A return to model building and flying. Part 70


March 2011

It seems like an eternity since I last wrote anything, the long interminable spell of cold wet damp and windy weather, has made working in on my Open University course and other computer projects in the warm and dry seemed a lot more appealing. A health scare just before Christmas didn't do much to concentrate my mind on modelling either.

But here I am again turning up like a bad penny. You won't get rid of me that easily. :)



Please note: Motorvation Model Engines subsequently went out of business. I have no idea what the present situation is so cannot answer any queries. MME Contact details have been removed to avoid confusion.


News Flash hot off the wire..... My Friend John Walton has finally got his fledgling dream business off the ground, and literally within spitting distance of where I live.


Motorvation Model Engines

now open for engine repairs.


John

John has taken over the repairs and maintenance of model internal combustion engines skillfully carried out by John D Haytree for the last 40 years. Where as John Haytree's service included spares 'and' repairs, Motorvation will concentrate on engine repair. Stocks will only be held for the more common fast moving spares. John is also authorized by Steve Webb as an Enya Authorized repairer, and PAW have given him permission' to say that he is a repairer of PAW Diesels. John also has the capability to service almost any model of Fox engine.

Still trawling through a lock-up full of spares, with enough new or near new components to bring back into circulation a number of DC Sabre, Spitfire, Merlin,  some Dart, and DC Wasp glow engines, John is also offering a full reconditioning service to all makes of engines which can include, de-greasing, glass bead blasting, powder coating, and anodizing, depending upon the customers needs for the engine. I think his biggest problem will be fighting off the hoards of customers! The workshop is full of reconditioned vintage engines, that will have anyone of a certain age drooling. There is also a cornucopia of new boxed engines which I hope he will eventually have priced and listed.

With a Boxford TUD Lathe installed that is quite capable of cylinder reboring and piston turning, he will be offering a rebore' service for diesel and glow engines in the very near future. Quote: "I have done three rebores on DC engines, and my honing and lapping skills are improving all the time to a point where the mountain of metal beneath the lathe is getting smaller, and the pistons actually fit the cylinders now!" I certainly vouch for an MK17 he resurrected from near death for me. He also managed to find a fault on my ASP30FS, but more on both those engines later.

Out if interest, John will not return any of his work without running it first. This proved a wise precaution with a 40 glow that had a slightly bent crank. it straitened OK., but when run the shaft sheared across the inlet port, resulting in the the prop and front half of the shaft flying out of the engine. I don't think the owner would have been pleased, and possibly injured without this test.


engineslathe




Tigercat


tc wing1I have finally started on the Brodak Tigercat kit. As usual the misfitting parts are there but the die 'crushing' is better than usual, even if the ribs and trailing edge  slots don't line up in any dimension you care to mention? The design is on the whole sensible, so shouldn't take me too long, HA! to build.

I am beginning to get an uneasy feeling about the design of the wing at an early stage. I get the distinct impression that it was designed as a conventional  CL model, then was converted to a carrier kit. Certain things don't add up. it is impossible to thread the fuselage onto the wing when the throttle pushrods are in place for instance. I will split it anyway as it's much easier to align things accurately in this fashion. The fuselage shouldn't be taking much strain either as the engines and main undercarriage are wing mounted. The nose wheel will take some thought as I have experience of trike's from my RC days.

If you are ever tempted to build one get the all the cranks when you buy the kit. I had the bellcrank but made the other three. Being a twin complicates things. I'm sure there must be a simpler way of doing it but I am following the plan. It's only taken two weeks of try, give up, then try again, to get bits of wire to not bind and move both wing cranks in the same arc. I can't afford to get this wrong as it will all be buried in the wing and very difficult access once finished.

The pictures below illustrate my now standard method of mounting engines. It's more work but the advantages are greater. With a larger surface area there is less tendency for the engine lugs to sink into the wood. In a flash of inspiration last year I realised that the fixing holes can be placed anywhere, so I position them so that I can can get access from above the engine with everything in place, especially the silencer. This makes things soooo much easier, and also means the other side of engine mount can be blocked smooth with no access holes for nuts or screws, making things much cleaner and neater and with less places for oil to creep in. In this case I used M3 cap head screws because the fuselage position will stop me getting a screwdriver of sufficient size onto the mounts on one engine. Normally I use self tapping screws which have proved very effective so far. This method of mounting allows for very quick engine changes, and even types and sizes of engine, as only new mount plates are needed, with no butchering the wood as with the conventional method. Never a good idea with an oily front end.

tc engine1  tc engine2

With this and my other method of gluing metal fuel tanks in place, (something that can't be done with plastic tanks) front ends have become a lot cleaner and neater as well as longer lasting as there are less places for fuel to soak in. If anyone doubts the efficacy of epoxying tanks in place, remember full sized aircraft have been glued together for many years. It has been so successful, I have been contemplating using small section aluminium engine bearers glued into formers when I can find a suitable model to try it on. It would be relatively easy to add simple safety precautions just in case they should work loose. The advantages would be great, The bearers themselves could be tapped for a start, fuel would have no effect, and they will not compress with age and vibration. And before anyone says use an alloy radial mount, apart from the fact the fitting a radial mount to  profile fuselage is a bit of a nonsense,  I have never liked radial mounting and still don't. I build to datum lines. and bearers are easier to align accurately only having one dimension to worry about when flat on a building board. A radial mount has to be aligned in three dimensions... Go figure!

This model will be complicated further because I want to try and add flaps, auto line rake, and auto rudder, to use the model in Class1. I know...! I'm mad, and and a masochist..... Giggles insanely!




The ASP 30 FS saga

If you have been following my previous ramblings, you will know that for some time I have been struggling with an engine the whose name graces this piece. It has never been right from opening the box, singularly lacking in compression. Never having owned a 4 stroke before,  I am at a disadvantage, but not without experience of engines.

I want to hand start engines, and I know, because I have seen it done, that 4 strokes should be no more difficult to start than 2 strokes. feeling various engines at the club also told me that they have just as good compression. The only comment I get is, "Well it is a cheap engine." That however, does not necessarily equate to bad usually.

What concerned me was, what little compression it had to start with, diminished rapidly over the course of around 20 full tank flights, until the day I picked it up and could turn over the engine with prop driver with no resistance what-so-ever? Over that period it became more and more difficult to hand start, eventually impossible. I am sure it would start with an electric starter, but why should I when there is obviously something very wrong?

At this point I bundled it up and returned it to Just Engines, as it was still under warranty. A couple of days later I received a phone call saying that nothing was wrong with it and it was running happily in a test stand. I had a suspicion that it had been started with an electric starter, but I held my tongue, and accepted the the story of lapping the valves in, and the magnanimous offer of not charging me the full service charge. On return It did seem to have slightly more compression that before, meaning that I could actually feel some, so it was duly stuck back into the model and taken out to be flown. Why was I not surprised that after the first burst of life from a prime, it was back to absolutely no compression. At this point I gave up.

That was until I told John Walton the story and he offered to have a look at the engine. His reaction when I handed it over was telling, Hmmm! see what you mean." When it was dismantled it became abundantly clear that the valves had not been lapped in, and to the naked eye were only touching for about a third of their circumference. This left me feeling more than a little annoyed. I left the engine with John to tidy up and though that was that. However it wasn't!. On closer inspection it turned out that the metal insert that that forms the inlet, outlet  tracts, and valve guides,  had a leak where it is pressed into the cylinder head. No wonder the dammed thing has never been right. But why didn't Just Engines pick this up?  To be fair if you just want an engine or a spare part that you know how to fit yourself then they are fine, but servicing leaves a lot to be desired. As far as I am concerned, that's it, if I need an engine serviced I know where to go now.

As another rider to this, Just engines have refused to supply John with spares to service ASP engines. But as Super Custom (SC) are for all intents and purposes the same, and he can get those, it's not really a problem. My 30 will be fitted with a new SC head shortly, I have seen it, and it is indeed the same.




After writing the above we were blessed with a nice weekend, so I took both an MK17 and the ASP30FS that John had serviced for me to the field. There is only one way to try things and that is for real, at a flying site and in the air. Well what a difference! The 30 takes 4 chokes and it will kick and run with a bit of persuasion. I have yet find the ideal starting technique, but the fact is it tries and does start. There is no absolute dead feel anymore, and when cold I can feel compression with it plopping over TDC, and all with the flick of a finger no, starter required. This is what I wanted from the beginning, but it took someone that knows what they are doing to achieve it. It still plays awkward when hot, but what glow engine 2 or 4 stroke doesn't? It's not a high quality engine and I don't expect miracles. But now it does start as it should.

I may be able to actually fly a schedule with the Buster now, it's only taken since April 2007,  with modifications to the model, three changes of 2 stroke engine and a duff 4 stroke, none of which would work as they should, to get to this far..............?????

The MK 17 diesel was a similar story, I had stuck it into a box as spare parts because the compression had gone to that place in heaven that it all goes to at some point. MK17's are so far, still easy to obtain; and I do still have another three after all LOL. But I wondered what John could do with it. Well FWIW it feels like all the others now. and runs just as well. So if you have a tired MK17, John is your man.



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