when you may need it most.

Presumably, the N1 is as good an indication of changing thrust on the IAE as on the CFM (at a given density altitude), so CFM-sized N1 "gauges" would be the answer. The two snags that spring to mind are:
1) lack of space on the display;
2) the misguided (in my opinion) policy of most airlines to discourage or even ban the use of manual thrust, despite the A320 having the best "manual" throttle of the seven jet types I flew. Most of the once-a-month brigade would never dream of it. And the A/THR never fails, does it?

The other thing I liked better about the CFM was the comparative ease of inspection on a walk-round, particularly if you were wondering about a bird encounter on the previous sector.

[SIDSTAR]

Almost impossible to fly the 2500 on EPR as already explained due to small range of movement. Everyone I've spoken to flies it on N1.

Dont forget the potential inherent errors in any EPR indication (737 Potomac accident). Engine speed is the best indicator of real thrust.

Apart from that, the 2500 may be more fuel efficient but is a bit of a pain for the long start cycle, the slow response in levelling off and the EPR/N1 issue. However, they both work ans as long as they keep turning ....

[Wireflyer]

Agree with all I've read.

We had IAE's on the fleet before, changed to new ACFT with CFM's.
Nevertheless I believe that in high altitudes the older IAE's had more power than the brand new CFM's. No data to confirm my "feelings" :hmm:

[N1 Vibes]

An engineers perspective:

- IAE - do NOT trust the -A1 variant of the V2500, it a piece of :mad:
- IAE - the -A5 is much better, but not so mechanic friendly, lots of grazed knuckles and burnt elbows
- CFM - A much better creature, lasts forever, has very little in service issues

Just to pick up on some pilot comments on the EPR, if you're only issue is the guage then consider this, from an efficiency point of view (fuel burn/thrust) EPR/thrust relationship over time is much more accurate than N1/thrust, since it is based on pressures, not rotational speed.

The relationship of N1/thrust is only as accurate as the day the engine comes off the test-cell, and the N1 trim is set. When the fan track wears out, the airfoils get dirty and the blade l/e's erode etc the N1 speed is no longer related to the thrust it was in the test cell - therefore on a high time CFM engine you may be 2% down on thrust.

So please if you're issue is with the guage - ask the aircraft designers to make a bigger display!

[FlightDetent]

N1: Good point. Instead of the engine lot had so far focused on implementation. Even the Potomac reference is historical and things may have evolved over time. But I wouldn't know being CFM dependent. :cool: To bite one's lip, A319 with IAE looks way too cool, one of my favourites. Somewhat scary, think 262. Steed of the breed, imagewise.

Photos: Airbus A319-131 Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/British-Airways/Airbus-A319-131/1406129/M/)

[galaxy flyer]

A Pratt and Whitney engineer once told me that EPR is better because a 1% error in EPR indication is a 1% error in thrust. Using N1, a 1% error in rotational speed could be as much as a 4% error in thrust depending on actual engine speed. The Potomac crash was not caused by faulty EPR, but a whole host of other problems which caused, among other things, incorrect power being set.

[Chris Scott]

Quote from N1 Vibes:
The relationship of N1/thrust is only as accurate as the day the engine comes off the test-cell, and the N1 trim is set. When the fan track wears out, the airfoils get dirty and the blade l/e's erode etc the N1 speed is no longer related to the thrust it was in the test cell - therefore on a high time CFM engine you may be 2% down on thrust.
[Unquote]

Point taken. [And maybe the N1 VIB off-scale at 9.9(+) means one of the fan blades is missing anyway?] ;)

Trouble is, if memory serves, there's something non-user-friendly about EPR readings, particularly at the medium and lower power settings; like in the hold and on instrument approaches. But I can't quite put my finger on it. This was particularly true on the JT3D and the later Speys, both of which had analogue gauges where you'd struggle to see the difference between 1.20 and 1.25 (= quite a power difference).

Perhaps someone like Mäx Reverse can remind us how many places of decimals are displayed on the presumably accurate, digital V2500 EPR display. Is it 2, or 3? If so, maybe the trick I never learned might be to knock off the "1" mentally, and concentrate on the decimals. Then come up with some rules of thumb as-per N1.

But for those who fly both engines, like BA and currently easyJet, it's going to be a challenge to remember both sets of figures. Particularly if the management frown on (or ban) the use of manual thrust anyway.
Here I go again... :ugh:

[Mäx Reverse]

That's the way the Engine/Warning Display looks for a CFM-engined Aircraft. N1 Displays (digital and analogue) in the uppermost part of the display and pretty well readable. Notice Fuel Flow Indication is in the 4th line.

http://img530.imageshack.us/img530/775/a320ewdqf7.png (http://imageshack.us)
http://img530.imageshack.us/img530/a320ewdqf7.png/1/w604.png (http://g.imageshack.us/img530/a320ewdqf7.png/1/)

For an airframe with the IAE-installation the display looks like this.

EPR indication in the first line with three mickey-mouse-style decimals. Far too small to be well readable, especially during turbulence or darkness.

N1 now in the 3rd line and N2 in the 4th, moving FF out of the way to the right, completely different place than on the CFM-Display. Hard for those setting power according to FF.

For an A321 with 'usual' LWs (ie not empty) the rule of thump is target on approach = 1.0xx where xx is the LW. 70 Tons would give you a target EPR of 1.070. No idea how this works on an A319 with 47 tons (A3192/320s are CFM-ships with us).

If you are unlucky enough to loose EPR-Mode the fun really begins. Instead of interchanging the position of the now xxxed out EPR and the N1 the blank EPR gauges stay at the top and you find yourself looking for the N1s in the 3rd line.

[FlightDetent]

Is it me or, is the IAE display arranged so that the most relevant digits are designed the tinyest?:yuk: Still speaks nothing about the engine itself ...

[Chris Scott]

Thanks Max,

The V2500 display looks depressingly familiar. They should definitely enlarge the decimals to the same size as the "1", reducing the size of the latter if necessary. I'm a purist, but I still think the "1" is over-emphasised at the expense of the other digits. Correct me if I'm wrong (it's been 7 years), but by definition the EPR is never less than 1?

The fuel flow display is squeezed over to a non-ergonomic position, which is also a shame.

To sum up: room for improvement.

Was I right (Post#10) that digital fuel-flow readings go haywire during engine accel/decel? It's a pity, because fuel flows used to work brilliantly as a thrust indicator on early Speys, for example. They are pretty-well independent of ambient temps at a given altitude, and, flying on one engine, the total fuel flow is about the same (well, maybe 10% more to allow for the sideslip).

Interesting that the graphic shows the No.2 engine N1 spooling up slower than No.1's, although the EPRs are the same. But it illustrates well that the FADEC's basic job is to provide an EPR.

[Mäx Reverse]

Hi Chris !

Your comments are spot on.

Correct me if I'm wrong (it's been 7 years), but by definition the EPR is never less than 1?

Not as long as the engine is producing thrust:}

Obviously AI has already discovered the room for improvement on their own. The Display on the newest ships with the LCD-Screens (instead of the old CRTs) looks completely different again.

As I was told several restrictions imposed by an old DMC-Standard in combinaition with the slow cursor of the CRTs made these changes impossible until the advent of the LCDs.

The IAE-Display looks like this on an LCD:

http://img217.imageshack.us/img217/5210/a320familykey2a651a3cdefk0.png (http://imageshack.us)
http://img217.imageshack.us/img217/a320familykey2a651a3cdefk0.png/1/w604.png (http://g.imageshack.us/img217/a320familykey2a651a3cdefk0.png/1/)

Much more spacious and the numbers are all the same size. Bravo!

However the LCD-ships take a lot of getting used to, especially if you fly mixed as EVERY page looks more or less completely different. But us lowely outstation-folks are not normally even allowed to touch them, so why do I bother? My broad experience one year after EIS: 1.0 legs!

[Dani]

Still, even when they are enlarged, it's still not user-friendly.

Problem is, that the IAE V2500 engine still produces about 1.2 thrust on idle, and about 1.6 when full thrusting.

Contrary to some opinions, EPR is not non-user-friendly, just when it's displayed the way AI does. They should enlarge the scale of the operating thrust, i.e. 1.2 - 1.6 and forget about the rest. Or you could enlarge the operating thrust and reduce the rest, like an algorithmic indication. Additionally, they should forget about the real EPR value. We are not interested if it's above one, we are just interested in the relative value. You could easily convert the 1.x figure into a percentage figure. Or just show as the value above 1.0, i.e. 200 to 600 (equivalent to 1.2 to 1.6). There are endless possibilities how to make it better than now.

There are very good examples of how to display EPRs user-friendly, inclusive the type I fly presently.

[FLX/MCT]

Dani,


I think they invented a parameter called "thrust" on the A380, whereby 0% represents idle and IIRC 100% represents the maximum possible thrust for the current flight phase...
Seems quite comfortable and intuitive to me...

[Dani]

Excellent! :ok:

Hopefully all future types and versions will have that.

[xerxesdk]

I'm not sure if this has already been touched upon but,
EPR is an indicator of actual thrust.
An EPR of say 1.15 is associated with XX,000lbs of thrust at sea level and at the same FL200.
However, an N1 fan speed of say 60% will correspond to a higher actual thrust value at sea level than at FL200.
That being said as a pilot you want to be able to be able set a thrust lever angle that gives you the thrust you need to maintain your required speed alt etc.
N1 gauges are easier to use but the EPR is more accurate.
I wonder if anyone has ever considered setting the EPR as a function of its scale and not the number.
Say EPR needles at 9 o'clock to reduce from high speed.
Or say 10 oclock for flap full MLW VAPP ETC.
nyone with me?

[vilas]

FLX/MCT
Zero is not idle thrust. Zero is zero idle is ahead of that.

[vilas]

I had started a thread about IAE and CFM engines I had observed following shortcomings of IAE engines:
CFM VS IAE Engines A320
IAE engine takes longer to start than CFM. Also thrust response to thrust levers appears sluggish as compared to 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 requires or puts on ignition for more conditions than 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.

[Bkdoss]

Having flown for 3 years with an operator having a mixed fleet of IAE and CFM engines, this is what I perceive as discernable difference between the IAE and CFM engines, in addition to what has been already elucidated in this thread.
1) IAE has higher thrust idle, hence as a pilot you'd have to apply brakes considerably more during taxi. Leads to frequent usage of brake fans to keep the brake temperatures under control. The difference is significantly noticeable when with the parking brakes on, you feel that the aircraft is constantly pushing against the brakes, causing a bobbing motion.
2)IAE has higher start time compared to CFM due to the extended motoring to get rid of an unique problem called 'Bowed rotor condition'. And the idle time required before take off after a cold start is higher compared to CFM.
3) IAE is much more noisier compared to the CFM, though as a pilot I'd complain because, pun intended, I'm made more aware of the thrust changes without having to look down at the gauges.
4) IAE gives you a remarkably lower fuel consumption compared to CFM engines.
5) The target speed achieving characteristic of the ATHR on the IAE engines was inferior to the CFM ones, though I've my suspicions that it's the software standard of the specific ATHR that makes it look that bad.

[vilas]

IAE's lesser fuel consumption may come from the fact that it is under powered. CFM has many thrust variants so may be the lowest one has higher consumption as compared to IAE. Requirement of KOZ, Ignition, fan flutter. bowed rotor, not a hallmark of a better engine.

[Bkdoss]

In addition to what has already been said, the Engineering folks in my company were of the opinion that IAE engines had a longer life time compared to the CFM engines. I'm not sure if there's empirical data supporting the argument. Can anyone support or contradict the same?

[Wireflyer]

IAE:

Better deceleration by the reverser
Lower fuel / ENG oil consumption
Had the "feeling" of more Thrust in high density altitudes


CFM:

Quicker ENG start sequence
N1 engine instruments are easier to handle vs. EPR

Regards!

[tubby linton]

Would anybody have any data for thrust available from these engines at normal cruise level?I think around the tropopause it should be about 20% of max sea level thrust.

[KayPam]

I think it should be a little more, shouldn't it ?
Thrust should not decrease faster than atmospheric pressure, else you're not gonna be faster at altitude.
You're gonna be slower because of greater drag (due to greater Coefficient of Lift required)

[Denti]

CFM used to have that information on its website, but thats been dumbed down considerably so try wikipedia...

[vilas]

CFM has higher thrust at higher levels and the drift down ceiling with OEI is at least 5000ft. higher than IAE.

[Minderbinder]

I have been flying the A319 with IAE V2500-A5 and CFM 56-5B and some protoype A320 with CFM 5A engine
(double digit msn).
Additionally to the items mentioned above:
1. V2500s stink. Doing an outside check shortens your live. I try to hold my breath when nearing a V2500. Sometimes you see the vapours rising from the oilbreather or lingering near the fan
2. V2500 AP speed control is sluggish. But when a speed just above green dot is selected you have the occasional "TOGA" thrust surge to gain 5 knots of speed.
3. Speed deceleration is slower on IAEs due to high idle setting and the slightly smaller engine diameter.
4. During landing you need to retard the throttles (yep I am aware its called thrust levers, spent my formative years on a boeing) earlier on the V2500 than on a CFM otherwise the AC will float.
On the CFM retarding the thrust levers early might result in a firm touchdown.
5. In gusty conditions the IAE engined aircraft seem to react more sluggish than CFMs. CFMs react prompt
BTW Our company policy is "manual flight, manual thrust" and raw data is encouraged. Never done an A/THR landing in real life except during autoland.
With regard to EPR, I use fuel flow as prime parameter when flying IAEs. Values are the same across both fleets for all intents and purposes.
All be said I prefer the cfm.
Speaking to our engineers low oil and fuel consumption for the IAE seems to be a valid argument.

[macdo]

Flew several thousand hours on V25A1 and CFM.
V25 was generally unreliable in service and always 'felt' fragile.
Met a design engineer at a party years ago who had been involved with the hot section.
His comment " yeah, I think we were trying to be too clever with that engine"