KAVAN Twin Shark 304TS
A nice-looking, semi-scale EPO glider with performance similar to its full-size cousin.
While this article appears under my byline, note the excellent pictures were a collaboration with Joël Marin to whom I offer my thanks for helping to create this article. — PR
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.
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’.
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!
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 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 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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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
©2023 Pierre RONDEL and Joel Marin
Resources
- KAVAN Twin Shark 304TS — “now you can enjoy flying with our 2700mm wingspan semi-scale model of this beautiful sailplane powered by a brushless motor…”
- HpH 304 Twin Shark — The full-size version of the aircraft presented in this article.
- Loctite 60 Sec. Universal Glue — “the first all-purpose glue that bonds in only 60 seconds. No more waiting and no more clamping! It quickly forms strong bonds…”
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