58 AVIATION WEEK & SPACE TECHNOLOGY/NOVEMBER 3/10, 2014 AviationWeek.com/awst
J-20 vs. F-22
J-20 F-22
Overall length (ft.) 66.8 62
Wingspan (ft.) 44.2 44.5
Wing area (sq. ft.) 840 840
Operating empty weight (lb.) 42,750 43,340
Internal fuel (lb.) 25,000 18,000
Normal takeoff weight (lb.) 70,750 64,840
Max. thrust (lb.) 55,000 70,000
Min. thrust (lb.) 34,250 52,000
Clean-fuel fraction, normal T/O 0.35 0.28
Max. thrust-to-weight ratio, combat weight 0.94 1.25
Military thrust-to-weight ratio, combat weight 0.59 0.93
Wing loading at combat weight, lb./sq. ft. 69 66.5
Sources: Lockheed Martin, AW&ST analysisup moments. One way to resolve this,
the paper notes, is to use smaller, all-
moving surfaces. The J-20 resembles
the Sukhoi T-50 in being directionally
unstable, and is actively controlled with
the all-moving verticals. Song’s paper
also says the canard layout provides
positive post-stall recovery, without the
use of thrust vectoring.
The paper identifies supersonic
cruise as a requirement for a next-
generation fighter and often refers to
the need to reduce supersonic drag.
The J-20’s supercruise performance
will nevertheless be strongly afected
by engine technology. China may well
hope to acquire or emulate the tech-
nology being developed by Russia for
the Su-35S and T-50. UEC’s 117S en-
gine, developed for the Su-35S, is more
powerful than the AL-31F (32,000 lb.
maximum versus 27,500 lb. for the ba-
sic AL-31F) and has a digital control
system. The T-50’s 117 engine is similar
to the 117S, but it is further uprated
to 33,000 lb. thrust, and according
to a UEC engineer, the hot-end tem-
perature limits are increased, to allow
the engine to sustain maximum non-
afterburning thrust to higher speeds.
However, the J-20 will not match the
F-22’s thrust-to-weight ratio, even with
an engine equivalent to the 117.
The J-20’s weapon arrangement
is similar to the F-22, except that the
ventral bays are shorter and narrower,
and are apparently capable of accom-
modating only four weapons the size
of the SD-10 AAM. However, they do
appear large enough to accommodate
bigger folding-wing missiles—and Chi-
na is reported to be negotiating to buy
the Russian Kh-58UShKE, a Mach 4ZHUHAI 2014The paper addresses the design of a
fighter with a delta wing, canards and
leading-edge root extensions (Lerxes),
and discusses how the three interact.
The J-20, unlike the J-10, has a broad
body and the canard and wing are not
close-coupled. However, according to
the paper, the Lerx and canard, usedtogether and in combination with a
high degree of instability, can achieve
maximum lift coefcients that are as
high if not higher than those from a
close-coupled canard.
The paper also discusses the verti-
cal stabilizer design of a stealth config-
uration with outward-canted surfaces.
Fixed, canted tails are exposed to pow-
erful crossflows at high angles of attack,
because of the formation of vortices
from the wings and canard. The result
is that the tails can develop powerful
moments, and because the tails are
canted, those forces will include pitch-ics and materials remain uncertain.
The J-20’s wing and control surface
layout is very diferent from that of the
Lockheed Martin F-22, but the body
layout is quite similar, with twin main
weapon bays under the belly and side
bays for rail-launched air-to-air missiles
(AAMs), all located under and outside
the inlet ducts. On both aircraft, the
main landing gear is housed in the
fuselage behind the weapon bays and
the engines are close together. The big
diference, however, is that the J-20 is
9.5 ft. (17%) longer than the F-22, from
the nose to the engine nozzles. Most of
this is in the widest part of the fuselage,
and since the weapon bays are similar
in size, it is almost all available for fuel.
It is a reasonable estimate that the
J-20 could have as much as 40% more
internal fuel capacity than the F-22. The
longer body will also improve fineness
ratio, with benefits for transonic drag.
Despite the larger body, the empty
weight of the J-20 may be close to that
of the F-22, largely because it has less-
powerful engines without the heavy
two-dimensional thrust-vectoring
nozzles of the F-22’s F119s.
The J-20 prototypes are
believed to be flying with
United Engine Corp. (UEC)
AL-31F engines. The thrust
diference between the two
designs is very large: The
F-22 has almost as much
power in intermediate
thrust as the J-20 does in
full afterburner, although
newer versions of the UEC
AL-31/117S/117 could close
the gap in later versions of
the Chinese aircraft.
The conventional circu-
lar nozzles and the aft-body
shape are less conducive
to stealth than the F-22, as
is the case with the T-50.
This is most likely a conscious deci-
sion because a fast aircraft can toler-
ate a higher radar cross-section in the
aft quadrant. While some observers
have suggested that canards are in-
compatible with stealth, an engineer
who was active in Lockheed Martin’s
early Joint Strike Fighter eforts says
the final quad-tail configuration was no
stealthier than the earlier canard-delta
design.
A detailed Chinese technical paper
published in 2001 by Song Wencong,
designer of the Chengdu J-10, points to
key aerodynamic features of the J-20.
Diferences between the newer J-20 configuration (left) and the first of two
aircraft (right) include a recontoured lower-aft fuselage and longer tailbooms,
with the ventral fins moved slightly aft. The leading-edge root extension of
the new aircraft has a straight edge, and the canard and vertical stabilizer tips
are clipped. Electro-optical sensor housings are installed under the nose and
beneath the right-hand side of the fuselage, aft of the weapon bays.Podcast Aviation Week editors discuss the
design characteristics of the J-20.
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