boss351

My Feedback: (6)

There is a nice looking Mosquito kit by TurnkeyRC, it is 55" wingspan (1/12 scale) and designed to fly with two 0.15 gas engines. There is no information on weight. Is there a general rule of thumb to figure out what type electric motors would be suitable for a kit like this? Has anyone already converted it?

Here is a link to the site:

[link=http://www.turnkeyrc.com/]TurnkeyRC[/link]

There is also a nice looking Typhoon that I am also interested in for electric power. Same question on suitable electric power conversion.

Has anyone coverted any of these kits?

Matt Kirsch

My Feedback: (21)

There are a few rules-of-thumb, but none have anything to do with the motor. They do, however, make choosing a motor much simpler.

First is the Watts-per-pound rule pioneered by Dr. Keith Shaw (the hairy guy in the picture in the latest Model Aviation, NEAT Fair article). For every pound of airplane weight, you need a certain number of Watts (Volts x Amps measured at the battery) to make the plane fly in a certain way. General sport planes, for example, need at least 75 Watts per pound. 100 Watts per pound will give you performance similar to a typical overpowered glow engine.

Second is the cells-per-unit-wing-area rule, or Orme's Law (you know, Ohm's Law, har-dee-har-har), by Matthew Orme of Razor Motors fame. His law specifically addresses .15 to .60 size conversions, and assumes the use of Sub-C NiCd/NiMH cells and a current of 25 to 35 Amps. For trainer-like performance, your battery needs one cell per 50 square inches of wing area. For high-performace sport plane performance, you need one cell for every 35 inches of wing area. Really, Orme's Law is just a "boiled down" version of Keith Shaw's rules, adding lots of assumptions about things like wing loading.

Both these rules are a bit dated, but still useful.

I've further boiled down Orme's Law and have come up with a table of cell counts based on the recommended engine size for a particular airplane. Assuming a typical sport plane wing loading (around 20oz per square foot), a current of 35-40 Amps, and the use of Sub-C NiCd/NiMH cells:

.15 - 8 cells
.25 - 10 cells
.46 - 14-16 cells
.61 - 20-24 cells

If you look at a few conversions, not necessarily mine, you'll see that they fit this table pretty well. There are, of course, exceptions.

Once you have a cell count and a current, it's rather easy to find a motor that can handle them.

boss351

My Feedback: (6)

Thanks for the information. Both these planes appear to be heavy kits, I plan on getting some more details from TurnkeyRC and the figuring out whether to attempt one of them as an experiment.

I have been thinking of buying a a HIMAX 2025-4300 to use with a C GWS gearbox to fly in my MM Dandy. I think that this should be enough engine for the 41" wingspan Typhoon. I have some info that the Typhoon weighs about 2.5 lbs but that is with the .20 engine installed. Maybe a lighter built Typhoon electric would be ok with this motor using 3s1P lipos, what do you think?

boss351

My Feedback: (6)

By the way, All-e-RC list the 2025 motors as 180Watt class.