Michael Oates reports on the Basingstoke MAC’s model of choice for their 2023 club challenge
Words & Photos: Michael Oates
In looking for a new challenge for Basingstoke Model Aero Club I came across streamer combat, where pilots try to cut an opponent’s trailing 30-foot crepe streamer with their propeller. The concept developed into a team challenge to be demonstrated at our warbird festival with points and prizes awarded and the top team crowned. Each participant would have a similar spec plane: size, weight, motor and propeller. However, when searching for suitable model kits a lack of stock prevented the purchase of the number of models required. So, we would need to build our own and in searching for planes and plans I came across the Spitty. It would fit the bill, being a small, light foam model that was easy and cheap to build and repair. It flew well on a YouTube video and seemed very agile. The plan was free, in German, and the plane could be built for around £30.
The key material for the build was Depron, which was difficult to source as the white Depron was no longer manufactured and the grey version was found not to be suitable. However, we sourced a supply at a reasonable price from Germany.
A prototype was built and flown, trailing its streamer, and was found to be an excellent flyer. The combat event and the build requirement were presented at one of our club nights with the aim to recruit participants and sixteen members signed up.
Regarding prizes for the event, Deluxe Materials kindly offered a prize for the best model and sponsored a build that would be raffled. To support future builders, it was suggested that we create a build log and list any useful alterations provided by our own early builders.
One great thing about this model is that it can be customised to suit personal preference. Most models have been built as Spitfires but some have had their outline changed to resemble other aircraft, such as a P-40 Warhawk, Bf 109, P-51 Mustang and the P-47 Thunderbolt. We have even had a twin-boom EDF version representing a Vampire and it flies really well. We have also seen models ‘improved’ to represent the Spitfire shape more accurately by lowering the wing, changing the fin outline and adding dihedral!
At a more detailed level some variations in construction method and detailed design have been tried. Of these, the most important is to consider the CG position as we have found that models really need the CG at least 1 cm further forward than stated on the plan, at least for the first flight. This is easier to achieve if you and extend the nose and move the motor forward 15 mm. Make sure that you have made any decisions about modifications before you start your build!
You can download the Spitty plan from here:
PLAN & CUTTING OUT PIECES
There are two options for the plan: print out A4 sheets and stick them together or print out at A3 for a complete plan on one sheet of paper (around £3.00 from a local printer). Some parts are only printed once, e.g. the fuselage side, so either use the cut piece as a template or use two plans. Our Depron came in a 620 x 800 x 6 mm size so one and a half sheets were required per plane.
Cut out the shapes from the plan and place on the Depron sheet to ensure they all fit. Stick down the shapes using low tack tape. Allow room for two sides of the fuselage as only one is shown on the plan. You don’t need the fin and cockpit as they are covered by a separate piece. The wing has a central piece (the complete wing on the plan) but also requires two stiffeners that will be glued on, one above and one below.
Cut out the parts. When cutting do not lean on the Depron as it will dent easily. Use new scalpel blades and change them after several long cuts. Blunt blades will tear the Depron. I found it best to cut from a corner towards you to prevent over cutting the piece.
When cutting the fuselage sides, formers and the base of the fin and cockpit, ensure you make a right-angle cut. These parts will be glued to a flat surface so a right-angle cut will achieve the best adhesive surface.
I use a pin to mark the centre line of key parts to help line up the pieces, i.e. the wing, top and bottom of the fuselage, the formers and where they attach to the fuselage sides, the ailerons, the rear stabiliser and where the servos will go. You can then draw a line between the pin holes to mark where pieces should go.
Using the plan cut out the wing into a Spitfire-ish shape then cut out the two wing stiffeners. Cut one, then use that as a template for the other. Cut out the ailerons from the main wing. These will need a bevelled edge where they join to the wing to allow for downward movement.
Stick together the wing pieces using Deluxe Materials Foam-2-Foam contact glue, with one wing stiffener on top and one below at the leading edge of the wing. Use the centre lines as a guide, if you drew them. When dry sand so all three parts create an even shape and a tapered and rounded edge to the leading edge.
The ailerons need to be trimmed to create a small gap at the ends so they can move freely in the cut out in the wing. Secure in place using Blenderm tape. The gap at the bevelled edge is on the bottom. Horns will need to be attached to the ailerons. I did this after I had positioned the aileron servos in the fuselage. Blenderm works very well and hinges are not necessary. You can put Blenderm on the bottom surface as well, but I found this was not essential.
The upper and lower surface of the fuselage are stuck to the top and bottom of the sides. So, when cutting out the sides ensure you cut using the correct outline, i.e. not the outside line, the inside one.
Use the pin method to mark where the formers will go. When cutting out the sides I cut the inner shapes out first before cutting around the outer edge. This keeps the plan in place on the Depron. Use the first side to act as a template for the second side. The key is to ensure that the hole for the wing is identical and level in both fuselage sides and also the slot for the rear stabiliser is level. I put the two sides together and pushed the wing through its hole. I also put a piece of Depron in the stabiliser slot. This enabled me to check they were level and were a snug fit. It is easier to make adjustments now rather than when the fuselage is built. I then sandpapered the outer edges of the fuselage sides to make them identical, ensuring I had a right-angled outer edge to the fuselage side.
As the fuselage sides have a curved shape it helps if the top and bottom pieces are rolled to create a slight curve, particularly at the nose. Stick the base of the fuselage to the bottom of one fuselage side using Deluxe Materials Foam 2 Foam glue. Use a set square to ensure the side is at right angles to the base. You may need to tape the base to the side at the nose to keep them together due to the curved shape. Once dry glue the second fuselage side, again ensuring it is at right angles to the base. Glue in the Depron formers F2 and F3. Check that the wing and rear stabiliser are still both level when put in their slots.
MOTOR & MOUNT
Cut out the firewall from 4 – 5 mm plywood. You can mount your motor in various ways but for this build I used an X-mount with a prop adapter. Draw lines from corner to corner on the firewall to produce an X which indicates the centre of the mount.
The plan requires one to two degrees of right thrust but no down thrust. To set right thrust at two degrees I worked out that it would require a 0.88 mm gap so I used small washers of the correct thickness and placed them behind the two right hand holes of the X shaped motor mount when looking from the front. I found this method easier than trying to angle the firewall itself.
Drill a hole in the centre of the firewall to ensure the rear of the prop shaft does not catch the wood. I also drilled additional holes of about 10 mm diameter in the firewall for the motor wires to feed back into the fuselage and to allow air to pass through for cooling.
Glue in the motor mount using the marks you made from the plan on the fuselage side walls (using the pin method above) using Deluxe Materials Super ’Phatic! or Speed Epoxy. I used bolts with washers to secure the motor to the firewall.
WING, TAIL & CANOPY
Cut out the slots in the top of the fuselage and glue on the fin/canopy. Use a set square to ensure it is at right angles to the fuselage.
Cut the elevator off the rear stabiliser part and cut a bevelled edge to its leading edge. Attach to the rear stabiliser using Blenderm tape with the bevelled gap on the bottom.
Fit the wing into its slot in the fuselage and the rear stabiliser. Ensure the fuselage is level then check that both the wing and rear stabiliser are level when the plane is in a horizontal flying position and at 90 degrees to the centre line of the fuselage. I used a horizontal line marked on the wall of my workshop. Should either not be level you can adjust using thin veneer at the wing root/stabiliser slot to raise either side to achieve a level wing or stabiliser. Glue the wings and stabiliser. To check that the wing and tail are square to the fuselage (when viewed from above) use string to measure from the wing tips back to a point on the fuselage centre. Repeat for the rear stabiliser. Contact glue is not easy to use for this so either use epoxy or a glue that gives you time to make adjustments before setting e.g., Deluxe Materials Super’Phatic! I would not recommend hot glue as the heat can dent the foam.
Cut out holes in the fuselage side the size of your servos at the marks indicated on the plan. I used a piece of 3 mm ply to screw my aileron servo to and stuck the ply to the outside of the fuselage side. This pushed my servo further out to achieve better alignment with the horn on the aileron. I found without the ply the pushrod was at too much of an angle. Fix the control horns on the ailerons. I used horns which screwed through the Depron to a base plate. For mechanical adjustment of the ailerons, I used a pushrod keeper screw on the aileron arm and a Z-bend for the horns.
Glue the elevator servo to the underside of the wing so that the servo arm and pushrod line up with the rear slot in the base of the fuselage. I cut a hole at the rear of the wing with the servo arm below the wing. You can cut the slot before the base is attached or do it when you fit the servo. You can also put Depron packing around the servo to ensure it is secure. Pass the pushrod through the slot and attach to the horn. Fix the horn to the elevator.
There are numerous options for where to put the ESC, battery and receiver.
Here I made a change to the plan by having the battery hatch on the top of the fuselage. So, my ESC was as per the plan, behind the firewall on the bottom of the fuselage. My battery position was on the top of the wing near the leading edge and close to the CG. The receiver was behind the battery, also on top of the wing under the cockpit.
Connect all the leads, position and secure the receiver aerial(s), test the direction of the propeller and that the ailerons and elevator work correctly.
For the ailerons and elevator throws see the Datafile.
BATTERY HATCH & FUSELAGE TOP
Chamfer the bottom rear of the fuselage top so it fits neatly to the rear stabiliser. You may wish to roll the front of the fuselage to create a curve that better fits the fuselage sides. Dry fit the fuselage top and mark the length of the battery hatch you want, mine was 110 mm. Cut the top of the fuselage piece at the battery hatch marks. Glue the front piece, place the battery hatch in position and then glue the rear piece ensuring a snug fit.
The battery hatch can be locked in place by gluing a tongue of thin ply to the underneath of the hatch front. The rear can be held in place with either a catch made from a servo arm/plastic strip or magnets. If using a servo arm/strip allow enough space in front of the cockpit for the arm to swivel. I reinforced the underside of the Depron with thin ply and used a small nut and bolt to allow the arm to swivel. If using magnets, you will need to glue a magnet in the hatch and glue a piece of balsa just thicker than the magnet so it protrudes out into the battery bay to hold the magnet so that the hatch end can sit on top and the magnets engage. An alternative is to glue a small metal tongue that extends out into the battery bay and will engage with the magnet in the hatch. I used Speed Epoxy to glue the magnets.
I found it useful to glue two narrow strips of Depron matching the inside width of the fuselage to the base of the hatch so when the hatch was in place it could not slide side to side.
A Depron tail protector should be glued to the rear of the underside of the fuselage as per the plan. The streamer can be attached to this piece. Create a small hole and stick two small washers either side of the hole. This will prevent the string from pulling through the Depron.
SANDING & DECORATION
The plane is now complete so all edges can be sanded to ensure they are smooth and even. I rounded the edges of the fuselage. The leading edges should be sanded tapering to a round edge – wing, rear stabiliser, fin and canopy front. Any dents, dings or gaps can be filled with Deluxe Materials Wonderfill, an easy sanding light weight filler, and sanded down.
Decoration is up to you, either warbird decals or a jazzy paint job. I used acrylic paint (brushed or sprayed), with decals, coloured Fablon and Deluxe Materials Eze Tissue to make the plane’s colour scheme. Eze Tissue is a light weight patterned tissue and packets provide a selection of coloured patterns and shapes and are applied with Deluxe Eze Dope.
The plane can also have added protection from dings by applying Deluxe Materials Foam Armour to the leading edges of the plane parts or cover the whole plane with Deluxe Materials Eze Kote. Both are water based resins that create a tough, ding and water resistant film/hard layer that can be sanded and painted.
BALANCE & FLYING
The C of G is marked on the plane’s fuselage side, 60 mm from the leading edge at the wing root. But on several planes the club members have now built we have found that the plane fly with more stability when balanced with a C of G one centimetre forward of its plan position at 50 mm. However, this is personal preference and the best position for you will be determined by flying the plane. Just use 50 mm for the first flight.
The plane, when balanced, flies very well. From a hand launch it flies straight and true. It rolls, loops and flies inverted without problems. It is very agile but is easy to control for an average A certificated pilot. It is small and quick and so should be flown close rather than in large circuits.
The plane flies very well as per the plan. However, model builders love to tinker so listed below are suggested amendments from our club builders:
• Move CG to 50 mm from leading edge of wing for better stability.
• Elongate the nose by one to two centimetres to move the firewall forward.
• Add balsa or ply fillets behind the motor mount to strengthen the bond to the fuselage sides.
• Place the battery hatch on top for ease of use.
• Hinge the battery hatch along the front using a Fablon strip or Blenderm, with a magnet or catch at the rear.
• Fit a hatch on the bottom for easy access to the elevator servo and receiver.
• Position the receiver under the wing and access through a bottom hatch.
• Use ball headed pins on the side of the hatch to ease lifting it off to reduce wear on the Depron.
• Position the LiPo on the CG so different batteries can be used without affecting the balance of the model.
• Use one servo to control the two ailerons to reduce weight.
• Sand and round the rear edge of the wing stiffeners to aid to air flow.
• Cover with a lightweight hardener to stiffen and protect the Depron, but beware of adding too much weight.
• Add a slot in the chin to improve cooling.
• Enlarge the hole for the elevator pushrod or make an additional slot in bottom at the rear to allow air out.
• Make a hole in the former above the wing to provide airflow over the battery.
• Make additional formers to F2 and F3 for strength and stiffness.
Basingstoke Model Aero Club Electric Day, 10th September 2023
Two teams took part, with six pilots for the red steamer team and five pilots for the yellow streamer team. The combat flying time was four minutes.
- Each streamer being cut. A victory! – 2 points
- Surviving without own streamer being cut – 1 point
- Bonus points for cutting more than one opposing streamer. An ace! – 2 points
- Not returning (crashed!) or landing on the runway after combat – 1 point
A safety briefing was given on where to stand, the flying area, holding area, launching with two second intervals, action on losing your plane in the melee, access onto the runway and landing. A flight line controller stood behind the teams to command when to launch, call out the time and land. After launching each team flew to their holding area (each end or the runway) until all were assembled and the command to start combat was given. Two observers stood behind each team to record results and watch out for safety issues.
|Deducted (off runway)
|Bonus x2 cut streamers
John Bristow of Deluxe Materials presented prizes to the winners of the best Spitty build competition. First was Mike Roberts with Colin Low second. Winner of the Deluxe Materials sponsored Spitty was Jim Vart.
I wish to thank Deluxe Materials for sponsoring our 2023 project, providing interest and incentive through the best model competition and the Spitty raffle. As one colleague said, “The main thing is that 16 people got to actually build something from scratch. Many of those with little or no experience of building.”
Thanks also to Peter Love and Alan Haskell, part of the team that supported the research, organisation and editing.
In summary, Spitty is a really good flyer and even flying out of combat with its streamer flowing behind is great fun. But a word of warning when in combat – do keep a good eye on your own plane!
|Foam combat plane
|Plan available from:
|290 – 325 g
|1400 – 1450 kV brushless motor, 30A ESC
|To suit motor: 7 x 6, 8 x 6, 7 x 5
|3S 1000 – 1300 mAh
|3 x 6 – 9 g
|Ailerons (2), elevator (1), throttle (ESC)
|C of G:
|50 mm from L.E. (60 mm on plan)
|+/- 13 – 18 mm
|+/- 15 – 20 mm
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