Interactive Performance Predictions of Wright Aircraft (1900 - 1905)
Glenn
Research
Center
We present here a Java applet derived from
FoilSim
which solves the modern
lift equation
to predict the performance of the Wright aircraft from
1900 to 1905.
Due to IT
security concerns, many users are currently experiencing problems running NASA Glenn
educational applets. The applets are slowly being updated, but it is a lengthy process.
If you are familiar with Java Runtime Environments (JRE), you may want to try downloading
the applet and running it on an Integrated Development Environment (IDE) such as Netbeans or Eclipse.
The following are tutorials for running Java applets on either IDE:
Netbeans Eclipse
You can download your own copy of this applet by pushing the following button:
The program is downloaded in .zip format. You must save the file to disk and
then "Extract" the files. Click on
"Lift.html" to run the program off-line.
Operation
You can change the values of the velocity, angle of attack, and wing area
by using the
sliders below the airfoil graphic, or by backspacing, typing in your value,
and hitting "Return" inside the input box next to the slider.
By using the drop menu labeled "Aircraft" you can choose to investigate any of
the Wright aircraft from 1900 to 1905. At the right bottom you will see
the calculated lift and to the right of the lift is the weight of the
selected aircraft.
The aircraft designated "-K" are kites and the weight does not include
a pilot. The aircraft designated "-G" are gliders and the weight does include
a pilot.
For design purposes, you can hold the wing area constant and vary the speed and
angle of attack, or hold the speed constant and vary the wing area and angle of
attack by using the drop menu next to the aircraft selection.
In this simulation, the change in weight due to change in wing area has been
neglected.
For output,
you can choose to have a plot of the lift or the lift coefficient by using
the drop menu. You can plot lift versus angle of attack, velocity or wing area by
pushing the appropriate button below the graph.
You can perform the calculations in
either English or metric units by using the drop menu labeled "Units".
Finally you can turn on a "Probe" which you can move around
the airfoil to display the local value of velocity of pressure. You must
select which value to display by pushing a button and you move the probe
by using the sliders located around the gage.
Background
The objective of this game is to
find the flight conditions that produce an aircraft
lift
greater than the aircraft
weight.
You will be determining the combination of
velocity,
angle of attack,
and
wing area
which are
necessary for flight.
You can check your results for a particular aircraft by comparing
with the individual aircraft page to see how
the Wrights solved this problem.
However, determining the lift is only a part of the design problem.
Real aircraft designs are a compromise imposed by several
conflicting design factors.
A higher angle of attack
produces more lift than a lower angle, but it also produces more
drag. The
lift to drag ratio
is the important design factor for the aircraft because it is directly
related to the
angle
at which a glider descends in flight.
The Wrights were aware that they needed both high lift and low drag (which they called
"drift").
Increasing the wing area increases the lift,
but it also increases the weight which you have to lift.
Higher speed produces more lift, but it also increases drag. To provide higher
speed for a powered aircraft you need a larger engine, which typically increases
weight. All of these various design trades must be considered to arrive
at a final, successful design.
During the
design process,
engineers make mathematical predictions of the performance of a
new aircraft.
These predictions use the best data and mathematical techniques
which are available to the engineer. As the Wright brothers were
designing their
first aircraft,
the basic principles of
aerodynamics
were being discovered. The brothers had preliminary data on the
lift coefficient
of certain airfoil shapes based on Otto Lilienthal's flights and tests.
The lift coefficient is used in a lift equation
to predict the lift of the wings.
The lift coefficient is just a number which contains all of the complex effects
of shape, angle of attack,
compressibility, and viscosity on the
lift of an object.
In the modern
lift equation,
lift (L) is equal to the lift coefficient (cl)
times one half the air density (r) times the velocity squared (V^2) times the
wing area (A).
L = .5 * cl * r * V^2 * A
If you know the lift coefficient, you can use the
lift equation to determine the value of one unknown parameter when
you are given the value of all the other variables.
For example, you can determine how fast you have to fly to lift a certain
weight with a given wing area. Or you can compute how big a wing you
need to lift a certain weight at a given speed. Or you can compute
how high you can fly with a given weight at a given speed with a given
wing area. The lift coefficient is hard to determine in general. It is
usually determined through
wind tunnel testing. For some simple
shapes, like a flat plate, or a plate with very small curvature, there are
theories which give values for the lift coefficient.
NOTICE: In this simple program we have approximated the
entire aircraft (both wings and the canard) by a single flat plate. So
you can expect that our answer is only going to be a very rough estimate.
Engineers used to call this a "back of the envelope" answer, since it is
based on simple equations which you can solve quickly. Engineers still
use these kinds of approximations to get an initial idea of the solution
to a problem. But they then perform a more exact (usually longer, harder,
and more expensive)
analysis
to get a more precise answer.
