Airbus A340 - Why only CFM56?
AdenOne
SuperFan geared turbofan which would have produced more thrust with
less fuel than the CFM56-5C.
However, when SuperFan was canceled, Airbus went with the CFM56 which
was not really powerful enough for the A340 - its highest thrust is
34,500 lbs. The A340 is known to be underpowered and should really
have scaled to much higher operating weights than its 608,600 lbs
MTOW.
To achieve, say, the same thrust-to-weight ratio as the 747 (0.26:1)
the A340 would have needed 4x 39,560 pound engines - the CFM56
obviously cannot scale to this - but what about the RB211-535 or
PW2040 as used on the 757?
Surely with 4x 43,000 pound RB211s the A340-300 could have been pushed
to about 660,000 pounds MTOW - same as the 777-200ER - and with the
same thrust-to-weight as the 747. This would have improved payload,
range and economics - except if the RB211 or PW2040 use vastly more
fuel than the CFM56 - which I don't think is the case.
I know the A340 is considered dead and gone, especially the 200\300
models - but if airbus had used the RB211-535 or PW2040, could it have
improved the A340's chances against B772ER?
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AdenOne
AdenOne
John L
>models - but if airbus had used the RB211-535 or PW2040, could it have
>improved the A340's chances against B772ER?
Seems to me that a four engine plane can't just be as good as a
comparable two engine, it has to be significantly better or the costs
of maintaining those two extra engines will still kill it.
The 777 line killed the 747-400 dead, so simply matching the -400's
economics wouldn't have helped.
R's,
John
matt weber
>I know originally the A340-200\300 were planned to have the IAE
>SuperFan geared turbofan which would have produced more thrust with
>less fuel than the CFM56-5C.
>
>However, when SuperFan was canceled, Airbus went with the CFM56 which
>was not really powerful enough for the A340 - its highest thrust is
>34,500 lbs. The A340 is known to be underpowered and should really
>have scaled to much higher operating weights than its 608,600 lbs
>MTOW.
>
>To achieve, say, the same thrust-to-weight ratio as the 747 (0.26:1)
>the A340 would have needed 4x 39,560 pound engines - the CFM56
>obviously cannot scale to this - but what about the RB211-535 or
>PW2040 as used on the 757?
>
>Surely with 4x 43,000 pound RB211s the A340-300 could have been pushed
>to about 660,000 pounds MTOW - same as the 777-200ER - and with the
>same thrust-to-weight as the 747. This would have improved payload,
>range and economics - except if the RB211 or PW2040 use vastly more
>fuel than the CFM56 - which I don't think is the case.
>
>I know the A340 is considered dead and gone, especially the 200\300
>models - but if airbus had used the RB211-535 or PW2040, could it have
>improved the A340's chances against B772ER?
I think there were two issues that prevented the use of the RB211 and
PW2040 power plants. One is political. Both IAE and CFM have
substantial European participation. Whether RR was considered European
at the time of the A340 decision is debatable.
The other problem is and was weight and wing loading.
The CFM56-5C engine only weighs 5600 pounds
the PW2040 is 7300 pounds, and is nearly 12 inches larger in diameter,
so you have both a weight and a ground clearance problem with the
PW2000, it is also about 4 feet longer than the CFM56-5C
The early RB211-535 (The C model is a turkey)., the later versions are
OK fuel burn wise, but you are still looking at 7300 pounds per
engine, and another foot in lenght.
Also the key to the higher MGTOW on the A340 was the reduced
structural loads from the engines as a result of both the lower
weight, and lower thrust than the A330 engine.
2 x CFM56-5C engines is 11,200 pounds and and 68,000 pounds thrust
spread across a fair bit of wing.
1 PW4168 gives the same thrust, but from a single point, and weighs
12,200 pounds.
The effect of the single point higher thrust, and higher engine weight
is to in fact whack 100,000 pounds out of the MGTOW to stay within the
design load limits for the wing even though the thrust to weight ratio
on the A330 is significantly better than it is on the A340 at MGTOW...
The higher weight and higher thrust of the 2040 or 535 engines would
in fact have reduced the MGTOW.
JF Mezei
A320 ? If so, perhaps Airbus saw an advantage, when forced to choose a
compromise, since the customers would then have greater parts
commonality in their fleet with the 340 sharing engine cores with the 320 ?
.
matt weber
wrote:
>Is there much commonality between the CFM56s used on the A340 and the
>A320 ? If so, perhaps Airbus saw an advantage, when forced to choose a
>compromise, since the customers would then have greater parts
>commonality in their fleet with the 340 sharing engine cores with the 320 ?
>.
There are two series of
CM56-5 engines.
The 5B engines are in fact mechanicall probably all the same.
The levelof mechanical compability between the 5B and 5C engines is
debatable. The diameter of the 5C engine fan is larger, and it has an
extra stage in the LPT. , and about an inch longer, and weigh about
400 pounds more than the 5B engines. There is some degree of
commonality, but exactly how much is debatable. Obvious the casing,
fan, and a turbine stage are different, beyond that it is hard to be
sure. Presumably the boster, compressor and HPT are the same.