A return to model building and flying. Part 24

Scary Flying

February 2005

Silencer

First off, my attempt at fitting a PAW silencer to an MK-17 was an acute failure. It so nearly fits, but not quite. The picture below will give some idea why I was so optimistic about it fitting.

silencer fit

The outside diameter of the silencer is exactly the same as the head fixing lugs on the crankcase. The result of my trying to ease the very brittle silencer casting over the last lug is plain to see.

broken silencer

So until I can find an easily available substitute, I am a bit stuck.


Little Green Thing

The small Dwing racer I have been working on was plagued by an OS10 that would not start when needed. After this happening on over two consecutive months and races. It was sold on and another installed. This one does at least start. I would much prefer a diesel for this model, but 1.5cc diesels and not cheap at least the ones I would want. I may have a solution but that will have to wait for another month before I write about it.

halfA

The model itself flies OK. The CG is way too forward, this always manifests itself as a non existent or barely controlable descent when the engine cuts. It's also a small model physically, so ground handling is critical for take off and landing, to try and avoid those Mini Goodyear cartwheeling arrivals that are so common on grass. It has an undercarriage, large balloon wheel, and silencer to carry, so design is critical if the whole thing is to work reliably on none too smooth grass. Hand launches are permissible but then I am at the mercy of whoever is to hand to perform the task. Most are OK, but some are not, and have caused me some grief in the past. Having an undercarriage gets round a lot of the problems but is not easy to implement on a small model flying of grass.

Future modifications include more wing area, a longer fuselage. If you can call it that? A shorter wheel mount, and get the wheel as far forward as is practical without it fouling the prop. And last but not least build a club A class version. We can use up to 3.5cc, so that should be fun.


Big Yellow Thing

I acquired an OS21SE-B last year for an obscenely low price on eBay, everyone must have gone to sleep that night or people did not know what to make of the engine. Well, that's their loss and my gain. The engine is designed as for powering cars, but had been rebuilt for RC pylon racing. On paper, it should develop a large amount of power. Looking around for something to try it out in, I dragged out the old first Goodyear model I built, the one that performs and weighs something resembling a brick out house. With some small modifications the OS fitted.

OS21

OS21 close

Flying it caught me by surprise. I now believe OS's quoted power figures. The model being it's usual self, was almost uncontrollable at the speed it was flying, but I did manage to hang in long enough for the tank to run dry, and get it down in one piece. A big sigh of relief followed.

Now all I have to decide is what model to put the this engine in....? Is it worth modifying a model that scares me to death every time I pick up the handle, or build a new one with half a chance of flying well. Decisions, decisions.


Weather

We had a very unusually calm Saturday this month, and not wanting to miss it I when to flying field. The Wildcat is great fun to fly in the calm as it can be hung just on the stall. Seen the previous instalment for pictures if you don't know what I am talking about. Unfortunately I can do many things, but take picture while I am flying is not one of them; I'm working on it though. I am not used to seeing a CL model, at least one of mine, in this attitude. At one point it actually rotated round into a vertical prop hanging attitude. As I am new to this sort of thing, very inexperienced, and not wanting to damage a model I am having so much fun with, I chickened out and applied down and full throttle to rotate it back into level flight without incident. I would love to be able to prop hang it but I need a lot more experience. I found out the next day in freezing, wet, windy weather, (typically English changes in weather from day to day) that the wild cat is a bit of a handfull in a blustery wind. Bigger wing area and engine for the next model then.


In Slow-Mo

I had the most strange experience when running up an Irvine 20 I had converted to diesel, with a proper Irvine diesel head I might add. I had just managed to find the settings and was adjusting the compression screw when the engine suddenly stopped. But the prop kept spinning. Prop nut loose, I thought. Then in slow motion as the prop slowed down, it moved forward complete with front bearing and half a crankshaft still attached until it just flopped onto the floor. I have never seen that happen before. It was one of those moments you just wish someone had been filming as it happened.

broken crank

As the Irvine only cost me £12 on eBay and I had used it for 6 months it's hardly a great loss, but very annoying as it sounded great running as a diesel and I wanted to find out what it was capable off. So far I have not managed to track down a new crankshaft as it is quite an old engine, but the search goes on.



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