A return to model building and flying. Part 22

Damned Paint. Clapped Engine

December 2005

Strange how periods come along happen when nothing seems to be going on. Then I look back and quite a lot has happened. It may be something to do with having a lot of projects going on and getting involved in new things. Individually not much progress, but taken together a large volume of things going on.

I do know that trying to sort out models is a time consuming business, and any damage on the flying field probably means another week before I can try again. This is what happend with the model built for our open class race. It was flying reasonably reliably with an old Merco 35, and actually became quite sprightly on 20% Nitro, the down side being the fuel consumption increased dramatically.

I had earmarked this model for an upgrade to my mew MDS 38. and decided I had gone as far as I could go with the Merco. Shoehorning the MDS into the airfame was a week long job, that made all the forgotten problems with paint reappear. Anything I put on the rebuilt area caused old paint to bubble and generally create a mess. Even my recently procured TufKote seems to have been changed, it's thick, too thick to brush easily and sets so quickly that the brush marks don't have time to level. thinning with cellulose thinners as recommended can be a disaster, as it attacks any non cellulose finish you happen to apply it to. Just as I feared, TufKote's final re-emergence onto the market has not been without a price, it's quality is not what it was I'm afraid.

I was also in the process of building a new 1/2A team race design for our club comps.As usual I work better when I design my own rather than building an existing design.

1/2A

All was going swimmingly until I tried to apply the first coat of TufKote. As I knew it was too thick I thinned it a little, then in a rare moment of caution I decided to only coat the underside of the fuselage, so if anything went wrong it might not be so noticeable. Good job I did! The car spray finish I had applied and found quite acceptable, bubbled and blistered. Was I p***** **f!

For pities sake, there must be some damned fuel proofer somewhere that works, and doesn't ruin every paint finish that's going. The crap that is sold in model shops under various names, is just that, CRAP! The stuff that doesn't destroy the base coat, just flakes off with age, or eventually dissolves under the action of fuel. I never had this problem with the old TufKote, my models where the same after a few years of use whether the base coat was cellulose based or enamel or even household emulsion. The finish lost it's gloss eventually but never attacked anything or let any fuel, of any type, through.

As if to rub salt into the wound, the open class racer ended up weighing over 1kg. This is an alarming wing loading. I flew it anyway and was surprised that it did not fly too badly. That was until the engine cut. Out leaped all the same characteristics I had with the overweight Goodyear model. As it is a low wing design there was a tendency for the nose to rise slightly as the engine cut. I made the mistake of letting it rise a little too much, thinking that as the airspeed dropped it would settle down. Instead it just stalled and the nose dropped, exactly the same behaviour exhibited by the goodyear. In this stalled state the elevator is useless, whipping as hard as I could managed to turn a dive into a shallow one, but not enough to prevent a very heavy landing which did some internal damage to the undercarriage and ripped off the elevator as it flipped over. Yet another weeks work loomed. Even more work than I anticipated as the engines consumption is a bit on the high side so I have to turn up a smaller venturi as well.

After a weeks work repairing and fighting paintwork, things started to go a little better. The 1/2A was flown and flew remarkably well. A few modifications are needed on the next incarnation, but not many. All I need to do is get used to starting an OS10 quickly, bit of an unknown quantity at the moment. I would have preferred a diesel, unless I buy a new PAW, not exactly cheap, and MVVS stopped making the 1.5 many years ago, to hunt round for something else suitable, is a bit of a chore. And even if I could locate one I could probably not afford it.

It also looks like the original car paint is fuel proof, although I have no idea what type of paint it is, as manufactures seem to fight shy of actually stating such basic things on spray cans, So all the mess up with the TufKote was an unnecessary waste of time.

The open racer with a smaller choke suddenly became extremely efficient, trying a bigger choke seemed to make no difference to the fuel consumption, so I can shoe horn in a smaller tank and open up the choke a little. The MDS38 is beginning to feel right with an increase compression which feels quit snappy, this also helps with starting, and a steady increase in power. All this seems to vindicate my progressive running-in theory, which I have written about before, and read similar processes recommended by others. It will never be super fast with a huge extra quiet muffler on it, but that is not my aim, reliable performance and easy starting is.

MDS quiet silencer

Most of our club races are won and lost on whether an engine will start and restart, not on ultimate speed.

The Goodyear model has not been performing right for some time, or I should say the MVVS 2.5 diesel is not performing as well as it should. I have been suspicions of the mini pipe for some time as it makes it almost impossible to hear when the engine is set right, diesels have a distinct note or change of tone either side of the the best point. I had read somewhere that diesels will not run properly on tuned pipes, it looks like that statement has truth in it.

There was only one way prove if it was the pipe or not, and that was to get hold of a standard silencer. Another simpler way would have to have run it without a silencer but that is a definite NO NO at our flying site. The difference with a standard silencer was quite dramatic. The noise level was not much different, but the fuel consumption halved, almost doubling the lapage, and now it is much easier to hear what the engine is doing. The design of the silencer is not one of the best in the world, in fact the engine fixing is decidedly bad in design, the single socket head cap screw that clamps the silencer to the exhaust port, screws in from the bearer side of the engine, not the head side, making it almost impossible to tighten it up in situ, unless it was designed for use in a boat or car, where it could face forward towards the prop driver. It is also trying to close a gap in a thick alloy casting, a recipe for breakage if excessive force is used. So a bit of modification was needed.

MVVS silencer

In case anyone is unfamiliar with what a mini pipe is, they look like this one below.

mini pipe

I am still having problems with the large change in fuel head because of the now unnecessarily large fuel tank, but as the efficiency has now improved I can try a smaller one, hopefully reducing the effect.

I have also finally completed the Hallam Models 'Swift' kit, so hopefully I will have something I can practice the stunt schedule now. Not the prettiest model in the universe, but functional.

swift 1

swift 2

The only problem I had, was trying to ascertain the probable position of the centre of gravity. Usually achieved by fixing as much of the model together as possible then shifting the engine backwards and forwards in the bearers. This can help with the amount of lead that has to added at some point to get it right, thus keeping the overall weight down: no bad thing. I'm using an Thunder Tiger.15 glow engine, second hand but hardly run, so it probably needs running in. It is probably a little heavier than the recommended engines, so ended up almost on the leading edge of the wing, with the model looking like a combat wing with a tail.

After covering with Solarfilm (I'm only using up what people have given me to save money, it's not my finish of choice), the centre of gravity was too far back so it was a good job I had allowed extra holes to reposition the engine if the need arose. This also also means the plastic film is heavy, and something I will have to take into account in future.

I was told by George C., a CL flier in our club, of a method that works for making Solarfilm stick better to sheet wood, is to coat everything with Solarfilm Clearcoat before appling the film, it's a fuel proofer of sorts and smells as strong as dope, then apply Solarfilm Prymol to any over lapping edges. George also pointed out that all this information is on the instruction sheet that comes with the film, This is so obvious, I felt slightly foolish for never reading the wrapper. However, I can't help thinking that at this rate I may as well paint any future models.

The only advantage to any film is it's speed of application, everything else is far from being ideal. So far, Oracover (Profilm in the UK), is the best I have used, also the most expensive. Oracover does exactly what it says on the packet, and so far has stood the ravages of hot diesel exhaust and neat fuel with no sign of anything happening to it with no special preparation; it's also extremely tough. It's only weakness, like any film, is a tendency to lift at stress points, but it's much less pronounced that Solarfilm. This makes a very thin sheet wing covered with iron on film a bit problematic. It's possible, I have done it, but the result is a very floppy non rigid wing.

So things are creeping forward, but the cold weather is definitely slowing things down a bit. I certainly plays havoc with glowstarts, batteries, and glow engines in general, and any exposed bits of me, as you will read later; a problem diesels don't seem to have, although they can snap at fingers in these conditions.

The next project in the pipeline is Jan Odeyn's profile all sheet Grumman F4 Wildcat carrier deck trainer. If I am to try and organise a very basic club carrier event in 2006 I had better have a suitable model to fly, even if I am the only one that enters the event..? Having flown Jan's built up wing version I can't think of anything better to start with, if anything it will ultimately be me that is the weak link, not the model.

F4 construct

Also it's a chance to get away from the Roberts three line system which I am beginning to dislike, because of it's lack of in flight adjustment and general clumsiness, in favour of the pretty standard simple floating bellcrank arrangement, which I had the pleasure of experiencing when I flew Jan's much battered model in Holland. That experience also highlighted the limitations of the Roberts system for me.

F4 construct

Whilst on the subject of the three line system, I recently changed the ageing O.S.20 for an Irvine.20 Sport (ringed), and came across a strange problem. The carburettor appears to be spring loaded internally to full open, no problem on an RC model with a servo pushing and pulling, but not so clever for my purposes, I just want it to stay put in whatever position I set it to. The end result is any lack of line tension causing the engine to throttle up. The Irvine throttle seemed to be behaving strangely after the O.S., picking up more revs on its own the slower I flew. How big a problem this was became apparent touching down after a test flight on my own. There was no way I could get to the model from the centre of the circle without the model attempting to take off like a jack rabbit. In the end the only way I could achieve this feat was to hang onto the appropriate slow lines and keep pulling as I walked towards the model, always apprehensive that the model may take off at any moment with me nowhere near the handle. I managed it in the end, but until I can think of a way round this conundrum, being able to fly the model solo is a bit of a problem. Fitting a spring to pull the throttle closed didn't work and loosing power in flight with a lack of line tension is a recipe for uncertainty/panic/lots of rebuilding. I may have to ultimately dismantle the carb to see if the spring can be removed.

Having been impressed by the power of the second hand Irvine .20 I had been using I hunted round for a .25 on EBay. I won an almost new looking on that tuned out to have almost no compression at all, if I can turn over the engine holding the propdriver with only minimal resistance at T.D.C., something is wrong. To cut a long story short, I got my money back and started looking for another one. Eventually I found another EBay item new in box one, never been run complete with an Irvine Quiet Pipe as well as the standard silencer. Something too good to miss: I thought?.

After receiving it, I was a little perturbed when I tried to turn it over as it seemed to have as little compression as the other one, although it did feel slightly different when flipped over quickly, and it had obviously never been run. With this niggling away at the back of my mind, it was bolted to a test stand and pinned to the flying field, on an extremely cold Sunday morning! (age does not necessarily bring wisdom). After a lot of flicking and trying different batteries, all I could get out of it was a Pop! occasionally as it fired, and a tired arm. After a whole morning of repeatedly trying this, and bits of me going numb with the cold, I gave up, thinking I had somehow managed to buy another dud.

At home I decided to cycle my starter batteries as it's almost impossible to tell the charge state unless they have been charged from flat. That's when I discovered that both where nearly flat. But was this the cause of the Irvines reluctance to start or not?

The next weekend saw the Irvine finally struggle into life, and after three tanks of fuel it seemed to have gained some compression. The batteries had obviously not only been nearly flat, but the intense cold was probably reducing their efficiency as well. Now this compression thing has me puzzled. Is it a characteristic of Dykes rings that they have no seal until they are bedded in, or is it just Irvines that suffer with this problem; as I have been told? If anyone knows the answer I would love to hear from you.

A bit of good news is that our club is gaining a second control line circle. The RC flight line is being realigned to take it further away from a nearby farm, the source of complaints about the noise in the past. This has left enough room to squeeze another circle in. This should help relieve some of the congestion on busy days. How long it will all take take, I have no idea, as the whole site looks like a bomb has exploded at present.

field

It takes a lot of spoil to fill in part of a valley.

circle

The stake in the forground will be the centre of the new circle. The grass area behind is the existing circle. Club hut at the rear.



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