Bulletin of the SAS, Winter 1998
Note: The following was scanned, OCRed and converted to HTML.
Please be advised, Errors have crept in.
The Amateur Scientists'
Volume 5, Number 1, Winter 1998
, By Shawn Carlson
- person powered aircraft, By Mike Garrison
, By Richard Hull
By Sheldon Greaves
By Lisa Bridenstine Chaddock
, By Ely Silk
By Jan Herron and Martin Bailey
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These sorts of interrelated design improvements have been happening in all
aviation-related technologies since the time of the Wrights, but the most important
in propulsion. All powered airplanes, from the Wright Flyer
to the latest military and civilian jets,
designed around their engines.
Human-powered airplanes are the ultimate expression of this design philosophy.
Their range can not be extended by adding more fuel. Nor can it be extended
(to any practical extent) by using a more powerful or fuel efficient engine.
The range can only be increased by increasing speed or time aloft, while using the
same engine.
THE POWER SHORTAGE
To illustrate the problem, let's look at the current record holder. The Daedalus flew at
about 15 miles per hour (airspeed) for about four hours at a power output of about 0.27 Hp.
Since the airplane is in constant, level flight:
1) Lift = Weight = constant.
If the airplane is flying near its maximum lift to drag ratio (L/D, a good measure
of the aerodynamic efficiency of an airplane), then:
2) L/D is approximately constant
3) Drag is approximately constant.
Power is determined by:
4) Power = (I/eta_p) * Weight * Velocity/ (LID)
where eta_p is the propulsive efficiency, the fraction of the power applied to the
pedals which actually is used to overcome the airplane drag.
In order to maximize the propulsive efficiency at both cruise and takeoff,
RAVEN will have a two-position variable pitch propeller. RAVEN's cruise propeller
efficiency will be about the same as that Daedalus.
All of this means that in level, constant speed flight, the power required to
propel the airplane is equal to the speed times the drag times the inverse of the
propulsive efficiency.
If RAVEN tried to keep the same design as the Daedalus but increased the speed
to 25 miles per hour, it would need 1.7 times as much power.
But the amount of power which can be provided by a human is inversely proportional
to the length of time over which the power must be supplied.
The RAVEN pilot could never supply 0.45 Hp for any where near the four hours that
Daedalus flew.
In fact, RAVEN's testing program shows that the pilot should be able to provide
0.25 Hp for five hours. With the Daedalus design, this would translate to a speed
of 14 miles per hour (and thus a range of 70 miles).
To give a 100 mile range, RAVEN will need to fly at 20 miles per hour for five
hours. To do that with 0.25 Hp, the L/D of the RAVEN will need to be about 60
(as compared to 40 for the Daedalus).
and RAVEN will weigh the same, they will have the same lift.
Therefore, RAVEN will have to have only 2/3 as much drag as Daedalus.
A drag reduction like that requires a major advance in aerodynamic technology.
BUILDING THE SAME OLD AIRFOILS IN A WHOLE NEW WAY
Daedalus tripled the range of the previous record holder, Paul MacCready's
Gossamer Albatross, by using a technology breakthrough in airfoil design state-of-the-art
low speed air foils designed for it by Professor Mark Drela of MIT. In effect, the
improved aerodynamic technology of the airfoils went directly into improved airplane
aerodynamics.
RAVEN, however, will use the same airfoils as Daedalus. "I did not feel it was
possible to achieve any significant improvement upon the Daedalus airfoils," Illian
explained. "Any improvement would have to come from somewhere else." "I
improvement would come from two main areas: reduction of surface area and elimination
of interference drag between airplane components," he elaborated.
Taking a page from the designers of the late 60s commercial jets, Illian decided to
technology advance in one area into a design improvement in another.
Until now, state of the art human-powered airplane construction has been balsa wood
and foam covered by mylar skin. This requires guy wires to keep the wing in compression
and give it strength. This form of construction also required the pilot's
separate from the wing.
RAVEN, however, is using carbon/foam composite skins and carbon/Nomex (TM)
composite spars to support the wing without any external guy wires, eliminating
a major source of drag.
Similar construction techniques for the fuselage also allow RAVEN to integrate
the pilot fairing into the wing. This allows the pilot to be in a recumbent position,
again dramatically lowering the airplane drag.
This aerodynamic improvement because of structural and material technology is
roughly the same thing that happened when
monoplanes replaced
fabric biplanes in the 1930s, except the new materials are so light that the entire
plane (without pilot) should end up weighing about 80 pounds.
WING SPAR CONSTRUCTION HAD A FEW TWISTS
The hurdle RAVEN had to leap in order to use this semimonocoque wing construction
was the weight of the stiff skin and the beams used to support it (called the wing spars).
For the skin RAVEN uses a composite material of carbon fiber and foam, drawn by
vacuum into 60-foot-long, airfoilshaped aluminum forms. But even though the skin is
strong enough to support the aerodynamic loads upon it, it would buckle if it had to
carry all of those loads into the fuselage structure.
The wing spar, an internal beam which runs from the tip of the wing all the way
to the wing root, is the traditional airplane design solution.
RAVEN's spars are made of Nomex honeycomb, capped on top and bottom with carbon
fiber. The main spar is about 6.0 inches high and 1.5 inches wide at the wing root.
It tapers to 1.5 inches high and 0.25 inches wide at the wing tip.
This spar carries XO per cent of the flight loads. A secondary spar, with similar
construction, carries the remaining 3_0 percent and also controls the wing twist
during flight. The secondary spar is only 4.0 inches by 0.5 inches at the root.
It tapers to the same size at the tip as the primary spar.
To cure the spars, Illian designed 60-foot long wooden ovens lined with fiberglass
insulation and electrical resistance heating coils. Unfortunately, during the cure cycle,
the honeycomb cells kept collapsing.
It turned out that the heat from the oven expanded the volume of the air in the
cells. The air simply squeezed past the end caps while they were still flexible.
When the spar was removed from the oven and the air cooled, atmospheric pressure
crushed the Nomex from the sides.
Eventually,
the RAVEN volunteers realized that pinpricks in the cell
walls would not hurt the strength of the spar, but would allow the air pressure to
equalize inside and outside of the honeycomb cells.
A sewing machine with a diamond-tipped needle was used to perforate the honeycomb
before curing the spars, and the problem was solved.
FLY-BY-PEDAL RUNS INTO FLY-BY-WIRE
Another RAVEN feature new to human-powered airplanes is fly-by-wire flight controls.
Instead of directly controlling the elevator and rudder, the pilot will use a control
pad similar to those found in video game machines to tell the flight computer which
direction the airplane should be heading.
The main computer is a Model 8 microcontroller donated by Onset Computer.
"It is very fast, takes very low power, and weighs about one ounce." according to
Roger Johnson, who headed the RAVEN flight control team. About eight people have
worked on this team since 1995.
The computer relies on eight on-board sensors to measure altitude, heading,
airspeed, and various other flight parameters. These are converted to analog voltages,
then digitized and fed into the computer.
Converting the sensor readings into analog is not necessary for the operation of
the flight controller, but it did help solve a problem Johnson faced.
In order to use the help of student
volunteers,
Johnson needed each part of the
system to be able to be designed and tested in small, separate chunks. This made it
easy to assign individual subsystems to separate volunteers. Converting everything to
analog signals allowed the volunteers to test and debug the systems they worked on.
Once the analog signals are converted back into digital form, the computer takes
the data from the sensors and the pilot's control pad and sends signals to electric
actuator motors in the airplane tail. These actuators drive the vertical and horizontal
stabilizers, allowing RAVEN to fly without control cables from the pilot to the tail
(another reduction of drag and weight).
The side benefit, of course, is relieving the mental workload of the pilot.
The computer will sense pedal RPM and calculate a target RPM, then display those
to the pilot. Instead of flying the airplane, he or she will only have to tell
the RAVEN where to go while concentrating completely on the pedaling effort.
In fact, the suite of sensors which feed into the flight computer are much
more sensitive than a human pilot could be. They can detect and correct any deviation
from optimal flight attitude, allowing the plane to fly at peak efficiency all of
the time. That's important in an airplane which never gets more than 20 feet off the ground.
PROJECTED RAVEN SCHEDULE
In effect, the new construe tion materials and flight control systems available
today allows RAVEN to decrease drag by 33 percent compared to 19X8 technology, even
though the basic aerodynamic technology is the same as the Daedalus.
At least, that's the theory. At the time this article was written, the RAVEN was
nearing the end of final assembly. The next step (targeted for February 1998) is a
flight test program to measure just how successful the drag reduction effort has been.
The current wings have been deliberately oversized in order to give RAVEN a large
safety margin and ensure the airplane will fly. The data from the flight testing will
tell Illian how small he can then build the record-attempt wings.
About the same time, the pilots and ground crew will have learned the best ways to
handle the airplane, and the program leaders will know what sort of weather conditions
the airplane can withstand.
With pilot, support crew and airplane tested and ready to go, hopefully RAVEN
will be taking to the air a year from now.
For more information and the latest reports about the RAVEN, check the RAVEN
web site at http://www.ihpva.org/ Raven *
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GROUNDING?
A true and properly driven electrical ground just for an electrometer would be a
costly and time consuming business. A good alternative would be an AC plug which has
only a single wire connection. A modern three wire grounded plug can be purchased from
a hardware store and used to supply an electrical ground for the instrument in this
article. I would recommend a 10 piece of common lamp cord in which both of the two
18 gauge wire leads are connected to the ground lug of the plug.
Please be sure that
the connection is made only to the ground of the plug!!! The hot AC connection must
never come into contact with the wire and is left unconnected as is the neutral connection.
I use a hot glue gun to cover and insulate the hot and neutral connections inside the
plug in order that no accident can occur. The other end of the cord can be hooked to an
alligator clip, spade lug or other convenient method of attachment to the case
electrometer. Needless to say, never use a two to three prong adapter. If you use this
type of plug it would defeat the whole concept. If you have only two terminal outlets in
your home, you must secure a good ground elsewhere. This may mean driving a 6 or 8 foot
ground rod just outside a window. These copper clad steel rods are available at most
home builder supply stores. You should then run a wire lead
house through
a window. Both the noise immunity of the instrument and reliable results rely heavily
on the excellence of the ground connection.
primary plant used by the Kumeyaay was the acorn.
From the acorn many things
were made, including acorn soup, biscuits,
Soup was flavored for daily use, however there were many more medicinal and tonic
uses for the acorn than simply making a meal
of the mush. The soup or mush was used as a medicinal wash for sores because of its antiseptic
properties.
Another use for the oak tree comes from the tea, made from budding oak leaves.
The tea was used to reduce fever, as a goiter remedy, for a "female remedy," and for
hemorrhoids and boils in a sitz bath.
Another very important plant
the elderberry.
Elderberry
mexicanal was a favorite in combination with acorn soup.
was also a necessity. The elderbeny can cause nausea when eaten raw, but is rendered
harmless when cooked.
The elderberry blossoms were boiled for tea to reduce fever
The Kumeyaay also used elderberry in a tea for eye infections.
If you have an elderberry
tree, cooking the berries and adding them to pie crust bakes them into a sweet treat.
Among the Kumeyaay numerous remedies are recorded for colds and lung diseases. The
mahogany (Cercocarpus beteloides) bark was pared from the tree and put on
the patient to dry, then removed and boiled into a tea for treatment of colds and for
diseased lungs. White sage (Salvia apiana) tea was used for respiratory
sicknesses,
including asthma. It is a strong antihistamine.
The leaves
were burned as a
fumigant and to cleanse a place for sacred ceremonies. Flattop
buckwheat (Eriogonum
fasciculatum) was used in
coughs, as
(Paeonia californica), and sugar bush (Rhus ovata).
sage leaves were rubbed on the body to ease sore neck muscles. Skin
allergies such as
oak (Toxicodendron diversilobum) were treated by picking
a branch of white sage
was growing nearest to the poison oak, crushing
the leaves with the hand, and vigorously rubbing the affected area. White Sage contains
camphor, which is an active ingredient in many muscle creams and respiratory medicines
currently on the market. For other itchy skin ailments, including skin fungus, creosote
bush (Larrea tridentato) was used as a salve to rid the patient of the offending fungus.
Mistletoe (Phoradendron californica) was used as a mash to eliminate lice and bugs from
the scalp.
Chia sage (Salvia columbariae) was an extremely useful plant, even though the seeds
are small. Although one would normally use the seeds to season soup, these seeds were
invaluable medicinals. The seed produces a mucous-like substance, which was useful in
removing foreign objects from the eye. The patient would insert a chia seed in the eye
prior to going to sleep, and would awake with the eye clear of the object.
Chamise (Adenostoma fasciculatum) was used as a disinfectant.
The leaves and branches
were boiled and used to bathe infected, sore or swollen areas of the body.
The Kumeyaay
also used Chamise for firewood. Some of the desert bands used bound branches of the chamise
for torches.
Dove Weed (Eremocarpus setigerus) was used in an infusion as a laxative. The stems and
leaves were crushed into a mush, then placed in decaying, open wounds on horses to kill
the maggots and allow the wound to heal.
Deer Vetch Lotus (Lotus bicolor) was primarily used for food, however the plant was
added to dry pine needles andspread as a layer in the pit roasting the yucca. The decoction
of this foliage was used for coughs. The Kumeyaay also fed lotus leaves to their
domesticated animals.
A very important plant in the Kumeyaay ethnobotany was Toyon (Heteromeles arbutifolia).
The fruit of the plant blooms in December, and is eaten as food. However, the plant also
has a medicinal use. The plant yields a treatment for skin ailments, including using an
infusion of leaves and bark to wash infected wounds.
Another medicine widely used by the Kumeyaay grows in three varieties, but is commonly
called Yerba Santa (Eriodictyon crassifolium, E. chrysanthemfolia, E. trichocalyx).
The primary use of these plants was to chew the small, new leaves to ease a sore throat
or to relieve a cough or cold. This plant was also used blended with other medicines,
such as Horehound, to cure colds and fever. During the field work on Volcan Mountain
these plants and other medicinals were found adjacent to each other in areas containing
medicine rock configurations. This was a significant find by SAS volunteers!
SAS is working with professional archaeologists to survey and record the distant
and recent history of San Diego at a variety of locations. If you are interested in
the continuing research on Volcan Mountain, contact Susan Hector at the County of
San Diego, at (619) 694-3037. For either the Bancroft House project (Carol Serr),
or for Silverwood Wildlife Sanctuary project (the author) ca11(619) 5788964.
ACORN MUFFINS:
If you are are interested in making acorn muffrns, try making the acorn mush by
husking and food processing acorns. Gather the acorns while still light brown. Take
the mush and boil in water, draining and replacing the water 3 or 4 times until it is
no longer purple in color. Then, add the mush to your favorite corn muffin recipe or
boxed corn bread mix. This makes a much lighter version of the acorn cakes, and one of
them will satisfy your hunger for most of the day. *
But the glass can be used for heating materials as well, and that is what this technique
for the microscopist is all about. A piece of 2 x 2 electroconductive glass is prepared
with two thin copper strips epoxied to the outer margins. One needs a conductive epoxy, and
I used a silver epoxy (40-3900 resin and catalyst) obtained from Epoxies, Etc. of Greenville,
RI (401-231-2930).
In the center of the conductive glass surface, place a small drop of a high boiling point,
non-reactive liquid such as glycerol (bp 290 degrees C). Next, lay a thin microscope cover
glass (#O is ideal) about 22 x 30 mm in size on top of the drop of liquid. Place a few
crystals of the material being studied on the cover slip either in solid form or dissolved
in a suitable solvent. If a solvent is used, allow it to evaporate,
and lay another cover
glass about 18 x 18 mm and #1 to #2 thinness on top of the crystals, centering the smaller
cover glass in the larger. See Figure 1 .
Place the heating device on the microscope stage and connect the leads to a DC power
supply (variable 15 volts @ 1 amp is fine). Then set up the polarizers (if these are being
used) in the crossed position. While examining the crystals, slowly raise the applied
voltage and look for melting. Fine adjustment of the applied power will increase, decrease,
stop, or reverse
rate. Examining anisotropic crystals forming or melting
while viewed under polarized light is an unforgettable
experience. Orchestrating the
growth and melting of the crystals at the twist of the dial is even more unforgettable!
A few safe materials to try include thymol, camphor, menthol, stearic acid, and
myristic acid. I extracted the myristic acid
using methanol. Trimyristin
also crystallizes out of the impure nutmeg extract. The combined mixed crystal is
interesting to observe, albeit slow to crystallize when viewed under the microscope.
Studies of crystal habits, changes of polarization, etc., may now be easily and
inexpensively performed. Bear in mind that the device is unsealed. If materials
such as naphthalene,
anthracene, biphenyl, and other hazardous compounds are
to be studied, some provision must be made to produce a sealed heating cell.
If you need to measure the temperature of the plate, use a digital thermometer
with a fine metal probe tip and immerse the tip in a drop of glycerol (or similar high
boiling point liquid) placed on the glass surface in
Alternatively, the temperature can be measured using pure organic solid reagents with
known melting points. Also, liquid crystal sheets are available which can be placed in
contact with the glass to map the temperatures.
The benefits of this simple to-construct hot-stage include: low-cost,
very rapid response and low thermal lagging
(due in part to the liquid interface between the tin oxide and lower cover glass), and
transparency which allows transmitted light viewing. The thinner the glass,
of hot-stage plates and see how high a temperature you can reach safely. Be aware
that prolonged viewing of a high-temperature surface
high-power microscope
objective may be detrimental to the objective. Also, evaporating solvents and
the better as far as being able to set up critical (Koehler) illumination, but under
low power, even the thicker glass will perform well. With this setup I easily achieved
100 degrees C on the surface. How long this would last before the glass cracks is an unknown.
melting points up to 85 - 90 degrees C may be readily examined
with the setup. There are dozens and dozens of compounds which can be studied with
melting points in the range of room temperature
C. Definitely
construct a number subliming crystals could harm an objective. In the event that
these deleterious conditions are encountered, some means must be taken to protect
the microscope objective. A gentle flow of air near the objective lens (lowpower)
could help keep the heat, solvent, and crystal vapors away.
Uses for this setup include:
Observing and recording growth of bacteria and other microorganisms at
different temperatures in an inexpensive onstage
incubator.
Studying the behavior of liquid and ordinary crystals at different
temperatures to study phase changes. Crystals may be observedduring
melting,subliming,
or solidifying either as the pure crystalline
compound or in a saturated solution.
Viewing crystal changes under polarized light is most instructive and beautiful.
Testing for the purity of low-melting point solids by checking the melting
points in comparison to suitable standards of pure substances.
Examining the effect temperature
on refractive indices.
Looking for liquid inclusions in minerals and crystals.
phase changes of low boiling point liquids (with a suitable
housing to protect the microscope objective).
Examining plastic and polymeric films for their behavior during
polymerization.
Studying denaturing of proteins.
There are many other uses as well. I hope you and other amateur scientists find
this technique of interest. *
Temperature Conversions:
F" to C": Subtract by 32; multiply by 5 and divide by 9.
Ex: 125F"-32 = 93 x 5 = 465 /9=51.67C"
C' to F': Multiply by 9; Divide by 5; add 32.
Ex: 18C' x 9 = 162 / 5 = 32.4 + 32 = 64.4F"