A return to model building and flying. Part 61


November 2009

4 stroke

On one of the seemingly rare reasonably calm days, we seem to have had infrequently at the club site  for the last couple of years, I stood watching Andy Green flying his xxx with a new Saito 40 stunt motor, the ones made for CL use by Saito, not an adapted RC one. It started somewhat reluctantly and need the help of an electric starter to coax it into life. but start it did, and purrrrrred round the sky if an exemplary manner. What was even more impressive was what seemed like a very steady run no matter what attitude the model was in. And to see the same model suddenly transformed into what looked like proper stunt model with potential was quite something after the iffy flights with different 2 stokes.

This started me thinking...... ? always a bad sign LOL .

I have a Brodak Buster, which has had more engines and fuel tanks in it than a council estate teenage mother has had children, and none have given consistent performance, to the extent that it has sat in a corner of my crowded bedroom defying (and probably sniggering) me every time I look at it. it's easy to note that 4 strokes use less fuel, and I have always had problems finding space for a fuel tank sufficiently large enough in the Buster nose, so if I could get the consistent run as well, that was two ticks for a 4 stroke.

The next week I cogitated for a few days, I couldn't justify forking out the money for a Saito or an OS, but ASP/SC do a 30, and as the Buster had flown happily on a .19 2stroke, I hoped 5cc of 4 stroke would do the trick.The next size up  in the ASP range would be too big and heavy. 

asp30fsFinally falling off the fence, I put fingers to keyboard and ordered an ASP 30fs from Just Engines; who must have one of the worst online ordering systems I have come across. On the last page when the button is hit to OK the transaction, the whole thing closes down, leaving you not sure if the order has been accepted, rejected, or just wants to piss you off! No email confirmations follow either. but having had this before, I waited.... And sure enough 24 hours later, there was the postman handing over the package.

So it sat there for a couple of days, whilst I got on with other things; but finally the forecast of yet more windy weather (will it ever stop?) drove me to doing silly things. After reading the somewhat generic instructions for the engine (yes! I have been known to read instructions on the odd occasion), with dire warnings involving chicken sticks and electric starters, and fuel mixtures, I decide to try and see if it was possible to start the thing by hand using The Great Bert's method* of prodding it with those appendages at the ends of my arms.

So we stood in the kitchen facing each other like a scene from a spaghetti western. It, strapped firmly into a test stand and a work mate and wearing a 10x4 prop, and me suitably attired in old clothes and wearing both leather gloves. OK punk!........... Make my day.....!

I hit it.... I hit it again.... and again..... nothing! The motor was tight and it was difficult to find that compression spot and prop angle to smack it from, or to get fuel into the head for that matter, as every choke had most of it flow out of the manifold due to the vertical positioning as on most 4 strokes. But the relentless onslaught by my myself eventually produced a few coughs and splutters, with even more bashing producing a few seconds sustained combustion. This was still not easy to achieve and left my pride a little deflated. After a lot of experiment, and finding that the 1 1/2 turns open factory setting of the needle was fine, and the instructions recommended 2 1/2 was not, I found that like their 2 stroke brothers and sisters, they need to be wet, very wet, to start. Once I stumbled on this fact, hand starting became predictable and not too  difficult at all. This was with a standard 10% nitro methane 2 stroke fuel I use, so probably far too much oil?

The ensuing cloud of exhaust residue and smoke, as I marveled at the lack of noise compared to 2 strokes, filled up the kitchen and drifted down the hallway doing my freshly washed underwear drying on on rack there no good at all; so I quickly stopped it, open all windows, switched on fans and retreated to a safer place to breath.

At the club flying site, the getting it wet trick seemed to still hold true, so next stop... The Buster.

addon silencerI have also been experimenting with an Irvine semi tuned pipe on my OS21 BX. The engine came with it, as the previous owner had it breathed on for RC pylon racing. I had never used it because it is noisy (no baffles). But i had always been curious as to what it would do for the performance. Short answer is a lot! big increase in revs and a big grin from me. But a big increase in fuel consumption and noise.

No Idea what revs, as I don't possess a rev counter. as far as I am concerned it either goes well or it doesn't; and anyway it's difficult to measure the revs in the air, and that's where it matters.

Needing some form of after silencing to avoid the attention of the noise police, I utilised some toilet scent sprays I had been using  for year and purchased on the pretext that they looked like they may be good for this sort of thing, My work room smelled lovely after I drilled holes in them.

The first attempt was a strait through affair, which reduced it noise a little, but seemed to increase the back pressure a lot resulting in half a turn in on the N/V to restore the revs

Second attempt has a baffle pipe inserted into the end of my home made bit. I have yet to try this out as the weather has closed in again.

Watch this space!

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