northrop f.5 case study in aircraft design

100 Pages·2009·2.67 MB·English

AIAA PROFESSIONSATLU DYS ERIES
NORTHROFP. 5
CASES TUDY
IN AIRCRAFDT ESIGN
PRESENTEBDY
WILLIAMG .S TUART
MANAGERF, -5S YSTEMISN TEGRATION
NORTHROCPO RP.
AIRCRAFGT ROUP
SEPTEMBE1R97 8
Abstract
First the overall development of the T-38/F-5 family is presented in terms of configuration development
motivation and constraints. Then selected systems are examined in some detail, including the constraints,
specifications and trade-offs that led to important design decisions, that taken together have resulted in the
success of both aircraft.
The technological upsurge of the 1950s had made possible the development of more sophisticated fighters
for the air forces of the world. However, the new, advanced aircraft systems were unaffordable and
unsupportable within budget of developing nations or their cost was not proportional to their military worth.
The achievement of a less costly, less complex solution to defense problems became a challenge which still
confronts the defense establishment and aircraft industry.
INTRODUCTION
This paper outlines the developmento f the T-38/F 5 family of fiplhter/
trainer aircraft from 1956t hrough the present. The F-5E Tiger tr is the latest
model of this line .
ln discussing the aircraft's development, we will highlight someo f the more
interesting design challengesw hich occurred over a period of Z0 years and m a:ry
millions of man-hours of effort. This is a large undertaking for a 3 hour lecture.
'f
he re are additional equally important subjects which also could be covered only
superficially in 3 hours.
Here are some three-hour lectures which will not be given:
1) PHILOSOPHYA ND GROUNDR ULESF OR DESICN
2) A DISCIPLINEO R TECHNOLOGY/S YSTEMI NTERACTIONI \]ATRIX
3) AIR-TO-AIR and AIR-TO-GROUNDC OMBATE FFECTIVENESS
4) THE SELECTIONO F AVIONICS/WEAPOND ELIVERYS YSTEIIISA ND
ARMAMENT
5) VULNERABILITY/ SURVIVABILITY
6) THE SENSITIVITYO F LIFE CYCLE COSTST O DESIGNF ACTORS
A) PEACETIME
b) WARTIME
These subjects are mentioned to emphasizet he tremendous scope of
rbonsidered"
irterrelationships and factors which must be in the design process.
rtconsidered[
The word is put in quotes because an intuitive application of the
information is more often used than a rigorous analysis.
For the F-5, this evolution started in 1956w ith the Northrop N-156
project and is continuing at the present time with development of advanced
modelso f the F-5. The F-5 gradually evolved over the years in response to
the needs of the customer.
The first member of the T-38/F-5 family to fly was the Mach 1.25 T-38 which
became the standard supersonic jet trainer of the USAF and was also used by the
cerman Air Force for pilot training in the U. S. The T-38 is still the standard trainer
in the USAF and is also used by NASA and the USAF Thunderbirds aerobatic team.
Tbe T-38 is a very reliable, highly successfuI airplane and more than 1100w ere built.
The F-5 developmenti s typical of the steps involved in the design of a supersonic
jet fighter. The F-5 is only unique in that it was developedo ver the years, nd for the
USAF but as :rn aircraft for the foreign military sales program (FMS) and the military
assistance program (MAP). FMS customer nations have the financial resources to pay
for their aircraft whereas MAP customers receive their aircraft cost-free from the
U. S. where overall defense consideraJions outweigh the ability of the nation to pay.
Ag a MAP/FMS aircraft, greater emphasis was placed on low initial cost and lower
maintenancer equirements performed by less highly skilled technicians,
OBJECTIVEFSO RD EVELOPTIENT
0F NEWlL IAPA TRCMFT
. COMPLEXITY
R€VEREE
a OPERATINCGO ST
TREND6
a MAINTENANCE
PIIOVIDMEA XIMUFMO RCEEF FECTIVENTEHSRSU
APPLICATIOOFNA DVANCETDE CHNOLOGY
The objective for the developmento f a new military assistance program aircraft
in the late 50rs was therefore to reverse the trend in complexity, op€rating cost and
maintenance. It was realized tlat the utilization of small bigh thrust-to-weight
ratio engines previously designed for missile application, in manned aircraft
would result in significant reductions in aircraft size and weight. Decreased
size and weight are fundamental to reduction in procurement and operating cssts
and are major contributors to easier maintenance and improved operational readi-
ness. Studies were begun to spply these newer engines to applications in
manned aircraft, This in turn led to the development of the T-38 trainer as
well as the developments in the utility and lightweight cargo fields undertaken by
several other major aircraft companies. The application of advanced technology
was to be used to provide a maximum force effectiveness at minimum cost. This
became the Northrop philosophy in the development of the T-38 and F-5 Ught-
weight trainer and fighter aircraft.
IlEW TECHNOLOAGPYP UED7 0 THE
-5
F 70 tl'IEETft lAP REQr4Ts
The new technologyt hat was to be applied included secondg eneration
supersonic aerod5'namics,t he latest high thrust-to-weight ratio engines avail-
able, and the latest structural and fatigue technology combined with a design for
lorv maintenance and operation costs. We were fortunate to be on a crest of the
wave of the secondg eneration aerodynamic theory. Previously developeda ir-
craft had exhibited performance deficiencies and major problems in longitudinal
and lateral-directional stability which had caused loss of several aircraft, prob-
lems such as pitch-up on T-tail aircraft and roll coupling phenomenao n aircraft
with highly swept wlngs. The primary areas to be considered would be reducU.on
of transonic wave drag, transonic wing atrfoil development for effective cruise
performance, with empbasis on horizontsl and vertical tail configurations to pro-
vide superior flying qualides. The development of the J-85 engine with
the major increase in thrust-to-welght ratio was to be paramo{rnt in the design
and will be discussed later. The advanced struchrres technology would include
design disciplines wbjch would afford the minimum weight structure airframe
possible. The new technology to be applied would include chem milling, tapered
machined 8kins, and honeycombb onding, A further discussion of other struc-
tural considerations will follow. Because the maintenancea nd operation of
any weapon s,€tem is a major cost factor, emphasis was to be placed on compo-
'bne
nent placement using the component layer" concept.w ith easily removable
componenta as well as grornd level accessibility without use of ladders or
ground personnel stands, another payoff of reduced 8ize.
MIIESTONHElg TORY
T-35/f-5 FAA,ilLY
*'-'---f;2
ztl:S
'l-t|'.
The F-5 series started with the F-5A which first flew in 1963. The F-5A
was developed to meet the needs of the Military Assistance Program (MAP) for
developing nations. Versions of the F-SA and two place F-58 were also
developed to meet the needs of Norway, Canada, which manufactured both the
CF-5A/3 and the NF-5A,/B for the Netherlands. The SF-5A/B was also manu-
factured in Spain. The F-5E was developed in 1970a nd more than 850 F-5E
and two place F-SF airplanes have been manufactured, The airplane is also
manufactured in Switzerland and by the Republic of China in Tajwan. More than
3500 T-38/F-5 family aircraft have been manufactured and are in service in more
than 25 nations. Production is scheduled through 1981 and follow-on contracts
for later model F-5's are exDected.
l0
WN6 LOADINj
e; ,;j;t,.
d-
{.65 N
a- o WIN6 LOADINO
60-
l '33i:
:B
12,00t8B
[,302r 8
ro,'7rL B FUEU
rqo92L B
tuo)qrl
170 e-+
I t1
q( 1960 65 1970 7<
CALENDARY EAR
The chart above and the following chart show the growth in airplane
weight over the life of the airc ra-ft as the customer established the need for more
and more equipment and higher armament loads. The above chart shows the steady
wing loading increase of the T-38, N-156, F-5A through the CF-5A which led to the
wing area change in the F-sE. The increase in weight over Cme is typical of all
aircraft, not only fighters. Note tha.t despite t}te wing area incr€ase, the wing load-
ing is now once again higher than that of the CF-5A.
tz
L/FE CYCLE WE/OHT
GROWTHE THPUST
24,000
lvlAxI o. WEIGHT
U) 20,000
J
r6,000
ro.w Erexci rrnH
I
F
r
t2,000
EIAPTVW EIGHT
il
6,000
3
ENGINET HRUSLI,8 S
4,000
UPDATED
T-38AN -t56 F.5A CF-5A F-58
0 USAELFEU EL F.5E
r955 1960 65 t970
.CALENDARV EAR
The above chart shows the growth in maximumt akeoff weight, clean
takeoff weight and empty weight over the life of the aircraft. Engine
e
rady thrust (per engine) and usable fuel are also shown. The engine thrust
plot shows the change from the T-38 -5 engine (3350l b) to the -13 engine
the
.I in the F-5A (4080l b) to the -15 engine in the CF 5A (4300l b) and finally
to the -21 engine in the F 5E (5000l b).
oad-
The weight trend curves show the weight growth of the airplane
which occurred despite the stringent weight control restrictions applied.
One of the difficult tasks was to establish the value in dollars per airplane
of a given number of pounds saved. This task was necessary because
there is a known dollar cost for each proposed weight savings item due to
higher engineering, tooling, material or manufacturing costs. If the selec-
tion process was to accept only those weight saving ideas of real value to
the customer, a method had to be devised for eliminating those ideas
where the cost exceeded the value received.
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