Indoor flying

Went to the local market venue Junction 24 last night and met about fifteen other pilots having a go in what was a very enjoyable evening. There were loads of mid air collisions (I had two, one with a helicopter) and no-one suffered any damage. I've heard people talk about the Vapour but I've never seen one untill last night. Even more lightweight than the Ember, and it can fly a lot slower.

Phil shows how its done.

One thing that surprised me was the noise, it got very loud at times and the high pitch really gets on your top note. Its not the propeller or the motor, but the speed controller that makes the noise. Next time I'll wear ear muffs and maybe, if I remember, I'll take along a decibel meter. We might have to fit silencers for indoor work.

The Vapours

Progress, but with Major Modifications

Today I discovered that the valve and rocker assemblies were not going to fit together with the correct geometry. I had to remove 5.5mm from the length of the valve guide as I'd designed the posts on the cylinder heads for the rocker shafts too short. This also means the valves need to be shortened to 22mm from 25mm leaving just enough room for the spring to almost fully compress. Bottom line is, it looks like I've recovered from the disaster I thought it was and saved some weight in the bargain. Phew!

Exhaust Valve, Retaining Seat and Collet Set

Click on the picture to enlarge the image

To give you an idea of the size, the valve stem is 2.5mm diameter and the overall length is 22mm.

New parts made today include four valve spring retaining seats and two pairs of collets, two more to make.

Even more on Rockers

This engine is all about design and development. Having learned a lot during the making of the KT54fs more thought has gone into the KT120fsT. I've decided to scrap the steel rockers and go for aluminium to reduce the mass/inertia problems that may occur at high speeds. Not that I'm expecting massive RPM figures, but every little helps, and it reduces the overall weight. The tips at the valve end are, of course hardened and tempered Silver Steel, and I've fitted Phosphor Bronze bushes at the fulcrum.

New design Rockers

I've also redesigned the cams, based on my original design but larger to prevent stress and wear to the gearbox housing. The radial holes are strategically placed for timing purposes when setting up the lobe separation angle. Here I have a choice, two of the holes in alignment will produce 106 degrees and the other two 110 degrees. The profiles were generated using a zig-zag of co-ordinates worked out on AutoCad and the resulting ridges dressed out with a file. The inlet cam is designed to open comparatively sooner and quicker than the exhaust, stay open longer and close later, thus allowing more mixture into the cylinder for combustion. Both cams have a 2mm lift.

New design cams, exhaust on the left

You should be able to take a closer look at the pictures by clicking on them. In the Rockers picture the cap head screws at the tappet end are M2.5 and the hardened steel tips are held on with M2.0 cap heads.