Air to Air Refuelling in Civil Aviation, An Opportunity & A Vision Dr ...

RAeS Conference “Greener By Design” Conference
“Aviation & the Environment, Where Are We Going”, London, 7 th Paper 9
October 2008
Air to Air Refuelling in Civil Aviation, An Opportunity & A Vision
Dr. R. K. Nangia
BSc, PhD, CEng, AFAIAA, FRAeS
Consulting Engineer, Nangia Aero Research Associates
WestPoint, 78-Queens Road, BRISTOL, BS8 1QX, UK.
SUMMARY
Over the last 70 years, the civil aviation industry has focussed on a growth model: upwards, bigger,
farther and faster on an economic productivity basis. With awareness of environmental issues, noise,
emissions and energy / fossil fuel reserves, there is an awakening for exploring ways to improve fuel
efficiency. ACARE & NASA objectives call for challenging 50 to 80% improvements over next 20 years.
As technology matures, the evolutionary ways are yielding improvements at a very slow rate. Operational
strategies need to be exploited e.g. staging, Air-to-Air Refuelling (AAR), Close Formation Flying (CFF).
This paper is concerned with AAR. It reviews the related previous work e.g. on a new set of efficiency
metrics that allow a “unified” consistent efficiency theme relating Payload, Range, Fuel consumed.
Smaller range aircraft need to be used for AAR and these imply 30 – 40% benefits in fuel usage.
Assuming fuel at $4.70/USG, the savings estimates with AAR are remarkable: $175/pax for 6000nm and
$320/pax for 9000nm. These translate to savings $25 million per aircraft per year on long-range routes.
The main focus is then on the consequences of adopting AAR. Several other features and synergistic
benefits arise. The benefits afforded by AAR appear an order greater than, and in addition to, those
achieved by current technology evolution. Next stage is AAR demonstration in civil context!
1. INTRODUCTION
Early civil jet aircraft were designed for moderate
ranges with staging being the norm for long ranges.
The later models of the B707 series with trans-
Atlantic capabilities set the scene for achieving
records for travelling further, faster or higher, in
productivity terms (Refs.1-2). Although fuel was
relatively cheap, there were still incentives to
produce structurally efficient aircraft to enable long
ranges with adequate payloads. As a result, aircraft
such as the B747 and MD 10/11 were produced.
As oil resources decline in the long run, there is
a stronger incentive to reduce fuel consumption.
This assumes that current trends of air travel will be
maintained. Together with environmental concerns,
this has prompted a shift in design philosophy.
Whilst we strive to further improve aerodynamic
and propulsive efficiency, alternative configurations
and operating procedures need to be considered.
Typical fuel burn rates for modern, efficient
aircraft are of the order of 3 litres / 100 pax km (67
pax miles / USG). The earlier B707-320B could
carry 189 pax over a range of 4540 nm (4.6 litres /
100 pax km). Derivatives of the B707 airframe are
in service today, typically as the KC-135 and cargo
versions. Currently, the B747-400 can carry 420
pax over 6750 nm (3.5 litres / 100 pax km). It is
interesting to note that with more efficient engines
the fuel burn rate of the B707 could approach that
of the B747. With the introduction of AAR into
civil operations, even old aircraft such as the B707
could offer a competitive or better fuel burn rate
than current long-range aircraft (see later).
1
Aviation Contribution to Environmental
Concerns / Awareness
There is an ever-increasing knowledge base on
environmental concerns from civil aviation (see
Refs.3-6). In the nature of such matters, not all
information is necessarily robust or fully
substantiated. We briefly mention typical facets.
In general, aircraft emissions are a small
proportion of the overall scene, but these are
growing in absolute terms. CO2 and non-CO2
distinctions have to be made.
Fig.1 shows CO2 Emissions from Transport. In
1990 transport was responsible for 14% to 16% of
the world total CO2 emissions (IPCC, 1999). Of the
transport contribution, 70% was attributable to road
vehicles (heavy and light duty), 12% to maritime,
10% to aviation and 8% to rail and inland water
transport. By 2000 (Stern Report 2006) the transport
contribution to world CO2 emissions remained at
about 14%. Of this, the Aviation contribution had
risen to 12% i.e. 1.7% of World emissions.
A research line is that currently CO2 levels are 3
terra-tonnes in the Earth’s atmosphere of 5140
terra-tonnes (582 parts per million by mass). A
thought is that by 2050, these may be capped at 4
Terra-tonnes implying a 2°C rise in Earth’s average
temperature. Aviation is expected to contribute 4-
5% of the total CO2 levels. The arguments get
involved as short/ long life CO2 have to be specified
and we shall leave that for scientists to advise us.
The non-CO2 effects are important and may be
more harmful. These comprise: CH4, NOX,
Contrails and Ozone changes. Currently, progress is
being made by the OMEGA community in the UK
to understand and quantify the implications.
© Copyright, Dr R.K. Nangia 2008. All Rights Reserved. Published by RAeS with Permission

Fig.2 shows Fuel Usage (USG per 100 pax mile)
against Load Factors in various forms of transport
(based on Boeing Studies). In this interesting graph,
we note several significant trends. For all forms of
transport, fuel consumption reduces dramatically up
to 50% load factor. Beyond this value, fuel
consumption continues to fall but at a lower rate.
European Inter-City train is the most fuel-efficient.
High-speed trains have twice the fuel consumption.
Air travel is comparable to the “Average” road
vehicle. However, range for road and rail travel is
limited by geographical and national boundaries. As
expected, large SUV is inefficient in cities and
towns; load factors are low 25 - 30%, for road
vehicles. At typical load factors of 70%, air travel
has a fuel consumption rate comparable to highspeed
trains at 50% typical load factor.
Fig.3 shows the variation of fuel consumed per
stage length as a fraction of the total fuel consumed
(Ref.8). The figure also shows the variation of NOX
produced per stage length as a fraction of the total
produced. In general, the percentage NOX produced
is equal to the percentage fuel consumed. NOX also
depends on combustion temperature – more fuelefficient
engines do not necessarily produce less
NOX. At ranges less than 3000 km, NOX emissions
are slightly less. The cumulative fuel burn is shown
in Fig.4 (Ref.6). Majority of flight ranges are below
6200nm. Currently 35% of air transport fuel is spent
on flights above ranges of 3000nm. In future,
budget airlines may fly long ranges shifting the
balance to 50% with a 7.5% swing! The industry
continues to offer aircraft with 9000+ nm ranges.
2. EFFICIENCY ISSUES AND METRICS
2.1. Payload Range Efficiency
Using standard texts, e.g. Refs.7-8, we begin
with the range parameter X = V L/D / SFC
The Breguet Equation in terms of Range R is:
Z = R/X = loge [W1 / (W2] where W1 and W2
signify the weights at start and end of cruise.
W2 = W1 - WFBC where WFBC is the weight of
the Fuel burnt during cruise.
W1 = MTOW - WFBS where MTOW is Take-Off
weight and WFBS refers to the Fuel used for takeoff
and manoeuvring additional to the cruise. This is
about 2.2% MTOW (Ref.5).
Total Block fuel is then WFB = WFBC + WFBS.
A measure of aircraft efficiency is Payload Range
Efficiency (PRE): See Refs.9-10.
PRE = WP . R/WFB (Payload x Range/ Block Fuel ).
The non-dimensional convenient form is PRE/X.
From this we can derive Nangia Value efficiency
parameters, Ref.10.
VEOPX = (PRE/X) / (OEW/WP) = (PRE/X) (WP/OEW)
VEMPX = (PRE/X) / (MTOW/WP) = (PRE/X) (WP/MTOW).
VEOPX denotes the Payload Range and Fuel
efficiency per structure weight per unit payload. It
can be related to the purchase cost per unit payload.
It also serves as a measure of approach and landing
noise. Higher values are better for lower structure
weight, costs (acquisition and operating) and
landing noise. VEMPX denotes the Payload Range
and fuel efficiency per total weight per unit
2
payload. It serves as a measure of take-off noise,
emissions and hence, airport and environmental fees
that may be incurred. Higher values are better for
lower noise emissions and operating costs.
Nangia (Ref.10) conducted an analysis on
modern civil (jet) aircraft, distinguishing between
maximum payload and design passenger payload
(Points A and D), as well as including fuel reserves.
Fig.5(a-c) compares payload-range characteristics
for three aircraft: a long range, large B747-400, a
moderate range B757-200 and an older generation
B707-320B. The Range parameters vary widely
(highest for the B747). Note the differences
between the usual interpretation in (a) and the nondimensional
interpretation in terms of WP/MTOW
vs Z = R/X in (b-c). Lines of PRE/X are also
shown. The non-D representation is clearly more
descriptive in terms of efficiency.
The B757 turns out to be more fuel efficient at
Pts A and D than the other two aircraft. There are
other useful interpretations. For example a combi
B747 (carrying full complement of passengers and
cargo, Pt A) will be nearly as efficient as a B757
operating at Pt D. However, the B747 can operate
over longer ranges. The B757 in combi mode (Pt A)
will be more efficient than a B747. Increases in X
will result in corresponding increases in the Payload
- Range capabilities in dimensional terms.
Such data on various current and near-future
aircraft has been analysed with cross-plots to help in
understanding and establishing credibility.
The ratios, with respect to MTOW, of the main
weight variables (OEW, WFB and WP) are plotted
against Range R in Fig.6 for Pt D. For a given
aircraft, Pt A range is shorter than that for Pt D.
Fig.7 shows fuel reserves as a proportion of the
payload at Pts A and D. Note the remarkably large
values required for the longer range aircraft. For
9000nm flight, the reserves amount to 70% of the Pt
D payload. In contrast, for a 3000nm aircraft, the
reserves are less than 20% of the payload.
Such ratios have been correlated into reliable
“first-order” non-dimensional trends in terms of
PRE/X and Z. Figs.8-9 summarise the WFB/WP
and PRE/X trends, distinguishing between A and D
point operations. Radial lines of constant WFB/WP
are shown. In fuel efficiency terms, aircraft perform
better at Pt. A and the optimum design range is
about 2500 - 3500nm, depending on the aircraft
range parameter X. From practical size and range
considerations, Pt A curves extend to Z near 0.4.
Fig.10 shows VEOPX and VEMPX correlations
with Z using point D values. Note that the shortrange
aircraft are strongly favoured.
Often, aircraft do not fly at full capacity
(passengers and/or cargo), introducing penalties.
2.2. Interpretation of the Metrics
For long ranges, the take off fuel (engine start to
end of climb) is a relatively small fraction of the
total fuel consumed. At short ranges (limited cruise
duration), the take-off fuel is a significant
proportion of the total fuel consumed. These effects
give a non-linear nature to the trends.
Peak efficiency is achieved for aircraft designed
for about 3000 nm range. For longer ranges the

efficiencies drop off markedly. The high efficiency
of the short range aircraft can be maintained over
the longer ranges using AAR.
Reserve fuel policies vary between regulatory
bodies, domestic / International flights, airlines and
pilots. Pilots may opt for extra reserve fuel over and
above that required by relevant regulations.
Typical average values for X are 15000+ nm.
The current trend is for ever-larger more
powerful engines. Naturally, the emphasis is on
increasing fuel efficiency for the larger units. Some
of the favourable design developments can be
scaled for smaller engines, fuel efficiencies are
relatively less for the latter. Geared fans may help.
The development of Prop fans may result in
quieter and more fuel-efficient power-plants. The
effects on X values due to the resulting changes in
V and SFC need to be assessed.
3. AIR-TO-AIR REFUELLING (AAR),
CIVIL AIRCRAFT
3.1. Comparing 3000, 6000, 9000 & 12000 nm
Range Aircraft with and without AAR
Based on Refs.8, 11 & 12, the approach is to
design representative aircraft to carry the same
payload of 250 pax. over 3000, 6000, 9000 & 12000
nm and then estimate the fuel saved by using the
base 3000 nm range aircraft with AAR for the
longer ranges. The base aircraft requires less than
50,000 lbs of fuel per 3000 nm stage, dispensed
fairly easily from current tankers, provided the
operational tanker range is kept low. Each tanker
may accomplish 3-4 operations in a mission.
The relative sizes of the aircraft designed for 250
passengers over the different ranges are compared
in Fig.11. The fuselage size remains constant, the
wing area increases rapidly to contain fuel needed
and to maintain CL as design range increases.
The base aircraft weight variation over 3000 nm
is shown in Fig. 12. The block fuel used to carry
250 pax over this range is 46,147 lb (MTOW =
261,932 lb). An aircraft designed to carry the same
payload over 6000 nm, Fig. 13, uses 161,269 lb fuel
(doubling the range has more than trebled the fuel
required, MTOW = 505,438 lb). The increased fuel,
over and above that required for the doubled range,
is needed for the additional aircraft weight. This
arises from landing gear / wing structure required to
carry the additional fuel weight and provide the
extra tank volume. Fig. 13 also compares the weight
variations with range for the 6000 nm aircraft and
the 3000 nm aircraft refuelled at 3000 nm. Note the
fuel used and the savings offered by AAR, 42%
over 6000 nm (not including tanker fuel at this
stage). This amounts to saving in fuel cost of nearly
$190/pax (at $4.7/USG). With an allowance of
tanker fuel, the comparable figure is about $175.
Fig. 14 refers to the weight variations for 9000
nm range (250 pax). An aircraft without a refuelling
option would have MTOW of 656,262 lb, and burn
263,073 lb of fuel. With the 3000 nm aircraft and
two AAR operations, the block fuel would be
138,441 lb, a saving of 47% (without tanker fuel).
This amounts to saving in fuel cost of nearly
3
$350/pax (at $4.7/USG). Allowing for the tanker
fuel, the comparable figure is about $320.
3.2. Size. Cost & Noise Reductions Using Smaller
Aircraft
Even with current technology levels, using the
3000nm aircraft for all long ranges with AAR
implies not just size reduction but also associated
reductions in noise, cost, emissions, etc. We look
briefly at aircraft sizing, cost and noise trends.
Fig.15 shows the span correlation against
MTOW for several current aircraft (www.Boeing).
Ideally, wing Aspect Ratio and hence span should
be as large as possible for aerodynamic benefits.
For larger design payloads and ranges, the size and
span are subject to physical / structural / airport gate
limits (e,g. ICAO).
Fig.16 shows the acquisition cost trend against
OEW (lines C1 & C2 represent the lower and
higher quoted costs). Fig.16 shows an approximate
correlation against range. Such trends reflect the
economic situations (supply, demand, numbers built
etc.) and may be somewhat hypothetical. Essentially
large aircraft cost more.
Fig 18 shows ICAO Stage 3 noise certification
limits. Lighter aircraft have more stringent noise
requirements than heavier aircraft. In any case,
smaller aircraft do tend to be quieter because of less
installed thrust.
By using smaller, 3000 nm range aircraft with
AAR, the increases in costs, noise and pollution
associated with long-range flights can be avoided.
3.3. Cruise Climb or Constant Altitude Flight
It is useful to examine the cruise and altitude
relationships with the different range aircraft.
Aircraft wings are optimised for cruise at a
constant CL value of about 0.55. Assuming start of
cruise at 28,000 ft, if CL and M are held constant the
3000nm aircraft would climb to 32,000ft during the
cruise phase. The 6000 nm aircraft climbs to about
36,000ft and the 9000nm aircraft will reach
39,000ft, see Fig.19.
Air traffic control requires 2000 ft vertical
separation between aircraft and consequently
aircraft fly at constant stepped altitudes. Decreases
in CL, (in spite of L/D reduction) are accompanied
by a reduction in drag and thrust required. So the
compromises are lessened.
The long-range aircraft undergo the greatest
change in altitude during cruise. The fuselage has to
withstand an increased pressure differential with
obvious implications on stress, fatigue and initial
design weight. Short-range aircraft are naturally
better balanced for altitude effects and these could
be maintained over long ranges with AAR.
At constant CL, simple estimates indicate a 2%
degradation in L/D during cruise for a 3000 nm
range aircraft. For 6000 and 9000 nm range aircraft
the degradation is of the order of 7% and 12%
respectively. With 3000 nm aircraft and AAR on
the long ranges, the L/D degradations can be small.
With variable camber, constant CL need not be
maintained and altitude relationship become easier.
3.4. Fuel Burn & Operating Costs Issues
The variations of fuel burn and costs with design
range are summarised in Fig.20. The projected fuel

urn trend using the 3000 nm aircraft and AAR to
complete the longer ranges is also shown. The fuel
savings with AAR can be deduced and converted
into costs and economics.
Oil prices remain volatile. Fig.21 shows the fuel
cost escalation (Ref. Moody, IATA & Ref.13).
There has been 5.5 fold increase in the last 4 years.
Fig.22 shows the impact of doubling fuel costs
($1.74 to $3.48 /USG) on Cash Operating Costs
(COC) of B737 and B777 series of aircraft (Ref.14-
15). This data has been super-imposed on the DOC
data obtained from preliminary analyses of fuel cost
using the 3000, 6000 and 9000nm aircraft, Fig.23.
Note the rapid increase in fuel cost proportion as
fuel cost rises. For the B737, a doubling of fuel cost
increases the fuel cost fraction from 36% to 55% of
the total COC. For the B777, the fuel cost fraction
of COC would rise from 44% to 65%. Note the very
strong leverage on cost saving percentages as fuel
cost increases. As fuel costs rise still further, the
percentage overall costs savings that can be
achieved by reducing fuel burn (most effectively
with AAR) will rise significantly.
Overall the cost issues are a “form of art rather
than science” and remain subject to further
scrutiny. An A320 (2500 - 3000 nm range) costs
about $6000 per hour and an A330 (4500 nm range)
would be about double that. Operating costs and
productivity vary widely with range and airlines.
4. TANKERS, AAR & EFFICIENCY
It is opportune to mention our previous work in
Refs.16-24. These also include Close Formation
Flying (CFF). Some new interpretations arise with
respect to AAR.
4.1. AAR Tanker Fuel Off-load Capability and
Effect on Operation Fuel Efficiency
A key point is that tankers for civil work would
operate differently from military tankers. The latter,
essentially, operate as a “garage in the sky”, with
long endurance. The civil tankers will be more
“purposeful” and shorter efficient flights are
envisaged with flights planned to rendezvous with
passing civil airliners, Fig. 24.
We need to take into account the fuel consumed
by the tanker itself during AAR operations. Fig.25
(Ref.12) shows the fuel saving (%) achieved by
using a 3000 nm design, with AAR, over aircraft
specifically designed for the 6000, 9000 and 12000
nm ranges, all carrying the same payload. It is
interesting to note that we begin to make fuel
savings with RT (ratio of fuel given to that used by
the tanker) slightly less than 1 and beyond. For RT
values about 3, we are close to being within 5 - 7%
of the max. benefit obtainable. We need to further
study design ranges between 3000 – 6000nm.
All this implies that reasonably efficient tanking,
with RT near 4, should be adequate. Although more
efficient tanking will help in terms of costs and
operations, the enormous incentives offered in the
short term do not require extensive advances in
tanker design. Tankers currently available will
allow significant fuel savings to be made for
refuelling over long ranges.
4
It is interesting to note from Fig. 26, the increase
in PRE/X achieved by the refuelled 3000 nm design
aircraft over the PRE/X achieved by the designed
longer range aircraft, expressed as a percentage of
the PRE/X achieved by the respective long-range
aircraft. The improvements are large and higher for
the longer range situations. For a “reasonable” RT
value of 4, we are touching gains in PRE/X of 60%
for 6000nm and 80% for 9000nm ranges, compared
with the datum 3000 nm aircraft.
4.2. Benefits of AAR, Price, Thrust, Noise &
Airports
Fig.27 shows the effect of fuel price on savings
in costs using the 3000nm aircraft for journeys of
6000 and 9000nm. It is interesting to note that once
civil AAR is in place and cost savings of say 26%
(6000 nm range) and 37% (9000 nm range) are
achieved, further fuel price increases will maintain
and possibly increase these costs savings.
The variation of total thrust required for specific
aircraft designs with range is shown in Fig.28. We
note immediately that with AAR, the basic 3000 nm
aircraft can operate all ranges with a constant
maximum thrust available of 88,000 lb. The aircraft
designed for 9000 nm requires total thrust of
219,000 lb. The 3000 nm aircraft requires 60% less
thrust. The savings in engine size, cost and noise
emissions are evident.
Further reductions in take-off noise can be
achieved if the aircraft takes-off very light, with
only sufficient fuel on board to fly to an initial AAR
rendezvous. The aircraft would then receive more
fuel to complete the first leg to the next AAR
rendezvous. An additional safety advantage is that
during the most dangerous phase of any flight (takeoff)
the aircraft is now carrying minimal fuel.
Reductions in take-off noise would allow
extended night time operations at most major
airports (relieving congestion etc.). If the aircraft
take-off lighter, then de-rated engine operation is
possible. This will enable a prolonging of aircraft
life, introducing further DOC reductions.
Further expansion of large hub airports may not
be necessary, as regional airports would now be
capable of providing long haul services. Expensive
airport developments, runway lengthening for larger
planned aircraft and additional runways for
increased traffic can be diverted from the Hubs to
the Regional airports.
4.3. Part Range Refuels & Maximum Pt A
Payload
We have taken as examples the B757-300
(MTOW 270,000 lb) and the A330-200 (MTOW
507,065 lb) to assess the effect of part-range
refuelling, flying with maximum Point A payload,
maximum efficiency.
The B757-300 could transport its maximum
payload of 68,200 lb over a range of 2388 nm
(Point A operation) without refuelling. A typical
weight breakdown is shown in Fig. 29(a). Fig.
29(b, c & d) shows the weight breakdown starting
off with different take-off weights (Light,
Intermediate and MTOW) and a single refuel of
47,850 lb (WFREF) at the respective ranges
completed. After AAR the aircraft are at MTOW

and can complete a further 2388 nm as shown. Fig.
29(e & f) shows the weight breakdown starting off
at MTOW and then refuelling after 2388 nm with
either 10% or 50% WFREF.
The A330-200 could transport its maximum
payload of 106,800 lb over a range of 4200 nm
(Point A operation) without refuelling. Fig. 30(a)
shows typical weight breakdown. The above
exercise is repeated for the A330-200 in Fig. 30(bf).
WFREF is 113,730 lb.
Fig. 31 shows the PRE / X - Z relationships for
both the A330-200 and the B757-200 with AAR.
For each aircraft, the lower line results from taking
off at less than MTOW and then refuelling with
100% WFREF. The upper line results from take-off
at MTOW and then refuelling with various fractions
of WFREF. Note the improvements are very
substantial compared with the current PRE/X trends
for Pt A and Pt D. Further work is needed on
different types.
4.4. Effects of AAR on Environment, Airlines,
Airports, ATC and Design
With global acceptance of AAR, greater use will
be made of medium size civil aircraft in the 250
pax, 3000nm range category. This will serve all
medium and long-haul operations. There will be
less need for very large long-range aircraft. The
knock-on effects will multiply, affecting every
aviation aspect positively. Complexities also arise.
Environment
Aviation fuel reduces - obvious global benefits.
For Airlines
Fuel costs to the airline will reduce.
Fleet operators and airlines will benefit from a
uniformity of aircraft type. This will improve
maintenance standards and reduce costs. Crew
(flight and cabin) training costs will be reduced.
Purchasing large numbers of smaller aircraft
should be more economical than purchasing a few
very large aircraft. The quantity of spare aircraft
(maintenance, delays, diversions, etc) and spares in
general that is required for efficient daily operations
can be reduced.
It is unlikely that passenger or cargo trends will
reduce in the future and therefore with 200 - 250
seater aircraft operating instead of 400 - 500 seater
jumbos, additional flight crews will be required.
The ratios of cabin crew and ancillary staff to
passengers will be maintained (no appreciable
changes in staffing levels).
Airports, Regionals, Wakes, Night-time
With Regional airports able to cope with a
greater proportion of aircraft and passenger
movements, pressure on the Hub airports will be
reduced. Further expansion (additional and
extended runways, additional or expanded
terminals) at the large Hub airports will not be
necessary. Congestion, in and around the Hub
airports will be reduced making them more
convenient / attractive for passengers and freight.
This will also impact on reducing emissions.
The trailing vortex strength K of an aircraft
(elliptic loading) is equal to 2/π CL cav. Assuming
similar values of CL for the conventional types, K
becomes proportional to cav.
5
It is interesting to reflect on wake strength for
different classes of aircraft. Concorde’s low speed
CL was about 0.6 and its combination with a large
cav yielded a vortex strength very similar to that of
the B747. The low aspect ratio (about 1.7)
“encouraged” a strong dissipation rate in the wake.
The separation of aircraft at take-off and landing
is dictated by the strength of the vortices shed by
the previous (lead) aircraft. By utilising smaller 250
seat, 3000 nm aircraft, separation times can be
reduced affording a 50-70% increase in actual
aircraft movements at each airport. The vortices
spread outwards in ground effect. Smaller aircraft
imply weaker vortices and hence a reduced affect
on adjacent runways. This will lead to a safer use of
adjacent, parallel runways. Smaller aircraft behind a
larger one still need longer separations.
The smaller, lighter aircraft are quieter and this
will allow an increase in night-time activity. This
will, again, reduce congestion at airports both in the
air and on the ground. The possibility of aircraft
taking-off with only a minimum of fuel on board,
sufficient for them to fly to an AAR rendezvous 250
to 500 nm away or divert if necessary, will further
reduce take-off noise and reduce pollution.
ATC facilities
Initially, as greater use is made of Regional
airports, it is likely that ATC activities will reduce
near the Hubs and increase near the Regional
airports. Overall, using smaller aircraft, ATC
activity will increase but local, high intensity hotspots
will be eliminated resulting in a more uniform
and safer level of activity.
Aircraft Design
The current design philosophy is for an aircraft
to be sized for a given payload over a certain range
with sufficient fuel and reserves. For long-range
flight, the payload becomes a relatively small
fraction, whilst the weight of fuel at take-off may
touch 50% of the total weight. The engines have to
be selected and rated accordingly. Maximum thrust
is required at take-off to accelerate the aircraft over
a limited runway length and then climb to a safe
height before throttling back. During the take-off
phase the engines are often over-rated, a
requirement that is “designed-in”. Effectively,
current long-range aircraft have to be “overwinged”
and “over-powered”.
With the knowledge that AAR is available,
aircraft could be designed to take-off with minimum
fuel on board, sufficient to reach a first AAR
rendezvous. The wings could be sized to
accommodate fuel tanks with the capacity for 3000
nm cruise range fuel only, resulting in much smaller
wings and a lighter design. The thrust required to
accelerate this smaller, lighter aircraft within
existing runway lengths is significantly reduced.
Smaller, lighter engines can therefore be specified.
The requirement to over-rate the engines during
take-off and climb-out could be reduced or even
eliminated. The result is a much quieter take-off.
Engine life can be extended.
4.5. What is Demanded of the Tankers? – The
Options

Fig. 32 shows possible options. Reverse tanking
(tanker behind the receiver) with boom and
receptacle may well be the preferred option. The
tanker aircraft will do all the positioning and control
work whilst the receiver aircraft continues on its
way. There have been many recent advances in
AAR systems e.g. in differential GPS and
autonomous refuelling, RARO, night vision etc. as
mentioned in previous papers
Fig. 33 shows various tanker capabilities (fuel
off-load and radius) currently envisaged by the
military. The civil interest will be over a range of
about 1000nm (radius 500nm).
4.6. Phasing in AAR
This is related to the time and finances available.
A worldwide network of bases for tanker operations
can be envisaged. This would serve airlines using
3000 nm range aircraft equipped with AAR
receptors. At present, operators tend to fall into
various categories: Cargo, Passenger, Passenger and
Cargo, Domestic (short haul), International (short
and long haul), National (“Flag carriers”) and
privately financed. Some diversity will exist with
the introduction of civil AAR. A small carrier,
equipped with short to medium range aircraft, could
buy-in AAR services and offer long-haul flights.
The AAR services may operate along the same
economic principles as airport and ATC services.
Based on figures already introduced, each
tanker, in a day, can undertake 8 to 12 flights and
service 20 to 30 aircraft. ICAO world airline data
indicated 1,672,000,000 passenger movements
worldwide in 2000, together with 33,500,000 tonnes
of cargo. We assume that 25% of the passenger and
50% of the cargo departures were long haul (6000
nm). Using our 3000 nm aircraft with AAR for
these long haul operations we would need 3,260
AAR operations daily. This equates to a global fleet
of about 160 tankers. Such estimates can be further
refined in due course.
The civil AAR operations will be phased in over
a period of time. It would be prudent to commence
with cargo aircraft to build up public confidence for
accepting the new procedures. During this
introductory phase, AAR service suppliers would
begin to generate finances, thereby encouraging
financial interest.
It is possible that a cargo carrier would seize the
opportunity of providing the tanker services,
especially if they already had operational /
maintenance bases, strategically placed along the
long-haul routes.
The United States Transportation Command
(USTRANSCOM) coordinates the movement of
materials and supplies worldwide for the US
military. Aircraft used for these operations include
the C-5 and the C-17. Frequent use is made of AAR
for the longer ranges. A proof of concept and initial
evaluation of AAR in civil aviation to reduce fuel
consumption could be undertaken by the military.
Market Forecasts
Using the latest Boeing Studies (Ref.15), one
can conjecture with AAR, a change in the new
deliveries at least, See Table 1. There is always
6
need for more detailed work including fuel savings
and costs!
In the above forecasts for 2027, 3,890
Freighters are included. These comprise 35%
standard body (80 tonnes).
With AAR, the Twin-Aisle aircraft needed will
be the smaller range versions, either modified or
new (more fuel efficient with increased payloads,
pax + cargo). These will affect the Single-aisle
numbers also. About 200 Tankers will be added.
_
5. CASE STUDIES AND COST
IMPLICATIONS
We consider a set of scenarios as illustrated in
Fig.33. Depicted are possible routes (a, b and c) and
tanker base locations.
(a) Based at Anchorage
North America to Asia could utilise AAR
operations based at Anchorage. This is one of the
busiest International air cargo airports, with 2.15
Million Tonnes handled in 2005. This gives an idea
of the scale of operations passing through / over
Anchorage. Typical distances are Tokyo to
Anchorage, about 3000 nm and Anchorage to New
York, 2935 nm.
(b) Europe to Australia
This would allow an airliner to depart, for
example, from London with a full complement of
passengers and freight and fly non-stop to Sydney.
It could take off using de-rated thrust, climb quickly
to best cruising altitude and use AAR to achieve a
direct flight. Avoiding a technical stop would help
in potentially halving the life-cycle costs and
extending its service life.
This case follows the example of the 9000nm
aircraft potentially saving 40% fuel.
(c) US West Coast to Australia
West coast USA to Australia could use the old
“Flying Clipper” routes of PAA - Honolulu, Guam,
Nadi, etc as tanker bases. Typical distances in this
region are Los Angeles to Honolulu, 2220 nm and
Nadi to Sydney 1710 nm. The early “Flying
Clippers” pioneered such routes.
An Example with Freighters, B747F & B767F
The B747-400F, operating close to Pt B
(MTOW), can carry a payload of 123,000 lb over
7,200 nm. At reduced TOW, it can carry twice that
payload over 3600. The B767-300F, at Pt A, carries
123,000 lb over 3,300 nm. Using various
combinations of aircraft and payloads we note, in
Table 2, fuel savings afforded by AAR. Tanker fuel
has been taken into account, RT = 4.
Refuelling the B767-300F with 88,451 lb and
later ‘topping-up’ with 16,082 lb is not the most
efficient scenario or use of tankers. Greater savings
could be achieved with alternative arrangements,
e.g. taking off light and refuelling to maximum
capacity twice, or naturally, more efficient aircraft.
In addition to the DOC estimates we currently
employ for civil passenger aircraft, it would be
useful to have some idea of two associated tanker
costs. The first of these is the tanker operating cost
per hour. This could be derived from military
figures with a conversion to civil operations. The

second is the basic cost of converting say, an A330
or B767 into a civil MRTT. The cost will be
appreciable but not restrictive.
The possibility of converting an existing airliner
to a pure freighter is factored in to the life cycle of
most types. The additional cost of including AAR
and tanking facilities is actually quite a small
percentage of the total conversion cost. Freight
doors and floor strengthening are the costly
structural items. If, by utilising AAR, a technical
stop can be avoided then a valuable ATC slot can be
traded or sold. At London, Heathrow (LHR), at
peak time, a paired departure and arrival slot would
be worth about £30 million.
6. AN UNCONVENTIONAL
CHALLENGING CONFIGURATION
We have shown that maximum fuel efficiency is
achieved by aircraft designed for approximately
3000 nm range. Using AAR, this high efficiency
can be maintained over longer ranges. Currently,
the B757 is a fuel-efficient aircraft. It carries 200 to
220 pax (single-aisle) over 3000 nm. It may not
offer adequate comfort for long-range flights.
It is opportune to consider possible challenging
unconventional designs, exploiting the 3000nm
range and the advantages afforded by AAR.
A current interest is the design of moderate
range aircraft, broadly in the class of the Airbus
A320 series. We aim at 220 seats (as in A321) in an
economy twin-aisle cabin. This implies a shorter,
stubbier, fuselage than the A321. With emphasis on
fuel-efficient flight, the Range parameter (X = V.
(L/D)/SFC) needs to be increased. For conventional
layouts, although near maturing technology levels,
respectable gains are still feasible with lighter
structures etc. It is always difficult to include
radical changes in an established line!
It may be useful to consider unconventional
types such as a Joined-Wing layout enabling a high
aspect ratio (AR) wing to improve L/D. Many
related structural issues exist as shown in Fig.35,
Ref.25. The join is at 0.6 y/s. The power-plant
location offers several choices. The immediate
benefit of reduced cabin noise afforded by rearmounted
engines is evident.
Structural integrity of fuselage or tail-mounted
engines requires further thought. Similarly, the
effects of thrust-line on high mounted engines
compared with those at the fuselage side will have a
bearing on wing-tail location. Design considerations
(structural and aero-elastics) need to include the
height of the rear wing and its join on the fuselage
or vertical fin. An alternative proposal is with
forward swept tips with a different set of
compromises. All this will be an interesting future
topic. It may be useful to think also in terms of a
strut-braced version.
The main sizing driver is the integration of a
fuselage in a joined-wing layout coupled with the
requirement for adequate fuel storage. The payload
- range performance demands, therefore, lead to
reasonably thick aerofoils (t/c normal to the LE,
between 12 and 15%) operating at moderately high
CL values, near 0.6. Depending on wing sweep,
7
thicker aerofoils can be adapted for hybrid laminar
flow. Coupled with efficient propulsion, there is the
prospect of 10-20% increase in X. This in turn
implies weight reductions / fuel efficiency gains.
7. SUMMARISING, LIST FOR FIRST-
LEVEL ANSWERS FROM DIFFERENT
VIEWPOINTS
It is useful to begin a list emphasising the key
features / benefits using AAR from different
viewpoints. Some questions have been answered at
a first level. Now is the time for initiating serious
studies. Most features are inter-related. It is hoped
that these will provide insights into understanding
AAR operations / feasibility. No doubt, readers will
contribute, with a positive outlook.
AAR is a "multiplier" and Enabler
- All efficiency improvements currently envisaged for
future designs and upgrades will be enhanced
- Co-exists with Close Flying Formations (CFF) ideas
- Long range fuel consumption down 30%
- Should enable Laminar (natural or hybrid) flow
achievement (+15% say) with lesser penalties
- Works naturally with Close Formation Flying. L/D up
10%
- Long range, direct flights enabled with full load, pax
+ cargo. Fuel cost savings: $175/pax for 6000nm
with AAR, $320/pax for 9000nm with AAR
(Assuming fuel at $4.7/USG). Extending the sums
to 250 seaters, fuel cost savings are $43,750 and
$80,000 for 6000nm and 9000nm flights
respectively. Over a year, the savings for 6000nm
and 9000nm aircraft are $16 & $29 million
respectively.
- Life cycle costs halved
- Service life extended
- Costs of technical stops eliminated
- Aircraft operate at max. payload, max. efficiency
Airframe and engine manufacturers modify
design requirements
- More, smaller aircraft required (3000 nm range)
- More, lower thrust and smaller engines
- Alternative, more suitable airframe shapes may
evolve (Joined-wing)
Smaller (and more uniform) aircraft imply
- Reduced wake strength (function of weight and span
or cav, given CL)
- Reduced separation time, Increased frequency of
aircraft movements
- Reduced lateral translation of wake (ground effect)
- Improved utilisation of adjacent runways
- Reduced thrust requirements, climb quickly to
requisite best altitude
- Less engine noise, increase night flying capability
- More movements from a given airport (up by 30%)
- Fire hazard less with smaller aircraft, easier on
Equipment (Aviation Week, 2008)
Operators modify procedures
- Reduced investment needed (smaller airframes cost
less)
- Operate at maximum payload for maximum
efficiency

- Combi payloads of passengers and cargo, existing
large aircraft usage, taking-off lighter with AAR
- Noise reduction, Night Flying
Airport Capacities (expansion or not?) - Hubs
- Lots of passengers are in transit at hub airports. At
LHR, 40% are in transit, cf during 90’s:10%
- With AAR, passengers travel direct, reducing the
need to expand
- Regional airports expand to accept more movements
- Less need for extending runways
- Reduced activity at Hub airports to more
environmentally acceptable levels
- Reduced traffic near Hub airports
- Local airports more convenient for passengers and
cargo
- Current airport life extended indefinitely
- Reduction in cargo flights
- Probably more total ground staff, but more evenly
distributed over many airports
Tankers, tanking operations (locations & how)
- Assuming 2-3 hours flight, a tanker could re-fuel
between 20-30 aircraft during a working day.
- Tankers operate from dedicated airfields, near fuel
supply but away possibly from habitation/airports
Safety issues
- Proximity during AAR operation: Differential GPS,
RARO, Autopilots linked
- Autonomous Refuelling is being developed by the
USAF. Demonstrations are at advanced stage.
- Take-off and Landing, safer with smaller aircraft
- Less intermediate stops but more aircraft
- Safe, used to extend range of Air Force One (a
Boeing 747 200 series) for the last 20 years, Fig.36.
Challenges posed by AAR to technical and
business community.
- Less types of aircraft needed
- Investments and ever-changing cost scenario e.g. Fuel
price volatility
- As fuel prices increase, this provides an added
impetus. This is certainly a key.
- At first sight, it may appear to be expensive, but not
in long run.
- Procedures, technology and much of the hardware
already in place
- Costs and benefits appear relatively straight-forward
and convincing
Partnership opportunities with Military &
Existing Commercial groups, Alliances, etc.
- Increasing the Tanker Values. In general, the military
use is relatively less (

6. JUPP. J.A., “Mitigating the Environmental Impact of
Aviation”, Presentation, AeIGT, 2006.
7. FIELDING, J.P., “Introduction to Aircraft Design”,
Cambridge University Press, 1999.
8. JENKINSON, L. R., SIMPKIN, P. & RHODES, D., “Civil
Jet Aircraft Design”, Arnold, 1999.
9. NANGIA, R.K., “Efficiency Parameters for Modern
Commercial Aircraft”, RAeS Aeronautical Journal, Volume
110, no 1110, pp 495-510, August 2006.
10. GREEN, J.E., “Kuchemann’s weight model as applied in
the first Greener by Design Technology Sub Group Report:
A Correction, Adaptation and Commentary”, The RAeS
Aero Jo., Vol.110, No. 1110, August 2006.
11. NANGIA, R.K., “Operations and Aircraft Design Towards
“Greener” Civil aviation Using Air-to-Air Refuelling”, The
RAeS Aeronautical Journal, November 2006.
12. NANGIA, R.K., “ “Greener" Civil Aviation Using Air – to
- Air Refuelling - Relating Aircraft Design Efficiency &
Tanker Offload Efficiency”, The RAeS Aeronautical
Journal, September 2007.
Present State
13. WARNER, M, Boeing Presentation, 2008.
14. VerWey, J., “Discovering the Right Balance – Perspectives
on Next-Generation Commercial Jet Engines”, Boeing
Presentation, September 2007.
15. www.Boeing.com
Recent Lectures & Papers (AAR & CFF)
16. NANGIA, R.K., “A Vision for Highly Fuel-Efficient
Commercial Aviation”, EUCASS 2007, Brussels, July
2007.
17. NANGIA, R.K., “Highly Fuel-Efficient Civil Aviation – An
Opportunity for Present & Vision for Future”, CEAS 2007-
264, Berlin, September 2007.
18. NANGIA, R.K., “Commercial Aircraft Efficiency
Considerations & Meeting Environmental Challenges using
Air-to-Air Refuelling & Close Formation Flying”, AIAA,
ATIO meeting, AIAA-2007-7720.
19. NANGIA, R.K., “Highly Fuel-Efficient & Greener Aviation
– A Step Jump, Why & How”, Presentation to RAeS,
Bristol, 15 th October 2007.
20. NANGIA, R.K., “Highly Efficient and Greener Civil
Aviation - Step Jump, Why & How, An Opportunity for
Present & A Vision for Future”, COIAE - AIAE, Madrid,
21 st November 2007.
21. NANGIA, R.K., “Highly Efficient and Greener Civil
Aviation - Step Jump, Why & How, An Opportunity for
Present & A Vision for Future”, IAR, Cambridge
University, 4 th February 2008.
22. NANGIA, R.K., “Highly Efficient and Greener Civil
Aviation – Organising a Step Jump towards ACARE Goals
& How, An Opportunity for Present & A Vision for
Future”, RAeS Conference “Aerospace 2008 – The Way
Forward”, London, 22-24 April 2008.
23. NANGIA, R.K., “Way Forward to a Step Jump for Highly
Efficient & Greener Civil Aviation, An Opportunity for the
Present & a Vision for Future”, Presentation to NASA
Langley Research Centre, Virginia, USA, 11 September
2008.
24. NANGIA, R.K., “Achieving Highly Efficient Civil
Aviation - Why & How with Air-to-Air Refuelling, Review
& New Developments”, ICAS-2008-4.10.1. September
2008.
New Fuel-Efficient Types
25. NANGIA, R.K., PALMER,M.E. & HYDE, L., “Exploiting
Joined-Wing Layout for Efficient Civil Transport Aircraft
9
for Moderate Ranges”. Paper 13, RAeS Applied
Aerodynamics Conference: “The Aerodynamics of Novel
Configurations. Capabilities & Future Requirements”,
London, Oct. 2008.
Useful General References
26. WHITFORD, R. ”Fundamentals of Airliner Design”, Air
International, July 2003
27. KUCHEMANN, D. "The Aerodynamic Design of Aircraft",
Pergamon, 1978.
28. KULFAN, B., Presentation to NRC, USA, 2001.
NOMENCLATURE
AAR Air to Air Refuelling
AR Aspect Ratio
ATC Air Traffic Control
b = 2 s, Wing span
c Local Wing Chord
cav = cref = S/b, Mean Geometric Chord
CD = D /(q S), Drag Coefficient
CDi Lift Induced Drag Coefficient
CL = L/(q S), Lift Coefficient
Cm =m/(qS cav ), Pitching Moment Coeff.
COC Cash Operating Costs
D Drag force
DOC Direct Operating Cost
GPS Global Positioning System
kt Knots, nm/hr
L Lift Force
L/D Lift to Drag Ratio
m Pitching moment
M Mach Number
MTOW Maximum Take-Off Weight (=TOW)
OEW Operating Weight Empty (also WOE)
OEWR = OEW / MTOW
Pax Passengers
PRE Payload Range Efficiency WP*R/WFB
q = 0.5 ρ V2 , Dynamic Pressure
R Range
s semi-span
S
SFC
= 1/hr
Reference Area (SL Lead Wing, ST Trail)
Specific Fuel Consumption, lb (of fuel)/hr / lb (thrust)
T/W Thrust to Weight Ratio
USG US Gallon
V Airstream Velocity (kt)
WP Payload (WP) W F
Fuel Load (Block + Reserves = Total)
WFB Block Fuel
WFREF Maximum Refuel Load
WFT Tanker Fuel
x,y,z Orthogonal Co-ordinates, x along body
X = V L/D / SFC, Range Parameter
Z = R / X, Non-Dimensional Range
α AoA, Angle of Attack
λ Taper Ratio, c t/c r
Λ LE Sweep Angle
η = y/s, Non-dimensional spanwise distance
ρ Air Density
© Copyright, Dr R.K. Nangia 2008. All Rights Reserved. Published by RAeS with Permission

-------------------------------------------------------------------------------------------------------------------------------
In service New Deliveries With AAR
2007 2027 By 2027 By 2027
747 & Larger 910 1,340 980 200 (Possibly Less)
Twin-Aisle 3,480 8,290 6,750 7,000 (But Smaller Range Versions)
Single-Aisle 11,450 23,540 18,100 20,000 (say)
Regional Jets 3,160 2,630 2,510
Totals 19,000 35,800 29,400
------------------------------------------------------------------------------------------------------------------------------
Table 1 MARKET FORECASTS (Boeing) & EFFECT OF AAR
Aircraft Payload
(lb)
Range
(nm)
Fuel
(lb)
Tanker
Fuel (lb)
Total
Fuel (lb)
% Fuel
Saving
A B747-400F 123,000 7,200 338,016 - 338,016 Current Long-Range -
B B747-400F 246,000 3,600 190,043 - 190,043 95% MTOW, WPA -
C B767-300F 123,000 3,300 88,451 - 88,451 Current Point A -
D B747-400F 246,000 7,200 2 x 338,016 - 676032 Requires 2 x a/c -
E B747-400F 246,000 7,200 2 x 190,043 47,500 427,586 1 x a/c Pt A + AAR 36.8 cf D
F B767-300F 123,000 7,200 2 x 88,451
+ 16,082
8%
10%
12%
Fig.1 CO2 EMISSIONS FROM TRANSPORT
26,133 219,117 1 x a/c Pt A + AAR 35.2 cf A
Table 2 EXAMPLE WITH AAR ON FREIGHTERS
USG/100
pax.
miles
Fig. 2 FUEL CONSUMPTION PER 100 PAX MILES v LOAD
FACTOR
10
lt/100
paxkm
8
6
4
2

© Copyr
B747-400
Max Payload
B757-200
WP/MTOW
Fig.3 DISTRIBUTION OF STAGE LENGTH, FUEL
BURN & NOX EMISSION
B707-320B
WP lb
A
B,D
(a) Usual
0.20
0.15
0.10
A
B757-200
0.234
Z = R/X
0.181
A
B,D
A
B, D
R 1000 nm
WP/MTOW
New
Designs
B777
B747
B787
A380
A350XWB
WP/MTOW
B747-400
0.15
0.10
B757-200
B747-400
(c) Non-D with PRE/X lines
11
0.187
-
0.123
Current
65%
Fig.4 CUMULTIVE WORLD FUEL BURN vs
STAGE LENGTH
B757-200
B707-320B
(b) Comparing Non-D Versions
WP/MTOW
7.5% shift
Future 50% !
B747-400
B707-320B
0.15
0.10
New
Designs
B777
B747
B787
A380
A350XWB
Stage Length
Z = R/X
PRE/X
0.163
Z = R/X Z = R/X
FIG. 5 PAYLOAD - RANGE DIAGRAMS, USUAL & NON-D INTERPRETATION
B757-200 X=13,646nm, B747-400 X=14,473nm, B707-320B X=9,493nm
B707-320B
0.097

Ratio to
MTOW
HBP
HBP
HBP
HBP
Fig. 6 DERIVED WEIGHT RATIO TRENDS
WFB / WP
Refs at
3000nm
RANGE R
28%
44%
R nm
51%
Pt A
Curve
Range R
61%
Sum=1
OEW+WP
Z = R/X
OEW
WFB
Payload
Reserves
X nm
Fig. 8 WFB / WP vs Z = R/X, Pt A & Pt D
Note: Parallel Scales of R Implied for Different X Values
Refs at
3000
nm
VEMPX
Fuel
Reserves
Ratio
WFR/WP
Increases
with With Range
Range
12
A321 - 100
PRE / X
1.0
Refs at
3000nm
1.0
A300 -600
28%
Pt A
A310 - 300
R nm
Pt D
Pt A
WFB/WP
51%
44%
Pt D
Fig. 7 FUEL RESERVES RATIO WFR/WP
61%
Z = R/X
X
2.0
RANGE R 1000 nm
3.0
70%WP
A340 -500
PRE
nm
X nm
Fig. 9 PRE/X vs Z = R/X, Pt A & Pt D
Note: Parallel Scales of PRE Implied for Different X
VEMPX= PRE/X*WP/MTOW
VEOPX=PRE/X*WP/OEW
VEOPX
Fig. 10 CIVIL AIRCRAFT, NON-DIMENSIONAL EFFICENCY
PARAMETERS VEMPX & VEOPX
Z = R/X
Fuel Reserves
4.5% MTOW

3000nm
MTOW 261932 lb
Wing Area 1943 sq ft
WEIGHT lb
MTOW = 261932 lb
6000nm
MTOW 505438 lb
Wing Area 3750 sq ft
13
9000nm
MTOW 656262 lb
Wing Area 4868 sq ft
Fig. 11 COMPARING AIRCRAFT DESIGNED FOR DIFFERENT RANGES, 250 Pax.
WFB = 46147
WFR = 11506
WP = 52360
DIstance nm
Fig. 12 AIRCRAFT WEIGHT VARIATION WITH
DISTANCE FOR 3000 nm RANGE NO REFUELLING, 250
PAX., OEWR = 0.58, X = 15077 nm
WEIGHT lb
Wing Area 1943 sq ft
MTOW = 656262 lb
MTOW = 261932 lb (3000 nm) [38%]
WEIGHT lb
MTOW = 505438 lb
MTOW = 261932 lb
12000nm
MTOW 860445 lb
Wing Area 6383 sq ft
WFB = 161269
WFR = 24943
WP = 52360
WFB Saved = 65975 [ 43% ]
Tanker Fuel = 9000 [4% ]
Total Saving = 37%
WFB = 92294
Distance nm
Fig. 13 AIRCRAFT WEIGHT VARIATION WITH DISTANCE FOR
6000 nm RANGE AIRCRAFT, REFUELLED ONCE cf AIRCRAFT
WITHOUT AAR, OEWR = 0.528, 250 PAX. 3750 ft 2 , X = 15077 nm
Distance nm
250 pax, 9000nm
MTOW 656262 lb
Wing Area 4868 sq ft
WFB = 263073
WFR = 32387
WP = 52360
WFB Saved = 124632 [ 47% ]
Tanker Fuel = 18000 [6% ]
Total Saving = 41%
WFB = 138441
Fig.14 AIRCRAFT WEIGHT VARIATION WITH DISTANCE FOR 9000 nm RANGE AIRCRAFT (X = 15077nm)
REFUELLED TWICE cf AIRCRAFT WITHOUT REFUELLING, OEWR = 0.47, 250 PAX., S = 4968 ft 2 , X = 16897

$Usm/pax
42
40
38
36
34
32
30
28
26
24
22
20
$Usm/lb
Ref
+48
+80
Fig.15 SPAN vs MTOW
Fig.17 ACQUISITION COST INCREASES
WITH DESIGN RANGE
Altitude
kft
Re.s at
3000nm
9000 nm
6000 nm
A380
Range
Fig.19 ALTITUDE ATTAINED AT END OF
CONSTANT CL CLIMB CRUISE
EPNdB
Take-off
14
350
300
250
200
150
100
50
upper
lower
A
O
0
0 100000 200000 300000 400000 500000 600000 700000
+10%
Ref.
+7%
TOW tons
ICAO Stage 3, Jets & Transports
Fig.18 ICAO STAGE 3 NOISE
REGULATIONS REFLECT THE MTOW
3000 nm
Aircraft
start
0.4 0.5 0.6 0.7 0.8 0.9 1
W2/MTOW
5000
4000
3000
FUEL lb
2000
1000
0
US$ millions
Ref. at
3000nm
Fig.16 COST vs OEW
Without AAR
Side - line,
Approach
+3%
Ref.
+6%
TOW tons
B747-400
396.9 tons
Noise Measuring Points
Total Fuel
(including reserves)
AAR
Block
3000 6000 9000 12000
Range (nm)
Fig. 20 FUEL SAVED WHEN FLYING 6000 or 9000 nm,
USING AAR ON 3000nm AIRCRAFT, INCLUDING TANKER
CHARACTERISTICS, 250 Pax
C1
C2

45%Fue 36%Fue
B777-300ER
65%Fue
$0.8/USG
$4.3 /USG
M. Warner, Boeing
July 2008
Oil Prices Volatility, 5.5 Fold increase in 4 years!
15
2001-04
level
Fig. 21 FUEL COST ESCALATION FROM 2001 (Moody, IATA & Ref.13)
B737-800
55%Fue
l
FIG. 22 IMPACT OF FUEL COSTS ON AIRCRAFT
CASH OPERATING COSTS, 737 & 777 SERIES (Ref.10)
Refuel
Operations
3-4, 5-6, 7-8
0.6
0.5
0.4
0.3
0.2
0.1
Tanker Weight & Range
0
Fuel cost/Total cost
COC
777-300ER
COC
737-800
Fig. 24 TYPICAL CIVIL AAR TANKER OPERATING SCENARIO
Settle ?
DOC Ref &
Others
$/USG
$/USG
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Fig. 23 FUEL COST AS A FRACTION OF TOTAL COST,
FRACTION INCREASES WITH FUEL PRICE (COC & DOC)

60
40
20
0
0 2 4 6 8 10
-20
-40
-60
Thrust
35000
30000
25000
20000
% Saving in Fuel
RT = Fuel Given / Tanker Fuel used
Fig. 25 SAVING IN TOTAL FUEL CONSUMED
3x11000
4x75000
2x110000
0
-0.1
-0.2
-0.3
-0.4
-0.5
12000
9000
6000
nm
0 1 2 3 4 5
Fractional
Change
16
% GAIN IN PRE / X
160
140
120
12000
100
9000
80
6000
60
nm
40
Using a
20
3000nm
0
Aircraft
-20 0
-40
2 4 6 8 10
-60
RT = Fuel Given / Tanker Fuel used
Fig. 26 % IMPROVEMENT IN PRE / X USING a 3000 nm
AIRCRAFT WITH AAR,
VARIATION WITH TANKER FUEL OFF-LOAD
$/USG
6000 nm
9000 nm
Fig. 27 30-40% SAVINGS IN COST USING 3000 nm AIRCRAFT FOR
6000 & 9000 nm RANGES WITH AAR
169 klb
219 klb
NO AAR
15000
10000
2x45000
88 klb
88 klb
AAR
5000
0
0 2000 4000 6000 8000
Range nm
10000 12000
Thrust Required Increases WITHOUT AAR
287klb
0 3000 6000 9000 12000
0
-10
-20
-30
-40
-50
-60
-70
-80
$USG
Thrust Reduction Proportion using the 3000 nm aircraft
Noise also reduces
Fig. 28 VARIATION OF AIRCRAFT THRUST REQUIREMENT WITH DESIGN RANGE,
WITHOUT AND WITH AAR AVAILABLE
Range nm

Fig. 29 VARIATION OF WEIGHT WITH DIFFERENT REFUELLING OPTIONS ON B757-300, One Refuel, 47,850 lb
lb
lb
270,000
507,065
230,000
TOW lb
250,000
400,000 450,000
17
270,000
507,065
270,000
(a) (b)
(c)
(d) (e) (f)
Ranges (1000nm)
TOW lb
Ranges (1000nm)
MTOW = 270,000 lb
MTOW = 507,065 lb
507,065
270,000
(a) (b) (c) (d) (e) (f)
507,065 lb
(a) (b)
(c)
(e)
(f)
Fig. 30 VARIATION OF WEIGHT WITH DIFFERENT REFUELLING OPTIONS ON A330-200, One Refuel, 113,730 lb
PRE/X
Pt A Curve
MTOW
35%
85%
With AAR
B757-200
Lighter
Pt D Curve
A330-200
Z= R/ X
125% benefit
Fig. 31 PRE/X – Z, CURRENT A & D POINT TRENDS (Fig.5) AND
VARIATION WITH DIFFERENT REFUELLING OPTIONS FOR A330-200 and B757-300
Note the Benefits with respect to PT A & Pt D Curves
P

Fuel Offload
1000 lb
300
250
200
150
100
50
0
Tanker Above
Receiver
Receiver
Civil Interest
Receiver
Alternative
Fig. 32 POSSIBLE CENTRAL RECEIVER OPTIONS
0 1000 2000 3000 4000 5000
18
“Conventional”
Raise a Telescopic Boom
Short Probe
Tanker Below
Lower Fuselage
Receptacle
Tanker Above
Lower a Telescopic Boom
Short Probe
Fin Top
Receptacle
KC135
R KC-10
A310
B-767
A330
BWB1
BWB2
Fig. 33 DIFFERENT TANKERS
CAPABILITIES. Note Civil Interest
(a) Anchorage as a Base (b) Europe to Australia (c) USA West Coast to Australia
PAA “Flying Clipper” routes
Fig. 34 DIFFERENT ROUTES SCENARIOS

Forward
Swept Tip
19
210 Seats, Typical Twin-Aisle
Useful !
Alternative Arrangements
FIG. 35 POSSIBLE JOINED-WING CONFIGURATIONS BASED ON A321-100 PARAMETERS
FIG. 36 AAR IS CONSIDERED SAFE FOR US PRESIDENT & HIS MEN !