conceptual aircraft design
TRANSCRIPT
Chapter 7. Drag PolarDirector: Francisco Javier
Sánchez-Velasco
Co-director: José Serna Serrano
Curso: 2014/2015 – convocatoria: Junio
ACADEMIA GENERAL DEL AIRE
CONCEPTUAL AIRCRAFT DESIGN
MILITARY TRAINING FIGHTER
Tribunal nombrado por la dirección del Centro Universitario de la Defensa de
San Javier, el día ____ de ____________ de 20____.
Presidente: Dr. D. Manuel Caravaca Garratón
Secretario: Dr. D. Alejandro López Belchí
Vocal: Col. Dr. Andrés Dolón Payán
Realizado el acto de defensa del Trabajo Fin de Grado, el día____ de _________
de 20____, en el Centro Universitario de la Defensa de San Javier.
Calificación: __________________________.
CONCEPTUAL AIRCRAFT DESIGN
MILITARY TRAINING FIGHTER
ABSTRACT: The following work deals about the draft/conceptual design of an airplane,
specifically, a lead-in fighter trainer. Within we will describe the general characteristics
of the aircraft, obtained by simple design rules.
RESUMEN: El presente trabajo trata sobre el anteproyecto/diseño conceptual de una
aeronave, concretamente de un entrenador militar avanzado de tipo caza. En el mismo
se describen las características de la aeronave obtenidas mediante leyes de diseño
sencillas basadas en un análisis de aeronaves similares existentes en el mercado.
A mi hermano José Eugenio, incansable trabajador
y constante ejemplo a seguir
Content
1.2. LIFT concept ............................................................................................................................. 3
1.3.3. Basic training ................................................................................................................................... 5
1.3.5. Operational transition .................................................................................................................. 8
2.2. MiG-21 [1] ............................................................................................................................... 13
Chapter 3. Fuselage design......................................................................... 17
4.2. Operative Empty Weight (OEW): .................................................................................. 23
4.3. Fuel weight (FW): ................................................................................................................ 24
4.4. Maximum Take-off Weight (MTOW): ........................................................................... 27
Chapter 5. Wing loading and T/W ratio ................................................. 29
5.1. Stall ............................................................................................................................................ 30
6.1. Airfoil Geometry ................................................................................................................... 35
6.7. Tail arrangement ................................................................................................................. 38
Chapter 9. Conclusions and further studies ......................................... 47
9.1. Methodology .......................................................................................................................... 47
.1. T-38 Talon ................................................................................................................................. 51
.2. MiG-21 Fishbed ....................................................................................................................... 55
.3. Sidderley Hawk ....................................................................................................................... 57
A.G.A. Academia General del Aire
T.F.G. Trabajo Fin de Grado
LIFT Lead-In Fighter Training
HOTAS Hands On Throttle And Stick
HUD Head Up Display
HMD Helmet Mounted Display
1.1. Goal and definitions
The goal of this work is to perform the evaluation of an advanced military training jet.
With the appearance of 5th generation of fighter aircraft and the rapid advance in
technology, the training platforms used by some Air Forces are beginning to be
obsolete. In advance to the expected obsolescence, it is necessary to provide new
systems to meet the demand.
We will start by explaining the concept of a military training jet, best known as
“trainer”. When we talk about a military trainer we make reference to a jet that
belongs to an air force and it is used mainly as a training platform for the future pilots.
As we will see later, these jets also fulfill a secondary role, such as that of advanced
trainers, prepared to carry weapons and perform low profile missions, such as
counterinsurgency, when necessary.
As the technology advances, new generations of fighter aircraft appear, thus, it
becomes necessary to upgrade the technology used for future pilots training. The first
jet trainers were modifications of the original design of an aircraft, however, nowadays
most Air Forces own trainers that correspond to an operative fighter or a group of
them.
In Table 1 we can see how the concept has changed through the years.
Chapter 1. Introduction
1940
Table 1. Operative fighters and their jet trainers
One of the common characteristics of these jets is the existence of dual controls to
allow the instructor and the student to fly the airplane, giving the instructor the
capacity to control the airplane to facilitate the student’s learning and to ensure it is
being flown safely. For the achievement of this goal, there are two main arrangements
of instructor-student, side-by-side cabin or in tandem (one in front the other). It
depends on the type of training mission, but normally when flying in tandem the
student is placed in the front position while the instructor is in the rear one.
Chapter 1. Introduction
1.2. LIFT concept
Our goal is to evaluate the design of a LIFT type jet. The acronym stands for Lead-In
Fighter Training, and it is necessary to define this concept correctly.
LIFT is defined as a jet that emulates advanced fighters to train the student to operate
this weapons system. LIFT jets are usually propelled by a turbofan or turbojet engine.
This type of jet also has advanced avionics systems to habituate the user to work in an
advanced environment and in different scenarios that could be found in a modern
conflict. To achieve this goal, the jet is able to receive information from an instrument
similar to a memory stick, and show the information in a Multifunction Display (MFD),
or, in the best case, it receives the information using real-time software and tactical
data exchange networks such as the Link 16 used by the North Atlantic Treaty
Organization (NATO).
In order to manage all this information, and the typical in-flight workload (such as pure
flying tasks or communications) the pilot rely on MFD’s, HOTAS (Hands on Throttle and
Stick) and HUD (Head-Up Display) (Figures 1, 2 and 3) that make the information
clearer and manageable. In some cases even an autopilot system (AP) is available to
relieve the pilot’s workload. In a critical situation, such as an emergency, the pilot can
couple the AP and focus on solving the problem.
Since new generation aircraft start to show all the information on HMD (Helmet
Mounted Display), some LIFT jets have begun to incorporate this type of technology.
The training received in this kind of platform is divided in: contact, instruments,
formation, air-to-air tactics and air-to-ground tactics.
One of the examples of these jets is the T-38 Talon (Figure 3) used by the United States
in the advanced flight training program.
Chapter 1. Introduction
Figure 3. HUD and American T-38 Talon[9]
1.3. Training
A short summary of the different phases of the training, focusing on the LIFT and
transitional operation phases follows.
This classification is based on the American specialized undergraduate pilot training
[4].
1.3.1. Screening
Many Air Forces use light aircraft, sometimes similar to those used in the civil
industries to evaluate the skills and capabilities of the candidates. Since the first
moment the predisposition can be intuited in relation to what kind of plane each
candidate will pilot in the future.
1.3.2. Primary aircraft training
During this phase, propeller driven aerobatic aircraft are normally used, so that the
student can learn the behavior of the aircraft during aerobatic maneuvers.
Figure 4. ENAER Pillán T-35[10]
1.3.3. Basic training
This phase is carried out inside an aircraft with greater capabilities (more thrust, higher
service ceiling and in general more advanced flight features). The aircraft used are
normally aerobatic jet aircraft. For example, the Spanish Air Force use the CASA C-101
(Figure 5) for this purpose. Approximately one hundred hours of flight training are
completed in it.
Chapter 1. Introduction
1.3.4. Lead-In Fighter Training
The aircraft used for this task are low profile airplanes, light fighters, normally
propelled by one or two turbojets. These aircraft normally fly in the high-subsonic
range, even having the possibility of reaching the sound speed.
Inasmuch as they are generally light fighters, they are highly maneuverable, allowing
the plane to perform tight turns.
A great difference in comparison with the other aircraft used in previous training
phases, the aircraft used in this phase have the ability of carrying armament. However,
for the training missions the used weapons are simulated or unloaded.
During this phase, the student begins to use radar technology, simulated in some
cases, like in the Spanish F-5. This type of aircraft is equipped with a very advanced
avionics system, with MFD,s and HUD,s, these last show the pilot the information on
the windshield, so that he does not have to look inside the cabin and lose the enemy
during a dogfight.
These aircraft are used by some countries to carry out low profile missions in spite of
not being prepared to operate in a real-life
scenario, unless they do it with the support of more advanced fighters.
The case of the Spanish F-5 it is because it was designed by the Northrop Corporation
as a light attack aircraft. It has been used in some real-life scenarios; it was used during
Chapter 1. Introduction
7
the Vietnam War, serving the South side against the North. Between October 1965 and
April 1967 the Skoshi Tigers flew a total amount of 9985 missions in Vietnam in which
they lost nine aircraft.
Figure 6. Skoshi Tiger dropping napalm in a misión at Bien Hoa in 1967 [12]
The Spanish Air Force uses a version of the Northrop F-5 with an avionics upgrade
carried out by Israel Aerospace Industries.
The fighter pilot training course in the Spanish Air Force comprises five phases:
transition, instruments, formation, air-to-air an air-to-ground. Each of these phases
will be explained below:
-Transition: it comprises fifteen missions in which the student learns how to handle the
aircraft, performing aerobatic maneuvers, coordination maneuvers, traffic patterns,
and “confidence maneuvers” to reach a high level of familiarization with the airplane.
An example of the “confidence maneuvers” is the zero-velocity maneuver, in which the
aircraft is flown at an extreme angle of attack (AOA) and loses almost all the
translational velocity before being recovered. During this period, different emergency
situations are also practiced. A “solo flight” is included in the program so that the self-
confidence of the student increases.
-Instruments: like in the basic phase, the student is instructed in the handling of the
aircraft having only the flying instruments as a reference. During this phase, flights to
other fields and night flights are included along with a solo flight. This phase comprises
16 missions.
8
-Formation: It includes basic formation of 2 or 3 planes and tactical formation of 2 or 4
planes. A total amount of 19 missions are completed during this phase
-Air-to-ground: It includes the sub-phases of: low level, aerial interdiction, close air
support (CAS) and air-to-ground dropping; the last one completed at Bardenas
(Zaragoza). A total amount of 19 missions are flown.
-Air-to-air: this one is the most extensive phase, consisting on 26 missions of: aerial
interdiction, basic combat maneuvers, dogfights and night interceptions.
As it can be observed, it is a really extensive and demanding course having the goal of
forming the fighter pilots of the Spanish Air Force to fly the most advanced fighter
planes, after passing through the operational transition of which we will talk about
below.
1.3.5. Operational transition
Once the pilot has completed the training and is able to fly fighter planes and perform
basic maneuvers, he has to learn how to handle the aircraft he will pilot from now on,
the plane that he will pilot at his unit.
For this task, modified operative aircraft are used, with two-seat configuration with
minimized modifications, so that the transition to the combat-ready aircraft is simpler.
However, despite the modifications, these aircraft could be used in a real combat
situation.
An example of this kind of plane in Spain is the F-18 used in Zaragoza.
Chapter 1. Introduction
9
Figure 7. Spanish McDonnell Douglas F/A 18 Hornet in Zaragoza [13]
All this training is accompanied, in most cases, by missions in the simulator, in which
the pilot is able to practice situations that due to the risk, should not be practiced in
flight. One of the main roles of the simulator is the presentation of simulated
emergency situations that allow the pilot to learn the inputs needed in anomalous
flight situations.
In this work we aim to design a LIFT aircraft, similar to the Spanish version of the F-5
Freedom Fighter. To do so, we will start studying a series of similar planes.
We will calculate the main characteristics we want our aircraft to have, from simple
design rules. And finally we will make an invitation to a further study.
Chapter 1. Introduction
Chapter 2. Similar aircraft
The following chapter collects all the information regarding the similar planes that we
are going to study. The T-38 Talon, the MiG21 and the British Hawk.
In the Appendix A we will find the tables that represent the characteristics of the
aircraft.
12
First of all, we will make an introduction to the main characteristics of the airplane.
This introduction will be based on the official World Wide Web site of the United
States Air Force Factsheet. [5].
The T-38 Talon is a supersonic jet trainer used by the USAF future fighter pilots, to
prepare them to pilot jets such as the F-15 Strike Eagle, the F-16 Fighting Falcon, or the
B1-B Lancer.
This aircraft is also used by the NASA to train their pilots.
Its characteristics allow this aircraft to be used in a great variety of roles, although its
main use is the Air Education and Training Command.
It is easy accessibility to critical parts of the airplane make it very easy to maintain.
Depending on the version, it incorporates a gun sight, a practice bomb dispenser, and
a “no drop” bomb scoring system, facilitating the Air-to-Ground and Air-to-Air training
for the pilots.
A great variety of test pilots use this platform to put into test new technologies.
New modifications of the airplane will extend the service life to 2020 at least.
Chapter 2. Similar aircraft
2.2. MiG-21 [1]
As we did with the F-5 Freedom Fighter, we will make an introduction to the main
characteristics of the airplane. This introduction will be based on [6].
The MiG-21 is a soviet aircraft of the 50’s decade. It is a supersonic aircraft, with
retractable landing gear.
Along history, this airplane has suffered over 30 modifications, to turn it into a 4th
generation aircraft. During this time, it has served around 50 countries, and has been
present in several wars, such as Vietnam, Yom Kipur, Libia, or Ogaden.
The MiG-21 can reach Mach 2, with its single engine. The first design presented
problems with its low autonomy.
Its wing configuration allows the aircraft to perform very sharp turns, which represent
an advantage in a dogfight.
Chapter 2. Similar aircraft
14
The training versions are the “U” and “UM”. The Soviet Union built over 1200 training
versions. The final training version is the MiG-21MF, built in 1971.
All these characteristics make the MiG-21 an airplane worthy of study.
Chapter 2. Similar aircraft
2.3. Hawker Siddeley HS-1182 Hawk [1]
All the information shown in the introduction is based on reference [7].
The Hawk is a low-wing, tandem seat, subsonic aircraft that allows the RAF pilots to
carry out the advanced training. The Hawk is used to teach air combat, air-to-air firing,
air-to-ground firing and low-flying techniques and operational procedures. This
airplane is able to carry Sidewinder missiles.
This aircraft originated from a requirement of the British Royal Air Force (RAF) to
obtain a new jet trainer in 1964.
Chapter 2. Similar aircraft
16
The British Royal Navy also operates this aircraft, for the training of ship gunners and
radar operators. Another important operator is the British aerobatic team called “Red
Arrows”.
The airplane suffered some modifications that aroused the export interest. Among its
operators we can find Dubai, Kuwait, Finland, or South Korea.
17
Chapter 3. Fuselage design
To obtain an initial sizing of our aircraft’s fuselage, we will elaborate a list with the
main components of it, and we will study the main characteristics and size of each
component:
RADAR
EQUIPMENT
CABIN
FUEL
ENGINES
RADAR
EQUIPMENT
CABIN
FUEL
ENGINES
18
We proceed to obtain information of the dimensions of the different equipments.
Radar and equipment:
We can estimate this data observing the similar aircraft’s plans on Chapter 2. Simply
measuring from the T38’s plan we obtain 136 centimeters, assuming the equipment
we will need in our aircraft will be similar.
Cabin:
We will base our cabin dimensions according to an ergonomic study carried out by
Tony Bingelis called “Basic Cockpit Accomodations”[8]. We can observe the dimensions
expressed in inches. We remember 1 inch = 2’54 cm.
Figure 8. Basic cabin dimensions[8]
Chapter 3. Fuselage Design
We can estimate then:
60 inches * 2 cabins + 6 inches between cabins: 126’’ * 2,54cm = 320 cm
Engines dimension:
We want our aircraft to obtain a nominal thrust in the range of 8000 to 10000 pounds,
since it is the nominal thrust of similar aircraft.
A good solution to our requirements could be to install two engines AI-222-25F with
vector thrust.
Figure 9. Engine AI-222-25F[16]
The maximum thrust of the engine is approximately 5000 pounds, so it meets our
demand.
According to [16], the length of the engine is 1’96 meters. And the diameter is 64 cm.
Fuel:
Taking into account the mission profile, and the consumption of the engines, we can
estimate that 3000 pounds of fuel will be necessary to carry out the mission. So a good
solution could be to introduce a 3000 pounds tank behind the pilot.
Since our widest part will be defined by the engines, we will approximate our tank to a
parallelepiped like this:
x = 204 cm
In [26] slenderness is defined as:
where lf is the length of the fuselage an af the width.
As 8 < < 12 an intermediate value an intermediate value of 10 is chosen to begin the
calculations
; ; af = 102’2 cm
This solution is not possible, because does not meet the demand of the width of the
two engines needed, therefore a different lambda value needs to be chosen:
; af = 130 cm
With this value he initial solution will be a cylinder with the following dimensions:
Figure 11. Initial sizing of the fuselage
Afterwards, this form will be streamlined to obtain a bluff shape.
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Chapter 4. Weight calculations
The theoretical concepts used in this chapter are based on [26].
The Spanish Air Force Northrop F-5 Freedom Fighter aircraft has been used as a
reference. Inasmuch as it has different configurations, the one used will be the most
restrictive, and will be defined later.
The great importance of minimizing the plane’s weight is obvious, since the heavier
the plane it is, the greater lift is needed to make it fly. Higher lift generates higher
drag, thus a higher weight traduces into an increase of the need in thrust, and
therefore in fuel consumption.
4.1. Maximum payload (MPL):
As dictated by [26], we will start calculating the MPL.
The first thing we have to do is to define the concept:
“The payload is the explosive power of a warhead, bomb, etc, carried by a missile or
aircraft”.[18]
In our case, the payload shall consist of the weaponry carried by the plane. All
calculations needed about it will be included in Chapter 8.
The formula that will define our MPL shall be as follows:
MPL = number of people * [weight/pax + baggage/pax] + weapon’s weight
(1)
22
The guidance document establishes that the baggage weight will be 16kg for short or
medium range flights and 18kg for medium/long range flights. Considering all the
equipment carried by a pilot in a real mission (helmet, anti-g suit, boots and even a
knife and a shotgun in some cases) the estimated weight will be 18kg.
MPL = 2 * [78 + 18 (KG)] + weaponry’s weight
MPL = 2 * [209 (LBS)] + weaponry’s weight
The weaponry’s weight is estimated as follows:
The new aircraft aims to replace the existing one and the capacity for carrying
weapons cannot be reduced. So it will be at least the greater F-5 configuration:
Figure 12. Aircraft configuration
Number Model Weight Picture
23
Adding all these weights:
JAR OPS defines de OEW as:
The total weight of the aircraft for a specific type of operation, excluding all usable fuel
and traffic loads. It includes such items as crew, crew baggage, catering equipment,
removable passenger service equipment, and potable water and lavatory chemicals.
The items to be included are decided by the Operator. The dry operating weight is
sometimes referred to as the Aircraft Prepared for Service (APS) weight. The traffic
load is the total weight of passengers, baggage and cargo including non-revenue load.
[JAR-OPS 1.607 (a)].
There is a expression that stablishes a relationship between the OEW and the MTOW
(Maximum Take-Off Weight).
24
OEW = α * MTOW (2)
The α term is defined though a state of the art observation as:
α =
F5 9558 20000 0.4779 0.5232
Talon 7200 12474 0.5772
Hawk 8778 17061 0.5145
OEW = 0.5232 * MTOW
The graphic below shows the typical profile of a flight.
Figure 13. Typical flight profile
The expression that defines the fuel weight is the following one:
FW = TF + RF
Where TF will be the mission fuel and RF the reserve fuel.
Chapter 5. Wing Loading and T/W Ratio
25
(3)
Many of the relationships shown in this expression could be estimated according to
this table:
= 1 – = 1 – 0.995 * 0.99 *
For the cruise parts a distance of 450 NM (Nautical Miles) will be considered, since it is
approximately what a LIFT plane travels in an hour, and the time of a typical mission.
R = k * ln
Chapter 5. Wing Loading and T/W Ratio
26
Then k = 2700
450 = 2700 ln W3 / W4 ; 0.17 = ln W3 / W4 ; e 0.17 = W3 / W4 ; W3 / W4 = 0.84
For the relationship W7 / W6 :
We consider 200 NM :
200 = k ln W7 / W6 ; 200 / 2700 = ln W7 / W6
W7 / W6 = 0.928
Table 5. Suggested values for L/D, Cj, Cp and np for several mission phases
Considering W9 / W8 as a minor contingency, such as going into a holding pattern in an
alternative field, the same proportion that in taxi and take-off will be approximately
maintained i.e. 0.99.
27
= 0.3343
4.4. Maximum Take-off Weight (MTOW):
Once the other weights have been estimated, the expression that defines de MTOW is
a function of these other parameters:
(3)
If we look at the similar aircraft’s MTOW, we can see that our initial result could be
correct. Even though it is not an exact result, the minimum value of it represents a
good approach.
Chapter 5. Wing loading and T/W ratio
All the calculations and theoretical concepts expressed in this Chapter are based on
Daniel P. Raymer’s book: Aircraft’s design: a conceptual approach [26].
These two aspects are basic to describe the performances of the aircraft, so they will
be fundamental when designing.
Due to the importance of these parameters, it is essential to perform a precise
estimation, since the calculations carried out in this chapter will affect notoriously to
the initial sizing of the plane.
Wing loading and T/W ratio are interconnected when we have to meet demand of a
performance request.
For the same class, the T/W parameter shows a lower statistical variation, so it will be
the first parameter to guess. According to the following table [26]:
Figure14. Typical T/W [26]
Once we have this parameter, it is easier to guess the wing loading. According to the
literature, we will calculate the wing loading for different situations (stall situation,
take-off distance, landing distance…), and having all this results, we will discard those
Chapter 5. Wing Loading and T/W Ratio
30
who are “outliers”, i.e. too high or too low. According to the rest of the results, we will
choose the lowest, since it will be the most restrictive.
According to illustration 11, our wing loading should be around 70 lb/ft2
Now we will proceed to express several situations:
5.1. Stall
W = L
W = qS S CLmax = ½ ρ VS 2 S CLmax (4)
According to [21], we will estimate the maximum lift coefficient (CLmax) to 1,6.
Then, we have to estimate de stall speed (Vs), to do so, we observe the similar aircraft:
Vs Hawk Talon F-5 Average Vs
Full Flap 102 kts 160 kts 130 kts 130 kts
Table 6. Average Vs
130 kts = 65 m/s
W/S = (TOP) σ CLTO T/W (5)
The expression (5) represents the wing loading during the take-off. As we can see, it is
related to the Thrust-to-Weight ratio.
TOP represents the take-off parameter.
σ , since we are at sea level, is 1.
Chapter 5. Wing Loading and T/W Ratio
31
There is a relationship between the lift coefficient at take-off and the maximum lift
coefficient, we will use this relationship to introduce the CLTO in our expression:
CLTO = CLmax / 1.21 = 1.32
Now we will estimate the Take-Off Distance, observing the similar aircraft’s values,
shown in this Table:
TODistance 3500 ft 2700 ft 3000 ft 3000 ft
Table 7. Average TOD
Now that we know the Average TOD, the Take-Off Parameter can be obtained by this
graphic:
[26]
Now we obtain the TOP, 200. The only thing we have to do now is to replace all the
terms in expression (5).
32
As we said in the introduction, this value will be discarded since it represents a too
high value.
5.3. Landing distance
Our reference document [26] shows an expression of the landing distance relating this
one with the wing loading. We will use this expression to estimate the wing loading as
we did before:
There is another expression to represent de landing distance:
Sland = 0.3 * Vs 2 = 5070
CLmax = 1.6
According to D. Raymer, Sa is 600 for general aviation planes and 450 for STOL [26],
since our design does not correspond to neither of them, we will take an average
number between them, 525.
Now that we know all the terms of the expression:
5070 = 80 (W/S) 0.625 + 525
W/S = 90 lb/ft2
5.4. Instantaneous turn
According to [26], the expression that represents the instantaneous turn situation is
defined as:
W/S = q CLmax / n
The speed we have to introduce is the corner speed, since it optimizes the turn, for our
situation, this value reaches 320 kts [26].
Our CLmax will be 0.7 [26]
Chapter 5. Wing Loading and T/W Ratio
33
We want at least that our g factor reaches a value of 8.
Introducing all these data in the formula:
W/S = 0.5*0.0238*1602*0.7 / 7
(6)
W/S = 30.464 lb/ft2
According to the methodology explained in the introduction, our final value will be the
one obtained for the stall situation:
W/S = 80.444 lb/ft2
Chapter 6. Geometric definition
In this section we have used the results obtained in the previous chapters and the
information in [26] to get a sketch of our plane.
It is important to say that this is not going to be the final design, it is just an
approximation to the final one, that will be obtained through a further study
referenced in Chapter 9.
6.1. Airfoil Geometry
As we are building a supersonic jet, a relatively sharp airfoil will be chosen. But it is not
going to be a radical sharpened airfoil, since we want to reduce the drag.
As many of the similar aircraft, we will use a cambered airfoil that will increase the lift
and will enable our airplane to fly at low speeds, this is achieved by avoiding the
separation of the boundary layer as shown in Figure 13.
Figure 15. Effect of camber on separation [26]
Chapter 6. Geometric definition
36
The airfoil selected will be the 64 A010, a six-series airfoil from the NACA family.
Figure 16. Typical airfoils [26]
The 64 A010 is a typical airfoil for high-speed wing aircraft, designed for an increased
laminar flow. This NACA airfoil will cause a gradual loss of lift in an stall situation,
which will be much safer for the pilot, giving him time to react.
Figure 17. Types of stall [26]
6.2. Wingtip
At the wingtip, missile rails will be placed. This will have two intentions:
1. Ability to carry wingtip missiles.
2. Reduce the 3-D effects on drag, since the aspect ratio of our aircraft will be
relatively low.
6.3. Wing Sweep
As we want our aircraft to be supersonic, we will need to reduce the effects of
supersonic flow, just like aerodynamic center movement, or drag increasing due to
shock formation.
Our leading edge sweep will be of approximately 40 degrees, according to wing sweep
historical trend (Figure 16). This fact will allow our aircraft to fly at supersonic speeds.
Figure 18. Wing sweep historical trend [26]
6.4. Tapper ratio
“Tapper affects the distribution of lift along the span of the wing. As proven by the
Prandtl wing theory early in this century, minimum drag due to lift, or “induced” drag,
occurs when the lift is distributed in an elliptical fashion” [26].
As an elliptical wing is very difficult to be built, we will approximate our wing to an
elliptical one by using the tapper ratio “λ”.
λ = Ct / Cr (7)
Chapter 6. Geometric definition
λ = 100 / 280 = 0,35
According to [26], most swept wings have a tapper ratio of about 0,2-0,3.
6.5. Wing incidence
This aspect use to be determined in wind tunnels, this corresponds to a further study
of the conceptual design, so initially our wing incidence will be approximately zero, as
it uses to be for military aircraft.
6.6. Wing vertical location
A mid-wing arrangement will be selected. This arrangement will allow the aircraft to
carry bombs at a safe distance from the ground.
6.7. Tail arrangement
Twin tails have been proved to be more effective for the use of the rudder, since they
avoid the fuselage shielding. For this reason, a twin tail will be selected for our aircraft.
Figure 19. Aft tail variations [26]
Chapter 6. Geometric definition
Chapter 6. Geometric definition
41
Chapter 7. Drag Polar
It is known that a direct relationship between drag and lift exist. The lift force affects
to the drag one and this can be expressed through a diagram known as drag polar.
A parabolic approach is used to express this relationship:
CD = CD0 + KCL 2 (8)
We will calculate CD0, the parasite drag, according to (8).
In accordance to the flat plate analogy:
Figure 23. Flat plate analogy
D0 = ½ ρ V2 CD0 Sw = ½ p V2 Cf Swet
CD0 = Cf Swet/Sw
(9)
CD0 = [Cf Swet/Sw + Cf Swet.fus/Sw] FF*IF
Now we will have to calculate the three unknown parameters: Reynolds number,
Mach number and the wet surface (Swet).
Chapter 7. Drag Polar
42
To estimate the wet surface, we will approximate the aircraft to the initial solution
obtained in Chapter 3, a cylinder.
So the wet surface of the fuselage will be:
S = 2 π r l = 41’74 m2, obviating the front and the rear parts, since in the further design,
the fuselage will be more aerodynamic.
For the wings:
W/Sw = 80
MTOW/Sw = 80
12500/80 = Sw
Sw = 29’032 m2
For the rest of the parameters, we will consider an altitude of 20.000 ft and 260 KIAS,
characteristics that will resemble a cruise.
According to the atmospheric calculator [27]:
µ = 1’26 * 10^-5
ρ = 0’6527 kg/m3
Re/D = 5485432 being D the fuselage length = 10’22 m
Re = 54854320
CD0 = 1’7 * 10^-3
Now we can estimate the “k” parameter:
k = 1/πAφ (10)
k = (1 + ζ) 1/ πA (11)
. ζ = [0’015 + 0’016 (λ – 0’4)2] (βA – 4’5)
Being λ = Ct/Cr = 0’35
. ζ = 4’62*10^-3
Chapter 7. Drag Polar
CD = 0.0017 + 0.0319 CL 2
Representing this result in a graphic:
CL
CD
Chapter 8. Payload-Range Diagram
For this Chapter we will use some of the data calculated in the previous Chapters, such
as the MTOW, OEW, or the specific fuel consumption.
Using the calculations we will explain later, we achieve this diagram:
Figure 25. Payload-Range Diagram
The A point represents the Operative Empty Weight plus the Maximum Payload (both
values calculated in Chapter 4.
A = MPL + OEW = 1976 lbs + 7255.04 lbs = 9231.04 lbs
Chapter 8. Payload-Range Diagram
46
To obtain B we will calculate the range using the Breguet expression (12) and see
where it crosses with the horizontal line drawn from A.
The expression (12) maximizes the range of the aircraft:
(12)
CJ = 0.64 kg/kgf*hr [16] = 1.77 E -4 N/(N·S)
Considering the same conditions as in Chapter 7:
ρ = 0.6527 kg/m3 [27]
S = 70.722 m2
The initial weight (W0) and at the final weight (We) will be:
W0 = MTOW = 6289.8157 kg (from Chapter 4)
We = OEW + MPL = 4187.12931 kg (from Chapter 4)
We know CD0 and K from Chapter 7:
CD0 = 0.0017
K = 0.0319
Now that we have all the terms from expression (12):
RB = 7406.901 km
Now, using the same procedure, we will calculate the range in C:
The only changing parameter will be We.
WeC = OEW = 3290.83 kg
RC = 10621.4 km
We have already taken all the Payload, without reaching the Maximum Fuel Weight
(MFW), so points C and D will match.
47
9.1. Methodology
First of all, we will start reviewing the way we proceeded to obtain all our results, and
the expression of the main of them.
With the knowledge obtained and the documentation needed for the beginning of the
project, added to Chapter 1. We obtained a cursory knowledge of the state of the art.
According to the interests of this work, similar aircraft were selected as references for
our design.
Though the research in the literature and the T.O,s (Technical Orders) we get most of
the data needed for a further analysis and use.
Starting from the general knowledge of the aircraft’s content (two pilots, needed
equipment, fuel…) we proceeded to the approximation of the dimensions of the
airplane.
Later, we adjusted all these data to slenderness requirements according to our
aircraft’s characteristics, obtaining:
Fuselage length 1022 cm
Fuselage width 130 cm
Table 8. Sizing results
For the main weights, the bibliographic query proposed a series of approximations for
the calculations. Using these approximations and the data obtained from similar
planes we get some estimative results:
Chapter 9. Conclusions and further studies
48
Fuel Weight FW/W1=0.3343
Table 9. Weight results
For the wing loading and the thrust-to-weight ratio, we followed the approximations
proposed by Daniel P. Raymer at his book “Aircraft design: a conceptual approach”, for
different flight situations. Obtaining:
Table 10. T/W and W/S results
According to the results obtained in the previous paragraphs, as well as the study of
the different aerodynamic shapes, we get the initial three view drawing.
Using the parabolic approximation formula:
CD=CD0 + KcL 2
And estimating the parameters “CD0” and “k”, we get the initial formula for the
representation of the drag polar.
9.2. Further research
The obtained data is an initial approach to the aircraft design, we cannot forget the
initial aim was to get a CONCEPTUAL design. To continue the development we should
delve into the procedures followed, so that we can obtain a more accurate design. A
deeper study should also include a selection of the materials that should be used to
meet the demanded requirements that our results show (what type of flying profile is
Chapter 9. Conclusions and further studies
49
going to be used, what engines we are going to incorporate…). We should also perform
an accurate design of the aircraft (the exact measures of each surface).
A scale model could be built, maintaining the main parameters as Thrust-to-weight
ratio or the wing loading, to carry out a study in wind tunnels.
If we are going to design an aircraft, we should also consider the maintenance aspects,
like how we are going to plan it.
To finish, it is necessary to calculate the initial budget of the project, and compare it to
similar plane’s budget.
9.3. Technological improvements to implement
Since the design of similar planes to ours, some technological improvements have
been carried out, that could make the difference with this similar planes if we
implement them to our design:
-Thrust vectoring: this technology allows the nozzle to move changing the direction of
the thrust vector. The use of thrust vectoring has proved to provide some advantages
in combat, since it facilitates the aircraft to perform some maneuvers that
conventional planes cannot do.
Chapter 9. Conclusions and further studies
50
-Helmet mounted display: most of the similar planes incorporate a HUD that allows the
pilot to control the aircraft and all the basic parameters at the same time he is looking
outside. But the problem comes when the pilot has to turn his head to look for the
other plane in a dogfight for example. The helmet mounted display finds a solution to
this problem, since it shows the information on a reticle incorporated to the helmet.
Apart from this, another capabilities comes with this technology like optical or
electromagnetic tracking.
Figure 27. Helmet Mounted Display [25]
-Better simulation systems implementable by data-link. In most cases, a real situation
is very difficult to represent, or the big exercises carried out to represent them are
expensive and dangerous, and require a big coordination. For this reason, it is
necessary to do more emphasis in the development and implementation of simulation
systems allowing the pilot to experience all kind of situations that he could find in a
real mission.
.1. T-38 Talon
hmáx 3,8 m
lmáx 14 m
WINGSPAN 7,6 m
KIND OF ENGINE turbojet
Ce
RATIO lf/b 1,842105263
CABIN LENGHT lc 3,09 m
CABIN WIDTH bc 0,76m
WING
b ( 3,36 m
Ct (cuerda que hay al final del ala) 0,86 m
Cr 2,9 m
53
bh 1,54 m
Vcr optimal
V3 185 kts
Vasc 270 kts
Hser 50000 ft
KIND OF ENGINE turbojet
Teng 8708lb military power // 13635 with afterburner
at idle 97 kg/(h·kN) (0.95 lb/(h·lbf)) at idle
with afterburner 242 kg/(h·kN) (2.37 lb/(h·lbf))
WEIGHT
FUSELAGE AND CABIN
RELACIÓN lf/b 12,285 / 1,24
dmin 0,95 m
lc 1,90 m
bc 0,66 m
WING
bh 1,64
bh/b 0,229242382
Cth 1,39
Crh 2,05
Hser 16100 m
MiG-21F 1300 km
TYPE OF ENGINE turbofan
MODEL Turboméca Adour Mk151-01
2 in tandem
bh 1,95
bh/b 0,207667732
Cth 0,54
Crh 1,22
[2] http://www.rockwellcollins.com/Data/Products/Displays/Head_Down_Displays_
[15] http://dad.walterfamily.org/rv/TonyBingelis/Part%201%20%20Homebuilt%20Air
craft%20Interiors%20-%20Basic%20Cockpit%20Accommodations.html
[16] http://www.motorsich.com/rus/products/aircraft/tde/ai-222-25f/
[20] http://www.globalsecurity.org/military/library/policy/navy/ntsp/ale-47-
A6teoJnRwYQm3bwngf-QL_KOpM1PsgkvJYtA
[26] D. P. Raymer, Aircraft Design: A Conceptual Approach. American Institute of
Aeronautics and Astronautics, 1992.
[27] http://www.newbyte.co.il/calculator.php
[28] E. Torenbeek, Synthesis of Subsonic Airplane Design. Delft University Press, 1982.
Co-director: José Serna Serrano
Curso: 2014/2015 – convocatoria: Junio
ACADEMIA GENERAL DEL AIRE
CONCEPTUAL AIRCRAFT DESIGN
MILITARY TRAINING FIGHTER
Tribunal nombrado por la dirección del Centro Universitario de la Defensa de
San Javier, el día ____ de ____________ de 20____.
Presidente: Dr. D. Manuel Caravaca Garratón
Secretario: Dr. D. Alejandro López Belchí
Vocal: Col. Dr. Andrés Dolón Payán
Realizado el acto de defensa del Trabajo Fin de Grado, el día____ de _________
de 20____, en el Centro Universitario de la Defensa de San Javier.
Calificación: __________________________.
CONCEPTUAL AIRCRAFT DESIGN
MILITARY TRAINING FIGHTER
ABSTRACT: The following work deals about the draft/conceptual design of an airplane,
specifically, a lead-in fighter trainer. Within we will describe the general characteristics
of the aircraft, obtained by simple design rules.
RESUMEN: El presente trabajo trata sobre el anteproyecto/diseño conceptual de una
aeronave, concretamente de un entrenador militar avanzado de tipo caza. En el mismo
se describen las características de la aeronave obtenidas mediante leyes de diseño
sencillas basadas en un análisis de aeronaves similares existentes en el mercado.
A mi hermano José Eugenio, incansable trabajador
y constante ejemplo a seguir
Content
1.2. LIFT concept ............................................................................................................................. 3
1.3.3. Basic training ................................................................................................................................... 5
1.3.5. Operational transition .................................................................................................................. 8
2.2. MiG-21 [1] ............................................................................................................................... 13
Chapter 3. Fuselage design......................................................................... 17
4.2. Operative Empty Weight (OEW): .................................................................................. 23
4.3. Fuel weight (FW): ................................................................................................................ 24
4.4. Maximum Take-off Weight (MTOW): ........................................................................... 27
Chapter 5. Wing loading and T/W ratio ................................................. 29
5.1. Stall ............................................................................................................................................ 30
6.1. Airfoil Geometry ................................................................................................................... 35
6.7. Tail arrangement ................................................................................................................. 38
Chapter 9. Conclusions and further studies ......................................... 47
9.1. Methodology .......................................................................................................................... 47
.1. T-38 Talon ................................................................................................................................. 51
.2. MiG-21 Fishbed ....................................................................................................................... 55
.3. Sidderley Hawk ....................................................................................................................... 57
A.G.A. Academia General del Aire
T.F.G. Trabajo Fin de Grado
LIFT Lead-In Fighter Training
HOTAS Hands On Throttle And Stick
HUD Head Up Display
HMD Helmet Mounted Display
1.1. Goal and definitions
The goal of this work is to perform the evaluation of an advanced military training jet.
With the appearance of 5th generation of fighter aircraft and the rapid advance in
technology, the training platforms used by some Air Forces are beginning to be
obsolete. In advance to the expected obsolescence, it is necessary to provide new
systems to meet the demand.
We will start by explaining the concept of a military training jet, best known as
“trainer”. When we talk about a military trainer we make reference to a jet that
belongs to an air force and it is used mainly as a training platform for the future pilots.
As we will see later, these jets also fulfill a secondary role, such as that of advanced
trainers, prepared to carry weapons and perform low profile missions, such as
counterinsurgency, when necessary.
As the technology advances, new generations of fighter aircraft appear, thus, it
becomes necessary to upgrade the technology used for future pilots training. The first
jet trainers were modifications of the original design of an aircraft, however, nowadays
most Air Forces own trainers that correspond to an operative fighter or a group of
them.
In Table 1 we can see how the concept has changed through the years.
Chapter 1. Introduction
1940
Table 1. Operative fighters and their jet trainers
One of the common characteristics of these jets is the existence of dual controls to
allow the instructor and the student to fly the airplane, giving the instructor the
capacity to control the airplane to facilitate the student’s learning and to ensure it is
being flown safely. For the achievement of this goal, there are two main arrangements
of instructor-student, side-by-side cabin or in tandem (one in front the other). It
depends on the type of training mission, but normally when flying in tandem the
student is placed in the front position while the instructor is in the rear one.
Chapter 1. Introduction
1.2. LIFT concept
Our goal is to evaluate the design of a LIFT type jet. The acronym stands for Lead-In
Fighter Training, and it is necessary to define this concept correctly.
LIFT is defined as a jet that emulates advanced fighters to train the student to operate
this weapons system. LIFT jets are usually propelled by a turbofan or turbojet engine.
This type of jet also has advanced avionics systems to habituate the user to work in an
advanced environment and in different scenarios that could be found in a modern
conflict. To achieve this goal, the jet is able to receive information from an instrument
similar to a memory stick, and show the information in a Multifunction Display (MFD),
or, in the best case, it receives the information using real-time software and tactical
data exchange networks such as the Link 16 used by the North Atlantic Treaty
Organization (NATO).
In order to manage all this information, and the typical in-flight workload (such as pure
flying tasks or communications) the pilot rely on MFD’s, HOTAS (Hands on Throttle and
Stick) and HUD (Head-Up Display) (Figures 1, 2 and 3) that make the information
clearer and manageable. In some cases even an autopilot system (AP) is available to
relieve the pilot’s workload. In a critical situation, such as an emergency, the pilot can
couple the AP and focus on solving the problem.
Since new generation aircraft start to show all the information on HMD (Helmet
Mounted Display), some LIFT jets have begun to incorporate this type of technology.
The training received in this kind of platform is divided in: contact, instruments,
formation, air-to-air tactics and air-to-ground tactics.
One of the examples of these jets is the T-38 Talon (Figure 3) used by the United States
in the advanced flight training program.
Chapter 1. Introduction
Figure 3. HUD and American T-38 Talon[9]
1.3. Training
A short summary of the different phases of the training, focusing on the LIFT and
transitional operation phases follows.
This classification is based on the American specialized undergraduate pilot training
[4].
1.3.1. Screening
Many Air Forces use light aircraft, sometimes similar to those used in the civil
industries to evaluate the skills and capabilities of the candidates. Since the first
moment the predisposition can be intuited in relation to what kind of plane each
candidate will pilot in the future.
1.3.2. Primary aircraft training
During this phase, propeller driven aerobatic aircraft are normally used, so that the
student can learn the behavior of the aircraft during aerobatic maneuvers.
Figure 4. ENAER Pillán T-35[10]
1.3.3. Basic training
This phase is carried out inside an aircraft with greater capabilities (more thrust, higher
service ceiling and in general more advanced flight features). The aircraft used are
normally aerobatic jet aircraft. For example, the Spanish Air Force use the CASA C-101
(Figure 5) for this purpose. Approximately one hundred hours of flight training are
completed in it.
Chapter 1. Introduction
1.3.4. Lead-In Fighter Training
The aircraft used for this task are low profile airplanes, light fighters, normally
propelled by one or two turbojets. These aircraft normally fly in the high-subsonic
range, even having the possibility of reaching the sound speed.
Inasmuch as they are generally light fighters, they are highly maneuverable, allowing
the plane to perform tight turns.
A great difference in comparison with the other aircraft used in previous training
phases, the aircraft used in this phase have the ability of carrying armament. However,
for the training missions the used weapons are simulated or unloaded.
During this phase, the student begins to use radar technology, simulated in some
cases, like in the Spanish F-5. This type of aircraft is equipped with a very advanced
avionics system, with MFD,s and HUD,s, these last show the pilot the information on
the windshield, so that he does not have to look inside the cabin and lose the enemy
during a dogfight.
These aircraft are used by some countries to carry out low profile missions in spite of
not being prepared to operate in a real-life
scenario, unless they do it with the support of more advanced fighters.
The case of the Spanish F-5 it is because it was designed by the Northrop Corporation
as a light attack aircraft. It has been used in some real-life scenarios; it was used during
Chapter 1. Introduction
7
the Vietnam War, serving the South side against the North. Between October 1965 and
April 1967 the Skoshi Tigers flew a total amount of 9985 missions in Vietnam in which
they lost nine aircraft.
Figure 6. Skoshi Tiger dropping napalm in a misión at Bien Hoa in 1967 [12]
The Spanish Air Force uses a version of the Northrop F-5 with an avionics upgrade
carried out by Israel Aerospace Industries.
The fighter pilot training course in the Spanish Air Force comprises five phases:
transition, instruments, formation, air-to-air an air-to-ground. Each of these phases
will be explained below:
-Transition: it comprises fifteen missions in which the student learns how to handle the
aircraft, performing aerobatic maneuvers, coordination maneuvers, traffic patterns,
and “confidence maneuvers” to reach a high level of familiarization with the airplane.
An example of the “confidence maneuvers” is the zero-velocity maneuver, in which the
aircraft is flown at an extreme angle of attack (AOA) and loses almost all the
translational velocity before being recovered. During this period, different emergency
situations are also practiced. A “solo flight” is included in the program so that the self-
confidence of the student increases.
-Instruments: like in the basic phase, the student is instructed in the handling of the
aircraft having only the flying instruments as a reference. During this phase, flights to
other fields and night flights are included along with a solo flight. This phase comprises
16 missions.
8
-Formation: It includes basic formation of 2 or 3 planes and tactical formation of 2 or 4
planes. A total amount of 19 missions are completed during this phase
-Air-to-ground: It includes the sub-phases of: low level, aerial interdiction, close air
support (CAS) and air-to-ground dropping; the last one completed at Bardenas
(Zaragoza). A total amount of 19 missions are flown.
-Air-to-air: this one is the most extensive phase, consisting on 26 missions of: aerial
interdiction, basic combat maneuvers, dogfights and night interceptions.
As it can be observed, it is a really extensive and demanding course having the goal of
forming the fighter pilots of the Spanish Air Force to fly the most advanced fighter
planes, after passing through the operational transition of which we will talk about
below.
1.3.5. Operational transition
Once the pilot has completed the training and is able to fly fighter planes and perform
basic maneuvers, he has to learn how to handle the aircraft he will pilot from now on,
the plane that he will pilot at his unit.
For this task, modified operative aircraft are used, with two-seat configuration with
minimized modifications, so that the transition to the combat-ready aircraft is simpler.
However, despite the modifications, these aircraft could be used in a real combat
situation.
An example of this kind of plane in Spain is the F-18 used in Zaragoza.
Chapter 1. Introduction
9
Figure 7. Spanish McDonnell Douglas F/A 18 Hornet in Zaragoza [13]
All this training is accompanied, in most cases, by missions in the simulator, in which
the pilot is able to practice situations that due to the risk, should not be practiced in
flight. One of the main roles of the simulator is the presentation of simulated
emergency situations that allow the pilot to learn the inputs needed in anomalous
flight situations.
In this work we aim to design a LIFT aircraft, similar to the Spanish version of the F-5
Freedom Fighter. To do so, we will start studying a series of similar planes.
We will calculate the main characteristics we want our aircraft to have, from simple
design rules. And finally we will make an invitation to a further study.
Chapter 1. Introduction
Chapter 2. Similar aircraft
The following chapter collects all the information regarding the similar planes that we
are going to study. The T-38 Talon, the MiG21 and the British Hawk.
In the Appendix A we will find the tables that represent the characteristics of the
aircraft.
12
First of all, we will make an introduction to the main characteristics of the airplane.
This introduction will be based on the official World Wide Web site of the United
States Air Force Factsheet. [5].
The T-38 Talon is a supersonic jet trainer used by the USAF future fighter pilots, to
prepare them to pilot jets such as the F-15 Strike Eagle, the F-16 Fighting Falcon, or the
B1-B Lancer.
This aircraft is also used by the NASA to train their pilots.
Its characteristics allow this aircraft to be used in a great variety of roles, although its
main use is the Air Education and Training Command.
It is easy accessibility to critical parts of the airplane make it very easy to maintain.
Depending on the version, it incorporates a gun sight, a practice bomb dispenser, and
a “no drop” bomb scoring system, facilitating the Air-to-Ground and Air-to-Air training
for the pilots.
A great variety of test pilots use this platform to put into test new technologies.
New modifications of the airplane will extend the service life to 2020 at least.
Chapter 2. Similar aircraft
2.2. MiG-21 [1]
As we did with the F-5 Freedom Fighter, we will make an introduction to the main
characteristics of the airplane. This introduction will be based on [6].
The MiG-21 is a soviet aircraft of the 50’s decade. It is a supersonic aircraft, with
retractable landing gear.
Along history, this airplane has suffered over 30 modifications, to turn it into a 4th
generation aircraft. During this time, it has served around 50 countries, and has been
present in several wars, such as Vietnam, Yom Kipur, Libia, or Ogaden.
The MiG-21 can reach Mach 2, with its single engine. The first design presented
problems with its low autonomy.
Its wing configuration allows the aircraft to perform very sharp turns, which represent
an advantage in a dogfight.
Chapter 2. Similar aircraft
14
The training versions are the “U” and “UM”. The Soviet Union built over 1200 training
versions. The final training version is the MiG-21MF, built in 1971.
All these characteristics make the MiG-21 an airplane worthy of study.
Chapter 2. Similar aircraft
2.3. Hawker Siddeley HS-1182 Hawk [1]
All the information shown in the introduction is based on reference [7].
The Hawk is a low-wing, tandem seat, subsonic aircraft that allows the RAF pilots to
carry out the advanced training. The Hawk is used to teach air combat, air-to-air firing,
air-to-ground firing and low-flying techniques and operational procedures. This
airplane is able to carry Sidewinder missiles.
This aircraft originated from a requirement of the British Royal Air Force (RAF) to
obtain a new jet trainer in 1964.
Chapter 2. Similar aircraft
16
The British Royal Navy also operates this aircraft, for the training of ship gunners and
radar operators. Another important operator is the British aerobatic team called “Red
Arrows”.
The airplane suffered some modifications that aroused the export interest. Among its
operators we can find Dubai, Kuwait, Finland, or South Korea.
17
Chapter 3. Fuselage design
To obtain an initial sizing of our aircraft’s fuselage, we will elaborate a list with the
main components of it, and we will study the main characteristics and size of each
component:
RADAR
EQUIPMENT
CABIN
FUEL
ENGINES
RADAR
EQUIPMENT
CABIN
FUEL
ENGINES
18
We proceed to obtain information of the dimensions of the different equipments.
Radar and equipment:
We can estimate this data observing the similar aircraft’s plans on Chapter 2. Simply
measuring from the T38’s plan we obtain 136 centimeters, assuming the equipment
we will need in our aircraft will be similar.
Cabin:
We will base our cabin dimensions according to an ergonomic study carried out by
Tony Bingelis called “Basic Cockpit Accomodations”[8]. We can observe the dimensions
expressed in inches. We remember 1 inch = 2’54 cm.
Figure 8. Basic cabin dimensions[8]
Chapter 3. Fuselage Design
We can estimate then:
60 inches * 2 cabins + 6 inches between cabins: 126’’ * 2,54cm = 320 cm
Engines dimension:
We want our aircraft to obtain a nominal thrust in the range of 8000 to 10000 pounds,
since it is the nominal thrust of similar aircraft.
A good solution to our requirements could be to install two engines AI-222-25F with
vector thrust.
Figure 9. Engine AI-222-25F[16]
The maximum thrust of the engine is approximately 5000 pounds, so it meets our
demand.
According to [16], the length of the engine is 1’96 meters. And the diameter is 64 cm.
Fuel:
Taking into account the mission profile, and the consumption of the engines, we can
estimate that 3000 pounds of fuel will be necessary to carry out the mission. So a good
solution could be to introduce a 3000 pounds tank behind the pilot.
Since our widest part will be defined by the engines, we will approximate our tank to a
parallelepiped like this:
x = 204 cm
In [26] slenderness is defined as:
where lf is the length of the fuselage an af the width.
As 8 < < 12 an intermediate value an intermediate value of 10 is chosen to begin the
calculations
; ; af = 102’2 cm
This solution is not possible, because does not meet the demand of the width of the
two engines needed, therefore a different lambda value needs to be chosen:
; af = 130 cm
With this value he initial solution will be a cylinder with the following dimensions:
Figure 11. Initial sizing of the fuselage
Afterwards, this form will be streamlined to obtain a bluff shape.
21
Chapter 4. Weight calculations
The theoretical concepts used in this chapter are based on [26].
The Spanish Air Force Northrop F-5 Freedom Fighter aircraft has been used as a
reference. Inasmuch as it has different configurations, the one used will be the most
restrictive, and will be defined later.
The great importance of minimizing the plane’s weight is obvious, since the heavier
the plane it is, the greater lift is needed to make it fly. Higher lift generates higher
drag, thus a higher weight traduces into an increase of the need in thrust, and
therefore in fuel consumption.
4.1. Maximum payload (MPL):
As dictated by [26], we will start calculating the MPL.
The first thing we have to do is to define the concept:
“The payload is the explosive power of a warhead, bomb, etc, carried by a missile or
aircraft”.[18]
In our case, the payload shall consist of the weaponry carried by the plane. All
calculations needed about it will be included in Chapter 8.
The formula that will define our MPL shall be as follows:
MPL = number of people * [weight/pax + baggage/pax] + weapon’s weight
(1)
22
The guidance document establishes that the baggage weight will be 16kg for short or
medium range flights and 18kg for medium/long range flights. Considering all the
equipment carried by a pilot in a real mission (helmet, anti-g suit, boots and even a
knife and a shotgun in some cases) the estimated weight will be 18kg.
MPL = 2 * [78 + 18 (KG)] + weaponry’s weight
MPL = 2 * [209 (LBS)] + weaponry’s weight
The weaponry’s weight is estimated as follows:
The new aircraft aims to replace the existing one and the capacity for carrying
weapons cannot be reduced. So it will be at least the greater F-5 configuration:
Figure 12. Aircraft configuration
Number Model Weight Picture
23
Adding all these weights:
JAR OPS defines de OEW as:
The total weight of the aircraft for a specific type of operation, excluding all usable fuel
and traffic loads. It includes such items as crew, crew baggage, catering equipment,
removable passenger service equipment, and potable water and lavatory chemicals.
The items to be included are decided by the Operator. The dry operating weight is
sometimes referred to as the Aircraft Prepared for Service (APS) weight. The traffic
load is the total weight of passengers, baggage and cargo including non-revenue load.
[JAR-OPS 1.607 (a)].
There is a expression that stablishes a relationship between the OEW and the MTOW
(Maximum Take-Off Weight).
24
OEW = α * MTOW (2)
The α term is defined though a state of the art observation as:
α =
F5 9558 20000 0.4779 0.5232
Talon 7200 12474 0.5772
Hawk 8778 17061 0.5145
OEW = 0.5232 * MTOW
The graphic below shows the typical profile of a flight.
Figure 13. Typical flight profile
The expression that defines the fuel weight is the following one:
FW = TF + RF
Where TF will be the mission fuel and RF the reserve fuel.
Chapter 5. Wing Loading and T/W Ratio
25
(3)
Many of the relationships shown in this expression could be estimated according to
this table:
= 1 – = 1 – 0.995 * 0.99 *
For the cruise parts a distance of 450 NM (Nautical Miles) will be considered, since it is
approximately what a LIFT plane travels in an hour, and the time of a typical mission.
R = k * ln
Chapter 5. Wing Loading and T/W Ratio
26
Then k = 2700
450 = 2700 ln W3 / W4 ; 0.17 = ln W3 / W4 ; e 0.17 = W3 / W4 ; W3 / W4 = 0.84
For the relationship W7 / W6 :
We consider 200 NM :
200 = k ln W7 / W6 ; 200 / 2700 = ln W7 / W6
W7 / W6 = 0.928
Table 5. Suggested values for L/D, Cj, Cp and np for several mission phases
Considering W9 / W8 as a minor contingency, such as going into a holding pattern in an
alternative field, the same proportion that in taxi and take-off will be approximately
maintained i.e. 0.99.
27
= 0.3343
4.4. Maximum Take-off Weight (MTOW):
Once the other weights have been estimated, the expression that defines de MTOW is
a function of these other parameters:
(3)
If we look at the similar aircraft’s MTOW, we can see that our initial result could be
correct. Even though it is not an exact result, the minimum value of it represents a
good approach.
Chapter 5. Wing loading and T/W ratio
All the calculations and theoretical concepts expressed in this Chapter are based on
Daniel P. Raymer’s book: Aircraft’s design: a conceptual approach [26].
These two aspects are basic to describe the performances of the aircraft, so they will
be fundamental when designing.
Due to the importance of these parameters, it is essential to perform a precise
estimation, since the calculations carried out in this chapter will affect notoriously to
the initial sizing of the plane.
Wing loading and T/W ratio are interconnected when we have to meet demand of a
performance request.
For the same class, the T/W parameter shows a lower statistical variation, so it will be
the first parameter to guess. According to the following table [26]:
Figure14. Typical T/W [26]
Once we have this parameter, it is easier to guess the wing loading. According to the
literature, we will calculate the wing loading for different situations (stall situation,
take-off distance, landing distance…), and having all this results, we will discard those
Chapter 5. Wing Loading and T/W Ratio
30
who are “outliers”, i.e. too high or too low. According to the rest of the results, we will
choose the lowest, since it will be the most restrictive.
According to illustration 11, our wing loading should be around 70 lb/ft2
Now we will proceed to express several situations:
5.1. Stall
W = L
W = qS S CLmax = ½ ρ VS 2 S CLmax (4)
According to [21], we will estimate the maximum lift coefficient (CLmax) to 1,6.
Then, we have to estimate de stall speed (Vs), to do so, we observe the similar aircraft:
Vs Hawk Talon F-5 Average Vs
Full Flap 102 kts 160 kts 130 kts 130 kts
Table 6. Average Vs
130 kts = 65 m/s
W/S = (TOP) σ CLTO T/W (5)
The expression (5) represents the wing loading during the take-off. As we can see, it is
related to the Thrust-to-Weight ratio.
TOP represents the take-off parameter.
σ , since we are at sea level, is 1.
Chapter 5. Wing Loading and T/W Ratio
31
There is a relationship between the lift coefficient at take-off and the maximum lift
coefficient, we will use this relationship to introduce the CLTO in our expression:
CLTO = CLmax / 1.21 = 1.32
Now we will estimate the Take-Off Distance, observing the similar aircraft’s values,
shown in this Table:
TODistance 3500 ft 2700 ft 3000 ft 3000 ft
Table 7. Average TOD
Now that we know the Average TOD, the Take-Off Parameter can be obtained by this
graphic:
[26]
Now we obtain the TOP, 200. The only thing we have to do now is to replace all the
terms in expression (5).
32
As we said in the introduction, this value will be discarded since it represents a too
high value.
5.3. Landing distance
Our reference document [26] shows an expression of the landing distance relating this
one with the wing loading. We will use this expression to estimate the wing loading as
we did before:
There is another expression to represent de landing distance:
Sland = 0.3 * Vs 2 = 5070
CLmax = 1.6
According to D. Raymer, Sa is 600 for general aviation planes and 450 for STOL [26],
since our design does not correspond to neither of them, we will take an average
number between them, 525.
Now that we know all the terms of the expression:
5070 = 80 (W/S) 0.625 + 525
W/S = 90 lb/ft2
5.4. Instantaneous turn
According to [26], the expression that represents the instantaneous turn situation is
defined as:
W/S = q CLmax / n
The speed we have to introduce is the corner speed, since it optimizes the turn, for our
situation, this value reaches 320 kts [26].
Our CLmax will be 0.7 [26]
Chapter 5. Wing Loading and T/W Ratio
33
We want at least that our g factor reaches a value of 8.
Introducing all these data in the formula:
W/S = 0.5*0.0238*1602*0.7 / 7
(6)
W/S = 30.464 lb/ft2
According to the methodology explained in the introduction, our final value will be the
one obtained for the stall situation:
W/S = 80.444 lb/ft2
Chapter 6. Geometric definition
In this section we have used the results obtained in the previous chapters and the
information in [26] to get a sketch of our plane.
It is important to say that this is not going to be the final design, it is just an
approximation to the final one, that will be obtained through a further study
referenced in Chapter 9.
6.1. Airfoil Geometry
As we are building a supersonic jet, a relatively sharp airfoil will be chosen. But it is not
going to be a radical sharpened airfoil, since we want to reduce the drag.
As many of the similar aircraft, we will use a cambered airfoil that will increase the lift
and will enable our airplane to fly at low speeds, this is achieved by avoiding the
separation of the boundary layer as shown in Figure 13.
Figure 15. Effect of camber on separation [26]
Chapter 6. Geometric definition
36
The airfoil selected will be the 64 A010, a six-series airfoil from the NACA family.
Figure 16. Typical airfoils [26]
The 64 A010 is a typical airfoil for high-speed wing aircraft, designed for an increased
laminar flow. This NACA airfoil will cause a gradual loss of lift in an stall situation,
which will be much safer for the pilot, giving him time to react.
Figure 17. Types of stall [26]
6.2. Wingtip
At the wingtip, missile rails will be placed. This will have two intentions:
1. Ability to carry wingtip missiles.
2. Reduce the 3-D effects on drag, since the aspect ratio of our aircraft will be
relatively low.
6.3. Wing Sweep
As we want our aircraft to be supersonic, we will need to reduce the effects of
supersonic flow, just like aerodynamic center movement, or drag increasing due to
shock formation.
Our leading edge sweep will be of approximately 40 degrees, according to wing sweep
historical trend (Figure 16). This fact will allow our aircraft to fly at supersonic speeds.
Figure 18. Wing sweep historical trend [26]
6.4. Tapper ratio
“Tapper affects the distribution of lift along the span of the wing. As proven by the
Prandtl wing theory early in this century, minimum drag due to lift, or “induced” drag,
occurs when the lift is distributed in an elliptical fashion” [26].
As an elliptical wing is very difficult to be built, we will approximate our wing to an
elliptical one by using the tapper ratio “λ”.
λ = Ct / Cr (7)
Chapter 6. Geometric definition
λ = 100 / 280 = 0,35
According to [26], most swept wings have a tapper ratio of about 0,2-0,3.
6.5. Wing incidence
This aspect use to be determined in wind tunnels, this corresponds to a further study
of the conceptual design, so initially our wing incidence will be approximately zero, as
it uses to be for military aircraft.
6.6. Wing vertical location
A mid-wing arrangement will be selected. This arrangement will allow the aircraft to
carry bombs at a safe distance from the ground.
6.7. Tail arrangement
Twin tails have been proved to be more effective for the use of the rudder, since they
avoid the fuselage shielding. For this reason, a twin tail will be selected for our aircraft.
Figure 19. Aft tail variations [26]
Chapter 6. Geometric definition
Chapter 6. Geometric definition
41
Chapter 7. Drag Polar
It is known that a direct relationship between drag and lift exist. The lift force affects
to the drag one and this can be expressed through a diagram known as drag polar.
A parabolic approach is used to express this relationship:
CD = CD0 + KCL 2 (8)
We will calculate CD0, the parasite drag, according to (8).
In accordance to the flat plate analogy:
Figure 23. Flat plate analogy
D0 = ½ ρ V2 CD0 Sw = ½ p V2 Cf Swet
CD0 = Cf Swet/Sw
(9)
CD0 = [Cf Swet/Sw + Cf Swet.fus/Sw] FF*IF
Now we will have to calculate the three unknown parameters: Reynolds number,
Mach number and the wet surface (Swet).
Chapter 7. Drag Polar
42
To estimate the wet surface, we will approximate the aircraft to the initial solution
obtained in Chapter 3, a cylinder.
So the wet surface of the fuselage will be:
S = 2 π r l = 41’74 m2, obviating the front and the rear parts, since in the further design,
the fuselage will be more aerodynamic.
For the wings:
W/Sw = 80
MTOW/Sw = 80
12500/80 = Sw
Sw = 29’032 m2
For the rest of the parameters, we will consider an altitude of 20.000 ft and 260 KIAS,
characteristics that will resemble a cruise.
According to the atmospheric calculator [27]:
µ = 1’26 * 10^-5
ρ = 0’6527 kg/m3
Re/D = 5485432 being D the fuselage length = 10’22 m
Re = 54854320
CD0 = 1’7 * 10^-3
Now we can estimate the “k” parameter:
k = 1/πAφ (10)
k = (1 + ζ) 1/ πA (11)
. ζ = [0’015 + 0’016 (λ – 0’4)2] (βA – 4’5)
Being λ = Ct/Cr = 0’35
. ζ = 4’62*10^-3
Chapter 7. Drag Polar
CD = 0.0017 + 0.0319 CL 2
Representing this result in a graphic:
CL
CD
Chapter 8. Payload-Range Diagram
For this Chapter we will use some of the data calculated in the previous Chapters, such
as the MTOW, OEW, or the specific fuel consumption.
Using the calculations we will explain later, we achieve this diagram:
Figure 25. Payload-Range Diagram
The A point represents the Operative Empty Weight plus the Maximum Payload (both
values calculated in Chapter 4.
A = MPL + OEW = 1976 lbs + 7255.04 lbs = 9231.04 lbs
Chapter 8. Payload-Range Diagram
46
To obtain B we will calculate the range using the Breguet expression (12) and see
where it crosses with the horizontal line drawn from A.
The expression (12) maximizes the range of the aircraft:
(12)
CJ = 0.64 kg/kgf*hr [16] = 1.77 E -4 N/(N·S)
Considering the same conditions as in Chapter 7:
ρ = 0.6527 kg/m3 [27]
S = 70.722 m2
The initial weight (W0) and at the final weight (We) will be:
W0 = MTOW = 6289.8157 kg (from Chapter 4)
We = OEW + MPL = 4187.12931 kg (from Chapter 4)
We know CD0 and K from Chapter 7:
CD0 = 0.0017
K = 0.0319
Now that we have all the terms from expression (12):
RB = 7406.901 km
Now, using the same procedure, we will calculate the range in C:
The only changing parameter will be We.
WeC = OEW = 3290.83 kg
RC = 10621.4 km
We have already taken all the Payload, without reaching the Maximum Fuel Weight
(MFW), so points C and D will match.
47
9.1. Methodology
First of all, we will start reviewing the way we proceeded to obtain all our results, and
the expression of the main of them.
With the knowledge obtained and the documentation needed for the beginning of the
project, added to Chapter 1. We obtained a cursory knowledge of the state of the art.
According to the interests of this work, similar aircraft were selected as references for
our design.
Though the research in the literature and the T.O,s (Technical Orders) we get most of
the data needed for a further analysis and use.
Starting from the general knowledge of the aircraft’s content (two pilots, needed
equipment, fuel…) we proceeded to the approximation of the dimensions of the
airplane.
Later, we adjusted all these data to slenderness requirements according to our
aircraft’s characteristics, obtaining:
Fuselage length 1022 cm
Fuselage width 130 cm
Table 8. Sizing results
For the main weights, the bibliographic query proposed a series of approximations for
the calculations. Using these approximations and the data obtained from similar
planes we get some estimative results:
Chapter 9. Conclusions and further studies
48
Fuel Weight FW/W1=0.3343
Table 9. Weight results
For the wing loading and the thrust-to-weight ratio, we followed the approximations
proposed by Daniel P. Raymer at his book “Aircraft design: a conceptual approach”, for
different flight situations. Obtaining:
Table 10. T/W and W/S results
According to the results obtained in the previous paragraphs, as well as the study of
the different aerodynamic shapes, we get the initial three view drawing.
Using the parabolic approximation formula:
CD=CD0 + KcL 2
And estimating the parameters “CD0” and “k”, we get the initial formula for the
representation of the drag polar.
9.2. Further research
The obtained data is an initial approach to the aircraft design, we cannot forget the
initial aim was to get a CONCEPTUAL design. To continue the development we should
delve into the procedures followed, so that we can obtain a more accurate design. A
deeper study should also include a selection of the materials that should be used to
meet the demanded requirements that our results show (what type of flying profile is
Chapter 9. Conclusions and further studies
49
going to be used, what engines we are going to incorporate…). We should also perform
an accurate design of the aircraft (the exact measures of each surface).
A scale model could be built, maintaining the main parameters as Thrust-to-weight
ratio or the wing loading, to carry out a study in wind tunnels.
If we are going to design an aircraft, we should also consider the maintenance aspects,
like how we are going to plan it.
To finish, it is necessary to calculate the initial budget of the project, and compare it to
similar plane’s budget.
9.3. Technological improvements to implement
Since the design of similar planes to ours, some technological improvements have
been carried out, that could make the difference with this similar planes if we
implement them to our design:
-Thrust vectoring: this technology allows the nozzle to move changing the direction of
the thrust vector. The use of thrust vectoring has proved to provide some advantages
in combat, since it facilitates the aircraft to perform some maneuvers that
conventional planes cannot do.
Chapter 9. Conclusions and further studies
50
-Helmet mounted display: most of the similar planes incorporate a HUD that allows the
pilot to control the aircraft and all the basic parameters at the same time he is looking
outside. But the problem comes when the pilot has to turn his head to look for the
other plane in a dogfight for example. The helmet mounted display finds a solution to
this problem, since it shows the information on a reticle incorporated to the helmet.
Apart from this, another capabilities comes with this technology like optical or
electromagnetic tracking.
Figure 27. Helmet Mounted Display [25]
-Better simulation systems implementable by data-link. In most cases, a real situation
is very difficult to represent, or the big exercises carried out to represent them are
expensive and dangerous, and require a big coordination. For this reason, it is
necessary to do more emphasis in the development and implementation of simulation
systems allowing the pilot to experience all kind of situations that he could find in a
real mission.
.1. T-38 Talon
hmáx 3,8 m
lmáx 14 m
WINGSPAN 7,6 m
KIND OF ENGINE turbojet
Ce
RATIO lf/b 1,842105263
CABIN LENGHT lc 3,09 m
CABIN WIDTH bc 0,76m
WING
b ( 3,36 m
Ct (cuerda que hay al final del ala) 0,86 m
Cr 2,9 m
53
bh 1,54 m
Vcr optimal
V3 185 kts
Vasc 270 kts
Hser 50000 ft
KIND OF ENGINE turbojet
Teng 8708lb military power // 13635 with afterburner
at idle 97 kg/(h·kN) (0.95 lb/(h·lbf)) at idle
with afterburner 242 kg/(h·kN) (2.37 lb/(h·lbf))
WEIGHT
FUSELAGE AND CABIN
RELACIÓN lf/b 12,285 / 1,24
dmin 0,95 m
lc 1,90 m
bc 0,66 m
WING
bh 1,64
bh/b 0,229242382
Cth 1,39
Crh 2,05
Hser 16100 m
MiG-21F 1300 km
TYPE OF ENGINE turbofan
MODEL Turboméca Adour Mk151-01
2 in tandem
bh 1,95
bh/b 0,207667732
Cth 0,54
Crh 1,22
[2] http://www.rockwellcollins.com/Data/Products/Displays/Head_Down_Displays_
[15] http://dad.walterfamily.org/rv/TonyBingelis/Part%201%20%20Homebuilt%20Air
craft%20Interiors%20-%20Basic%20Cockpit%20Accommodations.html
[16] http://www.motorsich.com/rus/products/aircraft/tde/ai-222-25f/
[20] http://www.globalsecurity.org/military/library/policy/navy/ntsp/ale-47-
A6teoJnRwYQm3bwngf-QL_KOpM1PsgkvJYtA
[26] D. P. Raymer, Aircraft Design: A Conceptual Approach. American Institute of
Aeronautics and Astronautics, 1992.
[27] http://www.newbyte.co.il/calculator.php
[28] E. Torenbeek, Synthesis of Subsonic Airplane Design. Delft University Press, 1982.