Re: 2 Vs 4 engines - CFM56 Engineering Dept Costs

Date:         17 Dec 99 01:57:43 
From: (Burkhard Domke)
Organization: Colt Telecom GmbH
References:   1 2
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On 03 Dec 99 02:10:12 , Ernie Fidgeon <> wrote:

> wrote:
>> If you were an airline running a CFM56 fleet B737 / A320 etc. and you
>> wanted to buy a wide bodied Airbus would the A340 cominality (sp?) with
>> the CFM56 be much of an advantage when compared to the greater fuel
>> burn etc. of a 4 engined aircraft?
>If you do your own engine mtce and already are familiar with the CFM, it
>would be an advantage to do this.  In addition, IMHO the CFM family of
>engines is extremely operation friendly and very reliable compared to other
>types available.  Also, for its size, the 4 engined A340 is extremely
>efficient.  The fan area is smaller than othe 4 engined beasts and offers
>drag benefits therein.

Two large engines should yield less overall drag than 4 smaller
engines and also weigh and cost less, but then wing weight will be
considerably lower with 4 engines due to a more favourable load
distribution and inherently enhanced flutter resistance. Hard to
compare though, because wing area is a function of the number of
engines installed to begin with (takeoff considerations, much higher
wing loadings possible with number of engines going up), this in turn
having a major impact on cruise (altitude) capabilities (initial
cruise ALT of 777 much better than A340's FL270 at max weight).

Burkhard Domke
Berlin, Germany