Welkin Mk III

[PR19_Kit]

Glad you think so Chris, it occurred to me that it's ages since I saw any pics of the process and a repeat probably wouldn't do any harm.

I've sanded both halves of the nacelle now and glued them together. Most vacform instructions suggest you use Mekpak or similar for this, but if the styrene is thick enough I prefer to use my usual Revell Contacta liquid glue, the one with the needle nozzle as it's so precise in application. Then, when the two parts are aligned and glued primarily, I run over the glued edges with a brusfull of Mekpak. That re-energises the Contacta and gives a firm joint.

Of course if the styrene is too thin, and it often is with vacforms, there isn't enough 'edge' for the Contacta to sit on, and then it's more effective to hold the parts in contact and run Mekpak around the joint with the brush.

I've also glued the front end of the MB5 fuselage together before cutting off the engine. As this part of the conversion is so vital I thought I'd do an engine nacelle assembly first, rather than do the usual cockpit-fuselage-wing assembly sequence.

[b29r]

This is really going to be sharp, Kit!  Vacs are way above my paygrade, so much respect for what you are doing here.  Will be watching for the next update.
Best regards,
Kem

[PR19_Kit]

They usually aren't as difficult as they're made out to be Kem.

True, there are some vacforms that are real beasts to build, usually those where the manufacturer has been too optimistic with the thickness of the styrene they've used compared to depth of the draw. In general the larger the model the thicker the styrene needs to be. Beware of Airmodel vacforms as they almost always end up with silk thin sides!

A good quality vacform can be of similar difficulty as a basic injection kit, Rareplanes kits being some of the best IMHO. Find a simple one to kick off with and have a go, you'll learn new skills and hopefully end up with a model that you may not otherwise have been able to own.

[PR19_Kit]

I've sawn the engines off both parts of the MB5 and Welkin, a totally different experience on each. The MB5 styrene is so thick it took many passes of my razor saw to get through, and that of the Welkin was so thin I could have done it with one pass of a scalpel!

I've glued a 15 thou bulkhead onto the front of the Welkin nacelle as the edges are so thin, and the MB5 engine will be glued directly to that rather than rely on an edge to edge joint.

The MB5 engine is a lot wider than the Welkin nacelle at the bottom so I'll be filing that down and building up the nacelle sides to match later on, but from side view it doesn't look too bad. I'm assembling the MB5 contraprop at the same time to see what the overall side view looks like.

Pics of the assembly tomorrow I expect.

[rickshaw]

True, there are some vacforms that are real beasts to build, usually those where the manufacturer has been too optimistic with the thickness of the styrene they've used compared to depth of the draw. In general the larger the model the thicker the styrene needs to be. Beware of Airmodel vacforms as they almost always end up with silk thin sides!

Early ones, perhaps but the several I've made have all had adequate plastic in them.  Nowadays, they are made with thicker plastic.   The ones I've made (twin-seat F-8 Crusader and TF-86 and CA27 Sabre and I'm presently working on a Gannet AEW) have turned out quite well.   Airmodel have changed.

[PR19_Kit]

I've cut out the main gear doors from the nacelle, a relatively easy job with a scalpel, maybe only 4-5 passes and they were off.

From the side view you can see how well the MB5 engine and prop line up with the Welkin nacelle, but the Merlin air intake is blanked off as the MB5 engine is so deep. That's OK as it has its own intake right under the prop.



However, in the head-on view things are not so good.



The MB5 engine is MUCH wider than the Welkin nacelle over almost its entire height, and I'll have to file off the bottom edges of the Griffon, while padding out the Merlin nacelle as shown by the red lines.

Never mind, if it was easy everyone would be doing it. 

[NARSES2]

The MB5 engine is MUCH wider than the Welkin nacelle over almost its entire height, and I'll have to file off the bottom edges of the Griffon, while padding out the Merlin nacelle as shown by the red lines.

Now you've gone way beyond my abilities Kit so forgive me if this is daft, but why not just make the Wellkin nacelle wider using a shim so that it fits the Griffon ?

[PR19_Kit]

The MB5 engine is MUCH wider than the Welkin nacelle over almost its entire height, and I'll have to file off the bottom edges of the Griffon, while padding out the Merlin nacelle as shown by the red lines.

Now you've gone way beyond my abilities Kit so forgive me if this is daft, but why not just make the Wellkin nacelle wider using a shim so that it fits the Griffon ?

It's not daft Chris, in fact it's a good idea. 

I'll have a look at doing that tonight, but I'll still taper off the MB5's engine a bit at the bottom, it looks too big and bulky for the slim Welkin.

[PR19_Kit]

Putting Chris' idea into place right away, I measured the width of the MB5 engine, 15 mm, and cut a replacement front bulkhead for the nacelle at the same width. Then I slit the nacelle along most of its length and cut the original bulkhead in half from top to bottom, so the nacelle was only glued together right at the aft end. I glued the new bulkhead on top of the old one with the nacelle front spread apart by a small spacer and then filled in the gaps with styrene strips. Lastly I glued the MB5 engine onto the front.

Voila, job almost done. I'll file down the lower sides of the engine to match the nacelle shape when it's all dried tomorrow.

It's a lot easier doing things like this with a vacform, there's none of that tiresome sawing and filing stuff, you can do it all with a scalpel. 



Upper view, you can just see the edges of the new bulkhead between the nacelle and the engine




Underside view, you can see the spacer strip and the other added bits and pieces up inside the main gear bay

So far I've posted 11 pics of this build and I've not finished one engine yet! At this rate I'll break my all time record of 71 build pics that I managed for the Monterey. 

[zenrat]

Ah yes, but a lot of them were for the beaching trolley.

[PR19_Kit]

Ah yes, but a lot of them were for the beaching trolley.

Please don't remind me! 

But yes, that's very true, perhaps well be in the 30s for the Welkin?

[Tophe]

I'll file down the lower sides of the engine to match the nacelle shape

you can just see the edges of the new bulkhead between the nacelle and the engine

These distances between parts, will you fill them with putty? Does this work with vacform? I remember I used putty with vacform clear canopy and this destroyed it Is this different with white parts?

[NARSES2]

So far I've posted 11 pics of this build and I've not finished one engine yet! At this rate I'll break my all time record of 71 build pics that I managed for the Monterey. 

Yes, but I'm starting to understand what were previously just dark mysteries. Going to dig one of my vacforms out this weekend, and maybe just maybe ?

[PR19_Kit]

These distances between parts, will you fill them with putty? Does this work with vacform? I remember I used putty with vacform clear canopy and this destroyed it Is this different with white parts?

Most of them won't be visible when it's all assembled anyway Tophe, the wing will fill in the big gap on the top and the landing gear goes in the hole in the bottom. But yes, I will use some putty on it where needed, and it works OK with vacforms but you need to do it in thin layers or it tends to dissolve the thin styrene.  Canopies are made from a different material and I've never had to putty one so far, but then mine are all modelled clear.

[Scotaidh]

One nice result of the nacelles ending up wider is that you'll have more room for the beefier undercarriage - which the heavier engines would require, anyway.    Don't you love it when the unintended consequences balance out?