From the Executive Director
SAS GOING AFTER A QUARTER-MILLION DOLLAR ROCKETRY PRIZE.
In December's "The Amateur Scientist" in Scientific American magazine. I wrote about an exciting new competition which is being sponsored by the Foundation for the International Non-governmental Development of Space (FINDS), a Washington DC-based lobbying group. Dubbed the "Cheap Access to Space" (CATS) prize. FINDS will pay $250,000 to the first amateur group that can launch a 2 kilogram payload to an altitude of 200 kilometers. After developing a computer program to explore the feasibility of the contest, I discovered that if special care is taken to optimize the design. 200 kilometers should be achievable with a relatively small rocket.
Then it hit me. SAS counts as members over one thousand talented amateur scientists who are all looking for exciting projects. Why shouldn't we go after this prize? So I phoned SAS Roard member Dr Paul MacCready. Paul is a world famous engineer and technologist who, early in his career, won several large cash prizes for achieving mile stones in human powered-flight, including the first human-powered plane to cross the English Channel. Naturally, I figured Paul would be a kindred spirit.
Paul enthusiastically introduced me to Edward J. Dempsey, CEO of World Record Performance Associates (WRPA). a company created just to set world records WRPA agreed to join the effort as an equal partner and has frunded us with $30,000 for the attempt. In addition, dozens of volunteers and companies have already donated materials and work worth tens of thousands of dollars.
We are building two small rockets, standing about six feet tall. They are single stage, and will be propelled by essentially the same propellant used by the Space Shuttle's solid rocket boosters We plan to launch from San Nicholas Island, about 60 miles off the coast of Los Angeles. If all goes well, the rockets will reach speeds in excess of Mach 6, and coast to altitudes well above 200 kilometers- that's about as high as the Space Shuttle orbits.
However, the rockets will not circle the earth Once reaching their maximum altitude, they will fall back down and disintegrate in the atmosphere The current verified altitude record for an amateur-built rocket is 36 kilometers. So if we do shatter the altitude record. we will also set another mark the lowest ratio of cost per altitude obtained by any rocket program (professional or amateur) in history We will use any prize money we might win to continue to push back the frontiers in amateur rocketry annd all other areas of research.
I am heading the rocket team Jack Herron is heading up a team of volunteer machinists and rocket enthusiasts in Tucson. Arizona This team has built our "secret weapon." a most unusual launch platform which should dramatically improve our chances for success. Although we still have a ways to go. the project is well on its on its way to completion. We don't want to reveal too much just yet. but we will share the full details of our attempt in a future edition of the Bulletin.
If you would like to get in on this or future exciting space adventures, please contact our main office at (617)-239-8807. We especially need machinists, ham radio experts, electronic hackers, writers, html aficionatos and cash donations.
JOIN THE NEW INTEACTIVE FORUM ON WEB
Check out Amateur Scientists' Forum in the SAS 'Web page! The new Forum already features dozens of ongoing discussions on all kinds of science-related topics. Get involved in some, or start your own discussions on any scientific topic you want. The Forum is your resource for intactactive science how-to's, general informatlon and materials.
In addition to the general discussions, you'll also find the following resources in the new Forum.
Additional information about projects featured in "The Amateur Scientist": We have started a discussion group from every column I`ve written for Scientific American, going back to Novemher. 1955. You`ll find important additional information that wouldn't fit in the original article, links to our index page, and links to other web sites that can provide you with even more assistance Also, if you have any questions about an AmSci project, go ahead and post them there. I check every folder once every two days and answer every question I can.
New interactive Snap Meet: Are you looking to purchase some equipment or perhaps sell something? The new interactive Swap Meet allows you to post your requests and offerings free of charge. And your messages won't become obsolete because thev are automatically deleted after four weeks. Feel free to post as many messages as you like and update them as long as you like. This is your resource at buy and sell the necessary materials of science.
Letters to the Editor: Feel free to share your suggestions about how SAS can better serve your needs as an amateur scientist.
Partial membership roster: Find out who shares your interests and let others know about you.
It's easy to get involved. Just connect to the SAS home page at: www.sas.org and click on the Forum button. Follow the directions to register (its FREE and open to all) and log on.
My special thanks go to Ed Thelen and Craig Chaddock for getting this going. Ed is doing an outstanding job as the Forum's sysop. The entire amateur community owes both of them a deep debt of gratitude.
SAS also wishes to express its gratitude to Lundeed and Associates, who donated their outstanding WebX software to SAS. WebX makes this new interactive Forum possible.
BACK ISSUES OF AMSCI TO SOON BE AVAILABLE
Thanks to a generous donation by SAS member Sam Hobbs, we will soon be able to supply our members with reprints of old issues of "The Amateur Scientist" from the days of CL. Stong and G. Walker. The rocket project is eating up all of our volunteer staff's time right now but we will soon publish a list of available articles in the Bulletin. We will also post the same index on our Web page.
My deepest and most sincere thanks go out to Sam for his generous donation. His generosity will help many amateur scienists for years to come. Also. it you have back issues of Scientific American and would like to donate copies of "The Amateur Scientist" we would very gratefully receive them. One day, we hope to have a complete set of reprints available online.
Dragonfly is a wonderful publication for the younger investigator. A subscription to this entertaining and educational publication is offered to new members of the SAS when they sign up at the family level. See page 22 for more details. *
The RAVEN
When we watch a 747 take off, it's easy to forget that flight used to be the province of
amateur scientists and engineers like Wilbur and Orville Wright.
Probably this is because of the swift pace of aeronautical history. Just 44 years
after the Wrights' first flight, the X-l was breaking the sound barrier. And it only
took 66 years to land men on the moon.
But the amateur spirit is alive and well in at least one area of aeronautics.
And it just happens to be one of the most challenging applications of flight technology.
Human-powered flight has proven to be more elusive than anyone ever imagined
it would be. Who in 1903 could have thought that we would have sent space probes
completely out of the solar system before anyone managed to fly a human-powered
airplane over a 100 mile distance?
Nevertheless, the current distance record for human-powered flight is only
115.11 km (72.4 miles) and the record for women is only 6.83 km. What keeps these
records from being broken?
The designer of the RAVEN thinks he knows the answers.
RAVEN PROJECT
The RAVEN is the brainchild of Paul Illian, a Seattle engineer and human-powered
airplane enthusiast. Illian has worked on many human-powered airplanes, mostly in
concert with another amateur designer, Wayne Bliesner.
Back in 1988 (the year MIT's Daedalus set the current record), Illian decided he
could design an airplane which would break the 100 mile barrier. Bliesner, however,
was more interested in working on highspeed designs, so Illian decided to set up
The RAVEN Project, a non-profit educational organization affiliated with Seattle's
Museum Of Flight.
Hundreds of volunteers have worked to design and build the RAVEN. Almost all of
the materials have been donated by
Puget Sound area businesses. Much of the labor has been done by undergraduate students from
11 Puget Sound area schools, who worked in industry-style design/build teams. Illian handled
the preliminary design, but the design teams worked out the details.
Students have designed and tested the RAVEN flight control system. They have done most
of the machining and composite lay-up work. They have designed and built the 60-foot
transport trailer necessary for moving the RAVEN. In fact, they have been involved with
everything from the initial design sketches to the final assembly.
But what is it about humanpowered flight that requires this much engineering and
scientific effort?
THE PROBLEM OF LONG RANGE HUMANPOWERED FLIGHT
Aeronautics is perhaps the most delicately balanced engineering discipline.
Every aspect of the design of an airplane influences every other aspect, usually
in a convoluted manner. For instance, in the 1960s aerodynamicists designed new transonic
airfoils with greatly increased lift-to-drag ratios, but the new airfoils were not
used to reduce the overall drag of the airplane. Instead, they were built into much
thicker wings, with the same lift-to-drag ratio as the older, thinner wings.
This increased the amount of fuel which could be carried and decreased the weight
of the wing structure. Thus, a low-drag airfoil led to an airplane with the same
drag but less structural weight and much greater flying range.
These sorts of interrelated design improvements have been happening in all
aviation-related technologies since the time of the Wrights, but the most important
changes have been in propulsion. All powered airplanes, from the Wright Flyer
to the latest military and civilian jets, are primarily 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
and thus:
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).
Since 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 felt the
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
try to translate a 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 fairing to
be 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 metal monoplanes replaced wood and
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, one of 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 *
An Experimenter's Electrometer
Sniffing out subtle electrostatic phenomena
By Richard Hull
The field of Electrostatics concerns itself with charges, potentials, and forces,
and is often considered to have first been studied in the late 18th and early 19th centuries.
In today's modem world, electrodynamics is the dominant study in electrical engineering.
Electrostatics is making somewhat of a come back, and the forces and charges involved can
be used for a number of novel purposes in our day-to-day lives. Xerography is a
prime example.
The experimenter can arm him or herself with an old classic electroscope and
investigate a number of rather large electrostatic effects. In order to gain real
insight and do more subtle and difficult experiments, an electrometer is often needed.
The electronic electrometer is nothing more than an ordinary voltmeter. The salient
difference between your digital VOM and the electrometer is one of input impedance.
This relates to the amount of load that the instrument places on the circuit under test.
Most good electrometers have input impedance's of 200 teraohms. This is tens of thousands
of times greater than the average electronic VOM(I - 10 megohms). It will immediately
amaze the experimenterjust how electrical the world really is, once armed with an
electrometer.
Modern electronic electrometers are very expensive. $5,000 will buy a
fairly nice instrument, while $10,000 would be needed for a superlative one.
Keithley Instruments and Victoreen are major suppliers of these specialized instruments.
This article will supply the experimenter with schematics and a broad overview for
assembling a first class electrometer with a very modest outlay of cash. Actually,
this is a unity gain impedance translator or electrometer IX amplifier, in the s
trictest sense, as the experimenter will have to supply the readout system,
(usually a VOM or oscilloscope.) It will be assumed that the experimenter has a
modicum of experience in assembling simple electronic circuits.
DISCUSSION OF THE CIRCUIT REQUIREMENTS
As the frequency response of this junior electrometer is limited by the low pass
filter circuitry to around 10Hz, no special PC boards are needed. Point to point or
wirewrap type connections are all that is required. I have assembled many of these circuits
on the simple pad per hole, 2"x3" circuit boards found in local Radio Shacks.
The key point is shielding and insulation. The front end of the system utilizes a
special precision CMOS FET Integrated Circuit by National Semiconductor. (LMC 6081)
This special IC can be purchased from DigiKey. The only other IC is an LM-324N and
can be found at most Radio Shack stores. I recommend first quality machined pin
IC sockets (DigiKey). Radio Shack also has aluminum chassis cases which will be needed
for shielding. The input connector must be a Teflon insulated, chassis mount, female,
UHF connector type PL-259.
The output connector is unimportant and can be a RCA type
phonojack. I chose a BNC chassis jack for my output connector. The system is powered
by two common 9 volt transistor radio batteries. Parts layout is only critical in
that the part of the PC board containing the input IC (LMC 6081) be located immediately
at the input connector.'The critical input pin to this IC (pin #3) is carefully
lifted and not inserted in its socket at all. The two components from this IC lead
to the input connector center terminal are connected floating in mid-air!! All
batteries and
wiring should avoid this area and be on the opposite side of the board and shielded
container box. Beyond this, the builder is totally at liberty to do as he or she pleases.
I have a proposed lay out diagram included.
GETTING STARTED
Begin by soldering the sockets to the PC board. Next make all connections to all the
various tie points. When the board is wired, add the battery clip leads. The box should
be a fully enclosed all metal item. Place the input connector at one end and the output
connector at the other end of the box. For convenience in some models, I put the input
connector on the top of the box at one end. Holes must be drilled for standoffs or long
machine screws to support the board near the input connector. The batteries are best
placed in the opposite side of the box near the output connector. Make sure at each step
of the drilling process that all components will fit in the box and not short out or
touch one another. The power switch should also be positioned near the output end of the
box. If you still haven't picked up on it, the input end of the box is special and
PRIVATE! Only the input IC and the ultrashort input connection, and air, are allowed.
You are on your own from this point! Good luck. I expect the builder to rely heavily
on the supplied visuals to complete the circuit.
TESTING AND CALIBRATING THE INSTRUMENT
With the shielded box still apart. get a 1.5 volt battery and connect it to the input.
Turn the unit on. Measure with a VOM the voltage on the battery. Write it down. Now go
to the output with your VOM and adjust the gain potentiometer until the reading exactly
equals the input voltage of the battery. `This sets the instrument for unity gain.
You are calibrated! Next, we have to check out the finished system. Assemble the box
and case for final use. I prefer to use a banana plug with a stiff 24 gauge rod
soldered inside the plug to make a vertical whip antenna if the input connector is
on top of the instrument. If not, just use a short flexible wire soldered to a banana
plug and connect it to a stainless steel salad bowl which is setting on a clean drinking
glass. It is crucial that no path of any resistance exist to ground from the isolated and
insulated metal object. Ground the chassis of the instrument (a good solid earth ground
is needed.) Connect the output to an Oscope or VOM. Set the scope's sweep for a long period
sweep of 10 seconds across the screen or more. Set your meter for the 10 volt range if
you have no scope. Turn on the instrument. Now move about a bit and notice the varying
voltage you are impressing on the bowl or antenna! The impedance is so high (teraohms)
that the instrument can resolve voltages that would be overloaded and swamped back to
zero by other meters of lower impedance. If you have encountered any problems in getting
the system to work, you have made a simple mistake somewhere. Check your batteries.
Are they good? Are they hooked up right? Are the ICs in their sockets correctly?
Recheck all wiring. You can blow the input IC very easily by touching the input lead
while your body is electrostatically charged. I hope you purchased a spare!
PROTECTING YOUR INVESTMENT
It seems bizarre that we use static sensitive components in an instrument and then use
them in static experiments. The instrument gets its ultrahigh impedance from the use of
feedback and the delicate micro thin layer of insulation separating the FET gate lead
from the main substrate in the device.'This is a layer which is easily punctured by
static. Needless to say, such puncture means the destruction of the device and IC.
The wise application of the electrometer device is the best precautionary measure
one can take. Never leave anything hooked to the input connector when the instrument
is not in immediate use! The size of the isolated capacity (item hung up as an
antenna and hooked to the input) relates to the amount of charge collected, and
thus the voltage collected. This instrument will respond to voltages in the range
of +/- 7 volts or so. Large collectors around high voltage equipment such as
Van DeGraf Generators, Wimhurst machines, Tesla Coils, etc., will collect hundreds
of volts and thus destroy the input IC. The voltage collected also relates to
proximity of the source of charge for any given collector size. If in doubt, use
small collectors or a whip antenna hooked to the input. Never walk across the
room and just touch the input collector or connector. You may carry thousands of
volts on your body! Always ground yourself on the grounded instrument box. Remember,
the box must always have a solid connection to a real earth ground to function properly.
SUMMARY
Your meter can be used to determine the polarity of various insulators. Plastics
are all negative. Polished, clean glass is always positive. Tapping one's toe in time
with a piece of music while sitting on a modern carpet can induce +/-10 volt potential
change on a can of Spam 5 feet away! The study of atmospheric electricity can be
investigated. A people proximity detector could be devised. No matter what your use,
you will see in short order, that every object is continuously exchanging charges
with other objects in our everyday world. We exist in a sea of charge. For more
information on electrostaties, an excellent book by A.D. Moore entitled Electrostatics
is available again at a very modest cost and many experiments are suggested to introduce
the amateur scientist to the fascinating world of electrostatics.
PARTS LIST AND SOURCES FOR THE EXPERIMENTER'S ELECTROMETER
Model of completed RAVEN
(92 K bytes)
Sources:
Fig 1. Electrometer Amplifier Layout on Bottom of Board 40 K bytes
Fig 2. Basic Electrometer Circuit 25 K bytes
