Curtiss-Wright CW-21B, Rareplanes 1/72 vacform

[Mitch K]

I have a real soft spot for the fighter aircraft of the early part of the second world war, in the period before uniformity and standardisation on a few (albeit highly successful!) designs.

 

The Curtiss-Wright CW-21 is a classic example of what I'm talking about. The aircraft was designed purely for export, as a high-speed, fast-climbing interceptor aircraft, for use by nations where there was limited strategic space to ensure enough warning to respond effectively to air raids. The type was built around a Wright R-1820 Cyclone engine (which was export permitted), and achieved a rate of climb of well over 4500 feet per minute, which is quite astonishing considering that neither the Spitfire I nor the Bf 109 E could achieve even 3000 feet per minute.

 

Of course there was a price for this and the price was a very light structure, light armament and a total lack of protection (no pilot armour, no self-sealing fuel tanks etc). The Nationalist Chinese Air Force was interested, having seen the prototype deal with a high-flying Japanese bomber during the sales pitch. Three were delivered complete by Curtiss (all of which were lost in accidents) and 27 were supplied in kit form for local assembly but none were completed before the factory was overrun by the Japanese.

 

The Dutch Air Force too had been looking for additional fighters and had spotted the CW-21. They ordered 24 of a revised version, the CW-21B. This version had an inward-retracting undercarriage, rather than the rearward retracting version with fairing used on the original, plus a partially retractable tailwheel and the addition of a small amount of armour plate in the rollover pillar behind the pilot. These changes slightly reduced the climb rate to "only" 4500 fpm but allowed a top speed of 315 mph.

 

The Dutch wanted some other changes: four Browning-made 7.7 mm machine guns were to be fitted, and the armament was to be relocated from the nose to the wings. Additional wing fuel tanks of 20 gallons each were also requested. Curtiss-Wright suggested that the Dutch might be better leaving the nose guns where they were and adding two additional 0.5" Brownings in the wings. The eventual compromise was to leave the four nose guns and not alter the wings at all as the time to complete these redesigns was too great. As it was, the Netherlands was overrun by the Germans before any of the CW-21 were delivered, and the whole lot ended up in the Netherlands East Indies.

 

The kit comes as a single sheet of mouldings, plus a vacform canopy. The only plans and instructions are printed on the two sides of the cartons. Later Rareplanes vacforms I built in the past (F3 Demon, Supermarine Swift etc) included white metal undercarriage parts, but in this case all you get are the tyres!

 

 

The reverse:

 

 

There is some evidence of over-attenuation of the mouldings, especially at the edges of the fuselage where the cowling fits and near the tailplanes. I filled the back of these with layers of Milliput and car body filler to provide strength.

 

 

Over in the "Tips and Tricks" area there's a fantastic vacform build guide, written by the great John "Aeroclub" Adams. There, he talks about outlining the parts and being guided by this line at the sanding stage. This is invaluable advice, as I found out back in the 1980's and it's as true today. Follow the line on the part!

 

 

Building a vacfom propellor really is too much like hard work, but based on the kit part and some plans, I sourced one from the spares box. I think this is from a Hawk 75, but it looks very close. Other than the fact it was a constant speed unit I haven't been able to find any definitive details. The next stage is scoring around all the parts with a scalpel and popping them out of the sheet. The spinner was filled, as the end is just about transparent unless you do.

 

[Beard]

The CW-21 is an interesting aircraft (didn't some of them fly into a mountain on a ferry flight?) and it's interesting to see a vacform being made, especially as I have a couple in the stash and am always looking for tips.

[gingerbob]

Cool- I recently- finally- got a 48th vac of this.  I like those early "oddballs", too.

[kev67]

Nice to see another vac form being made

[Courageous]

A vac build, brilliant. 

 

Stuart

[Mitch K]

On with the usual vacform process: score around the parts and pop them out, then sand down to the pencil line. Back in the day, I used do all of this sanding with 600 grade wet and dry. It took AGES! I've done all this with 240 grade, which is vastly easier.

 

 

I don't like the kit seat, so I scratched this one up, plus a new rear bulkhead. 

 

 

I found a resin Wright Cyclone on Ebay, so I'll re-do the cowling to fit this.

 

 

So far, so good! So, therefore, we hit an issue. With the wing sections sanded down, I compared them to the Rareplanes plan. The upshot of this is that the wing appears too short in span.

 

 

The frame line on the kit part indexes correctly on the drawing, but if you do that, there's a gap between the wings, where there should be a butt joint. A check on available data gives the span as 35 feet, scaling to 148 mm, which agrees with the Rareplanes plan and other drawings I have. The kit wings are too short in the root area, by about 14 inches overall!

 

I cant see any way to correct this, as the kit has the wing root/fuselage area moulded into the wing.  The real kicker is not just that the model might look odd in plan. Let's face it, the number of people who will know it's wrong will be very small: this isn't a Spitfire/Bf 109 where even the most subtle errors are obvious to a multitude on here. The error makes the undercarriage wrong, both in position and length, and that will make the stance and ground line odd: I just hope the prop clears the ground!

[Mitch K]

This build feels a bit like you can't do anything until you've done everything else, so I've just bitten the bullet and decided to go at it.

 

I've assembled the wings. The right-hand side is the upper surface, left-hand side is the lower surface. They're intended to butt together along the underside centre line, and the bulges on the upper wing index with the fuselage to allow you to set the dihedral. To be honest, I think that will work about as well as a chocolate teapot, so my plan is to build the wheel wells, then open up the mating surfaces and fit a balsa spar. OLD SKOOL BABY!!!

 

 

The centre line of the wheel wells was taken from the drawings. Problematic, but what else to do?

 

 

The wheel wells were scored with a compass, cut out with a scalpel then reamed with a large drill bit to get them properly rounded. There's quite a lot of scoring damage near the holes but hopefully a little filler will cure that. Hopefully.

 

 

After that cutting the gear leg sections was simple enough. Next step is to fit floors and sides to the wells. I can't find a single picture of the wheel wells, so the detail here will be pure "creative gismology" as Shep Paine used to say.

 

 

The wheels aren't up to much, not helped by my ham-fisted construction. I wish the spares box had something the right size!

 

[thorfinn]

Being an old and experienced Rareplanes fan, I'm filled with admiration for anyone who tackles one of these little jewels. Thoroughly enjoying your work thus far!

Cheers

[Courageous]

It's good to see a Vacform in progress. You're making good headway.

 

Stuart

[Mitch K]

I installed some sprue in the outer end of the wheel wells, pre-drilled to take the scratch-built undercarriage legs (not even started yet!). The first stage of boxing in the wheel wells was to fit the roof.

 

 

From the floor, I added straight sides (easy) and then a ring of 10 thou plastic card to wall in the wheel area itself.

 

 

I scratched up an instrument panel and radio (the latter sits directly below the former on the Dutch aircraft);

 

 

And a seat;

 

 

[bristol boy]

Excellent, you can’t beat an obscure subject made from a vac kit, proper modelling !

[Beard]

Lovely stuff. Unless it's a trade secret, how did you do the instrument panel?

[gamevender]

I may have come a bit late for this, but instead of using a pencil to line around the parts, which can be lost if you are wet sanding, before I do anything I lightly primer the entire sheet some color that contrasts with the white of the vacu-form sheet. Cut out the parts as normal. You'll see a white edge where you've cut through the primer. Sand until this white edge is gone and you're at the kit part. It's much easier to see if you are wet sanding. 

[Mitch K]

50 minutes ago, Beard said:

Lovely stuff. Unless it's a trade secret, how did you do the instrument panel?

It's a piece of 40thou plastic card, and the instruments are drilled part-way through. Painted black, drybrushed panzer grey. The dials are made by filling the well with mid-grey acrylic, then part-filling over this with Indian ink, then using white for the markings on the dial faces. Slow, but cheap! I was lucky that I found one photo of the CW-21 instrument panel I could crib off.

[Mitch K]

22 minutes ago, gamevender said:

I may have come a bit late for this, but instead of using a pencil to line around the parts, which can be lost if you are wet sanding, before I do anything I lightly primer the entire sheet some color that contrasts with the white of the vacu-form sheet. Cut out the parts as normal. You'll see a white edge where you've cut through the primer. Sand until this white edge is gone and you're at the kit part. It's much easier to see if you are wet sanding. 

That would work. Might be generally easier too. I've used the pencil line technique since way back (cough 1980's cough...) and I've got accustomed to it. Incidentally, I sanded this one dry, which was a first for me, but it seemed to work as well/better than when I've done it wet in the past. 

[Courageous]

Nice bit of scratch work there.

 

Stuart

[gamevender]

If it work for you, go for it. Who am I to tell you with the results you're getting?

[Mitch K]

1 hour ago, gamevender said:

If it work for you, go for it. Who am I to tell you with the results you're getting?

Thank you! My approach to vacform modelling seems to end up needing a lot of going back over things to remediate stuff that I've bodged. Sort of like my signature line really😄

[Mr T]

I use a variation on the pencil line using more modern technology, a Sharpie, it works on most plastics and stays around long enough when sanding. 

[Mitch K]

Starboard side of the cockpit:

 

And the port side:

 

 

The instrument panel and radio, in situ:

 

Cockpit. now completed:

 

Finally, I couldn't put off closing up the fuselage any longer. The fit isn't great (OK, it's pretty ropey), but it's about what I expected. I'll fill this next, then look at the horizontal stabilisers.

[Brandy]

Looking good!

 Re the wings, that's an awkward error to fix but I'd be tempted to find out roughly where the error is by lining up the tips to check aileron length, then the roots to check the wheel wells. If they are ok the error is between them and you have a great panel line to cut along just outboard of the wheel wells. You'd need to add some miliput or similar inside the leading edge of the outer section too as you'll have to sand that back.

A lot of work, but it would be worth it to have it accurate.

 

Ian

[Mitch K]

The resin engine is a lovely bit of kit: I gave it a coat of aluminium to start with:

 

 

The crankcase, push rods and the like got different colours after this, then a series of washes to represent use and build depth.

 

 

[Mitch K]

The next stage was to coarsely file the tailplane roots to shape.

 

The tailplanes themselves needed a lot of filler, which was not a great surprise.

 

After a repeat run of filler around the wheels wells, I turned my attention to the huge seam between the lower wings. Joining them allowed me to fix the dihedral.

 

After an evening of careful measurement, drawing in of witness marks and much trepidation, I finally fitted the wings to the fuselage!

 

The fit of the wing was about what I expected, i.e. somewhere between awful and worse. The gaps on the underside can be seen above, and those at the wing roots above aren't much better!

 

This is about as good as it got!

[Marklo]

Quote

This is about as good as it got!

So long as it can be filled it's perfect. Actually I wouldn't call it that bad.

[Mitch K]

4 minutes ago, Marklo said:

So long as it can be filled it's perfect. Actually I wouldn't call it that bad.

It was bad. Believe me, it was BAD. You could look through the gap on one side and see the opposite side of the room through it!😨