Product Sija Model Kit
Code AS15
Description
Among the usual ways of free flight model evolution we look for alternative and unordinary solutions. One of them is use of tube instead of spar sandwich and D-box. As you know the tube is the strongest form of beam construction that restrains the bending and turning load simultaneously. After many calculations and tests we chose to use Awerianow airfoil and 9mm outer diameter tube made of glass + uni-dir-carbon + 45 deg. carbon + glass fiber. For wingtip a 7mm diam. tube was used. The result is incredible -wings are stiff and crash resistant - completely unbreakable! Of course they are not as strong as ordinary D-box composite wings, but 6-7 kg pressure on the towhook is normal and no wind is too strong! Even on very hard crash only the balsa leading edge suffers. And what is the most important -the assembling of wings takes only few ours instead of days and can be performed even on kitchen table without any additional accessories. One more aspect -the airfoil remains perfect along the chord what is impossible to reach using traditional spar-box construction. Covered with polyester tissue wings weight only 130g! Sija kit includes all wing, fuselage and stabilizer parts plus instructions and full size plans. Sija model has an RDD (Rudder Delay Device) to ensure the high launch performance as it can be accelerated much more than wooden model. The gliding characteristics are much better than Junior's due to thinner airfoil. In our line of products Sija is the middle step between Junior and Superba. This construction now is the most perspective and has the high potential of improvements. The most popular product on W Hobby list ever! Parts list.
Download full size plan.

Aeromodeller magazine review on W Hobby F1A Sija Kit
Beer Sheva (Israel) Aero Club members with the Sijas, built during the Summer Course 98.
On the left of the photo is Instructor Mr.Avi Manor, on the right -Mr.Evan Peretz.
Dimensions, mm wingspan 2100
Price (EUR) 150.00
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F1A Model Kit SIJA
CONTENTS:
 Nr.  Detail
Qty.
 Material
 1.  Wing Root Rib
2
 Balsa
 2.  Wing Rib
34
 Balsa
 3.  Wing Joint Rib
2
 Balsa
 4.  Tip Joint Rib
2
 Balsa
 5.  Half-Rib
36
 Balsa
 6.  Wing Tip Rib
2*12
 Balsa
 7.  Tip Half-Rib
2*12
 Balsa
 8.  Tip End Block
2
 Balsa
 9.  Main Spar
2
 Glass/Carbon/45 Carbon
 11.  Wingjoiner Tube
2
 Glass
 12.  Wingtip Spar
2
 Glass/Carbon
 13.  Root Leading Edge
2
 Balsa
 14.  Tip Leading Edge
2
 Balsa
 15.  Root Trailing Edge
2
 Carbon
 16.  Wingtip Trailing Edge
2
 Carbon
 17.  Rib Strip
128
 Carbon
 18.  Spar Joint
2
 Aluminum
 19.  Wingjoiner
1
 Steel
 20.  Stabilizer Leading Edge
1
 Balsa
 20A.  Stabilizer Rib
18
 Balsa
 21.  Stabilizer Trailing Edge
1
 Balsa
 21A.  Stabilizer Root And Edge Rib
3
 Balsa
 22.  Stabilizer Top And Bottom Spar
2
 Balsa
 22A.  Web
1
 Balsa
 23.  Body Shell
1
 Carbon/Glass
 24.  Frontend Block
1
 Wood
 24A.  Timer
1
 Steel
 25.  Towhook
1
 Steel
 25A.  Towhook Cover Plate
1
 Steel/Carbon/Glass
 26.  Tailboom
1
 Carbon/Glass
 27.  Rudder
1
 Balsa
 28.  Stabmount
1
 Aluminum
 29.  Mounting Screw
4
 Steel
 30.  Towhook Adjustment Bolts (+bushings)
2
 Steel
 30A.  Towhook Pin
1
 Steel
 31.  Straight Tow Adjuster
1
 Wire
 32.  Line Tube
1
 Plastic
 33.  DT Line
1
 Fishing Line
 34.  Rudder Line
1
 Wire
 35.  Wing Fixator Wire
1
 Steel
 36.  Piece of Lead
1
 Lead
 37.  Tissue
1
 Polyester Paper
 38.  Wing Building Jig
3
 Blue Foam
 39.  Full Size Drawing
1
 
F1A Model Kit SIJA
ORDER OF ASSEMBLING
W Hobby "SIJA" is easy to build - no special skills and additional materials are needed. All details can be glued with epoxy or CA.
Wing: The unique construction of the wing allows you to collect it in only few hours. Use the full size plan enclosed into box. The main element of the wing is tubular spar. First of all string all the ribs on the spar, place over the plan and check intervals and parallelity of ribs. Apply some glue on joint places. After that use CA to mount leading edge (13) to the front and trailing edge (15) to the back ends of ribs. All this work should be done on the straight and flat board. Put some balsa sticks under the ribs to hold the construction as shown in cut-view. Then you can glue (with CA) the carbon strips (17) to the upper edge of each rib. Be sure that strip comes over the trailing edge and at least 1-2mm over the leading edge. After that take the wing off, turn it upside down and glue on the bottom rib strips. Again check all the joints and apply some additional glue wherever is needed. Wrap the wingjoiner tubes (11) with some thread or glassfibre and glue into the root part (marked white -it contains more layers of carbon) of the main spar (9). Put the balsa triangles as shown on the drawing to force construction.
Wingtip: Collect it the same way as central part, but cut the supporting plank to tapered shape according to the airfoil height difference. Glue balsa blocks (8) to the last tip rib and brush it to shape. Brush the joint ribs (3 and 4) off to get right angle at the dihedral. Join tip to root panel using the aluminum joint (18) and wrap the spar ends with strong thread to prevent tearing off the spar. The wing is ready to cover.
Use the tissue enclosed or any other material (Japanese paper, Mylar, etc.). Use cellulose dope for paper covering (nitro dope is available at any local hobby shop).
Stabilizer: The regular construction -with top and bottom spar. Collect over drawing then brush edges as shown in cut-view.
Frontend: The construction of frontend is very simple. First of all find out how devices work. You can put them into Frontend Block (24) without the Shell (23) -that allows you to see if everything works well. Then disassemble the frontend and glue (use epoxy) the carbon Shell (23) onto the frontend (24). It is convenient to put some lead inside the ballast space slot before assembling the frontend. Glue the bushings (30) into the top holes of frontend. These bolts adjust the tow and glide circles. The third hole is for access to the zoom bolt on the towhook.
Now brush the frontend outline and paint it the color you like. Put all devices inside and check how do they work. Be sure that the timer starts after the towhook latch is released.
Fuselage: Glue-on the stabmount (28), rudder (27) and plastic tube (32) to tailboom (26). Then thread the lines, connect the rudder line (34) to towhook. Join the tailboom to the frontend, put the wire-adjuster (31) to the other end of rudder line, and finish both ends of stabilizer line (33). Adjust the length of RDD line as shown on the drawing (rudder positions during the flight).
Flying: Use 50m of fishing line (0.8mm) to tow model. Towing circles are adjustable at towhooklocation through the hole on the top of fuselage. To adjust zoom angle take out the cartridge and turn the round-headed bolt on the towhook. Gliding circles can be set with the RDD bolt. Set timer for the 10-20s on the first few flights. To make glide flat adjust the stabilizer's angle, or change the center of gravity by putting some lead in ballast box. RDD system eliminates the loss of height after launch of glider. It will not spin down on the highest speed, but will jump straight then after 1-2s after speed reduces turns into gliding circles. Remember that model's weight must be not less than 410g according to the FAI rules.
Have a good time building and flying your SIJA !
F1A Model Kit SIJA
REVIEW
(published in AEROMODELLER magazine 1997.10)
by Mr.Philip Owens, UK with W Hobby comments and remarks 1998.08
Phil Owens checks out a remarkable F1A glider kit from Lithuania
The background to this kit review was the disastrous loss of a brand new high-tech A2 whilst I was trimming it in France last year. Such a setback necessitated a quick replacement. Whilst searching through various catalogues, I came across a Lithuanian company, W Hobby, who market a range of products which are used in modern F/F contest machinery and, in addition, manufacture a small number of kits. One of these kits, the 'Sija', provided a possible solution to my problem. This kit is unusual in that it utilises tubular carbon fibre wing spars which are claimed to be excellent in resisting bending and twisting loads. Furthermore, this form of wing construction was claimed to be much simpler, and consequently faster, to build than those based on carbon D-boxes. The makers also claimed that the finished wing was exceptionally crash resistant.
WHAT YOU GET
The kit is extensively prefabricated and remarkably complete. It included all the necessary hardware, including two-function timer, circle towhook with rudder delay mechanism and an excellent 6.0 mm steel wing joiner. The model makes extensive use of carbon fibre for the fuselage shells, tailboom, tubular wing spars, trailing edge and rib caps. The wing and tail ribs were very accurately cut and the quality of the balsa excellent, as was that used for other components. The clearly drawn, full-size plan, together with parts list and brief building instructions, were all conveniently written in English.
Epoxy or cyanoacrylate (CA) adhesives were recommended for building the model. Regular readers will already be aware of the techniques employed when using carbon components and the need to ensure that no traces of release agents (used in moulding) or grease (ex-fingers) are present when bonding such materials. As a precaution I rubbed down all carbon parts with 800 grade wet and dry and then wiped them with a tissue soaked in acetone (or thinners) immediately prior to gluing.
BUILDING
The wing structure is based on tubular carbon spars of 9 mm diameter for the inner panels and 7 mm for the tips. The recommended method for building the wing panels was unusual in that the pre-cut ribs and riblets were slid along the spar and spaced according to the plan. Once all the ribs were parallel and in contact with the building board they were fixed into place using thin CA. The excellent fit of the ribs on the spars made for a really sound joint. The pre-shaped hard balsa LE was glued to the ribs using PVA and, when dry, the carbon TE was added using CA. During the construction it is recommended that appropriate packing for the undercamber be used to support the ribs which are very thin at their rear. With care this may not be necessary but probably is advisable. I was fortunate to have a cambered building board which suited the Averianov wing section and this made construction exceptionally fast and easy. Now we include blue foam wing building jig into kit.
The most tedious part of the wing construction was adding the carbon rib caps (0.2 x 1.5 mm). These were pre-cut overlength and it was essential to overlap the caps at least 3 mm over the LE and TE in order to ensure a strong wing. Medium viscosity CA was used to attach the caps and I found it helpful to hold them in place with small tabs of masking tape. Thick balsa ( 10 mm) ribs were used at the end of each panel and appropriately wide rib caps were provided. The inner panel spars were reinforced with an additional tubular spar which was a snug fit inside the main spar and extended approximately two thirds the span of the panel.- The reinforcing spar is no longer used, as the structure of the main spar is different, - it has more carbon layers inside at root end (marked red or white).  In view of the towing loads likely to be applied to the centre panels, these reinforcing spars were epoxied in place as were the short glass fiber wing joiner tubes.
Wing tips were constructed in a similar manner but were built around a 7 mm spar tube. Because
of the taper on the wing tips it was necessary to taper the undercamber packing accordingly. The plan did not indicate any wing warps but I chose to build in approximately 3 mm of washout on each tip as a precaution. It should be noted that, with these high tech structures, it is very difficult, if not impossible, to change the warps once built.
Whilst building the tip panels I noted a serious draughting error on the otherwise excellent plan. The LE and TE tapers on the port tip were reversed on the starboard side. Needless to say, both panels were built with the same LE (and TE) taper! The mistake is already eliminated, thanks to Phil. An unusual feature of the model was that the tip panels were joined using a hard aluminium dihedral brace epoxied inside the wing spars and the spar ends were wrapped with Kevlar thread to reinforce this highly stressed area.
The resulting wing was very light -l30 gm and remarkably stiff. White polvester tissue was supplied
in the kit and this was used for covering
the centre panels. This was applied dry using thinned PVA and wrinkles removed hy warming with a hair dryer as water shrinking has little effect on polyester tissue. The tips were used for testing samples of a new heavyweight tissue, Star Span, kindly supplied by 5 star Products of Liverpool. This material (20 gm per sq. metre)
looks similar to heavy Modelspan but the wide range
of colours is more intense. In the dry state it is rather stiff but handles beautifully when lightly sprayed with water and has excelent wet strength and shrinkage.
The finished wing was given four coats of 50% dope and tipped the scales at just 150 gm - remarkably light given the stiffness.
The lightweight version of Star Span ( 10 gm per sq. metre) was used to cover the tailplane which was of conventional balsa construction and
went together quickly using thc pre-cut ribs. The resulting tail weighed 9 gm after two coats of thin dope.
FUSELAGE
The high degree of prefabrication made fuselage construction very straightforward. The fuselage uses the W Hobby multifunction cartridge. The basis, of the cartridge is a 0.5mm steel spine which carries the two
function clockwork timer, circle tow hook. rudder delay and timer start mechanisms. The cartridge, which bolts directly into the fuselage, also serves to strengthen the front of the fuselage and carries the considerable towing loads.
The pod was built by epoxying the two carbon shells together and the pre-painted carbon tail boom epoxied onto a spigot which was moulded on the pod. The multifunctional Cartridge system is no longer used on Sija, as was too complicated for unexperienced builders. Now we offer semi plastic fuselage pod with the same features, but more convenient in building. It has a wooden frame, where all machinery is set and Carbon shell that covers bottom and sides of fuselage pod. The fuselage was completed by adding pre-built fin and machined aluminium tail mount, having first removed enamel from the boom to enable a decent joint to be made. Finally, the pod was sprayed to match the tailboom. A minor problem was experienced here as the aerosol spray primer did not take to the carbon surface, despite thorough flatting prior to spraying. I suspect that the problem was due to contamination of the carbon shells by silicone release agent used in the moulding. It took several attempts before an acceptable finish could be obtained.
The model required 35 gm of lead to bring the CG to the position shown on the plan (52%) and the completed model was one gram over the minimum - 410 gm weight required for FAI contests.
FLYING
Altogether the model was very satisfying to
build but the proof of the pudding is in the flying. The cartridge system employed greatly simplified trimming since it allowed independent adjustment of timer start, straight tow, circle tow, glide circle, zoom launch and rudder delay settings. The latter function maintains the rudder in a straight position for one or two seconds following launch, thereby eliminating any tendency for the model to spin following a high speed launch. Trimming proved to be very straightforward and the glide and towing characteristics are free from vices. So far, it has not been necessary to use the rudder delay facility. Perhaps when I become more confident and launch the model harder it will be needed...
Overall the kit offers exceptional value and has provided me with a model which excellent potential which I look to using in competition.
 
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