Building
and construction Ideas and Techniques.
Page under construction. Check this spot for update. Updated
5/5/99
This page will preview section from books that will be available
in 1999
on various aspects of aeromodelling. See link to Reference and
books.
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MADE FUEL REGULATOR
With the arrival
of non pumped 140 2 stroke motors which are
considerably cheaper(
Super Tigre 2300 and K&B 150), trying
to put the fuel
tank on the CG poses problems with fuel delivery
to the carbi.
Some may say that with the new 2+2's the effect of
putting the fuel
tank on the CG to minimize trim changes during
flight as the
tank empties is negligible. For the purist or for
those that need
consistent flight performance a regulator is a
must in order
to achieve this. It also stops the effects of the
engine leaning
in a climb or richening in downward attitudes.
A simple combination
of a regulator supplied with fuel under
crankcase pressure,
teamed with or without a one way valve
located at the
exit of the crankcase out let is all that is required.
There are many
commercial units available but they are so simple
in construction
that even someone like me could make one. The
materials required
are cheap and the regulator can be made with
household tools.
The regulator is made from aluminum or plastic,
the diaphragm
was made from an old umbrella with silicon sealant
used to seal the
surface, the diaphragm mounts were made
from a COKE can,
the spring was made from a single strand of bowden
cable wire (throttle
cable wire), 2 Dubro pressure nipples
and 5 small Dubro
bolts bought from the hobby shop....the valve is
one of these bolts
that has been filed while it was spun in a drill.
Operation was
flawless.
CUTTING
RIBS FROM SCRATCH.
For the scratch
builder. One way to cut very accurate ribs and other parts from
plans is to photocopy
the drawings of the pieces. The step of transferring them to
the balsa is a
big problem. Well here is a good way using some simple office glue.
(1) Carefully
cut with a scissors or blade the shapes of the photocopied part.
(2) Glue these
to the balsa with UHU glue..paper office glue that comes in a
wind out lipstick
like dispenser. This glue is not liquid and doesn't penetrate
the balsa. When
it dries it sticks to the paper not the balsa and can easily be
pealed off the
balsa part without any residue. I suggest that you use it just
around the edges
of the shape/rib.
(3) The part can
then be cut accurately from the balsa/ply. I actually don't
cut the parts
free hand. I cut them out roughly leaving 3 mm edge around the
part then I use
a vertically mounted disc sander to sand the ribs etc. to the
final shape. Remember
that no one can cut perfect curves or straight lines free hand.
FOAM
CUTTING
Here
is the home made foam cutter I use to cut my cores. It operates
by
a winding mechanism that will correctly introduce taper into the
wing
without any hassle. Adjustment for different shaped wings is
easy.
Typhoon stab finished.
Note that the block is put onto a board that
swivels as the
cutter advances along the rails so that the correct
taper can be obtained.
The designer of the cutter Mr Charles Leeson
spent countless
sleepless nights dreaming up this Rolls Royce of
foam cutters.
WING
TUBES MADE EASY
Have you ever
wanted to build your own custom wing tube holders that will
probably be lighter
than than the ones available. If you have access to aircraft
grade alloy tube
or carbon fibre tubes try the following construction technique.
For the average
2+2 pattern plane aluminum tubes can be purchased from
aviation suppliers
considerably cheaper than commercially available wing
tube kits. Specifications
for strengths are available from tube manufacturers.
Tubes can be purchased
after careful consideration of the loads that will be
subjected to them.
This of course depends on the weight of the aircraft and
the type of flying
conditions that the model will be subjected to.
Consult an aero
engineer if uncertain as your safety and the publics is important.
Tubes can be purchased
in long lengths and cut to size. Carbon fibre tubes from
kite manufacturers
are also a good source of wing tubes. The problem has been
to obtain the
fitting phenolic/cardboard tubes that will fit these tubes like a glove.
For a while now
I have been making my own wing tube holders using a
technique I developed
to produce even lighter tube holders than commercially
available. The
tubes are made out of 2 layers of 3 oz. Crows Foot(2*2twil)
closely woven
glass cloth. The cloth is very fine and silk like in appearance.
Construction
Steps
Firstly obtain
an off cut of the tube that you will be using as a spar. Paint the tube
with PVA release
agent and while it is wet carefully apply a new piece of high
quality, non wrinkled,
grease proof, wax lunch paper to the tube. You must
remove all of
the air from under the wax paper. Wax side on the outer. Try to trim the
edges so that
there is no overlap or minimal overlap but make sure that you don't leave
the tube exposed
or the tube cover will stick to you wing tube and make life difficult
when it comes
to removing the tube. Next lay one layer of the fibre glass on and
wet it out with
epoxy. Only overlap the edges about 5 mm. Allow this to dry and
cure. Once cured
cut the thin fibreglass tube longitudinally and peal it off the tube.
You will not be
able to slide the tube out. If you can then the fit is too loose and
you need to start
again. The wax paper should have remained on the tube or if
not you need to
remove it from the glass. Apply the tube cover to the tube that you
will be using
in the aircraft (ie. the final tube you will be using). WAX THIS TUBE.
It
Is important that
the last glassing stage be done on the final wing tube. Obtain some fine
sewing thread
and roll it on the tube over the glass. First tack one end with ZAP
then roll it on
diagonally to space it out at about a 1-1.5 cm. On reaching the other end
continue winding
and it back to the start like a binding. One should ensure that the
thread is holding
the tube in proper alignment and that the edges that were cut meet up
again. Also note
that the tube should fit snugly in the cover. If it is not then reapply
the
thread but a little
tighter. The aim of the thread is to get the right tightness around the
wing
tube. The last
step is to simply glass a final layer of cloth over the thread and first
layer. Be
careful not to
get resin on your wing tube at this stage. You should wax the wing tube
with mold release
wax a few times before this last step just in case some resin seeps
onto the tube.
Note that you should not allow the overlap of the last area to be
near
the join of the
first layer of glass for obvious reasons. Allow the tube to cure and you
have a set of
wing tube covers perfectly matched to your wing tube. These fibreglass
tubes are very
light and strong. The ends are then trimmed and a 2mm balsa sheet is
glued in at one
end for added support. The tube is now ready for use.
Note that the
first glassing step is not done on the final wing tube because cutting
it
off, dripping
epoxy etc.may damage the wing tube spar.
This method has
been proven by my friends and myself using the method and materials
described. It
is for our personal use and not intended for commercial use. Any individual
wishing to use
this method may do so at their own risk as we do not have control of the
quality of the
finished product.
Wing
Jig for Built Up Wings
Jig designed for
building built up wings extremely accurately.
The technique
was taught to me by master craftsman and
ingenious inventor
Mr. "Arrow" Chan of Singapore who
developed and
patented the technique. This jig is best suited for
the construction
of any built up balsa wood wings. It especially
lends itself to
the construction of pre dye cut ribs from an
average balsa
kit. If use in with Cyanocrylatic glues e.g.. ZAP
it dramatically
cuts building time. No pins are used. The ribs are
fastened to the
vertical right angled plates by double sided tape.
The whole wing
is built over a glass plate under which the plan is
placed so that
the plan is protected from the glue. The flat glass
also acts as a
level base. A small LASER pointer mounted onto
an adjustable
stand was used to ensure all the ribs lined up perfectly.
(not shown in
the Pics). Note that washout or wash in can be in-
cooperated in
the wing. See diagram below to see how ribs are
set up against
a perspex datum line so that the incidence of each
rib is exactly
the same. Once the ribs are placed over the plan
in position the
spars and TE, LE blocks are simply ZAPPED
into place while
the whole structure is held firmly over the plan.
ABOVE PIC.
Pic showing
right angled block with brown vertical Aluminum piece which
has the double
sided tape stuck to it then pressed against the balsa rib. Note
that the rib is
lined up accurately on a datum line line scribed into the perspex
vertical. Each
rib is mounted with double sided tape in this way accurately.
The ribs are then
lined up onto the glass plate under which the plan has been
placed and fastened
to the glass by double sided tape. If thick glass is used
the top spars
leading and trailing edges are then slipped into placed and
ZAPPED on to place
the the whole glass can be lifted up and turned upside
down and supported
so that the underside can be completed. That is really
what you would
call building in thin air.
Note that the
method of course lends itself to use with other glues but a wing
can be built in
an afternoon completely sheeted using this method if Cyanocrylatic
glues are used
as drying time is instantaneous.
ABOVE PIC.
Pic showing all
the ribs in alignment with spars ready for gluing.
LE TE already
glued in place. Method is extremely quick and accurate.
THIS METHOD IS STRICTLY PATENTED & MUST NOT BE
REPRODUCED
FOR COMMERCIAL USE WITHOUT PERMISSION.
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