Teach me about RC fuel?

I used to use 30% nitro in helicopters. My go to shop was S&W Fuels in PA. They had the best price around at the time.
 
To get the lowest oil in a premix glow fuel get RC car fuel. Those guys are so HP hungry that they will go low oil for more power and just replace a lot of worn out parts, the cost of racing.
On the other end of the spectrum is Helicopter and four stroke fuel, this will have the highest oil content since helies are run at a constant speed just below red line and have very weak cooling systems and 4 strokes crankcases are only lubed by the ring blowby.
You definitely want a synthetic oil instead of castor oil. Castor is a great lubricant for these engines but it does bake on and leave behind a mess of dark brown discoloring on your pretty engine that is very hard to clean off.
I do add 1% castor to all of my fuel as it has some very beneficial properties that the synthetics have not yet matched, 1% is low enough that I do not get the discoloring.
Similar commercialy made radial engines run in the neighborhood of 6K RPM with the recommended props. Depending on your prop selection, you can get almost any WOT RPM that you want.

As mentioned above, make sure that you have some form of c'case ventilation for the blow by and do a lot of oil changes to get the fuel contamination out of the oil.

Please do NOT use WD40 on this engine (or any engine). WD40 is designed as a Wire Drier, hence the name. WD40 will dry up and gum up the moving parts. It is also a very poor lubricant since it was not developed to be a lube.
 
So you have an oil sump? Surprised to see separate oil. You are in the area of Kavan engines. Look up their 50cc from the 80's.
 
Flyinfool said:
To get the lowest oil in a premix glow fuel get RC car fuel. Those guys are so HP hungry that they will go low oil for more power and just replace a lot of worn out parts, the cost of racing.
On the other end of the spectrum is Helicopter and four stroke fuel, this will have the highest oil content since helies are run at a constant speed just below red line and have very weak cooling systems and 4 strokes crankcases are only lubed by the ring blowby.
You definitely want a synthetic oil instead of castor oil. Castor is a great lubricant for these engines but it does bake on and leave behind a mess of dark brown discoloring on your pretty engine that is very hard to clean off.
I do add 1% castor to all of my fuel as it has some very beneficial properties that the synthetics have not yet matched, 1% is low enough that I do not get the discoloring.
Similar commercialy made radial engines run in the neighborhood of 6K RPM with the recommended props. Depending on your prop selection, you can get almost any WOT RPM that you want.

As mentioned above, make sure that you have some form of c'case ventilation for the blow by and do a lot of oil changes to get the fuel contamination out of the oil.

Please do NOT use WD40 on this engine (or any engine). WD40 is designed as a Wire Drier, hence the name. WD40 will dry up and gum up the moving parts. It is also a very poor lubricant since it was not developed to be a lube.
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Lots of good info here. Thanks @Flyinfool.

I'll be venting the crankcase to an auxiliary oil tank. And I'll have some sort of other port in the crankcase as well to draw in some fresh air. A breather of sorts I guess. Haven't figured out exactly how to do it yet, but it's on my list.

Dhal22 said:
So you have an oil sump? Surprised to see separate oil. You are in the area of Kavan engines. Look up their 50cc from the 80's.
Click to expand...
Yup, I just finished the pump and the sump in the past few days. My build thread has some info on them.
 
Most of the fuels that are readily available seem to have nitro in the 20-30% range.

Does it hurt to go substantially above the 3-5% nitro recommended in my build drawings?

I assume the nitro percentage is tied to what you set your compression ratio at. My plans call for a CR of 8.5:1, though I've not yet set that so I've got some wiggle room.
 
Got it.

So does this seem like a reasonable plan?

Ask for a custom blend (of about a gallon for starters) from these guys to include the following:​
  • 5% Nitromethane
  • 9% Synthetic oil
  • 1% Castor oil
  • 85% Methanol
  • + Whatever other corrosion inhibitors/additives they typically use for an airplane engine

I'll probably order some additional synthetic oil on the side to use for the separate oiling system.

And maybe a quart or so of plain Methanol as well, in case I want to dilute the concoction to something less than 5% Nitro.
 
@Flyinfool's good advice.

One other difference between modern commercial hobby engines and a shop-made engine are friction and durability coatings, heat-treating, and spec metallurgy. Also, commercial motors may or may not have tapered bores and oblong pistons to improve the seal and engine life. It's a good call to run with oil.

I think castor oil is important too, because it smells like memories! I'd love to see video when you get it running. That prop is a monster compared to anything I've ever run. My planes are mostly under 1 meter wing span and 5 lb auw.
 
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