The Black Arrow

[Jmk89]

One of the hazards of the exercise that Nigel_M and I have been through of scanning and uploading the early AeroModellers that Nigel was able to borrow from Paul Briggs is seeing a whole lot of interesting models that we would like to build!

There's only one thing I can't resist, and that's starting a new project before entirely finishing another.  So my current new project is to make a version of The Black Arrow which appeared in the May 1938 issue.

Here's the plan and article (but you can find the whole magazine in the Plans Gallery.
Black Arrow article.pdfBlack Arrow Plan.pdf 
I've added a photo of the plan on the building board.  You can see that I've already been unable to resist making a few changes - the wing tips and fins are being turned into laminated outlines. 

One question - the original was powered by a "Paulownia-style" prop.  I know Paulownia timber and I could easily make a suitable 8" prop from that and I've seen ads for Paulownia props in early AeroModellers, but does anyone know if these had any particular characteristics that distinguish them from props of the time carved from balsa?

[pb_guy]

I was also intrigued with that plan which is also available on OZ https://outerzone.co.uk/plan_details.asp?ID=1116

The construction looks great. The laminations are a nice addition. The Pawlonia prop was likely to keep prop breakage to a minimum. 
ian

[lincoln]

Maybe you already know this, but Paulownia is supposed to be heavier and stronger than balsa, though still very light. The figures quoted in the Wood Database were 18 and 9 lbs average density. I don't know if Paulownia is quite as variable, but I've encountered balsa densities between 3 and 24 lbs per cubic foot. The lightest usable balsa I've seen was 3.5 lbs per cubic foot.

Presumably, a prop from average Paulownia could be a bit thinner than one from average balsa, though not thin enough to be of equal strength. Also, if I'm not mistaken, a Paulownia prop on a model treed in a very damp location would rot more slowly than a balsa one.  ;-)  They use it for boats. If I was to build another boat, I might try to locate some.

If I lived on a larger plot of land, I might try to grow some and wouid have a lifetime supply in several years. (It grows VERY quickly.) At least if it can grow this far north. Apparently, there are places in the US where it can be a pest, and other places, further north, where it can grow, but not necessarily spread.

https://www.wood-database.com/paulownia/

[dputt7]

Hi Jeremy  Well they say you should learn something new each day, I certainly did.   When I was 8 or 9 (alooong time ago I heard my father and older brother talk about Paulownia props on rubber models.  Now I thought that Paulownia a brand of prop and it wasn't until your post the other day that I learnt it was a wood (some 65 years later).  Now I need to carve a prop for my 48" Avia after it broke the balsa one, I had carved for it.   So I thought I will just Google Paulownia and see if I can buy some wood in Australia. Imagine my surprise when it came up Bunnings. Known as Craft Wood, I managed to buy 2 sheets of 6.5mm so I will be able to laminate my prop blank.  Thanks for that!

[Jmk89]

Hi Dave

If you'd like a bit of Paulownia large enough to carve a one piece prop, I'm happy to cut you a bit and post it to you (you may pay the postage, if that's ok)

Cheers

[dputt7]

Hi Jeremy, that's a very kind offer and I'm in two minds whether to accept it. I like the idea of the laminated prop for appearance, but the one piece would be easier. I'm not in any hurry as I have a long list of things to do before I get to that also the prop is 16"dia. which is a fair lump of wood.  Can I let you know later?
                                            Dave

[Jmk89]

Can I let you know later?
                                            Dave

Of course. I have a slab which is about 1800mm x 300mm x 50mm,  so I doubt that I'll have got through it by the time you make a decision!

[dputt7]

Thanks Mate!

[Jmk89]

Some progress has been made:

The wing has been constructed - some variations from the original plan:
1.  The top spar touches the top surface - as Dave Hipperson points out in his articles in AM recently on the Senator, this is a turbulator for free. It's also much easier than back-filling the gap with little bits of balsa.
2.  The whole wing was made in one piece (leaving out the rib that needs to be sloped to generate the dihedral and then split up to insert those two ribs and then join together to make one wing.

The fuselage sides are made in the usual way - only variation is that I stuck the parasol struts to the inside of the relevant spacers and then used shorter spacers between them rather than notching out parts of the struts to fit around the horizontal spacers.

[dputt7]

Good progress looks neat.

[Jmk89]

Ready for a motor and test glide.

I think that I will have to rebuild the tailplane with a top spar to stop the upward warp!

[Jmk89]

Here's the picture

[Jmk89]

Except it isn't there - I see it in the draft and it is within the parameters, but it just doesn't show on my 'puter.... Help!

[Jmk89]

Resize it smaller and try again

[Jmk89]

Still nothing there