Let the SUN shine !

Airtech Sun review

Introduction

It is not easy being a student! Especially when you have aircraft modelling as a hobby and want to make the most of both worlds.

I came from France to study in UK three years ago and got into the hobby not much later. Since then, I have acquired a few e-powered gliders and aircraft, crashed some of them…but always had a good time. One of the things you have to face when you get into the hobby is the need to go bigger.

I started with a Great Planes Spectra 2.0m, then got an Altus XL (in fact a 1.8m Highlight), now own a Jazz Xtreme flying wing, an Easy Street…but with my flying skills getting better, I had to go for a 2.5 m or so.Here began my search for a new glider. Having purchased the Altus XL from Airtech, I naturally asked them for advice when I thought I was ready to make such a purchase.

Airtech has a very wide range of gliders (distributed in UK by South Coast Sailplanes), some of them able to be e-powered. One of my requirements was that it should have an electric motor (possibly brushless), offer good aerobatics, stay up in light lift conditions and behave well in the windy conditions we often meet here in UK.

As an answer, I was advised to go for their Sun, an all-round slope and field soarer that can be very fast (or very slow) and a very efficient thermal soarer. This is the same glider used by Airtech in F3F/F3J competition inFrance to compete against all-moulded aircraft. It has a wingspan of 3.33m (a bit scary when you are used to flying a 1.8 metre glider!!!) with the new wing (different repartition of the dihedral) and weighs 2.2 Kg to 2.5 Kg in the glider version. But most of all, it is very easy to fly according to its manufacturer.

After much thought and a lot of overtime to put the money together, I took the opportunity of a trip back home to visit to Airtech in their workshop. My Sun was ready, with its white fuselage and wooden wing, along with the Multiplex Micro 3BB for the flaps and ailerons, Graupner C3341 for the elevator and rudder. The receiver chosen was the Multiplex Micro IPD 7.A gorgeous geared brushless motor (Maxon gearbox with a ratio of 3.7:1 and 14.5*10 slim RFM carbon folding propeller) with matching controller were also added to my order. Electronic Model (www.electronicmodel.com) manufactures the Elios 25 engine and the Flash 40/60 controller. This is a french company that produces very high quality motors at a very competitive price.The cells chosen were the new CP 1600 mAh, in the form of 10 cells packs along with another pack of the popular RC 2400 mAh.According to Airtech, this set-up should make the Sun climb like a rocket.I was about to find out the performance of such a combination…

The Kit

The first impression when you receive the kit is that this is a truly quality product. Care has been taken during packaging even so I noticed a slightly damaged flap on its trailing edge (probably done in the workshop) and some marks on the fuselage.

Not many bits come in the box but this is because most of the work has been kindly done as part of the manufacturing process. All the control surfaces are pre-cut and articulated under the skin with a ribbon that is proper to Airtech, the leading edges fitted and sanded, and the servo wells machined in the wing. I would not call it an ARTF kit so.

The box contains:

ü A 1.6 m centre wing panel which is already made (Obechi skinned rigid foam). Two holes have been drilled in its centre for the wing screws. Some aluminium tubes have been moulded for the wing tips carbon joiners

ü Two 85 cm wing tips similarly made with tubes as well.

ü The two pieces that make the elevator (all moving and removable, made in a similar manner to the wing).

ü A built up balsa rudder, providing the lightweight required at the tail end of the aircraft. The rudder can be made removable for ease of transport and the fixation system is provided.

ü The fuselage is made of glass reinforced with Carbon/Kevlar. It comes in a choice of 5 different colours: white, red, yellow, orange and blue. A carbon canopy is also included and already trimmed. The snake outers are already in place with the tail plane crank and piano wires already connected.

ü All the accessories including transparent servos covers, epoxy horns, 2x8mm carbon wing joiners, aluminium rods and tubes, 5mm plywood…

This is no beginner kit either; some building experience is needed to build this superb model.The instructions come in (have a guess!)… French but there are a lot of drawings that should help and for those of you who are not familiar with our language, I will happily give a hand with the translation (South Coast Sailplanes provides English instructions).

Building

All the gluing on the Sun is done with epoxy 5 minutes.

The wings

The first job is to position the wing:The two 5mm plywood pieces need to be sanded and glued. A tip from the instructions is to make a thin joint between the fuselage and the plywood so that they are not in contact. I recommend keeping the fixation system loose for now until the wing has been correctly positioned on the fuselage (check distance wing tips/tailplane and wing tips/fuselage). Once done, the threaded inserts for the wing screws can be glued whilst the previous distances are still being verified. This ensures an accurate positioning of the wing.

The pins that hold the wing tips in position with respect to the centre wing panel then have to be fixed.

Finally, the ailerons and flaps need to be given their up and down movements. To do so, some balsa needs to be removed on the underside. A 4mm drill does most of the job nicely but the rest needs sanding to achieve a nice finish. A thin saw is be used for the upperside of the hinge, and this until the ribbon can be seen. Once this operation is finished, the result should be a very smooth and friction free movement of the surfaces, meaning that they will come back to their neutral position each time.

The tail

I found that the rudder needed cutting because it was too long to fit the tail perfectly. A few minutes are needed to do to sand it to a round shape. The rudder only needs covering with a light film such as Prolite. I decided to use the removable system provided. I glued the 3 nylon hinges into the rudder after covering, making sure they were aligned. 3 other hinges were glued to the tail. A long piano wire then articulates the rudder.The elevator is all moving and also removable. It first needs reinforcement at its root with the provided plywood. I was a bit disappointed when I found out it had to be repositioned. I had to remove the tube and drill a bigger hole, then put it back and fill the space around it with epoxy at the same time as hold the elevator parallel to the wing. This sounds simple but actually requires every bit of attention to make a perfect job.

The fuselage

It is now down to the fuselage to be looked after. Here, only the electronic components need installing and this should take a few hours only. I started with the plywood engine support. The nose of the Sun is already cut to a 42mm diameter.I made three trays, all from 3mm plywood:

ü One for the receiver, which is attached to the tray with a rubber band and placed in between the two holes for the screws.

ü One for the battery with some velcro on it and, since I do not trust velcro for 100%, I secured it with a rubber band at one end so that the battery does not move in flight. The battery tray is positioned at the front of the receiver and behind the servos.

ü The last tray is the servo one. I used a block of balsa in which I cut the servos shapes and then glued it onto the plywood tray. The servos lay flat on the tray so that there is plenty of room to take the batteries in and out.

Radio installation

As said before, I used the Graupner C3341 standard servos for the elevator and rudder along with some Multiplex Micro 3BB for the ailerons and flaps. The controller lays above the servos at the front of the fuselage.I glued the Micro 3BB after having enlarged the servo wells by removing the foam that makes the wing core. The horns are made of epoxy board cut to a nice shape then glued in the surfaces.I also used some Multiplex ferrites which I found very efficient for the ailerons and motor wires.

I installed a Multiplex high voltage plug to connect all the wing servos to the receiver. This allows to quickly plug 4 servos at the time into the receiver.Although the instructions advised the antenna to be kept in the fuselage, tests showed that there was less interference when taped along the outer fuselage.All together, about 19 /20 hours are needed to build the Sun.

I did not cover my model (simply varnished it, which saves some weight as well as looks good) but this can be done easily with vinyl or heat shrink covering.

Flying

I was very anxious before the first flight because I had never flown or even seen such a big model in the air. Of course, I only did it when I felt I was ready for it.

All the throws were verified twice (and set to the manufacturer’s recommendation), my radio programmed, I made sure everything was a tight fit in the fuselage, the centre of gravity positioned…

On a cloudy but quiet afternoon, I headed to my favourite flying area: a big football field on which one can only feel secure, with its thick and flat grass that makes it a welcomeful landing area. After a safety check with engine on and off, I finally launched the Sun.

First impression was a good climb rate, but I did not get that rocket-like climb told by the manufacturer. Nevertheless, the handling was easy and no trim was needed (apart from the one the position the elevator).

It was a very strange feeling to know that I was flying a 3.33m glider after some many times with a 1.8m glider. But an interference problem soon appeared with the motor on. I decided to land using the butterfly mix but some down elevator was needed in the program and the Sun only came down after a long low pass.The climb rate with the second battery was similar and the same radio problem occurred so it was safer to stop there for the day.

I ran the receiver antenna outside the fuselage as an attempt to solve the interference problem, programmed some down elevator (2mm) in the butterfly mix…and the third flight was magic. With no interference, a more powerful battery (charged on-site), I finally got the rocket-like climb. After 30 seconds of motor, the Sun had sufficient altitude to make some tests. With some down-flaps, it becomes a real thermal soarer and can be slowed down a lot.

With no flap mixing, it is a very fast model and produces a magic whistle (probably due to the spinner). The basic aerobatics are good too (with some aileron to flap mixing) considering its size, but it needs a lot of altitude since it comes down very quickly. I also played with the elevator to flap mix (F3F style) and the turn are very tight but not advised from a flat field.

On a day with no lift, I normally get some 25 minutes flights. With the warm days coming, the Sun will stay up for more than 45 minutes when thermalling. Thermal turns are very flat and very little height is lost doing so. The amazing thing about the Sun is that it is very easy to control and so much can be achieved so easily, it looks like one has been doing competitions for a long time.The new CP 1600 mAh give about 2 minutes of motor (3/4 climbs) against 7 climbs with the RC2400. With some practice, the landing can be achieved by the feet using the butterfly mix and the proportional stick.

Conclusion

After some thought regarding its size, the Sun turned out to be a safe upgrade to a 1.8m glider. A good experience with building and flying with ailerons is needed before having a Sun but I think it is very easy to handle and therefore would make a great model for someone who is looking for an upgrade to a 2.0m glider. A competition flyer will also enjoy the Sun because it can be very fast and a great performer once correctly set… and at this price, one is not scared to take it to the field on a busy and sunny day whilst moulded are grounded.

DATAFILE

Name: Sun

Model type: Electric F3J glider (also called F5J)

Manufacturer: Airtech (www.airtech-rc.com)

UK Distributor : South Coast Sailplanes (www.south-coast-sailplanes.com)

Tel: 01202 395 707

Price: 379 euros + p&p (about £240)

Construction: Carbon/Kevlar reinforced Epoxy fuselage

Obechi skinned wing

Wingspan: 3.33 m (130 “)

Length: 1.54 m (60.6 “)

Weight: 2.81 Kg (99.1 ounces)

Wing area: 65 dm²(1007.5 sq inches)

Wing loading: 43.2 g/dm²(0.098 oz/sq inch)

Wing section: S3021

Motor & Controller: Brushless Electronic Model Elios 25 geared 3.7:1 with Flash 40/60 controller

Receiver: Multiplex Micro 7 IPD

Propeller: RFM 14.5 x 10” slim

Servos: 2 x Graupner C3341 + 4 x Multiplex Micro 3BB

Control functions: Rudder, Elevator, Aileron, Flaps, Throttle