Cyclic Hardover

My Feedback: (3)

I am curious as to why "Dar" is promoting OS plugs?

DarZeelon

Cyclic,


I am not! MVVS glow plugs are much better; cheaper too...

What I am saying is that many hobby shops, including Tower/Hobby Services, the OS dealer for the US, are doing us wrong by 'pushing' that cheap OS A3 plug, into any engine that would accept it, forcing it to use fuel excessively and causing it to misbehave in the mid-range.

...This, instead of just supplying the right glow-plug for the application in the first place.


...The right fuel too. The .91FX and all STs becomes better engines, when you run them on 5% nitro, but most Americans, for some reason, can see nothing but 15% nitro theses days...

piper_chuck

My Feedback: (12)

Is it possible for OS to provide a plug that will work right for every end user?
Not THAT discussion again! Seems like it's time for Jan to add his commentary on castor versus synthetic and 18% oil versus the 10% that he asserts is so widely used in Europe!

DarZeelon

Don't worry, Chuck....

We'll get to that too .

DarZeelon

Yes!

If OS engineers decided that the A5 is the right glow-plug for the .61-.91FX, they must supply these engines with this plug; not with the A3, which is clearly the wrong glow-plug.

Please go back to the first post, for the link to OS' glow-plug page.

...Or, at least, they must sell (and have any and all their dealers do the same) you the A5 plug, when you buy a glow-plug for these engines. It is clear that using a hotter glow-plug will only make the engine run worse.


Even the so-called 'universal' #8 is a bit too hot for larger engines and a bit too cold for smaller ones.

You wouldn't just use a 'universal' spark-plug in your motor-car, would you?


If OS makes a range of glow-plugs, they should also make sure you use the right one for each engine.

Kostas1

Dar i have to say that the OS 61 FX & OS 91 FX are supplied with OS #8 glowplug,NOT with the A3 that is supplied with OS 46 AX,50 SX, and LA series.

piper_chuck

My Feedback: (12)

Dar, you missed my point. If everyone used the same fuel and prop size and ran at the same altitude, temp, and humidity, it might be possible for the manufacturer an engineer to recommend a single glow plug. However, as you're well aware of, we don't all use the same fuel, or fly in the same conditions. This is why there is a range, and why no one plug will work for everyone.

DarZeelon

I do get your point, Chuck.

However, about 97% of the world's population live below 2,000 ft. So S/L conditions are in effect.


This is why OS should supply the .61-.91FX with the A5; not with the #8 (Kostas...) and for sure, not with the A3.

It may be possible to use even the hottest A3 plug, at a rich mixture setting, but even the medium #8 will require a richer mixture setting than the correct A5.

With the cold plug and 5% nitro, a 10-12 ounce fuel tank should be enough for a 10 minute flight, even with the .91FX, yet with the hot plug and 15% nitro, even 16 ounces are often consumed before 10 minutes are up.

If you do live at a higher altitude, like Cyclic, or run very high RPM and 11" props on your .91FX, you can always opt for a hotter glow-plug, but then you are about as rare as a one-eyed owl... Definitely not the 'general population' material, who will do 'very well, thank-you' with the A5.

Hobbsy

My Feedback: (102)

I bought an OS LA .46 and a .65 about a year ago and neither came with a plug which is the way I prefer it.

TimC

This could explain some of the problems experienced by .91FX users.

downunder

That's a ridiculous argument. With 20% oil (to keep things simple) the ratio of 5% nitro to the remaining 75% methanol is .0666, in other words the nitro content is 6.67% of the actual fuel. Go to 15% nitro and methanol content drops to 65% so now the ratio of nitro to methanol is 23% or about 3.5 times more of a fuel that an engine drinks like it's going out of style! The huge increase in consumption will far outweigh any small difference a change in plug might make.

TimC

What Dar said made sense to me. With a glowplug of the right heat and less nitro, a longer flight would be possible. I can't argue with that.

Kostas1

OK DAR here it is.
After a few e-mails into OS engine support mail,
Nick A.
Product Support,
wrote to me these.

So,it hasn't anything to do with the engine(so the manual is correct),but with the percentage of fuel.
Enjoy.
Kostas

DarZeelon

Kostas,


I am not saying it cannot be done; just that using a plug which is hotter than OS recommend in their own Japan web site (A5), would force you to richen the mixture setting beyond what is optimal, for best performance and economy.

The page at the OS web site does not tell you the nitro percentages you should use with each glow-plug; just what glow-plug to use in each engine.

With an A3, your engine would empty the fuel tank within about 2/3 of the time, compared to the A5... If you want this, just go ahead...

I stand by my primary claim; the manual is wrong!

Kostas1

Using the A5 or the #8 glowplug on an OS 65 LA instead of an A3 will increase top power?
I mean you can lean the high speed needle even more?

DarZeelon

Kostas,


Yes, it is so.

Let us look at it this way:

With a given mass of air (i.e. oxygen) in the cylinder, you can burn only a certain mass of fuel, according to the stoichiometric ratio of that fuel. This is not a volumetric ratio!

Actually, you will get a bit more power with a little bit of extra fuel, since a certain amount is wasted, or burnt in an inefficient way.

For gasoline (petrol) the stoichiometric ratio is 14.7 (the mass of air is 14.7 times larger than the mass of gasoline) and the maximum power (around 2% more than at the stoichiometric ratio) is achieved at a ratio of about 13.5:1.

Methanol has a stoichiometric ratio of about 6.5 and an ideal power ratio of about 6:1.

If you let even more fuel into the engine, you will not get more power. The excess fuel will leave the engine unburnt and will even hamper the combustion process, possibly reducing the power somewhat.

If even less fuel is allowed, power will be reduced for sure, but such a condition is hard to attain in a glow engine (it is always the running condition in a Diesel, however).

So going from very rich to an ideal and maximum power fuel mixture, the potential for power is nearly unchanged.


Changing the ignition timing is what actually changes the effective power the engine will make from the fuel.

It is clear how the ignition timing is changed in a gasoline engine.

But for a glow engine, with a given glow-plug (all other conditions; i.e. compression ratio, ambient conditions, prop load; are all unchanged), the only control you have is the fuel mixture settings...

And this is your control for the ignition timing. Confusing? Not at all.
A cold, rich mixture will ignite later and burn up more slowly, reaching maximum pressure later.

A warmer, leaner mixture will ignite sooner and burn up quickly, reaching maximum combustion pressure sooner.

So when you lean the mixture, you are actually advancing the ignition timing.
At a certain mixture setting, the ignition advance is ideal and gives you maximum power from the engine.

So, how does that relate to the selected glow-plug, you are asking...

If you use a glow-plug, which is hotter than the engine needs, the ideal ignition timing is achieved with a mixture setting that is too rich. More fuel will run through the engine than it can actually use to produce power.

If you use a glow-plug, which is colder than the engine needs, the ideal ignition timing is not achieved even with a maximum power (a little lower than stoichiometric) mixture setting.
Leaning the mixture setting further will reduce the power, because the engine will be running at a fuel deficit (too much air, too little fuel; like a Diesel).

If the glow-plug is ideally suited to the engine, the optimum advance will be reached at the maximum power mixture setting. No fuel will be wasted. No power will be lost.


This is the reason for the importance of the choice of the right glow-plug.

Saving wasted fuel costs you nothing, except selecting the ideal glow-plug.

Runway

I'm confused about the A3 plugs. OK, so the site that Dar references in his first post says they are for "engines smaller than .32 capacity".
However, on what ALSO seems to be an OS website, namely:-

http://www.osengines.com/accys/glowplugs.html

...it says about A3 plugs... "a long lasting hot plug for most 2-strokes up to .60".

Any thoughts to help out a simple weekend flyer, please?

DarZeelon

Runway,


This is what happens when the same huge company sells you both engines and fuel....

As I explained, using a hotter-than-recommended glow-plug, will have your engine guzzling more fuel than necessary.

The web site you referred to belongs to the American importers of OS, Hobby Services, Great Planes, or an affiliated company.

They may want to make their products, including some glow-plugs, appear more flexible than their manufacturer intended them to be. If the engine would be using more fuel than necessary, it will not matter much to them, since chances are you would be buying your fuel from them as well...

...But you would be paying more...

Shouldn't we all want this hobby to be more affordable?
This is achieved by only paying for what is necessary, or beneficial for your enjoyment from this hobby.

Wasting fuel unnecessarily qualifies as neither...

I would trust the OS company's web site over that of any dealer.

Get the right glow-plug for your application! As per OS Japan.


...But, as to the break-in technique illustrated in the manual... I trust only my self and my own experience.

Kostas1

Thank you Dar gor your information!
So,instead of using the A3 in an OS 65 LA,
what glowplug to choose?
The A5 or the #8?
Οnce again thank you.
Kostas
Greece

Runway

Many thanks Dar Zeelon. All is now clear.
Regards.
Runway

piper_chuck

My Feedback: (12)

Dar, that's ridiculous. It's highly unlikely that there is such a plot by Hobbico to sell more fuel. The shipping costs on small quantities of fuel in the US is excessive. Because of this, most fuel is purchased from the local hobby shop. If they are guilty of anything it's probably just that they didn't bother to put enough information on their web site or in the manuals. Over the years they've probably been conditioned that the more they put in there, the more people challenge it. Here's an example of the kind of complaint they are probably trying to avoid: "You told me this plug would work with that fuel, but it's not. I want my money back!"

DarZeelon

Kostas,


I would get some A5 glow-plugs for the .65LA.
It is good for your .91FX that you have also.

The #8 is a very good glow-plug (and it's expensive...).
I sometimes use it myself, in lieu of the MVVS/Novarossi C6, but with the A5, your large engines will be just as reliable and your fuel bill will be lower.

DarZeelon

Chuck,


I did not say there is a specific 'plot'... But they gain both ways, from selling both engines and also some fuel.

It may be they are trying to avoid arguments, but how about this: "This engine guzzled up the whole 16 ounce fuel tank within 9 minutes. That's why I crashed. Now, give me a new kit for free!..."

piper_chuck

My Feedback: (12)

I'd love it if I could get 9 minutes out of a 16 ounce tank on my .45 boat engines Tell me, is the problem that I'm running too hot a plug?

DarZeelon

Maybe not, Chuck...

But if you do, you may only get 7 minutes out of that tank...