Dear Capt Kay,
My question with regard to the Boeing 777.
In these days when Airbus is testing its new version of the
A340-600,
I have asked myself what are the benefits of equipping two or four
engine on
an aircraft. Both planes are about of the same size and
range capability
and they are believed to bring about an interesting competition.
1) Will Boeing be capable of making the B777-200 flying more fuel
efficient and therefore fly further as only two engines are in action?
2) Is Airbus A340-600 able to compensate this loss by flying
direct routes as no
ETOPS regulations force it to cruise along potential diversion
fields
instead of the straight path.
3) Is it maybe also a plus when one can distribute
the requested thrust on
four engines?
Chris Jeker
Hi Chris,
Thank you for your questions regarding the Boeing 777 design.
Here are the
answers to your 3 questions:-
(1) Improving the fuel efficiency of the aircraft will
require more fuel
efficient engines. The Boeing 777 are fitted with either the
Rolls Royce,
Pratt and Whitney or General Electric engines. Fitting which type
of engines
on the Boeing 777 will depend on the preference of the individual
Airlines.
You will notice that the
Boeing 777 does not have winglets like the A340-600
or Boeing 747-400. Someone once asked me whether fitting
winglets on the
Boeing 777 will make any difference to the efficiency of the
wings. I am
made to believe that it does not, as the Boeing 777 is the first
aircraft to be completely designed by computer. Therefore, the
current wing design is the most efficient one in terms of fuel
saving.
Remember that even with only two engines as compared to the
A340-600 with
four, the Boeing 777 engines are larger and produce more
thrust each. Further, Boeing has produced the Longer Range
B777-200 with a range of 8820 nautical miles as compared to the
A340-600 with 7500 nautical miles.
So your question, will
Boeing be capable of making B777 more fuel efficient, the
answer is yes if more fuel efficient engines are fitted.
Currently, from the data that I have, the Longer Range Boeing
777-200 with two engines flies further than the A340-600.
(2) You are right that the A340-600 is not governed by the
ETOPS (extended
twin-engine operations) Regulations. The Regulations prohibit a
twin engine
aircraft to operate over a route that contains a point further
than 60
minutes flying time from an adequate airport at the selected
one-engine-out
diversion speed. This is based on a single-engine flying
time to an
adequate airport. The diversion time may be 90, 120, 180 or
207 minutes.
This diversion time varies depending on the safety records of the
particular
Airline (many factors taken into account). The maximum
diversion time is
only used for determining the area of operation and only granted
by the
individual country's Department of Civil Aviation.
Back to your question. With the advantage of four engines, the
A340-600 can
certainly fly direct routes as they are not governed by the ETOPS
Regulations.
(3) The issue of two versus four engines has its pros and
cons. Your view,
if I interpret it correctly, that with four engines, you can
distribute the
thrust when you needed them, is true in the sense that you only
lose 25
percent of the take-off power in the event of an engine failure.
So you can still
distribute 75 percent of the power to the aircraft. In a
twin-engine
aircraft, you lose 50 percent of the take-off power (which is not
necessarily the maximum power). However, Design Regulations
required that the remaining single engine must have sufficient
power to meet all the
requirements that are applicable even to a four engines aircraft
that
suffers from single or twin engines failures.
Thus, with four engines, whether it is a plus is debatable.
Power-wise, it
makes no difference. ETOPS, yes, range-wise, no. You also
have to consider
operation and maintenance costs, noise level, comfort and many
other factors before you can decide which is better. Since I
fly the Boeing 777-200, my choice is still with two engines.
I hope I have been able to answer your questions satisfactorily. I
do not
represent any Manufacturers and my views are my personal ones.
Regards,
Capt Kay
Dear Capt Kay,
I would like to say that your web page is really great. It is useful for
passengers and the airline industry because it creates air-travel culture
and demystifies air travel.
I only have a note; in your article B777 vs. A340, you gave
all the pluses
for the B777 and only obvious pluses for a340. When an engine fails on a
twin-engine plane, you don't have 50% thrust, you have about 30-35percent
thrust. The available thrust remains the same, (if you increase thrust on
the remaining engine, Vmcg, V1 and Vr increased and you need more runway
for takeoff; so usually you don't increase it on most planes - I don't know
about B777, but the logic is the same. Your required thrust increases
for annulling the slipping and the deflection of the rudder control, the
wind milling of the inoperative engine, the unbalanced drag etc.)
So, that is also a disadvantage for B777. The other
advantage of A340 is that if an engine fails, you can remain on higher level,
thus saving fuel and increasing the
probability that you will reach the adequate airport in complicated weather
situations. The cockpit is same as other Airbuses and crew needs much less
training for changing types.
If an engine fails you don't loose only thrust, but also
electrics, hydraulics, bleed air
etc., (the other engine takes over....) and that is also less problematic if
you have 3 engines left. Larger engines have higher centrifugal force and
stress and also are more sensitive to rotation-related vibrations.
Passengers feel better if they know the plane has 4 engines
and they will stay in it
for 12 hours. To see which plane is better, you have to see it through many
eyes. For a businessman the better one is the one which gives better
mile/gallon, gallon/passenger relations, range, (but real , including
ETOPS restrictions), maintenance cost, crew training cost, airport taxes,
dispatch reliability, etc.
For a pilot and a passenger, a 4 engines plane is better (you
have to admit it), for a mechanic a plane with no engines at all would be the
best, etc. The other thing is that many pilots dislike Airbus concept, and
until the try it and familiarize with it, then they would love it.
Anyway I didn't want to write so much, but I wrote in to
tell you that although you like B777 more, you should give all the
advantages/disadvantages, so that the people can decide on their own.
Best regards,
S.Bedic
P.S. Merry Christmass and a Happy New Year!
Hi Bedic,
Thank you for giving the views from the side of the A340. As I have said,
the pros and cons are numerous. If you have traveled on both the
aircraft,
you will find that it is more comfortable and spacious on the B777 and it
can take turbulences and bad weather better than the A340.
You are right to say that in deciding as to which is the better airplane, you
must see it from different views, namely the Airline Management, the pilots,
the engineers and most important, the passengers.
Merry Christmas and Happy New Year to you too!
Capt Kay.
