From my own point of view, not only would it have to be suitable for hand-launch, thereby eliminating the usual need for catapult or bungee equipment, but said launch would have to be an underarm lob! Its clear that even the mention of needing a catapult or bungee puts about 90% of electric flyers off trying an EDF model, so together we had a point to prove. After a short development period, then, the model presented here appears to have addressed the design brief perfectly.
POWERTRAIN FOR PEANUTS?
You may recall my 30 Tucano published in RCM&E some eight years ago? If you do you might remember that one of the reasons for its popularity was that the motor, controller and flight battery could be purchased for £55. Who would have thought back then, that I’d be presenting another 30″ flat sheet wing design, but this time an EDF model using a brushless motor and ESC unit, with a Li-Po flight battery, all for just £65? What”s more, this package consumes twice the power (i.e. 200 watts) and at 1700mAh offers double the battery capacity. The future is surely bright.
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The fan unit can be epoxy glued to the wing using the slot for location, but first you’ll have to razor saw the inlet flange to allow the fan unit body to sit exactly horizontal, i.e. at zero incidence. At the same time, modify the top of the flange and the upper mounting lug to later accept the main fuselage boom.
When everything is ready, glue the fan unit to the wing using epoxy or cyano (roughen up the plastic areas to be glued for better purchase) and allow to thoroughly set whilst constantly checking that zero incidence has been maintained. The ailerons can now be chamfered for downwards movement and temporarily hinged in place, this before profiling the rear of the wingtips to match. Incidentally, dont make the hinges permanent until after covering.
REAR FUSELAGE BOOM
When assembled, the tailplane can be glued squarely and centrally underneath the boom, making sure the chamfer in the rear of the boom will allow sufficient up elevator movement. All tail surfaces are made from firm but light 1/8 (3mm) balsa sheet, as is the large rear gusset, which can be cut out and glued centrally along the fuselage pod. Note that there will need to be appropriate cut-outs for the tailplane itself, and for the elevator servo which is mounted beneath (using a very short pushrod for slop-free control) and a 300mm extension lead to connect it to the receiver.
Perhaps the most important thing to get right is that the cut-outs at the bottom not only match the wing curvature correctly but that in making them, the incidence of the rear boom is not affected. On final assembly the wing, boom (and hence tailplane) and motor thrust line should all be in line with no incidence deviation whatsoever.
Underneath, the firm 1/4 (6mm) sheet skid can be glued in place, making sure it mates with the bottom of the rear fuselage gusset – this will be blended in with abrasive paper towards the end of the build sequence, so do remember to leave a small area uncovered.
Wrap each major component before final, permanent, assembly. In this respect, Solarfilm is ideal for the EZE-Fan as its both colourful and strong without adding too much weight. You should be able to cover the entire model from a single pack, but do remember to leave the all-important gluing surfaces clear of film. Oh, and by the way, I always use a contrasting colour for the underside so its easy to tell which way up the model is at a distance. The apertures for the aileron servos should be made at this stage and if desired the servos can be attached using the usual screws or, according to preference, permanently glued in position. After covering, the elevator should be hinged to the tailplane and the servo and linkage fitted. Don’t fit the ailerons just yet, well leave that job until last knockings.
On the plan you’ll see a dotted line in the rear fuselage gusset that highlights an optional cut-out just behind the motor. Before final assembly, simply cut this section out with a very sharp knife or scalpel, and put the piece to one side. This allows the motor to be fitted after final assembly, as there will be sufficient access through the intake at the front to reach the motor mounting bolts and impeller centre bolt with a long screwdriver, albeit at a slight angle.
When the motors in position, the cut-out section can be simply tack-glued back in place to hide the ugly gap, and can even be covered in Solarfilm if required. All you need do in the event of a motor change, then, is remove this piece again to allow sufficient space for the motor to be removed.
The fan unit is now completely sandwiched between the wing and the fuselage boom, this providing an extremely tough assembly which will take a fair amount of punishment. Finally, glue the rear fuselage gusset to the skid, i.e. where they meet behind the fan unit, and then blend the junction of the two parts with abrasive paper. With this, the remaining bare areas can be covered with scraps of Solarfilm.
Whichever way you decide to go, the EZE-Fan provides for simple motor, impeller, ESC and flight battery changes if you later wish to experiment with different set-ups.
Inside the pod you can connect the ESC, elevator and aileron servos to the micro receiver and route the aerial in a way that avoids the fan unit. Along the underside of one wing is the neatest and most effective route.
The entire forward section of the fuselage pod is home to the flight battery, which can be anything from a 1500mAh 10C 3s pack to a 2200mAh 20C 4s pack, depending on the set-up you’ve chosen. These, incidentally, are the extremes of flight battery I’ve managed to use so far, whilst still maintaining the C of G by careful battery shifting. You’ll see from the plan that the C of G is just forward of the dihedral brace but can be moved by up to 5mm each way depending on taste: that said, don’t forget that this is a fan model with no direct prop-wash over the flying or control surfaces so you will still have to fly it like a jet.
FINAL CHECKS AND FLYING
The best approach to landing most EDF models is to fly them onto the ground and cut the throttle as soon as contact is made. I’ve seen many an EDF landing end in tears when the pilot has tried to stretch the glide too far and the model has literally dropped out of the sky. Fortunately, you’ll have no such worries with the predictable EZE-Fan.
Model type: EDF sport jet
Designed by: Nigel Hawes
Wingspan: 30″ (760mm)
Fuselage length: 25″ (635mm)
Wing area: 180sq. in.
All-up weight: 16 – 24oz
Wing loading: 19oz / sq. ft.
Control functions: Aileron, elevator, throttle
Rec’d no channels: Three
Rec’d powertrain: 68mm fan unit with
3300 Kv motor and 3s 2100mAh Li-Po
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