Back in 1952 a German glider designer, Rudolf Keiser, was beginning to make quite a name for himself. During those early years after the Second World War there was a vast amount of activity going on in glider design and production and Rudolf Keiser played a very major roll in this.

Rudolf Kaiser

I met the man himself some 15 years ago at a model glider meeting in Germany and we became good friends. Sadly now he is no longer with us but his design creations I'm sure will be around for many years to come.

One of his early designs was the Ka-3, a diminutive sailplane of some l0m span – it first flew in 1953. It was simple to rig and extremely light. The fuselage was made from thin gauge steel welded tube and spruce shape longerons were along the fuselage to give it its final shape when covered. The wings and tailplane were of wooden construction and the entire aircraft was fabric covered. Spoilers were fitted on the top of each wing and the landing gear was an ash skid with a single rubber bungee cushion for suspension. The only unusual feature of the Ka-3 was its 'V' tail form. My only personal encounter with a Ka-3 was when I helped my late friend, Jeremy Menzies, refurbish the wings. New ribs had to be made and others repaired. It was during this work that I made up my mind to build a 1/4 scale model of the Ka-3.

With the drawings I had from Rudolf and some from my friend, preparing a set of drawings was no problem.

My previous model scale designs had all been to 1/4 scale but of course they were modelled on subjects that were much larger in the full size i.e. ASK-l3, K-18 both of which had wing spans of I6m so my Ka-3 model would only be 2.5m span. With this in mind I kept the model design as light as possible in its construction within reason.

Constructing the Ka-3 I do not intend to give you a blow by blow account of the construction as space will not permit, nor do I think it will be really required. The Ka3 design is aimed at modellers that have a fair experience of building from scratch.

Fuselage The fuselage construction simulates fairly closely the welded steel tube structure. All longerons are in 3/16" sq spruce or hard balsa. All diagonals are in 3/16"sq balsa. All ply formers want to be in good quality plywood. There are a fair number of metal fittings and these are fashioned from dural sheet. The best method of assembling this type of fuselage structure is to assemble it in a simple wooden jig, a small sketch on the drawing shows the type of jig I mean. Providing the stringer notches in your formers are carefully prepared and the longerons are steamed to allow them to bend easily, then you should not have any problems building the assembly.

On the drawing of the fuselage you will note that there are metal fittings for fixing the wings to the fuselage. This is an exact replica of the full size method; if you consider this to be too much of a good thing then look further on the drawing and you will see a sketch showing a much simpler version of attaching the wings, but you will have to modify the main formers slightly.

When the fuselage is completed in the jig don't remove it; it is very useful at this stage to finish the wings and tailplane and accurately set them up correctly on the fuselage. Other items like servos, mechanical mixer, if used, and control rods can all be installed and checked. The main skid can be added after the fuselage is finally removed from its jig.

Wings The wings on the Ka-3 are relatively simple to put together. However they are different from most models i.e. you should make the wing spars up first from plywood and spruce, as shown on the plan. Add lightening holes as shown but be careful about the quality of your cut line when cutting out these holes. The spars when built up in this fashion are exceptionally strong and are in line with fuselage practice.

When the spars are completed I lay the spars flat on their side and add the L/edge part of the ribs and then add the false L/edge to form the 'D' box. With both D boxes complete lay over the plan and ensure that the main spars are vertical i.e. 90 degrees to your building board, now add your trailing edge ribs and trailing edge. Don't forget to build the 4m/m washout in when assembling.

Ailerons are built into the wing and cut out later on completion of assembly. When you have marked the position of all auxiliary spar notches on the basic wing assembly, cut notches and add spars and ensure that spars are flush with out surface of ribs.

The wing tips are laminated from 1/4" x 1/32" balsa and all laminations are applied in a wet state to assist in forming the contour of the tip. Prior to sheeting the 'D' box you must decide what to do about servo installation. If you happen to have computer radio then the favourite installation would be to install your servos opposite the aileron drive position and one opposite the spoiler. This will cut out heavy linkages and the torsion drive to the spoilers.

The original model of the Ka-3 carried all the controls as laid out on the drawings. However as this was some 14 years ago methods have changed and r/c gear has advanced beyond our dreams.

The tail feathers of the Ka-3 must be built as light as possible so items like the leading edge of the elevator/rudder are made by rolling 40m/m ply around thin balsa formers, and the leading edge of the tailplane is covered in 1/32" med balsa. These items though small all add up when it comes to weight saving at the critical rear end.

Final items like the canopy frame are built up with the wings assembled complete with their flying spars connected to the fuselage. Care must be taken to make a sound job of the support spar fittings as these really do stop the wings from clapping hands unless of course you have opted to simplify the wing fitting to the fuselage.

Going back to the canopy frame, the prototype was made from annealed square brass tube which is easy to bend, cut and solder but if this is not your scene it can be made from thin spruce and ply quite satisfactorily.

Covering The prototype was covered using Solartex apart from the tallplane which was covered in tissue. Being a 'V' tail aircraft the tail is well out of the way of obstructions during the landing process so a tissue covered tallplane has proved quite OK.

The model was finished by applying two coats of 50/50 dope (none shrink) to fill the weave of the Solartex, then it was trimmed in accordance with the full size colour scheme using a cellulose spray.

Final checks and Flying With all the r/c gear installed it is time to check the balance of the aircraft. Make sure that your moveable items such as the RX and the RX battery pack are as far forward as possible and they are in no way interfering with the aerotow release. Check the CofG and if still tail heavy add ballast to the inside of the nose until a satisfactory attitude is achieved.

I always test fly my gliders initially off a suitable hill slope and during the flight correct any slight faults by trimming out.

The day I checked the Ka-3 out it was blowing fairly hard from the SW and having checked all the controls I launched her off. At a finished weight of 4lb l4ozs it felt so light on the launch. The Ka-3 quickly gathered airspeed as I pushed the stick forward to get her away from the edge of the slope and then when I took the pressure off the stick she started to climb at a fair rate. I thought at the time she performed well on the glide for a vintage machine, banking turns are a sheer delight and there was little or no adverse yaw. (Those short wings are doing their stuff).

I tried the stall and the result was a very tame affair, all it did was nod its nose slightly and carried on flying, so I climbed back up to l00ft or so and tried the spoilers out. The effect was instant, she lowered her nose into a fairly steep descent and lost a lot of height very quickly so when I lined her up for a landing later on I only popped the spoilers out half way and she adopted an approach angle of approx 15 degrees which was almost right. Because of the wind strength and lift on the slope the speed on landing was very slow and not, in my opinion, typical of a flat field landing, so what I was really looking forward to was having the Ka-3 aerotowed on a nice flat site and on a good day.

This came very soon at the White Horse Aerotow the following Sunday. Martin Spackman and his trusty tug towed the Ka-3 aloft to around 800ft, there was a good sky with a gentle 5mph wind from the East and quite a lot of cumulus that was growing. The Ka-3 went up behind the tug as if it was on rails and needed little input from the TX on her way up. At 800ft it's a bit small in the sky so your distance sight wants to be good. The colour of the model helped a lot; being basically red it tends to stick out quite well against a blue sky background.

Having released off the tow I flew east over the valley where I picked up considerable thermal activity. I then settled down and enjoyed thermal turns in both directions. The flight handling in this type of environment was excellent and after a total elapsed time of 44 minutes I was well chuffed with the model's capabilities. Because of the very gentle breeze I was able to do a large landing circuit with the spoilers 50% extended, which gave me the correct rate of descent which culminated in a great landing.

The Ka-3 is not a project for the beginner, but I feel it will appeal to many modellers who like a challenge building something a little different. Its performance is excellent considering that it is of vintage status. My advice to anyone considering modelling such a project would be to go to any of the full size vintage glider meetings in the UK and soak up the atmosphere, also the people that fly them are a very friendly bunch of people.