Impulse

1500mm EPP Crash Resistant Sports Aerobatic Slope Soarer

Designed by Stan Yeo

Produced by PHOENIX MODEL PRODUCTS

Introduction

The Impulse is a stylish, high performance, crash resistant, sports aerobatic slope soarer designed to meet the ever increasing demands of the discerning everyday sports flyer. It will do all manoeuvres expected of a flying wing i.e. sustained inverted flight, loops, rolls and bunts etc., and more besides such as a bun-roll (an outside loop with a roll at the bottom). Few models claiming to be aerobatic slopers can do this manoeuvre let alone a flying wing! Despite this the Impulse is a graceful docile model to fly and will thermal turn with the best of them.

As with all flying wings a control mixer is required to mix the elevator and aileron controls. Although this can be done using an on-board mixer better control set-up will be achieved using a computerised transmitter. Please do not attempt to use plastic geared servos - they do not last long in EPP models!

Whilst our EPP models are a little more complex than most of their contemporaries, hence the performance, building time has been kept to a minimum and typically a quarter to a third that of an equivalent wood foam model.

Tools / Materials Required

The only tools required are a modelling knife and spare blades, 180 grade Wet & Dry sanding block, a set square, soldering iron and a hand drill with a 5mm bit. Glues required are spray impact adhesive (Stikatak), runny super glue and 12 minute epoxy. Please observe safety precautions!

R/C Equipment

The R/C Equipment used in the prototypes consisted of two metal gear micro servos (HS81MG / 85MG) a 2/3 AF size Rx flat Nicad pack plus a JR R700 / Hitec Slimline / Webra 6 / Futaba 147F Rx. All the items are available from PMP at competitive prices.

Building the Fuselage

1. Lightly sand the fuselage sides, top and bottom with 180 grade wet and dry to remove the 'release' agent. Remove dust with a small brush or vacuum cleaner.
2. Mark position of 4.5mm distance pieces to fuselage sides ensuring you have a left and right side!
3. Superglue 4.5mm sq. strip and triangular nose strips to fuselage sides.
4. Superglue wing seats in position.
5. Superglue nose former and the other four 4.5mm distance pieces to one fuselage side ensuring they are all perpendicular (use set square). Check dowel former can be slid in position.
6. Join fuselage sides together over plan checking that the fuselage sides are correctly aligned using set square.
7. Cut 1.5mm fuselage top to length and superglue in position.
8. Repeat Step 7 above for fuselage bottom allowing for wing dowel plate.
9. BUILD WING
10. Construct Wing Nut block assembly as per plan. Slide into and hold in place with scrap foam rubber. Slide into position the 6mm ply Wing Dowel plate.
11. Fit the wing to the fuselage and mark position of wing dowel hole on dowel plate. Tip - wet end of dowel tube with felt tip pen to leave impression on dowel plate. Ensure dowel hole is in middle of dowel plate and drill dowel hole. Do not allow centre of dowel hole to drift towards bottom of fuselage as this could prevent wing fitting snugly in wing seat.
12. Superglue dowel former in position. If necessary, slide former 'in & out' as appropriate to compensate for any inaccuracies in drilling dowel hole.
13. Fit triangular strip to front of former (see plan).
14. Fit wing to fuselage and locate position of wing nut assembly.
15. Glue nut assembly in position.16Glue EPP sheets to fuselage sides using spray adhesive (spray both surfaces). Allow a couple of minutes for solvent in adhesive to evaporate before fitting EPP to fuselage. Allow the EPP to extend past the nose former by at least 12mm (see plan). Also remember this is a ONE shot operation!
16. Trim the EPP to shape of fuselage using White Spirit to lubricate knife. The best tool for this operation is one made from a broken piece of hacksaw blade approximately a 75mm long. Grind the teeth off without getting the blade so hot that it loses its temper and goes soft. Sharpen blade on a whetstone or oilstone so that you could almost shave with it! The advantage of this blade over commercial blades is that it is flexible allowing the 'handle' to be bent out of the way when cutting the EPP to achieve an acute cutting angle.
17. Fit 6mm square strip to base of Fin at front.
18. Glue Fin in position checking that is perpendicular to fuselage.
19. If applicable fit optional 3mm dia. Carbon rods in the Fin (see plan).
20. Glue plastic aerial tube / Fin fairing to Fin leading edge using impact adhesive such as Evo-Stick. Tape in position until glue is set (24hrs).
21. Glue 10mm thick EPP to fuselage top again extending EPP forward of the nose former and stopping at Fin base.
22. Glue 8mm thick strip of EPP to fuselage bottom at nose. Again extending beyond nose former.
23. Glue 10mm thick EPP to rear of Fuselage and trim to shape.
24. Using spare 10mm thick EPP glue foam to base of Fin and trim to shape.Glue approximately 150grams of roofing lead to front of nose former in cavity formed by EPP sides. This is typically 2mm thick and equates to 5 layers of lead. Flatten lead before fitting. Roofing lead is available from the scrap yard at approximately £1.00 a kilo.
25. Trim EPP in front of nose weight to provide flat surface on which to glue EPP nose-block.
26. Fit nose block and shape fuselage i.e. round corners using sharp knife and 180 grade wet & Dry (use dry!).
27. Cover fuselage using CW tape. Overlap each strip by 6 - 10 mm or 1/4 to 3/8 inch. Use Film Iron to remove wrinkles around compound curves. Temperature required for this operation is fairly critical. Do not dwell in one spot too long to avoid damage to the foam. Use white spirit to lubricate cutting knife.
28. Excess impact adhesive can be removed using white spirit.

Building the Wings.

1. Lightly sand wing surfaces and remove dust as before. Trim and sand spar slots to accommodate mainspars. Unfortunately cutting tapered wings with spar slots result in a tapered spar slot. Remove waste from wing bracing slots.
2. Remove waste from wing bracing slots.
3. Fit top wing spars using Epoxy keeping spar bracing slots free of Epoxy. Place packing tape along spars, place wing on a flat surface. Hold flat with weights until epoxy set.
4. Trim spars to length.
5. Fit 6mm sq trailing edges using epoxy again keeping bracing slots free of epoxy. Use masking tape to hold spar in position whilst Epoxy sets. Trim to length.
6. Dry fit bottom mainspars and trim to size.
7. With wing upside down fit wing brace and bottom wing spars. Note trailing edges should form a straight line i.e. not be swept back or forward.
8. Fit rear spar brace and trim to size when epoxy set.
9. Fit rear wing brace using epoxy.
10. Manufacture Elevons and wing centre by laminating 0.8mm ply and balsa trailing using spray impact adhesive. Place under weight until adhesive has properly set.
11. Glue centre section to wing observing wing reflex (apparent up elevator). Refer to wing seat on fuselage.
12. Fit 0.8mm ply ends to centre section and one end of each Elevon.
13. Sand wing tips to shape and trim Elevons to size. Sand to shape.
14. Epoxy balsa block in position at wing join. Bottom of block should be flush with bottom surface of wing.
15. Trim top surface of block to shape of top surface of wing. DO NOT trim bottom of block.
16. Locate centre of balsa block and centre of wing leading edge. Drill hole for 5mm diameter brass tube the houses 4.5mm diameter hardwood wing locating dowel.
17. Epoxy wing dowel tube in place. Mark centre of tube hole on 6mm ply dowel locater in fuselage. Use felt tip pen to assist in this.
18. Manufacture a long drill using 4.5mm diameter piano and drill dowel hole in 6mm ply.
19. Drill for M5 wing bolt. Do not drill through rear spar!
20. Fit 1.5mm ply wing bolt reinforcement and drill hole for wing bolt.
21. Construct Pronged Tee nut housing as per plan and using wing to find correct position glue wing nut plate assembly in position.
22. Mark position of wing servos (plan drawing is NOT full size. Position of servo is dependant on servo lead length. Allow 30mm from end of plug to servo lead exit from wing for connecting to receiver extension lead when fitting wing. Note servo arms both point outboard of wing.
23. Cut rectangular hole for servo in wing ignoring servo mounting lugs.
24. Cut slot in EPP for servo lugs and fit servo so that it is flush with top of wing. Note gap between top of servo and bottom of wing. From block of EPP removed for servo from wing slice off the required amount and fit in this void.
25. Remove wing servos for covering.
26. Shape wing tips.
27. Spray wing with spray adhesive and cover wing with GW tape. For torsional rigidity cover the wing with CW tape diagonally. There is no need to wrap around rear spar but do overlap by 5 - 10mm at leading edge. For smooth finish do not overlap CW Tape. Use film iron to remove wrinkles at tips.
28. After covering fit aileron servos. Cut vertical slot in wing to hide servo leads.
29. Cover wing with either coloured vinyl tape or an iron on polyester film (NOT polypropylene it stretches!). This is necessary for two reasons, one to decorate the model and secondly to protect the CW Tape from the effects of ultra violet light. If film covering roughen surface of CW Tape a lightly spray with impact adhesive.
30. Cover Elevons in an iron on film in suitable colour. DO NOT use CW or vinyl tape.
31. Hinge Elevons using Sellotape diamond as shown on the plan.
32. Fit control linkages and adjust to obtain required throws(see flying section).
33. DO NOT replace the plastic mini-snaplinks with metal devises. In the event of a mishap the plastic snaplinks will break thereby reducing the risk of damage to the aileron servos.

Flying

To achieve the design performance of any model care must be taken in setting up the controls and balancing the model both laterally (wing tip to wing tip) and longitudinally (nose to tail). The Impulse is no exception. Control movement must be symmetrical i.e. the same for both Elevons.

1. Set the controls to give the following movements for initial flights: Ailerons +/- 18mm Elevons +/- 6mm Balance Point 125mm +/- 3mm from LE at back of dowel former.
2. Adjust balance to within recommended limits. This can be done by taping a hexagonal shaped pencil along the bottom of the wing at the balance point and resting the model on a flat surface. Prototypes required a small amount of additional nose-weight to that fitted in the nose.
3. Check than Fin is perpendicular to wing. Adjust wing seat as necessary.
4. Launching the Impulse is easy. Place the thumb and second finger either side of the fuselage just in front of the wing leading edge. The forefinger is placed on the underside of the wing. This is important as the forefinger ensures the model is launched in a level attitude and stops you pulling the nose down and launching the model into the ground! The transmitter is naturally help in the free hand.
5. Remember all aerobatic manoeuvres require energy to perform them. If the model has insufficient speed it will fall out of the manoeuvre or perform it half-heartedly. Vertical or near vertical dives are not an efficient way to build up speed, 20- 30 degree dives are much more efficient. Avoid sudden control inputs. In most cases all they do is scrub off speed and lose height but they could also result in a violent 'flick' roll. Try to fly smoothly with the minimum of control input 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, paying particular attention to positioning. Be creative and set yourself targets for each flying session.
6. If the lift is very good or you are having difficulty penetrating into wind try ballasting the model. This will increase penetration and help the model maintain speed through manoeuvres. Note when adding ballast take care not to disturb the balance point. We have found the optimum ballast to be about 200 grams. Over-ballasting any model will lead to a degradation in its performance, often accompanied by a tendency to tip stall.
7. The suggested control settings are a starting point and can be adjusted to suit your personal tastes. An indication that the balance point is about right can be gauged by the amount of down elevator required for smooth inverted flight and how the model recovers naturally from a dive i.e. sticks in neutral and no pilot input.
8. If you are using a computerised transmitter program in positive (JR) Exponential on the Aileron and Elevator controls. This will 'soften' the controls around the neutral position and facilitate smoother flying particularly on the elevator control.
9. Impulse 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.
10. The MH64 wing section is very efficient and performs well in light lift so with good ballast selection Impulse will cope with almost wind / lift conditions you are prepared to fly in.
11. 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.

Impulse Design Features

1. It uses the highly efficient MH64 wing section.
2. It has an ultra slim, EPP clad, ply box fuselage. Not only is the fuselage extremely, strong overcoming the detaching nose syndrome of other similar designs, but it also has up to 50% less cross-sectional area than most if its contemporaries. Fuselage volume has a large impact on a model's performance. The more air that is displaced the higher the drag!
3. The Impulse is a two piece model. The wing is attached to the fuselage via an easily replaceable M5 nylon bolt and a 5mm hardwood dowel (housed in a brass tube). These are designed to shear in the event of a 'mishap thereby minimising any resultant damage.
4. The Impulse has excellent directional stability. This is due to the combination of a generous fin area coupled with a respectable tail moment arm and the almost flat fuselage sides. Round fuselages look good and are arguably more streamlined but do not offer much resistance to the air to counteract any tendency to 'fishtail' or aid spin recovery.
5. The hardwood mainspars extend all the way to the wing tip. This not only stiffens the outboard section of the wing but offers protection to the control surfaces should the model land on a wing tip.
6. The top spar is thicker than the bottom spar. This significantly strengthens the wing as most wing failures in flight are due to the top surface failing in compression.
7. The leading edge of the Correx fin is dressed with a 4mm diameter plastic tube. This not only provides a fairing for the fin leading edge but acts as a conduit for the receiver aerial improving reception (better aerial positioning).
8. The thin balsa control surfaces are laminated with 0.8mm ply to add stiffness and make them more 'ding' proof.

Happy flying, safe landings

Stan Yeo

Impulse 050306