Build your first flying scale model - Chapter 9 - Prop, wheels and final details
Just one or too final jobs to do before assembling the model. Firstly making the headrest from paper. This can be simply cut out from the plan,
and the folds of the two tabs scored with the back of a modelling knife.
The paper can be formed by rubbing it over the edge of a table as shown here. It will curve like this,
which helps when fitting over the headrest former.
I found I needed to alter the shape a little as shown to stop it overlapping the balsa former at the top.
UHU all purpose glue was used to attach the headrest, applying adhesive to both tabs and under the front
face. If you get glue anywhere you don't want it, dope thinners works well at removing it.
The headrest was given a coat of sanding sealer, plus about 1/8 inch onto the fuselage both sides. A specially
cut piece of dry tissue was then applied over the white part and attached by flooding dope thinners through the tissue. The sanding sealer overlap
onto fuselage ensures that the edges stay stuck down as well.
Notepaper was also used to create the main undercarriage struts. A strip was cut, scored and folded as shown.
A length was cut to match the length of the wire leg. I found it necessary to cut away the inside face as shown to get a neat fit.
To give the paper fairing a nice streamlined shape, it was rubbed over the edge of a ruler to curl the paper. The inside faces were
given a layer of UHU glue, and the fairing folded over the wire leg (fold at the front). Any excess glue that emerges
from the join at the rear can be removed with dope thinners.
Here are the finished legs - I think they look so much better than just a skinny piece of wire.
Time to think about the propeller and removable nose block now. This might be a good time to decide what we are going to stick on the front of our Comper Swift.
Here are a selection of possible propellers we could use.
On the left, just for a laugh, is an original Veron plastic prop from a 1950's Tru-Flite kit. It is 5 inch diameter,
has tiny blades, and they do not have any twist in them at all. This is one of the reasons we tended to only get powered glides out of these models when we bought and
built the kits as youngsters.
Next (moving left to right) we have a 7 inch Peck Polymers prop. This is the one Chris Strachan uses on his Swift, and I also had success with one of these on my
second Tru-Flite Jodel Bebe.
To the right of this are a Tern 6 incher, and a modern IGRA copy of the same prop. The Tern is very popular with scale model flyers, including myself,
because it has generous blade area for its diameter and a decent amount of pitch. The freewheel clutch is a weak point, however, and can strip at
inappropriate moments - the IGRA version is beefed up in this area. The genuine Terns can be spotted by the letter T engraved on the prop blades.
Finally, in red, we have a newcomer to the scene, a 6 inch prop by IKARA designed by the famous Czech modeller Loubomir Koutny.
I am looking forwards to trying this one out on my Diels Nakajima Ki43, as it has more pitch than a standard Peck prop, and could be a viable alternative to the Tern. It also has
the advantage of being perfectly balanced when you buy it.
Flitehook in the UK can supply all the illustrated props (apart from the old Veron one!) and SAMS Models can supply all but the IKARA one. Both offer an efficient mail order service.
For this model I decided to stick to the tried and tested Tern 6" prop.
We need a nose bushing as well as a prop, and I find the Peck Polymers nylon ones as good as any.
If you want a clever adjustable one, then KP Aero Models make a nice one (see Useful Adresses page). Due to the lack of room in the nose of the Swift I just went for the smallest Peck item.
Note these can be bought with different internal diameters either 1/32" or 3/64"- the one shown here is for the larger wire size. I had a root through my piano wire collection until
I found a bit that would fit both the bearing and the prop. In fact is was just a touch loose in both, so I employed my bodging skills to reduce the play.
I am a bit reluctant to admit what I did, as it seems so inelegant and low tech. What you COULD do is drill out the prop and re-bush it with some aluminium or brass tube of a slightly smaller internal diameter.
What I actually did was smear cyano glue on a spare piece of wire, and
push it through the prop a few times. The glue collects on the inside of the prop hole and when it sets, the hole is a bit smaller. I did the same with the nose bush. Shocking really. Still, it is quick, and seems to work, and the cyano glue
is probably harder than the plastic used for the prop and bush, so wear should not be an issue.
We need to make a removable nose plug, and I think it would also be a good idea to face the seating for this plug with some thin ply. This will resist wear, and
should mean that if during the trimming you add a sliver of downthrust, it will not dig into the balsa nose when the motor is fuly wound, and thus change the thrust angle.
I aquired a large sheet of 1/64" ply a few years ago from a trader at a model show, and I think it will turn out to be a lifetime's supply. It is
extremely useful as a thin facing material. Here you can see a disc being cut out of the plywood using an Olfa Compass Cutter. This is a very useful tool for
cutting out perfect circles in wood or paper. It is also relatively inexpensive and should be available in most good art and craft shops.
A hole was cut in the front of the disc to roughly mimic the hole we have in the nose, The disc was then attached to the fuselage nose with Cyano.
When the glue was set, the aperture was trimmed with a sharp knife to exactly match the hole in the balsa nose.
I could also not resist sanding the top and sides of the nose to make sure the ply blended in reasonably with the nose. The bare balsa areas show
without doubt why it would have been better to fit this disc BEFORE covering (especially if you are planning a coloured tissue finish)
The removable nose plug is made from two components plus the nylon nose bush. On the left is the part that fits inside the nose, laminated
from three sheets of 1/16" hard balsa.
A hole was cut in the middle of each lamination to roughly clear the nylon bush.
in the centre is the front of the plug, which is laminated from a second 1/64" ply disc plus 2 laminations of hard 1/16" sheet.
All of these were cut out using the Compass Cutter. A hole was opened up in the centre with a round needle file to give a tight fit to the back of the nylon bush.
What may not be too clear from this picture is that the front of the this part had an angle sanded into it. To give you an idea how much, at one side the front 1/16" lamination was taken down to less than 1/32".
This means that when the nylon bush is pushed into the nose, it angles over slightly to sit snugly on the front face. In this way we can build in a bit of down and right thrust.
Adjust the shape of the rear of the nose plug until it is a reasonably tight fit in the nose. Then push it in as shown,
leaving it about 1 mm proud.
Now glue on the front of the plug, making sure you only put glue on the plug rear, not the fuselage nose.
Adjust the position of the plug so that the angled front points down and slightly to the right.
When the glue is completely set, pull out the plug. Hopefully it will not leave the rear part in the fuselage!
The Nylon bush can now be glued in position (using cyano). You will probably have to open out the hole in the rear plug portion a
bit more with a round needle file, to take account of the angle.
Now the plug can be firmly pushed into the nose, and shaped to match the nose contours as well as possible.
This plug came out rather small, and I think if I was doing it again, I would follow Chris Strachan's
example and use his "half a nose block" method. That would certainly give you a bigger opening to get the rubber through.
By putting a length of wire into the bush, you can see the downthrust angle. I have taken a guess at this, as most high wing models require at least some downthrust. I have not measured
the angle, but as usual used the TLAR principle (That Looks About Right). Time will tell if I got it right....
The wheels shown on the plan are a bit undersize, and the plastic wheels
supplied with the kit would have also been rather too thin for realism. Seems a good
opportunity to show you how I make laminated balsa wheels though, so let's make a new pair.
The real Comper swift had quite fat little tyres on it so I decided to laminate each wheel
from 4 discs of 3/32 sheet. The centre two solid, and the outer ones with a hole
in the middle to represent the tyres.
Eight balsa discs were cut out of light 3/32" sheet using the Olfa Compass Cutter.
The diameter chosen was around 23 mm, so just under one inch.
Four of these had the centres cut out, again using the compass cutter, but this time set to its smallest
radius. This is much harder to do than the outer cut, and seems to work best if you use a chopping action with the blade as you
work your way round. You will most likely have to finish off with a sharp knife.
Here are all the bits for two wheels
Before laminating, I find it much easier to shape the inner contours of the tyre now rather than later.
You can start things off using the more pointy end of a sanding block as shown here.
Another useful tool is a roll of wet and dry sandpaper. You can wrap this round a dowel, or just use freehand
as shown here.
The inner hole is unlikely to be perfectly round, so just play around until it looks reasonable.
Use the two neatest ones for the outside of the wheels.
Now we can laminate all four bits together. I use Aliphatic wood glue for this, and place a weight on top to hold
the laminations together while it dries. If your centre holes are not perfectly concentric, ignore the outside,
and centre the tyre on the compass hole in the middle of the centre laminate.
When everything is set, a piece of tube needs to be inserted through the centre of the wheel to act as a bearing.
You can use aluminium, brass or plastic (which is what I used). I have what is probably
a lifetime stock of assorted extruded plastic rod, strut and tube produced by Contrail for the plastic model market.
The hole made by the Compass Cutter needs to be enlarged first. You could do this with a small drill, but I like to use a round needle file
to gradually open up the hole, working from both sides, until the tube is a comfortable push fit.
Insert one end of the tube into the wheel, and rotate the tube between your fingers to see if the wheel runs true. If not, adjust accordingly and try again.
satisfied that the wheel is running more or less wobble-free, apply some cyano where the tube joins the wheel on both sides.
Two options now. You can leave one end of the tube extra long, then use this to mount the wheel in a hobby drill,
so you can use it like a lathe while you shape the tyre with sandpaper. Aluminium tube would work better for this than plastic as it is much stronger and stiffer.
Alternatively, sticking to the minimal tools approach, just cut off the tube close to the hub, and
carve and sand the outer profile of the tyre by hand. If you keep looking at it end on, you can make sure that the
section through the wheel is constant on both sides, and consistent round the wheel. Without turning the wheel
in a drill, you are never going to get it perfect, but once on the model, any iregularities
will be hardly noticable.
Here are before and after photos.
When finished, give each wheel 3 coats of sanding sealer, gently sanding between coats.
The final parts that need making before painting are the wing struts, which are simply cut from 1/16" sheet,
and all the edges rounded off to give a vaguely streamlined section. Each of these pieces will produce two struts, but
they do not need to be cut to length until after painting. If you are going for a coloured tissue finish,
they need to be covered with tissue. Otherwise just give them a couple of coats of sanding sealer.
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