Airborne Magazine

HomeArticlesPlansSubscriptionsEmail

Felix

by Ron Passlow

Plan No. 691

Specifications:  
Wing Span: 1.42 metres
Length 1.1 metres
Engine .40 - .55
Plan Detail

Plan No. 691
Price:
AU$40.00 plus P&H (AU$3.00 within Australia).  

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: 
PO Box 30 Tullamarine Vic, Australia, 3043
LET’S GET BUILDING!
The first thing to do is to study the plan very closely. I look at plans for a day or two before I start to do any cutting out or construction. As has been said in many articles it is a good idea to “kit” the plane as far as possible before starting construction. This helps with the flow of building and it also gives an indication of whether more materials are required for the completion of the project.
If you are like me you usually start by building the more involved sections. With the Felix the more involved section is the fuselage, but as will be seen in this article I built some parts simultaneously or at least whilst setting one section aside for the glue to dry (yes I still use aliphatic resin on some high strain joints and those that do not necessarily match perfectly) while working another section.

 

WING
This wing is reasonably straight forward to build. It has sixteen 1.5mm and four 3mm balsa ribs that have a semi-symmetrical section for a tapered wing, so I chose to cut each rib individually. I transferred the profiles onto tracing paper and then used these to mark the balsa. When cutting the 3mm ribs, I cut them as a one piece rib and then cut out the section to allow for the wing brace (WB2) plus the centre ribs (W1) which need to be cut for the servo tray and servo bay if you go for the singular aileron servo installation as per the plan. I deviated a little here and decide to use two wing mounted servos, one for each aileron.
Now to assembling the wing. As with any wing, it will only be as good as the building board used so ensure that your building board is true and large enough for this wing.
First lay the plan over the building board and cover with your favourite protective covering (mine is clear plastic cling wrap). A straight piece of 6mm square balsa is laid parallel to the trailing edge and along the line for the trailing edge sheeting and is pinned to the board. This is to ensure that all the ribs sit at the right height thus ensuring a straight wing. Then the bottom, 6.5 mm square, spruce spar is pinned in place and ribs W3 to W10 are secured in place being certain that they are 90 degree to the building board and pinned securely to the 6mm balsa square laid earlier. Once I was certain all is true and straight I then glued the ribs to the bottom spar. Next is to fit and glue the rear section of rib W2 in place. I do not glue the centre rib (W1) in place at this stage because it needs to be glued on an angle because of the dihedral.
Next fit the top spar then add the 9.5mm balsa leading edge oversize enough for shaping and to allow for the leading edge sheeting top and bottom. I placed (not glued) the wing joiner (WB2) against the ribs. This is to ensure the correct spacing for placing and gluing of the front section of W2 to the leading edge. Now attach the 6.5mm balsa trailing edge followed by the 1.5mm balsa trailing edge sheeting. Once this is done, fix the 1.5mm ply WB1 to the leading edge and glued rib W1 in place, set at half the angle of the dihedral. Then fit the dowel support in the form of some 12.5mm balsa between W1 and W2 against the leading edge. It is now necessary to put in the 1.5mm balsa webbing in front of spar from W3 to W10 and behind the spar from W1 to W3.
Now you will be able to put the leading edge sheeting on the top of the wing. I usually start with this sheeting because it allows me to use a single sheet from the tip to the root rib. Now the centre sheeting and the cap strips are attached and allow the adhesive to dry.
This half of the wing now may be removed from the building board. The second wing can now be built in the same manner. After the removal of the second wing from the building board, test fit them together checking the dihedral and the fitting of WB2 into both wings before gluing together. You can now add the sheeting and cap stripping to the under side of the wing. The ailerons are full length strips and are shaped from 12.5mm balsa. The only break in the ailerons is for the fuselage and this centre section houses the aileron torsion rods. The 1.5mm plywood reinforcement plates are glued on the bottom of the centre section for the wing bolts to pull down on.
The wing tips are made by laminating four pieces of 9.5mm balsa together and then sanding to shape. I hollowed out the wing tips and then attached them and the whole wing is shaped, some final sanding is done and the hardwood dowels fitted. After this is done the hinge slots may be cut but do not fit the hinges just yet. Also do not forget to cut out the hole for the aileron servo in the top of the wing.
There is still one job to be done, and that is to build the under wing section of the fuselage that is attached to the wing. But do not build this yet because it needs to be matched to the fuselage profile.

THE TAIL FEATHERS
The tail feathers are of the open structure type and are built up from 9.5mm balsa. I build over the plan that is again covered with clear plastic wrap to protect the plan from glue. Construction consists of cutting the required pieces and ensuring that they fit together and simply glue them together in place over the plan. I used this method for both the horizontal stabiliser and the fin. Then the whole setup needs to be sanded and rounded ready for fitment to the fuselage. The only work left is to bend the joiner for the elevators from 2.5mm piano wire and to put the hinge slots in ready for assembly after covering.

 

FUSELAGE
It is not impossible to build this fuselage without a jig, but I found it certainly made it easier because the formers are greater in height than the height of the laminated fuselage sides. The formers are designed for curved turtle deck top and a curved bottom section of the fuselage. This can make it difficult to build a true and accurate fuselage without the aid of some sort of jig. s can be seen from the photos I used a jig. See the article on building a fuselage assembly jig in Airborne issue No149.


Having kitted the plane this means that you are ready to start putting the fuselage together. Start by laminating the ply doublers to the 3mm balsa fuselage sides being sure to make one left and one right side.
The 6.5mm X 3mm spruce longerons need to be installed where indicated, along the top and bottom edges of the fuselage. There is also a 6.5mm square balsa longeron attached to the fuselage side between F1 and F5. Under this longeron the 3mm balsa wing seat (WS) is laminated. Once this has dried it is time to start putting the formers in place. It is a good idea to mark the fuselage sides for the location of the formers.
Fit formers F1 to F5 between the fuselage sides in the jig and when happy with the fit and alignment these can be glued in place. It is important that former F5 is on the correct angle because this becomes the back wall of your cockpit. When you have done this it is now possible to fit and glue formers F6 to F9 in place, ensuring that all is aligned with the centre line. Of course you have made these formers when kitting your model at the start of construction haven’t you? The 6.5mm square stringers are now fitted in place between F1 and F4, and then between F5 and F8. I found that I needed to sand the stringers so that the edges would not cause problems when applying the decking.
I usually leave the fuselage overnight for the glue to dry and whilst this is set aside to ensure everything has dried properly it is a good idea to build the tank bay from 3mm and 6.5mm ply. When I install the firewall, I use epoxy and I usually mix enough so that I can “paint” the inside of the bay to fuel -proof the area.
Then the engine mount is fitted and holes drilled for throttle control and the fuel lines. Here it is necessary to decide whether to put the engine upright, inverted or at some other angle. I chose to have it at 900 to upright as shown on the plan. This gives a cleaner profile of the plane and it also gets rid of the exhaust down and under the wing.
Next the 3 mm balsa turtle deck needs to be fitted between F2 and F8. I chose to do this in a few different ways. First, it is important to choose a soft grade of balsa that will bend more easily but definitely do not try to just bend 3mm balsa and expect it not to split. I used my wife’s food steamer to steam the pieces so that they would bend to the required shape for the front section of the decking. For the rear section of the decking I used the planking method because this area has a far sharper bend than at the front. I decked the whole of the top of the fuselage and then cut out for the cockpit opening. The cockpit floor needs to be fitted at this point of the construction.
The decking of the bottom of the fuselage requires the removal of the fuse from the jig. Once removed it is necessary to fit the two 6.5mm ply (WM) plates in place. For this again I use epoxy because these plates are what hold the wing to the plane. Now fit former F5b at the desired angle and again there are 6.5mm balsa stringers to be fitted between F5b and the rear of the fuselage. These also need to be sanded and shaped to facilitate the fitting of the decking. This lower decking takes a bit more patience because it comes down to 9.5mm at the rear of the fuselage.
I now test fitted the wing (ensuring the correct incidence) and marked the wing bolt positions. These were drilled out and tapped so that the wing could be attached so that the under wing section of the fuselage could be constructed. This was reasonably easy. First glues the formers F2b to F5a in place and fit the 6.5mm balsa stringers. Sand to shape and then cover with the 3mm balsa decking. I chose to use 1.5mm sheeting here (steamed again) and laminated a second 1.5mm sheet over the first. I found that this was easier than trying to use just 3mm sheeting. When this sheeting is in place it is necessary to make access holes for the wing bolts. I made these big enough that the wing bolts could be fully removed. With the holes this size I decided to make tubes large enough for the heads of the bolts and inserted then into the lower decking so that this would stop fuel from getting inside the decking. I made the balsa block fairing pieces and glued them in place with the wing fitted to the fuselage. These were finished off with filler and sanded smooth to blend into the sides of the fuselage.
The tank bay can now be fitted ensuring that all is aligned correctly and that the engine mount is set at the correct thrust lines. Once this is in place the undercarriage mount can be installed (again using epoxy). The section between F1 and F2 now can have the 6.5 sheeting fitted and sanded to shape. The section over the undercarriage mount used balsa block to complete, again sanded to shape and the part cut out for the undercarriage to be mounted. The piece cut out is then glued to the undercarriage to give it the finished outline.
The tail feathers can now be fitted making sure that the stabiliser is set at the correct incidence and is square to the centre line of the plane. Also the fin needs to be set at right angles to the stabiliser and checked that it is also straight down the middle of the fuselage. On each side of the fin there are fillets made from scrap balsa and these may now be shaped and attached. The headrest can be made from off cuts. I used pieces of 9.5mm balsa and laminated them together and shaped and hollowed to the desired profile.
I installed the servo tray as per plan, behind former F3. There is enough room even with standard servos. I used nylon snakes (Nyrod style) for the rudder and elevator controls, so these need to be installed before the bottom sheeting is put on.

The undercarriage is made from 3mm aluminium that is cut, drilled and bent to shape as shown on the plan.
The cowl is made next. This can be a pain of a job but if you use my method it can be a little easier. First laminate C1 to C2. Then I cut out a 3” circle of 1.5mm balsa and make the hole in the middle the size of the prop driver on the motor. I tack glued C1 to the balsa circle and put it over the prop driver with the spinner on the prop shaft. This gives a gap of 1.5mm between the spinner and the cowl. This gives the base for the construction of the cowl. This cowl is made up of 9.5mm balsa that is sanded to the desired shape. The plan also calls for 9 cowl blisters to be made from 12.5mm balsa and fitted. I made 8 and only used 7 because of where the engine head and the muffler protrude from the cowl. I also used the Dremel to remove excess thickness from inside the cowl. This also reduces weight up front.
The whole fuselage now needs to be sanded to shape ready for final smoothing.

FINISHING
The fuselage was given two coats of dope, sanding between coats with about 320 grit paper. When dry this was sanded with 600 grit dry wet and dry paper. The insides of both the cowl and the firewall were given a coat of epoxy resin to seal against fuel penetration.
I then masked the tail feather section ready for painting. The entire fuselage was then given two coats of white “Lustrecoat” undercoat (including inside the cowl) and allowed twenty-four hours to dry before masking and spraying the final choice of colours (allowing 24 hours drying between colours).
Next the wing, ailerons and tail feathers were covered with heat shrink and the control surfaces fitted being sure to glue and pin the hinges. Now it is possible to fit the windscreen. The method I chose was to put four tags on the bottom of the screen that went through slots cut in the decking and then epoxied in place. The beading around the cockpit was then secured in place, and this gives it a real finished look.
After this was finished I refitted the engine and the radio gear and checked that the C.G. was set at 25% of the mean aerodynamic chord, which is 80mm back from the leading edge. The control throws and directions were checked. I set the elevators at 12.5mm, the rudder at 35mm and the ailerons at 12mm. On checking the total weight it was found that the model came in at 2.5 kg.

TO THE FIELD
Once at the field (Rebel Flying Club) the plane is assembled and I again checked that the C of G (set at 80mm from the leading edge) is correct. The usual checks for control movement direction and radio range check is done and we are ready for the first flight. The OS 46 FX was kicked into life and I was ready for the maiden test flight.
The Felix tracks well on the ground as most tail-draggers do but is not too happy in a cross wind, although it is quite manageable. In the air this plane is very controllable and is a joy to fly. The Felix will do just about anything you want it to, even though to look at this model it looks like it would only be a plane to putt around the air and enjoy flying. Well I enjoy flying it, but if you want to throw it around you can and this plane will handle it well. On the first flight I not only set up the trim for straight and level flight (which was only a couple of clicks on the rudder to the right), I was able to put this model into some very nice axial and barrel rolls, and it has good inverted performance. I took Felix up high and put it onto a stall and all it did was to get mushy on the controls and then dropped the nose a little and just kept flying. The plane slows nicely for landing and with 3.5” wheels it rolls very well on the grass field we have. I then asked our club’s young gun (Trent) if he would fly Felix for me so that I could take some photos. When he had finished with the passes for the camera he started to have some real fun. He started barrel rolling and just continued to fly the circuit whilst barrel rolling! The he put it on knife edge in both directions, stall turns and remarked what fun it is to fly. He was enjoying himself so much that I had to remind him that it was getting low on fuel. He just wanted to keep flying because he was having such a great time. The Felix can be what ever you want it to be, a Sunday flyer or a real ‘ring its neck’ sportster.

 

Plan Detail

Plan No. 691
Price: AU$40.00 plus P&H (AU$3.00 within Australia).  

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: PO Box 30 Tullamarine Vic, Australia, 3043
Airborne Plans Service: P.O. Box 30 Tullamarine Vic, Australia, 3043