Thursday, August 10, 2017
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Engine Oil Know-How

Gas Powered Thoughts: Engine Oil Know-How

Every mainstream gas helicopter currently on the market uses a two-stroke engine that requires oil to be mixed with the fuel (usually by you). Glow fuel, on the other hand, already has the oil mixed in and the percentage of oil is much higher.

Oil content in glow fuels is typically referenced in percentages based on the total volume of fuel (gallon or liters). Oil content for gas helicopters is typically referenced as ratios like 32:1, 40:1, etc. You can calculate the actual amount of oil by dividing the ratio into the total amount of fuel (gallons or liters) and the result will be the amount of oil in ounces or milliliters to add in order to achieve the target ratio.

As a comparison, most glow fuels contain between 16- and-20 percent oil; somewhere around 20 ounces of oil per gallon of fuel. Because of the high oil content, a large percentage will go through the engine unburned and can make quite a mess on your model as it sprays out the exhaust. Gasoline motors contain only two to three percent oil, (three to six ounces per gallon) which is a much smaller percentage. They survive this because they use rolling bearings on virtually everything that turns and since they use less oil, they produce very little residue on your model.

Gas Powered Thoughts: Engine Oil Know-How
Two of many possible oil choices.

Of course there are many types of oil and if you fly gas-powered helicopters you’ve probably spent time researching which oil you should be using. It’s an important topic, but in my opinion, modelers spend way too much time focusing on this. Remember, for the most part we are using re-purposed industrial motors to power our models. They are designed to work with a large variety of oils as long as they meet general rating types. I am not going to spend time in this column discussing the details of oil ratings, but you can easily find out more about the rating process by searching Google.

In our case you always want to use oils that carry a rating of JASO FC/D or ISO EGC/D. These are designed specifically to deal with the heat and tolerances of air-cooled engines. These ratings are pretty common for most of the two-stroke pre-mix fuel you’ll find on the shelf and it’s also what is recommended by Zenoah, the largest manufacturer of gasoline hobby engines.

Always follow the engine manufacturer or modifier’s oil and ratio recommendations. This will be important for both longevity and warranty considerations. Believe me, if they take your engine apart for service, service technicians can tell if you’re using the right oil and ratios from the wear on the engine and its components. Depending on the oil and its intended purpose, it will have different additives that affect parts wear, varnish and carbon buildup (both inside and outside of the engine).

If you’ve been around gas helicopters for a while, you’ll have noticed that there always seems to be the next “new” oil that you must use or your helicopter just won’t work right. The latest fad seems to be the use of synthetic marine pre-mix oil. This oil is designed for water-cooled marine engines and carries a TC-W3 rating. It’s more expensive (about 50-percent more) than most of the premium oils and supposedly produces minimal deposit buildup in the engine. Is it right for these engines? I’ll have to say that I’ve received mixed feedback on the engine deposit aspect. Some folks I’ve talked to indicate little buildup while others have shown me what looks like typical or normal buildup. Some of the air-cooled motorcycle and snowmobile manufacturers explicitly prohibit its use due to the higher engine temperatures involved. Regardless, one of the engine modifiers recommends it exclusively for use in their helicopter engines.

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Gas Powered Thoughts: Engine Oil Know-How
RatioRite oil measurement container.

re there other implications to using oil designed for water-cooled use in an air-cooled engine? The answer is maybe. Hatori, one of the manufacturers of helicopter muffler systems, has found that exhaust deposits from extended use of this oil can clog the baffling in their muffler. They have never seen this with the oils rated for air-cooling use so they don’t recommend it. My point here is there’s more than one aspect of choosing the right oil to be considered.

Depending on the formulation of the oil you chose, its manufacturer will have a recommended and/or minimum mix ratio. Pay attention here! If you want to experiment, you may find you do more damage than good. Again, if you are using a modified motor, follow their instructions. They have detailed procedures for break-in and which oil and ratios to use for each.

All of the oils in this list are being successfully used by pilots around the world so if you’re not sure what to use, you should be able to find one of them locally wherever you are.

• AMSOil Saber 100
• Belray H1-R
• Castrol Power-1 2T
• Honda HP2
• Klotz Techniplate
• Motul 800 2T – Off road
• Stihl Ultra
• Yamalube 2R (mineral blend)

Finally some words about oil mix ratios. Every helicopter engine (modified or not) comes with instructions on what oil pre-mix ratio to use. I would suggest the following approach; if you don’t know EXACTLY what you are doing, just follow the instructions and you’ll stay out of trouble.

If you look around you’ll see suggestions about using everything from 25:1 to 100:1 oil mixing ratios. As a rule of thumb, 32:1 to 50:1 covers most circumstances. There are, of course, exceptions like the OS GT15 and the CY460 which both require a 25:1 ratio. Some oils really can support as low as 100:1 ratios, but I strongly urge you to not run a ratio higher than 50:1. If you make a mistake and go too lean on the carburetor mixture setting, you’ll ruin your motor in one flight.

Gas Powered Thoughts: Engine Oil Know-How

If you want to really simplify your mixing process, look into one of the “RatioRite” containers. They have graduated indents on the site for all relevant mixture ratios and are very simple to use.

Lately there are gasoline alternative fuels surfacing that have oil already mixed in them. Powermix and Tru-Fuel are examples but currently they are not widely used in model helicopters. Another brand that we have been working with is VP Small Engine Fuels, which comes pre-mixed. I know a number of pilots having great success with this fuel.

Hopefully I’ve given you enough insight into the topic of oil to make you more curious.

WHAT’S NEW?
There is a new company in Australia called HelixHeli.com that is working on gas helicopter conversions. They have released the Helix G700 for the Trex 700. From what I have seen, the Helix models have some different features, but are very similar to the popular Helibug conversions. I will have more information about the Helix models in the future.

Speaking of Helibug, they are working on a new model as well. By the time you read this, they will have released the Icebug 600 which is a complete gas powered helicopter. This will be the first complete helicopter that Helibug has marketed. 

For more detailed information about gasoline powered helicopters visit:

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Words and Photos: Carey Shurley

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