A return to model building and flying. Part 23

Wildcat and How To Ruin Engines

January 2006

Well here we are in 2006. When I started this epic journey I had no idea how many twists and turns it would have, or the directions I would spin off in. Attempting a carrier deck model was the last thing on my mind, but here I am building one.

Apart from the world and it's dog trying to squeeze every last penny out of my bank account until the pips squeak at this time of year, I hate local bureaucracy and large companies. I am still managing to complete models, although the club subs will have to wait a while longer.

Back to more pleasant things, this is the model, Jan Odeyn's 'F4 Wildcat' carrier trainer. I must say it has been a pleasure to build a well designed model for a change, nothing unnecessary, and everything just as I would expect it to be.

I can still remember the surprise I got when I asked Jan what engine it use, after watching him prop hanging in a howling gale at the 2005 UK Nat's, "2,5cc" (0.15) was the answer. I was expecting some huge horse powered beast of an engine. After flying it in Holland I can safely say it does not need anthing bigger, unless you are a masochist, or on some, mines bigger than yours, male ego trip.

The only truly confusing thing was looking at a drawing of the bellcrank assembly viewed from the top when the actual one is mounted beneath the the wing. Obvious when the penny drops but until I made a cardboard and pins copy and tried to make it work, just could not work out how it 'could' work. A minor setback, and the exercise at least gave me a clear view of how things fitted together.

wildcat right

Jan O'deyn's, GRUMMAN F4 WILDCAT carrier trainer

wildcat left

Below, the bellcrank and connection to the transverse throttle linkage


The other side of the transverse linkage.

throttle linkage

Arrestor hook release mechanism.


The only thing I had to rethink was the fuel tank. I could not get hold of a plastic clunk tank that would fit between the wing and the engine. Jan's suggestion of putting it on the other side of the fuselage, I was not keen on, as on a fast run the relative fuel head would increase making the engine run rich. I want to keep the fuel head changes as small as possible.

I had a nice eBay purchase to hand, in the form of some metal C/L stunt tanks. One fitted almost perfectly, except for the fact that the feed pipe came out exactly in line with the back of the engine with no room to spare. After a bit of brain massaging, I came up with the idea of just moving the pipe outlet to a new position, the feed end is in the same place as before. This solved the problem and should not affect the working of the tank.

Detail of the fuel tank feed pipe modification

fueltank modification

The Stupidity of a Failing Mind

I now have to admit to a piece of crass stupidity that left me feeling very stupid and annoyed at myself and paying out money I can ill afford at this moment in time.

The SC 15 engine in the Wildcat was won on eBay for a good price. It was secondhand and in what seemed like very good condition. On a cold Sunday morning at the flying field the engine was started up for the engine for the first time, and I was surprised when it burst into life and was screaming it head off, in a quite powerful way. I got so carried away I peaked the engine just to see what it would do, It felt like it was quite capable of pulling the model out of my hand vertically.

After stopping it and laying out the lines for the maiden flight, could I start it again? Could I B*****y! All the compression had gone to a far distant place that only the gods know about. There was also a loud Clack! sound every time it was turned over TDC. Then The penny dropped, The description on eBay had said, "only bench run." So in a couple of minutes I had managed to completely ruin a perfectly good motor.

Back home, on dismantling the engine it was obvious that the big end had gone and the piston could be pushed up and down the bore with almost no resistance. After a lot of agonising about whether it was worth trying to repair it or look for another motor, I decided to repair it, on the grounds that it had sounded so good when I did run it, and another second hand one may not be as good.

Monday morning the parts where ordered from John Haytree (are there any engine parts he does not have in stock?) after manageing to sort out precisely which model I had. Apparently SC originally made the 15 by using a thicker liner in in a 19, then at some point bored out the 10. As mine is the latter, it may explain why it likes to rev so much. They arrived the next morning and the repairs were carried out. I noticed the new conrod had bushes in it, the old one did not. The only difficult bit was wrestling with a minute gudgeon pin circlip.

Wednesday dawned with me heading for the flying field determined not to repeat the disastrous exercise. The only guidance for running it in was from another engine, a new AP 15., which had quite precise and detailed instructions, another ABC twin ballrace engine of Chinese origin like the SC. For anyone that has not seen one, a rear exhaust engine with a unique pancake silencer arrangement, and a very sensible needle valve assembly; every intriguing.


(No! I haven't a clue what the 'Yellowjacket' in the name refers to either? Certainly not the engine.)

The running in process stipulates a Castor based fuel and requires 5 minute run periods with a cooldown period in between. The first as rich as it will stand, gradually increasing the needle setting with each run from a very rich setting to a steady two stroke on the last one, when 30 minutes running has been achieved. Then followed by a further 1 hour in the air running, quote: 'As rich as you can set it and the model still take off', and gradually leaning out each run.

Strangely this running in procedure flies in the face of current perceived wisdom. I hear and read so much about ABC engines requiring little or no run in period. The usual explanation is that the temperature of the liner needs to rise as quickly as possible to take the strain off the conrod. This may well be, if you have a fit that is so tight you can hardly get it over compression. Most of the new engines I have felt, are not this tight, in fact they feel quite loose.

My understanding of the ABC combination was that the expansion rates of all the materials was roughly similar, therefore keeping the clearances close over a wide range of temperatures. If this is true and I have not completely got hold of the wrong end of the stick, if the engine is tight when cold it will be tight when hot, leaning an engine out under these circumstances would not be a good idea. The same applies if the fit was almost right or slightly loose, Any points of contact will undergo rapid wear if leaned out, thus ending up with no compression at all. This is indeed what happend to SC.15.

I also read somewhere that when a cylinder and liner are new there is a microscopic transfer of material from the liner to the piston, or from the harder material to the softer over a period of time, that actually alters the composition of the metal surface. In other words, gives the softer material a hard coating. I suspect that this is something to do with the hot and cold sequence that AP recommend. If the time involved is ignored, the softer material will just wear away at a rapid rate.

I do know that my father had a brand new Irvine .40, not known for their flimsy construction, and followed the running in instructions to the letter. Something along the lines of two tankfulls and then let it rip. The result was a completely clapped engine that had to be rebuilt by Irvine under guarantee. There have been other examples of ruined new engines too numerous to mention.

So on balance I think I will run ABC engines in with caution and over a period of time. After all one and a half hours with one hour of that in the air is still a hell of lot shorter than the the running in time for an original Fox 35 stunt, as anyone else that has ever experienced that dubious pleasure will tell you.

As I had both the AP and the SC to run in, I could run one, then swap engines in the test stand whilst the first cooled off, thus running in both engines over roughly the same period of time.

This time everything worked with both engines sounding like they really want to go. I looked like I had been in a mud wresting contest when I got home, bench running is tedious business and kneeling in mud, in wind and drizzle, does not help. Now at least I can do the rest of the running in in the air, which I much prefer.

A Flying Wildcat

The next weekend things went a little better. The wildcat flew and only required a some adjustment to throttle line length to make things a little more comfortable. Taking off for the first time I wondered why with full up the prop was trying to plough a furrough in the ground, until I realised the interaction on the the simple bellcrank system and the line being the wrong length was causing the control system to feed in a lot of down elevator. Easing off the throttle cured the problem and the model took to the air normally.

The tank also needs a pressure feed as there is a tendency to lean out as the flight progresses. Another thing that is easily remedied

I can't really set the carb up properly until the engine is fully run in, but it works well enough to control the speed in the air. I can't fully close the carb, it seems to be the adjustment of the carb itself and nothing to do with the model control system. This is something to be tackled in the warm and dry not on the flying field. As I am still running in this was no particular problem, only a slight annoyance.

Video Clip

A short video clip of me flying the Wildcat after most things had been sorted out. However, the quality is only just tolerable, and all I could salvage from some gross over-exposure. Early days with, and not quite got the hang of my cheap mini dv camcorder. It will give some idea of what it's slow flying characteristics are like.

vid icon  Vid-Clip   2.9MB 1m:11s .wmv

A Pile of Junk and a Diesel

This seems to be an engine month. I recently won a batch of old engines on eBay that where so dirt encrusted it was difficult to make out what they where. But what I did recognise under the filth was what looked like an MVVS 1.5 diesel, MVVS stands for 'Modelarske Vyzkumnev Vyvojove Stredisco' as if you didn't know? I have been after one of these engines at the right price for a long time, and obtaining that was the target of this exercise


The 'BEFORE' picture, as they were received

In the end it turned out to be a Modela Junior 2. which I believe is 2cc. the only thing wrong with it apart from some cosmetic scratches, was a broken engine lug. This would not prevent me using the engine as there are ways of mounting such things.


Modela Junior 2 diesel
This is the 'AFTER' picture, after I worked the clean up magic

The engine itself proved to me that there is nothing wrong with it. After cleaning off the external grime, I put a few drops of fuel into the carb just free things up a bit. After a couple of flicks to see what it felt like, it burst into life and ran quite happily clutched in my hand. I am glad the surprise didn't make me let go....!! Not much wrong with this engine then?

Now begins a small mystery. The engine looks suspiciously like an MVVS. and on the Internet are lots of references to these engines being made by MVVS for Modela, which as far as I can make out was the Czech equivalent to today's Ripmax, or yesterdays KeilKraft. After contacting Just Engines and finding they still had some spares they rounded up a new propdriver, the original had the requisite plier gouges round the edge, prop bolt, and a screw in backplate, to replace the original with the obligatory chewed up tool slots. But unfortunately no crankcase was to be had. So I decided to email the source, MVVS. This is the reply I received:


Unfortunately, we did not produced this engines. The firm Modela, which produced it, exist no more and spare parts are not available.

Best regards:

Josef Svajda Technical Support / Technická podpora


So I am left puzzled as the origin of these engines? And thinking I would be nice to find a whole crankcase, just to restore a bit of history.

I must mention the other engines in the job lot as they show how some people have no feel for anything mechanical what so ever.

First an Enya 09 that was only good as scrap.

An OS 25FP, that under all the grime was in surprisingly good condition, except, for the fact that someone had decided, for reasons best known to themselves? to bore out the mounting holes to 5mm with a blunt drill. WHY? this is a ludicrous size of bolt when you consider the standard size is 3mm. I managed to sleeve the holes back down to 3mm, but there was precious little metal left at the edge of the holes to work with.

Next was an old Super Tigre 35. Again under the grime it seems to be in reasonable, if not good condition for it's age. The the parts of the crankcase casting that hold the silencer fixing bolts are both broken, but that is a common thing on Super Tigre's of that age. But why! oh why! would anyone take off a cylinder head from a perfectly good engine, then screw it back with the fins at a peculiar angle? Not only that but butcher the screw heads with an oversized screwdriver blade that damaged the fins around the screw holes in the process, making them almost impossible to get out. Things like that leave me feeling incredulous, and wondering what else they wield unsuitable tools on, sometimes the thought is quite frightening.


And the result of cleaning up the other engines

Hopefully with a bit of restoration work and a good test run they will be sold on to recoup some of the money expended in obtaining the Modela J2. It is certainly a testament to Super Tigre engineering that the 35 has stood up to the neglect and abuse it has, and still survived in a reasonably intact and functional condition.

Soviet Engineering

As you may have noticed I have an interest in old, and new, Russian diesels made in Russia or the old soviet satellite countries. This started because I was, and still am a little perturbed, by the slowly diminishing availability of diesels especially of the smaller capacity variety. Yes high performance modern diesels can be found from around the world, at a price, but the general purpose equivalent of Davis Charlton's or Frog's diesels of my dim and distant past do not exist today. Also I am actually quite intrigued by the old soviet union's engineering, which had a bad reputation in the past caused by bad workmanship and shoddy materials. I am not sure that taking everthing into account this was altogether deserved. But if that can be looked at from a different angle, the basic design was usually quite sound, for example a common feature was ball race crankshafts, something that was only found on high performance engines in the west at the time.

I have been looking at MK-17 1,5cc diesels for some time now as I would like something other than a PAW 1.5 to play with. Part of the attraction is that there are so many new ones available at very low prices, but what has put me off in the past has been the fact that all engines must be silenced at my club field. Radially ported engines are not the easiest thing to fit a silencer to. Then I started to wonder if PAW silencers would fit, after all the PAW is a radially ported engine, and still available.

Taking the plunge, I won a new in box MK-17 on eBay at a very reasonable price.


At the first opportunity the head was removed and the a PAW 1.5 silencer held up for comparison. Much to small. So the silencer was removed from a PAW 3.2/.19 which according to PAW is the same size as a the 2.5. This one was an almost exact match, even the screw holes match up. Some gentle easing is needed to fit it over the liner and a bit of careful sculpturing needs to be done to let the bottom fit over the existing crankcase, but it is do-able. my aim is, not, to alter the original engine during the process of fitting a silencer, that way I can use it as intended if the opportunity arises, or sell it on in original form.

This will be a suitable subject for my future pages, as I have a Marz 2,5 and a KMD 2,5 winging their way from Siberia as I write this (Isn't eBay a wonderful thing). Both, I hope, are suitable candidates for adapting silencers to fit

Suitably encouraged I put a few drops of fuel into the intake and gave a few flicks to see what it felt like. Lo and behold, I could feel it firing. not wanting to repeat the running in the hand incident with the J2, I clamped it in a test stand. One smart flick later it fired and ran off the charge. All ways a confidence builder when that happens.

Now all the bits are in place except for one. A new PAW silencer would cost near as damit the same as I paid for the engine......???

This has led me to the conclusion that getting an old PAW with a silencer off eBay, removing said silencer and selling on the engine, makes more economic sense than buying a new silencer. I should be able to pick an engine silencer combination for around the same price as a new silencer.

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