Re: A 777 with four engines.

Date:         06 Jul 98 03:24:41 
From:         JF Mezei <jfmezei.spamnot@videotron.ca>
References:   1 2 3
Followups:    1
Next article
View raw article
  or MIME structure

Stephen H. Westin wrote:
> I think you're leaving out another factor: efficiency. I believe
> bigger engines have lower specific fuel consumption. So an aircraft
> with four engines, each of 50,000-lb thrust, will always be less
> economical than a similar one with two 100,000-lb thrust engines,
> other factors being equal.

The question should be:

If a 4 engined plane has 4 50k lb-thrust engines (200k total), how much
thrust would a comparable twin have ? Since they must be able to survive
on a single engine after having reached V2 (or is it V1 ?) during
takeoff, surely there must have to be some "spare" thrust into each of
the 2 engines ?

So, if a twin engine aircraft must have spare capacity in its engines,
how much does that spare capacity cost to carry/maintain/build compared
to the cost of 4 smaller engines which do no stretch materials to their
limit ?

Is it not logical to say that the 777's engines, being state of the art
and challenging engineers and materials to their limits, would cost more
to build/research than building smaller engines for whom today's
materials represent little or no challenge ?

I am not familiar with jet engine prices (they don't carry them in stock
at the local supermarket:-). It would be interesting to see a comparison
of *purchase* price for 4 A340 class engines compared to the price for
2 777 class engines.