After fitting the duct to the hull it is time to fit some flow straightener vanes. There are some basic rules here.
- You need a different number of flow straightener to the number of blades you have. This avoids a nasty beat frequency as all of the blades pass in front of all of the straighters at the same time.
- They need to have some shape to guide the air from its swirling path off the blade to a flow parallel to the sides of the duct.
I borrowed some moulds to make a set and all was going well unitl I tried filling them with foam for strength and the deformed beyonr recognition 🙁 My old freind Dan came to the rescue wth various vanes he had lurking in his collection. Not only that but he came rounod to help me fit then and also had a pair of rudders. Top man.
The duct is 1M in diameter, quite large for an F3 but I figured it would be about right for this craft. The duct was made by my old friend Dan who was doing it as a plug for a duct he was building and it was no longer required.
I collected it on a filthy night, strapped to the roof of the car as you can see. You can make out the Kevlar containment area that should hold everything together if a blade lets go and tries to leave through the side.
There is also a flat “plate” running all round the duct. This is to help to keep it circular, particularly where the blades run. It’s quite hard to stop a duct from flexing and as long as the part with the blades in stays circular, the rest can move around a little.
By now I had a new mould for a top deck/hull and a polished mould for a planing surface that I thought would give me one piece from which I could take another mould.
But, we’re getting a little ahead of ourselves here. I mentioned in the introduction to the Outlaws that I had formed a plan. the plan was to build a new craft on a light, interesting hull. It also involved twin ducts because I like twin ducts and a four stroke engine because I like four stroke engines. I’d still go shaft drive because otherwise engine choice is a bit limited.
We’ve seen how the top deck plug was mounted, buffed and a mould taken. The next step was to take a part from that mould.
For reasons unknown I don’t have any pictures of the new mould. Suffice it to say that the plug was pulled of the frame and the mould put onto it. Now I have a mould on a nice frame that can be rocked over at a jaunty angle to make laying up easier.
First up, after waxing and polishing comes a couple of layers of gelcoat. I chose a letterbox red. Then a mix of CSM and Diolen. I think I put down one layer of CSM followed by Diolen followed be CSM. It’s been a while, cut me some slack.
The front duct.
The plan was to use two fans, one for thrust, another for lift. The list fan duct is made from GRP as to be expected and was given to me by a freind who has moulds for this kind of thing and a spare duct.