Oddball engines and prototypes

[Lightbulb]

Burn marks (carbon) form where the raw fuel meets a surface that is above its ignition temperature.

That's Exactly what I'm trying to avoid by limiting exhaust heat transfer.

Besides My engine doesn't need to run for hours between pull downs.

Cheers, Daryl.

What I do know is the polished piston crowns and heads only stay polished for like a couple of runs so like 3 mins of running.
Inside the pipes, a new pipe stays clean only for maybe 1 run if that and only if it is never run close to being lean. If it goes lean for just the shortest of time, it turns in colour. The irony for the model engines, it seems that as they build a carbon/ dark something layer inside the pipes, the better they run. Which is the opposite of your object or ideas.

Neil

[Pursang]

What I do know is the polished piston crowns and heads only stay polished for like a couple of runs so like 3 mins of running.
Inside the pipes, a new pipe stays clean only for maybe 1 run if that and only if it is never run close to being lean. If it goes lean for just the shortest of time, it turns in colour. The irony for the model engines, it seems that as they build a carbon/ dark something layer inside the pipes, the better they run. Which is the opposite of your object or ideas.

Neil

3 minutes might be enough.

So many other variables, Fuel & Oil & A/F ratio, ignition timing & exhaust temperatures, warm up, piston & rings & bearing run-in time.

I would really prefer not to fabricate a water-cooled exhaust duct with auxiliaries, if I can find any way around that.

Cheers, Daryl.

[Frits Overmars]

What I do know is the polished piston crowns and heads only stay polished for like a couple of runs so like 3 mins of running. Inside the pipes, a new pipe stays clean only for maybe 1 run if that and only if it is never run close to being lean. If it goes lean for just the shortest of time, it turns in colour. The irony for the model engines, it seems that as they build a carbon/ dark something layer inside the pipes, the better they run.

All of the above is true, Neil. But wait, there's more.
Assuming you're talking about your 6,5 cc F3D engines, one should know that they run on too-rich a mixture because otherwise that darn glowplug would ignite too early and cause detonation.
Secondly, they burn methanol. The stoichiometric fuel/air ratio of that stuff is 1 kg of fuel to 6,4 kg of air, and too rich would mean something like 1 kg of methanol for every 5 kg of air, or 200 grams of fuel per kg of air.
Next, the mandatory oil/fuel ratio in F3D-competition is 20% by volume. That is 200 cc of very greasy castor oil to every litre of methanol. And since castor oil and methanol have about the same specific density, we can say that the fuel contains 200 grams of oil per kg methanol.
Bottom line: for every inhaled kg of air that F3D engine consumes ('is smothered in' would be a better description) 40 grams of oil.
That is ten (10 !) times as greasy as the lubrication in the Aprilia RSA! No wonder you have carbon build-up while-u-wait.

[Lightbulb]

Yeah that's all True Frits. When they run lean though, it is amazing how little oil comes out. Like the oil becomes a fuel as well.

With that picture of the golf ball effect inlet tract, it was done using EspritCam 5d cam solutions. Not sure what engine it is though.

Neil

[Pursang]

I would really prefer not to fabricate a water-cooled exhaust duct with auxiliaries, if I can find any way around that.

Methanol & Castor Oil is certainly an option.

I've raced a B33 500 BSA on Methanol and It's amazing how cool they run, compared to petrol.
So much so that this one had all the head fins broken off, to save weight, way back in the early 60's.



But I'd rather run the Victa in "Fuel" class sometime later on.

Cheers, Daryl.

[husaberg]

All of the above is true, Neil. But wait, there's more.
Assuming you're talking about your 6,5 cc F3D engines, one should know that they run on too-rich a mixture because otherwise that darn glowplug would ignite too early and cause detonation.
Secondly, they burn methanol. The stoichiometric fuel/air ratio of that stuff is 1 kg of fuel to 6,4 kg of air, and too rich would mean something like 1 kg of methanol for every 5 kg of air, or 200 grams of fuel per kg of air.
Next, the mandatory oil/fuel ratio in F3D-competition is 20% by volume. That is 200 cc of very greasy castor oil to every litre of methanol. And since castor oil and methanol have about the same specific density, we can say that the fuel contains 200 grams of oil per kg methanol.
Bottom line: for every inhaled kg of air that F3D engine consumes ('is smothered in' would be a better description) 40 grams of oil.
That is ten (10 !) times as greasy as the lubrication in the Aprilia RSA! No wonder you have carbon build-up while-u-wait.

do they have it that "greasy" because of the nitro fuel, or because they have no rings?
Why would the rules define how much oil to run was it to stop a Belray style no but mines on 300:1 ration pit bragging contest?

[Lightbulb]

The 80/20 fuel came about from the 1960's when engine had Steel liners and cast iron pistons and a plain bronze shaft bearing.
Lower oil contents ,tended to make them wear out prematurely. The Diesel engines, especially in competition would use lower oil content fuels, down to 10% in the early days for a speed advantage and range advantage, but were happy to replace a piston liner set every competition.
The nitro fuel use synthetics if the nitro content exceeded 40% as it does not mix with castor after that.
They never lowered the castor content. But at the level of power now being generated, if the oil level is reduced to even 18%, if they run lean, apart from the glow plug failure, they will pick up and ruin the rod Big end bush and pin.
Neil

[WilDun]

The 80/20 fuel came about from the 1960's when engine had Steel liners and cast iron pistons and a plain bronze shaft bearing.
Lower oil contents ,tended to make them wear out prematurely. The Diesel engines, especially in competition would use lower oil content fuels, down to 10% in the early days for a speed advantage and range advantage, but were happy to replace a piston liner set every competition.
The nitro fuel use synthetics if the nitro content exceeded 40% as it does not mix with castor after that.
They never lowered the castor content. But at the level of power now being generated, if the oil level is reduced to even 18%, if they run lean, apart from the glow plug failure, they will pick up and ruin the rod Big end bush and pin.
Neil

Neil,
So really the model engines don't bear a lot of resemblance to competition engines used in bikes, karts etc. mainly because of the use of ringless pistons and plain bearings (where lubrication is concerned) and where pollution is really of no consequence (at present) and the use of "excess" oil which either comes out raw or as smoke!

What I am interested in and would be keen to understand is, how the ignition event timing is controlled (with either glow or diesel) - is it controlled by compression and what happens as the compression gets lower with wear? - more oil required? Is the compression more dependent on the oil content than with ringed pistons?

Just another (more mundane) thing - I have an OS 45 AX motor (not the Mk.2) which has been sitting a few years partially run in (with standard glo fuel I assume) I have heard that on the odd occasion the plating has been "flaky" on those - how to run it in properly, is what I want to find out!

[Lightbulb]

Neil,
So really the model engines don't bear a lot of resemblance to competition engines used in bikes, karts etc. mainly because of the use of ringless pistons and plain bearings (where lubrication is concerned) and where pollution is really of no consequence (at present) and the use of "excess" oil which either comes out raw or as smoke!

What I am interested in and would be keen to understand is, how the ignition event timing is controlled (with either glow or diesel) - is it controlled by compression and what happens as the compression gets lower with wear? - more oil required? Is the compression more dependent on the oil content than with ringed pistons?

Just another (more mundane) thing - I have an OS 45 AX motor (not the Mk.2) which has been sitting a few years partially run in (with standard glo fuel I assume) I have heard that on the odd occasion the plating has been "flaky" on those - how to run it in properly, is what I want to find out!

Well the modern model engines like the one Frits had involvement with is like a miniature motor bike engine with the full cast jug transfer ports, integral ceramic balls running directly on the crankshaft for the main bearing with an outer shell in the case. With a domed piston and a head to suite. The only thing old fashioned is the 20% castor oil supplied fuel. Being that Castor oil is from plants and is natural, I think that they are actually environmentally friendly, as the methanol and the castor when burnt are making compounds that nature will readily break down anyway over time. But that's another story all together. The ignition timing in the glow plug engine is controlled by the compression ratio to a point, the wire diameter and length(of the glow plug itself) the chemical make up of the platinum wire, and the over all temperature of the cylinder/head. So you can have the head at a certain volume, like in a sport class that does not allow for any compression changes to the engines for example. So on cold days, you run a hot glow plug. A hot glow plug is made when it has either a smaller diameter wire in it and/or a bigger hole in the glow plug body surrounding the helical wire coil. Another way is using what is called a glowbee plug, which utilises a flat coil wire, and comes in different wire diameters, different wire lengths, and different wire alloy mixes. In general, the thin wire plug with a long coil will be a hot plug , while a larger diameter coil wire with a shorter length will be cold plug. So thick wire is like 0.3mm dia or 0.35mm dia, while thin wire is in the 0.12mm dia or 0.15mm dia with 0.2mm dia being a standard wire diameter. With the globee style, if the coil is left laying fairly flat in it's geometry, it will behave like a colder plug, and a lifted coil geometry will behave like a hotter plug.
So with the combination of heat ranges in glowplugs it has about the same effect as raising or lowering the head by as much as 0.07mm or 3 thou with a 6.5 cc engine. On the smaller 2.5 cc engines, the various plug selections like raising or lowering the head by 0.05mm or 2 thou. So from 1 extreme to the other on the 6.5 cc engine, the plugs can give a head setting change equivalent of upto 6 thou and the 2.5cc engine about 4 thou. So they become with the high power output engines more difficult to find the middle sweet spot.
The diesels have a variable compression head, with a small contra piston for raising and lowering the engines compression setting. The diesels are more temperature sensitive than the glow engines, and are also more sensitive on the fuel mixture setting as well. So the cooling of the engine in the model of the diesels is far more critical and so is the loading on the engine more critical at the same time. If the diesel is slightly over loaded, as it is flying through the tank of fuel, it will build heat and after about 34 to 40 laps will be over heated, ie a head temp will exceed 180 deg C. If it is under loaded, it will rev higher, and will keep at the heat setting for the whole run, ie about 165 deg C A too under loaded engine will chill off if it has too much cooling as well, and then will under perform. So then you put on more compression etc to get more heat and it will over heat early . The fuel id very critical on the racing 2,5cc engines and generally the exact formula the teams us is kept quite secret. But in general it will be a kerosene type compound for 50 to 65 %, an ether for 20%to 35%, an oil (usually castor oil 5% and a synthetic combined total 8% to 15%) an ignition improver, Like Diesel cetane improver, Amyl Nitrate, Amy Nitrite, IsoPropyl Nitrate, or a mixture of any of the above ignition improvers in a percentage from 1% to 3%, and sometimes they then add TEL, tetra ethyl lead, or Ferrocene to the fuel mix as well, even though it is a diesel, they add these anti knock additives as well. So you can see that the modern model diesel engine no longer run on the old 1 part kero 1 part castor oil and 1 part ether.
A long post I know, but this gives a basic run down on the state of current model aircraft engines with only a few moving parts. Yes I have made and designed and run variable compression glow plug engine heads as well over the years.
As to your OS engine, just take the back plate off it, and the head off(if you take the head off, do not disturb the rotational position of the liner) and use glow fuel to clean it out and make sure it is not gummed up. Run it with a 9X6 prop, so 9 inch diameter 6 inch pitch APC or what ever you can buy. When you run it up, use full throttle, wind in the needle till it starts to sag, then open the needle from that point 3/4 of a turn.It will be very rich, if it is too rich for take off lean about 1/8 tun at at time. You should be able to pinch the fuel supply line momentarily, and the engine pick up RPM. If it sags, then it is too lean. Then just go fly it. Look at the glow plug. If the body of the bottom of the plug is black after a flight , it is too lean or to over loaded. The glow plug body should look like a new plug. Over time, you can lean in the needle a little bit, but keep an eye on what the colour of the plug is. Over time it will darken of course, so when it gets to a light brown honey colour, clean around not to break the wire, the bottom of the plug with a maroon coloured scothch brite fine pad. Gerrn is too course. Washa nd then keep checking the colour. Over time, the plug will wear out. You will know this, as the mixture will require leaning out to make it run as good as it used to. Then put in a new plug. The plugs for the 45 is a OS #8, or OS #3. The fuel can be from 5% nitro to 15% nitro. It can run on no nitro fuel, but is more difficult to tune day to day. I recommend 10% fuel. After running for the day, let it run out of fuel or pinch off the fuel line, drain the tank, draw air through the fuel line to make the needle area dry of fuel, and then oil with any ATF fluid. Auto transmission fluid. It has buffers for both alkalines and acids.
Neil

[Frits Overmars]

do they have it that "greasy" because of the nitro fuel...

The mandatory 80/20 fuel for F3D contains 80 % methanol and 20 % oil - no nitro allowed at all.

What I am interested in and would be keen to understand is, how the ignition event timing is controlled (with either glow or diesel) - is it controlled by compression and what happens as the compression gets lower with wear? - more oil required? Is the compression more dependent on the oil content than with ringed pistons?

I have no experience with model diesel engines, but glow plugs are a pain. If and when they ignite, depends on the temperature and mass of the glow plug filament, whether the filament is conceiled in the plug body are hanging free in the combustion space, and on the purity of the fresh charge, its fuel/air ratio, its temperature,
and the compression pressure rather than the compression ratio. Improve one of those factors and ignition will occur earlier in the compression phase.

In practice the ignition timing is controlled via the fuel/air ratio: you turn the fuel needle and play it by ear; experience should tell you when you have found a setting with good power that will likely survive the race without detonation setting in and destroying the filament.

When the plane has completed its ten laps, the fuel line is pinched by a servo in order to stop the engine (there is no throttle valve). Just before it stops, you can hear the revs go up, and because of the propeller it can only do that if the power goes up: a clear indication that is has been running too rich.
The alternative is a borderline setting than may either win you the race or, more likely, won't let you finish because detonation blows the glow plug filament away.

When a model airplane has been unusually fast in a race, it often turns out that most of the filament is gone and only a small part is still present, shifting the ignition timing towards TDC. This is an indication that most engines are running with too much ignition advance.

Spark plug ignition would allow a better timing control and a better mixture. But radio control and the necessary high-energy sparks (because of the abundant oil)
don't go well together, and a normal spark plug would about double the height of the engine.
I've tried miniature spark plugs, meant for low-power four-stroke model engines, but in an F3D engine they were destroyed within seconds.



EDIT: seems that Lightbulb and I have been writing at the same time .

[Lightbulb]

Great to have you cover what I missed Frits.
Neil

[WilDun]

Thanks guys, it'll take a few reads to digest that lot! I could sit here all night and tell you some hilarious stories about my "self taught" efforts in (attempted) model aircraft flying ....... but I won't, because i would be permanently banned from every Model Aircraft Club in the country!

[Lightbulb]

Hey Will, the important part is you are having fun.
I can't fly radio models. I just don't have the eye thumb brain control.
I do fly the control line speed models and used to fly the combat F2D if you look for youtube video's
and did for a short while do some F2C team race in the early 80's but only made up the numbers really.
I have however kept up with the small changes in the F2C diesel technologies, and try to keep up with the
F2A and F3D pylon piped engines technologies as well.
The model engines fit my budget, but the materials that we are now playing with costs are about the same or more than
some full sized engines. LOL, but I do get to play with some leading edge stuff at times and that is kind cool.
Neil

[T.W.R]

There's roughly $6k of odd ball engines you'll have never seen nor will see again....seeing model aircraft engines are being banded about
2nd & 3rd pics are a friends built in the 70s; the 4cyl was a idea for a prototype drone engine and the Harley just a build exercise but looking at it now very very similar to a evo block

[Pursang]

There's roughly $6k of odd ball engines you'll have never seen nor will see again....seeing model aircraft engines are being banded about
2nd & 3rd pics are a friends built in the 70s; the 4cyl was a idea for a prototype drone engine and the Harley just a build exercise but looking at it now very very similar to a evo block

Is the 4cyl a 2 stroke or a flathead like a vintage Plymouth 4?

cheers, Daryl.