Mad-dog tells us about his enlarged petrol BigUn

Wing: 82.5" Length: 68" Wing Chord: 17.75" Weight: 17.5lbs Engine: Zenoah: 38cc Servos: 6 (futaba 148) Channel: 4 Battery: 2100mAh 6v (5 cells) Receiver: GWS 8 channel Closed loop on Rudder and elevators

I am a member of Chesham Model Flying Club and have been flying power radio control models for 3 years now, but these have been based on the popular glow engines, ranging from 0.15 to 1.20, both 2-stroke and 4-stroke. I wanted to design and build something simple to fly but much bigger, to take a McCulloch 28cc converted petrol strimmer engine which i had aquired.

One of my favourite models which never let me down was my ATS Super Sport which was fitted with an SC53 2-stroke and a weston tuned pipe, this model was very nippy but also reasonably simple to fly. Last year I passed my 'A' Certificate using a model called a Gambler, very similar to the Wot 4 which was another popular model with some of the other club members. This style of model seemed to me the most sensible to base my project of an enlarged model for petrol power.

I borrowed a well known kit from a fellow club member to base my ideas on, but this kit is not supplied with a plan so could not be easily enlarged.

I looked at the components in the kit and roughly based my drawing on this, for the fuselage and tailplane. I produced 1 fuselage side which would give me an idea of the finished model and also enabled me to base a wing around.

For the wing, I turned to my friend and fellow club member John Barber, a well known popular aeromodeller and gas turbine flyer, and also the designer and builder of the Fluff 1 gas turbine model featured in August edition of RCME. I gave him the one side of the fuselage which i had cut and asked if he could cut me a foam wing. He gave me a rib template which he used when cutting the Fluff 1 wing, this wasn't quite big enough so i enlarged it 1.6 times. This gave me a wing span of 82.5", and a wing chord of 17.75", which well suited the fuselage i had in mind. I had to reshape the wing seating to suit the wing and also to make sure the incidence was correct.

The foam for the wing came from Wicks building supplies and consisted of 2 sheets 8' x 2' x 2", which cost just under £10.00. I took the foam to John and along with John Wilkins another fellow club member, we went about the task of cutting the wing.

In the mean time I started building the fuselage with ply sides and ply/blasa formers, with 1/4" top and bottom decking. For the firewall i used 1/4" ply and built side thrust in at this stage. Tailplane was from 1/4" sheet blasa and laminated with 1/16" balsa cross grained. I cut lightening holes in the fuselage, fin, rudder, tail and elevators to reduce weight from the back end. I fitted the engine, under carriage and radio gear. Test balancing looked good.

When i received the cut wing i strenghthened it with 2 x 1m ply braces and sheeted with 1/16" balsa, added and shaped a balsa leading and trailing edge and constructed 2 built up ailerons. Heavy ply was used for the wing bolt plates and 1/8" balsa for the wing tips.

The whole model was covered in 'Cub Yellow' and 'Red' solar tex.

1/4 scale carbon-fibre undercarriage, 1/4 scale tail wheel assembly and 1/4 scale cub wheels where fitted.

At the flying field the initial 28cc engine was underpowered so back to the drawing board. I contacted Practical Models and spoke with Richard Rawle who was very helpful and suggested the 38cc Zenoah would be more suited to the model. I Bought and fitted the Zenoah 38cc and back once again to the flying field with my ol'mate Alan Spicer, aka Big Al, chesham model flying club cheif examiner, who i talked into test flying my big shed. After checking the model over Al ground tested it and hopped it on the runway before taking off, as a final check.

Big Al, went to his flight box and grabbed the trusty and well used bicycle clips, with them in place and a look of concern he opened up the throttle, my model greased down the strip and took to the air in a very pleasing manner. After a couple of circuits of trimming, 2 clicks of up elevator only, he started to loosen his bike clips and put the model though a few paces, stall turns, loops, rolls and a test of the stall which consisted of a wing waggle and a slight drop of the nose, no nasty suprises there. Al flew an approach and greased a three pointer, beautiful...

His comments were summed up in one word - Excellent!

I then changed into my brown chords and borrowed the bike clips from Al. Take off was problem free, flew some circuits, rolls, loops, and pulled off another greaser landing.

The plane is a pussy cat to fly but looks very impressive in the sky, an ideal first petrol powered large model and a very successful project.

I would like to thank my friends John Barber, John Wilkins and last but not least Al Spicer for all the help and encouragment thoughtout the 19 days it took to build this model!!

Watch out for next project, for zenoah 23cc coming soon...

Kevin 'Mad-dog' - fastest builder in the west!