Transcript Leading Edge

Sopwith Pup & Albatros
DIII "Foamies"
Ron Wanttaja
August 2011
Features
• Two airplanes, nearly identical in construction
• Weight, with all electronics
– 175 grams ready to fly with 500 ma battery – 6.2 oz
– 145 grams (not including battery)
• Wing area: 1450 sq-cm (148 sq inches)
• Recommended motor/prop
– Park 250 – 8 x 6 slow flyer prop
• This is almost too much motor –produces ~230 oz of thrust with a fresh
battery (greater than 1:1 thrust to weight ratio)
– Can fly with small ~180-class motor…but the extra thrust is nice, when
you need it.
• Construction material – Everything!
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Fuselage 6 mm Depron foam
Wings 6 mm Depron foam (3 mm is OK)
Fuselage stiffener/motor mount – ¼" x 5/8" bass or balsa stick
Wing struts: 1/16" plywood
Assembly: foam-safe CA, #4 nylon bolts/nuts
Design Philosophy
•
The design is a true "composite" using a variety of materials
– Depron foam (3 mm & 6 mm) for large surfaces like wings and fuselages
– Plywood for stiffening
– Bass or Balsa "motor stick" to provide a basic structure
•
Biplane design gives good wing stiffness using even 3 mm Depron
– Thin leading-edge reinforcement helps, too
•
Commercial kits/ready-to-fly designs put you at the mercy of the
manufacturer for spare parts
– These planes let you make all your parts
•
The airplanes are designed to be easily repaired
– Wings are actually bolted to the fuselage using #4 sized nylon nuts/bolts
• The ~5 nut/bolt sets used on the design weigh a total of only 2 grams
– Break a fuselage? Glue it back together, or cut out a new one, bolt the motor
stick and wings to it
– Break a wing? Glue it back together, or unbolt the assembly, cut off the foam
from the plywood struts, and glue on another wing
– Break a motor stick? Glue it back together!
• Never have broken any other wood part on a biplane!
•
Design supports experimentation, too
– Can make other types of aircraft with just minor changes to wing or fuselage
shape
The Real Machines
• The Sopwith Pup was a predecessor to
the famous Sopwith Camel
• Its actual name was the Sopwith
"Scout," but was called the Pup due to
its similarity to larger Sopwith 2-seater
• It entered combat in late 1916
• The Albatros DIII entered combat in
early 1917
• It had a plywood semi-monocoque
fuselage, similar to a modern aircraft
only in wood
• Most of the WWI German pilots used
Albatros
• von Richthofen had more "kills" flying
an Albatros than his Fokker Triplane
A Construction Note or Two
• The "glue" is "Foam Safe" Superglue (Cyanoacrylic, or CA)
– Non-foam-safe kind can be used to bond the wood parts
– Get the small spray bottles of "catalyst" or "Kicker" to get the CA to cure
fast
• Cut the Depron foam with an Exacto knife
– The 3mm foam can be easily cut with a good set of scissors
– Buff the rough edges with ~80 grit sandpaper
– Don't worry about cutting smooth curves…cut it out, then smooth it with
the sandpaper
• When cutting foam, consider making spare parts
– It's a lot easier when you're set up for it
– The wings are quick and easy to cut out…make some spares
• These instructions assume using an interconnected rudder and
aileron system
– Can go to full four channel (throttle, aileron, elevator, rudder)
– Can go rudder-only if desired, but need to build in a bit more dihedral
angle (see notes on strut pages
Front Half of Pup Fuselage Pattern
Print out the two halves of the fuselage, tape together at the line
This notch sets the angle of
incidence for the wing system
Best Fuselage thickness seems to be 6 mm. 3 mm
works, but is a bit more brittle
Rear Half of Pup Fuselage Pattern
Approximate Horizontal
Stabilizer Slot
Rudder Line
Include the entire shape of the tail (rudder included) when
cutting out the fuselage. Then cut off the end for the
rudder as shown. If using 6 mm foam, use the cut-off
rudder as a pattern for a 3 mm rudder.
Front Half of Albatros Fuselage
Print out the two halves of the fuselage, tape together at the line
Approximate Horizontal
Stabilizer Slot
Pup Wings
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Basic wing shape is a rectangle – 4.25" high, 26 inches wide
Use pattern to shape the wingtip
Need two wings!
6 mm depron, can go 3 mm for
less weight but more fragile
–
Surprisingly little weight advantage
Leading Edge
Wing Construction – Make Two
Cut Rectangle 26" long and 4.25" Wide
from 3mm or 6 mm foam
Lay template at each end and cut wingtip
shape
Wingtip Shape
Wings are 26" span
Albatros Wings
• Basically identical to the Pup, just
with a different wingtip shape and
the short length of the wing
forward
• I actually made the first Albatros'
wings from a set of spare Pup
wings
Leading Edge
– Just re-shaped the tip
Wing Construction – Make Two
Cut Rectangle 26" long and 4.25" Wide
from 3mm or 6 mm foam
Lay template at each end and cut wingtip
shape
Albatros Wingtip
Shape
Wings are 26" span
Pup Horizontal Stabilizer/Elevator
• 3 mm depron
• Notch at leading edge is the width of the fuselage foam
1”
Construction
Cut out from 3mm
foam (scissors
works fine)
Cut 1" wide strip at
end (elevator)
Join with hinge material
(Packing tape or 1/8"
strips of hinge fabric)
Bond in wire "Bridge"
using foam-safe CA on
sides ONLY
Cut out elevator
"notch" to let
rudder swing
No Glue Here!
~.032" piano wire
Glue here
Albatros Tail
• Elevator shown in actually a bit too big!
– A bit sensitive in flight
– Cut a bit off the trailing edge of the elevator if your controller
won’t reduce travel
More on Hinges
Strips of clear plastic
packing tape
Strips of ½A control hinge
fabric - External
• Cut to 1/8" wide
• Lay on surface
• CA in place
Strips of ½A control
hinge fabric - Internal
• Cut to 1/8" wide
• Use exacto to cut slot
• CA in place
Hybrid
• Glue hinge material to control
surface only
• Use packing tape to attach surfaces
• Easily removed/repaired
Wing System
Center Struts and Wing Struts
are the same height and slant –
easy to keep straight during
assembly
Leading Edge/Landing Gear
Brace installs in slot in
Center Strut
All are one-piece
1/16" plywood
Odd bumps
and bulges at
the ends of
the struts are
just for
drawing
convenience.
Formerly had a triangular
brace in the middle of the
lower wing - Deleted
Cut slot to the thickness of
the wood used
Leading Edge & Landing Gear
Brace
Holes for Gear Bolts
Center Strut
Pup Wing Struts
Top and bottoms are
basically identical, so the
struts can go either way
Glue to plywood with rubber cement, or
print on label stock
Alternate Pup Wing Struts
(Easier to cut out)
Structurally, these are
identical, but they are
different appearance if
flipped.
Glue to plywood with rubber cement, or
print on label stock
Deeper brace for more dihedral
(rudder-only systems)
Leading Edge & Landing Gear
Brace
"Firewall"
Same 1/16" plywood, cut
to match motor mount.
Can be trimmed after
assembly
All are one-piece
1/16" plywood
Albatros Wing Struts
Leading Edge & Landing Gear
Brace
Formerly had a triangular
brace in the middle of the
lower wing - Deleted
Albatros has less wing spacing than
Mid
Pup…these
Brace struts are shorter
Simple Albatros Wing Struts
Deeper brace for more dihedral
(rudder-only systems-either plane)
Leading Edge & Landing Gear
Brace
Mid
Brace
Strut Assembly
Center Strut
Off-Center, since it bolts to
the SIDE of the fuselage!
Hold gear in place with
#4 nylon bolt with
plywood washer
Leading Edge & Landing
Gear Brace
Do not glue Mid Brace until
final assembly of wing
Leading Edge & Landing
Gear Brace
Albatros
Landing Gear (0.049"
piano wire)
Why, yes, it IS
asymmetrical!
Pup
#4 nylon bolts attach center strut
and motor stick to opposite sides
of foam fuselage
Leading Edge of upper wing
is even with the upper part of
the center strut
Leading Edge of lower wing butts up
against (and is glued to) the forward
brace
Asymmetrical nature
accommodates for the offset of the
foam fuselage from the strut
Bottom Posts go through
slits made in Wing. Trim
off excess with side
cutters.
Wing Assembly
Score shallow cut in top of lower
wing, down the centerline. This is
to let the wing bend in Step 4
1
Position Center Strut assembly just to the right of the
centerline, with the landing gear brace flush against the
leading edge of the wing. Press to leave dents from the
bottom posts. Leave off the mid brace from the center
strut until the slits are finished
2
Albatros is identical, except the wing is the other
way around
4
Shove Center Strut through slits (it'll pop
through). Forward edge of wing should be flush
against back of landing gear brace.
Add the Mid Brace to the center strut, press
against the wing to mark its location, then cut
slits.
Slots MUST be parallel to
the centerline!
3
Remove center strut, use exacto knife to cut slits
where the bottom posts made dents.
4
5
Apply foam-safe CA to the center strut ONLY (not the
landing gear or mid braces). Keep strut vertical to wing until
CA sets
6 mm wing shown. For
3mm wing, the bottom of
the wing doesn’t go to
the bottom of the brace
Bend up each side of wing, use CA to bond it parallel to the bottom of the
Landing Gear Brace. This sets the dihedral. Bond the top and bottom of
the wing leading edge to the back of the brace
Bond the mid brace also to the wing, trim off excess with side cutters
More on Attaching the Center Strut
• Wing alignment isn’t hyper-critical, but attaching the struts to the
wings needs a bit of care. The Center Strut is the key component
The slots for center strut MUST be parallel to the centerline!
Draw a guideline perpendicular to the wing, press the forward tab
into the wing, then carefully set the tab location for the rear tab at
the same offset to the guide line
If the strut is at an angle, the overall wing alignment to the fuselage will be at an angle, too. In flight, the
airplane will tend to roll away from the wing that’s “forward.” If necessary, add a shim to where the wing
strut bolts to the fuselage to take out the angle
Shim added between
strut and fuselage to set
wing at right angle to
fuselage
Center Strut installed at an
angle
Wing-attach bolts (nylon)
Upper Wing System
1
Lightly score top of upper wing
to allow flex for dihedral
Set the wing lightly atop the strut in the
right position (leading edge of wing
2
even with top part of center strut)
Remember to offset wing slightly to left
to match lower wing
Apply pressure to lightly dent the bottom
of the wing to show where the tabs go
3 Use Exacto to cut out tab slots at the dents
Check fit (no glue), alter slots as necessary
4
Pup and Albatros built the same way
Glue wing struts to lower wing and repeat
Don't glue the upper wing in place until the
entire airplane is done (easier access)
Lower Wing Leading Edge Reinforcement
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The "Box" of the biplane wing structure is pretty strong, but there still can be some
flex (especially with 3 mm wings)
Bonding reinforcement to lower-wing leading edges adds more stiffness
Use 1/16 x 1/8" spruce strip (available at hobby stores) or thin carbon-fiber strip
Should go at least 3/4ths of the wingspan
IMPORTANT: Need "bridge strip" across front of main strip and landing gear brace to
carry load
Without bridge strip, loads are
concentrated here
Bridge Strip is bonded to both the center
section and the wing reinforcement strip
Pup and Albatros built the same way
Landing Gear Attachment – Leading Edge
Graphite Strip Leading Edge
Landing gear mounting bolt
with plywood washer
"Bridge" to center section
Receiver velco'd to
bottom of wing
Ailerons
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Cut out 1" x 3" notch in trailing edge
Make 3mm aileron to fit notch (leave room to move)
Install with hinges
Bend root end of aileron torque wire as shown (~0.038" piano wire)
Cut plywood strip~ 1/8-1/4" wide, 1.25" long, with small holes top and bottom 1" apart ("Horn")
Slide over wire
Slide two bearings over torque wire
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Anything that goes loosely around tube
Bend the outer wire to fit under aileron
Cut thin slot near root of wing for the horn, and insert under wing
Position the wire so that it runs from the root to the front part of the notch
Tape the bearings to the bottom of the wing so the wire can still turn
Tape the aileron to the bend end of the wire
plywood
aileron horn
1"
4"
CA wire to
plywood
aileron horn
Plywood strip with two
small holes 1" apart
Bearings (section of thin tubing, like
wire insulation or nylon tubing)
Pup and Albatros built the same way
Also can use commercial aileron system
Aileron Close-up
Fabric Hinge Material
Bent end of torque wire, taped to aileron
"Bearing" (piece of plastic
tube) wire, taped to lower
surface of wing
Wing Struts Attachment
About 3½" inboard of wingtip
– not critical!
Both wing struts parallel with
Center Strut
½" behind the leading edge of
wingtip – not critical, but both sides
should be the same
Pup and Albatros built the same way
Upper Wing Attachment
Place top wing on Center Strut,
hold in place
Re-assemble wing,
repeat on other
wing strut
Pup and Albatros built the same way
Press top tabs of one wing strut
into bottom of upper wing to
mark position, then slit with
Exacto
• This method works very well at making a box wing
structure with minimum warp
• Key factor: top wing should be resting LOOSELY
on top of wing-strut tabs prior to marking
• Flick the upper wing up slightly before marking
to be sure it isn't caught on a sharp point of the
strut
Assembly Sequence
Glue Center Strut First
Top wing is just resting
atop tabs on outer struts
Lift one wingtip gently so that the strut tabs no longer touch, then
set it gently just atop the strut tabs. Then press lightly atop the
wing, and cut out slots for the tabs based on the impressions
The basic goal is to find where the struts want to attach without
friction causing them to touch in a different spot. The foam is
stiff, both wings will want to be at the same angle.
Glue the wing to the outer strut.
Repeat the lifting/gentle touch on the
other wingtip, and cut the slots
Do NOT glue the second outer strut yet
Bonding the final strut
• Attachment point for second outer strut determines if there’s any
twist in the wing
Right
Looking at Wing assembly from directly in Front
Wrong
Lengthen
slots for strut
tabs
Twist means you see less of
the underside of the wing on
one side
If the wing is twisted, lengthen the attachment
slots for the unglued outer wing strut and slide
the attachment to minimize the twist
The airplane is tolerant of a surprising amount of twisting, as long as you can adjust the
ailerons or rudder to compensate
Motor Stick
• Main structural member in fuselage is the "Motor stick"
– Supports the motor, and provides the solid mounting for the
wings
• Made of ~1/4" x 5/8" basswood or balsa running length
of fuselage
– Hobby stores sell stock pieces of these dimensions… don't have
to cut them out
– Exact dimensions don't really matter
– Basswood is more durable…have broken many balsa sticks, but
few bass ones
Pup and Albatros built the same way
Making the Motor Stick
• Cut stick length equal to nose to tail plus a bit extra
• Cut two short pieces ~ 1" long
• Use CA to glue them both to ONE SIDE of motor stick
Top View
• Use Razor saw & miter box, band saw, or very good
eyeballs to cut stacked end straight
Top View
• Use CA to glue "firewall" to front of stick
• Note the center of the firewall is even with the
CENTER short stick
Top View
Pup and Albatros built the same way
Motor Stick
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Press Motor stick lightly in place, make impression with "side sticks" in
fuselage
• Cut out foam to clear Motor Stick "side sticks"
• Drill hole through motor stick near tail, bolt to
fuselage using #2 or #4 nylon bolt and nut
Pup and Albatros built the same way
Assembly
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Slip fuselage over wing, with center strut on the OPPOSITE side of the wing
from the Motor Stick
Cut slot in fuselage to clear
center support
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Drill hole through Motor Stick, through Fuselage, and into wing strut on
opposite side – install #4 Nylon bolt/nut
Cut slot for
horizontal
stabilizer
parallel to
motor stick
Other Details
Two-sided arm used for rudder/aileron servo. One side has two
pushrods, one to aileron, one to rudder
Cut out Fuselage foam
and mount rudder/aileron
servo on right side of
motor stick with foam
double-faced tape
Battery
Long strip of Velcro for
battery to allow CG
adjustment
Aileron Pushrod (both
sides)
Bend landing gear legs
slightly forward
Stub of toothpick for tail skid,
glued into a hole drilled into
motor stick
Mount elevator servo on left
side of motor stick with foam
double-faced tape
Aileron Pushrod
Commercial aileron hardware
shown…this piece is normally
the thin plywood strip
Other Side of Servo
Inboard easy-link is connected
to rudder
Outside (both sides of servo
arm) to Aileron
Other Details/2
Velcro for Speed
Controller
Rudder Pushrod (one side)
Aileron Pushrod (both
sides)
Radio Receiver
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Radio receiver installed under bottom wing, near center. Cut holes in lower
wing as necessary for running servo wires
Other Details/3
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Glue a thin strip of wood (1/16 ply, leading edge strip, etc. on trailing edge of lower
wing, bridging the junction between left and right wings
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Due to the scoring to allow the wings to bend to the dihedral angle, this is a stress point…the
wood keeps the wing from splitting
Pop holes in the upper wing near the center to allow a long screwdriver to reach the
quick-adjusts on the aileron/rudder servo arm
Thin Strip of wood (like leading
edge) bonded to junction at
trailing edge
Sopwith Markings
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Print this page on a color printer
Cut out roundels, glue to surface using thin line of foam-safe
CA just inside the outer edge edge
– By putting the bit roundels ONLY on the top wing, you can tell
from a distance if the plane is turning towards you or away from
you
•
Color on the rudder is blue-white-red
– Make rudder from white foam, color with magic markers
Albatros Markings
• If installing on Gray foam, cut out iron crosses right at the square to
give white background
Flight
• CG should be roughly midway between forward edges of
the two wings
– Built as shown, CG should be about right with the battery near
the motor
• Should easily take off at 3/4th power with Park 250 motor
– Drag of wheels can cause slight nose-over tendency for
takeoff…hold a little back pressure
– Full power with a Park 250 gives very short takeoff roll
• If turning tendency, leave ailerons set neutral and adjust
out with Rudder
Repairs
• Can fix most foam damage with heavy clear packing
tape and/or CA
• Most common damage is the wingtips breaking off
outboard of the aileron
– Airplane will still fly with one wingtip gone!
– However, easy fix with tape or superglue
• Most common problem is an aft CG
– Version V4 moves the wing attachment ~1/2” further aft to help
correct
Variations
• Wing and tail shapes are just cosmetic…can reproduce
other aircraft very easily (or do your own design)
• Big motors can sometimes be more trouble than they’re
worth
– More torque tendency, harder to compensate for
• Wing attach system works for monoplanes as well
– Leave off struts that go above fuselage
– Works a bit better with 6 mm foam for the wings
• If use 3 mm foam, put reinforcement strips on trailing edge as well
as leading edge
– Easier to build, harder to fly (higher wing loading)