A beginners guide to PSS - Part 2

Once you've selected a kit, it will probably need some modification to convert it into a good PSS model. The extent and number of changes you decide to make is really up to you - almost anything will fly if the slope is big enough.

I offer the following for your consideration:

I normally start with the colour scheme, and then decide which kit/plan to build. If you haven't got any documentation, a visit to the reference section of your local library may net one of the collections of Profile publications, or one of the Blandford colour series (e.g. Fighters 1939-1945).



The aircraft in action series by Squadron/Signal publications are good for details, and the Osprey "Combat Aircraft" and "Aircraft of the Aces" series are also very useful.



Failing that, a plastic kit can sometimes be a good source of inspiration. A visit to the local print shop with your colour scheme and the percentage size increase will net you a full-size drawing with all the marking and details to the right size; it might be better to do the initial enlargements yourself on the office photocopier.


Balsacraft Hurricane finished as a tropical Mk1, modified so that it can be used for PSS as well as electric.

Because we're dealing with scale models here, the nose will usually be short compared to the average slope soarer, so we will probably have some sort of balance problem. The kit will usually be designed for an I.C. or electric motor, removing this will require an equivalent amount of ballast unless some of the other components can be moved forwards to compensate. In order of priority:

a) The battery should be moved as far forward as possible; on the Speed 600 kits, a square 1200 mAh NiCad will just about fit (with a bit of packing) were the motor used to go.

b) It might be possible to move the rudder and elevator servos forwards; ideally, they should be just behind the battery if they're accessible below a hatch, otherwise at the front of the wing seat.

c) The receiver should be towards the front of the fuselage, perhaps at the front of the flight battery compartment for a converted electric kit.

If it's a WW2 fighter, the model will probably still be nose-heavy so it might be a good idea to provide a ballast box that will take lead shot, or a flat surface that stick-on weights can be adhered to. Another thing to consider here is that the lighter the tail, the less weight will be required for the front of the model so as you build, look for ways to remove weight from the rear end. Lightening holes is one way of doing this but bear in mind that you need quite a few holes to save a little weight and you don't want to compromise the structure. If your chosen model has an all-sheet tail (as many do), try making a built up version but keeping to the same outline.


Forward locations of the radio installation.

The servos have been moved forward one bay and a plug-in spinner made that contains the NiCad. Expected flying weight is about 35 oz.


Plug in spinner containing 700 mAh NiCad.

Spinner was carved from laminations of 3/8" balsa, backed by a ply disc and covered in three layers of 1.5 oz cloth and acrylic varnish (HSB sealing resin)

A typical power model might have significantly-sized plywood fuselage doublers; you can build it as it is, but it will be lighter and probably strong enough if you replace them with 1/32" or 1/64" ply. Obviously the engine bearers can be thrown away, and we don't really need a 1/4" ply firewall. If the real aircraft had fabric-covered control surfaces, building them up from a core of 1/16" sheet with 1/16" ribs, and covering the finished component with litespan or film can save a useful few grams. If you don't know what the ribs spacing is, guess - that's what I do (...oops).

If the wood supplied in the kit is unsuitable, replace it. Be ruthless. By unsuitable, I mean either;

a) Too heavy - tail surfaces should be cut from medium-light sheet (6-8 lb cu/ft), not stuff you could build a kitchen table out of. Fuselage sides should be medium (8-10 lb cu/ft) or medium-light if the sheet is thick (1/4"+). Triangular or block sections that are going to be sanded and planed away should also be medium-light.
b) Too light - wing leading edges should be medium-hard (12 lb cu/ft) so that they can withstand the odd ding without crushing, this is particularly important if you have a fancy newfangled wing section.

c) The wrong cut - it's no good trying to bend 1/4 grain (speckled) sheet around formers because it will just break.

You may find that the wing might have quite a lot of incidence relative to the tailplane (don't forget to take account of any washout); this is fine for a power model that can employ brute force to beat the laws of physics into submission, but if it's left like that on the slope it will tend to fly slowly unless you fly with a lot of down-elevator (which is of course inefficient) or move the C of G forward to balance out the tail download - and that's when the trouble starts. The faster the model then flies, the more the nose will want to rise, with the result that it will try to pitch whenever you fly through a patch of lift. It's flyable, but it's less efficient and is not the sort of neutral behaviour that makes models nice to fly.

If you have the time and inclination, you might wish to consider adjusting the wing incidence to a more reasonable value. Making generalised recommendations is difficult, but here goes; for a wing section with roughly 2% camber (e.g. E374), I suggest no more than about a degree in effective incidence between the wing and tailplane - that's measured from the point of the leading edge to the trailing edge, after the effect of any washout has been accounted for. A section with about 3% camber (e.g. S3021, E205) will usually be producing enough lift for you to consider setting the wing/tailplane difference to 0 degrees.


Click picture to see a full size version of these wing sections.

Just one final note on this subject; if you decide to change the wing or tail incidence, some aircraft have a definite nose-down sit in the air (e.g. Mosquito, Whitley, Corsair) so it may be more appropriate to increase the tailplane incidence instead of decreasing the wing incidence.

There may be transfers in the kit, otherwise those nice people at Pyramid decals may be able to provide you with some ready-made self-adhesive decals that will be close enough to the right size. Alternatively, with a bit of practice and one of those circle cutter thingies whose name temporarily eludes me, it's possible to cut out your own decals from Solartrim or Protrim.



Letters and other designs can be cut by tracing onto the backing sheet, or if a full-size photocopy of the letter and a couple of layers of trim is taped to the workbench, a few minutes careful work with a scalpel and a straightedge will produce some perfectly acceptable stick-on decals.



Applying stick-on decals is easy if you do it wet; take off the backing sheet under water (with a few drops of washing-up liquid added), wet the surface of the model and slide the decal into position. When you're happy with it, carefully squeegee the water out from under the decal and leave it to dry.

Quite a few successful PSS models are covered in film, Solarfilm is widely used as it's cheap and light, but you have to be careful with some of the lighter colours, as they may be slightly translucent. Monokote isn't readily available in this country (don't get me started on this!), but there are some good camouflage colours available if you're prepared to order from the states.


Jet trainers make good PSS subjects.

Profilm has good colour density and can be painted with enamels if it's scuffed up with wire wool first, Solarfilm will also take paint if it it's treated with a THIN coat of Prymerol - too much will make it wrinkle. Solartex can be used and will make the model stiffer, also it will take car spray paint, but it is heavy and does tend to soak up an awful lot of primer.

My personal favourite at the moment is Profilm. It has good colour density and has a reasonable range of colours, and can be painted with enamels if it's scuffed up with wire wool first although many people don't bother and just spray straight onto the film. If silver is used as a base colour, you can get an instant "worn" look by carefully scraping away some of the paint at the nose, leading edge, removable panels and wing root. The procedure is to give it a wipe with a cloth soaked in cellulose thinners first to get rid of any finger marks, then a tack-cloth (if you have one) to get rid of any dust. After that it can be sprayed with enamels. Several people have had excellent results with small Humbrol spray cans; an airbrush can of course be used if you have one. Water-based acrylics can be used but they will tend to flake off with time.

The level of detail you add is really down to personal preference. I always try to fill the cockpit with a pilot (Pete's Pilots do a useful range), an ejector seat and a gunsight/HUD if appropriate - I can't be bothered with the instrument panel and switches.


Bumpy Greens Modeltech Mustang cockpit detail.

Real aircraft usually have bumps, intakes, pipes and who-knows-what protruding from the surface, and it's usually only necessary to simulate the most important features.


Underside view of Hurricane showing vokes filter and radiator finished in medium-weight glass cloth and epoxy, primed and rubbed down ready for painting.

The trick is deciding which ones they are! I usually use a photograph, photocopied to about 3" x 5" - if it doesn't show up on that image, it doesn't get modelled.

Small details like cannon bulges can either be carved from Jelutong or Lime (from model railway suppliers), or moulded from acetate sheet.

Panel lines are sometimes a controversial subject. Some people use a very thick black pen the draw them, but personally I don't think you should be able to see them at all from more than about 10 feet away. What you're usually seeing on the full-size aircraft is a slight difference in colour between different panels, rather than a hard line between each one. It is possible to get this effect by using several different shades of the same base coloured film or paint, but it's an awful lot of work compared to a couple of hours spent with a straight edge and pen.

A very quick way to achieve the effect of different-coloured panels is to mask off the desired panel and using very fine pencil lead shavings or chalk pastels on the end of a finger, gently shade the panels in opposite directions (see part3 of Daren's Modeltech Mustang review).


Panel line detailing with pencil shavings.

I suppose I should come straight out and admit that none of my panel lines are accurate; with a few exceptions, they're all guessed and interpreted from 3-view drawings. I do try and make the left hand side of the model accurately mirror the right side, but that's as far as it goes.

I use a 6B pencil if the surface has been painted, or a Pantone cool grey (11F) marker for film surfaces, with a flexible plastic straight edge held in position by blobs of blu-tack. The landing gear doors are usually simulated by cutting the right shape out of Bristol board and drawing round it with a (thin) indelible black marker.

Some aircraft had gear doors that overlapped the wing surface rather than lying flush (e.g. Hurricane), these can be simulated by silver Solartrim applied before painting and then the paint can be carefully buffed off the edges when dry.

Building a kit for PSS is just like building any other model. I should just point out, however, that a model that is nice to fly would usually have some or all of the following characteristics:

a) Centre of gravity optimised - I have a page that provides some pointers.

b) Wings laterally balanced - this makes more difference than you'd think.

c) Left and right ailerons both move exactly the same amount

d) No warps.

e) Elevator and aileron movement harmonised - this is purely a matter of feel, and can only really be done once the C of G is in roughly the right place.

Go fly PSS.

Next month I shall be discussing The Competition Scene and outlining what's involved for those of a vaguely sporting nature.

Article by Andy Blackburn for Bumpy Green Model Aerodrome
7th April 2002