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03-01-2013 05:04 AM

Flyinbullmax

Re: Old engine oil content

Quote:

Originally Posted by OLD PRAIRIE RED NECK

Mike, could you explain to me how nitro methane could be an ignition timing modifier and "slow burning" at the same time?

In the old days we used ether as the timing modifier and it definatly was not slow burning!

Thanks Merv

I know its weird the way it happened. There must be something else I did that caused all those engine problems. When we add castor oil in a jug, how long do we have to shake or mix it before use? If not it may be my glow plugs, its O'Donnell Super Sport Glowplugs, type med/hot standard plugs. Or may it be the gas itself? I use Magnum Fuel 15%. Will have to analyse all this this summer.
Thanks
JP

02-28-2013 08:06 PM

OLD PRAIRIE RED NECK

Re: Old engine oil content

Quote:

Originally Posted by MJD

Thanks MJD.

I think that that is mostly true for ether as well. Perhaps there is a perception that the primary purpose for nitro(or ether) is power related as opposed to timing because both DO increase power for the reasons you outlined.

Quote:

Originally Posted by MJD

Ether has an extremely low autoignition temperature relative to the other fuels mentioned, something like 320F. I would think small amounts would advance glow engine timing considerably. Never run it in glow fuel myself.

Generation gap!

I had really not heard about nitro before the 70's!

02-28-2013 07:43 PM

OLD PRAIRIE RED NECK

Re: Old engine oil content

Quote:

Originally Posted by Flyinbullmax

Thanks Kip, that is the Sig oil I have. Funny still that it happens. All my engines that always ran troublefree started to run iratically the minute I added the oil.
JP

Something is odd there Jean, I have cut a jug of 15% with methanol to make 3 jugs of 5% then topped up the oil content to 20% oil with castor only. This would make the majority of the oil content castor. The ONLY problem encountered was an increase in slime to wipe off the plane after! I have done this several times when I couldn't get 5% sport fuel.

02-28-2013 02:37 PM

MJD

Re: Old engine oil content

Quote:

Originally Posted by OLD PRAIRIE RED NECK

Merv, as I understand it the timing advance is not due to the rate of combustion, but to the 'willingness' of the mixture to ignite under compression and catalysis from the glow plug - related to the autoignition temperature, the amount of fuel in gas phase, combustion chamber temperature and a bunch of other hoodoo. It's rate of combustion is stated to be slower than methanol and gasoline in any literature I have found on the subject. Autoignition temperature and burn rate are different properties.

Ether has an extremely low autoignition temperature relative to the other fuels mentioned, something like 320F. I would think small amounts would advance glow engine timing considerably. Never run it in glow fuel myself.

02-27-2013 05:26 AM

OLD PRAIRIE RED NECK

Re: Old engine oil content

02-26-2013 08:17 PM

MJD

Re: Old engine oil content

Quote:

Originally Posted by OLD PRAIRIE RED NECK

The main purpose that nitro serves is the same as spark advance on an ignition engine.

Nitromethane content has an effect on timing, but that is secondary to its purpose. It is nearly a monopropellant - increasing the percentage increases the total energy content per cycle of the fuel/air mixture, increasing cylinder pressure and thus torque - resulting in an rpm increase on the same shaft load or the ability to turn more load at the same rpm. It is relatively slow burning and favours increasing torque more than increasing rpm once the rpms get up there. These days CL speed fliers in the larger classes, limited to 10%, are running higher rpm than they ever did to recover the power lost relative to the high nitro blends. If you can't burn a more powerful mixture, then burn more of the same fuel per second, that works too.

Advancing timing, if it is not as far advanced as it can be for the conditions, can increase power, no argument there. But nitromethane is not there just to advance the timing.

02-17-2013 11:14 AM

Flyinbullmax

Re: Old engine oil content

Quote:

Originally Posted by kip51035

Hey Flyanbullmax you need to use Bakers AAA de-gummed castor oil not the stuff from the drug store, it has lots of impurities in it. Sig use to sell it. I never had a problem.

Thanks Kip, that is the Sig oil I have. Funny still that it happens. All my engines that always ran troublefree started to run iratically the minute I added the oil.
JP

02-17-2013 08:36 AM

kip51035

Re: Old engine oil content

Hey Flyanbullmax you need to use Bakers AAA de-gummed castor oil not the stuff from the drug store, it has lots of impurities in it. Sig use to sell it. I never had a problem.

02-16-2013 04:05 PM

OLD PRAIRIE RED NECK

Re: Old engine oil content

Quote:

Originally Posted by Cougar429

10-15% nitro is also the average so there is less stress on the internals. That brings up another point. Personally, I think in anything but helis, anyone requiring over 15% nitro to get the power they need, (or just want) has mismatched the engine to airframe. This can also stress even a good engine towards a short life expectancy.

I agree totally!

The main purpose that nitro serves is the same as spark advance on an ignition engine. So - the higher the rpm - the more advance/nitro you can use. Also the lower the compression ratio the more advance/nitro you need. So to use 30% heli fuel in a 4 stroke is totally backward from both the rpm & compression stand point!

I would not knowingly buy any 4 stroke that has been abused that way! Of course if you have a worn out engine with next to no compression left it will run much better on high nitro, in fact it may not run dependably at all on low nitro, but any engine in good shape will run well on 5 - 15%.

Quote:

Originally Posted by COUGAR427

AJ, I'd take you up on that offer if you weren't so far away.

I'd love to get my hands on some too Andrew but this is such a vast country...

02-16-2013 03:15 PM

Cougar429

Re: Old engine oil content

I'm surprised Fox got such little mention. They're still in business and still building tough engines.

As with many the key to long life is proper break in and IMO, after run treatment, (with Fox taking a longer time than most due to their hard cylinder liners) and this is where I see a lot of skimping. It seems very few have the patience to do a proper break in and the engines suffer because of it. Nothing like firing a motor up and flying in short order, either new or ignoring a warm up any time at the field.

True, there are quite a few with questionable quality in materials or design and likely sold more than they should have due just to price point. Even OS has produced a few dogs, but I suspect it was in an attempt to try and cost match the previously mentioned offerings.

Many times I've had the chance to pick up engines for a steal where they've been lunched in very short order. If careful and know what to look for you can find some hidden gems, (how about a virtually new Saito 125A for $80? All that's wrong is a stripped plug hole). I think many ended up on the block because a person either could never get it to run right since mounting and/or gave up since it would not perform to their satisfaction. In a lot of cases the bearings, a good cleaning and proper setup were all that was required to have them back at the field since otherwise very little internal wear was experienced.

As for oil content, I run my entire fleet of 2 and 4-strokes, including several of my mid 80's gen OS and Fox, on 18% semi/castor mix. Starting in this hobby 30 years ago all we had was castor and as mentioned I still have several engines in near perfect condition that weaned on it so I'm a bit biased about its use. 10-15% nitro is also the average so there is less stress on the internals. That brings up another point. Personally, I think in anything but helis, anyone requiring over 15% nitro to get the power they need, (or just want) has mismatched the engine to airframe. This can also stress even a good engine towards a short life expectancy.

AJ, I'd take you up on that offer if you weren't so far away.

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