AerMacchi MB339

1245 mm Span (with Tip Tanks)

EPP Power Scale Slope Soarer

Designed by Stan Yeo

Produced by PHOENIX MODEL PRODUCTS

Introduction

The AerMacchi MB339 is a stylish crash resistant character scale EPP slope soarer designed for the sport flyer looking for something different. It will fly in relatively light winds up to very strong winds with added ballast. Whilst the inverted performance is limited (it will perform outside loops (bunts)) this is more than compensated for by its manouvreability and docile handling characteristics. Building time is anything from 6-8 hours upwards depending on the care taken and the finish required i.e. whether decorated using coloured vinyl tape or as, like the protoype, covered in Easycoat.

Tools / Materials Required

The only tools required are a modelling knife with spare blades, a pair of sharp scissors, 180 grade Wet & Dry sanding block, a tube of impact adhesive such as Evo-Stik, Epoxy, some runny super glue (please observe safety precautions on packets!) and a soldering iron.

R/C Equipment

The R/C equipment used in the prototypes consisted of standard size servos for the elevator and ailerons (single servo installation), HS300 size, a square 700mA nicad pack and a Hitec mini Rx. For the twin aileron servo installation any mini / metal gear micro servos can be used. We recommend the Perkins SuperTec 3002BB minis and HS81MG servos along with a Webra 6 ch. Rx / Hitec 7 ch. Dual conversion receivers. All the items mentioned are available from PMP. Impact adhesive is used for all 'foam' joints EXCEPT the mainspars and the wing brace where Epoxy is used. Superglue is used for all wood to wood joints except wing brace.

Building the Fuselage

1. Lightly sand the fuselage and doublers with 180 grade wet and dry. Remove dust with a small brush or vacuum cleaner.
2. Glue nose & tail sections together using impact adhesive and drill wing dowel holes in ply nose doublers in positions marked.
3. Glue nose and tail doublers in position using impact adhesive. Note tail doubler position on plan.
4. Drill dowel holes in foam. Glue nose former in position. Fit B5 & B6 12mm balsa blocks in position (fit wing dowels and use as a guide to get fuselage square).
5. Fit elevator servo to blocks B1 & B2 glue in position ensuring they are flush with the top of the fuselage but not protruding.
6. Join fuselage at rear using surplus foam from fuselage bottom. Taper underside of fuselage top in tailplane area and dry fit. Cut to shape and radius corners at base of fin.
7. Mark elevator hinge line on Correx tailplane and remove strip of plastic on one side to form hinge line. The elevator hinge line is 6 whole flutes forward of the trailing edge. Push fit elevator joiner in position.
8. Fit Fin to Tailplane using strip of 25mm CW (cross-weave) tape. Glue tailplane to fuselage. Fit fuselage top, cockpit and nose cone.
9. Check which side the control rod must be connected to the elevator servo for the controls to operate in the correct sense and plan route for elevator control rod.
10. Install elevator control rod. Bore hole in foam by heating the end 10mm of elevator control rod. Drill and fit control rod support blocks B3 & 4. Support control rod in middle using scrap foam from wing outers.
11. Fit fuselage bottoms (front and rear) checking that fuselage is not bent or twisted.
12. Cover fuselage using CW tape. In restricted areas such as the base of the fin etc strip CW tape to 25mm wide. In high stress areas such as under the leading edge of the tailplane and above the wing trailing edge apply an EXTRA layer of tape for added strength.

1. Lightly sand wing surfaces and remove dust as before. Using a SHARP scalpel and straight edge trim spar slots to size. Unfortunately due to restriction in the CNC foam cutting machines tapered wings produce tapered spar slots. Remove waste from wing brace slot.
2. Fit 3mm x 10mm hardwood trailing edges using impact adhesive. Ensure that the TE is straight otherwise difficulty will be experienced in fitting the ailerons.
3. Fit top wing spars using Epoxy, cut to length and join wings upside down (helps overcome the droop wing look). TE should be STRAIGHT i.e. no sweep either way.
4. Fit wing brace and bottom wing spars, again using Epoxy. Trim spars to length and shape wing tips.
5. If fitting individual wing servos cut boxes for the servos in the wing behind the main spar. Distance from wing joint will depend on the length of servo lead. If servo lead is too short use servo extension leads to allow mounting of the servo further outboard. With mini servos the servo may protrude slightly from top of the wing.
6. If using a single servo to drive the ailerons mount the servo along the wing join behind the mainspars and use the torque rods supplied. Relieve ply doubler to accommodate the torque rods to prevent any unnecessary friction. Using 50mm CW tape, tape torque rods in position.
7. Make a rectangular template of the aileron servo(s) ignoring lugs but allowing for output arm and cut rectangular hole(s) in wing. Servo(s) should be a snug fit in hole. If fitting outboard wing servos use foam block removed to restore wing lower surface and a hacksaw blade to cut recess for servo lugs.
8. Before covering the wing with CW Tape remove the aileron servo(s) and prime the foam with a spray on impact adhesive. Hold nozzle 40 to 50 mm away from foam and allow 10 minutes for solvent to evaporate before covering.
9. Cover wing with CW tape. Start by laying a strip along the TE of each wing panel. Each strip should overlap the wing joint by 100mm each side. This provides increased strength and stiffness at the wing joint. Work forward, bottom first, overlapping the previous strip by 6-10mm. At the leading edge overlap tape by 10 mm.
10. Cut ailerons to size and shape aileron leading edge. The ailerons are top hinged for twin servo installation and centre hinged for single servo installation.
11. Cover the ailerons, starting at TE using either CW tape or coloured vinyl tape etc.
12. Hinge ailerons using M&M Developments Sticky Hinge supplied in kit. If top hinging use either aileron covering tape as a hinge or the M&M Developments Sticky Hinge. Cut Sticky Hinge into 50mm lengths, 3 per aileron. If desired ailerons can be sealed between hinge sections using 6mm sq soft draft excluder trimmed to 1.5mm thick.
13. Decorate model using stick on trim such as Protrim / Solartrim / Fablon or coloured vinyl tape which is available from PMP. Alternatively an iron-on film such as Easycoat can be used (Easycoat comes highly recommended and is a polyester film with excellent shrinkage properties)
14. Fit control linkages and adjust to obtain required throws (see flying section).
15. Fit tip tanks if desired using Velcro.

Flying

1. Set the controls to give the following movements for initial flights:
   • Elevator +/- 12mm
   • Ailerons +/- 15mm
   • Flaps (if fitted) +/- 7mm
   • Rudder (optional) +/- 30 degrees
2. Adjust balance to within recommended limits (100mm +/- 5mm from LE). Prototypes required 20 - 40gms of lead in the nose. Check alignment of wing and tailplane and wing to tailplane incidence (bottom of flying surfaces should be parallel). Laterally balance wing and check that it is not twisted. If the wing is twisted, twist back in the required direction and re-smooth covering tape with warm iron. If model is fitted with flaperons check zero flap is in fact zero flap otherwise performance will be impaired!
3. Please remember all aerobatic manoeuvres require energy in the form of speed to perform the manoeuvre. If the model has insufficient speed it will fail to complete the manoeuvre or perform it half-heartedly. Vertical or near vertical dives are not an efficient way to build up speed. A 30 deg. dive is much more efficient. Avoid sudden control inputs. In most cases all they do is scrub off speed and lose height. Try to fly smoothly as not only do the manoeuvres look better but you will be able to perform more of them before having to regain height. With tip tanks fitted and only aileron elevator control the AerMacchi spins well and takes approximately ONE turn to come out of it.
4. Pay particular attention to positioning and where others are in the sky.
5. If the lift is good or you are having difficulty penetrating into wind try taping ballast under the balance point. This will increase penetration and help the model maintain speed through the manoeuvres.
6. The suggested control settings are a starting point and can be adjusted to suit your personal tastes. Adjust the balance point so that when the model is trimmed the elevator is more or less in the neutral position.
7. The AerMacchi will take a lot of punishment although the tiptanks can get knocked off in 'screwed' landing. It is excellent for building confidence and will add another dimension to your flying but please remember if you take a big enough hammer to anything it will break. Store the model away from direct sunlight in a cool place as the CW tape degrades in UV light. Do not rest anything on the Correx tailplane as this will deform it.
8. Finally should you require further assistance or advice please contact us either by letter, telephone, email or visit our website (http:///www.phoenixmp.com) where you will find useful information on sloping etc.

Happy flying

Stan Yeo

AerMacchi 000330