Review of Eraser EPP Combat/Trainer - Canterbury Sailplanes

By Peter Collier

Introduction

Canterbury Sailplanes recently offered the opportunity to review a re-production version of their latest release the EPP (Expanded poly propylene) Eraser. Described as a Trainer and Combat Slope Soarer it follows on from the Dodger and Solo models previously offered as their trainer model. The contents of the kit include everything required to construct the model except a modeling knife and other basic tools plus your choice of colour tape and radio. The first reaction on opening the kit was o the aerofoil section, a Selig 3016, is semi symmetrical and very thin hen compared with a previously constructed and flown Dodger. This resulted in a great feeling of anticipation imagining what the flying performance would be like. The quality of the EPP cut finish is excellent requiring very little if any sanding prior to spraying with adhesive and covering with tape.

EPP is an excellent material for construction of foamies, compared with EPS (Expanded Polystyrene), EPP is more resilient when deformed such that when compressed it returns to its original shape and is more resistant to tearing. On the other hand EPP is not quite as stiff as EPS and for this reason the strip ailerons are made of EPS. On balance an EPP model would be expected to be almost totally indestructible.

Assembly

The instructions are comprehensive and need to be followed step by step, although several minor omissions were noted and these have been communicated to Canterbury Sailplanes for modification. The experience of having previously constructed a Dodger and Zagi (flying wing) using foam construction helped overcome the omissions in the instructions. This also led the builder to race along to the point where "when in doubt read the instructions", so some back checking was required to ensure all steps were completed

The precut holes in the fuselage for correct location of the radio gear certainly helped. Neat fit holes for the battery, Rx and the aileron and elevator servos, needing slight enlargement in this case, ensured correct location of the radio gear with only a small amount of lead being required behind the battery to achieve the correct location of the c of g.

The internal mounting of the servos is a new (to the author) innovation and some resistance to removing the mounting lugs was encountered until it was realised that in many installations the lugs are not used anyway. Internal mounting of the servos reduces aerodynamic drag and the extra care taken to ensure free movement of the pushrods and correct surface movements in both directions is worth the effort. For once everything is taped up any changes become difficult. The wires between the servos, receiver and battery can be squeezed into slots cut into the foam. Some doubling back of the wires is required to take up excess length of wires. Care should be exercised when cutting slots not to cut any wires. A switch can be similarly mounted, but an additional hole is required. In the case of this review model the switch was mounted on the right hand side of the fuselage below the leading edge of the wing, with the "ON" position forward for the obvious reason that an enthusiastic launcher may otherwise switch the radio "OFF" at the moment of launching. Some precautions to prevent switching "OFF" during combat action may also be worthy of consideration.

Covering with tape

It was noted that the EPP foam was more difficult to get the tape to stick compared with EPS. The recommendation is to ensure that an adequate amount of the spray adhesive is used; otherwise the tape may detach and bubble.

The strapping tape supplied is barely sufficient and must be used strictly as directed; otherwise none will be left for the aileron horn reinforcements. It is probably a good idea to add the 4 x 50mm pieces to the ailerons early on in the construction, to ensure this important area is covered. Take care not to waste any tape by allowing it to fold over and stick to itself. Any short falls can probably be tolerated nearer the wing tips.

The clear tape included in the kit is sufficient to cover the model, but the alternative use of coloured packaging tape from the same maker is a worthwhile alternative. Although on closer inspection the clear tape appears to be superior in strength and stick ability and initially covering the model with clear before colour is probably a good idea. A range of basic colours is available from selected Warehouse Stationery stores, such as the one in Porirua. The use of PVC and cloth tapes is not such a good alternative as they are heavier and the PVC tape is liable to move

The finished weight was 700 gm, just over the 650 gm expected, maybe in part attributed to the radio gear being slightly heavier.

Finishing Touches Taping around the edges of the Corflute tailplane, with the clear tape supplied, covering the holes is likely to reduce drag. A fillet of glue where the two pieces of the tailplane join improves the durability of the tail.

Flying Performance

Two test glides in the paddock behind work showed the Eraser did not require any trim adjustments. Gliding was effortless in almost still air, so concerns about low speed performance were unfounded.

Next destination was the Wellington slope at Titahi Bay, the wind at the airport was 35025KTand the Mana weather site showed a NW at 11KT, ideal conditions for a trial flight. At the top of the slope the wind was more like 30-40KT, into the air and the Eraser showed good penetration. A quick sortie to check out the extent of the lift and the handling in no time the Eraser had easily gained 300 to 400 feet altitude and handling of the model was excellent; next it was into some aerobatic maneuvers.

Rolls - sharp and crisp with a dab of down while inverted and level rolls were possible.

Loops - a series of increasingly tighter loops showed no tendency to snap roll.

Inverted flight - half roll and slight down elevator for level flight, circuits with left and right turns were easily executed.

Stall turns/Wing over - after a high speed across the slop run pulling up into a steep climb and the slightest touch of windward aileron allowed tail to weathercock around and complete the turn.

Spin - some difficulty in initiating a stall, but once speed was reduced full elevator and aileron resulted in a tight spin with fuselage at about 45 degrees.

Snap rolls - both left and right and very tight, once coordination of the elevator and aileron movements was mastered.

Outside loop - this was a total surprise and would not have been attempted if the Eraser's ability to climb while inverted had not been noted. In level flight gently increasing down elevator to increase speed all the way to full down resulted in effortless diving outside loops. Similarly while flying inverted, a shallow dive to increase speed and then full down elevator produced a climbing outside loop.

Dive and pull up - a vertical dive of 200 to 300 feet and pulling up into a steep climb regained most of the height lost, perhaps assisted in a small part by the strong lift.

Landings - landings at Titahi Bay have never been easy for this pilot, but the Eraser EPP is the first model seen to bounce off the ground. Seriously though with the clean aerodynamics the Eraser could be positioned easily for touchdown and with more practice rebounds will be reduced.

Light air performance could not be tested, a bit of a problem around Wellington, but Canterbury Sailplanes claim this is excellent and based on the test glides is expected to be the case.

Inverted spin - was not attempted because the pilot didn't think of it, to be tried on next flight.

Summary

A great slope soarer that is easy to fly, very responsive, fast and stays where you put it. As a trainer model it needs to be flown by the pilot, rather than fly itself, given that it is virtually indestructible an adventurous novice will soon gain confidence in their ability to control the model knowing that it will survive many prangs along the learning curve. As an advanced model it can be pushed really hard and aggressively, and probably beyond the limited repertoire of this pilot, above all no undesirable vices were found which made it a delight to fly.