Canberra Nacelles

[Andy Blackburn]

On reflection, the original Canberra B.2 article or build blog didn't really explain how the nacelle patterns were made; as you'll appreciate, there are a limited number of words available for a magazine article and there's a limit to how much stuff you can put in a build blog before it takes every waking hour to write down...

I didn't find any particular difficulty with it because I apparently stumbled on the correct technique at the outset - the three magic ingredients seem to be:

1. Use a long, thin piece of paper
2. Masking tape
3. Trace the pattern multiple times (iterate)

So this is a (hopefully) short thread that describes how to make patterns for the Canberra nacelles;

There are the tools required to to do the job; the pencil is the softest that I could find so that it's less likely to mark the balsa.

The first thing to do is to cut the paper into strips of about the size above and tape together as shown.

...and then the crucial (magic) bit is to hold it in place with masking tape (run it through your fingers first to make sure it peels off the paper cleanly) and just run your fingernail along the junction between the wing and nacelle...

...pencil-in the line (try and get it right but it doesn't have to be dead accurate), unstick it it and cut with the scissors. Then stick it on again and go through the tap-mark-pencil-cut process again and it'll look a bit like this:

Then do it again and you should be nearly there:

...as you can see, it's converged onto the correct cut profile. More to come in a few minutes, I'd better post this because I'm not sure how much text/photos I'm allowed per post.

 

Edited By Andy Blackburn on 19/03/2018 10:26:20

Edited By Andy Blackburn on 19/03/2018 10:26:34

[Andy Blackburn]

Here's a detail of what happens at the leading edge:

...basically, you just fill-in any gaps with masking tape and draw on that.

At this point it's probably a good idea to mark the nacelle quadrant on the back of the pattern - the longer and thinner the pattern is, the more tolerant it is of errors.

This is the glass-slipper moment (it fits!). It took me less than 20 minutes to get to this point.

Here's the roughly-finished item than can be used to cut some nacelle quadrant, although you'll need another one to cut the quadrants that fit on the bottom of the nacelle:

When the text talks about "darts", it's talking about these bits:

- they're just bits cut from the wood to help it go around a 3D curve; but DON'T cut these until the 3/32" sheet nacelle quadrant (which should be the softest straight-grain balsa you can find) is glued to the wing; if you cut a dart that's too big, just fill the gap with another triangular shaped bit of wood and no-one will ever know. I've never done this, of course, and if I had I'd pretend that I hadn't...

When glueing the nacelle quadrants, the really important thing is to follow the instructions on the plan and glue it securely to the wing surface before attempting to curve it around the formers - dampen the wood a bit if you have to but don't put it under any strain until the glue has fully set. Medium cyano and kicker is very useful here.

Edited By Andy Blackburn on 19/03/2018 10:52:27