Take one Dynam Spitfire...

[The Wright Stuff]

Wiring all done. I pushed the extensions through the tunnels, and then fed through an extra 6 inches or so, to allow me to later pull the joined section back inside the wing. Once it's through, the end of the cable can be carefully separated with fingernails and stripped.

Remembering (of course), to slide the heat-shrink tubing over the individual wires before they are soldered, it's quite a simple task to create a joint that is at least as strong as the cable itself (nice shiny bright solder), and probably much more robust than using plugs and sockets.

Finally, a larger diameter piece of heat-shrink tube over the whole cable, and it's ready to be pulled back inside the wing.

A word of warning (it's always when you least expect it, isn't it?). Be very careful when using a heat gun to shrink the tubing, because you have to work close to the wing. I managed to cause some of the paint on the wing underside to bubble up horribly - fortunately in this case without damaging the foam - and since I am repainting anyway, not an issue. A quick electrical test to ensure the servos are still working, and then the wiring's done!

[The Wright Stuff]

So with the wiring through the wing, the last thing to do is to sort the servos out at the other end. They are a fairly snug fit in the foam, so I just used a little epoxy to secure them in place - being careful to keep it well away from the moving parts. Then routing the wiring neatly by carefully tucking it into the channels. In the starboard wing, the aileron and flap servos are opposite to each other... this is the one I altered, cutting a small channel to join the one containing the aileron servo lead.

...in the port wing, by comparison, the two servos are the same way around, as the kit is designed.

I'll tidy up the area by making some thin slotted covers for the servos later on, but that will be one of the last tasks. Up next is joining the wings, and getting the dihedral somewhere near right!

[The Wright Stuff]

Joining the wings:

The dihedral on the model as designed, when assembled with the straight glass fibre rod supplied, is approximately 3 degrees. The full size aircraft has a dihedral of approximately 6 degrees (I think the exact figure varies between 5.9 and 7 degrees depending upon the model and wing type) but 6 degrees was the nominal figure I aimed for.

I was initially confused when offering a protractor to the leading edge of the foam wing, then realising, of course, that the dihedral angle is usually quoted as the angle between the wing and the horizontal plane. The angle between the two wings, is of course double this value, so 12 degrees was my target there. The difference between 3 degrees and 6 degrees might not seem much, but the human eye is actually very perceptive of small changes in angle, so it needs to be corrected in order to look right! I made a template in Powerpoint to use as a guide.

Therefore to increase the total angle from 6 degrees to 12 degrees requires that the glass fibre rod used for the wing joiner be supplied an additional 6 degrees of angle.

I used a solid rod of spring steel, slightly oversized and approx 6 inches long. Fortunately, I have access to a lathe at work, so was able to turn the diameter down until it was a snug fit inside the glass fibre wing joiner tube. Cutting at a slow speed left a banded surface which will improve glue adherence.

Once a good fit was assured, it was bent to 6 degrees in a metalwork vice, ensuring not to overwork the metal. The total weight of the piece was 40 grams.

[The Wright Stuff]

Finally, the ends were bevelled, so not to scratch the inside of the wing joining tube.

And the completed dihedral brace compared with the original template:

[The Wright Stuff]

I've now completed the big step: gluing the two wing halves together. I did this all in one go, and I'm afraid it was all a bit of an epoxy-setting blur, so I didn't take as many photos as I would have liked. I should probably mention that it is not necessary to glue the wings together in the kit as provided, or at least, there is no mention in the instructions. Each wing half screws to the fuselage independently, with the wing joining rod just push fitted into the tubes moulded in the wing. However, even with stock builds, others have found that gluing the wings together reduces flexing, and since I have modified the dihedral, in my case it is pretty much mandatory. Since the total wingspan is only 48 inches, this doesn't cause me any inconvenience from a transportation point of view.

The actual geometry does require a bit of thought. It's tempting to think of the dihedral alteration simply as bending the existing join upwards until the dihedral is correct and the wing surfaces meet at the top surface. However, while it would provide a nice neat join, if I did this, I wouldn't be able to fit the wing assembly into the fuselage. The dihedral change is actually a rotation, and that rotation takes place about a point. In this case, the pivot point is above the top wing surface, allowing the alignment of the bolt holes for the assembly to the fuselage to be maintained. If I wanted to glue the wing assembly to the fuselage permanently, then this process would probably be much simpler, because I could just hack at it and then fill in the gaps afterwards. However, I prefer to have the option of removing the wing if I need to, so the fit needs to be reasonably good. I sketched it out (neater version copied below - not to scale but the angles should be somewhere near right). As can be seen, the net result is a gap at both the top and bottom surfaces of the wing. That's okay, it can be filled and strengthened after gluing the wing.

After cutting the supplied carbon joining tube in half using a junior hacksaw, I used 30 minute epoxy to glue the new metal dihedral brace inside each half of the tube. This was then glued into the corresponding holes in the wings, and set at the correct angle using packing under the wingtips (you see, GCSE trigonometry does come in useful)! I made a couple of spacers from scrap balsa, and wedged them into the gap between the wings. It did take quite a bit of jiggling to get everything aligned and true from every viewpoint (I was beginning to think 30 minutes wouldn't give me long enough), but it's satisfying to sit back and let the glue set once everything is done.

In hindsight, another simpler approach might have been to use the fuselage as a jig, and hold the wing halves in place by screwing them to the fuselage before it set. The obvious disadvantage of doing this is the lack of access to control where the glue is going, although it might be possible to use cling film or similar to prevent the wing accidentally sticking to the fuselage.

[The Wright Stuff]

Anyway, the end result is pretty good. The wing fixing bolt spacing at the fuselage anchor point is unchanged, meaning modifications to the fuselage internals are minimal. There is a slightly different angle on the bolts, but I think this is okay: the bolts are nylon so allow for a little bit of flex. There are some minor modifications left to do to get the fairing between the fuselage and the top surface of the wing roots to fit properly, but I will fix this by building up the wing root attached to the fuselage a little: simply because from a modelling perspective it is far easier to shape a convex (sticking out) surface than a concave (recessed) surface.

Once set, the gap between the wing halves was then filled in with offcuts of balsa and gorilla glue, packing it to add as much strength to the join as possible. Even before this step, gentle testing of the wing flex was encouraging: with almost all of the flexing coming from the bending of the foam itself, rather than the joint.

Then I could stand back and admire the result!

[Colin Leighfield]

Good work, I'm sure that it will be worth the effort. I'd never thought about gluing the wing roots together as a means of reducing wing flexing, I'd always assumed that it was the foam wing panels doing that rather than bending from the centre. I might try it. Is there a reason for the colour difference between pictures 3 and 4 in your last post?

[The Wright Stuff]

Thanks Colin, no actual difference in the colour. I used a different camera for the outside shot, and the colour balance appears to be different.

[The Wright Stuff]

A little progress this week. I've started the flaps: two inboard and two outboard sections. I marked out the trailing edge shape using the wing lower surface as a template, and referring to photographs of the full size wing underside to scale off the shape and size. They are reasonably accurate representations apart from the length. On the real Spitfire, the split flaps went all the way outboard to the aileron: on mine they will stop about 5 mm short of the aileron. A few reasons for this. Firstly, the model ailerons are not quite to scale, so a bit of compromise is needed to get it to look right. Secondly, I'm not quite sure whether air spilling over the end of the flaps will have any adverse effects on the aileron effectiveness on the model. Thirdly, and the main reason, is simply for strength: it avoids leaving a weak point in the foam wing thickness where the flap meets the aileron on the full size bird.

The shape of each flap panel was cut from a sheet of 1 mm thick hard balsa, and the hinges epoxied in place, starting with the small inboard sections. A strip of thin ply was glued longitudinally along the hinged edge, to give the structure some stiffness. The 'ribs' were built up from strips of ply: it's not really possible to make them to scale on a model of this size, but it does give a representation of the internal structure, and stiffens the balsa sheet.

Finally, I laminated another section of balsa on top, sandwiching the hinges, using aliphatic resin to assemble and to fill in any gaps. Suitably encouraged, I built up the longer outboard sections in the same way.

Finally, they were sanded back on a sheet of wet and dry paper stuck down on a flat surface. This tapered the cross section, as is clear by the 'plywood contours' in the photo: I love the way it does that - it makes it very easy to see how much has been sanded off!

[Colin Leighfield]

You're doing a great job here. These slow down very well without flaps, so this one is probably going to hover!

[The Wright Stuff]

Yes.

The irony is, of course, that the extra weight of the flap servos and flap control surfaces means that it may well benefit from them after all!!!

[The Wright Stuff]

Not a huge amount of progress so far this week, but I did get around to finishing the fine sanding and then painting the flaps. It's probably not the most efficient way to work, but I find that painting bits as I go along helps with my motivation, because they are parts that are then 'completed'.

I also added the control horns to the outboard flaps, aligned to the servo arms: these are not symmetrical port to starboard because the servo positions are not symmetrical.

The 'inside' of the control surfaces are painted with Humbrol no. 78 (cockpit green). The outsides are painted with matt white for now (this will eventually be the base for the invasion stripes). the photo above shows the pilot holes drilled for the control horns.

The full set: upper (inside) surfaces above and lower surfaces below...

The control horns were the small SLEC ones, screwed into the balsa/ply laminate with a smear of epoxy for extra security.

Edited By The Wright Stuff on 03/09/2014 18:01:29

[The Wright Stuff]

Cutting the flap recesses in the wings:

Okay, so I've finally had a bit more time to work on this. The next (and quite big) job was to cut the corresponding recesses in the foam wing to take the flaps. This would have been a relatively simple task of slicing the foam with a sharp knife, but unfortunately the 'flap-ready' vee groove that is sliced into the as-supplied wing coincided with the required hinge point, so there's some filling in and reinforcement to do.

Using the finished flaps as templates, the area to be recessed was marked out on the wing underside with a fine-tipped permanent pen, and then cut with a sharp (new) modelling knife, all the way though to the vee groove. It was far from perfect - however careful I was, there always seems to be a couple of bits where the blade 'digs in': hence the filler in the picture below. The hinge line was defined by a length of hard balsa, which also acts to stiffen the wing, to partially compensate for the foam I removed. I just used a couple of pins to hold the balsa in place while the gorilla glue dried!

I also ran a strip of balsa along the bottom of the groove, again for stiffness and to fill in some of the volume. The expanding gorilla glue does the rest. Finally, excess glue was trimmed back flush with the foam surface (best done after the glue has finished expanding, but before it has hardened completely, so about 4-6 hours after application). I then used ordinary lightweight filler to smooth off the surface ready for final sanding. I found it took a few cycles of painting (to harden and bind the foam), filler and sanding to get the finish good.

I've not quite finished this yet, and also need to do the slots for the inboard flaps, but I thought an update was overdue

[Colin Leighfield]

I'm impressed. When I looked at what was needed to do this, I decided not to bother! It will be worth the effort though. When you've got it ready, from memory the flap angle on all production Spitfires was 86degrees.

[The Wright Stuff]

Posted by Colin Leighfield on 22/09/2014 19:08:01:

When I looked at what was needed to do this, I decided not to bother!

Oh dear! That means I'm not making it look easy enough to inspire!

Yes, 86 degrees would certainly look good, but I'll allocate it to a proportional control initially, so I can deploy a little at a time (yes, yes, not prototypical, I know). My experience with the Hurricane has shown that half flaps for landing tends to be optimal, since full flap robs so much aileron response that I've had a few 'moments' (thankfully resulting in just a slightly crinkled wing tip).

[The Wright Stuff]

I'm afraid that progress is fairly slow-going at this point, and I'm about to embark on a work trip, which won't help, but I did manage to complete the recesses for the inner flaps. First, the positions were marked out on the wing underside, using the completed flap panels as templates, as before.

The interesting geometry means that when viewed exactly from underneath, the inboard flaps appear to be on a perfectly straight line with the outboard ones. However, when looking from the trailing edge of the wing, the inboard flaps are angled upwards towards the fuselage centreline, following the dihedral of the wing.

Now, the lower fuselage at the wing root isn't exactly the correct shape on the kit, meaning that the recesses have to be cut relatively deeply in order to achieve the correct relative angles (and to ensure the inner and outer flaps don't foul each other when lowered). The fuselage bottom will be re-shaped very slightly at a later point.

As before, the recesses were cut out with a sharp blade, and any errors filled in and sanded. Finally, slots for the hinge locations were added to relieve the pinholes on the hinges. At this point, the flaps were test fitted in their final positions, but without actually gluing the hinges to the wings.

A slightly longer job than originally envisaged, but I'm getting there slowly...

This final shot shows the relative angles quite nicely. The flaps will splay as per the prototype when lowered, which will be hopefully worth the effort when viewing those low slow dirty passes!!!

[The Wright Stuff]

Well, inevitably, a pause turned into an extended break, but I've pulled it back out of the cupboard! I will finish this project. I will!

Easing myself back into it by doing the hinging for the flaps. I'm guessing this is a marmite-style love-it-or-hate-it task. I first assembled the hinges onto the pins, and used a tiny drop of cyno to stop the pins from vibrating out over time.

Fitting them was fairly straightforward, though, using a scapel to cut slots for the hinges to locate in the recess, and then test fitting until the correct location is found.

The hinges were glued in using 15 minute epoxy, tilting the wing so that gravity took the glue away from the pin, and filling in the gaps with extra glue applied with a needle, keeping the pin area as clear as possible.

The clamps are there to hold the flap panel shut against the lower surface of the wing, to ensure that in the closed position, the alignment is correct.

[Colin Leighfield]

Keep going!

[The Wright Stuff]

Thank you very much for the encouragement, Colin!

So I've been tinkering with the connections to the inner flap panels tonight, and have decided to keep it fairly simple. Good photos of the deployed flaps from the correct angle were quite difficult to come by, and crawling underneath the wings at Duxford tends to get some funny looks from the other visitors. This unusual photograph from Alfred Price's The Spitfire Story is fairly interesting, sadly after K5054 made a belly landing.

I'm sure there were detail differences between marks, but this gives the general idea of the geometry. My solution is to use a short section of 18 swg piano wire, slightly bent in the centre, and glued into the inboard panel only. It is left to rotate in the outer panel, which has a slightly oversize hole drilled to allow some accommodation to the slightly different angles in the open and closed position. I started with a small hole, and gradually opened it out as I test fitted: too small and the panels will bind, too large will produce slop in the inboard panel, although that is not likely to be critical.

The photographs show the hole drilled first in the inboard panel (above), which is then used to mark the corresponding axis and position on the outboard panel. This was then drilled to fit (below):

Today's work was short and sweet. Off to make pancakes, now!

[Colin Leighfield]

The prototype K5054 originally had a down flap angle of I think 64 degrees. It wasn't enough, so they increased it to 86 degrees and I think that remained all the way through the various marks. The flaps were two position, up or down! To assist rapid take-off of some Seafire's from aircraft carriers, they inserted wooden wedges between the flap and wing to give an angle of about 15 degrees(?). They were held in place by the upward spring pressure from the flap, to release them after take-off the pilot selected down flap very briefly so they dropped out, then raised them again.

All wings up to the Mk21 had split flaps, the revised stiffer wing on the Mk21, 22, 24 and Seafire 45, 46 and 47 had plain flaps, but I think the down flap angle was the same. Going to the trouble of creating the inner and outer flap sections on your Dynam Spitfire is really ambitious, it looks as if you're doing a good job. Even without flaps, mine slows down to a very low air-speed, so it seems likely that yours will be able to hover!

[The Wright Stuff]

Well, I've had a productive few days - sorry about the lack of updates. I've finally completed the flaps - which since they are probably the most ambitious part of the project hopefully means that I've broken the back of it, figuratively speaking of course!

I completed gluing the hinges, filling in the few gaps that remained carefully with epoxy, checking for any unwanted binding as I went along, and then let it all set hard. I fabricated some control linkages using 18 swg piano wire and then put it all together for testing. It all appears to work as expected.

Colin, I don't think I can quite get to 86 degrees but close enough that the eye isn't going to notice the difference. Here are a couple of photos showing the range of travel from up to down. The lines drawn on the bottom of the wing indicate the positions of the invasion stripes - but I'm getting a bit ahead of myself!

[The Wright Stuff]

The next job on the list is reinforcing the wing: the leading edge has a cut out section in the foam between the holes for the cannons and the retract bays. This is a weak point and allows quite a bit of flexing, so I decided to stiffen it by gluing in a wooden spar.

The colourful craft lolly sticks have a claim to fame: it was the last purchase I ever made from my local Woolworths! Now I finally have a use for them!

After marking out, I used a scalpel to cut two paralle tracks about a millimetre apart - enough to accept the thickness of the stick. It was not necessary to remove any foam material from the slot - the foam simply squashed down.

Being more liberal with the epoxy this time, the reinforcements were glued in place, and any gaps filled with glue, including the adjacent join between the foam pieces.

The addition certainly seems to have restored some rigidity to the section. Now to get the retracts sorted out...

[The Wright Stuff]

Despite having tested all of the hardware and found it to be working when I bought the plane, predictably enough, when I retested the retracts at this point, one of them had stopped working. I guess I wasn't so surprised, since they do seem to be a weak point of the Dynam products in general. I tried fiddling around with the microswitches, end point adjustment, and then decided that my time was more valuable than my money, and promptly consigned them to the bin, to be replaced by E-Flite 10-15 retracts.

The wiring appears to be fine, so I retained the existing connection through the wing, opting to solder a socket onto the end of the wires, so that the E-Flite units can be plugged straight in.

In fact, as the photo above shows, the Dynam retracts were not completely useless - I did cut up the plastic mounting plate to use as a spacer to rake the angle of the deployed undercarriage forward!

[The Wright Stuff]

In fact, now I have a dilemma. The undercarriage legs supplied with the Spit, complete with the plastic moulding to represent the shock absorbers and the connecting point for the gear doors, won't easily fit into the E-Flite units because the plastic parts obstruct the retract body when in the retracted position.

Do I cut away the plastic and use the existing leg, or replace it with the E-Flite metal and bend it to suit? Hmmm. Colin, I don't suppose you recall your solution, do you?

[Steve T]

I've only just found your thread! I have the dynam spit, in the appalling light blue. The only work I have done is a respray to an eggshell blue under wing and green and brown upper, the replacing the retracts with ones that actually worked. I shall now study your thread and make serious use of it, as if I didn't have enough builds on the go, but thanks anyway, well done it really does look the biz so far.