Need help for prop size on electric motor
06-02-2010 | 06:56 AM
#1
Thread Starter
Senior Member
Need help for prop size on electric motor
I have a Trunigy electric motor c28261650. I want to put that on a extra 42" WS foamie. 1st of all, is this enought motor and 2nd what prop size would you recommend for some 3D flying. This is a flat wing foamie. Here is a picture in the process of being completed.
06-02-2010 | 08:48 AM
#2
My Feedback: (53)
RE: Need help for prop size on electric motor
You might be better off asking in the Watt Flyer forum... I just converted an old MW Cardinal and figuring out the motor/prop plus the ground clearance for the landing geat was confusing to me since I have very little understanding of the electric stuff. The plane did come out great and flies fine.
06-02-2010 | 09:47 AM
#3
RE: Need help for prop size on electric motor
Hey Gene,
A good tool to use is [link=http://drivecalc.de/]DriveCalc[/link]. It's free and is constantly updated with motor info. You can put in the motor, the type of battery and then select a prop and see what kind of thrust and speed it will deliver. I use it will all of my Brushless conversions. Do you know what size battery you want to use? Number of cells? How heavy do you estimate the plane to be?
Curtis
A good tool to use is [link=http://drivecalc.de/]DriveCalc[/link]. It's free and is constantly updated with motor info. You can put in the motor, the type of battery and then select a prop and see what kind of thrust and speed it will deliver. I use it will all of my Brushless conversions. Do you know what size battery you want to use? Number of cells? How heavy do you estimate the plane to be?
Curtis
06-02-2010 | 11:13 AM
#5
My Feedback: (-1)
RE: Need help for prop size on electric motor
Gene, I have zero understanding of electrics so this year when I built my first one I went to wattflyer and discovered some of the nicest people with all the information I needed, it's really a great site. Anything you want to learn is right there as a sticky or in the beginners forum.
Gene
Gene
06-02-2010 | 12:35 PM
#6
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From: Poolesville, MD
RE: Need help for prop size on electric motor
Gorish
Unfortunately you are approaching this BACKWARD.
With electrics the prop size determines what the draw, thrust, power requirements, etc. will be.
In turn the prop size used is determined by the plane, weight, and expected levels of performance.
You already have a motor that has a rather high KV rating for props.
The HK/HC web site states that for a 3S LiPo the maximum prop you can use is a 7x4, and an 18A ESC is required.
It also puts the power output ( at max ) of the motor @ 140 watts
Knowing that we can work some things out....
140w / 11.1v = 12.7A max draw
1650kv x 11.1v = 18,315 RPM
18,315 RPM * .8 (to emulate static thrust values ) = 14652 RPM
14652 RPM on a 7x4 prop gives a pitch speed of about 56 MPH and a static thrust around 1.5lbs.
That is quite fast for a small 3D foamy.
A larger prop would overload the motor causing it to overheat and burn out.
This motor is really better suited to a small fast pusher foam jet than it is for your intended plane.
What you want is a higher thrust, lower pitch speed motor for 3D instead.
Unfortunately you are approaching this BACKWARD.
With electrics the prop size determines what the draw, thrust, power requirements, etc. will be.
In turn the prop size used is determined by the plane, weight, and expected levels of performance.
You already have a motor that has a rather high KV rating for props.
The HK/HC web site states that for a 3S LiPo the maximum prop you can use is a 7x4, and an 18A ESC is required.
It also puts the power output ( at max ) of the motor @ 140 watts
Knowing that we can work some things out....
140w / 11.1v = 12.7A max draw
1650kv x 11.1v = 18,315 RPM
18,315 RPM * .8 (to emulate static thrust values ) = 14652 RPM
14652 RPM on a 7x4 prop gives a pitch speed of about 56 MPH and a static thrust around 1.5lbs.
That is quite fast for a small 3D foamy.
A larger prop would overload the motor causing it to overheat and burn out.
This motor is really better suited to a small fast pusher foam jet than it is for your intended plane.
What you want is a higher thrust, lower pitch speed motor for 3D instead.
06-02-2010 | 12:50 PM
#7
Thread Starter
Senior Member
RE: Need help for prop size on electric motor
ORIGINAL: opjose
Gorish
Unfortunately you are approaching this BACKWARD.
With electrics the prop size determines what the draw, thrust, power requirements, etc. will be.
In turn the prop size used is determined by the plane, weight, and expected levels of performance.
You already have a motor that has a rather high KV rating for props.
The HK/HC web site states that for a 3S LiPo the maximum prop you can use is a 7x4, and an 18A ESC is required.
It also puts the power output ( at max ) of the motor @ 140 watts
Knowing that we can work some things out....
140w / 11.1v = 12.7A max draw
1650kv x 11.1v = 18,315 RPM
18,315 RPM * .8 (to emulate static thrust values ) = 14652 RPM
14652 RPM on a 7x4 prop gives a pitch speed of about 56 MPH and a static thrust around 1.5lbs.
That is quite fast for a small 3D foamy.
A larger prop would overload the motor causing it to overheat and burn out.
This motor is really better suited to a small fast pusher foam jet than it is for your intended plane.
What you want is a higher thrust, lower pitch speed motor for 3D instead.
Gorish
Unfortunately you are approaching this BACKWARD.
With electrics the prop size determines what the draw, thrust, power requirements, etc. will be.
In turn the prop size used is determined by the plane, weight, and expected levels of performance.
You already have a motor that has a rather high KV rating for props.
The HK/HC web site states that for a 3S LiPo the maximum prop you can use is a 7x4, and an 18A ESC is required.
It also puts the power output ( at max ) of the motor @ 140 watts
Knowing that we can work some things out....
140w / 11.1v = 12.7A max draw
1650kv x 11.1v = 18,315 RPM
18,315 RPM * .8 (to emulate static thrust values ) = 14652 RPM
14652 RPM on a 7x4 prop gives a pitch speed of about 56 MPH and a static thrust around 1.5lbs.
That is quite fast for a small 3D foamy.
A larger prop would overload the motor causing it to overheat and burn out.
This motor is really better suited to a small fast pusher foam jet than it is for your intended plane.
What you want is a higher thrust, lower pitch speed motor for 3D instead.
Hummmmm!! Don't understand a word you said
I guess I will put my 70 4 Stroke on it. I always go after things backwards Our club has an electric fly this weekend and I don't fly elect. But though I would put this together. Maybe I can find a club member that has a more suited motor for this. Or, maybe I will just go and watch again this year.[sm=sad_smile.gif][sm=sad_smile.gif]
06-02-2010 | 01:53 PM
#8
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From: Poolesville, MD
RE: Need help for prop size on electric motor
What you want to do is to start off by guestimating what the weight of the plane will be once it is ready to fly.
I use the manufacturer's stated flying weight multiplied by a factor to get an appropriate all up weight...
e.g. if the Manufacturer states 1.6lbs I'll multiply that by 1.3 to get 2.08 lbs flying weight.
Knowing that the plane will weigh about 2.08lbs I'll use that figure to determine what type of power system I want.
Let's say we want that 2.08lb plane to be a 3D'er with unlimted vertical.
That translates into about 140 watts per lb...
So 140 w x 2.08lbs = 292watts or approximately 300 watts will be required out of the power system.
Next I choose a battery pack... say 11.1 v ( 3S LiPo )....
So 300 watts / 11.1v = 27A expected draw at full throttle.
That tells me I'll need an ESC of at LEAST 30A for this setup.
Finally I'll want to prop the plane for 300watts and 3lbs of thrust.... ThrustHP ( which is a bit optimistic relative to electrics ... ) tells me I can get 3lbs of thrust spinning a 10x5 prop at 10000 RPM and a top speed of 47mph.
A prop unloads in the air, so we want a motor that spins faster than 10000 RPM when unloaded.
So 10000 / 11.1 = 900KV * 1.24 ( to give us more RPM's unloaded ) = 1100 KV...
That tells me I'll need the following
A 30A ESC.
An 10x5E Prop
A 300 watt motor with a 1100KV rating
A 3S LiPo pack capable of sustaining 27A draw WITHOUT taxing it ( e.g. a 2200mAh 20C 11.1v LiPo battery pack ).
So by starting off with the weight of the plane and how I want the plane to perform, I get the specs I need for everything else.
I use the manufacturer's stated flying weight multiplied by a factor to get an appropriate all up weight...
e.g. if the Manufacturer states 1.6lbs I'll multiply that by 1.3 to get 2.08 lbs flying weight.
Knowing that the plane will weigh about 2.08lbs I'll use that figure to determine what type of power system I want.
Let's say we want that 2.08lb plane to be a 3D'er with unlimted vertical.
That translates into about 140 watts per lb...
So 140 w x 2.08lbs = 292watts or approximately 300 watts will be required out of the power system.
Next I choose a battery pack... say 11.1 v ( 3S LiPo )....
So 300 watts / 11.1v = 27A expected draw at full throttle.
That tells me I'll need an ESC of at LEAST 30A for this setup.
Finally I'll want to prop the plane for 300watts and 3lbs of thrust.... ThrustHP ( which is a bit optimistic relative to electrics ... ) tells me I can get 3lbs of thrust spinning a 10x5 prop at 10000 RPM and a top speed of 47mph.
A prop unloads in the air, so we want a motor that spins faster than 10000 RPM when unloaded.
So 10000 / 11.1 = 900KV * 1.24 ( to give us more RPM's unloaded ) = 1100 KV...
That tells me I'll need the following
A 30A ESC.
An 10x5E Prop
A 300 watt motor with a 1100KV rating
A 3S LiPo pack capable of sustaining 27A draw WITHOUT taxing it ( e.g. a 2200mAh 20C 11.1v LiPo battery pack ).
So by starting off with the weight of the plane and how I want the plane to perform, I get the specs I need for everything else.
06-02-2010 | 02:14 PM
#9
Thread Starter
Senior Member
RE: Need help for prop size on electric motor
This is the kit that I have.
This is how you get to the kit.
BPhobbies.com
on-line catalog
Airplane kits/arf
flat wing foamies
extra 42"
Fun Foam Extra 32" Kit Item: 3 of 6
Click on image for larger or alternate view. Wing Span: 32"
Fuselage Length: 31"
Model Weight: 10.5 to 11.5 oz
Configuration: 4 ch. Motor/Aileron/Elevator/Rudder
Decals not included.
Features:
Laser Cut Smooth Skinned 5mm White Foam
Laser Cut Firewall Motor Mount and Stick Mount
Pre-Bent Landing Gear including Wheels
Includes Carbon Fiber Wing Spar & Pushrods
Includes Hardware Package
Illustrated Instruction Manual
Requires:
Motor and speed control (BP 8Y brushless and BP 18A ESC recommended)
4-channel receiver - Corona RS410, Berg Microstamp 4L, Hitec Micro 05S, Blue Bird BMR-04 or equivalent
3 micro servos
Optional:
Foam Friendly Acrylic Paint
Solartrim Polyester Film - Decal Stock
Available flight packs:
Fun 3D Brushless Flight Pack for 32" Planes
You will need one UM5 crystal with your flight pack
Price: $15.00
This is how you get to the kit.
BPhobbies.com
on-line catalog
Airplane kits/arf
flat wing foamies
extra 42"
Fun Foam Extra 32" Kit Item: 3 of 6
Click on image for larger or alternate view. Wing Span: 32"
Fuselage Length: 31"
Model Weight: 10.5 to 11.5 oz
Configuration: 4 ch. Motor/Aileron/Elevator/Rudder
Decals not included.
Features:
Laser Cut Smooth Skinned 5mm White Foam
Laser Cut Firewall Motor Mount and Stick Mount
Pre-Bent Landing Gear including Wheels
Includes Carbon Fiber Wing Spar & Pushrods
Includes Hardware Package
Illustrated Instruction Manual
Requires:
Motor and speed control (BP 8Y brushless and BP 18A ESC recommended)
4-channel receiver - Corona RS410, Berg Microstamp 4L, Hitec Micro 05S, Blue Bird BMR-04 or equivalent
3 micro servos
Optional:
Foam Friendly Acrylic Paint
Solartrim Polyester Film - Decal Stock
Available flight packs:
Fun 3D Brushless Flight Pack for 32" Planes
You will need one UM5 crystal with your flight pack
Price: $15.00
06-02-2010 | 02:33 PM
#11
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From: Poolesville, MD
RE: Need help for prop size on electric motor
So let's get a bit pessimistic, and assume that because you want a long flight time, the AUW of the plane will be 16oz.
Let's also shoot for over 140 watts / lb....
140 watts / 11.1 = 15A MAX current draw.
A 20A to 25A ESC will suffice, to save weight a 20A ESC would be good.
So we know that we want a 140 watt motor, a 20A ESC, and over 1lb of thrust...
This motor is just the ticket, when flown with a 10x4.7SF prop.
[link=http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=5354&Product_Name=FC_28-22_Brushless_Outrunner__1200kv]Click me![/link]
Let's also shoot for over 140 watts / lb....
140 watts / 11.1 = 15A MAX current draw.
A 20A to 25A ESC will suffice, to save weight a 20A ESC would be good.
So we know that we want a 140 watt motor, a 20A ESC, and over 1lb of thrust...
This motor is just the ticket, when flown with a 10x4.7SF prop.
[link=http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=5354&Product_Name=FC_28-22_Brushless_Outrunner__1200kv]Click me![/link]
06-02-2010 | 03:12 PM
#12
Thread Starter
Senior Member
RE: Need help for prop size on electric motor
WOW!!!!! what a great help. I may have to come to MD to buy you a McDonalds
Now see if I can find a motor like this closer so I can get it for the week-end. Would you suggest any =other brand that hobby shops may carry
/
Now see if I can find a motor like this closer so I can get it for the week-end. Would you suggest any =other brand that hobby shops may carry/
06-02-2010 | 03:33 PM
#13
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From: Poolesville, MD
RE: Need help for prop size on electric motor
An E-Flite Park 450 is in the same range, though the KV rating is a bit lower so I would opt for a higher pitched prop like the 10x5E or the 12x6E instead of a Slow Flyer ( SF ) prop.
