Introduction
KAVAN, a
well-known manufacturer in the world of aeromodelling, has been offering for a
few years a range of EPO (expanded polyolefin) foam kits, planes and motor
gliders. New for 2022 is a pretty cute baby of 2.7m wingspan, a semi-scale
model of the Czech company HpH’s Twin Shark 304TS full-size
glider, a modern two-seater. This is the review of this new kid on the block.
The look of
this Twin Shark is really nice.
A Few Words about the Full-Size Glider
The design
of the Twin Shark 304TS started with the idea of creating a
tandem glider as attractive and performing as well as a single-seater
glider and capable of competing in the FAI 20m
Multi-Seat class. The aerodynamic performance of the Twin
Shark is the result of extensive aerodynamic studies and wind tunnel
tests. It is based on the experience acquired on the single-seater Shark model.
The optimal elliptical leading edge and winglets are made possible by CNC
machining. Additional performance is achieved by the downward tailplane tips.
The spacious cockpit with a one-piece, side-opening canopy provides exceptional
visibility for both pilots. The main cockpit features that made the Shark cockpit
popular have been retained in the Twin Shark. The full-size Twin
Shark is available in a powered version — employing a retractable
pylon and soon in a version with a small and retractable jet engine — a ‘jet
sustainer’.
Nice
resemblance between the full-size model (bottom left) and the scale model shown
in the other photos.
The RC Model from Kavan
KAVAN’s
model is very similar with a high aspect ratio wing with very thin winglets, a
very similar fuselage shape and the same canopy shape with the small recess at
the rear end. Only the tailplane is a little bit different with a bit more
surface, but it still has the characteristic downward tips of the full-size
glider. The vertical stabilizer also has a bit more surface. It should be noted
the kit is manufactured under official license as indicated on the box. Kavan
has even gone to the detail of providing a flyer of the full-size glider,
should you wish to change the RC model for the real 20m version!
The
advertising brochure of the full-scale glider provided in the kit.
A Very Complete Kit
Now let’s
take a closer look at the contents of the box. The kit arrives in a large
cardboard/polystyrene box, very well designed, but very bulky which will
nevertheless remain perfect to store the model or to transport it even if it
takes up a lot of space in the boot of the car. The Twin Shark is
only offered in an ARTF (almost ready to fly) version. Only the propulsion
battery and the receiver are missing. No options either, everything is in the
box!
The bulky
cardboard box which hosts the Twin Shark kit.
The high
aspect ratio wings are of beautiful workmanship, the surface is very beautiful
and without visible extraction holes. Wing tip ends with a very thin and
pronounced winglet in plastic glued permanently. They are not removable, which
will make transport more complicated once the glider is dismantled.
The kit,
complete, ARTF and nicely assembled. Just missing the receiver and the
propulsion battery.
The double
carbon spars of different lengths can be seen with the natural transparency of
the wing. The main spar — a square section of 10mm x 10mm — runs quite far on
the wing. The second spar — smaller at 8mm x 8mm — stops at the aileron servo.
Their presence presages good rigidity in bending and in torsion. These same
spars protrude from the root of the wing and act as wing joiners. They come
nested in an aluminum profile located in the fuselage, a part which gives the
dihedral and maintains the wings laterally.
Detailed
pictures of the wings out of the box.
The flaps
and ailerons are rigidified by a carbon rod or tube of 3mm of diameter on 80 to
90 % of their length. The plastic horns with central ‘domino’ already have a
different angle of attack between the flap and the aileron in order to obtain
mechanically the right differential. The servos and extension leads are of
course installed and connected. The cut-outs are then masked with white vinyl.
The
tailplane is built in the same way, with a spar and a carbon tube or rod insert
in the elevator flap to give rigidity.
The
fuselage is molded around a large carbon tube that runs to the vertical
stabilizer and provides stiffness. The rudder and elevator servos are
respectively housed in the rudder foot and at the top. They are in direct
attachment by means of a piano wire. The horns are of the same type as on the
wings, with a central rotary ‘domino’ and removable, which will be convenient
to remove the stab at the end of the flight session. At the front, once the
canopy is removed (without pilot, too bad!), we discover a large volume which
will allow the use of a large variety of propulsion batteries. By the way, I
find that the canopy magnet is not strong enough for good retention.
Some
details of the fuselage. Under the canopy there is a lot of space.
The
KAVAN C3548–750 brushless motor and its 11x8" folding
propeller, as well as the 50A KAVAN R-50SB controller with
SBEC (switching battery eliminator circuit), capable of powering the six servos
are in place and do not encroach on the inner volume. You will just have to
find or buy a 4S LiPo battery 14.8V 2600–3300 mAh (at least 30C) to provide the
watts to your Twin Shark.
The Twin
Shark needs a 4S battery — here of 2600mAh capacity which already give a long
flying time.
The locking
of the wings on the fuselage is done by a big plastic screw which is at the top
of the fuselage. It is simple and effective.
All the
assemblies are of good quality and the decoration is done. In short, all that
remains is to connect a five or seven channel receiver and a propulsion
battery. I forgot to mention the accessory pocket which allows you to install a
fixed wheel quickly, and a plastic landing skid to cut and glue under the
fuselage to protect it from scratches. The wheel and the skid can easily
cohabit. For my part, I only put on the skid, glued with Loctite 60
Sec. Universal Glue (see Resources), a kind of
cyanoacrylate gel and slow curing that offers a good bonding in the end.
The
accessories with the optional wheel and a few Allen wrench tools allowing to
disassemble the tailplane or do some maintenance if needed. On the right the
skid, provided.
I found it
surprising that the flap servos are with plastic gears while the aileron servos
are with metal gears, which is a guarantee of a better lifetime. But for me,
the most annoying thing is the Y-cable harness provided by default for the
ailerons and flaps. This limits the mixing possibilities and restricts the
flight range. However, I understand the logic behind this choice, which is
indicated in the manual that comes with the kit. So, if you want to ‘open the
chakras’ of your Twin Shark and thus benefit from a real
‘quadroflap’, ‘butterfly’, or variable camber then plan the purchase of four
male-female extension leads of 20cm to 30cm in length — it should not ruin you
financially.
In Flight, Very like a Much Larger Glider!
On a glider
with high aspect ratio wings, performance and behavior are most often dictated
by this geometry, and this is verified with the Twin Shark.
The author
with smile and not worried before the first flight
Before
talking about the flight behavior, a short word about the motorization. The
climb rate is very good, thanks to the use of a 4S battery. The climbs are
decisive with a rather steep angle — more than 45° — and enables the glider to
reach a comfortable altitude quickly. That’s ideal in the mountains to get out
of a bad situation or at a flat field to go up sufficiently high to hunt
thermals. This also means a good autonomy, because we can hope to get a
significant number of climbs from a single battery. During my flying sessions,
certainly on the slope but sometimes in light conditions as well, I never
managed to go to the end of the battery. At the field, this good point is more
appreciated. After this side consideration, let’s turn off the engine and see
how the glider behaves.
The first
flights were done in the factory configuration — the ailerons on one channel
and the flaps on another — which does not allow to move up the two ailerons at
the same time during the landing phase or to have the flaps acting on the
opposite in quadroflap mode. In this configuration, the glider is quite usable
and functional, the flight is pleasant, the ailerons are sufficiently precise,
the landing is not problematic with the flaps down to the maximum, even if it
lengthens a little more. But the limit is felt at high angles and when you try
to do aerobatics and you need more efficiency in roll.
A superb
look and a flight behavior rather dynamic makes of the Twin Shark a pleasant
glider, but aimed at pilots already have a first experience with three-axis
piloting.
For the
rest of the flight tests, let’s go to the ideal configuration by replacing the
two Y-cables with the four male-female extensions of 20cm to 30cm.
Flyby!
In flight,
the glider has a rather fast cruising speed, it covers the distances with ease.
It accelerates well, can transit at sustained speed and recovers well when you
release the stick. This is interesting to explore the flight volume with
efficiency.
The spiral
must be worked with the rudder, with the ailerons at the opposite. If the lift
is rather strong, you can put a little flap to increase the rate of climb. On
the other hand, you can’t tighten the spiral as you could do with an F5J or a
more ‘specialized’ glider, here the spiral remains of a larger diameter.
Action!
Overall, I
found the wing section more efficient when it is neutral with no deflection.
Remain also at low speed and at high angles, the small wing chord reminding you
of its limits at first nicely, but if you ignore the message, then more
frankly.
The Twin
Shark has a real presence in the air and remains a pleasure for the
eyes with its shape and thin wings. You can’t get enough of making flybys over
and over again to enjoy its very sexy look!
Let’s move
on to aerobatics: with such a high aspect ratio, the Twin Shark is
not really made for this exercise, at least on paper. However, the basic
aerobatics are not a problem. The roll must be ‘worked’ to be true in axis. One
can help a little with the rudder in the last quarter. In any case, you need to
have enough speed before starting the maneuver. The reversal goes perfectly
with a sufficient efficiency of the rudder. We kick a little before the glider
stops, which favors the bite of the vertical stabilizer. Eventually you can
‘cheat’ a little on the ailerons in case the glider does not come out on the
right axis, or does not tip over fast enough.
Looping is
easy with a little bit of speed at the entrance. If the glider is well
positioned in relation to the wind, it will remain well-oriented. If not, a
small aileron correction will put it back on the right trajectory.
The
stiffness of the glider’s airframe is quite good, it bends a little under
stress, but this remains acceptable and adds to the realism of the flight.
Some
onboard pictures.
Finally
inverted flight — with the CG at the rear limit of the manufacturer’s CG range
— holds but when the conditions are rather good. We don’t wait too long for the
speed to decrease to put it back on the level in order to always have
efficiency on the ailerons.
A nice
place to fly in the heart of the French Alps!
Finally,
the landing is a simple formality with the butterfly mix. With the elevator
compensation trim set correctly, the approach at low speed and the final
landing are done without worries, and you can easily control the descent slope
with the elevator.
Before
concluding, I’m sharing two videos of the model. The first being from the
ground:
and the
second from onboard:
It’s
Time to Leave!
The Twin
Shark from KAVAN is a semi-scale model with a particularly nice look
and close to the full-size glider. It offers good performance in flight and a
rather dynamic behavior for a very reasonable price compared to the
competition. The assembly is of high quality and allows the modeler in a hurry
to fly in a few minutes. The Twin Shark is clearly positioned
as a formidable outsider to the market leader. Just like its competitor, it is
not aimed at beginners but at three-axis pilots sided able to combine ailerons
and rudder. Happy landings!
Specifications
©2021 Text: Pierre RONDEL Photos: Pierre
Rondel and Joel Marin
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