A return to model building and flying. Part 35

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January 2007

This episode will probably end up quite long; it's been a crap Christmas and New Year for me, for reasons you will read later, so I apologise in advance for boring you to death.

And Yet More Engine Problems !

This time it was not a cheap Chinese or Russian engine, but a supposedly high quality Super Tigre G34H (made in Italy). After it's last outing I was cleaning the model down, I hate having to handle gungy models and engines covered in dried or baked on oil, so I am quite fastidious about cleaning them when I get home. A spray on product called Hob Cleaner, from Aldi Supermarkets is quite good for this sort of thing and will even keep the engine looking clean as we ll if used regularly. It's just a case of spray on, wipe off, and rinse with water.

This cleaning process also helps show up anything wrong with model or engine that I may have missed at the field, So it is a usefull thing to do for that reason alone. What I noticed this particular time was the engine sounding like it was full of sand when I rotated the crankshaft back and forth. It was obvious that a bearing had gone.

I have wrestled with ST engineering in the past, so had some idea of what to look forward to. Dismantling and reassembling an ST.46 was always like trying to solve a Rubik's Cube, and involved jamming a wooden cocktail stick into a hole in the gudgeon pin and extracting it through a hole in the back of the cylinder, it took me a long time to work that one out. Now you know what those large screw plugs were for on the back of a .46. I think this design feature was incorporated to avoid the very problem I am about to describe.

Everything is made to quit close tolerances, requiring everything to be heated up before things could be removed. Things proceeded smoothly without too many burned fingers, and sure enough the rear bearing was rough. There were sign's of rust on the outer race, so it could have been corrosion. I have no idea how it's previous owner had stored it, probably badly.

Things went pear shaped when I was tidying up and decided to place the piston in the liner for safe keeping. The ST 34 has a ringed piston and would the ring compress enough to get it in the bore, would it hell. Try as I might I just could not get the piston into its rightful place. Deciding that something might be lodged in the ring groove preventing it from compressing, I tried to gently remove the ring, with the inevitable consequence, the ring broke.

Once in pieces, I got a good idea of what was causing the problem. The groove has a pin that locates in a notch on the inside of the ring. If the ring rotates out of position there is no way the piston will enter the bore because the ring is being held out of the groove.

faintAfter collapsing from a near fatal heart attack upon hearing how much a ring would cost, I had no choice but to bend the plastic yet again.

The parts arrived, and the bearing was fitted with no problems. The bottom end now feels like silk when rotated. So lets fit the ring. With everything lined up the piston slipped easily into the bore. Then I made a fatal mistake.

Turning the piston so the conrod would line up in the correct position, the piston just jammed, would not move up or down, and would only rotate through a small range of movement. As I could see the ring through the ports I guessed that somehow the ring had managed to move again, or I had somehow got it into the wrong position by rotating it. Now I was was in deep doo doo. No amount of pushing pulling or turning would free it up. Eventually the inevitable happend again, a piece of ring emerged from one of the ports and I could remove the piston again.

Now I know that this is all my own fault, but the way the ring is located is bound to cause problems. The only thought left in my head after it happend, apart from feeling very annoyed at myself was, 'I wish this had been an ABC engine, then this problem would not have existed.'

st34 ring grooveThe only way to reassemble the engine is by locking the piston at TDC, and lowering the liner over the piston whilst using my third hand to keep the ring compressed through the incredibly small gap between the liner skirt and the top of the crankcase, whilst at the same time making sure that the liner does not rotate out of alignment.

The picture left illustrates this, with my first finger in shot to give some idea of scale.

Then still holding everything in alignment with all my spider legs, heat up the crankcase so the liner can be pushed home. I makes me sweat just writing about it.

Looking at this picture with hindsite, it might just be possible to insert the piston and ring into the liner first, then keeping it just inside the liner, juggle the conrod onto the crankpin. This will still be far from easy. I think I will go and practice, to see if it can be done without a ring first.

I am reluctant to fork out for another ring in the near future; I could probably pick up another engine for a little more than the cost of the ring *. So it has been shoved into a corner of the my engine shelf, with the other uneconomical to repair engines, in the wait until I can be arsed to sort them out box. It will get repaired at some time, but I am so mad at the damned thing at present, that I don't want anything to do with it.

I was impressed by the way the engine performed, maybe not it's seeming total lack of compression when turned over slowly, and certainly not by it's repair friendliness, or the cost of spares. So in future I will avoid Super Tigre engines, and stick with Chinese/Russian cost/performance effectiveness. That way if things go catastrophically wrong, I have not lost much.

* Remarkably, after I wrote this I did indeed pick up another ST.34 engine for £2.00 more than I paid for the ring. Not that I specifically wanted an ST engine after the last debacle, I was just after something in the 5.5 cc size range at the right price (cheap). We live in a crazy world.


Cold Weather

mds28Incidentally, the MDS.28 I mentioned last month with the 90° out of alignment liner, has proved to be none the worse for wear since I corrected it, It has been dragging my new multipurpose model around the sky almost as well as the Super Tigre .34 did, which I find a little surprising; in more ways than one. In fact it is making my arms ache more than when powered by the ST.34, even though the line rake has been reduced to zero to take some of the strain off my arms; any further forward and it will be in front of the LE, I haven't had the chance to time it yet, so I have no idea if it's putting in a respectable performance or not. Propping it correctly is the next exercise. The concept of making the model accept the widest range of engines that I could has already paid off, as the MDS dropped strait in after the ST.

Flying this model for the second time with the MDS proved amusing. I had grabbed a day during the week when Britain was in the centre of a large depression, no wind, but very foggy, airports closed etc. This day was no exception, and the temperature was below freezing in the early morning when I got to the field. Call me weird, but I like flying in these odd conditions, there is something surreal about flying in a blanket of fog.

After around 80 laps I kept getting a quite violent shake of the lines at the same place in the circle each lap. As there was no wind, my first thought was that I was flying through my own turbulence, something I have experienced before. The second thought was that the lines might be icing up.

A few laps further the engine cut and the model landed without incident. When I got to the model end of the lines, each one was covered in a layer of ice making it around 3 times it's normal diameter, and the wing leading edge had the classic build up of an ice ridge. But what had me staring in wonder was the engine spinner. Ice crystals had formed forward and radiating outwards from the centre of rotation, but had been blown backwards at the same time, What I was looking at resembled a small Christmas tree stuck on the spinner; this had me both laughing, and cursing that I had left my camera at home. It's unlikely that I will see this effect again.


Tigercat, A Future Project

My finances are always in a dire state at this time of the year, and with that nice man from the council (pile on the sarcasm with a shovel), managing to stop my housing benefit just before Christmas, I was not exactly filled with Yuletide Joy. Looking on the bright side, I don't have to fill those endless forms full of pointless questions and ridiculous repetition ad nauseum. And what do you think of this for my local authorities organisation: in December I receive a notification that both council tax and rent benefit will be suspended from the 17th December, and any overpaid benefit backdated approximately six months will be recovered: in January my rent direct debit is exactly the same as it has been for the last year: in January I receive a cheque reimbursing me for overpayment of council tax.......?!.

This precarious financial situation allows no slack at all, and a month of praying that nothing else goes wrong usually ends in tears; as always. Do not mention car breakdowns or Fiat automatic clutches, or I will be forced to kill you.....!

magnum21As these dark clouds were piling up on the horizon just before the storm broke, I had noticed that I could get an Magnum/ASP.21 (pic. left) from Hong Kong, including postage, for £2.00 more than the price of two ST.34 rings. Now I have wanted to build a F7 Tigercat for some time, and two of those engines would do nicely. After an email to the seller to ascertain if the .21's are available with rear needle assemblies. It turns out only the .25 and upwards have the option, which is something I can live with. So I took the plunge and gave myself a Christmas present to cheer myself up. And that is the end of my engine buying for a considerable time.

It's a pity the photographer of the engine didn't notice that the carburettor was in backwards?

The engines where actually ordered on Christmas Day in a bored moment. They arrived on the 10th of January. Now considering when I ordered them, and the week long holiday over Christmas and New Year, that's pretty fast.

ASP 21The only slight dissapointment, was the engines being standard ASP.21 engines, not the one illustrated, which I think is a Magnum XL series of some indeterminate size. Pity, I quite like the idea of a blue cylinder head.

There where also no instructions with the engines; not a problem for an experienced engine dabbler, but not so good if you aren't. But then again, anyone inexperienced would probably not be importing engines from Hong Kong? However the whole package, inc shipping, was cheaper than I could get them here, plus ASP.21 engines are not exactly on every dealers list, the trend seems to be for bigger and even bigger engines to the detriment of the smaller sizes. Not that they are not made, just not stocked. It would appear that today's learner RC fliers would not be seen dead without at least a .46 in the sharp end of their RTF trainer model.

So I am happy with my purchase; and I won't have any reservations about ordering from the same source again if I need to. If anyone is interested in where I ordered them from, this is it: Gimmetoys-Wholesale-Models-Motors

tigercatWith my present financial situation, the prospect of buying a Brodak Tigercat kit is now right out of the question for a very long time; unless some minor miracle happens, like someone saying, "Here Zoe, take this kit I have have had in the loft for years, for nothing." or someone letting me have one for a silly price.

I would have to order it direct from Brodak in US, no one here stocks them, and by the time I had paid import duty and shipping, the kit would have doubled from it's US price, and then add some.

Fortunately, as you may have gathered from my previous scribblings, I have been slowly stockpiling kit's, materials, engines, and fuel for some time now, so I have enough to keep me occupied for a year and probably longer, without spending too much. Yes, there is method to my madness

However, all was not lost with the Tigercat; I placed a brief message on the Barton Club Forum. If you have not been to, or do not know about the Barton Forum, click on the link, it's a great place to get information about CL. My query produced a quick result, money changed hands, and I received copies of the plans a week later, this should make building a little easier. There is no excuse now, I have the engines and the plan. Ever had that feeling, that there are just not enough hours in a day?


Crusader Capers

crusader

Yes! I gave in and started building it, it was too much of a temptation.

When I started to write my 'Return to Aeromodelling' series. I had no idea how long it would run for and how much I would end up writing. But one thing I have managed to do, which was one of the basic ideas behind doing it at all, was doing the opposite to most magazine reviews on whatever; that is to do warts and all write ups on my exploits, with all the mistakes and cockups produced or encountered, if for no other reason than I learn the most from my mistakes. The following is a classic example of this. So sit back and be smug in the thought that, 'I wouldn't make that mistake.' Well you won't will you after reading this?

The first, previously mentioned, mistake, of cutting a hole for the wing in the fuselage had been had been repaired and neatly covered by the somewhat warped 1.5mm ply doublers. Nothing that a bit of aliphatic glue and every clamp I could find didn't solve.

doublersThe first flaw I have found in the kit was the fact that there was an assumption made about the bearer spacing, it being wider than the almost universal 3.1cm that most engines likely to be use in this size of model seem to standardise on these days. But then again this is a 1980's design, things have moved on. The pre cut engine clearance holes in the doublers were too wide, meaning that I had to epoxy thin ply strips in the gaps to make up the difference. No big deal, but slightly annoying.

Waiting for a message from the Fiat dealer about my car, I tried to do a bit more building to take my mind off things, and the longer I have to wait for my car the longer this episode will get. Whether that's a good or bad thing, only you can decide?

Next problem was partly my own and partly due to the extremely detailed building instructions. It wasn't immediately clear that the stabilator pivot assembly, this is a real challenge to understand let alone build, has to be assembled with brass bearing tube and 12mm dowel housing, then bent to shape BEFORE passing the whole lot through the fuselage and gluing into place. This is no men feat if you do it correctly; getting it wrong; requires a lot of lateral thinking.

Of course I just merrily glued the 12mm dowel pieces for the arrestor hook and stabilator mounting, in place in the fuselage. Then spent a long time puzzling over just how I was supposed to assemble the rear end of the plane. At this point the instructions just made me even more confused; maybe it's my age?

The only solution I could come up with in the end was to drill a 10mm hole through the 12mm dowel (I hadn't got any 12mm dowel to hand, and I wasn't looking forward to removing a piece of epoxied 12mm dowel from a piece of balsa). Then drill a 5mm hole through a piece of 10mm dowel, split it, epoxy the two halves to the brass bearing tube then pass the whole lot through the enlarged hole in in the fuselage and epoxy into place. Sometimes I think my talents have been wasted in this life.

The following sequence of pictures should make the problem and the solution a little clearer.

modded assembly
This assembly has to be made first.
Making bends to accommodate the dihedral next to the brass tube takes some care.

insertion
This procedure should illustrate why a large hole has to be left in the fuselage prior to assembly.

final position
And what I should have ended up with the first time.

Another error, partly my fault, was the fact that engine was mounted a little too far forward. I am used to having problems with spinners fouling the front of models, so tend to give a bit of extra clearance. Unfortunately on this model in particular the spinner is a central feature of the profile view of the fuselage. Look at any picture of a full size Crusader and imagining it without the nose; it just doesn't work.

Because the engine was a 5mm futher forward than it should have been, the cockpit line ended up severely out of alignment with the line of the spinner. Initially aligning the engine and bearers with the lower pre cut doubler hole would not have closed the gap, but these little mistakes tend to compound themselves. The only way I could cure this situation was by building up the nose and upper profile with balsa. I just could not live with it as it was. The final spinner be black not red. I know it's hardly a scale model. but at least I can try to get the spinner colour right.

In case you are wondering, why the hell has she left a strange angled gap behind the engine? It's to accommodate engines with a rear needle valve assembly, which I much prefer; if I can get them. Just a bit of forward thinking.

spinner spinner

So far the fuselage at least, is beginning to take on that, 'built like a brick out house,' appearance, of a lot of carrier models. If one of these designs was built purely for sport flying, you could turn grey and become old and die before it fell apart.

fuselage


More Crusader Capers

The stabilator bearing arrangement continues to give me grief. After thinking I had it all solved, I found a flaw in the design. There is nothing to stop the pianowire joiner/hinge floating from side to side and the dihedral bend jamming in the brass tube bearing. Something I do not want to happen whilst flying.

In an attempt to restrict this, I tried to solder two washers on the wire either side of the tube. Then things really went wrong. The washers didn't accept solder readily, but the wire and the brass tube did; not only that, the heat from the soldering iron melted the epoxy holding the tube in place. Oh Joy!

solder
The tube firmly soldered to the wire.

Now things had become serious. The only way to get round this mess was to remove a large part of the rear fuselage, glue in a replacement, then start from scratch with a few ideas of my own.

I can't help thinking that the original design of stabilator was needlessly complicated. But I must admit I can't think of an easier way of doing it and still maintain the dihedral, at least not with the thin stabilators. Although I am still not convinced that this is the only way of doing it.

Although it's easy to drill a round hole to accept a piece of 12mm dowel it's surprisingly difficult to drill a hole though it's centre. So the heart of the assembly will be a piece of square hardwood I had lying around

tail modification
The first stage of the attempted modifications.

Tubes and close shallow bends in wire, are a recipe for binding, so I used two small brass plates fixed either side of the fuselage to act as bearings; this should be a little more tolerant, and also help with the feeding them over the bent wire ends.

Now if I had engaged my brain and thought the whole thing through, the thing with the hardwood block was entirely unnecessary, because when the wire is supported by the brass plates either side, it does not need any support in the fuselage. Oh well, the next one I build should be a piece of cake.

Only shallow bends will be use at the extreme ends of the wire, there is no need to have the bends at rightangles. This will help with feeding the bearings onto the wire.

stabilator bearings

All the parts of the assembly shown in relation to each other. A bearing plate can be seen fitted to the inside of one of the fairings. The shallow bends at the ends compared to the old wire can be also be seen.

tail fairing

How the tail will look once every thing is glued in place, hiding most of the the carnage. The fairings need finishing and sanding to shape first.

stab complete

Finally, it's finished.

fuselage

Now I can start on the wing

Maybe these problems are why most carrier versions of the Crusader I have seen built or flying, have a flat wing and tailplane. I must be a bit of a masochist to try an build it the proper way? But Hey! A whole chunk of my life has been out of the ordinary.


Crusader wing

I have now got to the wing construction stage. As I have said before, the wing is of Detroit type construction. This among other things, means the spars are assembled with the fuselage and jigged at the tips, prior to the the cap ribs being attached.

crusader wing spars

In the picture the rear main spar and main 'I' spar are jigged and waiting for the epoxy to dry. When covering with plastic film, I tend to cover bits that are convenient as I go along, to prevent damage during construction; that's why the stabilators are covered. And a lot of the time this is necessary, because its almost impossible to cover some parts once the model is assembled.

crusader wing assembly

The original design as built round a J Roberts Fight Control System, This involved a very large 1.5mm plywood plate fitted through the fuselage in the middle of the wing. As I will be using the simple two bellcrank arrangement, there was a lot of puzzling over just how I was going to mount it all. The wing is not all that deep so there is not a lot of room to play with. The only ones that would fit into the available gap were two epoxy glass woven bellcranks I had just acquired, meant for combat models; plus a lot of guesswork and bodging in a ply bellcrank mount. I hope the bellcranks are man enough for this job. There is no doubt that hanging the leadouts and bellcranks outside the wing is a lot easier on a profile model of this size, but I would like a touch of finesse if it can be managed.

crusader bellcranks



Crusader wing - Big Mistake

Just having completed the upper wing and turning it over to glue on the lower ribs, I noticed a rather large blunder I had made. The wing tip jigs have a different spacings from the main spar to the leading and trailing edge. Somehow I had managed to get one the wrong way round.

wing jig

This was quite serious as there was no way I could shift the mainspar epoxied joint in the fuselage. After managing to free up all rib to mainspar glue joints and removing the offending jig, I could bend the mainspar in to position but the tension was deforming the trailing edge. The only solution I could come up with was to to put small saw cuts in upper and lower elements of the mainspar to relieve some of the stress, then reinforce the cuts once the wing was in the right position. The vertical member would still be intact and has a ply doubler at that point, so I think it will be quite strong enough anyway. A very annoying mistake none the less.

mainspar

And now for the only thing I think is totally needless and wrong with this kit. The large thick spar marked T.E. a couple of pictures above, is not the trailing edge. The trailing edge is built up from 1.5mm sheet and small ribs. then glued to it. Now unless this model was meant to have flaps at some time or other, I can see absolutely no reason for this additional complication, which also gives plenty of room for building errors. A normal T.E. built up or solid could have been incorporated into the wingtip jigs quite easily, saving a lot of building time and be less error prone.

trailing edge



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