If this kit was packaged in a glossy box and
made available from the shelves of your local shop, flying fields throughout
the land would be choc-a-block with examples of this excellent glider.
It could become in modern times what the Inchworm was in the 50 s and
60 s. As it is, it comes in a strange, if stout, wood grain effect box,
with no lettering or picture, and is only available to those in the know
- more is the pity.
The design is around 2 metres wing span and is almost a dead copy of Peter
Allnutt s Checkmate which was drawn and described in FFN2OO, a publication
which celebrated 200 issues of Free Flight News. I hope Pete got some
acknowledgement for the design. I think that they have been produced ready-to-fly
in China as well - the Chinese Checkmate !
Minor differences in the kit include different dihedral layout - flat
centre section, which makes withdrawing the wing joining dowel easier
from the fuselage, and the sheeting layout at the wing root. The tailplane
has less ribs than the original , and has a bottom spar which is webbed
to form an I-beam. The fuselage pod now runs right to the back of the
wing and is not cut away as on the original.
Junior could be described as an intermediate glider design. It isn’t
a rank beginner’s model - not because of its construction (which
is more straightforward than many so-called starterjobs), but because
of its systems and performance capabilities. Here is an FlA (A/2) design
which could be built right from the contents of the kit and flown in competition
at the highest level - well, at least until the seven minute evening fly-off
round!
Apart from the front fuselage covering shell and rear boom, Junior uses
no hi-tech materials or techniques. It is a straightforward balsa, spruce
and tissue (albeit polyester tissue!) design, which should be an encouragement
to those who find the latest constructional trends alien to them.
From the outset I decided to build the model as per , without being tempted
to add those little things you prefer, learned through long experience!
This way you get a true assessment as to how the average purchaser of
the kit might fare.
The only tools used (or required) were the usual balsa knife, razor blade
(sharp for trimming the tissue), sanding blocks and pliers.
Glues were UHU Hart balsa cement, aliphatic resin P.V.A., thick cyano
and 5-minute epoxy. Thinned dope was used to stick on the tissue.
CONTENTS OF THE BOX
There are no printed or die-cut sheets as we know them. All parts are
neatly and accurately cut, taped together with the appropriate number
on the tape. Unwrap as you go. The stripwood in my example was not of
the highest quality, but in general was quite adequate. Some pieces were
not particularly straight. J.O D s remark that warped strip leads to warped
surfaces came to mind, but harking back to my earlier statement, I didn
t replace anything.
THE WING
The wing halves are joined by two wire dowels - a long front one, 4mm
(approx. 9 S.W.G) and a short, incidence locating rear one, 1.5mm (approx.
18 S.W.G). The main dowel is smaller in diameter than I would have used
(my current designs have 6 S.W.G. or 5.5mm.), but there again, Junior
s wings are probably more flexible. I did change the rear dowel to 14
S. W.G. purely to bring it in line with all my other models, which use
that size.
The main joiner passes straight through plywood ribs with no ali. or brass
tubes. This is quite satisfactory as there is substantial
sheeting top and bottom. It is a good idea when assembling to slide the
appropriate ribs on to the dowel so that the holes exactly line up. Also
remember to pack up the ribs at the L.E and T.E. by lmm. to account for
the sheeting thickness. The ribs are slightly over length and should be
trimmed from the rear only to fit snugly in the ready-cut slots in the
trailing edge.
The wood provided for tip spars in my kit was rather soft so I increased
the size of the web to 1/8" (3mm.) for a couple of bays at the dihedral
joint. Conversely the tipblock wood was unnecessarily hard, so I carved
it down as much as possible consistent with keeping the profile shown
on the plan. The dihedral joint consists of a large, soft rib at the end
of each panel. These are sanded chuckglider fashion to provide a good
fit at the correct angle. I used 5minute epoxy tojoin the panels and when
sanded down, formed a cement skin top and bottom, so beloved by the late
Bill Dean on his designs!
The root sheeting provided was quite hard, but went over the aerofoil
curve easily enough. A knife and metal rule should be used to trim up
the edges for a good fit.
Finally, remember it is easier to cut the taper in the tip trailing edges
before
joining to the centre-section panels.
With all that root sheeting I thought that the wings would turn out heavy
but surprisingly, without the dowels, they weighed 140 gm. brut and 135
gm. sanded.
TAIL
I actually started with the tail to get the hang of the construction.
It is a very simple piece of building. Note that all the gussets etc.,
in the wing and tail are cut rough from a lump of soft block and then
sanded flush with the surface after assembly - quite a novel, but good
idea.
I find it easier to get a good fit with webs by building in the sequence
- bottom spar, webs, top spar. This seems better to me than gluing in
the spars, then trying to poke the webs between them.
The tail sanded, but uncovered weighed 7.5 gm.
FIN
The fin and rudder are from 3mm. sheet and need to be sanded to a thin,
symmetrical section. They are joined with small metal hinges which push
into the wood. One was missing in my kit, so I joined the two parts with
a sewn cotton hinge - C/L fashion. I have used this system for years and
it has never let me down. There is a neat little metal horn which should
be epoxied onto the bottom of the rudder firmly. It is not symmetrical.
If you want the model to turn RIGHT make sure that the shorter side i.e.
for the tension is to the right. The plan shows a rubber band for tension.
This is bad news! With a circle tow system with no position stops at the
rear end, i.e. at the rudder, the tension needs to be consistent if you
try to get the same rudder settings all the time. If you have to change
the band (and they do perish), you often change the tensions and hence
the rudder settings. A small coil spring gets over all this. Mike Woodhouse
sells good selections.
FUSELAGE
The fuselage consists of a front part, the pod, which contains the timer
and towhook (which comes ready fitted), and a boom which fits onto a spigot
on the pod. The boom appears to be of carbon and comes painted white.
The taper seems sharper than the typical British product, making for good
stiffness. At the rear, the tailplane mount is from a light alloy, and
is a good fit on the boom in the right position. The pod consists of a
wooden core, with holes for timer position and ballast. It is perhaps
lime and is quite heavy, as we were to find out later. The works are covered
with a carbon sheath which fits accurately and lines up on the small pin
which secures the towhook.
The timer, which is supplied with the kit, is single function, the D/T
arm coming out of a scroll. There is no on/off switch, like a Tatone or
K.S.B. The motion is stopped by a thin wire rod, (approx. 20 S. W.G.),
which is connected to the latch on the towhook. When the ring is fitted
on the hook, and the latch is engaged, the rod goes forward and interrupts
the works of the timer. Even when it swings back to circling position
the wire still engages the timer. However, when the latch opens, and the
ring falls away, the latch arm moves just that bit further back to allow
the wire to move away and permit the timer to start.
Naturally, this needs some fine adjustment to get it all to work! It helps
if you put a kink thus in the push/pull wire near the towhook. Then, by
bending it in or out with a pair of fine-nosed pliers you can alter the
effective length. The trouble is, once the carbon shell is glued in place,
and the timer screwed in position, there is no way that you can get at
the works . The answer is to screw the timer directly to the hardwood
core, and get everything working while it is relatively easy to get at.
Now enlarge the timer hole in the carbon cover so that it neatly clears
the timer faceplate. The carbon is quite easy to cut using a heavy blade.
On top of the fuselage pod are mounted two screws which adjust the circle
and glide towhook positions. They are housed in alloy bosses which are
a push fit in the wood of the core. They need to be cyano-ed in place
to be effective. I guessed the amount of nose ballast required by temporarily
assembling the model, and hammered sheet lead into a block which easily
fitted in the space provided. This was epoxied in place. Epoxy was also
used to glue on the carbon shell, many rubber bands holding it close to
the core as it dried. A certain amount of work was necessary with the
sanding block to take away the excess carbon and to streamline the nose
entry.
Turning to the boom, the fin was securely glued in place and holes made
for the auto rudder line exit near the fin, and D/T line entry, near the
front. A good way to make holes in carbon or fibre-glass booms is thus:-
Wrap the boom with masking tape at the position required. Tap a pin through,
using a small hammer. Now using a fine, pointed file rotate between the
fingers to open out hole to size required - in this case about 1/16" (l.5mm.).
Remove masking tape.
I must confess I did not use the metal auto-rudder line as supplied. It
seemed far too stiff to me, and I replaced it with light weight Laystrate
. Plastic coated trace wire, as sold for pike fishing, would be even better.
Linking up the A/R to the towhook is made easier by the following method.
To the appropriate cam on the towhook fix a short length of wire line,
say, 6" (l5cm.) so that it projects well past the spigot of the pod. Fit
it to the towhook with a crimped hook. Make a similar loop at the other
end. Of course this should all be done before the shell is fitted.
Now pass a longer piece of line down the length of the boom through the
hole in front of the fin. The piano wire wiggle shown on the plan is an
excellent idea which joins the line to the horn on the rudder and allows
easy fine trimming. Again, using a crimped loop, join the main line to
the short tag from the towhook. The boom can now be fixed to the pod using
epoxy on this important joint. Having already fixed the fin on to the
boom makes it easier to line things up.
The nylon line for the D/T is fine as supplied. Ifyou have to replace,
use 121b. breaking strain. Finer doesn’t stand up to repeated D/T
landings. Much heavier doesn’t go round the corner at the rear end.
Make some provision for adjusting the pop-up angle of the tailplane.
Finally glue on the tailmount, making sure that the tail will be square
to the wings when the model is assembled.
COVERING AND FINISHING
The Junior kit contains white polyester tissue for covering, very similar
to the Salzer tissue supplied by Mike Woodhouse. The panels are ready
cut to size with a slight overlap. This tissue has a rough side and a
smooth side, although this is not immediately apparent. The contrast is
much greater after doping! You want the smooth side outermost. The other
absorbs too much dope.
For those who have not used this material before, it has a definite grain,
which should go down the length of a given panel, but does not like compound
curves - no problem on Junior . It fixes easily in place with dope. Dope
the complete airframe with fulL strength. Let dry, and sand lightly. Now
dope again with a 50% dope/ thinner, and press tissue in place. Dope through
from the top for a really good fix. It is difficult to get this material
to lap round leading and trailing edges, but as it is white, it is not
really necessary. Trim off flush with a sharp razor blade. To shrink before
doping go over the panels with an iron on medium setting. It comes up
like a drum! Be careful not to induce warps, especially in the tailplane.
I used three coats of 50/50 on the wing and two on the tail, sanding with
used wet and dry between coats.
I did not use the stick-on decals supplied with the kit, preferring to
add a bit of colour with doped on Modelspan tissue decoration, numbers
and letters. The fin and wing tips were given a light spray of flame day-glo
for visibility.
Finally, the front fuselage was finished by fine sanding. The carbon was
degreased by rubbing with thinners, and then given three coats of dope/talcum
powder/thinners mixture as an undercoat to the final Humbrol enamel colour.
The table of weights shows that Junior came out way over weight even with
that lovely light wing.
Actually, it worked out slightly less than this, as the C.G. was too far
forward and lead had to be drilled out of the nose to get it where I wanted
it.
FINAL WEIGHTS
Wing
covered, decorated, doped 165 gm.
Tail covered,doped 10 gm.
Fuselage+joiners 275gm. Total 450 gm.
(410 gm. required minimum for FIA)
I know people say that a little extra weight doesn t hurt the glide, but
I prefer my A/2 s to be as near to the 410 gm. minimum as possible, keeping
in mind the comparison of a feather and a cannon ball being dropped from
an upstairs window!
FLYING
Before venturing to the flying field Junior was set up in accordanee with
the plan as near as possible in the workshop. The warps in the wing for
a right hand glide turn were adjusted in the steam of a kettle to be:-
Left outer panel 5 mm. wash out, left inner flat, right inner 2 mm. wash
in, right outer, 3 mnt. wash out. Actually, due to a slight inaccuracy
in my building, the whole right wing turned out to be slightly positive,
compared to the left. This was thought not to be a bad thing in view of
the intended right turn. The tail was flat.
Rudder settings were set up to be (at the rudder T.E. relative to the
centre line of the boom) - tow 2 mm. left - circle tow 10 mm. right -
glide 4 mm. right. A slight bias to the right came in from straight tow
accelerated for zoom launch.
The C.G. was 51 % of the wing chord.
Early March this year saw some good flying weather in Oxford, so I was
able to give Junior virtually a week of hard testing - thermal conditions
in the day - relative still air at dusk.
First test glides showed the trim to be nearly spot-on, with perhaps the
turn a little tight. Not having a helper with me, I solo launched and
circle towed from the off. First tows showed a strong right bias on the
line which was grudgingly moderated in subsequent flights with a lot of
extra left rudder. Jerked launches were quite difficult, the line being
reluctant to leave the model. 1t suddenly dawned upon me that the towhook
had a depression in its horizontal part. This held the hook even when
the latch was open. The answer was to throw the line (without the winch
of course). This gave a perfect release every time.
In free flight Junior had a tight, bouncy, thermal-prone glide, good for
windy weather flying, but I felt a lower sinking speed could be gotten
out of the model with less decalage and a wider glide circle.
My doubts about the wingjoining rod proved correct, and the wings showed
some centre dihedral after a few vigorous launches. This appeared not
the affect the flying, and probably helped the D/T action, which was gentle
and controlled, not the ungainly looking spiral necessary to get high
aspect ratio F1A s down.
Before the next flying session the following modifications were undertaken.
The wash-in was removed from the right centre wing panel. This was to
open the glide and to get away from the excessive left rudder for tow.
The C.G. was moved back to 54% by drilling out lead from the nose and
filling in the holes with soft balsa. This effectively meant that the
towhook was now 20 mm. in front of the C.G which should give less left
tow bias and lighten the model into the bargain. A sliver of packing was
taken from under the tailplane T.E. to restore the glide, which should
also mean that zoom launches could be harder without the looping tendency
which had previously been evident.
Junior is not an out-and-out performance machine, but it sits well in
the air and, carefully flown, responds to the slightest thermal lift.
Despite having no turbulator on the wing (none is shown on the plan),
it recovers well from disturbances with little or no rocking around. The
coming season should ascertain its competition worth.
For the rubber or power enthusiast who wants a glider on the side without
a lot of hassle, Junior is the ideal choice. It would also be ideal for
the vintage enthusiast who might wish to break in, by way of a complete
kit, to relatively modern glider technique. If the bug bites hard, there
are more advanced kits produced by W-Hobby, like the Sija with its tubular
carbon spar, reviewed by Phil Owens in the Aeromodeller a while back and
two versions of the Superba which are state-of the art bunters with full
carbon construction.
Remember - gliders are green, good fun and keep you fit.
**FMD&C** Andrew J. Crisp.
FLYING MODEL DESIGNER & CONSTRUCTOR Vol.7. No.3. |
