View Full Version : Does a conversion chart exist?

08-08-2005, 05:03 AM
The title of this thread is a little misleading?

I was hoping to see a chart that accurately converts a Gas or Glow I/C engine to the appropriate "electric" application.

Another good chart would be the battery configuration chart 2p4s, vs 4p2s and why. What are the battery continuous load times for each of the battery types?

I'm a heli pilot and would love to convert my Hirobo EC135 to electric. I currently fly it with an .90 and get approximately 15 minutes of flight - which, all things considered, I would like to maintain.

Matt Kirsch
08-08-2005, 02:26 PM
There are some general rules of thumb regarding airplane conversions, and more than likely, some regarding helicopters as well. I have yet to delve into the weird and wonderful world of helis, and my brother the heli nut isn't into electrics yet.

For airplanes, I've boiled all the rules of thumb regarding power-to-weight down into two that will cover 95% of all conversions:
1. For glow-like sport plane performance, 100 Watts per pound of all-up airplane weight.
2. For 3D performance, 150 Watts per pound of all-up airplane weight.

Once you figure out how many Watts your plane will need, you split it out into Volts and Amps to figure out the battery. Volts times Amps equals Watts. Generally you want to keep the Amps as low as possible, to work with the available equipment, keep the temperature down, and keep the flight times up. We can explore this facet of a conversion further if you'd like. It seems like a whole bunch of "voodoo" from the outside but it's really logical and quite easy once you've been through it. Full-scale airplane designers use similar methods for figuring out what kind of power they need, using horsepower, of which Watts is the metric equivalent.

The LiPoly "S&P notation" you see stands for "cells in Series, packs in parallel." To get the required Volts to power an aircraft, you stack cells in series to make a pack. To get the capacity to handle the Amps required, as well as longer flight times, you gang multiple identical packs in parallel.

In a situation where you need to decide between a 2S4P and a 4S2P, given that EVERYTHING else is equal (power requirements, cell type, etc.) you would ALWAYS choose the higher-voltage 4S2P over the 2S4P. There's no "versus" in that situation. Always choose voltage over Amps to get your power. You can get the same out of both packs, but you would have to draw twice as many Amps from the 2S4P pack. It won't bother the pack, and flight times will be roughly the same either way, but the higher Amps will be harder on the motor and ESC.

You can also skip the whole "figure it out" part and just use the same setup as someone else who has converted your helicopter. Imitation is the sincerest form of flattery, you know :)

What's that helicopter dealer that also runs giantscaleplanes.com? They're always in the back corner at Toledo.... Dangit, I can't remember, but they always have several converted electric helis on display. Is it quickworldwide.com? You might give them a call and see what they have to say.

08-10-2005, 03:58 AM
an article by Jim bourke in 1999 quoted "50 watts/pound to mantain a hover if this is of any help

08-10-2005, 05:04 AM
I believe he meant 50 watts to fly. Trust me, it won't hover on 50 watts per pound, it being a model airplane.

08-10-2005, 06:52 PM
here are a couple suggestions: The Ampeer by Ken Meyers and also Hobby Lobby has a list of electric conversions.
The Ampeer has an extensive list of glow to electric conversions which include details concerning power systems, batteries etc. The builders also rate the plane's flyability and quality as well. I got many of my first ideas from that thread.
Good luck with your conversion. jollyroger

Greg Covey
08-11-2005, 01:15 PM
My column in the November issue of Quiet Flyer will have a section called, "Glow Conversions Made Easy". It is a summary of my knowledge on the subject that works for any size plane.

08-18-2005, 06:14 AM
Ive used this page alot to research my conversions


09-21-2005, 08:36 PM
I've found that MotoCalc is an invaluable aid for estimating requirements and performance. http://www.motocalc.com/

09-22-2005, 11:06 PM
calc the load from the glow spec and then convert to power absorbed for the electric.

i.e. rpm v diam v pitch = load or power.

then spec that equiv for electric.

09-26-2005, 09:16 PM
Mega Motors USA has quite a few planes listed too:

Matt Kirsch
09-27-2005, 03:20 PM
The way I described earlier in this thread allows you to convert ANY airplane (i.e. "teach a man to fish"), but of course there are ways to cheat.

One such way is to find someone who has converted a plane of similar size, weight and flying style, then copy their power system. At this point, every size/shape/weight plane that can be imagined has been done, so you've got to try hard to NOT find a setup to copy. Just make sure to look at the time/date stamp on that posting. You don't want to be searching high and low for old, outdated technology.

Heck, that's how most glow designs get powered. There's no science to it; they just look for a plane that's close in size, weight, and flying style, then use the same engine recommendations.

You can always ask the experts, too.