1. Sopwith Pup & Albatros DIII "Foamies"
Ron Wanttaja
August 2011

2. 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: 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!
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

3. 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

4. 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

5. 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

6. 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

7. 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.

8. Front Half of Albatros Fuselage
Print out the two halves of the fuselage, tape together at the line

9. Approximate Horizontal Stabilizer Slot

10. Wingtip Shape Pup Wings Wing Construction – Make Two
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
Wingtip Shape
Wings are 26" span
Cut Rectangle 26" long and 4.25" Wide from 3mm or 6 mm foam
Lay template at each end and cut wingtip shape

11. Albatros Wingtip Shape
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
Just re-shaped the tip
Leading Edge
Wing Construction – Make Two
Cut Rectangle 26" long and 4.25" Wide from 3mm or 6 mm foam
Albatros Wingtip Shape
Wings are 26" span
Lay template at each end and cut wingtip shape

12. 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)
Cut out elevator "notch" to let rudder swing
Bond in wire "Bridge" using foam-safe CA on sides ONLY
No Glue Here!
~.032" piano wire
Glue here

13. Elevator shown in actually a bit too big!
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

14. More on Hinges Strips of ½A control hinge fabric - Internal
Strips of clear plastic packing tape
Cut to 1/8" wide
Use exacto to cut slot
CA in place
Hybrid
Strips of ½A control hinge fabric - External
Glue hinge material to control surface only
Use packing tape to attach surfaces
Easily removed/repaired
Cut to 1/8" wide
Lay on surface
CA in place

15. Leading Edge/Landing Gear Brace installs in slot in Center Strut
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

16. Leading Edge & Landing Gear Brace
Glue to plywood with rubber cement, or print on label stock
Odd bumps and bulges at the ends of the struts are just for drawing convenience.
Pup Wing Struts
Holes for Gear Bolts
Top and bottoms are basically identical, so the struts can go either way
Center Strut
Leading Edge & Landing Gear Brace
All are one-piece 1/16" plywood
Formerly had a triangular brace in the middle of the lower wing - Deleted
Cut slot to the thickness of the wood used

17. Alternate Pup Wing Struts (Easier to cut out)
Glue to plywood with rubber cement, or print on label stock
Deeper brace for more dihedral (rudder-only systems)
Structurally, these are identical, but they are different appearance if flipped.
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

18. Albatros has less wing spacing than Pup…these struts are shorter
Leading Edge & Landing Gear Brace
Albatros Wing Struts
Albatros has less wing spacing than Pup…these struts are shorter
Mid Brace
Formerly had a triangular brace in the middle of the lower wing - Deleted

19. Simple Albatros Wing Struts
Deeper brace for more dihedral (rudder-only systems-either plane)
Leading Edge & Landing Gear Brace
Mid Brace

20. Strut Assembly Albatros Pup 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
Landing Gear (0.049" piano wire)
Albatros
Why, yes, it IS asymmetrical!
Pup
#4 nylon bolts attach center strut and motor stick to opposite sides of foam fuselage
Asymmetrical nature accommodates for the offset of the foam fuselage from the strut
Leading Edge of upper wing is even with the upper part of the center strut
Bottom Posts go through slits made in Wing. Trim off excess with side cutters.
Leading Edge of lower wing butts up against (and is glued to) the forward brace

21. Slots MUST be parallel to the centerline!
Wing Assembly
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
Score shallow cut in top of lower wing, down the centerline. This is to let the wing bend in Step 4 1 2
Albatros is identical, except the wing is the other way around
Slots MUST be parallel to the centerline!
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. 4 3
Remove center strut, use exacto knife to cut slits where the bottom posts made dents.
6 mm wing shown. For 3mm wing, the bottom of the wing doesn’t go to the bottom of the brace 4 5
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
Apply foam-safe CA to the center strut ONLY (not the landing gear or mid braces). Keep strut vertical to wing until CA sets

22. 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
Center Strut installed at an angle
Shim added between strut and fuselage to set wing at right angle to fuselage
Wing-attach bolts (nylon)

23. 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 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 2
Use Exacto to cut out tab slots at the dents 3
Check fit (no glue), alter slots as necessary
Glue wing struts to lower wing and repeat
Don't glue the upper wing in place until the entire airplane is done (easier access) 4
Pup and Albatros built the same way

24. Lower Wing Leading Edge Reinforcement
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

25. 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

26. Pup and Albatros built the same way
Ailerons
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
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

27. 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

28. 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

29. Upper Wing Attachment Place top wing on Center Strut, hold in place
Re-assemble wing, repeat on other wing strut
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
Pup and Albatros built the same way

30. 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

31. 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

32. Pup and Albatros built the same way
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

33. 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

34. Pup and Albatros built the same way
Motor Stick
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

35. Assembly
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
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

36. 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
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 (both sides)
Long strip of Velcro for battery to allow CG adjustment
Bend landing gear legs slightly forward

37. Aileron Pushrod
Commercial aileron hardware shown…this piece is normally the thin plywood strip

38. Other Side of Servo Inboard easy-link is connected to rudder
Outside (both sides of servo arm) to Aileron

39. Other Details/2
Velcro for Speed Controller
Rudder Pushrod (one side)
Aileron Pushrod (both sides)
Radio Receiver
Radio receiver installed under bottom wing, near center. Cut holes in lower wing as necessary for running servo wires

40. Other Details/3
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
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
Upper Wing
Lower Wing
Trailing Edge of Wing
Thin Strip of wood (like leading edge) bonded to junction at trailing edge

41. Sopwith Markings 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

42. Albatros Markings
If installing on Gray foam, cut out iron crosses right at the square to give white background

43. CG should be roughly midway between forward edges of the two wings
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

44. Can fix most foam damage with heavy clear packing tape and/or CA
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

45. Big motors can sometimes be more trouble than they’re worth
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)