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Suggest an electric engine for my r/c plane

Old 07-17-2012, 09:51 AM
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Arad
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Default Suggest an electric engine for my r/c plane

Hi.

I have an r/c plane but I did not choose any engine on it.

I did not work with brushless engines and it will be my first experience.

Sizes and weight of my r/c:
Fuselage lentgh: 1.2 m
Characteristic distance: 0.25 m
wingspan: 2.2 m
MTOW (+estimated weights for engine, speed control and battery)= 3 - 3.5 kg

May I ask you to guide me?
Old 07-17-2012, 11:22 AM
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Default RE: Suggest an electric engine for my r/c plane

What kind of plane is it?

Trainer, Aerobatic, 3D, etc. ???

Old 07-17-2012, 02:09 PM
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Default RE: Suggest an electric engine for my r/c plane

Granted, these measurements are in ounces and pounds, but you can quickly convert them over to grams and kilograms. Use this as a guide to help you select a motor for your plane. For example, the conversion of pounds to kilograms is 2.2 pounds per kilogram. Use the inverse, or 0.453592 kg = 1 pound. If you are familiar with MS Excel, this can be put in a cell as a quick formula and refer to it to convert either way... from pounds to kg or kg to pounds.

Here are some guidelines:

1. Power can be measured in watts. For example: 1 horsepower = 746 watts

2. You determine watts by multiplying ‘volts’ times ‘amps’. Example: 10 volts x 10 amps = 100 watts

Volts x Amps = Watts

Therefore,

Amps = Watts / Volts ( / = divided by ). Simple elementary math.


3. You can determine the power requirements of a model based on the ‘Input Watts Per Pound’ guidelines found below, using the flying weight of the model (with battery):

50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
70-90 watts per pound; Trainer and slow flying scale models
90-110 watts per pound; Sport aerobatic and fast flying scale models
110-130 watts per pound; Advanced aerobatic and high-speed models
130-150 watts per pound; Lightly loaded 3D models and ducted fans
150-200+ watts per pound; Unlimited performance 3D and aerobatic models

4. Determine the Input Watts Per Pound required to achieve the desired level of performance:

Example:

Model: E-flite Brio 10 ARF
Estimated Flying Weight w/Battery: 2.1 lbs
Desired Level of Performance: 150-200+ watts per pound; Unlimited performance 3D and aerobatics
2.1 lbs x 150 watts per pound = 315 Input Watts of total power (minimum) required to achieve the desired performance

5. Determine a suitable motor based on the model’s power requirements. In this case, you will need a motor/esc/battery combination for 30 amps continuous... 3 cell LiPo at 11.1 volts (nominal) is 315/11.1=28.xxx amps, round out to the higher 30 amps.

So, get your paper and pencil out and work out the details. Let us know if we can help.
Old 07-18-2012, 02:18 AM
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Arad
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Default RE: Suggest an electric engine for my r/c plane

Thank you very much CGRetired;

It was very useful ...

Another question ... what about university projects like UAVs?

From your post:
50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
70-90 watts per pound; Trainer and slow flying scale models
90-110 watts per pound; Sport aerobatic and fast flying scale models
110-130 watts per pound; Advanced aerobatic and high-speed models
130-150 watts per pound; Lightly loaded 3D models and ducted fans
150-200+ watts per pound; Unlimited performance 3D and aerobatic models


For UAV 70-90 is suitable?
Old 07-18-2012, 02:43 AM
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Default RE: Suggest an electric engine for my r/c plane

If that is the performance you are looking for then those are the probable numbers.

CGr.
Old 07-18-2012, 03:02 AM
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Arad
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Default RE: Suggest an electric engine for my r/c plane

Just a simple UAV, I want an straight flight in a low velocity (25 m/s) ...
So ... for my UAV, ... I should find a motor that has about 792 wpp ... correct?
Old 07-18-2012, 03:37 AM
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Arad
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Default RE: Suggest an electric engine for my r/c plane

I think I found a suitable engine for my plane:
http://www.emaxmodel.com/pic/201101/28162839.jpg
Old 07-18-2012, 04:57 AM
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Default RE: Suggest an electric engine for my r/c plane

That looks like a good starting point. Of course we have no idea about the wing loading, fuselage size, drag, or actual size of the plane so it's hard to make a recommendation beyond just telling you how many watts you need. If the plane is particularly draggy, you'll want a motor with less Kv so you can turn a bigger prop at less rpm, while a more slippery plane that's designed to fly a little faster will like a higher Kv motor with a smaller prop turning faster. The motor you picked is in the middle and can run on 5 cells or 6 cells, so even if your first attempt at getting it set up isn't right you will have some room to change things.

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