Airborne Magazine



by Matthew Downes

Plan No.  668

Wing Span:
1.5 metres
.35 - .40
3 Channel required
Plan Detail

Plan No. 668
AU$30.00 plus P&H (AU$3.00 within Australia).
Moulded Canopy: $27.50 plus P&H

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: 
PO Box 30 Tullamarine Vic, Australia, 3043

Don’t be impatient lad, building off the plan means a bit of prep work in producing ribs, fin frame members, fuselage formers etc. Use your preferred method, if you are a first time from the plan constructor, I suggest a good method of transferring the plan to wood is to photocopy the plan detail onto A3 or A4 paper, place the desired piece ink side down on the balsa, rub a rag dampened with turpentine on the back and there you have the lines to cut around. Another excellent way to get accurate shaped ribs is to cut a ply pattern, pin over rough cut pieces of balsa and use a router to trim to size. I guess I’m lucky as I have the use of a router table!

Building the Wing
You wont get a much simpler wing to build, excepting ARF kits! Make 18 identical ribs from 1.5mm balsa and take the extra slot for WB out of 4 of them. Remember to cut holes to locate paper tubes for the elevon servo extension leads.
Cut WB from 3mm ply, slot as per plan and trial fit ribs into those 1.5mm slots. It is important to have WB prepared as it sets the position of centre ribs. Cut two main spars to length and pin the bottom one to the previously covered plan, you did cover it with cling wrap or similar plastic film to protect it didn’t you? Fit all ribs, and use WB to position W1s and the inner W2s.
Trial fit the top spar and use a square to ensure end ribs are perpendicular. The rib trailing edges need to be kept equidistant from the building board, a good method is to use a piece of 19mm balsa under the trailing edges. When satisfied all is well use your preferred glue to assemble the wing. PVA is excellent if you are not in a hurry or some minor gap filling is needed. Use weights, clamps or pins to hold in place ‘til the glue sets.
Strip a piece of 9.5mm balsa approximately 25mm wide for the leading edge, your width may vary slightly from 25mm depending on how accurate your ribs are cut. Don’t forget leading edge sheet butts into the back of the leading edge timber both top and bottom. For the trailing edge, strip a piece of 6.5mm balsa 12mm wide and sand to continue the profile of the wing ribs. Trailing edge sheeting covers this spar. Fit 6 or 9mm gussets into the outer corners of the wing for added strength.
Glue the leading and trailing edges in place. Cut and fit sheer webbing and paper tubes in for the elevon extension leads in place. Don’t forget the draw strings for when you need to pull the servo leads through the paper tubes. While the wing is pinned down, fit and chamfer the leading edge 1.5 mm balsa sheeting, remembering to leave around a quarter of the main spar exposed to take the rib cap ends.

Elevon Servo Decisions
You can either mount elevon servos to trays inside the wings or onto the hatch lids, I prefer the latter.
To make a hatch well between the wing ribs, fit a 6.5mm spruce stringer 75mm back from the main spar and between the second and third W2 ribs. Shape and fit balsa doublers to the ribs between the above stringer and main spar, flush with the top of the wing ribs. Glue a spruce gusset into each corner; these will be the fixing points for hatch cover screws. Sheet the wing as per the top but don’t cover the area where the hatch cover will fit i.e. don’t cover the doublers or half the spruce stringer. Make a hatch cover of 1.5mm ply for each servo. When the wing is complete they will be flush with the surface of the wing. Fit rib caps, shape the leading edge and sand the wing.

The Fuselage
To build the fuselage transfer the shape onto 100 x 3mm sheet, there will be a need to laminate sheets to get enough width. Cut out the wing slots taking care not to alter the incidence and trim until a snug sliding fit over the wing is obtained. Cut the doublers from 1.5mm ply and after accurate fitting glue to the inside of fuselage sheets, place some weights on top of these to stop curling as the glue cures. While waiting, build the fin over the plan, as this is built into the fuselage.
Assemble the fuselage using your preferred method, I use a jig as described in Airborne #149. Note the 1-degree right thrust of the firewall. Fit previously cut formers F1, F2, F3 (2part) F4 and F5, ensure that the cutouts will take 6.5mm square balsa. Check for accuracy regularly when gluing into position. Also temporarily position the fin as per plan. Next comes the 12.5mm triangle stock longerons. These may be difficult to bend, so soften with water or cloudy ammonia. Obviously the rear ends need to be faired to accommodate the fin, and side sheeting is chamfered to have a greater contact area with the fin post. Now glue in place, taking care the fin is aligned with the centre line of the fuselage. Fit 6.5mm square stringers to fuselage sides, they will slip into place easily if cutouts are accurate and any glue runs have been removed. These stringers act as a base for the top hatch to sit on.
A little preparation now makes constructing the top hatch easier later. Eventually the top of the fuselage, with triangle stock attached and part of F4 and Bs will be removed in one piece. With a sharp blade slit the fuselage side sheeting neatly along the top of the 6.5mm square stringers from F3 to the front of the fin, it is easy with a steady hand and good eye. That’s all for now. Drill a hole in the top of the wing sheeting so elevon servo leads can be passed through later.

Fixing the Wing in Place
Centre the wing in the slot and check diagonally from a point common to both outer ends of the wing to a point on the rear centreline on the fuselage. When satisfied mark a glue line on the wing, gently slide the fuselage sideways, apply glue (preferably epoxy) slide back to the glue line and re check measurements. Five minute epoxy will probably go off too quickly so consider a longer curing time product. Longer curing time epoxys also give greater strength.

Wing Tips
Again these are easy to construct, cut the tips and ribs from 3mm balsa, glue in position taking particular care not to build in artificial trim tabs (twists). Sand the ribs to compliment the wing shape out to the tip.

More Fuselage Stuff
Now that the fuselage and wings are one piece, remember to watch for light globes and other obstacles when manoeuvring the model! Fit and fix the undercarriage-mounting block.
Before sheeting the top and bottom of the fuselage, sand the triangle stock longerons flat as they will probably have risen in the centre when being bent. Use 3mm sheet cross grain from the under carriage back, and on the top from F1 back, including the soon to be made hatch area.
Shape the side / top / bottom junction as per plan. Build the top hatch cover / turtle deck using T1, T2, T3 and 6.5mm spine. Note T2 is smaller than T1 to accommodate 3mm sheeting which may be curved using cloudy ammonia. When gluing T1 and T2 it is a good idea to put a piece of cling wrap between so they don’t stick together.
At this stage shape the cockpit as the rear formers will be more rigid to work on than after the hatch area is removed. Now complete the removal of the hatch by cutting the fuselage top between T1 and T2 and in front of the fin with a razor saw. These cuts will meet the slits in the side put there earlier. Reposition the hatch cover and drill a hole of sufficient size for a centring pin through T1 and T2, glue to T2 only, I used a kebab stick. Yum! Locate a screw in front of the fin to hold down the back of the hatch.

Nose Cone or More Correctly.... Engine Cowl
This takes quite a bit of doing but the results are quite satisfying.
By now you should have decided on your choice of motor. The orientation of the motor to best fit in the cowl will decide the angle at which the mount is fitted to the firewall. Make a box as per the plan with triangle stock in the corners. Position, trim, position, trim etc until the desired fit is achieved. When satisfied glue in place along with the nose ring (N). Now you can shape the outside to the desired profile. Remember there is still a hatch cover to be fitted to the under side for fuel tank access.
Fair the fin leading edges, and angle the leading edge of the elevons as per plan, locate the hinge slots in preparation for after covering installation.
Fuel proof the engine bay and fuel tank area.
Cover the model using a good quality film; any supplier advertising in Airborne will be able to help with your choice. The Wingbat is an easy model to cover. I fitted the elevon servos to the inside of the hatch covers on rails, with the crank protruding through a slot. Fit elevons and rudder and obviously attach to servo cranks.
Fit the under cart, motor, fuel tank and radio gear, ready to fly.
Your models’ centre of gravity should be 70mm from the front of the wing, this has proven to be ideal, the plan shows a 5mm tolerance either side. If you end up with the C of G at say 75mm be prepared for an exciting flight as the fuel load lightens.

The Fun Bits
The maiden flight caused excitement at the Hamilton field; lots of banter, photos, comments like “It won’t fly”, etcetera then the range and last minute trim checks etc. Much to everyone’s delight, plenty of revs, and up she went. I must say a quite startling climb and flop back to earth more like a kangaroo leap than a takeoff, then up and away. Manoeuvres were fast and scary, “better come in and adjust the elevon throws”! Up wind approach, past the pits still at head height and no chance of a landing. Around again a longer approach and a couple of bounces to a stop. Wow did that try the nerves. What to do? Elevon throws were in excess of 25mm each way so no wonder the takeoff and manoeuvres were radical. They were reduced 15mm each way and the flying results were spot on. BUT, the takeoff was still a couple of bounds, like a metre and a half up after a 2 metre run, back to earth after pilot reaction and then a smaller leap which didn’t need correction. “Need to think about this”.
What can it be? The takeoff is still crazy while the flying is great yet the landing is similar to the takeoff. Elevon travel is perfect for flying but the model looks strange sitting on the ground. Ahaa, the undercarriage is bent as you would for a tail dragger but we only have a very short fuselage don’t we! This gives the wing a very high angle of attack on the ground and it tries to fly without enough airspeed, pilot reacts... model resumes a normal attitude and flop, luckily not a tip stall and snap! I guess this says plenty for the Wingbats’ stability. Well the cure was easy, spread the undercarriage, keep it well angled forward as per the plan to give the wing a lower angle of attack. Easy.

Flying Stuff
Flat spins, and I mean flat spins,Waterfalls and every manoeuvre you can think of it will do, even manoeuvres that aren’t even named yet! Read on and find out what a Drill Bit is! This bat style bird really is fun to fly.
This is a slippery model that creates real flying excitement,and it can be thrown around the sky powered by a 32 sized motor. The Wingbat is not a beginners model model and is suited for a more experienced pilot! “The Bat” is quite an agile machine, depending on the your choice of the centre of gravity position and amount of control throw. Be warned that small movements of the C of G will change its characteristics from mild to wild in the matter of only 5mm.
Initially, roll manoeuvres were cork screw like until the lateral balance was sorted out so don’t forget this important point. After that they were lovely and axial. Loops are conventional; knife edge flight requires quite a bit of pilot input to keep it in that position. The Bat will do nose high regular and inverted flat spins, these are induced by putting the ‘plane into an upright or inverted snap roll and then slowly centring the aileron stick at full throttle. There is a variation of the flat spin that is very unusual, all that is required is to then introduce opposite aileron and the plane will roll into a knife edge and spin around its own axis! This spin is incredible to watch, as the plane spins that fast that it cuts through its own prop wash and sounds great doing it! Because of the centrifical force, the motor nearly cuts out from fuel starvation. I’ve named the manoeuvre The Drill Bit.
The Bat will also tumble to the horizontal plane and carry out a similar manoeuvre, The Water Fall. This is not a loop but a rotation around the C of G. Centring the sticks has proven to be adequate to stop these radical manoeuvres and resume regular flight, or should that be, bring your heart beat back down from 200! Just to add to the excitement all manoeuvres were carried out using full throttle. When attempting these manoeuvres I suggest the old adage, fly at least two mistakes high.

The Wingbat as pictured comes out at 1956 grams. It is a robust model, almost to the point of being over engineered. It is quick and easy to build and stable to fly. It will give many hours of pleasure and excitement and will certainly be a talking point at the field.

Wingbat in flight


Plan Detail

Plan No. 668
AU$30.00 plus P&H (AU$3.00 within Australia).
Moulded Canopy: $27.50 plus P&H

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: PO Box 30 Tullamarine Vic, Australia, 3043
Airborne Plans Service: P.O. Box 30 Tullamarine Vic, Australia, 3043