Technical Tips

In this page I will attempt to help free flight scale modellers with a few ideas, be they new to the discipline or a seasoned campaigner.

All suggested technical tips, building ideas and flying techniques etc. used from this site are strictly at your own risk.
If more common sense was used by all, the world would not be going to hell in a hand cart!

Not an awful lot has changed in the structure of this type of model since Eric Coates DH9a was published in Aeromodeller. 
The advent of carbon fibre has proved to make a better structure. This is evident in the very clean lines and warp free models of  Bill Dennis.
If you wish to have a go at Free Flight Scale and you have a knowledge of basic model building you can do no better than to use the plan of the DH9a as a guide to building any similar type of model. Plans are available from www.xlistplans.demon.co.uk No: FSP 1243, along with most of the published classic free flight scale models, and lots more. You can also use plans available by other modellers that use a similar format to Eric e.g. Bill Dennis or Andrew Hewitt. My Martinsyde Elephant is available from the Xlist plan service and the Sopwith Dove plan is available from Model Flyer www.modelflyermagazine.com Ref no MF112 and featured in their June 2003 issue.
I can also recommend the book Scale Aircraft for Free Flight by Eric Coates and edited by Vic Smeed. Published by Nexus Special Interests. This book is taken from the series of articles written by Eric Coates that was published in Aeromodeller in the early 1970s. The photos leave a lot to be desired but most of the book is still relevant for our purposes.
I have adopted a few different building techniques in the structure of each of my models but this is a matter of personal preference. Some of these I shall detail. I will also include some of  the more established building practices for those modellers newer to Free Flight Scale.
If you have any relevant techniques that you are willing to share please contact me.
No matter how long you have been a Free Flight Scale modeller there is always a learning process, improvement and hence progress. But success in a competition can be quite elusive. You get 5 minutes to do the business and sometimes it seems as if 5 hours would not be enough. It took me 20 years, off and on, to win the Super Scale Trophy.

Wing Tips

  
These I have found to be a constant problem. In competition you have to take off to be competitive and if the model ground loops it inevitably grinds away the wing tips. The photo is self explanatory. To reduce this problem to a minimum I use the standard 1/32nd balsa sandwich and edge it all the way round with the appropriate size aluminium tube, 1/16th o/d here. Blend it in with the leading and trailing edges. This is far easier if you anneal the tube first. The old trick for annealing aluminium is to coat it with soap lather. On heating, this turns black at about 400 deg. C, which is the perfect temperature. Cool. Bend to shape around the wing tip or suitable former. You will probably need a slightly smaller radius than the actual shape of the curve. Tack the tube in place with cyno and when quite happy apply cyno all round. Another advantage is that the tube produces a very clean shape.

Tail Surfaces

                
This method is very standard now on this type of model. The sizes quoted are for a model with a wing span in the region of 45'' span. Adjust as appropriate. The sandwich core is 1/32nd .8mm medium balsa with ribs and riblets of 1/16th 1.5mm balsa top and bottom, positioned as required. The outer edges are of 3/32nd balsa. These are shaped around the corners by denting the inside edge with a thumbnail. Should you feel that the structure is too flimsy a fix might be  to "paint" the core with cyno. The sharper eyed visitor will have noticed that the Elephant surfaces, left photo, are edged with ali tube using the technique as described above. There is a small weight penalty but the added strength and very clean edges make up for it. The choice is yours. The Handley Page tail unit has 16 separate pieces.
These tail surfaces must be braced as per the real aeroplane. Use tinplate tags through the re-enforced core and brace with fine piano wire soldered to these. I have been known to brace these warped so beware.

Fuselage Bracing

     
Ever wondered why your model rattles after some use and, no doubt, some heavy landings? 
In order to prevent any undue distortion or twisting of the fuselage it is common practice to fit diagonal, non scale, balsa braces along the fuselage where required to help prevent this. Problem. In a hard landing the fuselage is stressed beyond the limits that the balsa will tolerate and ping loose leaving balsa pieces to jangle up and down inside the fuselage. My solution is to brace the fuselage with dark grey or black button thread (cotton is not strong enough) in a similar fashion to the rigging on the real aeroplane. The thread is zigzagged up and down the fuselage in as longer lengths as is practical. I apply only as much tension as is needed to remove any slack in the thread. It is important not to over tension as this will invariably twist the fuselage. When quite happy I  tack the thread with cyno in all the places it touches. If this thread is continued as far forward as possible it can bee seen in the cockpit which is a bonus statically. Ensure that the thread is glued well before covering particularly at the points where it wraps around the longerons and spacers etc. and has been sanded away. Two more plus points. It has almost no weight penalty and looks good through a translucent covering with no 4x2 logs where there shouldn't be any.

Silk Over Tissue Covering

This topic has been covered in many articles before but I make no apology for doing it yet again as this is the most important aspect of the appearance of the finished model. It seems we all have our slight variations on how this is done but it is generally done in the same fashion. Before I describe the method just a few notes on materials. 
Tissue
I have used both Japanese and lightweight tissue but the larger models that I currently favour are covered with the lightweight variety. Bill Dennis, on the other hand, builds models that are usually smaller than mine and he favours Japanese tissue. It is just a matter of personal preference. Dope will pass through lightweight so making adhesion of the tissue very much easier than the Japanese which has to be adhered carefully before doping, particularly on the undercamber of wings etc. I find the lightweight much more forgiving to use and with the larger model the very small weight penalty is negligible.
Silk
There are many types of silk available and supply can be very inconsistent. We are only interested in the very lightest grades. Esaki silk is the favourite but even with this make there have been inconsistencies in the quality. So beware. The cost is a bit steep but as I am only producing a contest model every couple of years it is not too crippling. My Sopwith Dove uses a realistic linen coloured silk purchased as an end of roll bargain from a silk shop in London's Soho. So there are other more cost effective options around. If you find a source buy as much as you can reasonably afford as sods law dictates, and next time around there will be nowt about. I have squirreled away a few square yards of a slightly heavier weight silk that I will use to cover a Premier Lion, a large power cabin model for the Bowden Trophy. But I suspect, like most scale enthusiasts, that I will need at least another lifetime to complete my "build next" list.
Method
Lightly sand model and give a coat of 50/50 dope/thinners to the structure/covering contact surfaces. Sand lightly. Cover the model with your preferred tissue in the normal way. Steam the tissue. I use an old saucepan with an angled lid to direct the steam. (I get a good telling off if I use the kettle) Allow to dry and pull tight. Apply two coats of  50/50 (shrinking) dope. A VERY light sanding between each coat. One coat I found to be not enough as the tissue goes into a soggy wrinkled mess when the silk is applied . Yuk. Allow to dry out, over night at least, pinning down any panels that may be vulnerable to warping (bending and twisting that is not the Star Trek, "she cannee take anymore Captain", variety) The silk is cut to shape, keeping the weave and weft square on to the panel you are covering, with approx' 20 - 30mm overlap. Esaki silk is starched and can be handled quite easily. Minimise the fold lines and creases in the silk by ironing with a cool iron, you won't get them out completely. Don't worry, this will not be a problem. To adhere the silk use wallpaper paste mixed to the standard consistency. Place the silk on the panel to be covered ensuring that the weave is square. Static will help to hold it in place. From the centre of the panel, using a soft mop brush, brush the paste through the silk working out to the edges. Any creases in the silk will brush out. Allow to dry. I use a hair drier to speed this up. All the panels can be done in a day not a week. Be careful not to get it too hot. Trim the edges and glue with more paste. Allow all the panels to dry out completely. Again pin down any panels that may warp. I tend to leave them for at least 24 hours. At this point the panels should be quite taught and technically flyable. If there are any panels you are not happy with it is very easy just to peel the silk off without damaging the tissue and recover. If you wish to add rib tapes now is the time. I use heavyweight tissue for 1/8th scale and lightweight for 1/12th. The Handley Page does not have any. At 1/18th scale the width of the ribs showing through the covering is sufficient. Anyway with that number of ribs and riblets I would have lost the will to live half way through. Fix in place with the paste. Again it is easy to remove and redo any if needed. What we need to do now is seal the silk. Use 2, possibly 3, coats 50/50 NON-shrinking dope or banana oil. There is enough shrinking properties in the doped tissue to keep things taught. More shrinking dope may exert too much shrinkage and over time risk warps creeping in. They may anyway but we don't want to encourage them. A VERY light sanding and you are ready for the colouring.

The Betto Tape Ploy

First obtain your Betto Tape. If you are not familiar, this is a fine type of masking tape with low tack properties.  Available from D Knight Ltd, Castle Road, Rowlands Castle, Hampshire, PO9 6AS. A list is available of all Derek Knights products. Other tapes, e.g. Scotch Draughting Tape, will work but not as well.
     
In left photo there are two uses for betto tape. The click picture is deliberately large to demonstrate the points.
On the real HP the wings folded back for storage. The panel shown is a fan like arrangement with a wire trailing edge that collapses when the wing is folded back. On the model these are separate, solid, units held in place with stub dowels and magnets so when the wings flex they can come away easily. Too easily as it happens. Problem. They are green and so is the grass it lands in. Wonderful camouflage and I can play hunt the triangle for ages. The solution is to paint betto tape strips the same colour as the model and cut thin strips to fix the panels in place. This will hold them and the low tack qualities of the tape will allow them to let go if they need to in a heavy landing. The gap, which should not be there, is also covered up. There is only one strip fitted in the photo to indicate their use.
Can you see the other use? To the left of the panel, in line with the windows, there is a temporary patch two inches long using the coloured tape. Almost invisible.

Wheels

  
The red wheel is plain for a sports model and the white wheel is on my Sopwith Dove.

Wheels were never my favourite items to make and the following method works for me.
Use aliphatic glue so that the wood is easy to sand. PVA, epoxy and  superglues are too hard.
Sandwich 3 discs of balsa, of appropriate thickness and slightly over diameter, so that the grain crosses in different directions to make it strong in any direction. Fix 1/64th ply discs to the outside of these. (1/32 for the larger models) To the outside of the wheel glue one disc of balsa thick enough to produce the cone of the wheel spokes. Only one piece of balsa is needed. Laminations of balsa are far more difficult to shape as the glue sticking them together can cause ridges. Drill the centre square to accept an ali tube to fit the axel. This tube must be an inch longer than needed. Roughen the tube with an edge of a file. Coat tube with epoxy resin and slide into wheel. The excess tube should protrude from the back of the wheel. remove excess glue. NO glue in the tube or your stuffed. Obvious thing this but I have done it and spent ages trying to clean out a tube only to find that is was quicker to make new wheel. When the epoxy is completely cured fit piano wire into the tube to prevent it crushing and grip in the chuck of a drill or lathe. Make sure the drill is secure and safe to use hands free. Spin the wheel and shape with sandpaper to the correct shape. Take a lot of care, especially at the beginning when the out of balance wheel tends to vibrate. The rim for the tyre can be shaped using the tyre with sandpaper wrapped around it. If there is any slight inaccuracy in the alignment of the axle this may be minimised by the sanding. This operation is best done outside as the dust it creates tends to make one very unpopular with "she who must be obeyed" as it drifts everywhere. Once you are happy with the shape remove from the chuck and cut the axle tube down to size. Seal the wood with sanding sealer. The spokes are reproduced by wrapping cotton thread repeatedly around the wheel at whatever intervals are required.  Coat with outside spokes with PVA and allow to dry. (I would not normally apply spokes to the inside of the wheels) Remove all the access thread. Cover the wheel both sides in silk or nylon pulling tightly to form the covered spoke appearance. Dope several times. The tyre is best fitted after colouring etc. Superglue and re-enforce with  headless pins pushed through the tyre into the core.

High Stress Wood to Metal Joints

Long gone are the days of binding with whatever thread and a poor glue. Where would we be without epoxy resin?
The photos are self explanatory but here are a few notes on how I do it. I've never had one let go, yet.
Score the surface of the metal parts with a file to create a rough key for the glue to adhere to.
Tube, wire and wood are tacked together using a minimal amount of thick cyno. 
Measure and make quite sure all is lined up accurately. Measure twice, stick once. 
The cyno tacks are easily undone but after you epoxy it you are in deep brown smelly stuff if it is wrong. Cut a suitable width (5mm or 8mm) nylon ribbon (baby bonnet ribbon from any haberdashery shop) about 2" long. Mix 5 min epoxy. Spread epoxy onto sticking part of tape and allow to absorb glue for a few moments. Meanwhile apply epoxy to joint. Nice smooth fillets is what you want. Don't over do it as extra epoxy only adds to the weight. Now one waits until the epoxy starts to set and becomes like a contact glue. Working quickly apply the ribbon to the joint and wrap around as in photo. Pull gently on both ends of the ribbon to seat it snugly around the joint.  
As the glue goes off, and before it goes solid, you can smooth out the joint using your fingers. Wet them first. Saliva works well. When quite set cut away the excess ribbon.
In the first photo you will note that there is additional binding with Boron thread as it is the undercarriage support joint.

Interplane Struts

Another high stress area is the point where the interplane strut is attached to the wing. For the struts I use lime wood, as opposed to spruce, which splinters too easily. Lime is not too heavy and flexible. Tin plate tags are epoxied into the ends of the struts, Note the three holes to improve the adhesion, filed to shape and drilled for the anchorage. In the trimming stages one can use electrical wire insulation to temporarily hold them in place on the strut anchorages and once the model is sorted a more permanent fitting is soldered brass tubing.