Interactive Performance Predictions of Wright 1900 Aircraft Replica
Glenn
Research
Center
We present here a Java applet derived from
FoilSim
which solves the
lift equation
to predict the performance of our Wright 1900 aircraft
replica.
Our Wright 1900 replica weighs 60 pounds.
Using the inputs, see if you can determine the flight conditions of angle
of attack and velocity which we need to fly the aircraft.
For our full scale replica
of the Wright 1900 aircraft, we have a wing area of 170 square feet.
We are going to fly the aircraft at the NASA Glenn hangar which is 700
feet above sea level, so the air density is near the standard .00237
slugs/cubic foot.
The lift coefficient used in the program is based on a thin
flat plate at angle of attack which you input.
The only other variable we need
to determine the lift is the wind velocity which you also input.
Engineers make mathematical predictions of the performance of any
new aircraft
as part of the
design process.
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 airfoils based on Lilienthal's flights.
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.
The lift coefficient is used
in the basic
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.
