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Synergy ACRO

1570mm EPP Crash Resistant Trainer / Sports Aerobatic Slope Soarer

Designed by Stan Yeo



The Synergy Acro is a stylish advanced sports aerobatic EPP model capable of virtually all aerobatic manoeuvres that a model glider can perform. In fact it's aerobatic repertoire is more limited by the imagination of the pilot and the prevailing conditions than by the model itself, particularly if flapperons and coupled flap elevator is used. Building time should be about to 1/3 that of an equivalent wood and foam construction model, i.e. 15 - 20 hours.

Before starting please read these instructions in conjunction with the full size plan and familiarise yourself with the parts. If you do require assistance please do not hesitate to contact us.

Tools / Materials Required

The glues required are thin Superglue, (used for wood joints), 2 part epoxy (12 minute recommended) used for wing spars and braces. Spray impact adhesive, used to glue EPP and prime foam prior to covering. Also required is an external covering to go over the top of the base covering material, which is cross weave filament tape (CW Tape) to decorate the model and stop the ultra violet light damaging the CW tape. This can be a coloured vinyl sticky back tape (recommended) or an iron film. Tools required consist of a soldering iron and multi-core solder, a modelling knife, sanding block and a pair of pliers. A long (75mm) bladed knife made from a hacksaw blade is also very useful. 10mm thick Sundela board is recommended for use as a building board, small fitters square or set square, lead sheet, masking tape, cling film plus a selection of long elastic bands.

R/C Equipment

As a basic three channel model the Synergy Acro requires 2 standard size servos for the rudder and elevator controls plus 2 metal geared micro servos (Hitec HS81MG recommended) for the ailerons, a 4 channel receiver and a square receiver battery pack. Please do not attempt to use plastic geared micros as in all probability a heavy landing will strip the gears and replacing them will cancel out any money saved; besides it could also spoil a good days flying! For flapperons and coupled flap / elevator a 6 channel receiver is required i.e. the GWS 8 channel micro Rx.

Building the Fuselage

  1. Lightly sand ply fuselage side to remove splinters and release agent.
  2. Drill wing dowel holes in ply sides. Ensure a tight fit.
  3. Fit balsa strip longerons to ply sides using Superglue leaving gaps for balsa blocks. Check there is a left and right side !!
  4. Cover plan with cling film and position fuselage sides above plan view of fuselage, using wing dowels to assist with alignment. Position balsa blocks. In conjunction with wing dowels use rubber bands stretched over top of fuselage to position sides correctly. Use set square for final vertical alignment.
  5. Fit balsa block at front and rear of wing, plus block at fuselage bottom under wing trailing edge (TE). DO NOT GLUE DOWELS.
  6. Fit nose former and join fuselage at tail. Fit ply tail seat.
  7. Fit ply fuselage bottom forward of wing TE and ply top at nose, forward of hatch.
  8. Spray with impact adhesive, one side of fuselage and one EPP foam side and allow a couple of minutes for solvent to evaporate. Fit foam side to fuselage ensuring that the 'spare' is at the nose end (required to form cavity for nose weight).
  9. Using sharp long bladed knife trim EPP foam ensuring that it is cut square to fuselage top and bottom.
  10. Fit other EPP fuselage side and trim as before.
  11. Decide which side of the servo the control rods need to be connected for the controls to operate in correct sense. Remember control exit is on opposite side. Insert piano wire push rod into control outer and fit elevator control rod checking that pushrod moves freely. Anchor to fuselage sides in between wing TE and tailplane using balsa strip off-cuts or CW tape.
  12. Fit fuselage bottom again ensuring any surplus is at nose end.
  13. Fit EPP to nose top forward of hatch aligning with ends of EPP sides.
  14. Cut sheet lead into 3 or 4, 30 mm sq. blocks and glue to front of nose former inside EPP foam cavity.
  15. Fit noseblock and trim any surplus.
  16. Remove 1.5mm strip of plastic from Correx Tailplane and Fin along hinge line to form hinge (as shown on plan).
  17. Fit, (using superglue) 10 mm triangular strip to base of Fin to line up with tailplane as shown on plan. Check using set square that fin is square when resting on base. Adjust as necessary.
  18. Mark tailplane centre on Correx and glue Fin in position using Superglue ensuring it is square with the Tailplane. TIP If fin is not vertical after gluing to tailplane, cut balsa strip along its length on inside of lean and insert sliver of thin card to correct lean. When satisfied fix with Superglue.
  19. Cut fuselage top to shape above tailplane seat and relieve inside of fin slot to accommodate 10 mm triangular strip at Fin base.
  20. Epoxy Tailplane to Fuselage ensuring that it is both square and in line with the axis of the fuselage i.e. Fin has not got built in left or right rudder.
  21. Position fuselage top hot wire 'drill' hole for Rudder control rod (use non - Z bend end of push rod). Only heat the last 10 mm. Drill a test hole in scrap EPP - you will be surprised at how easy the foam melts!
  22. Fit rudder control rod and check for freedom of movement as before.
  23. Fit fuselage top. Trim to size as before and radius all corners using a sharp knife and 'carving' action before final finishing with 180 grade wet & dry.
  24. Manufacture hatch.

Building the Wings.

  1. Using epoxy assemble main spar on flat surface as per plan and mark centre line and spar top (determined by dihedral as a result of spar tapes)
  2. Epoxy rear spars to wing TE sections using masking tape to hold in place.
  3. Epoxy one half of wing to main spar. Use a combination of masking tape and not too tight rubber bands to hold EPP in place whilst epoxy sets. Take great care to ensure that wing is properly seated against main spar and equally positioned along it top and bottom. Smooth / remove any surplus epoxy.
  4. Fit TE spar brace. Note this will not be a perfect fit due to wing taper.
  5. Cut out recesses in wing for aileron servo(s). All servos are fitted behind main spar. For twin aileron servo installation, lay wing upside down on flat surface. Position servo behind main spar, stretch servo lead in towards wing joint. Position servo so that the end of the lead extends 30 mm beyond wing join and cut 'snug' rectangular section out of wing to accommodate servo. A long bladed scalpel is required for this operation. Cut small slots for servo lugs and servo lead. Position servo in wing. Turn wing right way up and slice top off 'rectangular' block to fill cavity above the servo. Remove servo and glue insert in position. Repeat for second servo.
  6. Shape leading edge of ailerons according to wing servo installation (see plan).
  7. Check length of ailerons, adjust as necessary. Shape tips (ailerons & wing)

Covering Wing

  1. Before starting covering remove any dust that has collected in the foam pores with a vacuum cleaner.
  2. Lightly spray (nozzle 60mm from work) the wing with impact adhesive and allow a couple of minutes for the solvent to evaporate.
  3. Lay a strip of CW tape along edge of trailing edge such that the overlap is equally spaced between top and bottom surface. Allow tape to overlap wing joint each side by 50 - 60 mm.
  4. Apply the next layer of tape on underside, of one wing panel, again overlapping the wing joint by 50 - 60 mm. Allow for wing taper by overlapping first strip at root by 5 mm and abutting rear spar at tip. Repeat for opposite wing panel.
  5. Repeat Step 4 for top surface of wing.
  6. Repeat Steps 4 & 5 until wing is covered. Where there is loose tape around compound curves slice tape to allow it to overlap. The technique for leading edge is similar to that of fuselage corners, i.e. hold tape at right angles to wing surface and run long bladed knife along tape using opposite surface as a cutting guide. Lubricate knife blade with White Spirit.


  1. Check fit of wing to fuselage and wing alignment with tailplane. Adjust as necessary.
  2. Remove control push rod if fitted and block ends of tubes to prevent ingress of spray adhesive.
  3. Spray fuselage with impact adhesive. Allow 2 or 3 minutes for solvent to evaporate.
  4. Start taping fuselage by laying first strip of CW tape full length of fuselage in line with underside of tailplane. Repeat for opposite side. Lay second strip alongside with an overlap of 8 - 10 mm. Trim, using long bladed knife lubricated with white spirit, by using fuselage bottom as a guide for the knife blade and using free hand to keep tension on tape whilst cutting. It may be necessary to place weight on fuselage during this operation to stop it moving whilst trimming the CW tape.
  5. Repeat above until fuselage is covered. Treat the Fin / Tailplane joint as a separate item.

Final Covering

It is recommended that the top surface of the wing and the fuselage is covered in an opaque material such as a coloured vinyl sticky back tape or iron on heat shrink film such as Profilm or Easycoat. There are two reasons for this, one to protect the base covering (CW tape) from the effects of Ultra Violet light, the other simply for decoration. For this type of model we recommend the vinyl tape as it is cheaper and is considerably quicker and easier to apply. Remember a sports model's flying takes priority over looks. Even so a more than creditable finish can be achieved with the coloured vinyl tape.

If covering with coloured vinyl tape, use a similar procedure to that of the CW tape. On the rudder elevator wing, to prevent the tape lifting at the trailing edge, overlap with Sellotape Diamond. Sellotape Diamond is also used to seal the leading edge of the tailplane and fin to reduce drag. The coloured vinyl tape we supply can be shrunk slightly with a cool iron if required to remove small wrinkles. After covering fit wing dowels (use bent piece of wire inserted in dowel holes from inside of fuselage to determine external position) DO NOT GLUE DOWELS. Hinge ailerons using Sellotape Diamond.

Equipment Installation

Rudder Elevator Controls

After covering installation of the radio equipment can be carried out

  1. Assemble Rudder & Elevator servos onto their balsa blocks. Do not glue into place yet. Please note it will be necessary to offset the rudder servo to allow use of a longer servo arm to achieve the required rudder movement.
  2. Fit Rx battery in nose along with Rx and switch harness. Position rudder and elevator servos in fuselage ensuring they do not foul wing dowels or aileron servo (single servo installation).
  3. Check position of balance point. Adjust as necessary. This may require repositioning of rudder elevator servos.
  4. When satisfied dribble Superglue down sides of servo mounting blocks to secure. Use offcuts of 6 or 10 mm triangular strip at corners of front and back of servo mounting blocks to provide added support.
  5. Remove servo arms from rudder & elevator servos. Zero trims on Tx. Switch on R/C equipment and zero servos.
  6. Fit piano wire pushrods to servo arms (pushrod underneath servo arm) and install pushrod/servo arm ensuring arm is as near to neutral as possible. If using computerised Tx use Sub.Trim menu for final adjustment.
  7. Fit control horns and assemble snaplinks to threaded adapters. Check depth of hole in threaded adaptor. With control surfaces in neutral mark end of adapters on pushrods and allowing for depth of hole in adapter cut pushrod to length.
  8. Remove snaplink assemble and using a pair of pliers, spring loaded with a rubber band, tin the inside of threaded adapter hole. Do not spend too long on this operation as you will melt snaplink!
  9. Replace snaplinks on control horn and with control surface in neutral solder in place.
  10. Check controls for correct sense and range of movement. This may entail connections the rudder pushroad to outer hole on servo arm and inner hole on control horn to get maximum movement. It will probably be the reverse for the elevators as less angular movement is required.

Aileron Controls

  1. Cut away CW tape and install aileron servos.
  2. Cut slit along wing, each side, 1 mm wide, 3 mm deep to accommodate servo leads. Bury servo leads in wing and cover slit with length of 25 mm wide CW tape.
  3. If using non-computerised transmitter (Tx) plug Y lead into aileron channel in Rx and connect servos. Check ailerons are operating in correct sense i.e. on application of Left aileron the left aileron moves UP. Use servo reversing to correct if necessary.
  4. If using a computerised transmitter (Tx) plug aileron servo extension leads into the aileron and flap channels on the Rx and connect servos. Set transmitter up in Wing Flapperon mode and using Sub-Trim menu to align aileron servo output arms (look along underside of wing). Check for correct sense and adjust if necessary using Servo Reversing facility. If no matter what you do one function is always operating in the wrong sense swap the channels the servos are plugged into. This should cure the problem.
  5. When satisfied servos are set up correctly CW tape in position.
  6. Make a female template of the mid-wing section and slide over wing. This is used to set the ailerons to follow the line of the wing section.
  7. Manufacture aileron pushrods as per plan and fit. Adjust nylon clevis as necessary to achieve neutral (see above)


  1. . Set the controls to give the following movements for initial flights:
    • Rudder +/- 30 deg.
    • Elevator +/- 12mm
    • Ailerons +/- 15mm
    • Flapperons (if fitted) +/- 6mm
  2. Adjust balance to within recommended limits. Prototypes required 50 - 80gms of lead in the nose. Check alignment of wing and tailplane and wing to tailplane incidence (chord lines 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 in position. If model is fitted with flapperons check zero flap is in fact zero flap otherwise performance will be impaired! (see Prepare to Flap article on website).
  3. The Synergy Acro is not a beginners model but if you lack the relevant experience we suggest you get an experienced model flyer to test fly your Acro for you. We also recommend you take out third party insurance. This can be obtained through the British Model Flying Association (BMFA) Tel No. 0116 2440028.
  4. 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. Try stringing manoeuvres together i.e. do a stall turn and allow the model to gain a little extra speed to do a loop or roll on the crosswind leg before doing a stall turn in the opposite direction. Pay particular attention to positioning and set yourself targets for each flying session.
  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. On the fully aerobatic version confirmation that the balance point is correct is usually indicated by how little down elevator is required to maintain inverted level flight.
  7. Synergy Acro will take a lot of punishment. 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. The CW tape used for covering also degrades in ultra-violet light so store the model in a relatively cool place away from direct sunlight.
  8. The Synergy Acro has a fully sym-metrical section so do not expect it to stay up as well as an equivalent flat bottom section model in light winds. It won't. This is why nearly all kit manufacturers avoid using wings with fully symmetrical sections for aerobatic slope soarers. We are almost unique in offering a selection of slope soarers with fully symmetrical section wings without which the model, in our opinion, would not be fully aerobatic and able to do some of the manoeuvres it can.
  9. Finally should you require further assistance or advice please contact us either by letter, telephone, email or visit our website ( where you will find a number of useful articles on various aspect of model flying.

Happy flying

Stan Yeo

Synergy 021004


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