Boulton Paul duct fan – Part 1

It’s March 2020 and It is now a very strange and worrying time. As I write this, The coronavirus is wreaking Havock across the planet. I hope you keep well. This post and the subsequent ones that will follow, while uploaded now were written in 2018. I hope it offers some pleasant distraction in this worrying time.

Ok so here I go with the build of my free-flight 36″ span 2.5cc powered duct fan model. It’s gonna be fun! It’s now December 2018 and nearly Christmas. I haven’t done any serious building on any of my models, and just about managed a few flights of some control line planes. I did manage to 99% finish the Natsneez, which is documented within the Lovebalsa blog. It really looks great. there are a few detail bits to add on, but the constant rain and damp weather we’re having is preventing me from doing any spray painting. I did a cheeky little engine start but the plane caught fire!! I talk about this in the Natsneez blog.

So The Boulton Paul. When I started the Javahawk, I made the mistake of making the model before the fan. This time around I’m determined to make the fan first – which itself is posing a problem.

I don’t (yet) own a lathe, which I need to turn up a hub to fit the 8 blades into. I spent many hours wracking my brains on how I could accurately make a hub without a lathe and dreamt up a few hacks which have so far is proved unsuccessful.

My brother said ‘why don’t you use an aftermarket fan? – it would be easier?’ Yes, it would but the problem is that since these days they are designed for electric duct fan models (EDF), I would still need to make an adapter of some kind to fit it to the glow motor that I plan to use.- which basically means I need a lathe!

So I’ve decided to scratch build it. The hub for the Javahawk is made of aluminium which my brother turned up years ago (he’s a toolmaker). unfortunately, he can’t do me that same favour at his current place of work. So scratch build it is. Check out the pic below to see my solution.

What you see in the above pictures is my attempt to make a sort of make-shift vertical lathe. I bought an aluminium mini chuck from eBay and fashioned two metal clamping brackets. These are screwed to the side of the chuck and the whole assembly screwed down onto 1/2″ thick scrap plywood jig. This is then clamped to the table of my drill press.

The idea is to exactly line up a drill bit mounted into the drill head, with the centre of the chuck and then clamp the ply jig into position. For the fan hub, a small section of Nylon 66 plastic rod, cut into thin sections, is then clamped in the chuck. Lining everything up, I then drill down through the rod with a small drill bit. Hopefully, the whole deal should be dead centre…. or will it?

Well, as a matter of fact, this didn’t prove to be the case. You can see from the pic below that annoyingly, the small hole is slightly off centre. Daam!

I think what is happening here is there’s a slight sideways movement in the rotating shaft part of either the drill or drill bit, so as it touches the plastic surface, it moves.

Anyways, long story short, I eventually managed to get the hub sorted. I found on the web a local machinist who was able to take the nylon rod that I had and slice off individual pieces (5 in total), drill them centrally and cut 6 45 degree slots into the face. So I am now able to make the blades and insert them into the slots, making a fan.

Before I did this, however, I was able to make up some plywood hubs as detailed in one of the old P.E. Norman articles, drill them and mount a bolt into the face.,  clamp into an electric drill – which was also clamped down – and when started up, held a file against it sanding the hub into a circular shape. Worked too. The picture above shows one of my early attempts, but I did manage to produce a neat version. Hoping to make up some 8 slotted hubs in the future 🙂

Check out Part 2 here.

Posted in Free Flight.

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