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TOPIC LISTINGS
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Balsa Facts
BALSA
ID CHART :
THE STRENGTH OF BALSA IS DIRECTLY RELATED TO ITS'
DENSITY.
The heavier the wood, the stronger the Balsa.
A- GRAIN -
Sheet balsa has very long fibers that show up as long grain lines. It
is very flexible across the sheet, and bends around curves easily. It
also Warps easily. This is sometimes called the " Tangent
Cut".
GOOD FOR : Sheet
covering of rounded fuselages and wing leading edges, Planking fuselages
and makes for strong flexible Spars. Also is good for building Hand Launched
Gliders.
NOT GOOD FOR :
Sheet Balsa Wings or tail surfaces , FLAT fuselage
sides , RIBS, or formers.
B- GRAIN
Sheet
balsa has some of the qualities of type " A" and
type " C" .The grain lines are shorter than type "
A" and appears stiffer across the sheet . It is a general purpose
sheet cut that can be used for many applications. This is sometimes called
the " Randem Cut".
GOOD FOR :
Flat fuselage sides, Trailing Edges , wing ribs, Formers, planking
and wing leading edge sheeting.
NOT GOOD FOR :
Use where type " A" and type "
C" will do a better job.
C- GRAIN Sheet balsa has a beautiful
mollted appearance. It is very stiff across the sheet and splits easily.
When used properly however, it builds the lightest and strongest models.
This is considered the best for warp resistant balsa, and is sometimes
called the " Quarter Grain".
GOOD FOR :
Flat fuselage sides, Trailing Edges , wing ribs, Formers, planking
and wing leading edge sheeting. Best type for Hand Glider wings and tails.
NOT GOOD FOR :
Curved Planking, Rounded Fuselages, Round Tubes, Hand Launched
Glider Fuselages, or Wing Spars.
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Balsa Tips
OIL)
Using K2R Spot Remover in spray will get the oil out of
the balsa wood. Heavily saturated sections may take several applications.Oil
soaked balsa can also be successfully glued with thin CA.
(Curving Balsa)
Ammonia (Found the household section of the supermarket),
put in a spray bottle, works fine.
Just both sides of balsa sheet liberally. Carefully bend the sheet
to the right shape. You can even tape it to a form, such as aluminum soda
cans, and let it dry. Once dry, it may be used as turtle-decks, etc.
(Cutting Balsa)
When cutting a piece of wood with an Exacto knife,
draw the knife so that if gets "caught" by the grain, it will go towards
the scrap piece of material. This should always be done even with the
use of a straightedge as the knife could be drawn towards it and possibly
push the straightedge out of alignment.
(DINGS)
There is a way to get these dents out of balsa
without additional filler material.Just wet the dented area with plain
water. Let it soak in to the wood.Then a Monokote iron, set to its
hottest position, gently iron over the dented area. The steam being generated
in the wood forces open the compressed section (i.e. the dent).
Calculating the stiffness of balsa by Bernard Hunt
Balsaloc / Balsarite substitute
Thin down some PVA white glue. Brush
it on to the wood let it dry and apply your covering. It is the same stuff,
try a test piece. You can buy a gallon at a builders
merchant for the price of a model shop 1/2 pint.
Richard Crapp (South Africa)
Measuring Balsa Density
Knowing the density or weight of balsa pieces can be important.
It's especially useful when making ailerons or wingtips, because you
want the pieces to be "matched", which will result in a better
balanced and better flying airplane. To do this, choose balsa that is
similar in weight by weighing them on a gram scale. If you don't have
a gram scale, use the deflection method: Take the balsa pieces, and
using heavy weights or sandbags, hold down a few inches of one end of
each balsa piece onto the edge of a table. Make sure that equal
amounts of each piece of balsa overhang the edge. Place a smaller
weight onto the other end of each piece, and measure how far each one
bends from the floor. The one that bends the most generally is the
lighter piece. Using this method, you can choose balsa that is similar
in density. Keep in mind that if you build from kits, you don't have
to use the supplied wood if you don't like it!
When
a Little Makeup Will Help
A lot of us weigh and grade our balsa when we bring
it home. Like a lot of modelers, I’ll use a pen or magic marker and write
the weight of the sheet in grams, and the density in pounds per cubic
foot on one end of a 3 x 36 sheet of balsa. Every now and then I won’t
notice the black mark on the back side of the strip of balsa or on a former
or rib until it’s glued into place. My experience is that those marks
are tough to sand out.
Reader Mike Moskow in Maryland builds beautiful rubber
scale models. He has a solution for those black marks in the wrong places.
He suggests that you go to an art supply store and get a tube of titanium
oxide white artist’s paint. It will cover all other colors and when dry,
is a near match for balsa.
He says that you can use it to cover laser burns as
well. Using it for that purpose may save you a lot of time expended in
either bleaching or sanding the laser burn off kit parts. But you’ll still
need to sand the laser burn off the joint areas because glue doesn’t stick
as well to the laser-burned material as it does to bare wood. Using the
titanium oxide should speed construction on laser-cut kits.
—From the Southern California Ignition Flyers, Glendale, California
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Balance
Tips
Quit guessing at the setup of you airplanes.
An accurate deflection degree indicator that can be fabricated from scrap
found around your shop. You do need a clothespin, a plastic school type
protractor, some brass tubing, screws and a fishing weight. Start by drilling
a hole in the protractor exactly at the zero by ninety degree center axis.
The hole should be sized such that you can just slip in one of those brass
eyelets that come with your servo mounting grommets. Peen the small side
of the eyelet over the protractor plastic to keep it in place in the protractor.
Take a three inch long piece of 1/8" brass tubing and flatten the center
section over a length of about 1/2". Drill a #44 hole (i.e. the right
size for a 2-56 screw) through this flattened section. Take a small size
of music wire and solder it into one end of the brass tube. This music
wire will be the pointer to read against the protractor, so you may want
to file a point on to the end if the wire. The distance between the hole
drilled into the brass tube and the end of the pointer wire should be
slightly less that the distance between the hole drilled into the protractor
and the outside edge of the protractor. Solder the other end of the brass
tube to a lead weight. John used a one ounce fishing weight, but the less
weight you can get away with, the better. The amount of weight required
will depend on the freedom of movement when the pointer assembly is attached
to the protractor. Attach the pointer assembly to the protractor using
a 2-56 screw, flat washers and either Locktite or a jam nut to keep everything
in place. Set the protractor on a known level surface, such that the pointer
can move freely, and bend adjust until the pointer is at the ninety degree
mark on the protractor. Take a standard wooden clothes pin and cut about
a half an inch off of one leg. Cut a groove on the outside of the long
leg about one to two inches long. Epoxy one side of the protractor into
this groove. To use, simply clamp the device on to the horizontal
surface to be adjusted. For example, after a trim flight, set the airplane
on a suitable surface and clip the indicator onto the control surface.
Read the degrees deflection on the protractor. Reset the transmitter trim
to its center position, and then adjust the clevis until your previous
deflection reading is obtained.
Reprint with permission of Howard
Sullivan
Balancing Planes
Here's a good way to balance airplanes. While building your plane,
insert a half-inch square piece of plywood where the balance point
should be. For a low wing, this should be on the bottom of the wing,
and for a high wing this would be on top of the wing (Note: sometimes
something will be in the way, like a canopy, and you can't use this
technique). When the plane is finished, put a small hook into the
plywood and suspend the plane with wire or string. This way you can
check the fore-aft balance AND the lateral balance at the same time
(Note: a low wing will be suspended inverted).
BALSA TOPICS
Sig Manufacturing Co, Inc has been one of the Radio Control industry
leaders since 1951, manufacturing an extensive line of radio control,
control line and free flight model aircraft kits as well as numerous accessories
and a complete assortment of balsa for the modeler who enjoys scratch
building. The nice people at Sig have graciously permitted us to reprint
the following article from their catalog, which will tell you all about
balsa.
Interesting Facts about Balsa Wood. . .
Model airplanes are no different than any other type of flying
machine, large or small - THE LIGHTER IT IS BUILT, THE BETTER IT WILL
FLY! With that in mind, it is easy to understand why balsa wood has been
the standard material for model airplane construction since it first became
readily available in the U.S. in the late 1920s. Its outstanding strength-to-weight
ratio enables hobbyists to construct durable models that fly in a totally
realistic manner. Balsa also absorbs shock and vibration well and can
be easily cut, shaped, and glued with simple hand tools.
Where does Balsa Wood come from?
Balsa trees grow naturally in the humid rain
forests of Central and South America. Its natural range extends south
from Guatemala, through Central America, to the north and west coast of
South America as far as Bolivia. However, the small country of Equador
on the western coast of South America, is the primary source of model
aircraft grade Balsa in the world.
Balsa needs a warm climate with plenty
of rainfall and good drainage. For that reason, the best stands of balsa
usually appear on the high ground between tropical rivers. Equador has
the ideal geography and climate for growing balsa trees. The scientific
name for balsa wood is ochroma lagopus. The word balsa itself is Spanish
meaning raft, in reference to its excellent floatation qualities. In Equador
it is known as Boya, meaning buoy.
How does
Balsa Wood grow?
There is no such thing as entire forests of balsa trees. They grow
singly or in very small, widely scattered groups in the jungle. For hundreds
of years, balsa was actually considered a weed tree. They reproduce by
growing hundreds of long seed pods, which eventually open up and, with
the help of the wind, scatter thousands of new seeds over a large area
of the jungle. Each seed is airborne on its own small wisp of down, similar
to the way dandelion seeds spread. The seeds eventually fall to the ground
and are covered by the litter of the jungle. There they lay and accumulate
until one day there is an opening in the jungle canopy large enough for
the sun's rays to strike the jungle floor and start the seeds growing.
Wherever there is an opening, made either by a farmer or by another tree
dying, balsa will spring up as thick as grass. A farmer is often hard
put to keep his food plot clear of balsa. As the new balsa trees grow,
the strongest will become predominate and the weaker trees will die. By
the time they are mature, there may be only one or two basa trees to an
acre of jungle.
How
long does it take a Balsa tree to grow?
Balsa trees grow very rapidly (like all pesky weeds). Six months
after germination, the tree is about 1-1/2 inches in diameter and 10 -
12 feet tall. In 6 to 10 years the tree is ready for cutting, having reached
a height of 60 to 90 feet tall and a diameter of 12 to 45 inches. If left
to continue growing, the new wood being grown on the outside layers becomes
very hard and the tree begins to rot in the center. Unharvested, a balsa
tree may grow to a diameter of 6 feet or more, but very little usable
lumber can be obtained from a tree of this size. The basla leaf is similar
in shape to a grape leaf, only a lot bigger. When the tree is young, these
leaves measure a much as four feet across. They become progressivly smaller
as the tree grows older, until they are about 8 - 10 inches across. Balsa
is one of the few trees in the jungle which has a simple leaf shape. This
fact alone makes the balsa tree stand out in the jungle.
The perfect nurse!
Nature evidently designed the balsa tree to be a "nurse tree" which
would protect the slower-growing species of trees from the scorching jungle
sun during their critical early years. For instance, in an area of the
jungle that has been ravaged by a tropical storm or other natural disaster,
the balsa trees will quickly sprout and begin to shoot up to impressive
heights in a very short time. Their fast growth, and the extra large leaves
they have in their early years, provide shade to the young seedlings of
the slower-growing forest giants. By the time the seedlings are established
enough to take care of themselves, the balsa tree is beginning to die.
Undoubtably, the balsa tree's rapid growth, fast spreading crown of first
very large and gradually smaller leaves, and it's relatively short life
span were intended to make it the "perfect nurse" in the jungle ecosystem.
How are Balsa trees harvested?
While nature intended the balsa tree to be a short lived
nursemaid, mankind eventually discovered that it was an extremely useful
resource. The real start of the basa business was during World War I,
when the allies were in need of a plentiful substitute for cork. The only
drawback to using balsa was, and still is, the back breaking work that
is necessary to get it out of the jungle. Beacause of the way the individual
balsa trees are scattered throughtout the jungles, it has never been possible
to use mass production logging procedures and equipment. The best way
to log balsa trees is to go back to the methods of Paul Bunyan -- chop
them down with an axe, haul them to the nearest river by ox team, tie
them together into rafts, and then float the rafts of balsa logs down
the river to the saw mill.
The logging team usually consists of two native Ecquadorians, each armed
with a broad Spanish axe, a machete, and a long pole sharpened like a
chisel on one end for removing the bark from the downed trees. Because
of the hilly terrain, an ox team may only be able to drag two logs to
the river per day. At the saw mill the raw balsa is first rough cut into
large boards, the carefully kiln dried, and finally packed into bales
for shipment to the U.S. via ocean freighter. Final cutting and finishing
of our model aircraft balsa is done right here at the SIG factory. As
a result of the balsa tree's fast growth cycle, both the quality and lightness
of the lumber obtained from a balsa tree can vary enormously depending
upon the tree's age at the time of cutting.
Why is Balsa Wood so light?
The secret to balsa wood's lightness can only be seen with
a microscope. The cells are big and very thin walled, so that the ratio
of solid matter to open space is as small as possible. Most woods have
gobs of heavy, plastic-like cement, called lignin, holding the cells together.
In balsa, lignin is at a minimum. Only about 40% of the volume of a piece
of balsa is solid substance. To give a balsa tree the strength it needs
to stand in the jungle, nature pumps each balsa cell full of water until
they become rigid - like a car tire full of air. Green balsa wood typically
contains five times as much water by weight as it has actual wood substance,
compared to most hardwoods which contain very little water in relation
to wood substance. Green balsa wood must therefore be carefully kiln dried
to remove most of the water before it can be sold. Kiln drying is a tedious
two week process that carefully removes the excess water until the moisture
content is only 6%. Kiln drying also kills any bacteria, fungi, and insects
that may have been in the raw balsa wood.
How light is kiln dried
Basla Wood?
Finished balsa wood, like you find in model
airplane kits, varies widely in weight. Balsa is occasionally found weighing
as little as 4 lbs. per cu. ft. On the other hand, you can also find balsa
which will weigh 24 lbs or more per cu. ft. However, the general run of
commercial balsa for model airplanes will weigh between 6 and 18 pounds
per cu. ft. Eight to twelve pound balsa is considered medium or average
weight, and is the most plentiful. Six pound or less is considered "contest
grade", which is very rare and sometimes even impossible to obtain.
Is Balsa the lightest
wood in the world?
No! Most people are surprised
to hear that botanically, balsa wood is only about the third or fourth
lightest wood in the world. However, all the woods which are lighter than
balsa are terribly weak and unsuitable for any practical use. The very
lightest varieties don't really resemble wood at all, as we commonly think
of it, but are more like a tree-like vegetable that grows in rings, similar
in texture to an onion. It is not until balsa is reached that there is
any sign of real strength combined with lightness. In fact, balsa wood
is often considered the strongest wood for its weight in the world. Pound
for pound it is stronger in some respects than pine, hickory, or even
oak. Refer to chart below for comparison.
Strength of Balsa Compared to Other Woods
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Species
Balsa
Balsa
Balsa
Spruce
Yellow Pine
Douglas Fir
Hickory
Oak
Basswood
Black Walnut
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Weight
8
10
14
28
28
30
50
48
26
37
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Stiffness
72
100
156
230
222
241
379
295
261
301
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Bending
70
100
161
260
277
291
638
430
288
506
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Compression
75
100
149
289
288
341
514
366
288
512
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About
the Chart: Weight shown is in
pounds per cubic foot. The strength of balsa varies in direct
relation to its density or weight — the heavier
the wood, the stronger it is. The above chart was designed with
10 lb/ft³ balsa as the median. In other words, balsa at 10 lb/ft³
has been tested and given a value of 100. The other
woods were then tested in the same way and given a figure that
is numerically in proportion. By comparing the relative
strength figures in the chart, it will be seen that balsa is as
strong or stronger, pound for pound, than most of the species
shown.Selecting Balsa for Model Building
Common Modeler's Tools
for Cutting and Shaping Balsa Wood
You don't need heavy-duty power saws
and sanders like you would if working with a hardwood. In fact, even with
an extensive power
shop at their disposal, the professional model builders here at
the SIG factory find that they still rely primarily on 4 or 5 simple hand
tools for the majority of their work. If you are just starting out in
the model airplane hobby, here are the tools that they recommend you get:
X-ACTO No. 1 knife with No. 11 blade for general cutting
X-ACTO No. 2 knife with No. 26 blade for carving
Razor saw for cutting thick sizes of wood
Razor plane for shaping
A knife or razor blade will work well for cutting balsa sheets and sticks
up to 3/16". Always keep
replacement blades on hand — blades do wear our and a dull blade
can make it impossible to do a good job.
You Will Also Need Sanding Blocks. In addition to the cutting
tools, you will need an assortment of different size
sanding blocks. These are indispenable tools for model construction.
You can buy ready-made sanding blocks or make
your own. The most often used general-purpose sanding block in
our model shop is made simply by wrapping a full
9" x 11" sheet of sandpaper around a 3/4" x 3" x 11" hardwood or
plywood block. Use three screws along one edge to
hold the overlapped ends of the sandpaper in place. Use 80 grit
garnet sandpaper on the block during general construction.
Another handy sanding block to have can be made by gluing 80 grit
garnet sandpaper onto a 24" or 36" long piece of
aluminum channel stock. Most hardware stores carry a rack of aluminum
in various sizes and shapes. This long sanding
block is very helpful for shaping leading and trailing edges, and
other large pieces, accurately. Last but not least,
glue sandpaper onto different sizes of scrap plywood sticks and
round hardwood dowels. These are handy for working in
tight places and for careful shaping where a big sanding block
is too hard to control.
Most hobby shops have a large rack of balsa sheets, sticks, and
blocks that you can choose from if you are going to
build a model airplane from scratch. Undoubtably, because of the
nature of balsa, the actual weight of each piece of
wood of the same size can vary slightly. When you select the pieces
you want to buy you should keep their final use in
mind. Logically one should select the lightest grades for the lightly
stressed model parts (nose blocks, wingtip blocks,
fill-ins, etc.) and the heavier grades for important load bearing
parts of the structure (spars, fuselage stringers, etc.).
To a large extent, this selection is already partly done for you.
Here at SIG, we purosely cut up our lightest raw
balsa into blocks, and our hardest raw balsa into sticks.
A spray bottle of water on your bench comes in very handy for bending
balsa sheets. If you spray a lit le water on the wood before you use
filler it will stick much better and go on smoother.
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Battery Topics
INSTALLATION TIPS
(BATTERY and RADIO PLACEMENT)
Keep your weight forward. To balance a nose heavy aircraft, 1 oz.
at the tail could be all it needs. While the same aircraft,
if tail heavy, could take as much as 10 oz. or more to balance.
Temporarily place the battery, receiver and
servos in place and check the C. G. without adding dead weight.
With everything Assembled.. it is easy then to add weight where
you need it. Check also if the model is balanced laterally and add weight
as required at the wing tips.
The Battery Directory
When you first get your battery:
Run your rechargeable battery
through at least 3 full charge/discharge cycles before putting it into
ordinary service. This will help obtain maximum capacity of the
battery.
Storing
your battery:
Store your battery in a cool
dry place. Do not leave your battery exposed to direct sunlight
or temperatures below 30 degrees F and above 100 degrees F. Always
discharge NiCd, NiMH and Li-Ion batteries before storing; and fully charge
lead acid batteries before storing.
Charging
your battery:
Rechargeable batteries will
perform better when trickle charged. Rapid or Fast charging can
be used with NiCd, NiMH and Li-IOn batteries, but you must be sure that
your charger can handle the cell chemistry involved. Please consult
your charger manufacturer's user guide for these specifications.
To calculate charge time for your
battery, use the following equation
-
Slow charger:
Cell capacity in mAh
/ Charging rate in mA) x 1.4 = Time in hours
Fast charger:
Cell capacity in mAh
/ Cahrging rate in mA) x 1.5 = Time in hours
For example if you have a 1700mAh battery
and a charger charging at 700mA, you will need to charge the battery for
approximately 3 1/2 hours.
Exercising your battery:
Battery life will improve when you exercise
your battery. To exercise a rechargeable battery, first discharge
the battery to 1 volt per cell (or until your equipment complains of "low
battery"). (NiCd and NiMH batteries consist of 1.2 volts per cell
- i.e. a 4.8 volt battery contains 4 cells). Finally, charge your
battery with a trickle charge until fully charged. When fully charged
a NiCd battery will show approximately 1.35 volts per cell, and a NiMH
battery will show about 1.39 volts per cell.
NOTES
on Battery Chemistries:
NiCd
Nickel-Cadmium rechargeable batteries are very durable and reliable.
You may slow or fast charge most NiCd's, but some manufacturers make different
types of cells specifically for rapid charging or specifically for slow
charging. NiCd battery performance is improved dramatically by interspersing
discharge pulses between charge pulses. This is known as "burp"
or "reverse load" charging. This method of charging allows the battery
to more efficiently degass while charging.
NiCd batteries should not
be left in a charger for more than 30 hours. Also, NiCd batteries
should not be subjected to shallow discharge (i.e. using the battery for
a short period of time, then recharging). This type of use may result
in crystalline formation inside the battery which will diminish performance.
This is known as the "memory effect".
NiMH
Nickel-Metal Hydride rechargeable
batteries are the next level up from NiCd. They offer up to 40%
more run time per volume than NiCd. They are also more environmentally
friendly. The biggest advantage of NiMH over NiCd is their ability
to accept a charge at any time without suffering from the "memory effect".
The best way to charge NiMH batteries is either with the "burp" charging
described above, or with a Delta V terminating charger. Before charging
your NiMH battery, check with the charger manufacturer to make sure their
charger can handle NIMH.
Li+
Lithium Ion is the latest technology
in rechargeable batteries for portable equipment. They have the
highest energy density among commercial batteries; twice that of NiCd.
They also have a very low self-discharge rate.
Li-Ion batteries are the most
expensive batteries available commercially. Disposal of lithium
based batteries may cause some concern since any moisture which may creep
into the cell after corrosion could present danger of explosion.
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Battery Information
Quick! What size in mah is the receiver battery in that plane you
built 2 years ago? How old is it?
How many cells?
Don't know???? What
I do is type out this information like this….
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Dragon Lady Built 1996 |
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Battery Pack #4 |
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800 mAh 4 Cells |
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Charge Rate 125 mA |
|
Date Purchased 7/96 |
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