Moth Major for CO2

[g_kandylakis]

I have (better, had) a few principles in my modelling career. One was not to build the same model again in different sizes. There are plenty of subjects out there waiting to be modelled. Well, that went down the drain.

My PZL 24 CO2 model has had a good flying life, probably the best compared to other models of mine. But showing up again at an event with it was a cause for discomfort. I needed a replacement.

With only three months to go (now only two) for the coming IIFI I made the wild thought of repeating the build of last year, my Moth Major peanut, only slightly larger. The model flies nicely, the plan and documentation are already there, it i very simple to enlarge everything slightly and end up with a new entry for CO2.

Whether this works out in the end remains to be seen, so the PZL will be ready as a back up.

The model will be at 1/20 scale, about 46 cm wing span, which makes it a rather small model. This causes some questions regarding powerplant. I want to use again a Brown motor but they are a bit too large and powerful for such a small model. Which is ok, as long as they can fit inside the cowl. It is tight but looks feasible.

Work has started on the wings, one is completely finished, the other needs sanding and the other two need to be glued together.

So, not much to show yet. Starting with the wingtip laminations.

[g_kandylakis]

a mix of old and new, outline templates for the peanut version, riblets for the CO2 one and wing construction beginings.

[g_kandylakis]

And we have a wing, 3 more to go.

And size comparison with the finished peanut version.

[g_kandylakis]

Work continues with a rather slow pace, exactly two months before IIFI where it is supposed to fly.

Working on the 3rd wing panel. Also started the fuelage sides. When there are significan curves for the longerons, I always laminate them to achieve a stress free structure.

Compared to my peanut version of one year ago, I am one month behind.

Positive:
All, or at least most of the engineering and design work is done, so I only rescale and print what I need.

Negative:
A CO2 model is slightly more complicated than a rubber powered one, so it might take some extra time.

We'll see...

George

[TheLurker]

....it might take some extra time.
George

Ahh, just bunk off work.  I'm sure they'll understand that that "toy aeroplanes" are far more important than anything else.

[Squirrelnet]

Great project George, watching this with great interest. I'm a bit of a DH60 fan too so the thought of a CO2 Moth Major is exciting. Will this be the same scheme as your peanut one ?

[g_kandylakis]

Hi Chris,

Glad you like it. Yes, exactly the same, I admit with slight shame...

George

[marcin_pl]

George,

Do you cut ribs one by one using a single template or stack them and sand all together?
How do you cut openings for internal spars?

Marcin

[g_kandylakis]

Hi Marcin,

One by one.
Two templates, 0.6mm plywood. Individual balsa piece in between.
Sharp razor blade cuts easily along the template, minimal sanding required, very light so the templates are not worn in the end.

Slots are made with very sharp #11 blade or home made tools with sharp steel carbon blades, finished with small square diamond files.

I have pictures somewhere. Here in our Greek forum:
https://www.aeromodelling.gr/ForumS/index.php?topic=58377.msg330018#msg330018

I stopped block sanding years ago for a variety of reasons.

I like my wings to be built like the original, so the spar has to be centrally located. So holes are necessary for the spars, very difficult to achieve with a block. The same goes for lightening holes.
https://www.aeromodelling.gr/ForumS/index.php?topic=59547.msg341232#msg341232

These threads existed in the old HPA, now they are gone...

Also the ribs are not exactly the same, from end to center to end. They might move during sanding or you might oversand the template as well.

Excessive maybe but that is how I like it.

George