Once more into the Breach.....

by Steve Davis

How to Choose Your Weapon

As a result of a Sunday afternoon outing to Lasham for the SSS Scale Competition 2000, I was smitten with Colin Bond's 3^rd Scale Wilga tug and decided ;I should get one of those Typically Maisey got in there first and ordered the 1/4 scale from Alex Frisch, so I sat back and waited to see what turned up. Six months later when he began to fly it I thought ;I should definitely get one of those!

But which size - or 1/3 scale? The merits of the 1/4 scale being its handy size and smaller cost. The merits of the 1/3 scale are presence and visibility at altitude. Having chewed it over for a month or two more I came to the conclusion that the 1/3 scale version was just too big and what was needed was something in between. A revisit to Alexs website proved very timely as he had just announced the arrival of a 1:3.5 scale model. So fate having taken a hand so nicely, I placed my order.

The Power Struggle

Choice of engine was the next important decision. Alex recommended without hesitation, King Engines. 80cc being adequate and 100cc being plenty. As with most things in life I believe you can never have enough power and a close inspection of the King range revealed a 140cc engine producing 14 horsepower and weighing only 1/2lb more than the 100cc engine. Easy decision then! A phone call to Alex Frisch to confirm my choice solicited the comment ;Oh my god!. So with the kit on order and the engine choice made I felt confident that I had the right combination to tow anything the brothers Brigg dared throw at me!

Six Weeks Later.

A call from the freight forwarder confirmed the existence of a rather large box awaiting collection. ;No problem I said ;Ill be there in a tick. An hour later saw me on my way home with the back doors of the van struggling to contain a portacabin sized box! Upon opening the box I discovered a kit of superb quality and 12 black bags full of polystyrene chips (it was three days before we found the children again!).

Contemplation

I tried to read the instructions but not knowing any German this proved to be a fruitless exercise. I was, however, able to confirm from the diagrams that all parts were present and correct. For an experienced builder the diagrams proved sufficient since I had my own construction techniques and preferences that I intended to employ. Closer inspection of the parts revealed that they were very accurately made. All the positioning marks moulded on the fuselage to indicate where the undercarriage and wing joiners etc could be trusted and the finish of the moulding was excellent. There were no pinholes and the seams were clean. I was concerned initially about the flexibility of the floor of the fuselage but this has since proved groundless.

The wings are white Styrofoam with 1.5mm veneer skins bonded with epoxy resin and again the consistency of the panels was the best I had seen.

The hardware supplied was adequate with lots of captivated nuts and plated bolts, which I replaced with stainless steel (a personal preference). The tank was from Tony Clark and of good quality as with the fuel system accessories. I included a Dubro fuel filler valve here to help with the refills.

Construction

Fuselage

All the window apertures have to be cut out by hand, but before doing this some internal woodwork is necessary to stabilise the structure. The apertures can then be cut with a hacksaw blade, the radius corners finished with a flap wheel and the straight lines finished with a fine file. I strengthened the area of the fuselage, which would see the majority of the undercarriage loads with carbon fibre cloth. This was also used around the tow release area.

Over 200 holes were drilled to accommodate the window screws; the positions for these again were marked on the fuselage moulding by Alex.

I discarded the mid fuselage bulkhead supplied by Alex in favour of my own which would also accommodate the rudder and tail wheel servos, this was fabricated from 1/4 inch plywood and epoxyed into position.

The engine mount supplied was for the smaller King 100cc engine and to fit the longer 140cc engine the front was shortened by 1 inch and reconstructed with carbon fibre and 1/4 inch plywood. I also strengthened the 1/4 inch balsa wood fin post supplied by laminating a layer of 1/64 inch plywood to either side and some blue foam ribs were made to help strengthen the fin moulding.

The undercarriage was built as per instructions with the exception of the pivot point of the trailing links. I machined a proper phosphor bronze pivot to replace the cap screw pivot supplied.

Wings -Flap hinges were used as supplied, but I designed my own aileron hinges which consist of an O ring used as a bush and a machined aluminium pivot in the aileron. The O ring gives a degree of flexibility to the overall hinge which helps absorb the vibration in the surface whilst maintaining sufficient rigidity for accurate control. This was used for the fin and the elevator too.

Radio -when reflecting upon my choice of radio I had not only too consider the obvious, such as what size of servo should be used to power the surface in question, but too look more deeply at the safety of an aircraft this size and hence the kind of systems I would need to give me some redundancy in the control system. After some deliberations I came up with the following shopping list:

• 2 receivers, one to control the left hand side of the plane and one for the right (Ive had crystal failure twice in the past)
• Optical isolation of all channels
• Separate servo and receiver power supplies
• Twin servo batteries, 6AH total capacity
• Heavy duty switches
  
  

Equipment Used

• SMC 20 DS Graupner dual conversion receivers x 2
• SM Services Optoisolators x 2
• SM Services battery backer x 1
• 3AH 5cell NIMH cell packs x 2 for servos
• 0.5AH 4cell NICAD x 2 for receivers
• Voltspy x 2

Upon completion the whole model was finished with lightweight glass cloth and epoxy resin flatted back and painted with 2-pack car paint (instructions from Chris Williams here.)

Consternation!!

The maiden voyage took place in Caen during May 2002, upon returning home I visited the local club field for a "tuning" session, coming in for a landing I elected to go round again for another practice approach At that exact moment the engine cut. So with the flaps down, no airspeed, only 20 ft of altitude, no room to turn and too high to force a landing before running out of field I elected to stretch the glide into the next field. You know whats coming and so did I, it clipped the top of the field boundary (a rubbish heap) and rolled end over end!!! Bollocks!!! All that electronic safety gear couldnt prevent the dopey pilot running out of fuel!!!

Back in the workshop nothing much happened until the sick feeling in the pit of my stomach had worn off (about two weeks). Enquiries to Frisch for a new fuselage resulted in a quote of £450, so I repaired the original and two months I later was flying again.

Finally.

Although very intimidating initially, It has proved to be a delight to fly and has real presence in the air.

All the controls are nicely harmonised, the engine produces some 14hp so roll out is very short, vertical climbs are unlimited.

The position of the main wheels in relation to the cg make landing a constant challenge, half flap on approach with full flap for the flair at the end just prior to touch down on the two main wheels is the current method. Then a stab of down to hold the tail up before gently lowering the tail down. Get it wrong and the tail slaps down and a kangaroo session begins.

1/4 scale gliders require only half throttle, 1/3 scale stuff two thirds, and anything Dave Briggs brings needs nitro!

Aerotowing is such a fascinating aspect of RC modelling and neatly combines my love of sailplanes with my interest in large power planes. Being a tug pilot at a meeting such as middle wallop, is both a pleasure and a privilege. It tests your spatial awareness, landing in the midst of a busy field time after time. As I said earlier the Wilga demands total concentration for each landing, and it is easy to become mentally tired after a couple of hours without a break at which point the likely hood of a mistake rockets skywards.

It is a privilege to launch the gliders. The builders who have invested a great deal of time and money in their models deserve the best launch possible. That means a reliable tug. A focused tug pilot, a good steady climb that the glider pilot is happy with, and the communication of any changes in course or climb rate prior to them occurring.

Enhancements

The coming season will see a set of ball raced main wheels - the existing wheels sport a plain metal bush on a stainless steel axle, over the summer the bush has worn a little so at some throttle settings the wheels rattle on the axle slightly causing the occasional momentary fail safe; a fully articulating tail wheel complete with shock absorber to take the impact when I frequently get the landings wrong. A bulletproof tow release (Re Bills accident at MW) based on a full size version I have acquired. Also on the list is a dashboard and pilot