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and Tail Sizing
have already decided that I want to this airplane to hold two
full sized adults and I also want it to have adequate baggage
space. The JayBird is a conventional aircraft. I am not trying
to re-design the wheel so I can learn a lot of things from other
designers. By taking a look at other two-place airplanes I can
come to a general idea of what the approximate wingspan
on my airplane should be. There are two things that I must pay
particular attention to; wing
loading and aspect
ratio. A lower wing
loading will give increased takeoff and landing
performance and it will give us a lower stall
speed. A higher wing
loading will give us just the opposite, decreased
takeoff and landing performance with a higher stall
speed. From doing some research, I want to keep
my wing loading
around 15 pounds per square foot. I estimate that my finished
aircraft, fully loaded, will weigh between 1500 and 1800 pounds.
The wing I have designed for the JayBird has a wingspan
of 28 feet. The wing has an area of 111 sq ft. With a weight
of 1500 pounds I will have a wing
loading of 13.5 pounds per sq. ft. A weight of
1800 pounds will give me a wing
loading of 16.2 pounds per sq. ft. Using the spreadsheet
supplied with "Preliminary Design - Modern Aircraft Design
for the Non-Engineer" makes this all very simple.
provided with "Preliminary Design - Modern Aircraft Design
for the Non-Engineer" by
Jay S. McMullan
wing I have designed also gives me an aspect
ratio of just a little over 7. Takeoff, climb,
range and landing performance are all enhanced by a high aspect
ratio wing. There are two ways you can determine
the aspect ratio of a wing. For a rectangular wing with a constant
divide the wingspan
by the wing chord.
For tapered and eliptical wings it is a little more difficult.
In this case, divide the wing
span squared by the wing
area. For example. If a wing is 36 feet long and
the average chord
is 6 feet, you would divide the wingspan-
36 - by the average chord
- 6 - giving you an aspect
ratio of 6. You could also square the wingspan
- 36 x 36 = 1296 - divided by the wing
area - 216 - = the same aspect
ratio or 6. You will notice that many of the high
performance airplanes such as the Lancair IV have high aspect
ratio wings. By using the software included with my book, you
can quickly and easily make changes when designing your airplane.
Now that we have the
wing planform we can go ahead and determine
the size of the flaps
modern aircraft should have flaps.
The flaps will increase
the lift coefficient
and drag of the wing, allowing an airplane to have a lower stall
speed making landings safer. There are different
types of flaps
that can be incorporated into the wing but for simplicity's
sake, I will use a "plain" flap. The area of both
of my flaps equals
just over 1,741 square inches or 12.1 square feet. This gives
me a flap to wing ratio of 9.2. The chord
of my flap is 13.75 inches which is about 25% of the root
chord of my wing and about 30%; of the chord
where the flap ends. I have chosen to use the NASA NLF(1)-0215F
airfoil and the designer of this airfoil, Dan Somers, recommends
the flap chord to be 25% of the wing chord. Wind tunnel tests
have determined the maximum lift
coefficient of this airfoil to be 1.8. With flaps,
the maximum lift
coefficient increases to 2.2. These are useful
numbers that are essential for calculating performance estimates.
For more information on airfoils please refer to "Theory
of Wing Sections, Including a Summary of Airfoil Data"
by Ira H. Abbott and Albert E. Von Doenhoff.
past the flaps,
still using the same chord
makes the area of the ailerons
to be just over 1,482 square inches or 10.3 square feet.
all of this information and a rough sketch of the airplane we
can now go about calculating the volume
coefficients of the tail surfaces.