Is there a rough guide for electric motor equivalencies to gas engines?
07-31-2004, 02:31 PM
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Is there a rough guide for electric motor equivalencies to gas engines?
As in is it possibly to say a Speed 600 motor with an X cell battery pack will approximately equal a .40 ic engine?
(just pulled those numbers out of the air).
I'm trying to research an electric conversion of a gas plane because I can't find an electric model that meets all my criteria.
Thanks for any info on this.
(just pulled those numbers out of the air).
I'm trying to research an electric conversion of a gas plane because I can't find an electric model that meets all my criteria.
Thanks for any info on this.
08-04-2004, 01:13 AM
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RE: Is there a rough guide for electric motor equivalencies to gas engines?
I would also like to have a comparison list, but it would need to have brushed & brushless motors dealt with separately I suspect. Other comparisons would be on weight and watts.
John
John
08-04-2004, 07:14 AM
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RE: Is there a rough guide for electric motor equivalencies to gas engines?
Generally speaking, based on my casual observations and experience:
.15 glow needs about 8 cells
.25 glow needs about 10 cells
.40 glow needs about 14 cells (12 to 16 cells)
.60 glow needs about 20 cells (18 to 24 cells)
This is assuming brushless motor, Sub C NiCd or NiMH cells, at 40 Amps peak current, sport planes of average weight for their engine class, and about 100 Watts per pound. Of course, if you increase the Amps, your cell count can go down, but so does your flight time. Many planes don't need 100 Watts per pound to fly, and many need MORE to fly as they were meant to (e.g. 3D).
For example, I fly a .40-size Tower Trainer 40 on 10 cells. My table above says I should be running 14 cells, and I could. The plane would have more power, but it flies just fine as-is. It's also lighter and was cheaper to power.
Motor choice is easy with a cell count and peak current. Any motor that's rated to handle the cell count and current will work. You want to pick the lightest motor that will do the job for obvious reasons. For propellers, you generally want to spin the largest one that will fit on the airplane, just like the full-scale guys. Many motor manufacturers, like AXi (modelmotors.cz), now include example configurations on their websites.
With electrics, it's penny AND pound wise to only give an airplane what it needs as far as power; give it just what it takes to fly it the way you want it to fly. Otherwise, you're spending extra money and carrying around extra weight.
There are literally 100000 perfectly fine ways to power an airplane electrically. That's what makes electric difficult in the beginning. Seems counter-intuitive, but sometimes putting on the blinders is necessary to keep from getting overwhelmed.
Post your potential project over in Glow to Electric Conversions
.15 glow needs about 8 cells
.25 glow needs about 10 cells
.40 glow needs about 14 cells (12 to 16 cells)
.60 glow needs about 20 cells (18 to 24 cells)
This is assuming brushless motor, Sub C NiCd or NiMH cells, at 40 Amps peak current, sport planes of average weight for their engine class, and about 100 Watts per pound. Of course, if you increase the Amps, your cell count can go down, but so does your flight time. Many planes don't need 100 Watts per pound to fly, and many need MORE to fly as they were meant to (e.g. 3D).
For example, I fly a .40-size Tower Trainer 40 on 10 cells. My table above says I should be running 14 cells, and I could. The plane would have more power, but it flies just fine as-is. It's also lighter and was cheaper to power.
Motor choice is easy with a cell count and peak current. Any motor that's rated to handle the cell count and current will work. You want to pick the lightest motor that will do the job for obvious reasons. For propellers, you generally want to spin the largest one that will fit on the airplane, just like the full-scale guys. Many motor manufacturers, like AXi (modelmotors.cz), now include example configurations on their websites.
With electrics, it's penny AND pound wise to only give an airplane what it needs as far as power; give it just what it takes to fly it the way you want it to fly. Otherwise, you're spending extra money and carrying around extra weight.
There are literally 100000 perfectly fine ways to power an airplane electrically. That's what makes electric difficult in the beginning. Seems counter-intuitive, but sometimes putting on the blinders is necessary to keep from getting overwhelmed.
Post your potential project over in Glow to Electric Conversions
08-23-2004, 02:10 PM
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RE: Is there a rough guide for electric motor equivalencies to gas engines?
OK Matt,
Here is my question i this regard. I have drawn the plans for a SAAB 340 multiengine (2) aircraft. My estimated weight will be about 7.5 - 8 pounds, with a wingspan of around 76 inches. The plane will have foam core wings. Now if I were to put glow power in it, I would anticipate that two .46-60's would fly this plane. If I were to go with the AXI type motors and li-polys what would be your recommendations for engine size, number of cells and type, as well as an afforable ESC? I have been flying for years, but electrics are still a mystery to me.
Tommy
Here is my question i this regard. I have drawn the plans for a SAAB 340 multiengine (2) aircraft. My estimated weight will be about 7.5 - 8 pounds, with a wingspan of around 76 inches. The plane will have foam core wings. Now if I were to put glow power in it, I would anticipate that two .46-60's would fly this plane. If I were to go with the AXI type motors and li-polys what would be your recommendations for engine size, number of cells and type, as well as an afforable ESC? I have been flying for years, but electrics are still a mystery to me.
Tommy
08-23-2004, 09:36 PM
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RE: Is there a rough guide for electric motor equivalencies to gas engines?
Well, being both a glow and electric flier, twin .60's on an 8 pound airplane would be serious overkill. Two bushing .40s would throw this plane around like a rag doll, the way it sounds
Just like any other electric conversion, you need to start with the Watts. 8 pounds glow will probably necessitate 9 pounds electric. Warbirds and higher-performance scale models should have 100 Watts per pound, IMHO. 9 times 100 equals 900 Watts.
Twin motors means two motors each propped for 450 Watts. You can split this into cells and Amps any way you want. 10 cells (3S LiPoly) and 45 Amps would be one way. If it were me, I'd do 12 roundcells (i.e. NiMH/NiCd) or a 4S LiPoly (about the same as 14 roundcells). For the 12 cells, the current draw would be about 40 Amps. On a 4S Lipoly, it would be closer to 35 Amps. The lower the current, the longer the run time.
So, we've got a 4S LiPoly (or 14 roundcells) and 35 Amps. All you need to do is look up an AXi motor that can handle that load, and you're all set! From the looks of it, the AXi 2826/12 is the right motor. modelmotors.cz's chart doesn't list 4S LiPoly and 35 Amps, but extrapolating from what they have listed, something between a 12x8 and 13x11, perhaps a 12x10 or 13x8, would put you smack in the middle of the ballpark.
Just like any other electric conversion, you need to start with the Watts. 8 pounds glow will probably necessitate 9 pounds electric. Warbirds and higher-performance scale models should have 100 Watts per pound, IMHO. 9 times 100 equals 900 Watts.
Twin motors means two motors each propped for 450 Watts. You can split this into cells and Amps any way you want. 10 cells (3S LiPoly) and 45 Amps would be one way. If it were me, I'd do 12 roundcells (i.e. NiMH/NiCd) or a 4S LiPoly (about the same as 14 roundcells). For the 12 cells, the current draw would be about 40 Amps. On a 4S Lipoly, it would be closer to 35 Amps. The lower the current, the longer the run time.
So, we've got a 4S LiPoly (or 14 roundcells) and 35 Amps. All you need to do is look up an AXi motor that can handle that load, and you're all set! From the looks of it, the AXi 2826/12 is the right motor. modelmotors.cz's chart doesn't list 4S LiPoly and 35 Amps, but extrapolating from what they have listed, something between a 12x8 and 13x11, perhaps a 12x10 or 13x8, would put you smack in the middle of the ballpark.
