Figure 14.2 - Four-engine Lockheed
JetStar. [Peter C. Boisseau]
...aircraft was undertaken as a private
venture. The first two prototypes were equipped with two Bristol
Siddeley Orpheus turbojet engines. The aircraft was later entered
in an Air Force competition for a small four-engine utility and
personal transport, and in this version was equipped with four
Pratt & Whitney JT-12-8 turbojet engines of 3300 pounds thrust
each. The JetStar won the Air Force competition and in that
service is known as the C-140. The aircraft is shown in figure
14.2. Production of the original JetStar ended in 1973; however,
an improved version known as the JetStar II, powered with four
Garrett TFE 731 turbofan engines of 3700 pounds thrust each, was
offered by Lockheed in 1976. Production of the type ended late in
1978, at which time a total of 160 JetStar aircraft had been
The JetStar, with a gross weight of 42 500
pounds, is one of the heaviest of the business jets. A typical
cabin configuration accommodates 8 to 10 passengers; a range of
2415 miles is possible with a payload of 3500 pounds. Takeoff and
landing field lengths are 4700 and 3550 feet, respectively. These
field lengths are based on climb and descent over a 50-foot
obstacle, however, and are not to be compared with the FAR field
lengths given in table VII for transport aircraft. Maximum cruising speed is
567 miles per hour at 21 000 feet, which corresponds to a Mach
number of 0.80.
Wing of the JetStar is characterized by a
30° sweepback angle, an aspect ratio of 5.3, and airfoil
section thickness ratios that vary from 12 percent at the root to
9 percent at the tip. An instant recognition feature of the
aircraft is provided by the large external fuel tank located at
the midspan position of' each wing. Unlike most business jet
aircraft, the high-lift system of' the JetStar is relatively
complicated and consists of  a double-slotted
trailing-edge flap and a leading-edge flap. Lateral control is
provided by ailerons without the assistance of' spoilers, and
a speed brake is located on the underside of' the
fuselage. The longitudinal trim system is unusual in that the
stabilizer is fixed to the fin, which pivots to change the
stabilizer angle. An indication of' this pivoting action is
provided in figure 14.2 by the apparently unpainted portion of the
lower part of the fin. All controls are power operated.
Gates Learjet 24B and 55
The prototype Learjet model 23 made its
first flight in October 1963 and may be considered as the
progenitor of a whole family of Gates Learjet business aircraft of
different gross weight, passenger capacity, and range. All the
aircraft, however, are of the same basic configuration. The data
VIII are for the Gates Learjet
model 24B, shown in figure 14.3. Deliveries of model 24 began in
1966, and model 24B was certified in December 1968. Over 1000
aircraft of all versions had been built by the end of 1980, and
several models are in production at this time.
The Learjet model 24B is one of the
smaller business jets with a gross weight of 13 300 pounds and a
cabin configured to accommodate a maximum of six passengers. The
aircraft has a range of 1271 miles with a maximum payload of 1910
pounds; and with full fuel tanks and a reduced payload, the
maximum range achievable is 2041 miles. The maximum cruising speed
is 534 miles per hour, and the cost-economical speed is 508 miles
per hour. Both of these speeds are at 41 000 feet; the
corresponding Mach numbers are 0.81 and 0.77. The Learjet model
24B is equipped with two General Electric CJ610-4 turbojet....
Figure 14.3 - Gates
Learjet 24B. [Peter C. Boisseau]
2850 Pounds thrust each. These engines, together with the low
gross weight, give a high takeoff thrust-to-weight ratio of 0.43.
This value of' the thrust-to-weight ratio is much higher than any
of those given in table VII for transport aircraft and is about the same as
that of the well-known North American F-86D fighter of the 1950's.
11.) As can be seen from the table,
the high thrust-to-weight ratio, coupled with a wing loading of
only 57.4 pounds per square foot, gives an outstanding short
Wing-planform shape of all Gates Learjet
aircraft is characterized by a small sweepback angle of 13,
together with a straight trailing edge. Shape of the wing can be
seen in the view of a Gates Learjet 25C shown in figure 14.4. Wing
airfoil-section thickness ratio is 10.9 percent. The high-lift
system employed on the wing is simple and consists only of a
single-slotted trailing-edge flap; no leading-edge devices are
used. Ailerons, rudder, and elevators are manually actuated;
spoilers for increasing drag and reducing lift are located ahead
of the flaps and are power actuated. Longitudinal trim is achieved
by varying the incidence of the stabilizer. Possible deep-stall
problems (see chapter 10) associated with the T-tail are avoided by the use
of a combined stick....
Figure 14.4 - Gates Learjet 25C
showing wing-planform shape. [mfr]
As in the case of the JetStar, part of' the fuel load of the Gates
Learjet 24B is carried in external fuel tanks; the tanks on the
Gates LearJet, however, are located at the wingtip instead of' the
midspan position employed on the JetStar.
Latest version of the Gates Learjet to be
offered is the model 55, which is depicted In figure 14.5.
Comparison of the data in table VIII between this model and model 24B shows that model
55 is larger, heavier, more commodious, and has a much longer
range. Not shown by the data in table VIII is the cabin size of
the Gates Learjet, which for model 55 is about a foot larger in
both width and height than for earlier versions of the aircraft.
Power in the Gates Learjet 55 is supplied by two AiResearch TFE
731-3 turbofan engines of bypass ratio 2.79 and thrust of 3650
pounds each. The lower specific fuel consumption of these engines
as compared with that of the turbojets employed on model 24B is no
doubt partly responsible for the increased range capability of the
new aircraft. The large nacelles required to accommodate the
turbofan engines are clearly evident in figure 14.5.
Perhaps the most noteworthy recognition
feature of the Gates Learjet 55 is the small winglike vertical
surfaces located at each wingtip. These tip devices are a modern
development (by Dr. Richard T. ....
Figure 14.5 - Gales
Learjet model 55. [mfr] [Original
photo was in color, Chris Gamble, html editor]
 Whitcomb of the
NASA Langley Research Center) of an old concept that is intended
to trick the flow over the wing into behaving as though the wing
span, and thus aspect ratio, is greater than is actually the case.
"Winglet" is the popular name for one of these tip devices. The
use of winglets causes a reduction in induced drag and a
consequent increase of a few percent in maximum lift-drag ratio;
some improvement in climb performance is also attributed to their
use. At least two other new aircraft employ winglets.
Not evident in figure 14.5 is the
increased wing span of model 55 as compared with earlier models of
the Gates Learjet. The corresponding aspect ratio of the new
aircraft is 7.3, as compared with 5.4 of model 24B. Improved
airfoil sections are incorporated in the wing of model 55, as are
fences and other flow-control devices designed to improve stalling
characteristics. Control and high-lift systems are essentially the
same as described for model 24B.
The Gates Learjet 56 is similar to the 55
but has a larger fuel capacity and longer range, coupled with a
somewhat reduced passenger capacity. Detailed descriptions of the
models 55 and 56 as well as others in the Gates Learjet series of
aircraft may be found in reference 130.
Dassault-Breguet Falcon 20
The Falcon 20 is one of a series of
business jets manufactured by the French firm of Dassault-Breguet.
The aircraft, with a gross weight of 28 660 pounds, lies in a
weight class about midway between the JetStar and the Gates
Learjet 24B. Power is supplied by two General Electric CF700 aft
fan engines of 4315 pounds thrust each and bypass ratio 1.9. The
Falcon 20 is used extensively in the United States and is
frequently referred to as the Fan-jet Falcon in this country.
First flight of the aircraft equipped with the General Electric
engines took place in July 1964. A Falcon 20 is shown in figure
The aircraft has a maximum payload
capability of 3320 pounds and features a cabin that can
accommodate 8 to 10 passengers. With a reduced payload of 1600
pounds, the aircraft has a range of 2 220 miles. Maximum cruising
speed is 535 miles per hour at 25 000 feet, and cost-economical
speed is 466 miles per hour at 40 000 feet. The corresponding Mach
numbers are 0.77 and 0.70, respectively. The data in table VIII indicate about the same landing and takeoff field
lengths for the Falcon 20 as for the JetStar.
Configuration of the Falcon 20 is
characterized by a wing of 30° sweepback angle, an aspect
ratio of 6.5, and airfoil-section thickness....
 Figure 14.6 - Dassault-Breguet Falcon 20 business
jet with aft-fan General Electric engines. [Peter C. Boisseau]
....ratios that vary from 10 percent at
the root to 8 percent at the tip. Figure 14.6 shows a large
flow-control fence on top of the wing part way between the root
and tip. A leading-edge flap, similar to an unslotted slat, is
employed inboard of the fence and a conventional slat is utilized
outboard. A single-slotted trailing-edge flap completes the
high-lift system. Lateral control is provided by ailerons alone.
Spoilers located ahead of the flaps are deployed symmetrically to
increase the drag for braking and rapid descent and are not part
of the lateral control system. Longitudinal control is provided by
elevators, and trim is maintained with an electrically driven
stabilizer. With the exception of the stabilizer, all the movable
surfaces are hydraulically actuated.
The Falcon 20 and its derivatives continue
in production. In addition to use as an executive transport, the
aircraft is also available in a cargo version. The latest in the
Falcon series, the Falcon 50, is equipped with three engines
located in a manner similar to that of the Boeing 727.
Gulfstream Aerospace Gulfstream