| The wings are made up of a centre and two outer panels and a fairly traditional built up construction much like the tailplane. Unlike the Almost Ready to Fly kits around at the moment that have the dihedral set from the centre wing join, this semi scale version has the dihedral set at the correct point just outboard of the fuselage sides; just beyond the non slip walking strip in the photo. The centre section is straightforward but the outer panels have a taper both in cord and thickness; not so straightforward. The challenges here will be to jig the panels to ensure there is no warp, and joining the rear spar which is not parallel to that of the centre section. I also had a major disaster when bringing it all together but you'll have to read on for the details. |
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Just like the other surfaces, the ribs mark the start of the construction. Normal method of transferring a photocopy print to wood (no, not blown my self up or set fire to the workshop yet). In the foreground you can see a strange cutout in the lower part of the ribs; this is for the undercarriage (landing gear) plate. Also note the centre rib has no middle portion, this provides for the servo box, more on that later. The centre comes together quite quickly with the main spar laid on the plan and packing under the rear spar and trailing edge to keep everything square. |
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The top spar is added when everything is dry as is the aft part of centre wing rib. The leading edge doubler can also be added at this point. The dihedral needs to be set by the mating ribs of both the centre and outer panels. This could be done just with the outer panel rib but I chose to split the angle between both. |
There is no dihedral template on the plan but it wasn't difficult to work out, extrapolating a template from the ply wing joining braces. |
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Prior to sheeting, the leading edge ply tripler is added, this strengthens this area for the wing dowels fitted later. Following this the front portion of the centre wing rib can be added and the vertical web front and rear of the spar (not to full length notice). Start sheeting the lower surface from leading edge to mid spar. Pre fabricate a larger piece by gluing two sheets together flat on the building board and when dry, sheet from mid spar to trailing edge. |
Only the lower surface is sheeted as a lot of access is needed later for control runs, undercarriage mounting and bracing. |
| Making a larger sheet from
two or more pieces prior to sheeting avoids the problem of a joint occurring
on an un-supported part of a section which often leads to the sheet
gluing unevenly; requiring filling and sanding later. |
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| Again we start by building the panel over the plan but this time we have a taper so its not a good idea to put the spars flat on the board. With tapered wings the ribs don't sit at right angles to the spars so by jigging them you can still use a square when laying up the ribs. I had to make a couple of wing jigs so that the ribs would be kept parallel as they taper toward the tip. Again there was no hint on the plan, however, helpfully the rib templates had been drawn on top of each other. By drawing a line through the centre of the ribs leading edge to training edge and then another line parallel at the bottom of the the main spar I could calculate the packing using the datum of rib W3 on the building surface and the gap from here to rib W10 over the length of the spars. I had read from the little I could find about any model built of the Bulldog that they are susceptible to tip stalling so I paid particular attention to this part of the build and even work in a degree of wash out at the tip. |
Wash out reduces the angle of attack at the tip and helps to work the air in this area less; reducing the risk of the stalling. |
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Once the front and rear spar and jigs are pinned down
on the plan the normal process of adding the ribs begins. As I mentioned
before I am setting the dihedral with both centre and wing mating ribs,
here I've used the template made earlier. |
I like to leave the ribs to dry before adding the
top spars as I don't like to take the risk of everything moving when
I weight down the top set. |
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With the spars in place its time to add the leading edge doubler and vertical webbing, again front and rear of the main spar. I normally have a couple of jobs on the go so I have something to do while waiting out the glue. With the the wing made up of three panels even my restricted work space can be maximised |
so here I've started the other panel on another part of the board. Just like the tailplane the control surfaces, aileron and flaps, are initially built as one and then removed later. Here I've added the leading edge for these but not all the way to the inner rib just yet. |
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With a little rigidity built in its time
to flip the panel over and sheet. First sheet covers leading edge to
mid spar as before and the larger sheet is prepped. |
One of the reasons I did not add the flap leading
edge all the way to the inboard rib was the extra riblet at the trailing
edge. I tried adding this earlier but kept knocking it off so decided
to add this later.
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With centre and two outer panels reasonably complete its time to bring them together. This is a particularly critical part of the build and without great care it can all go Pete Tong. Read on and feel free to tut and roll your eyes. |
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| We start by cutting the slots for the ply wing braces, forward of the rear spar and front and back of the main spar. |
I've found the best way to create accurate slots is simple. Wrap sandpaper around a steel rule and open it up to the desirable size. |
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| The ply braces are of differing thickness. At this point the plan seems to have differing information regarding the the rear brace, in one instance it is stated as 1mm and another its 2mm. I only had 1.5mm ply so was wrong what ever it is. |
The wing braces are epoxied in place. You can see
now why the vertical web is not extended all the way to the root; the
braces are glued direct to the spars, filling the void. |
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If you've built the sections accurately
all should come together easily. Supporting the centre section so it
does not rock, lining up the leading edge, spars and trailing edge should
ensure good alignment. |
Again the plan was a bit shy on detail when it came to the dihedral, however, using the spar brace template and extending the line the length of the spar gave a measurement of around 3 to 3.25 inches if I recall. Find something that will support the wing tip at the correct height. I like to use biscuit or sweet tins, of course the contents must be consumed before use to avoid contamination in the workshop! |
You can see now why the rear spar brace has to be thin ply. getting it to bend forward to meet the outer panel spar is not easy. |
Okay here it is, the bit you were waiting for. At first sight all looks rosie here but look closely and the starboard (right hand) wing tip at the bottom edge of the picture. Remember I mentioned I had intended to build in a little wash out, well the angle of attack here is definitely out. At the time I came to join the wing panels the weather was very cold and this bright spark decided, while the glue was curing, to leave a small heater that is normally at the side of the workbench, set to low near by. I say normally, on this occasion it was stored under the workbench. Ten credits to the one that can explain what happens when a flat surface only secured at each end, is heated in the middle. Yep, the top surface of the bench, and with it, the building board took on the shape of Mount Snowdon and with it my well aligned wing joint. |
It took a week of evenings, very careful use of a hacksaw and a lot of coffee to recover this. I had to tease the joints apart clean them up, align and glue up all over again. This time no heat was applied. |
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| Time to fit the internal hardware. I started with the aileron and flap controls. With the surfaces still part of the wing this is a good time to sort this out as the rigging can't be out if you build everything in neutral. The plan provides most of the information you need but you could easily use a favoured method if you have one. |
Here I'm using a standard bell crank (90 degree horn) to turn the left and right movement of the control run into a fore and aft movement to move the controls surfaces up and down. This set up uses a single aileron and flap servo mounted centre wing. With the wing just over 60 inches and no mad aerobatics planned these should be fine. |
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| I used rigid wire snakes for both aileron and flap but a word of caution here. These need to be VERY straight to keep resistance down and in hind sight with such dihedral in the wing a good quality plastic snake may have been better. |
The horn mounting plates had to be fitted the other
way up than on the plan and at an angle to provide the range of movements
needed. Here I've used a drill to hold the horn in exactly the right
position while I made the control rods. |
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In theory bolting everything down should
make rigging later child's play. Lets see how many school boy errors
show up. |
The plan shows just two lens type lumps for the landing lights and a cutout for a clear cover on the leading edge. Never one to resist a gadget or two and we all like to personalise our models, I thought the addition of a couple ultra bright LED's would do nicely. | |
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| I added an extra doubler to the leading edge and created a torque box to keep the integrity in this area of the wing. The light box is lined with reflective tape and the two LED's and a resistor will be wired up to a micro switch driven by the Flap servo arm. I plan to get the power from a 'Y' lead from the receiver. |
The control snakes took some playing with and I admit to a bit of trial and error, lots of error. I fitted the undercarriage support plate and wing bolt blocks at this point also. The undercarriage plate needs to go in now as it will also support the aileron servo mount. | |
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| I'd planned all sorts of elaborate 'Z', 'T' and 'L' bends and probably even a figure of eight I'm sure but settled on a simple 'L' bend push / pull solution. |
Fabricating a basic right angle servo mount was pretty straight forward but there are commercial products on the market. I suppose you could even use servo tape but I've never been a fan. |
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| No surprise here, centre section gets the treatment first because the dihedral of the outer panels rule out doing this any other way. Completed in four sections, leading edge to main spar then either side of the servo box to rear spar and finally rear spar to trailing edge. |
Before sheeting the outer panels I had a good look at what was to come and decided to cut some of the dividing lines for the aileron and flap and also run a shape knife down between the rear spar and false leading edge of the control surfaces, leaving them attached only by the ribs. I've never built controls as part of the wing before and couldn't think of a way of accurately finding the cut lines after the top sheeting had been added. |
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| Remember the wing warp!!!!!!!! This was my final chance to make sure I could build it out. Making some packers from dimensions I extracted from the plan, I rigged the centre section level. |
Making another set of packers for rib 9 I made sure
the tip was pinned down with slight negative incidence (there's always
a little bounce back). |
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Again I made up a larger sheet on the building
board before sheeting the remainder of the wing from main spar to trailing
edge. |
Once the sheeting is dry its sanded back at the leading edge to the doubler then the leading edge stock is fitted. I've used shaped stock however the plan calls for 1/2 inch by 5/8 inch and plain to shape. | |
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| The shaped stock was not the correct profile and still needed shaping but I had it in my wood box and it meant less ended up on the floor. |
The wing tips are solid balsa block. These
were cut to shape over the plan. |
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| The blocks were added to the wing tips being careful not to glue the rear portion that would be the aileron end cap. |
Shaping and sanding is straight forward, just follow the profile of the wing for upper and lower surfaces. |
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| The underside has a taper (angled bottom surface), this is often seen on model training aircraft but is a real feature of the Bulldog as well. Again a lot ends up on the floor but the shape comes together if you follow the steps above. |
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| This is it then finally sheeted, roughly sanded to shape and with flaps and ailerons still part of the structure. |
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| The Bulldog has what is called a Plain flap which means the whole surface extends down rather than the Spitfire for example that has a Split flap were the lower surface extends but the top structure of the wing remains static. |
I used the saw cuts I made in the lower surface at the aileron and flap end caps as a guide to continue the job on the top sheeting. |
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| Following the part cut line made in the bottom sheet, the ribs are carefully cut through with a craft saw and then I used a long blade to cut the top sheet. |
This was a traumatic time as I slowly eased the parts
out to see if I'd managed to keep the cut line more or less where it
should have been. |
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Just like the tailplane, the sheeting is
sanded back to leave a fairing and the excess pieces of rib removed
and sanded back to the TE spar. |
Once removed, I labelled up each before I forgot which was which but with aileron and flap different lengths and the control horn holes already drilled only a donkey could get it wrong!!!. | |
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| The surfaces have a 1/2 inch square strip added and then sanded to a half round section. You do not need anything complex to draw the radii, If I recall I think this was a 5 pence piece, just as well we did not take the Euro I'd have been stuffed. |
Next the Robart hinges. I had marked on the plan where I had placed the reinforcing blocks so it was a simple task to transfer these back to the LE. Note: Robart hinges need to be positioned very accurately so pilot drill and keep checking. |
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| When all four surfaces are hinged I did a dry fit to check all went together well and that there would be good range of movements. The flaps only move down of course and although I haven't worked out how far just yet the movement did seem restricted. I found to get anything over 1/2 inch I needed to sand away the fairing in the lower sheet quite a bit. The other option would be to sand a different profile in the leading edge but I choose the easy option for now. |
Finally for the moment the control horns are refitted along with the links and a quick test with the servos connected proved there would be no major dramas later. |
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