WING CONSTRUCTION
The wing of the Sky Pup is of the internally-braced or cantilever type. Since it is
the heart of the primary structure, care in its construction is of utmost importance.
Building the wing represents at least half of the total project, so don't be discoursed if
it seems to go slowly at times. You will have no other fittings, struts, or brace cables
to fabricate, so your time will be spent in building the wing as carefully and
accurately as possible. This will
insure a good-looking and nice-flying aircraft.
The wing is constructed in three separate sections: two detachable outboard
panels, and a centersection which remains attached to the fuselage at all times. The
outboard panels are joined to the centersection with typical steel fittings, the
centersection containing the "male" portions, and the outboard panels bearing the
"female" portions. Each wine section features a single spar with a "D" type plywoodskinned torque/drag box
ahead of the spar. The spars in the outboard panels are mirror images of each other,
but the centersection spar is significantly different. Foam nose ribs are typically
spaced 8" from center to center down the front face of the spars. The ribs aft of the
spar are spaced at 24" intervals, and are also of foam with wood caps. For general
discussion purposes, foam pieces in the ribs or spars will be referred to as "webs" or
"cores".
Wing construction should begin with the three spars. Start by cutting out the foam
webs for these spars.
The dimensions of these webs are obtained by subtracting the spar cap thicknesses
from the total spar dimensions given in the plans. The foam webs can be cut in any of
several methods, but hot-wiring with the use of long straight edges is probably the
easiest. Since the foam webs can be damaged easily until the wood caps are added,
careful handling is necessary. Any dents or gouges in the foam will prevent a good
bond later on.
Available thicknesses of foam vary from one locale to the next. If possible,
obtain your foam in billets large enough that the entire foam web can be cut in one
piece. If pieces this large are not available, the webs can be built up using smaller
pieces. The best method for building up webs from smaller stock is to simply "spot
glue" the pieces together while you cut the total webs to shape, and then come back
and bond the pieces together permanently after they are cut. Five minute epoxy will
work well for spot bonding, but use only enough to hold
the parts in place while you cut them. If you use too much, the pieces will be difficult
to get apart for the final bond. If you try to bond the pieces together permanently
before cutting the web to shape, you'll find that the hot-wire will not pass through the
bondline, and erratic cutting will result. Butt joints in foam are fine, (since the epoxy
is stronger than the foam} as long as the joints are tight-fitting and have no gaps or
voids.
After the foam spar webs are cut to shape, set them aside and prepare the wing
attach bearing blocks.
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These blocks are very critical to the proper alignment of the wing joints, and
considerable care must be exercised in their fabrication. The ul¬timate purpose of the
wing attach bearing blocks is to transfer the fitting loads (via the
attach bolts) into the spar.
The most important feature of the bearing blocks is the proper alignment of the
bolt holes. This alignment can be achieved in several ways--select the method best
suited to your tools and capabilities.
1. If you have access to any milling equipment, or a very accurate drill press,
the blocks can be made in one piece and the 1/4" holes can be located exactly. Since
the drilling
operation involves considerable depth (four inches), precision is crucial.
2. The majority of builders will not have access to milling equipment, but can
accomplish the task with equal precision. If you have a router table, the
blocks can be made in upper and lower halves with each half routed 1/8"
deep with 1/4" round-tip router bit. During this operation, each block
should be routed at each fence setting to assure that all the block are
exactly alike. Always run. a piece of test stock through and measure it to
verify correct location and depth of "grooves" before routing the actual
blocks. Obviously, the same result can be obtained using a circular dado
blade in a tablesaw.
3. If neither a circular dodo nor a router table are available, the jig can be done
using a reqular tablesaw blade. Rather than cutting a semi-circular groove, kerf cut
the block halves so that they will have kerfs 5/16" wide and 5/32" deep, centered at
the correct hole locations. After the halves are made, bond them together with epoxy
while placing tubes in the kerfs so that the tubes will
provide bolt holes down their inside diameters. Steel or aluminum tubes may be
used, and the appropriate size is 5/16" O.D. and 1/4" I.D. The tubes should he cut to
four inches in length, and will be permanently bonded in place when the block halves
are joined. Care should be taken to insure that no voids are left in the epoxy between
the tubes and the inside of the kerf hole. The blocks on the center section would use
7/16" O.D. and 3/8" I.D. tubes in similar fashion for the 3/8" attach holes.
METHOD 1:
Block is made from single piece of
wood with holes drilled in the proper
locations. When using this method,
accuracy during the drilling operation
is of utmost importance.
METHOD 2:
Block is made from upper and lower
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halves with semi-circular groovs cut
in each half. When joining halves
together, clean glue or epoxy out of
holes before cured. This will prevent
holes from becoming clogged.
METHOD 3:
Block halves are kerf cut with dado
or regular saw blade. Tubes which
will provide bolt attachment are in
position when block halves are
joined with epoxy. Epoxy must fill
all voids between round tobes and
square kerf holes.
Regardless of wich method you chose to fabricate your blocks. The end result
must be four centerction blocks and four outboard spar blocks (they are different)
with holes perfectly aligned and located correctly down the length of the blocks.
Once you have completed your wing attach bearind blocks, you will be ready to
fabricate the steel wing attach fittings.
The fittings should be cut from 1/8” steel stock to the appropriate dimensions and
match drilled off of the bearing blocks. As long as all the holes in the bearing blocks
are spaced equally all the fittings can be match drilled from on of theblocks and a
perfect fit with the others will be guaranted. Do not drill the 3/8” attach holes in the
outboard fittins at this time. Pilot them with 1/8” bit and leave the drilling of the
larger hole until later. Test fit the fittings to the blocks using 1/4" bolts tu assure thet
ewerything is progressing properly up to this point.
The wing attach bearing blocks should now be inlade into the ends of the foam
spar webs. This is last operation where the proper mating of the fittings at the wing
joint is the question. Cut the foam away to allow the blocks to nest into the foam.
Proceede carefully, working on one joint at a tome, and check constantly for
alignement of the bearing blocks with the surfaces of the foam webs, and the proper
matong of the centersection to the outboard panels. Once these blocks are bonded in
place the alignement will be established. Don’t hurry. When you are certain that the
blocks are fit into the inlay cutouts with proper mating and alignment, go ahead and
bond them in place using a mixture of epoxy and micro balloons. Use enough micro
to keep the epoxy from “running”, and be shure to wipe of any excess on the spar
faces. The epoxy is difficult clean off after it’s cured.
After the wing attach bearing blocks are installed in the foam webs, the fuselage
attach bearing blocks should be inlaid into the centersection. These blocks are
located directly between the eventual location of the wing support members, and
require no drilling. Simply cut them to size and inlay them into the foam, taking care
that the surface of each block comes out even with the surface of the foam web.
There are four fuselage attach blocks in all. Bond them in place with mixture of
micro and epoxy.
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With all the blocks inlaid into the spar webs, you are now ready to add the spar
caps. The cups can be cut from the single piece of wood, or laminated up as material
permits. If the caps are laminated from more than one piece of wood, the pieces
sould be glued together edge to edge before adding the complete cap to the spar web.
Each piece must be continuous lengtwise—no splices.
When gluing the caps into place, be sure that no twist is introduced into the spar.
Keep one surface flat at all times. It may be necessary to stack weights (any thing
will work) onto the cap to insure good glue squeozeout and a consistent bond. Uhen
weights are used, they should not be laid directly onto the surface of the cap, but
rather, use wood blocks to distribute the load across the caps. Particular attention
should be given to the bonds between the spar caps and the bearing blocks. Large Cclamps and/or strapping tape may be used to obtain good clamping at the block.
Install the upper cap to each spar first, since it is thicker and will help provide
more stability in holding the spar straight until the lower cap is added. Note that the
lower cap of the centersection will be bowed slightly on installation. This will not
present any problems, as long as the upper surface is held flat and true. Strapping
tape and small blocks will be very effective in holding the cap tightly to the web
until the glue has dried.
Centersection wing spar assembly before gussets are added shows fuselage and wing attach
bearing blocks inlaid into spar web foam with capstrips glued on. Wote(Note) different thicknesses
of upper and lower cap-strips. Lower cap bends to conform to spar foam bend. Also note
lamination glue line in wing attach bearing blocks along which attach holt holes are drilled.
Precision drilling is required to assure alignment of these holes.
Once the spar assemblies are complete with wood caps, the plywood gussets at the
wing joints and the fuselage attachments should be added Since the attach holes in
the wing attach bearing blocks must be transferred into the gussets after they are
glued in place, only one gusset may be added at a time. (After one gusset is in place,
it should be back-drilled before the opposite gusset is installed to prevent "covering
up" the holes.) After the gussets are all in place, add the plywood spacers on the
outboard spars. These spacers will spread the fittings of the outboard spars so that
they will fit snugly over the centersection fittings. Try the fittings on for proper fit.
Sand the spacers, or add additional material until the correct fit is achieved.
With the fittings temporarily in place, the 3/8” attach holes should be back-drilled
(using the centersection wing attach fittings). A precision fit of the atach bolt in the
fitting is absolutely essential, so care must be taken not to over-size the holes. This
drilling should be done, one joint at time, with the centersection spar and the
outboard wing spar held in correct relative position tо one another. The easiest way
to jig the spars into, position is to block the centersection spar with the lower surface
of the appropriate side parallel to the table top and then block the outboard spar with
its lower surface parallel also. Be sure to block them up off of the table high enough
to allow access with the drill. The holes may be drilled slightly undersize and then
reamed to their final diameter it desired The successful completion of this step will
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be a landmark in the project: the basic spar assemblies are complete. Nothing in the
remainder of the construction will require as much precision as the wing joints, and
progress will be much more rapid and visible from this point on.
Centersection wing joint prior to back-drilling bole holes through gusset. Gussets are added and
drilled one at a time to assure perfect hole alignment with holes in wing attach bearing blocks.
Centersection spar (right) bolted to outboard panel spar assembly (left) prior to adding ribs. Note
plywood spacers glued to gusset under outboard panel attach fittings. Spacer allows outboard
panel attach fittings to slide neatly outside of fuselage attach fittings for a snug fit. All attach holes
must be drilled on centerline of metal attach fittings.
After the fittings have been corrosion-proofed with a primer of your choice, they are
ready to be permanently installed. Using appropriate bolts and washers, assemble the
fittings to the spars with epoxy between the fittings and the spar. The epoxy will add
strength to the joint, and serve the purpose of sealing the wood beneath the fittings
from possible moisture damage later on.
Completed spar assemblies are bolted together to check the fit and overall wing symmetry. Note the
shape of the centersection spar and positioning of gussets.
This plywood Joint nose rib is cut thicker than other nose ribs in the outboard panels and is capped
with a special plywood strip in order to accommodate the joining of leading edge D-skins. Note
that foam part of rib must he cut 1/16" under contour so it can receive the plywood splice doubler.
Addition of the doubler will bring the rib up to the shape of the other ribs. Front tips of all nose
ribs are cut flat to accept leading edge strip as shown.
Now you're ready to hot-wire the nose ribs for the outboard panes and bond them to
the front face of the spars at the intervals shown in the plans. Note that the ribs
located at the plywood D-skin joint stations are thicker than the other ribs and are cut
under contour to allow for the addition of the D-skin splice doubler. Also note that
the nose ribs at the fitting end must be notched and trimmed to accomodate the
plywood gussets, attach fittings and bolt ends. When hot-wiring the ribs, strive to
keep them all identical, and discard any which are undercut.
To outboard panel attach joint. Two 3/8" bolts are shown here inserted into main attach bolt holes
for temporary fit checking. Close scrutiny reveals lamination in upper capstrips on both spars.
Note notches cut into leading edge joint ribs to accommodate fitting attach bolts.
Next, add the leading edge strip to the forward ends of the nose ribs. It should be
glued to each nose rib except at the joint ends. These should be left unattached until
the leading edge fittings are in place. Chamfering the edges of the leading edge strip
stock on the tablesaw prior to installation will greatly simplify the process of shaping
the strip after it's on the wing.
Completed cantilever spar assembly with nose ribs attached is truly a work of arc and represents
about 1/3 of the work on the entire airplane. From this point on, building will progress
at a speedier rate.
After the nose ribs are installed on both outboard panel spars, they can be sanded
slightly to insure an unwavering contour down the wing and provide a good fit for
5
the plywood skins later on. A long block with sand paper over a short section will
work well for this step. The block should be contacting at least three ribs at all times,
and the sand paper should be near the middle. The tie-down straps should be sewn
and bonded in place, taking care to apply epoxy liberally on all sides.
The nose ribs for the centersection should be added at this time. Since the
centersection spar gets deeper as it approaches the fuselage sides, only the nose ribs
adjacent to the wing joint can be cut using the sane template you used for the
outboard panel nose ribs. The nose ribs at the sides of the fuselage will be developed
using the tried-and-true "eyeball" method. These ribs should be identical to all other
nose ribs from the chordline up. The contour of the nose rib below the chordline is
nearly a mirror image of the contour above the chordline, and should simply be
a smooth-flowing curve which will encompass the spar dimensions at the fuselage
sides.
The two nose ribs which lie at the fuselage sides should be cut and block-sanded to
match each other. The intermediate nose ribs which lie halfway between the wing
joint and the fuselage sides should be hot-wired in place by bonding a piece of foam
stock (larger than the rib) to the spar and then hot-wiring the contour using the ribs
on either side as guides. The wire can only be hot over the section of wire which will
do the cutting — it must be cold on the other ribs to prevent damage to then.
Contouring the intermediate ribs by this method will ensure an exact fit of the
plywood skins later on. Add the leading edge strip to the centersection at this time.
Photo shows front view of centersection attached to outboard panels with nose ribs and leading
edge strips installed. Note thicknesses of "special" nose ribs at wing joint stations and where
ending odge D-skins will weet. Note, too, that leading edge strip on centersection has not yet been
rasped to conform to rib contour, and that leading edge strip attach fittings have not been
added. All this must be done before plywood D-skins can be added.
With all the nose ribs in place, prepare the leading edge fittings before adding the
plywood skins. Glue the hearing blocks in place and fabricate the fittings. Hold the
fittings in place and match-drill the blocks using the holes already in the fittings.
Follow the same general procedure you used for the wing attach fittings to
permanently install these fittings. Remember to varnish any wood which will be
inaccessible after the fittings and bolts are in place.
The wino spar assemblies are now complete with the nose ribs, leading edge fittings,
and leading edge strips. If you haven't done it already, contour the leading edge strip
to the required radius. A hand-held rasp works well for this. Varnish any wood
surfaces in front of the spar which will be "hidden" after the leading edge is skinned.
The next step in the building process is to add the plywood D-skins to the
centersection spar assemblies. Skin the outboard panels first and leave the
centersection until last. Note that the portion of the centersection between the
fuselage sides will not be skinned until after the centersection is installed on the
fuselage.
6
To outboard panel attach joint. Two 3/8" bolts are shown here inserted into main attach bolt holes
for temporary fit checking. Close scrutiny reveals lamination in upper capstrips on both spars.
Note notches cut into leading edge joint ribs to accommodate fitting attach bolts.
Next, add the leading edge strip to the forward ends of the nose ribs. It should be
glued to each nose rib except at the joint ends. These should be left unattached until
the leading edge fittings are in place. Chamfering the edges of the leading edge strip
stock on the tablesaw prior to installation will greatly simplify the process of shaping
the strip after it's on the wing.
Completed cantilever spar assembly rich nose ribs attached Is truly a work of art and represents
about 1/3 of the work, on the entire airplane. From this point on, building will progress at a
speedier rate.
After the nose ribs are installed on both outboard panel spars they can be sanded
slightly to insure an unwavering contour down the wing and provide a good fit for
the plywood skins later on. A long block with sand paper over a short section will
work well for this step. The block should be contacting at least three ribs at all times,
and the sand paper should be near the middle. The tie-down straps should be
This is necessary so that access to the spar can be maintained tor bonding the wing
support members to the spar.
Since the plywood skins will "close up" the leading edge of the wing, their inner
surfaces must be varnished before they are installed. To insure a good bond between
the plywood skin and the nose ribs, no varnish should be applied to the bond areas.
The skins can be laid in position on the nose ribs and marked lightly with a pencil to
outline the areas which will be bonded. The skins can then be masked in these areas
to prevent varnish from contacting the wood. An alternative to the varnishing method
which will save considerable time is to use a finish for the inner sur
face of the plywood skins to which epoxy will adhere. Epoxy which is thinned to a
brushable consistency can be used for this. Also, Ramaset, a two part resin (see the
materials list) will do the job nicely. Whatever you use, remember that you won't
have access to the inside of the D cell once the skins are on, so preserve it
adequately.
Six pieces of plywood will be used to skin each of the wing sections. The skins on
the outboard panels are cut from 2' X 4' plywood sheets with no waste or leftover
material. The skins will overlap 1/2" onto both the leading edge strip and the spar
caps. Skin the upper and lower surfaces of the D cell consecutively. Start at the wing
tip end and work toward the joint end. Check-fit each skin prior to applying any
epoxy. Once a correct fit has been verified, the skin should be bonded in place
using epoxy and micro between the plywood and the foam nose ribs, and pure epoxy
between the plywood and the wood parts (leading edge strip, spar caps, and splice
doublers).
The skins must be held tightly in place, without wrinkles, while the epoxy is curing.
Use the heavy-duty stapler and nailing strips to hold the edges of the skins to the spar
7
caps and the leading edge strip. 3/8" staples will work fine. Wax paper should be
placed between the nailing strips and the skins to prevent the strips from becoming
bonded to the wing. Nailing strips should be approximately 1/16" thick and 3/4"
wide. Also, surgical tubing or rubber straps should be used to wrap the spar/D-tube
assembly at each nose rib and hold the skins against the ribs.
Affixing leading edge D-skin to the centersection demands careful atcention to ensure a good bond
between plywood and nose ribs. Softwood nailing strips stapled into D-skins hold the skins to
the upper spar caps and to the leading edge scrip аз shown. Liberal use of wax paper under nailing
scrips keeps epoxy from sticking to nailing strip. Rubber surgical tubing and strapping tape help со
apply even gluing pressure and assures a good bond line.
During the entire skinning operation, the spar must be held such that no twist is
introduced. Since these plywood skins provide virtually all the torsional stiffness of
the wing, any twist present at the time they are installed will be permanently built
into the wing. The Sky Pup wing requires no twist or washout.
Add the skins to both outboard wing panels before moving on to the centersection.
The centersection skins are installed in the same manner, but will not be rectangular
in shape like the skins on the outboard spars. Once again, remember that the
intersection skins across the middle 20" of the centersection will not be added until
the centersection has been glued to the fuselage.
Entire сentersection spar assembly with D-skins just applied. All wing attach bearing blocks and
fittings must be permanentiу installed and metal parts primered prior to this step. Note that centermost D-skinS are not yet applied to allow access for attaching the сentersection to fuselage wing
support members later.
When all the skins are in place, a general cleanup of the spar assemblies will be in
order. Scarf the plywood edges so that they blend smoothly into the other surfaces.
This can be done with a sanding block or a Dremel tool with a rasp blade.
The aft ribs (those portions of the ribs aft of the spar) can now he hot-wired and
installed to all three spar assemblies. In order to insure proper alignment of these
ribs, a few precautions must be taken. Install the join-end aft ribs to the centersection
first of all, by standing the centersection on its leading edge and using plumblines to
align the chordlinel of the ribs. Don't worry about the aft ribs adjacent to the fuselage
sides at
this time.
Install the aft ribs to each outboard spar assembly by using the aft ribs of the
centersection as a guide. This should be accomplished with the outboard spar
attached to the centcrsection, and will assure a perfect transition fron the outboard
wing to the centersection. Once the joint-end aft rib is in place the remainder of the
aft ribs on each panel may be added using a plumbline and checking to make sure the
trailing edge is straight. Bond the ribs to the aft face of the spar using a mixture of
micro and epoxy. Add the trailing edge to the aft ends of these ribs, and prepare to
install the rib caps.
Since the spar tapers as it goes outboard, each aft rib will require some trimming on
its lower surface to provide a smooth-flowing lower wing contour. These ribs are all
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the same length. The aft ribs should be installed on the spar with the chordline
correctly located (upper forward edge of rib will be flush with top of spar cap). Aft
the ribs are bonded in place, roll the wing upside down, and trim the ribs to provide
the correct transition at each rib station. The rib at the joint end should require no
trimming, and the trimming will increase as you work outboard from there.
The desired end result is u smooth transition both chordwise and spanwise.
After all the ribs have been trimmed to "blend" into the leading edge D cell contour,
small soft wood filler blocks will be added across the spar to fill in the contour and
provide a surface to glue the rib cap to.
The material for the rib caps can be most easily ripped from the edge of a good board
of appropriate thickness. Most of the rib caps are 3/4" wide, but a few are 1 1/2"
These caps will lap onto the D skins, and the trailing edge at their forward and aft
ends, respectively. These caps may be glued with Titebond or equivalent, and should
be held tightly to the foam using short pieces of masking tape every couple of inches.
The caps can be "nailed" at their forward and aft ends using the stapler and short
nailing strips {and wax paper).
When all the rib caps are on the outboard panels, they only need the wingtips, and
general sanding and varnishing before they're ready for fabric covering.
When the outboard panels are complete and set aside, finish adding the fuselage side
ribs and diagonal ribs to the centersection. The contour of the fuselage side ribs is
developed similar to the method used on the nose ribs of the centersection. They are
identical to all other ribs from the chordline up. Below the chordline, they must
provide a smooth-flowing contour which encompasses the spar. Make the fuselage
side ribs first, and then hot-wire the diagonal ribs on the assembly just like you did
the intermediate nose ribs. Although the rib caps can be added to the ribs adjacent to
the joints, and to the diagonal ribs at this time, the caps for the ribs at the fuselage
sides cannot be added until after the centersection has been installed on the fuselage
and the center D-skins are installed.
At this point, you've gone as far as you can go with the wing construction until the
fuselage is built, so set the wings aside and move on to other components.
Congratulations, you're over halfway through with your Sky Pup.
EMPENNAGE
The empennage, which includes all the fixed and movable portions of the tail, is
constructed in a manner quite similar to the wing, and will require considerably less
discussion.
Major features of the taf1-feathers arc foam-web and wood-rap construction of the
spars and ribs. Diagonal ribs are used in thn control surfaces to add torsional rigidity.
Side view of finished empennage shows airfoil shape of leading edges of horizontal surfaces. These
leading edge shapes are sanded from foam stork which has already been glued to the spars. Note
positioning, of wood capstrips on diagonal ribs.
9
Begin the empennage construction by building the spars. Eich foam spar web should
be prepared dimensionally and include appropriate hardwood blocks inlaid at load
points like control horn attachments and fuselage attachments, before spar caps are
added. Plywood doublers and gussets go on after the spar caps, since they are glued
to the edges of the caps.
Once all the spars are complete, the ribs may be cut and assembly of the surfaces can
be accomplished. The attach holes between the rear spar of the vertical fin and the
rear spar of the horizontal stabiliser should be match-drilled prior to assembly of the
horizontal stabilizer.
Since the vertical fin is part of the fuselage assembly, it must be built on the fuselage.
Simply make the spars for the fin and set them aside until the fuselage work has
begun. Go ahead and build the entire horizontal stabilizer, rudder and elevators and
set them aside.
Entire ampennage with rudder and elevators taped inlo position prior to final cover process. Note
how vertical fin must be built into the fuselage assembly.
Horisontal stabiliser, elevators and rudder can all be built separately. All wood must be varnished
prior to final cover. Disregard color difference between spar web foam and rib foam.
The foam which will form the leading and hinge edges is added after the surfaces are
assembled. Glue it to the faces of the spars in a rough-cut form, and shape it after it's
on. For notes on the cloth hinges which will be used for the control surfaces, see the
section on FABRIC COVERING.
Empennage shows leading edge and hinge foam blocks prior to airfoil shaping.
60 grit sandpaper works well to “rough out” airfoil shape in foam, followed by 180 grit to smooth
it out prior to finish and final cover.
The assemblies should be varnished before adding the control horns and their
accompanying hardware. They can then be stored until you begin fabric covering the
entire aircraft.
LANDING GEAR
The landing gear of the Sky Pup is very simple to construct. Although its general
appearance is somewhat crude, it is actually quite efficient and very durable.
The gear leg itself is a spring made of wood. The maple beam should be cut from a
single piece of wood with special attention given to proper grain orientation. Fit
check the parts in the fuselage before any finish is applied. The fit should not be
sloppy, but must be free enough to allow flexing of the gear without forcing the
fuselage sides to flex also.
Sideload blocks and aluminum control stops should be made and match-fit with tne
gear in position in the fuselage holes.
The axles should be installed on the gear leg after it is installed in the fuselage for
good. Fitting the wheels to the axles is straightforward and can be accomplished to
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suit the builder's preference as long as adequate attention is given to lubrication. The
size of the axle tube should not be changed.
Simple landing gear arrangement where steel tube axle is attached with U-bolts to wood landing
gear spring.
Note elevator control horn just forward of the landing gear spring and elevator and rudder control
cables running through the fair-leads. Careful inspection of control systems is important before any
flight.
FUSELAGE CONSTRUCTION
The fuselage is the major component which will join all the parts of the airframe that
you have built thus far. Its construction will progress very rapidly up to the point
where it really "looks" done, and then the tempo will slow down as you add the many
small items it takes to complete the structure.
Building the fuselage should begin with cutting the foam side panels. Since the sides
are longer than a stock sheet of foam, a splice must be included somewhere along
each side. The location of the splice is relatively unimportant, but will probably be
handiest if made near the tail. This splice is simply a butt-joint, but be sure that the
mating surfaces fit together very well.
Cut the side panels as one continuous piece from front to rear, disregarding tne wing
support members, which will be inlaid later on. Tape or toothpick the sides together
and block sand the edges to insure that the two sides are exactly alike. This is of
utmost importance in obtaining a straight fuselage.
Note when cutting out the sides that the actual foam dimensions must be determined
by first noting the overall dimensions of the fuselage sides, and then subtracting the
longeron thickness from the overall dimensions. Also note that the upper long eron
ahead of the forward wing support member is thicker than the longerons everywhere
else, and that the side will have to be cut to allow the upper surfaces of both the front
and rear upper longerons to come out at the same level.
Prior to inlaying the wing support members into the fuselage sides, add the seat
gussets and landing gear load blocks to the wing support members. Be sure to cut
holes in the seat gussets to accept the seat gusset splice strips later on. It will be
handy to leave the wing support members a little long at both the upper and lower
ends. They can be trimmed to length after they are inlaid into the fuselage sides.
Cut out the foam to accept the wing support members, taking care to position the seat
support gussets relative to each other - the end result should be gussets positioned to
accept the seat crossmembers, such that the seat will be perpendicular to the support
members, The dimensions of the fuselage should not change with the addition of the
wing support members. Be sure that the dimension between the inside faces of the
wing support members matches the spar width precisely. This will insure a perfect fit
of the centersection to the fuselage when you're ready to add it.
11
After adding the wing support members, inlay the other doublers and members which
must go on before the longerons. These include the upper engine bearers, horizontal
tail attachment doublers, and joining strips at the aft end of the side panels.
When the sides are complete with wing support members and inlays, its time to add
the longerons to the upper and lower edges. The longerons extend the full length of
the side panels. The upper longerons are actually made in three pieces, the longest
extending from the aft end of the fuselage to the rear wing support member, and the
shortest running between the wing support members. The portion of the upper
longeron which is ahead of the forward wing support member is laminated on
assembly, and will not be added until after the fuselage sides have been joined.
Compare the two sides one more time to insure that they are exact mirror images of
each other. The sides should be joined at the seat crossmembers first. During this
operation, the sides should be held parallel to each other and perpendicular to the seat
crossmembers. Some scrap pieces of wood or foam, and strapping tape make the job
a simple one. Glue the crossmembers in place, taking care to get a good bond to the
seat support gussets, and leave the assembly until the joints are fully cured. No
attempt should be made to join the fuselage sides at any other point until these joints
are secure.
After the sides are joined at the crossmembers, the aft ends should be joined with the
rear spar of the vertical fin, leaving the nose end til last. The aft ends are joined by
attaching each side to the rear fin spar using gussets as shown in the drawings. Note
that the taper of the fuselage sides is blended into the rectangular fin spar by bowing
the gussets at assembly. Use C-clamps and clamping blocks to do this job.
Adding the tailskid attach block and the upper gusset will secure the assembly and
prevent the side gussets from being peeled from the fin spar. Pulling the nose
together slightly with strapping tape and placing spreader blocks at intervals in the
aft fuselage will help the fuselage sides to assume their proper shape. Careful
attention should be given to the fuselage cross dimension at the station where the
front spar of the horizontal stabilizer will attach. Proper alignment of the sides can be
achieved by using a chalkline or grocery string as a centerline during the mating
process.
Inside of fuselage carly in construction shows wooden landing gear spring in foreground and seat
crossmembers with gussets attaching them to the vertical wing support members. Note that holes in
gussets the accept splice strips are in place before gussets are glued to wing support members,
foam piece in background is used to temporarily position fuselage side the proper distance apart.
Photo shows vertical ??? spars which are installed during fuselage construction. Note position of
tail gussets and doublers. Triangular gussets between vertical tail spar and foam fuselage sides
must bend in order to glue ???? against each surface. Disregurd temporarytail skid shown here.
With the fuselage sides joined at the seat crossmereber and the aft end, block the
sides apart the proper distance at the seat back bulkhead station and prepare to join
them at the forward end. Several things must happen together at this point, so have
everything ready to go. That way you won't be interrupted once you've started. The
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forward portions of the upper longerons, which have been left off until now, are
added and laminated on assembly to accomodate bowing the sides together without
putting undue pre-stress on them. They roust be supported at their aft ends, so the
upper-fusleage side qussets must be prepared and installed simultaneously. As the
longerons are installed, pull the fuselage sides together at their forward ends (top and
bottom, using strapping tape) and insure that the sides are coming together evenly
and to the appropriate lateral dimension. Do not add the engine mount board until the
longerons ore fully cured.
Next, add the lower engine bearers and gussets inside and outside. Don't forget to
position the slide blocks (for the rudder bar) and include them when adding the
gussets. With the engine mount board in place, the basic fuselage structure is
complete, and you are ready to begin adding the remaining gussets and doublers at
their appropriate locations. Leave the wing support side gussets off until after the
centersection has been glued to the fuselage.
Fuselage sides shown with assembled wing clamped into place. Note shape of landing gear bearing
blocks inlaid into lower fuselage
sides just ahead of front wing support members. A hole will be drilled into each of these blocks to
accommodate elevator control crosstube. Engine mount support members shown here are slightly
different than indicated in the plans.
After all the seat area gussets are installed, clamp the centersection of the wing into
place on the wing support members (be sure to use clamp blocks and protect the
members from damage by the clamps). Using the height dimension between the
upper
surface of the upper longeron and the lower surface of the centersection spar as a
reference dimension, try the fuselage on for size and insure adequate headroom to the
lower surface of the wing. The centersection can be raised or lowered a maximum of
1 1/2 inches from the reference dimension to allow proper headroom. Don't cheat
yourself - allow some margin for a flying helmet.
With the centersection clamped in place, start fitting the seat back bulkhead into the
fuselage, remembering that the bulkhead must run from the aft face of the rear seat
crossmember to the trailing edge of the centersection as shown in the plans. The
proper fit of the ends of the bulkhead to these members is a cut-and-fit operation.
Be sure to notch the seat back bulkhead to allow the seat gusset splice strip adequate
clearance. Both of these way be added at this time.
Wing support members are fabricated over — lenght so wing can be adjusted to proper height as
shown here.
Clamps are used to hold members against centersection spar. The wing support members are then
marked and centersection is removed so members can be cut to appropriate length. This method
allows builder to "custom build" enough headroom into cockpit to accomodate his particular body
dimensions.
After the seat back bulkhead is in place, add the remaining bulkheads in the aft
fuselage. Some of these are dimensioned, and the rest are simply cut to allow the
13
fuselage sides to form the desired teardrop shape. Note that the fin spar attach
bulkhead receives a plywood face either before or after installation.
Fuselage with centersection permanently attached and unfinished vertical tail surfaces in place.
Note how trailing edge wing support bulkheads are built up to meet trailing edge of centersection.
Also note how aft wing ribs at joint stations (between centersection and outboard panels) have
been contoured to each other to assure a correct fit at the trailing edge.
The centersection can now be glued permanently to the wing support memabers.
Make this joint carefully, it is very important. When bonding the wing support
members to the gussets on the spar, be sure to also bond than to the adjacent nose
ribs of the centersection. After the centersection is in place, add the fiberglass antipeel strips that wrap around the top of the spar. Be sure that the weave axis is parallel
to the length of the fiberglass strip. The portion of the centersection between the
wing support members can now be skinned with plywood. Be sure to include the
intermediate nose rib on the centerline of the fuselage. Note the kerf cuts which are
required on the lower skins to allow the skin to transition around the bend in the
lower contour.
Frontal view shows how wing support members are glued to spar gusset and nose ribs. Note how
plywood D-skin is lapped on to
leading edge strip about 1/2" and then scarfed to complete the leading edge airfoil shape.
Wing support members are glued to gussets on forward and aft faces of centersection spar. This
must be done prior to adding leading edge D-skins to center part of centersection. Note how wing
member glues to centersection fuselage side rib as well as spar gusset. The fiberglass anti-peel
strip has not been added yet.
Now, add the front spar of the vertical fin, the upper and lower seat back supports,
and any remaining gussets or doublers. Add the upper and lower fuselage panels,
making sure that every detail inside is complete before closing the structure. As with
the wing, any wood which will be covered up must be varnished prior to this
operation.
The addition of these panels is the last step in the construction where the straightness
of the fuselage is in question. Use the chalkline to accurately mark the centerlines of
the panels and hold these centerlines evenly between the two sides. The plywood
floorboard should be installed before the lower forward panel is added. Also, be sure
to add the fiberglass anti-peel strips at the year attach hole station before installing
the foam panel. Trim out the hole in the floorboard and line the edge with a strip of
plywood as shown in the plans.
Photo shows important details inside the cockpit of the Sky Pup. Wooden landing gear spring,
elevator control cross tube, seat support gussets splice and seat gussete splice strip are plainly
visible. Note wing support members at top of photo.
Photo shows wing centersection-to-fuselage join location after all gussets and plywood D-skins are
in place. Note how centersection leading edge D-skin has had inspeetion holes pre-cut. Side cuts in
some D-skins have been made to enable skins to conform to shallow bend in under side of loading
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edge airfoil. These are the final D-skins to be added after the centersection is permanently attached
to the fuselage.
Install the ribs in the
vertical fin, and add the aft fuselage stringers. These are
built up of wood and foam prior to installation. Note the fiberglass strips which wrap
around the trailing edge of the centersection. These must be in place before the
stringers can be added.
Aft fuselage stringers are built of foam with wood capstrips. Note butt-joint in the fuselage side
foam and control cable fairlead
blocks, drilled to accept fairleads betore installation.
Check the forward fuselage for all the required gussets and crossmembers, and add
the forward deck panel and throttle control mount doublers (see MISCELLANEOUS
Section)
Mock up the control cable routing using string and locate the fairlead blocks on the
fuselage sides.
Inside of Sky Pup cockpit showing step-through hole in plywood and foam floor-board. Note fit of
plywood seat and floor pieces and control stick. Hole in floor of cockpit will be cowered by a
removable fabric flap which will allow the pilot to step through
the cockpit floor hole and stand on the ground when
entering or exiting the cockpit.
Foam and wood fair lead blocks are glued to fuselage sides as shown. Foam fairings will be added
later to the fore and aft sides of these blocks.
Note wood longeron strips on top and bottom of foam fuselage side.
Be sure to complete all fitting and sanding operations before you begin varnishing
the fuselage. A minimum of three coats on the exposed wood and foam is needed,
with the exception of the area ahead of the forward wing support members where
additional coats will be needed on the foam to prevent inadvertant damage from a
fuel spill. The floorboard should also receive additional coats of varnish since it will
be subject to considerable scuffing during entry and egress from the cockpit.
CONTROL SYSTEM
The flight controls on Sky Pup are among the simplest ever used.
Rudder and elevator control are accomplished through straight cable runs with a
minimal use of fairleads and no pulleys whatsoever.
The rudder system utilizes a rudder bar with cables running directly from the ends of
the bar to the rudder control horns. The cables pass through two fairleads on each
side of the fuselage which serve the dual purpose of directing the cable around the
outside of the fuselage and providing support to prevent whipping of the cables.
Construction of the rudder bar is simple, and requires no discussion.
Foam pieces sanded to a "teardrop" shape are attached to the front and rear faces of cable fairlead
blocks—after the fuselage in covered — to afford streamlining. Note that at any point where a part
15
of the aircraft emerges through the fabric (such is fairlead blocks) extra fabric reinforcement is
needed to provide strength and resistance to tearing, as shown here.
Photo shows elevator control horn-to-cable attachments. Note aluminum control horn prop plate
and landing gear side-load block bolted to the landing gear on the front and aft sides of the
wood gear spring, next to the fuselage. Head of seat-belt securing bolt is seen on the fuselage side
aft of the gear spring.
ENGINE AND FUEL TANK INSTALLATION
Although the prototype Sky Pup has been flown with a Cuyuna 215 powerplant at the
time of this writing, there are an abundance of engines which will provide adequate
power for good performance. Installation of these engines will be quite similar to the
Cuyuna installation, but don't hesitate to call Sport Flight Engineering
if you have questions about the suitability of a particular engine.
The engine mount used on the Pup is unique and very simple. The engine is
hardmounted to a "breadboard" which is in turn shockmounted to the airframe using
rubber test tube stoppers for vibration isolation. These stoppers must be bored to
accept the spacer tubes which soperate the large diameter "wood washers" in the
mount hardware A common twist drill will not adequately bore the holes since the
rubber will simply stretch and "heal" back over the hole after the drill is removed. A
satisfactory way to bore the holes is to sharpen the end of a tube of the same diameter
and twist it through the rubber, lubricating it with soap as you cut.
After the engine is installed on the airframe, lay out the throttle, ignition wires, and
fuel pump location (if a fuel pump is required) so that they allow adequate room for
the engine to move during normal vibration. Tie these items to the airframe with
metal clips and small bolts or machine screws, taking care to always use large
washers to prevent crushing of the wood when the bolt or screw is tightened.
There is no particular fuel can which is best suited for use as a gas tank.
The prototype uses a standard two-gallon can available at any hardware store.
Choose a can which will fit behind the engine with a minimum of exposed frontal
area. The fuel tank can be tied to the airplane using aluminum straps or elastic tiedown straps (such as are used on motorcycle carriers). Add backing blocks as needed
on the underside of the forward deck panel to support the tank and accomodate tiedown.
When selecting a fuel tank, keep in mind the desired contour of any cowling you may
wish to add.
Although this description may seem somewhat open-ended, it is intentionally left
loosely defined so you can tailor the installation to best suit your overall purposes.
Be sure that the fuel pickup line will feed the engine regardless of aircraft attitude
and that the tank is adequately vented.
Above all else, be sure that the combination of engine weight and fuel weight will
leave the aircraft CG within the allowable limits.
Cuyuna 215RR engine installation with CPS 2.25:1 belt drive reduction affords ample power for
the Sky Pup at all elevations. Note common "hardware store" two gallon gas can with properly
vented cap installed between engine and cockpit,boot operated rudder control bar is seen emerging
16
through fuselage side beneath engine. Note "bread-board" engine mount and testtube stopper
shock mounts.
The elevator system consists of a conventionally oriented stick attached to a torque
tube which protrudes out either side of the fuselage and has elevator horns attached
to each end which operate cables running to the control horns on the elevator.
It should be noted that the elevator system is dual in nature, each elevator being
operated by its own set of cables. As is the case with the rudder cables, the elevator
cables pass through two fairleads on each side of the fuselage and an additional one
on the upper surface of the front spar of the horizontal stabilizer.
Wood tairlead blocks with tubular phenolic inserts are glued to the front horizontal stabiliser spar
to guide elevator control cables over the horizontal stabilizer. 1/16" cable is used to make all
control cables.
Each cable should bo fabricated to include one turnbuckle which will allow almost
infinite adjustment of the system after installation. Anti-chafe strips may be
necessary along the fuselage sides anywhere the cable cones close to contacting the
fabric. These may be made by gluing an extra layer of fabric or a thin leather "patch"
at the appropriate place after the fuselage has been covered.
Dimensions of the control stick can be altered slightly to accomodate your own
physical proportions.
FABRIC COVERING
The method used to cover the Sky Pup is a unique one which was developed during
construction of the Blue Light Special. Although not difficult, the covering process
does require some care to ensure a functional, as well as mce looking, finish to your
bird commonly known as "sheath lining," and is available at most fabric stores. This
material is generally used as lining for suit jackets and formal dresses and comes in a
standard 45" width. It is polyester (Dacron) and is heat shrinkage. Common brand
names are Gloriosa and Butterfly.
Since the fabric is obtained in a multitude of colors, no painting will be necessary.
The fabric is attached to the airframe with latex contact cement. Regular contact
cement contains solvents which will dissolve foam and thus can not be used.
Although the instructions on the can specify applying the cement to both surfaces
and then allowing it to turn clear before joining, the method used for fabric
attachment is somewhat.
The cement should be applied to the airframe at all places where fabric adhesion is
required. These include leading and trailing edges, rib caps, stringers, and the etire
perimeter of any panel. This first coat should be allowed to dry completely before
proceeding. When the fabric is cut to size and ready for attachment another liberal
coat of the cement should be applied over the first, and then the fabric should be
stretched out over the frame and laid onto the cement. The cement will soak through
the fabric and appear on the outer surface. Some pressing of these
17
areas with the fingers will be necessary to ensure even contact between the structure
and the fabric.
When laying the fabric onto the frame, care should be taken to position it
carefully before allowing it to touch the cement areas. This is important for two
reasons. First, the fabric will "sponge" away cement that is needed for attachment,
and, secondly, cement in areas other than where intended will appear unsightly on
the been covered, the edges should be carefully trimmed with pinking shears. All free
edges of fabric must be well attached to prevent subsequent separation.
Each component should be covered one side at a time, overlapping successive sides
as you go. Do not shrink the fabric in one area until you are reaoy to shrink the fabric
on the entire exponent. Shrinking can be accomplished with a hand iron or a heat
gun. Experiment with heat settings until you find one that works well.
CAUTION: It is possible to melt the fabric - don't hold the iron in one place - keep it
moving!
The wing is covered in the following sequence:
1. Cover bottom from D-cell aft to trailing edge, lapping fabric around the trailing
edge onto the upper surface.
2. Cover top frow D-cell aft to trailing edge, lapping fabric around the trailing edge
to bottom side.
3 Cover D-cell from top to botton, lapping onto first two pieces of fabric by at least 2
1/2”
The fuselage is covered in the foiloning order:
1. Inside of cockpit, including headrest ami diagonal panels.
2. Dottom, including bottom of centersection.
3.
Sides.
4.
Top of contersection.
5.
Top of turtleback.
When applying fabric to forward fuselage and cockpit, apply contact cement over
entire
surface to aid in fuel-proofing.
Right outboard wing, panel shown being covered with Dacron fabric. After fabric is initially glued
to the airframe with latex contact cement, three coats of polyurethane varnish are added for
weatherproofing. No pigments are required, as the color of the fabric will be the color of the
airplane. Note wingtip construction detail.
Tiedown strap hangs from underside of outboard wing panel enough to gut a chain or large rope
through without chaffing fabric. Note
pinked fabric reinforcement surrounding tiedown strap area. Reinforcement is necessary wherever
a part must emerge through fabric cover.
Finish is accomplished with three coats of polyurethane varnish — brushed or
sprayed. Brushing will save time and money, but will probably not produce as nice a
finish as spraying. Regardless of which method is used, care must be token to
provide adequate wetting of the fabric on the initial coat without dripping excess
18
varnish through the weave. Like any finish, varnish will run if applied too heavily.
The entire airframe should be treated like a cocoon with respect to finish application.
A couple of extra coats of varnish in the forward fuselage and inside the cockpit will
add immeasurably to durability. Remember that gasoline dissolves foam on contact
and adequate attention must be given to fuel-proofing areas likely to be contacted by
gas. When in doubt, put on an extra coat.
The cloth hinges of the control surfaces can be made one of two ways. Either way,
the hinges are added after the control surface and stabilizers have been fabric
covered. The first hinge type is in true model airplane fashion. Fabric strips 3" wide
are placed alternately as shown. Adjacent pieces should be very close together and all
edges should be pinked. Care must be taken to keep from gluing the strips too far
around the hinge line. Poor hinge operation could result.
The second hinge method requires sewing, but yields a "no leaks" gap seal. Two
pieces of fabric are joined by sewn seams, backed with reinforcing tape, as shown.
The seams should be straight-stitched with heavy polyester thread. After the fabric
strips are joined they can be cemented in place —first to the control surface and then
to the stabilizer.
MISCELLANEOUS DETAILS
There's an old saying in home building circles that, "Once you get to the point where
your airplane looks like an airplane, you're halfway done." In aircraft with complex
systems and lots of addons, this is almost literally true. Since the Sky Pup has almost
no systems, the saying doesn't fully apply. Yet cleaning up those loose ends will take
time.
.
Several of the items that fall into the "miscellaneous" category are optional.
The cowling and streamining of parts such as the landing gear and
fuselage/empennage intersection are definitely not necessary for flight. Close
attention to these items will, however, yield noticeable improvements in performance
and appearance.
Since fairings are not structural, some latitude in their fabrication is allowed.
In general, what looks smooth to the eye will work well to streamline the aircraft.
Many people may wish to include some type of windshield on their Pup. This will
present no problem as long as the windshield transitions into the surrounding
airframe smoothly. Pay particular attention to the upper edge of the windshield which
may lie along the leading skin of the centcrsection. A drastic bump at this
location can disturb the airflow considerably, and in exaggerated cases can cause
control problems due to "dirty" or turbulent airflow over the empennage.
Locate the throttle control wherever it feels good. Mounting of the control (a levertype lawnmower control was used on the prototype) can be accomplished by gluing
plywood doublers on the inner and outer surfaces of the fuselage side panel, and then
bolting the throttle bracket to these doubles through the fuselage sides.
The ignition on/off switch can be mounted in any convenient location and should
19
feature up-for-on and down-for-off actuation. This allows the pilot to kill the engine
easily by pushing down on the toggle switch.
Install a substantial scatbelt (good units are available from aircraft supply houses or
auto parts stores) utilizing the attach holes in the splice strips beside the seat. Scat
belt attach bolts should run clear through the fuselage sides. Use wood washers (AN
970's) to prevent crushing.
The metal plate on the tail skid is a ballasting device for the aircraft.
It should be the last thing installed after the remainder of the aircraft has been
checked for proper balance. Thicker metal can be used to correct a nose-heavy
condition. Make a spare as long as you're at it so that it can be used as a replacement
if the first one wears down.
Tailskid block is made of wood I then reinforced with a petal plate held in place by four wrint. Hole
in skid is for securing tail of Sky Pup.
For general information on fabric work, a good manual such as the EAA's Dope and
Fabric will be very useful. Anyone with previous experience in covering models or
real aircraft will find fabric work to be quite simple.
NOTE: After fabric and finish application are completed, vent holes should be added
at the lowest point(s) in each bay to allow the covered portions of the airframe to
"breathe". These holes will prevent moisture build-up and condensation from
becoming
a problem. The vent holes may be easily made by melting through the fabric with the
heated end of a 3/16" diameter soldering tip. This method will leave a hole the same
diameter as the tip and the heat will melt the thread ends and prevent any unraveling.
The fairlead blocks on the fuselage sides can be "teardropped" for drag reduction by
adding foam fairings in front and behind. This is done after fabric covering .
Wing joint gap fairings can be made from thin aluminum or plastic sheet. These
should be made so that they may be removed easily to facilitate rapid setup and
disassembly. Upholstery snaps or sheet metal screws will work fine here, but make
sure that the fairings are held on securely — the airplane won't fly without them.
Attach
the fairing to itself, not to wing members.
Although these items will be taken care of at a time when you are very near being
ready for first flight, don't get over-anxious and rush them. Careful patience here will
pay off in greatly enhanced "finished" appearance.
BEFORE YOU FLY
Once you've completed your Sky Pup you will be understandably anxious to start
flying. Proceed through this phase of the project with the greatest of caution You’ve
spent a lot of time and effort getting this far. It's no time to do something in haste
which you might reqret later.
20
The weight and balance of your Pup should be checked and adjusted, if necessary,
prior to flight. The easiest method of checking is as follows:
1. Block the aircraft up in a level attitude (upper longeron level), with a standard
weight pilot onboard.
2. Record the weight at each main gear and at the tailskid. Obviously, the sum of
these three readings is the total weight.
3. Multiply the load on the tail skid by the distance from the tail skid to the main
gear contact point and record the product.
4. Divide the number obtained in Step 3 by the total weight obtained in Step 2. The
result will be the longitudinal distance from the ground contact point Of the main
gear to the aircraft center of gravity.
5. If the number of inches determined in Step 4 is less than 2, the aircraft is noseheavy and a heavy tail skid is needed to correct the condition.
If the number is greater than 12, the aircraft is tail-heavy and the condition must
be corrected by lightening the tail skid or adding weight to the nose. Note that
tail-heaviness is much harder to cure than nose-heaviness and should not occur
unless an unusually light engine has been used.
The allowable CG range for the Sky Pup is from 13%. chord to 33% chord.
When assembling the bird for the last time prior to your first flight, proceed very
slowly and double-check every detail. All turnbuckles in the control system should
be safety-wired and have no threads showing out of the barrels. All castle nuts should
be cotter-pinned, and all nuts should have at least three threads protruding through
the nut. Wing attach bolts should be tight, but not over-torqued, and there must be no
slop between the bolts and the fittings. Fairings should be securely in place.
The engine should have at least the manufacturer's recommended break-in time
before flight. Make sure you have clean, fresh gasoline with the proper fuel-to-oil
ratio. Top the tank off so you won't find yourself airborne and out of gas.
Preflight the entire aircraft again immediately before you "strap it on” — it could
save your life.
If you have limited experience in flying light aircraft, you will find Jack lambie's
book, ULTRALIGHT AIRMANSHIP, to be very helpful.
FLYING YOUR SKY PUP
Test flying your Sky Pup will be a very rewarding experience —provided you adhere
strictly to the cardinal rules governing the flight of new machines.
First, do not, DO NOT, attempt to fly the Pup if you have no previous flight
experience. Even though the Sky Pup is probably the easiest-flying machine you will
ever encounter it is still different than operating a ground vehicle, and a minimum
of several hours flight time in other aircraft is highly recommended. Don't be too
proud to let someone more experienced make the test flight for you. They'll be able
to feel the airplane out and explain the sensations to you before you try it.
21
Test flights should be conducted only in the calmest conditions with a good firm
surface to operate from, and plenty of room for climbout and approach. Save the
short field and cross-wind training for later. All you want to accomplish at this point
is basic flight – nothing fancy.
Since the Sky Pup is fairly tail-light on the grouna, a few precautions are in order.
Never stand on the floor board when climbing in or out of the cockpit The floor
board is not designed to handle your weight and the aircraft will tip on its nose.
Always stand on the ground through the hole in the floor when entering or exiting.
The second precaution is that it is possible to raise the tail so high that the propeller
with contact the ground. This will not happen inadvertently, but don't let the attitude
go beyond level when on the ground.
Start out by taxiing the bird and practicing turns on the ground. Directional control is
very simple and even without brakes or steerable tailwheel, you'll get the feel of it in
jast a few minutes. The tail will come up easily with the addition of
power and forward stick. This can be used to aid in turning. Taxi at various speeds
until you can track straight down an imaginary line without wobbling from side to
side. For tight turning, your hand can be used to grab a tire and produce differen-tial
braking effect. Keep the prop out of the dirt.
Once you are extremely familiar with ground handling characteristics (you make the
correct control inputs instinctively rather than having to think about them) you are
ready to try some low-level hops. Practice making runs at increasing power
settings until you find the setting where the airplane will just barely fly. Make several
runs at this power setting, lifting off only a foot or two, and then reducing power and
landing. During the rollout, the stick should be held full aft to prevent any hobbing
tendency. At this point, you’ll find out jast how well-mannered the Scy Pup realy is.
Only after you've mastered flying at low level should you attempt a full-circuit flight.
On your first takeoff, apply full power and let the aircraft fly itself off the ground.
Don’t climb steeply and concentrate on using only the amount of control input
needed to accomplish the desired change. Climb straight out to several hundred feet
before making any turns. Remember that the rudder controls both yaw and roll.
Very gentle pressure on the rudder bar will produce a change of course without much
tendency to roll. On the other hand, rolling is accomplished by a quicker input of
rudder so that the aircraft rolls without changing heading significantly. The first few
turns should be very gentle and will probably feel a little awkward to a conventional
three-axis control pilot. This feeling will go away in a few minutes, so don’t let it
bother you. Fly at altitude until you feel that you are ready to make your first landing.
The Pup’s glide angle is similar to many conventional airplanes and much better than
most ultralights. Judge your approach accordingly and don't try to "put it on the
numbers” the first time. You won't roll very far once you're donwn so don't be
alarmed unless you float all the way to the other end. Set up a reasonable glide and
use the rudder to make heading changes which will keep the nose into the wind.
Continue the glide until you are about ten feet above the ground. Then begin a gentle
flare to arrest your descent and “feel” your way down to the ground. The Pup can be
wneel-landed or three-pointed with equal ease.
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Once you've rolled to a stop after your first flight, climb out and savor the moment.
You deserve it:
Conduct all initial flying under calm condition without gusts or other detracing
factors. You’ll soon be able to make the Pup go anywhere you want and operations in
slightly windier conditions will become second nature. Don’t push the weather.
Ultralights are simply not meant for those blustery days.
When you've become at home in your Pup you’ll develop a feel for the limitations of
the machine and yourself. Always abide by those limitations and don’t feel a need to
prove anything to anyone. Newer attempt aerobatics of anykind in the Sky Pup.
Enjoy your Pup and take good care of it. It will give you many years of fun flying.
MAINTENANCE AND STORAGE
Once you have built your Sky Pup you will be imminently qualified to understand its
care and feeding. However, a few words of caution could save you considerable
heartache.
Two-stroke engines being what they are. it is inevitable that your Pup will become
coated with a thin film of oil after prolonged operation. This will be primarily in the
cockpit area, on the leading edge of the lower portion of the centersection, and on the
horizontal tail. Besides being messy, this film will attract
dust and could eventually attack the finish if left on. The oil should be removed
periodically using soap and water. In fact, you will find that a periodic washing of
the entire airplane will enhance performance and appearance.
Since the wheels do not feature any type of elaborate bearings, they must be
regreased frequently to avoid galling of the axles. This is no problem. A good grade
of bearing grease will do the job just fine.
Avoid spilling fuel on the structure when refueling because of the danger of damage
to the foam. Any spills should be wiped up immediately and plenty of varnish in the
area where a spill could occur will help prevent problems.
The cloth hinges on the tail feathers will provide long life in all but the most severe
conditions. Inspect these often and don't hesitate to replace than if the fabric appears
to be weakening in any way. Good preflight technique for these hinges is to apply a
substantial load to the hinge as though you were trying to tear
the surface off the aircraft. If you can't, it's safe to fly.
Always check the tension of the belt on your reduction drive during preflight and
follow manufacturer's recommendations on maintaining proper tension.
The Sky Pup, like any other ultralight, will not stand outside storage for extended
periods. Prolonged exposure to sunlight will degrade both fabric and foam.
But more importantly, wind, rain, and snow can be very damaging. Even though the
Pup is provided with tie-down straps, it should not be tied permanently outside. A
severe wind or snow storm could easily destroy all of your efforts. If local
environment dictates, disassemble and store the aircraft during the off season.
Prefligliting religiously will ensure longevity of pilot and machine.
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The Sky Pup can be easily moved by one person even in rough terrain. Note the ever-present rag in
this operator's back pocket — a prerequisite for two-stroke engine operation to keep oil and gas off
of the airplane.
MATERIALS AND HARDWARE
Construction materials and hardware for the Sky Pup are easily obtained either
locally, or from a reputable aircraft supply house. Below is a list of materials needed,
which is exhaustive in most regards, and purposely open-ended in others.
Some of the locally available materials, especially wood and foam which may be
purchased at the lumberyard, are left undefined so that you may use your discretion
in selecting the best sizes to suit your purposes. Since the plans have allowed a
choice of wood types for many parts (e.g. "softwood" and "hardwood" callouts),
it would be confusing to try and tell you cxactly what size and type of board to look
for when buying wood. Instead, select wood on the basis of quality in a size which
will be cut into required stock with as little waste as possible. (See the discussion on
wood selection in GENERAL CONSTRUCTION NOTES). You will find that
many of the small pieces in the airframe can be made from wood left over from
cutting the larger members.
Items which are not available locally are indicated by " * ". Effective June 1, 1983,
Wicks Aircraft Supply is the exclusive distributor for Sky Pup materials kits. Always
specify that you are building a Sky Pup when ordering from them. Wicks can be
contacted at the following:
PLYWOOD: *
2' X 4' sheet .8mm (1/32"), 90*. 3-ply, birch or mahogany
2' X 4' “ 1.5m (1/16"), 90*, 3-ply, " "
2' X 4' “ 3mm (1/8"), 90*, 3-ply, " "
11 ea
3 ea
2 ea
(NOTE: When ordering plywood, specify grain direction parallel to length of each sheet.)
FOAM:
4' X 8' sheet 3/4" Dow Dlue Styrofoam (2pt/cu. ft.)
32" X 8' sheet 2 .....................
32" X 8' sheet 1 1/2 " Dow Blue Styrofoam
Foam for wing spar
6 ea
1 ea
2 ea
see text
DOLTS, NUTS, AND WASHERS: *
Bolts
AN3-5
AN3-6
AN3-11
AN3-11A
AN3-13
AN3-14A
4 ea
2 ea
6 ea
12 ea
2 ea
2 ea
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AN3-15A
AN3-17A
AN3-22A
AN3-24A
AN3-37A
AN4-24A
AN4-43
AM4-G0A
AM4-52A
AN5-34
AM 6-53
3 ea
4 ea
2 ea
4 ea
2 ea
2 ea
1 ea
18 ea
16 ea
4 ea
4 ea
Nuts
AM365-1032A
AN310-3
AN365-42aA
AJW10-4
AN310-5
AN310-6
30 ea
14 ea
36 ea
1 ea
4 ea
4 ea
Washers
AN960-10
AN970-3
AN960-416
AN960-416L
AN970-4
AN960-516
M970-5
AN960-616L
80 ea
25 ea
15 ea
100 ea
10 ea
10 ea
15 ea
15 ea
CONTROL SYSTEM HARDWARE AND MATERIALS: *
1/16" 7X7 galvanized or stainless steel control cable
AN130-BS turnbuckle assy
AN 135-BS " "
AN100-3 thimble
AN111-3 bushing
18-1-C 1/16" Nico-press sleeve
3/8" O.D. X 1/4" 1.D. phenolic tube
100 ft
4 ea
2 ea
6 ea
6 ea
12 ea
15 in
METAL STOCK: *
1 1/4" O.D. X .060 Wall (min) 4130 steel tube
7/16" 0.D. X .058 Wall 4130 steel tube
1" O.D. X .035 Wall 2024-T3 aluminum tube
.125" Thick 4130 steel sheet - 9" X 18"
.040" Thick 2024-T3 aluminum sheet
26 in
12 in
39 in
1 ea
2 sq ft
ADHESIVES:
25
Quart kit, Bondmaster M-666 epoxy (or equivalent)
Gallon, Titebond Wood Glue (or equivalent)
1 lb bag, phenolic or glass micro-balloons
2 ea *
1 ea
1 ea *
PURCHASED PARTS:
20" Moto-cross bicycle wheels, front (Troxel Trackmaster or equiv.)
2 ea
20 X 2.125 tires and tubes
Seat belt assy
ON/OFF toggle switch
Throttle control assy
2 ea
1 ea
1 ea
1 ea
MISCELLANEOUS:
No. 6 rubber test tube stoppers
Concave-type inspection covers (for 3 1/2" hole)
1 1/2" I.D., 1/4-20 thread, U-bolts
Fuel line
2" wide webbing strap
Fiberglass cloth
8 ea
3 ea
4 ea
as req’d
6 ft
1 sq ft
FABRIC COVERING AND FINISHING:
45" width sheath lining
High gloss polyurethane varnish
Latex contact cement (Elmer's or equivalent)
49 yd
3 gal
1 gal
OPTIONAL ITEMS:
Tubing for wing attach bearing blocks
Cowling and fairing material
Instrumentation
Seat padding
Wheel covers
Windshield material
Ramaset catalyst 45X21, and Ramaset finish 45X5
see text
*
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