Nijhuis 63" Spitfire IX

[andyb]

Model Selection

Had a long think before deciding to build a sport-scale Spit; one of the (many) things that I have difficulty with on scale models is any part of the engine or silencer sticking out of the cowl. The requirement to avoid this heinous crime suggested that the model would have to be larger than the sort of thing I'd normally build so that the engine would be easier to hide inside the cowl, or it'd have to be electric.

However, bigger models usually take a lot longer to build so electric was the favourite solution, and in any case I've recently managed to prise Gareth's Dad's Sebart Angel 50 out of his hands so a 6s model weighing about 8 - 8.5 lb could use the same packs.

So, Decision #1: the Spit was going to be electric using the same 6s packs as the Angel. It also had to have retracts, and it had to be a practical sport-scale model that can be flown every weekend - there's no point spending all that time and effort and then wrapping the thing in cotton wool.

I did think about ARTFs, but every ARTF that I know of has problems of one sort or another, some of them aren't too bad if you squint a bit and only view them from a distance, but they all seem to have the usual issues with design, quality control and/or robustness, particularly in the undercarriage department which, on our patch, isn't going to go well.

There are (regrettably) very few surviving "real" kits of Spitfires the right size, the only available one that I know of is the Top Flite Spitfire IX which, whilst being better than your average ARTF is still compromised in overall shape and is possibly slightly over-engineered.

That leaves plans. I didn't want to spend the time to cut the parts myself, so anything that didn't have CNC/Laser cut parts pack available was discounted. The best plans are probably the Brian Taylor range now sold by Traplet, but there are usually lots of parts because they are very accurate, and this had to be a relatively quick build. That left the Tony Nijhuis Spitfire IX, and it seemed to be a really good compromise between practicality and scale accuracy.

Subject Selection and Accuracy

At this stage, I still have no idea whether it will be a Mk IXC, IXE or XVI (Packard merlin), or whether it will have clipped wingtips and the later (more pointed) rudder, or whether it will have the later carb intake or the early one (converted from a Mk V airframe) . I did briefly consider a Mk VIII but that would require a retracting tailwheel and I can do without the complication. And there are at least two different shapes for the exhaust stubs, not yet sure if these are associated with Roll-Royce or Packard built merlins, or whether modern restored aircraft have some new-shape stubs.

Also, there's a scale fidelity issue that I've yet to resolve - the top line of the cowling is shown in some drawings as very slightly bulged, and it's remarked upon in some picture captions. However, no matter how hard I look at it, I'm not at all sure I can really see it and I suspect it might be an optical illusion caused by a slightly low camera viewpoint. Perhaps someone will be able to clear up the confusion before I get to the cowling...

Power System

I happen to have an AXI 4120/18 which ought to produce about 900 Watts on a 13 x 8 or 14 x 7 prop and 6s - some experimentation will be required (although a 7" prop might not have enough pitch speed to fly it properly). The final weight will probably be about a pound heavier than the original which was powered by an ASP 61 FS, so the total weight will probably be on the order of 8 lb, maybe 8.25 lb. This should be OK for just over 100 W/lb, or a bit more with a bigger prop and/or a battery with lower internal resistance.

Practicalities

The full-size Spit had a castoring tailwheel, but I'm not sure this is a particularly good idea from the point of view of ground handling and controlling the swing on take-off. There's a limited amount of space in  the rear fuselage so perhaps the decision will make itself, but the options seem to be:

• Fully-castoring tailwheel
• Spring-centered castoring tailwheel
• Steerable tailwheel

Luckily, the decision doesn't need to be made yet.

The other issue is going to be cooling; the power train will be capable of around 900-1000 Watts, so even if it's operating near maximum efficiency most of the time the motor will get hot and the ESC and battery will get warm, so there will have to be some cooling. It should be possible to get air out of the cowling by using vac-formed exhaust stubs and an air exit hole in the rear fuselage can probably be arranged, but I don't see how a hole in the lower cowling to get the air in can be avoided.

Plan and Parts

The plan and CNC/vac formed parts pack was ordered; I prefer to select my own wood and in any case, I have enough of the stuff to start a small model shop. There were a few anxious moments with the retracts but it transpired that the retract and oleo set were still available from Unitracts.

This is the plan pack as delivered from Tony Nijhuis Designs; overall quality and wood selection is generally very good:

Details

I'm intending to make this quite a detailed record because a couple of people who don't normally build have expressed an interest, and with a bit of luck it might inspire them to have a go. There is also the possibility that I might need a bit of inspiration if I flag a bit after a couple of months.

Have started on the wings, more soon...

[Swale]

I really admire you for taking on these kit builds, I simply wouldn't have the know how or even the time and pateince.....

But for an artf apart from the tailwheel whats wrong with this http://www.ytinternational.co.uk/spitfire_120/spitfire.htm ? I would certainly consider it and hoping to get one in the future I'm so far pleased with the quality of my hellcat even if the manual is well....lacking for a rookie builder like me .

or is it just me un-trained eye?

[andyb]

But for an artf apart from the tailwheel whats wrong with this http://www.ytinternational.co.uk/spitfire_120/spitfire.htm ?

Um. Apart from the non-retractable tailwheel?

Well, IMHO:

- Colours look wrong to me.
- Silencer usually exposed
- Undercarriage track too wide and angles not scale
- Wing fairing is wrong
- Nose looks a bit wrong from some angles
- I fear there may be problems with the robustness of the U/C
- Have a look on some of the public forums (e.g. RCMF?)

I'm not saying that a plan build is faultless, just that if any systematic issues such as these are identified, they can be corrected during the build. And of course, the colour and finish is entirely in the hands of the builder.

Sorry, but you did ask! 

[andyb]

So, remembering that a journey of a thousand miles begins with the first step, and making use of the PDF instructions that can be downloaded from the Tony Nijhuis Designs web site...

Construction - Wings

The first thing to do was to separate out the ribs from the CNC-cut liteply blanks, sand the edges smooth, chamfer the front edges to match the curve of the L.E. and make sure that the obechi spars were a good fit:

Details

As it happens, all the spar slots required a small amount of trimming with needle files, and the rear 6mm x 3mm slots needed to be enlarged quite a bit. And having looked at the 2mm liteply ribs used to support the retract bearers, I thought it wise to make a couple of doublers for ribs 2 and 3 - the bearer slots have to be offset to the rear by about 0.8mm to allow for the backward sweep of the retract bearers.

Luckily, the retract position on the bearers was checked before assembly and it transpired that there was a minor problem:

Details

In order for the undercarriage leg to extend all the way, the square-section aluminium rod has to slide through rib 3 but as you can just see, the slot is deep enough for the oleo leg but not for the rod.

The easiest way around this was to make the slot in rib 3 a bit deeper...

Details

...as shown here; this allows the actuation rod to slide all the way over and the  leg to extend properly, so all is now well.

The ribs can now be glued to the bottom spars; this is one model that will really benefit from fast cyano, I have to put up with the odourless stuff from Deluxe Materials that takes longer (15 - 20 seconds) to set:

Details

The top spars start to give the structure some rigidity, the front and outer sections are actually curved slightly which can just be seen in this view...

Details

The spars can easily be steamed to shape using a kettle, it's probably best to over-bend them slightly as they're more flexible for a few minutes after steaming and it's easier to bend them back slightly if required. The rear 1/4" x 1/8" obechi spar can be slotted into place by pressing the back end of the first half dozen ribs down to the building board, inserting the cut spar and just holding it until set.

The aileron spar is relatively straightforward...

Details

...I found it easiest to cut a piece of medium 1/4" to the right chamfer and then glue it to a couple of ribs at a time, just holding 'till set, starting from the root end.

The front 1/4" square obechi spar on my wing is sunk below the surface of the wing rib:

Details

One way round this would be to add a bit of 3/32" balsa at each rib and sand it back to the rib profile, but I think a better (stronger) solution would be to glue a strip of 1/32" balsa onto the spar and sand the spar to match the rib profile.

At this point the structure can be removed from the board and the bottom spars added, followed by the leading edge:

Details

The L.E. is made from soft 1/4" balsa, pre-curved to shape using the steam from a kettle as was done with the wing spars. Again, the easiest way to glue it is to do two or three ribs at a time and just hold until set.

The wing is now - amazingly - almost straight with perhaps a hint of unwelcome wash-in at the tips, although its still quite easy to twist and will be until both wing skins are attached. Not much else can be done to it until the false LE and spars are sanded to shape, so I might as well make a start on the other wing.

However, I really don't think I'm going to be able to build a straight wing using the method outlined in the instructions (top skin first, bottom skin last). And in any case, I want some washout in it because I don't want Mr tip-stall to be paying a visit, and I have seen one of these drop a wing when provoked. And if washout is added, it'll be safe to throw off a slope, should the need arise.

The real Spit had 2.5 degrees washout so that's what I've chosen to use. What I've done is to estimate the centreline of ribs W1, W6 and W11 and then calculate the amount of packing that will be required just forward of the rear spar to make the wing flat, and I've then added some additional packing to reduce the incidence at W6 by 1.25 degrees and the incidence at W11 by 2.5 degrees:

Details

The plan is then that when the wing structure has been sanded to shape, the wing halves can be temporarily clamped together and the retract units, oleos and wheels installed and checked, followed by the retract servos and pushrods. When everything is working faultlessly (and those few words will take hours and hours!), the retracts can be un-screwed, the aileron servo hatch bearers installed and the bottom of the wing can be sheeted.

When it eventually comes time to sheet the top of the wing, the structure will rest on the washout packing pieces so it should end up with the correct amount of washout, and it should (hah!) be the same on both sides.

[Mike71]

Great to see another warbird on the building board.

A note on castoring tailwheels. I had one of these on my Jungmeister. Not by design, the linkage broke very early on. I was surprised by how effective it was. The trick seemed to be to have a lot of up elevator available to keep the tail down and allow reasonably high power settings when taxying. It was a bit of a knack, but by increasing the up elevator travel I eventually could taxy round successfully in even strongish winds (I flew it in 15kts plus on one day) with just power and rudder alone. That said the Jungmeisters undercarraige was a lot further forward than the Spit, thus the risk of a nose over was less. During take off I believe it's the rudder that will control the swing, not the tailwheel.

I considered having a fully castoring tailwheel on my Spit, but as it was relatively easy to install, went with the steering option.

Full size light aircraft with this (very common) set up obviously have the luxury of differential braking. Believe it or not, the A320 can dispatch with the nose wheel steering U/S, though I've never done it myself.

Mike

[Swale]

But for an artf apart from the tailwheel whats wrong with this http://www.ytinternational.co.uk/spitfire_120/spitfire.htm ?

Um. Apart from the non-retractable tailwheel?

Well, IMHO:

- Colours look wrong to me.
- Silencer usually exposed
- Undercarriage track too wide and angles not scale
- Wing fairing is wrong
- Nose looks a bit wrong from some angles
- I fear there may be problems with the robustness of the U/C
- Have a look on some of the public forums (e.g. RCMF?)

I'm not saying that a plan build is faultless, just that if any systematic issues such as these are identified, they can be corrected during the build. And of course, the colour and finish is entirely in the hands of the builder.

Sorry, but you did ask! 

Yes to be fair now that you point it out after comparing pic with the real spit vs the YT your right there are some issues.

Not so sure I can agree on the colour.
Retracts I think will be fine if there anything like the hellcat (knock on wood) thery appear everybit as stong looking as what your pick is showing but hey what do i know.
Yes wing fairing is definatley wrong LOL (shame)
Silencer......surely a laser or RCV can be hidden if not flexi exhaust maybe?
Cant see a prob with nose but again probably cause Im a bit rookie in that dept.

''Sorry, but you did ask!  '' no need to apologise nothing wrong with learning.

I think all in all yours and mikes spitfire will most likely always be more true to scale and look prettier.....and I do admire kit builds and of course even more so scratch builds there way over my head mind you, unfortuantley I guess with todays life style and the ease of ARTF (well sometimes atleast) it seems that kits are dying out, I guess I'm guilty of being an ARTF guy.....but I just prefer to spend my free time flying.

As I say Kudos to the builders 

p.s sorry if Ive junked up your post a little although I think its likely a good thing pointing out the pros and cons....things like this might inspire a few more builds

[Mike71]

Just to enter the debate:

The nose looks wrong 'cos it's a Griffon engine mark. (I quite like these, unlike most Spit enthusiasts)

The Mark 9 had a fixed tailwheel, as has mine.

I build 'cos I enjoy it!

Mike

[andyb]

The nose looks wrong 'cos it's a Griffon engine mark. (I quite like these, unlike most Spit enthusiasts)

Sorry, my original post wasn't clear. What I meant to say was that it looks wrong when compared to photographs of the full size Spitfire Mk 14 - can't quite put my finger on why. The area around the windscreen looks a bit suspect as well.

The Mark 9 had a fixed tailwheel, as has mine.

Which is fine, it can be left dangling. However, the mark 14 has a retractable tailwheel so the model won't look right with one that doesn't retract. IMHO, anyway.

I build 'cos I enjoy it!

So do I. The difficulty for me is that I have quite a short attention span of maybe 3 or 4 months, so a build longer than that can become a bit of a slog, and it's something that I need to deal with somehow because life is too short to have a loft full of part-completed models... 

A.

P.S.
Any thoughts on the issue of the bulged cowling top-line for a Mk 9 / Mk 16? What does the Brian Taylor cowl look like?

[Swale]

Well that's the main thing if you enjoy it than thats great I guess it most be very satisfying.

[Mike71]

Andy,

Yeah maybe the YT nose looks a bit wrong even for a Mk14, which yes definitely had a retractable tailwheel. The YT machine is not a bad effort. At least it's painted. Iron on films just don't look right on warbirds, too shiny and they look tatty very quickly. Means to an end though.

You'll do well to get this out in 3-4 months, I doubt I could get the engine attached on mine in that time. 1 year and counting for me.

At the moment there's an excellent Mk 8 walkaround feature on Radio Control Scale Builder. You have to cough up $20 and subscribe to get it, but it's very good.

Failing that I have the traplet walkaround disc, which isn't nearly as good, but you'd be welcome to borrow.

My cowl looks like this.

Mike

[andyb]

I've been thinking about subscribing to RC Scale Builder for a while, so that what I'll probably do. I think I can detect a very slight bulge in the top of your cowl moulding, and I now think I might be able to see it in some photos.

You'll do well to get this out in 3-4 months

Yes  . I'm going to have to rely on regular motivational talks from fellow club members!

A.

P.S.
very nice F4F you've got there...

[Mike S]

Andy.

Good to see a build thread that goes in to detail not just about the build but also the facts about the chosen aircraft. I have a the MK IX Topflight spitfire which I brought part built as a future project from Gareth. The cowl has bulges moulded in. To me though the cowl rocker cover bulges seem over sized on the topflight cowl.

I am slowly working my way towards the spitfire but will tackle that when I have built the P47 as I should gain some experience from that as I need to reverse engineer the spitfire to rebuild it.

I am watching with intrest.

[andyb]

I think the sideways bulges are correct, it's just the top-line of the cowl that I'm wondering about...

A.

[andyb]

Not that much progress for a few weeks because I've been away on business and was then struck down with a lethal Scandinavian ear-nose-throat bug - sounded like Barry White for a week afterward. However, there has been a small amount of progress; here's how the LE & TE are shaped...

Details

...because I'm paranoid about taking a chunk out of the ribs with a razor plane or Permagrat block.

The other bit of progress is the other wing, which I've not documented because it's just like the first one:

Details

The next job is to fettle the u/c units with the oleos and wheels so that they can be fitted, set-up and glue the bearers in place with the units in situ, then add the webbing and extra reinforcement around the u/c mounts.

The other thing I suppose I should mention is that I have half an idea of making this a dual purpose Electric/PSS model; not completely sure how to do this at the moment but removing the retracts, retract servo, motor and ESC might get the weight down to about 5 1/4 lb, which will give a wing loading of about 18 oz/sq ft which for a PSS model of this size is very acceptable; but that's for later.

[andyb]

This build is going to have to go on the back-burner 'till the spring as I have over-committed myself in other areas... 

A.