This website is aimed at the advanced pilot mainly. The flyer who has learned to build a decent even if simple stunt capable model, can fly some basic stunt manoeuvres, and is prepared to dig a little deeper into those aerobatic peculiarities. Nevertheless I feel it quite appropriate to include some thoughts concerning the beginning aerobatic ace. It seems that this topic is a little underexposed. While some equipment is available for this skill level, in most cases the commercial solutions are offered without thorough consideration of beginner’s requirements. Just “thinking small” is not the only, let alone perfect solution. Let’s consider several aspects of what kind of airplane might be best suited for beginners.    
There has always been a trend towards the “ half A” size version. Obviously this term associates with thoughts about “ small, simple, easy, cheap”. On first glance there seems to be some merit in these thoughts, and some people like to follow this route ( not a problem if you are an expert already !). However – just as in real life – there’s always a back side to everything.
A small airplane usually builds faster than a big one and it needs less space to store and to carry around. But flight performance is definitely inferior. It’s difficult to control ( even experts hate to fly these little monsters ). It needs all the power of those tiny engines which are more difficult to set than bigger capacities, not to speak of the problems to get these miniature engines started.
If you think those simple RTF (= ready to fly ) plastic toys don’t require high building skills, you are right. Otherwise there’s no learning effect. ( Some might argue that this is not necessary. Please let’s leave this topic for another time ). More on this later.
Easy to fly ? I’ve got a different experience when testing one of these “yoghurt cup” toys before handing it over to the right hand of a little boy. Were it not for the limited strength of his right arm, I’d really have preferred to let him try my “full size” stunter instead which is MUCH easier to control !
Cheap ? I do not support this idea. When watching the activities - and airplanes! - flown by youngsters on my local RC field, I strongly doubt that cost is an issue. Many of these kids are using equipment which amounts to a level of expenses most family fathers would only like to spend if they dare to risk family war. Also, with the advent of Ebay expenses can be kept surprisingly low.
So - in the end this all boils down to a solution which is not more and not less than just “practical”.

There’s still one more aspect left, but this depends very much on your personal viewpoint. If we see aeromodelling as a very interesting activity and ( at the same time ) a highly recommendable means of education, we simply cannot overlook the “building” part of our hobby. In this context “building” doesn’t mean the construction of a product only. In the widest sense “building” also applies to the growth of our skills, capabilities, and character. Building or
producing that final craft makes it so much valuable, and teaches values so essentially necessary in this modern world ( I’m not going to dig any deeper into this topic; I don’t want to put oil into that fire ).
One last thought: if it’s too easy - it’s not worth doing!
As you can see I’ve never been an advocate of small engines. I’d rather prefer a capacity from 2,5 ccm ( .15 ) size up. Only at this size the airplane is capable of flying in a slight breeze, has enough line tension, and allows to execute the simple manoeuvres with sufficient exactness. This engine size will usually start reliably and is easier to set than those midget capacities. Nowadays the 15 engine is about the smallest size available at the local model shop, so one of those popular 20 to 25 size versions is suitable just as well, especially since their weights is still within acceptable limits. Which leads to the

In those ancient days when 15 diesels ( at least in Europe ) ruled the stunt empire, the preferred airplane had a 20 wing area ( about 310 sq. in. ). Today modern engines are definitely more powerful, and considering a 20 size engine the area can be increased accordingly. So a wing area of approximately 22 sq dm ( 340 ) should be practical. Remember that this size airplane is intended to help the raw beginner to survive the first laps - then allow him to dare his hand on some first loops , maybe even to refine these prime shapes. I’m fully convinced that those super simple toys ( which just allow round and round boredom ) have chased away more potential control line flyers from our sport than we dare to admit.

Experts know where to get what they need. Beginners depend on what is available at the hobby shop around the next corner. Construction should not exceed their capabilities. A profile fuselage is fully adequate. It’s been looked at as a primitive form for a long time. But since the advent of these highly popular slab sided RC Depron shelves the flat fuselage is totally en vogue. A flat wing might be suitable for the first ( more or less ) level laps. But we’ll need an airfoiled wing soon, and this will require building another airplane.
When choosing the dimensions for this kind of airplane other aspects should be considered, too. Balsa wood comes in standard sizes. It would be most circumstantial to require splicing in order to achieve certain dimensions of a special design. The design can be tailored to use stock material ( balsa sheets, spar lengths and cross sections, available accessories, etc. ).
A rectangular wing shape is the best solution. Other shapes don’t offer any advantages for this task. Sheet tailplane and fin are fully adequate. Of course the whole design should be as simple as possible. A few thoughts should be spent on fuselage construction. Profile fuselages are prone to vibration problems. To solve these some kind of stiffeners are added. Instead of just using plywood doublers thick balsa layers can be formed into pretty shapes, thus making for a more pleasant appearance without adding much weight. Fake engine cowlings can do the same trick.
I’m fully convinced that a pretty outward appearance can motivate much more than any technical finesse ( on the level we’re talking about here ). And - finally - a pretty shape doesn’t weigh more or fly any worse than an ugly one.
    Over 150 Koala kits have been sold in Europe. Some were even used in a "one design class" contest in Germany several years ago.          
We could easily renounce on a canopy, on undercarriage, on some rounded shapes for wing, tailplane, and fin, on rounded fuselage doublers. Will this noticably reduce building time? NO! It will do nothing for flying qualities, but it will create another boring craft, not only unable to please the eyes of the owner, but also those of onlookers and potential newcomers. At this stage designs are not chosen by their competence in competitive wars. Ease of construction and looks have higher priorities.
      Combining all these aspects lead to the Koala design. The somewhat roundish appearance suggested the name of this cute little animal. If the final product is a little overweight ( as was mine ) flight characteristics may be similar to a Koala bear’s movements : slowly and softly. That’s not a mistake for the intended purpose. Still this airplane can do all round manoeuvres, almost as described in the rule book ( after all, these little dishevelled plush pillows are not very often seen doing square corners ).    
wing span 104 cm
chord 22 cm
wing area 22,5 sq dm
tail span 44 cm
tail area 5,5 sq dm
tailplane 24 % of wing area
weight 8oo gr
CG at 5,5 cm = 25 % chord
airfoil 19 % thickness
engine OS Max 25
propeller 9 x 5