Revisiting the Concorde: A new approach to Delta-Winged Flight
James Johnston
[email protected]
Gina Trivellini
[email protected]
Nick Kirkby
[email protected]
Ryan Rodriguez
[email protected]
Chris Parraguirre
[email protected]
July 22, 2010
Abstract
3pm. Unfortunately, the planes were retired in
that same year due to economic reasons. When
the Concorde flew at supersonic speeds, it was
extremely efficient, yet it produced a great deal
of noise. People exposed to the engine noise such
as those living under flightpaths objected, and the
plane was forced to fly at less efficient subsonic
speeds to comply with regulations on noise. As a
result, it became unprofitable to fly. Since then, no
supersonic passenger jet has been developed to fill
its place, and the airline industry is not flying any
faster than it did before 1976, when the Concorde
made its first commercial flight.
The Concorde belongs to a special breed of
aircraft known as delta wings, so named because
the shape of their wings resembles the Greek letter
delta Δ . This type of aircraft offers several aerodynamic advantages. For example, the shock wave
produced by the nose remains in front of the wing,
thereby reducing the drag of the airplane. Additionally, the wings larger surface area produces
more lift and allows for more fuel storage. The
goal of our project is to research and use models to
develop and test a new generation of delta winged
passenger aircraft to fill the gap in high speed air
travel that the Concorde left behind.
Motivated by the lack of progress in the area of
supersonic passenger aircraft, our research group
attempted to design one. Our goal was to determine the viability of a delta-winged aircraft
inspired by the engineering success of the Concorde and certain other high-speed jet fighters
that also employed deltas. We planned to make
a representation of an aircraft that would feature
more streamlined aerodynamics (e.g. greater fuel
efficiency) and emit less noise pollution. To test
the subsonic aspects of the aircraft, we designed,
built and flew a radio controlled model aircraft. It
incorporated features such as winglets for vertical
stabilization, a passenger cabin below the main
wing, and an inverted airfoil to would spoil excess
lift and keep the plane level. After conducting
several test flights with an evolving series of prototypes, we have found that the final evolution of
the design was far more stable and controllable
than its predecessors. Although the planes we
tested were extremely simplified versions of actual
passenger jets designed solely to test the design
at subsonic speeds, we believe they can serve as
a template for future research, possibly applicable
to supersonic designs.
1
2
Introduction
As recently as 2003, the Concorde, which featured
the worlds most fuel-efficient jet engine, was crossing the Atlantic at speeds over twice the speed
of sound. To add some perspective, a Concorde
flight departing from London at noon would arrive in New York at 10am local time while a
normal commercial airliner would arrive around
Designing a Delta Winged
Aircraft
Ever since the Wright brothers first took to the
skies in 1903, scientists, pilots, and engineers have
pondered a deceptively simple question: what
makes airplanes fly? The most obvious answer
is lift, the force which overcomes gravity and allows the plane to leave the ground. The problem
1
add the dimension of vertical stabilization to the
aircraft to aid in the prevention of rolling. The
maintenance of pressure on the underside of the
wing due to winglets results in more lift, and the
decreased turbulence reduces drag. Because of
the reduction in drag, it is not uncommon for
planes equipped with winglets to experience efficiency gains of around five percent over those with
straight wingtips. The increased lift also allows
them to take off with greater payloads.[1] A high
sweep angle also plays a vital role in the design of a
delta wing. The sweep angle on any aircraft is the
angle at which the wings are positioned relative
to the fuselage, and it corresponds to the speed
at which an airplane travels. The sweep angle
is low for an airplane designed to travel at low
speeds; in contrast, the sweep angle for a delta
wing aircraft is high. An airplane with a high
sweep angle generates less lift than one with a low
sweep angle, but a greater sweep will offset drag.
Finally, aspect ratio plays another important part
in the design of the wing. The aspect ratio of a
wing is a comparison between the wingspan and
the wing area. It gives us a rough idea of the sweep
angle, the lift, and the preferable airspeed for an
aircraft. [3] Figure 1 shows the difference in wing
areas between two separate aircraft with identical
wingspans. Both winglets and aspect ratio were
considered, employed, and refined in the design
and construction of the model aircraft.
becomes more complicated when one attempts to
isolate what exactly is responsible for that lift.
2.1
Guiding Principles
In designing the model aircraft, we had to keep
a few key points in mind to ensure that it would
fly. One of these points is Bernoullis Principle. It
states that any fluid (e.g. air) exerts less pressure
on a surface the faster it moves. Since a wing is
curved on the top, the air on top has to travel
faster to meet the air traveling under the bottom
of the wing, and exerts less pressure than the
bottom air. Therefore, the greater pressure below
the wing pushes upwards and provides lift. No
matter how lift is generated, there is no disputing
that it is essential for flight. To calculate the force
of lift, we used the equation
1
Cl ρAv 2
(1)
2
where Cl is the coefficient of lift, Fl is the surface
area of the wing, ρ is the density of the air, and
v is the velocity. Since a delta wing has a greater
surface area than a conventional wing of comparative size, it has the potential to generate more lift.
Delta winged aircraft also have relatively high stall
angles due to the wingtip vortices that form and
stay attached to the upper surface of the wing.
Finally, the wings large internal volume permits
the storage of cargo or additional fuel.
Fl =
2.2
An Analysis of the Delta Wing
Despite its advantages, a delta wing design has
some drawbacks as well. The tips of almost any
wing are prone to some loss in efficiency due to
vortices of air that form. These vortices are the
result of high pressure air on the underside of the
wing spilling up to meet low pressure air on the
top. They are unfavorable due to the turbulence
and resulting drag that they incur. However, the
vortices can be disrupted when the tip of the
aircrafts wing is turned upwards. The upturned
wingtip, or winglet as it is known, acts as a
physical barrier between the pressure differences
and aids in the prevention of vortices. Because
they keep high pressure air under the wings and
prevent turbulence, the gains experienced with
winglets are significant. Delta wings tend to have
less intrinsic stability than standard wings. Fortunately, winglets remedy this problem. They also
2
Figure 1: Both aircraft have the same lengths and wingspans, yet the delta wing has much more wing area. A larger
wing area generally equates to more lift. Because the delta wing is streamlined with a more simplified wing
profile, it produces more lift per drag than the conventional aircraft.
3
2.3
Engine Noise
determine the best design features to employ, we
ran a series of tests. We first established a list of
variables: wing sweep, airfoil shape, and control
surface size. Some, like the addition of winglets
had simple yes or no options, while others, like
airfoil shape were almost completely open ended.
We also had to choose the extent to which our
model would mimic the real plane.
Finally, the most important part of the airplane
is that which differentiates it from a glider: the
engine. One factor to consider when designing
an engine for a plane is the level of noise it will
produce. Engine noise is a serious problem both at
and near airports. The intense sound makes work
dangerous for ground crews who may or may not
be wearing proper ear protection. Also, the noise
is a nuisance for those who live nearby airports.
In spite of this, there is a rather simple solution
to the problem. It is known that the diameter
of the jet exhaust is related to the frequency of
sound produced. A larger output diameter produces loud, low frequencies. These sounds are
particularly interfering. However, the diameter
of the engines exhaust can be reduced without
taking any major toll on thrust. This is done
through the use of a corrugated exhaust (see figure
2). The corrugations, or lobes, disrupt the cross
section of the exhaust stream enough to change
the sound produced. Smaller diameters produce
quieter, higher pitched sounds which prove far less
irritating to those in and around the vehicle. [4]
3.1
A delta winged aircraft can take numerous forms.
In order to decide on the best wing contours
for the aircraft, we tested three different wing
shapes. As shown in figure 3, the wing could be
truly triangular, or it could feature an enlarged
or diminished tail. Each modification produces
significant changes in surface area. A wing with
a larger tail region will have more surface area,
resulting in more lift. Conversely, a wing with
a notched tail will have less surface area, and
less lift. We narrowed our scope down to three
variables. The wing could have either a positive
or negative tail, or it could be truly delta shaped.
Most delta winged model aircraft have a notch in
the rear, taking on more of a V shape, as opposed
to a triangular one; however, this is purely for
the sake of extreme maneuverability. As we are
designing a passenger aircraft, we prize lift more
than anything. [2]
To begin testing, we created three small models
with equal wingspan, each having one of the previously discussed wing patterns. They were each
dropped from approximately the same height, and
results were recorded.
3.2
Airfoil Shape
An airfoil plays a huge part in the properties of a
wing. We first adopted the traditional high lift
airfoil that most everyday aircraft use. It was
not until we tested the airfoil that we realized
it was not fit for delta wings. During research,
we assumed that standard airfoils would function
similarly on a delta winged aircraft. As a result,
we modeled our first airfoils in that fashion. On
a delta wing, the center of lift is farther back
than the center of gravity, giving the plane a
tendency to nose over or dive towards the ground.
We experienced this firsthand when our models
consistently dove towards the ground regardless
of weight distribution. For this reason, the airfoil
Figure 2: A corrugated nozzle decreases the maximum
diameter of a jet engine exhaust without
inducing adverse effects on airflow
3
Wing Shape
Preparing for Takeoff
The focus of our project group was to prototype
a delta winged passenger aircraft. For the sake of
practicality, our team began on the small scale.
We planned to make a radio controlled model to
test the viability of our design. Along the way, we
made numerous decisions over design features. To
4
Figure 3: Delta Wings
3.4.1
needed to be redesigned to redistribute lift more
towards the front. We performed more in-depth
research on airfoils, and found that they can be
optimized to redistribute lift. Using this knowledge, we designed a new airfoil. Instead of being
curved downwards on the trailing edge, it curves
upwards. The upwards curve is known as reflex.
This serves the purpose of spoiling lift at the rear
of the plane to balance the entire structure.
3.3
In an effort to make the model as real as possible,
we hoped to add landing gear. However, our
project advisor recommended otherwise. All of
our tests would have to be done in grassy locations.
There, wheels would not fare well. Rather than
risking potential damage to the plane as a result of
wheels becoming snagged, we omitted the wheels
from the design. The model could just as easily
be hand launched and landed in grass by skidding
on the fuselage without damaging it.
Positioning the Powerplant
In the design, we chose to mount the engine on
the top of the vehicle to reduce noise. Jet engines
are notorious for the level of noise that they produce. By mounting the engine above the wings
and fuselage, we create a physical barrier between
it and the ground, restricting the travel of sound
to a significant extent. [4]
3.4
Landing Gear
3.4.2
Ducted Fan
An actual jet engine was not an option for us when
building the model. For our purposes, we chose to
use a ducted fan. A ducted fan is a small-scale,
electric alternative to a jet engine. It functions
similarly in that it uses a turbine to force air past
the plane. However, rather than burning jet fuel
to spin the turbine, it uses batteries to power a
high-efficiency brushless motor. The motor then
spins the turbine directly.
Realism Versus Ease of Prototyping
Although we wanted to design a large and exacting
prototype, we could not. It would have been
expensive and difficult to maintain and repair.
Instead, we opted to make a smaller model. We
strategically replaced complex and costly components with more accessible parts. Even though we
were frugal in the design process, our model still
proved to be effective in providing the results that
we sought.
5
3.4.3
Mount.jpg
Building Materials
The structure of most commercial aircraft consists
mostly of an aluminum alloy. A model plane
constructed from that material would prove both
difficult to build and dangerous to fly. Apart
from being expensive, aluminum is notoriously
hard to weld. Also, in the event of a crash, a
hard metal plane could do significant damage to
bystanders or property. Because of this, we chose
foam insulation as the building material. It is
dense, strong, light, and very easy to work with
and repair. Because we anticipated crashes, foam
was our best choice. Even something as serious
as a broken wing could quickly be remedied with
epoxy resin as an adhesive and carbon fiber rod as
structural reinforcement.
3.4.4
Figure 5: The ducted fan brace and mount made of
1/4” plywood. The semicircular brackets
grip the housing of the fan.
Fabricating the Aircraft
The first step in building the aircraft was the
transfer of a pattern made with CAD software to
a paper template. The shape was then cut from a
sheet of foam. While two of us worked on cutting
the wing, two others carved a fuselage from foam
to fit the wing. The remaining person cut winglets
from foam. After all of the foam pieces had been
cut, they were glued together with epoxy resin.
We designed the fuselage to accept the wing flush
with its surface (see figure 4).
battery, the speed controller, the receiver, and the
servo motors were all positioned in cavities inside
the wings to allow air to pass over them (for the
sake of cooling) without creating significant drag.
3.5
Calculating Lift
Recalling that Fl = 12 Cl ρAv 2 , we calculated the
force of lift in our model when it flew at a certain
speed. Based on the shape of the airfoil as well as
additional research, we assumed the coefficient of
lift to be approximately 0.25.[2] While flying, our
mentor estimated the speed of the aircraft to be
about 25 miles per hour. Using this information,
we can gain a rough idea of the force of lift produced by the aircraft and relate it to the force of
gravity on the aircraft to see how effective it is in
overcoming its own weight.
Figure 4: The wing was set inside the fuselage
Next, the control surfaces (tailerons) were cut
from the wing. They were sanded and fit with
hinges. After that, a mount for ducted fan was
made. This was a crucial part of the design because it held the fan to the aircraft. It had to be
sturdy to withstand the force of the fan. To ensure
that the fan was held fast, we designed a brace
to grip the circular shell of the fan. The brace
extended deeply in to the fuselage, acting as the
backbone of the aircraft. The final step was to fit
the model with servo motors and electronics. The
4
4.1
Results and Analysis of
Testing
Results of Wing Shape Testing
In testing, we observed that the model with the
negative tail region flew well, but dropped faster
than the other models. The model with a positive
tail would fly, but it would occasionally experience
instability. It would drop very slowly, to the point
6
that it lost airspeed and stalled. Just as our calculations predicted, the amount of wing area directly
affects the lift produced. Weighting the nose was
a quick fix to the problem, but it also made the
plane heavier than the others in comparison. We
were very pleased with a neutral combination of
the two wings. A triangular delta wing flew well
with minimal nose weight. We suspect that the
negative characteristics exhibited in the other two
models are nothing more than a surplus or lack of
lift.
4.2
throw it in to a downwards spin. We attributed
this to the lack of vertical stabilization. Although
we included winglets in the design, we modeled
our winglets after conventional aircraft with large
tail fins. It is the purpose of the tail fin to stabilize
that type of aircraft in similar conditions. After
the flight, we decided that our model needed more
vertical stabilization. To do this, we affixed two
vertical fins on the upper surface of the wing to
increase the planes stability (see figure 7).
Results of Airfoil Tests
A conventional airfoil did not fly with any success.
Lift was too great towards the rear of the plane.
This resulted in a consistent tendency towards
nose-diving. The inverted airfoil designed for delta
wings yielded much better results. The unpowered
models used to test the airfoil glided smoothly.
See figure 6 for an analysis of the effects of the
airfoil on the flightpaths of gliders. In addition,
we observed that the plane was less sensitive to
changes in weight distribution. When a small
amount of nose ballast was added or removed,
the plane continued to fly without any noticeable
change in performance. This showed that it was a
stable platform, capable of carrying a payload.
Although we found success with the reflexed
airfoil, it came at a cost. The airfoil does move the
center of lift over the center of gravity, creating a
stable aircraft. However, this lowers the maximum
lifting potential of the wing. Per square unit, the
wing is not as effective in lifting as is a standard
wing. Even so, the large area of the delta wing
compensates for that loss.
4.3
Figure 7: Positioning of vertical stabilizers on the top
of the wing
We conducted another test flight, and found
that the plane flew in a much straighter path and
was much easier to control. Gusts of winds still
buffeted the plane, but it would remain upright
and fairly stable. We believed that additional
vertical stabilization mounted on the bottom of
the plane may have further increased its stability.
Unfortunately, due to human error, the model
crashed, and additional tests could not be conducted.
Results of Powered Flight Tests
Having mounted the ducted fan engine and attached all the necessary electronics, we proceeded
to run our design through its first test flight. Our
lift calculations predicted a lifting force of 17.60N.
This indicated that the lift produced would carry
the 1.5 kg plane. As expected, the plane lifted
well. There was no indication of stalling or nosing
over due to bad weight distribution or a poorly
designed airfoil. Unfortunately, there was a rather
strong breeze on test day, so overall the flight was
not as smooth as anticipated. When faced with a
crosswind, the plane yawed greatly. A small gust
of wind could knock the plane out of its path and
5
Conclusion
The goal of our project was to create a small-scale
model of a supersonic, delta-winged, passenger
aircraft and to test it at subsonic speeds. The
final design generated more than enough lift to
make takeoff possible, even with the reflex airfoil
on the tail, and flew so that it was neither unstable
nor difficult to control. This shows that a delta
7
Figure 6: Effects of Airfoil Shape on Flight Pattern
8
wing, when made correctly, can produce more lift
than a conventional wing, which in turn can make
the plane more fuel-efficient. Through this, we
inferred that our design could prove a feasible
blueprint for an actual passenger plane. We realize
that there are many factors to be considered when
designing a full-size aircraft, but we hope that
the work we have conducted can serve as a base
for more advanced experimentation, and that any
research undertaken by the aviation industry will
focus more on delta wings.
6
10. http://www.hq.nasa.gov/pao/History/SP468/ch10-4.htm, 1980.
[4] Purdue University. Noise control (supression).
http://cobweb.ecn.purdue.edu/ propulsi/propulsion/jets/basics/noise.html, 1998.
Acknowledgements
The Engineering Flight Research Group would
like to extend its thanks to Amanda Gaetano
and Adrien Perkins of the AIAA, Rutgers chapter, for their expertise in the field of aeronautics
and use of their facilities. We would also like to
thank our mentor Monal Agrawal for her guidance
throughout this project, as well as Kristin Frank,
Jameslevi Schmidt, and the NJ Governors School
of Engineering and Technology (Ilene Rosen, Director), (Blase Ur, Program Coordinator), (Marguerite Beardseley, Chair, Board of Overseers),
(Laura Overdeck, Vice Chair, Board of Overseers).
Finally, we gratefully acknowledge the sponsors of
the Governors School program: Rutgers University, the Rutgers University School of Engineering, Morgan Stanley, the State of New Jersey,
Lockheed Martin, PSEG, the Tomasetta family,
the Provident Bank NJ Foundation, Silver Line
Building Products, and the families of Governor’s
School alumni. Their generosity provided us with
the opportunity to conduct this project.
7
References
References
[1] Robert Faye, Robert Laprete, and Michael
Winter. Blended winglets. Aero Magazine,
2001.
[2] Martin Hepperle. Airfoils for tailless airplanes: Design and selection. http://www.mhaerotools.de/airfoils/index.htm, 2003.
[3] Jr. Laurence K. Loftin. Quest for performance:
The evolution of modern aircraft: Chapter
9