Relative Engine Sizes
 

Does anyone have, or can you point me to, a chart or other information that provides relative engine sizes for 2-cycle glow, 4-cycle glow, and gas engines. For example, a .40 2c glow engine is relative to a .50 2c glow engine is relative to a 25cc gas engine. (The gas engine category can be broken down into 2- and 4-cycle, but probably 2-cycle predominates.) I've got a few gas engines that I may tinker with and I want to pick the right sized planes for them.
Thanks,
Bidwin

RE: Relative Engine Sizes
 

With glow engines, it used to be true that a 4-cycle had to have about 25% more displacement to equal a 2-cycle glow. For example, you could compare a .46 glow engine with a .60 4-cycle engine. The newer 4-stoke engines are closer to the 2-strokes, now. Still there are differences in that the 4-cycles generally swing larger props at lower rpms. The 2-cycle glow engines like to run higher rpm's and therefore are better at smaller props turning faster.

Now as far as gasoline engines: There really aren't any 4-stroke engines out there for aircraft use. They are all 2-strokes and they are generally quoted in cc's (cubic Centimeters) of displacement as opposed to CU (cubic inches). This is easily converted by multiplying the cubic inches by 16.4. So a .40 cubic inch displacement glow engine is also a 6.5 cc displacement. But in general, a gasoline engine produces less horsepower than a glow engine of the same displacement, on the order of about 20%. Say for example you have a 1.8 cu in glow engine (e.g. a Moki 180). This is 30 cc's. You might compare this to the same power as a 40 cc gasoline engine. The gasoline engines are invariably heavier than their glow counterparts, too.

RE: Relative Engine Sizes
 

Thanks for the reply, McQuinn. You've given me some useful information that will help my planning. A simple spreadsheet will make things easy. I didn't think there were any/many 4-stroke gas plane engines out there but I did see one mentioned recently in one of the mags. Maybe MAN or Model Aviation.

Since you mentioned prop use with various engines do you happen to have any guidance in that area? For example, if using an 11/6 prop on a .46 2-stroke glow engine change diameter/pitch by X on a .60 4-stroke glow or 40 cc gas engine. I recall a "rule" that states add one to the diameter and subtract one from pitch to get comparable props. Does this work here too, or should the pitch be kept with larger diameters?

Thanks again,
Bidwin.

RE: Relative Engine Sizes
 

typical prop for .46 glow is 10x6 or 11x6
typical prop for .60 glow is 11x7 or 12x6
Typical prop for 1.8 glow engine or 50 cc gasser is 18x10
typical prop for 100 cc gas engine is 28x10

we very seldom get above a pitch of 10 or 12 unless you are into a specialty area such as racing. there the props get higher in pitch.

RE: Relative Engine Sizes
 

Actually you multiply by .06102 to convert to C.I. (cubic inches). Therefore 41cc
equals 2.5 cubic inches. (41. x .06102.

Bob

RE: Relative Engine Sizes
 

"Typical prop for 1.8 glow engine or 50 cc gasser is 18x10"
I would compair a 1.8 glow to a 28-38 cc gasser not a 50 cc.
An 18x10" on a modern 50cc gas engine is way, way too small. Most are spinning a 22x10 or 24x8 @ around 7000

RE: Relative Engine Sizes
 

One inch equals 2.54 cm
2.54 times 2.54 times 2.54 equals 16.387064 cubic centimeters in one cubic inch
1 divided by 16.387064 equals .061023 cubic inches in one cubic centimeter

.061023 is the inverse of 16.387064

enjoy,

Jim