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 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 Dskins. 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
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.
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 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
center-most 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 atthis 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 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.
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
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.
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
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
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 anti-
peel 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 antipeel 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 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.