Category Archives: Random orbit 2

The end

b68814ddfa8520c9ffb976e0af494753I had a lot of fun with Random Orbit mk2 but I decided I wanted to move on and that I couldn’t get it to go much faster so I sold it on.
The last time I saw it the old thing was still going strong. The majority of the hull is about twenty years old by now and it’s not getting any lighter but it still gives me a wee twinge of pride when I see it. In 2008 it was driven be David Northall in the HCGB national championship. It was sold on to race again but I’ve lost touch with it now.

Keep your eyes on ebay.

Engine and fan frames

d6b6df4d18a828b64846c3aa3e62913cOne of my overriding design ideas for Version 2 was that the duct should be clear of obstructions and that the engine was to be as low as possible and out of the way. To achieve this I decided to put it down in the corner of the craft. In order to get it to fit and too make use of standard length drive belts that didn’t give me much height and so the engine frame couldn’t be the usual chunky steel affair.

a8b0c0b3ff33d3cd133b75bb52a1e901Because of this and also because I fancied having a go at it I made the engine frame out of carbon fibre. As you will see, I didn’t think to take a photo (despite it being a thing of beauty), but I did take one of the mould I made it in.9434348ec2baec326d616fb42f536b1e

The hull

The Hull

Firstly an apology. For some reason I didn’t take nearly enough photos of this… Sorry.

In most cases, when you fit a lift duct to a craft that didn’t have one, you cut a large hole in the front deck and fix in a glassfibre duct.

The Moto cyclone doesn’t really have a front deck to speak of so that’s not an option. You can see from the pictures of Random V1 that there was a black fly screen at the front. This was fixed to raised lip that runs all around the cockpit. The new duct is a large moulding that fits over this lip and about a third of the length of the craft.

The inside wall of the cockpit was removed as was the buoyancy up to about half way down the plenum. The new duct was fitted and because I needed the buoyancy and didn’t need a very wide cockpit, a large chuck of the foam was glassed in on each side of the cockpit.

At the back a 900mm duct was fitted in place of the 750mm. This tme there was no need for a splitter plate. The flow straigteners are standard this time and were bought from K&M products as was the duct.

A centre console was needed. The old one wasn’t long enough as there was going to be a prop shaft running the length of the craft and it’s not a good idea to crouch down over an un-guarded prop shaft that’ rotating at 3,500 RPM. A new console was built. This was made from GRP layed up on to a foam plug which was then removed. It wasn’t pretty but it was functional. Other guards were built from steel and aluminium to cover other exposeded bits. More on that later.

Random orbit 2 – The second coming

b68814ddfa8520c9ffb976e0af494753It started with an innocent enough conversation along the lines of “You know Andy, most people with a TZR have a bigger duct”… “Do they? (quick look round) Oh yes.”.

Out with the angle grinder.

Random Orbit version 1 had a 750mm duct and putting 45bhp through that is a bit of a tall order and so I decided to put a bigger duct on. I’d also heard that some time earlier, someone had put a lift duct on a Cyclone and raced it in F1.

I decided I’d have a go at putting a 900mm thrust fan and a lift fan on Random Orbit.

The rules in F3 say that you can run any number of two-stroke engines in any combination up to a maximuim of 250cc but it’s tricky finding a good combination to give lift and thrust so I decided to try a shaft drive.

[note. I’m writing this in 2008 and shaft drive craft are all over the place but when I did this job in 2001ish they were quite rare]

A shaft drive means you can get the advantages of twin ducts on a single engined craft but designing one does make things interesting.

A big note… I didn’t take nearly enough photos and without them it all seems a bit dry so this section is very short.