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Old Dec 08, 2008, 12:38 PM
Recycled Modeller
Wilf's Avatar
Dungiven, Northern Ireland
Joined Apr 2008
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Glow engine /electric motor equivalents

Can anyone point me in the direction of a table of Glow engine /electric motor equivalents, preferably giving motors available easily in the UK?

The one I am really searching for is the equivalent for a .29 - .35cu in glow motor, to power a reasonably light 60" span vintage model, but a range of equivalents would be handy to have.

Hope someone can help.

Wilf
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Old Dec 08, 2008, 01:58 PM
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Letchworth, Great Britain (UK)
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If nobody can point you to a ready-made table, you can look up the power of the glow motor you want to replace (it's usually quoted in horsepower) and convert it to watts (1hp = 746 watts) to find an electric equivalent.

There's other factors you need to take into account with electric power, such as the kv (rpm per volt input) which determines how fast the motor will spin and, hence, what size prop it will need to produce the power you want.

The more usual method of determining power requirement is to base it on the model's flying weight: Anything between 50 and 150 watts per pound, depending on the model and your flying style. As an example, my Flair Magnatilla weighs 6lbs ready to fly with NiMh batteries, and flies on about 400 watts I use the same size and pitch prop as when it was using an OS48 4-stroke engine, and performance is the same.
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Old Dec 08, 2008, 02:38 PM
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Great Planes has a table...

Take a look:

http://www.electrifly.com/powersyste...brushless.html


The biggest challenge I've encountered with the glow-to-electric conversions is prop clearance. Many of the conversions you'll see have a much larger diameter prop than the original glow setup. The electric option also spins the bigger prop slower.

Even if you have clearance to spin the larger prop, it ends up "looking funny".

So, if you have the coice of a couple setups, opt for the setup with more batteries, spinning a smaller prop... faster....
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Old Dec 08, 2008, 03:16 PM
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United Kingdom, England, Carlisle
Joined Mar 2007
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0.29 - 0.30 class is generally around the 300-400w range, so 3s Lipo range, BRC Hobbies in the UK have an excellent selection of motors, complete with prop data sheets to help kv selection.
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Old Dec 08, 2008, 10:19 PM
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United States, OH, Toledo
Joined Jan 2005
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hi there from Toledo

Some mfgrs actually specify their brushless motors as glow engine displacement equivalents. So go buy a .35, or a .46, or a .61, or a .91, etc. whatever the original model specified as the engine size of choice.

Some even have motor packages with recommended ESCs and batteries. Sky Shark, Common Sense r/c, and Astroflight are just a few that come to mind, there are others. This is a great way to get on with it with minimum fuss and bother.

However the weight, wing area, and projected flying style are parameters which can assist you in making more refined selections once you get the hang of it.

ciao -rjf
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Old Dec 09, 2008, 12:11 AM
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Fort Collins, Colorado, USA
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Quote:
Originally Posted by vmsguy
Take a look:

http://www.electrifly.com/powersyste...brushless.html


The biggest challenge I've encountered with the glow-to-electric conversions is prop clearance. Many of the conversions you'll see have a much larger diameter prop than the original glow setup. The electric option also spins the bigger prop slower.

Even if you have clearance to spin the larger prop, it ends up "looking funny".

So, if you have the coice of a couple setups, opt for the setup with more batteries, spinning a smaller prop... faster....
Ummm, your statement about an electric motor being able to spin a larger prop then a comparable glow motor(this is true) and then the bigger prop looking funny(this part is usually false) is highly dependant on the type of plane your referring to.
Most glow motors rated for a specific size/weight plane cannot spin a large enough prop to actually be the right scale size relative to the real plane.
For instance, a real F4U Corsair had a 3-blade prop of 13 foot 4 inch diameter.
Wingspan was 41 ft.
So, using the Hangar 9 Corsair for size reference, it has a 65" wingspan. Most ppl powering this plane witha glow motor will use anywhere from a .91 to a 1.25 size 4 stroke or a 60-90 size 2 stroke. The prop size usually installed when using a 3 blade prop is a 14x7x3 up to a 16x8x3. However, to be scale size, the prop would need to be a 21" diameter prop.
Maybe your just used to using props for glow motors and anything larger looks odd to you even though it would be closer to scale using a larger prop on the elctric motor.
Also, an electric motor is not necessairly spinning a larger prop at a slower rpm as you stated. Another example: Kyosho 50 FW-190. If your using a .72 4stroke, you can spin a 13x7 prop at maybe 8000 rpm's. A smaller 11x8 at 9500. An electric motor of the right size can spin a 14x12 at 8000...so yes the rpm's may be slightly slower, but, the pitch of the prop on the electric is making the plane considerably faster. A 12 pitch prop spinning at 8000 rpm's give a static speed of 90.9 mph. An 8 pitch prop spinning at 9500rpm's is giving a static speed of 71.9mph. If using a 2stroke, the 11x8 may be spinning at 11000, so static speed would be 83.3mph. Still a good deal less then the electric.
The only time you use a smaller prop in order to spin faster is if you have a very high KV motor(like over 1200kv), but then your amp draw goes way up relative to a lower kv higher torque electric motor. The torque is there to spin the high diameter and higher pitch prop.
An e-flite power 32 is equivalent to a .35 2 stroke. Its kv is 770. Most motors in the size relative to a glow motor of whatever size do not have a kv over 1000. If you use a small prop, your never gonna get enough thrust to fly well nor enough speed to maintain anything close to fast flight.

Electrifly motors are a good choice though and so are E-flite, AXI and Turnigy.
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Old Dec 10, 2008, 12:38 PM
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Harrow,London
Joined Jun 2007
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scorpion are good motors.i have used a couple of them and they are pretty reasonable to.
http://www.micronradiocontrol.co.uk/...omparison.html
try this link to there comparison chart.you probabley want a comparison to the eflight power 32. (3026-12).hope this helps
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Old Dec 10, 2008, 01:34 PM
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Wilf. Beware of some of the cheaper motors out there. I own 2 Scorpion which are good, several Hyperion which are good and among others 3 axi. My axi 2820/10 is in a sports winter hack that I designed and built a few seasons back. It is my most flown model. It started with 10 nicd or nimh and then flew with 3s 5350 lipos and now has 4s a123 cells. I have carried out various aerodynamic mods to the airframe in this time. I cannot count the flights but it is lots. The motor is still performing as well as ever and is still quiet. The point I am making is that it is not the cheapest motor but it is certainly long lasting. I have had to scrap some of my cheaper ones after a very short period of use. John Emms at Puffin models is very helpful as are the folk at Micron, BRC hobbies and Robotbirds. Any of these will help you. These are people that I have dealt with with no issues and I am sure that others like Overlander etc are equally as good. I have just remotored my Super 60 with my old Twister 29/60 to run on 3s 5350 lipo but I will be using a large prop ( 14 or 15" diameter) and I expect that it will fly well on this setup.
Chris.
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Old Dec 10, 2008, 03:15 PM
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Quote:
Originally Posted by kahloq
then the bigger prop looking funny(this part is usually false) is highly dependant on the type of plane your referring to.
I wasn't refering to scale airplanes. I was refering to a plane with a glow motor, sitting next to the same plane with an electric motor.

When building a scale aircraft, obviously you want the props to be in scale with the real thing.

But when you look at sport RC model aircraft that have traditionally been glow powered, and designed around being glow powered, putting a larger diameter prop on that plane looks funny.. You may have to modify the landing gear to make clearance for the prop, and now it looks even more... odd... Then to add salt to the wound, the longer gear may be more fragile for rough landings.

But yes.. it depends on the plane... and what you're doing with it.

But I would suggest, when electrifying an airplane, keep "from the prop back" in mind. Take into consideration what size, pitch, and RPM the glow equivelant prop would be/spin. And try to match that with electric.
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Old Dec 10, 2008, 06:22 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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"But I would suggest, when electrifying an airplane, keep "from the prop back" in mind. Take into consideration what size, pitch, and RPM the glow equivelant prop would be/spin. And try to match that with electric."

Umm- no- unless you're using a four stroke. The airplane you described was never well served by glow power plants (well, maybe something like a Brown Jr.) so matching the glow setup is a recipe for being overweight. I'll second the idea of starting with the prop and working back- or start with watts required based on weight (figure 25-33% of total aircraft weight for power system) just to make sure that you don't have too large a prop at too low an rpm.

Sam
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Old Sep 04, 2009, 05:42 PM
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Ireland, Dublin City, Dublin
Joined Jun 2009
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Quote:
Originally Posted by kahloq
Ummm, your statement about an electric motor being able to spin a larger prop then a comparable glow motor(this is true) and then the bigger prop looking funny(this part is usually false) is highly dependant on the type of plane your referring to.
Most glow motors rated for a specific size/weight plane cannot spin a large enough prop to actually be the right scale size relative to the real plane.
For instance, a real F4U Corsair had a 3-blade prop of 13 foot 4 inch diameter.
Wingspan was 41 ft.
So, using the Hangar 9 Corsair for size reference, it has a 65" wingspan. Most ppl powering this plane witha glow motor will use anywhere from a .91 to a 1.25 size 4 stroke or a 60-90 size 2 stroke. The prop size usually installed when using a 3 blade prop is a 14x7x3 up to a 16x8x3. However, to be scale size, the prop would need to be a 21" diameter prop.
Maybe your just used to using props for glow motors and anything larger looks odd to you even though it would be closer to scale using a larger prop on the elctric motor.
Also, an electric motor is not necessairly spinning a larger prop at a slower rpm as you stated. Another example: Kyosho 50 FW-190. If your using a .72 4stroke, you can spin a 13x7 prop at maybe 8000 rpm's. A smaller 11x8 at 9500. An electric motor of the right size can spin a 14x12 at 8000...so yes the rpm's may be slightly slower, but, the pitch of the prop on the electric is making the plane considerably faster. A 12 pitch prop spinning at 8000 rpm's give a static speed of 90.9 mph. An 8 pitch prop spinning at 9500rpm's is giving a static speed of 71.9mph. If using a 2stroke, the 11x8 may be spinning at 11000, so static speed would be 83.3mph. Still a good deal less then the electric.
The only time you use a smaller prop in order to spin faster is if you have a very high KV motor(like over 1200kv), but then your amp draw goes way up relative to a lower kv higher torque electric motor. The torque is there to spin the high diameter and higher pitch prop.
An e-flite power 32 is equivalent to a .35 2 stroke. Its kv is 770. Most motors in the size relative to a glow motor of whatever size do not have a kv over 1000. If you use a small prop, your never gonna get enough thrust to fly well nor enough speed to maintain anything close to fast flight.

Electrifly motors are a good choice though and so are E-flite, AXI and Turnigy.
HI,

I'M NEW TO ALL THIS BUT CAN FOLLOW MOST OF WHAT YOU ARE SAYING.

1. SURELY THE ULTIMATE COMPARISON IS IN POWER OUTPUT [BHP OR KW'S]
2. WHAT EXACTLY IS "KV" ? IS THE K VALUE A CONSTANT FACTOR FOR A GIVEN MOTOR?


JIM
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Old Sep 04, 2009, 07:11 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Jim

Umm- no. BHP or total watts is not a good way to look at flying an airplane. An old timer weighing 4 lbs with a 5" prop at 400 watts isn't going anywhere, whereas the same airplane will fly fine on a 12" prop and 200 watts.

Kv is basically the unloaded rpm constant of a motor- multiply by volts to get rpm unloaded. Not really all that useful on its lonesome- the motor calculators these days are pretty good though.

Sam
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