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Pilatus - Turbo Porter Fun Fly

by Ron Passlow

Plan No.694

Features Construction Articles

Plan Detail:
Plan No. 694
Price: AU$33.00 (3xSheets) 
plus P&H (AU$4.00 within Australia).

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When I’m about to build a model that has its origin in a full size aircraft, I try to find out as much as possible about the aircraft, so I went to the net and found that there are a number of sites by simply typing in the search box ‘Pilatus Porter’. I was mainly looking for specifications of the Turbo Porter and found that a number of sites also had colour photos of most of the Pilatus Porters made along with their history.

I printed off the general information about the specs and then had a look at the photos to choose a colour scheme for my model, (all of this before I started building). The colour scheme chosen was used because I believe that a profile model needs some pattern to take away the thinness of the fuselage.

The particular Pilatus Porter chosen was built in 1971 and had been used as a survey/photo plane and for parachuting until destroyed by fire in an act of vandalism in 2003.

Now to the Model
It should go without mention that when you receive a plan you shouldn’t start building until you’ve studied the plan thoroughly and worked out your own plan of attack.

After studying the plan carefully I decided to start by building the hardest part first - the wing. I also decided that because of the 1.4 metre wing span of this model and the fact that I only have a sedan, I would make it with a detachable wing, which created its own set of problems to resolve and these will be seen as we build the model.

The Wing
This wing has a constant chord with no dihedral and as such is quite easy to build straight and true.

First, cut out enough ribs from 1.5mm and 3mm balsa. They can either be cut out individually or as I did, they can be cut out using the sandwich method. The sandwich method is very simple for this wing because it is constant chord. I cut out two 3mm balsa ribs very accurately and used these as my templates. Between these templates I placed 12 pieces of 1.5mm balsa and 2 pieces of 3mm balsa. Some people use pins or bolts to hold these together for shaping. Then I used the balsa plane to bring the inserts to just larger than the templates and then sanded them until they were the correct profile. Then I cut out the spar slots (top and bottom) and the ribs were almost ready to start building. As indicated on the plan, the ribs have holes in them to lighten the overall wing, now is the time to cut these holes. I used a compass cutter that I bought from a discount shop for about $3.00. These are also available from craft shops, or stationery supplies places for around the $7.00 mark - maybe slightly better quality. The 4 x 1.5mm ribs to become W3’s and the 4 x 3mm ribs to become W1’s were removed and put together into their own little sandwich so that the slots could be cut for servo tray supports as these ribs are to be used for either side of the aileron servo areas in the outer section of the wings and for the other two servo bays in the centre of the wing. The only other job now is to cut the W1 ribs in half as shown on the plan and to cut out two W4 half ribs from 12.5mm balsa.

Now Let’s Start Building
You do have a flat building board don’t you? Because I am transferred regularly with my vocation, I check my board with a straight edge each time I use it.

Lay the plan on the board and cover it with plastic food wrap (or your favourite medium) to protect it from the glue. I then laid down the bottom spar and pinned it to the board, ensuring that it was straight. As this wing does not have any dihedral I decided to build the wing in one piece. I believe this gives a stronger wing. This can be achieved using 120cm lengths of spruce by splicing the extra needed, ensuring that the splice is on a rib and lace the spliced end of the top spar at the opposite end of the wing. Then I placed a length of 12.5mm balsa along the line where the trailing edge sheeting is marked on the plan. This lifts the trailing edge of the ribs and helps in building a true wing. Then test fit the ribs in place as indicated on the plan and when satisfied that all is well use a set square or something similar and pin and glue the ribs in place. When this has been done you are able to fit the top spar and glue in place. Next cut some 6.5mm hard balsa wide enough to suit and glue in place for the aileron spar. Before gluing the leading edge in place it will be necessary to fit the W4 half ribs against the appropriate rib in each side of the wing. Also, have you decided to make the wing detachable as I did? If you have you need to decide here what sort of strut attaching you will be using. I set a nylon control horn into each of the W4 half ribs before fitting them into the wing. Once W4 ribs are in place glue the insert and glue in place the 1.5mm ply ‘wing joiner’ - even though building the wing in one piece it still gives extra strength for the wing. If you are making the wing detachable it is also necessary place some block balsa between the centre ribs to secure the dowel for locating the wing in the fuselage and another piece of block balsa where the wing bolt hole is to be drilled. As with most wings, this one has sheer webbing between the top and bottom spars and sheeting from the leading edge to the rear of the spar top and bottom to ‘D’ box the wing for strength. Next, the trailing edge sheeting and the cap strips are added. In the servo bays, triangle gussets made from 3mm ply were glued into each corner, ensuring they are set low enough that the servo bay covers are flush with the surface of the wing. Then servo bay covers are made from 1.5mm ply. I chose to install the aileron servos on their side so that only the servo arm extended out of the servo cover (making for a neater finish). I also marked these covers because I have found that no matter how carefully I make these compartments they are always slightly different and one will not fit in another.

Now the ailerons and the rear centre section between the ailerons, which are open framework, are made over the plan from 9.5mm balsa and sanded to the desired profile. The ailerons and the aileron spar are slotted to accept the hinges, but the hinges are not installed at this stage. Once all has been shaped it is a simple job to transfer the outline of the total wing onto 12.5mm balsa to shape the wing tips. Sand the entire wing and the wing is ready for covering, but do not cover at this time.

Tail Feathers
The horizontal stabiliser and the fin are built up over the plan from 9.5mm balsa in a similar fashion to that used for the ailerons because these too are open framework. The rudder and elevators are made from solid 9.5mm balsa sanded to shape and then aerodynamic counter balance pieces added on the top of the rudder and outer edges of the elevators. It is necessary to make an elevator joiner from 2.5mm piano wire. Again I slotted the fin, horizontal stabiliser, rudder and elevators to accept the hinges, but again do not attach at this time. Sand the fin and horizontal stab leading edges to the profile shown on the plan.

Fuselage
I have left this until last because the wing and tail feathers are fitted to the fuselage and I use the outline of made parts to draw the lines for the cut outs to insert these.

The fuselage is basically made of four pieces of 12.5mm balsa with some substructure and then sheeted with 1.5mm balsa.

First it is necessary to mark out the four different pieces of 12.5mm balsa and then to cut them out accurately allowing for the engine bearer spacing to suit the engine you are going to use. I cheated here because I cut it out as per plan, leaving the bearers as part of the balsa and then cut out where the bearers would fit the old OS 40 FP that I had not used for some years. These bearers should be set into the fuselage using slow setting epoxy. The four pieces of 12.5mm balsa are then laid over the plan to ensure they fit together properly to give the correct profile. When satisfied that these fit together properly, I glued them together with aliphatic resin and installed the vertical and diagonal braces as shown on the plan. All the time ensuring that these are pinned over the plan and to the building board. The wedge piece at the rear of the fuselage is now installed along with a 12.5mm square hard balsa (grain vertical) to support the tail wheel. The tail wheel is bent from 2.5mm piano wire and according to the plan has a light spring that holds it straight, but on my model I used a rubber band instead. Also the 12.5mm square hardwood support for the struts and undercarriage is set in place using epoxy. It is now necessary to make the undercarriage mount (UM). I laminated four pieces of 3mm ply and then set it in place again using epoxy resin. If you are making this with a detachable wing as I did you now need to install the threaded nylon block and ply plate for dowel location into the appropriate place in the fuselage. Again epoxy this in place. Another dowel is to be located at the rear of the wing to stop the wing twisting on the narrow fuselage, but this is done at a later part of the construction. Whilst the fuselage is still pinned to the building board, the 1.5mm balsa laminating sheeting should be glued in place. It is necessary to join two pieces of 100mm wide sheets of 1.5mm balsa for each side. This can be done by laying the two sheets of 1.5mm balsa on a flat surface and using masking tape along the join edge. Then turn them over and either use thin cyno or fold the sheets back and run some aliphatic along the edge to be joined, then again lay it flat to allow the glue to set. I left it for 24 hours to set thoroughly before removing the fuselage from the building board to laminate the other side. Be sure to mark where UM has been installed so that it is easy to locate for fitting of the undercarriage holes. The undercarriage is formed from 3mm aluminium and once made needs to be test fitted and location holes drilled. Also mark the centrelines and location of the wing and horizontal stabiliser so that these may be cut out after tracing them onto the fuselage size. After cutting out for the wing installation, and if you are making the wing detachable, be sure to cut from the rear of the wing up to the top of the fuselage at about a 45 degree angle. This is where the other dowel is fitted to stop the twisting of the wing. Also fit and glue the wing saddle in place. Mark and cut out the slots to install the fin in the correct location. Fit and glue the horizontal stabiliser in place ensuring it is true and straight. This is easily done with a set square with a profile model.

The entire entire fuselage can now be sanded ready for the attachment of the horizontal stabiliser and fin. The fuselage is now ready for doping and painting in your colour scheme.

The Struts
For my model I made the struts from long threaded rods and laminated (using epoxy) two 9mm x 3mm pieces of spruce over the rods. These were shaped to the contour shown on the plan. On the wing end I use a metal clevis and on the fuselage end I fitted nylon strip underneath with a hole to take the bent threaded rod. This set up can be adjusted to ensure the wing is straight and secure.

Assembly & Finishing
Test fit everything to the bare bones stage, and visually check everything is right.
When satisfied, you can now start to cover the wing, ailerons, horizontal stabiliser and the fin. I covered these with Solarfilm because it is easy to use and light.

The radio gear used was my JR 662 with the R700 receiver and standard size servos. There are 5 servos in this model because it uses one for each aileron as well as throttle, elevator and rudder. I found that it was a tight fit installing all this into the wing, but it did fit. I used a short section of inner Nyrod to guide the aerial up through the top of the wing and I also fitted the switch into the top of the wing.

The fuselage, rudder and elevators were given two coats of dope and then painted in the scheme chosen, using spray enamel and allowing 24 hours drying between different colour coats.

The OS 40 FP set at the 3 degrees right thrust, along with the fuel tank, rudder, elevators, control linkages, tail wheel and undercarriage were all installed. Throws were set as follows: the ailerons 6mm up and down, whilst elevator was set on low rate at 10mm up and down and the rudder 25mm either way to give plenty of ground control. These proved to be sufficient to perform the desired manoeuvres.

The model balanced right on the main spar of the wing which proved to be the correct location. Overall weight was just on 2kg.

To The Field
The day was less than perfect because of a strong wind blowing down the strip, so I took the mandatory photos and did the range check of the radio and a final C of G check. I thought that I would still give it a go so I fuelled it up and fired up the motor and set it to run a little rich because it had not been run for a number of years.

The Pilatus was taxied out to the strip into the wind and the throttle advanced and within about 10 metres it was airborne. The climb rate was great, but I did continue to fly upwind until I believed it have enough air speed to turn down wind. I then flew around to get the trims set but this proved difficult because of the gusty wind, so I compromised and had it flying mostly straight and level into the wind. It only needed a couple of clicks on the rudder to have it behaving. This little plane is quite able to handle these conditions easily.

Time to try it out. It loops nicely and rolls well. When trying to put it into a stall, at first I first actually had it flying backwards in the wind until it just dropped the nose a little and wanted to continue on its way. Now it was time to bring it in for a landing in the gusty wind. I kept the speed up on the approach and over the field I just backed off the throttle and it almost helicoptered in with a roll out of less than 3 metres. Truly a STOL (Short Take Off & Landing) aeroplane just as the full size one was designed to do.

Added Flying Info
Since the initial try out day I have flown this little beauty a number of times and this is how it went. The first time back at the field was even windier than the first day and I had a flame out and had to come in dead stick, and it just kept on gliding into the wind because it is so light. The next couple of times to the strip were good weather and I was able to have some fun. It flies really well and considering it is only powered by a 40, it has heaps of power. Stall turns are simple, as are Cuban eights, inverted flight and knife edge. I even believe with a little more practice I will be able to hang it on the prop. The ailerons are very effective on the low rates but with high rates set at 12 mm either way it rolls very quick and is fun if you are an experienced pilot. I am still a little reluctant to put it through a snap roll because of the stresses placed on the wing anchoring point, but I believe that it will snap fairly slowly until the C of G is moved rearward a little to make it more responsive, not that it needs this for the learner to intermediate pilot.

One point to remember is that with wooden engine bearers it is important to check that the mounting bolts are tightened regularly (after each flight) especially for the first few flights whilst the wood compresses. I forgot this because I haven’t had a model with wooden engine bearers for some years and the plane got very noisy as the motor worked a little loose so I landed straight away and tightened the bolts. The vibration from the loose engine had broken one of the fuel tank straps. So a few rubber bands were used and another flight able. So don’t forget to constantly check the engine bolts.

As stated at the beginning I believe this would be a good model for your first scratch build, particularly if you are a learner to intermediate pilot, but it will perform for those who want throw it around the sky. So enjoy the experience of building and the fun of flying this little plane.

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wing construction

 

 

 

fuselage construction

 

 

 

complete model pre-finishing

 

 

 

control surface

 

 

 

servo and wing strut

 

 

 

tail wheel setup

 

 

 

servos in bottom of the wing

 

 

 

under cart and wing strut connection

 

 

 

The porter in flight

 

 

 

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