What is the difference in engines

[Mark]

What is the difference in a nitro engine for a car/truck to a model plane engine ?
On the outside all I can tell is the size of the cooling fins on the cylinder of cars and boats are larger than a model plane. This I imagine comes from the enclosed spaces car and boat people run these in compared to the cowl of a model plane.
What about fuel ? Say fuel for a .049 motor vs a "nitro" motor for a car/boat.
The last time I played with small engines ( late 70`s early 80`s) people mixed up castor oil and ........ it escapes me now. I think the ratio was 3:1
There is 1 1/2 gallons of nitro fuel under my kitchen sink. Maybe a gas model is..........

[Guest]

Helicoptor engines have larger cooling fins as do the car/truck/boat engines you mention. Engines for fixed wing planes have the high volume air flow from the prop to help with cooling and do not require fins nearly as large.

By far, the most popular type of fuel engine for model planes weighing less than 25 pounds is the 2-stroke glow-fuel engine. The most common size engine is 0.40 cubic inche (called the "40 size") and is typically used on planes weighing 3 to 6 pounds. The displacement on your little 0.049 glow-fuel engine is about 8 times smaller.

These glow-fuel engines use a glow plug, which must be connected to a battery for starting. After starting the connection to the glow plug is removed. The glow plug remains hot (i.e. "glowing") allowing the engine to continue running. Planes larger than 25 pounds will typically use a larger 2-stroke gasoline engine which requires an ignition system and spark plug.

The fuel used in 2-stroke (and 4-stroke) glow-fuel engines is a mixture of alcohol (methanol), oil, and, nitromethane. The amount of oil is typically around 20%. Castor oil, synthetic oil, or a blend of Castor and synthetic oil is typically used. The nitromethane percentage varies from 5% to 50%. Most flyers use 5%, 10%, or 15% nitromethane. Nitromethane gives the engine a better idle and more power.

Although the raw ingredients can be purchased separately and mixed, most hobbyists buy the fuel by the gallon from their local hobby store. The fuel manufacturers also add "special ingredients" in small amounts such as anti-foaming agents. One gallon of 15% nitromethane fuel currently sells for about $16.

[Mark]

Why do you mix synthetic oil and castor oil together ?

Does runnning higher amounts of Nitromethane create more heat for the engine ?

[eheitzeberg]

Castor oil, although good at providing the adequate protection, over time can leave a build-up in the engine called varnish. I understand that some varnish is required for good compression. The outside of the engine also becomes coated with this brown ugly varnish residue (i.e. just cosmetic). Synthetic oils do not have the varnish build-up problems. However, I've been told that the synthetic oil does not protect the engine as well especially during the break-in period of new engines when the temperatures are typically very high. Some people recommend using Castor oil fuels for engine break-in then switching to a synthetic oil based fuel after the engine is broken in. A castor/synthetic blend is a reasonable compromise for all engine conditions.

The higher percentage nitromethane will produce more power along with more heat. Percentages higher than 15% are popular for racing. Some sport flyers use 5% nitromethane in the summer and a higher percentages (i.e. 10% or 15%) in cooler weather to provide easier starting and better idling. I generally use 15% nitromethane for year around use for both my 2-cycle and 4-cycle engines.