Everything you want to know about electric flight
03-11-2008, 05:45 AM
#26
RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
ORIGINAL: Sh@rp3dge
Hi Ed,
Thanks for a great post! I am a beginner, and I found some very valuable information in this thread.
Swift, please dont spoil this thread with your personal attacks
Hi Ed,
Thanks for a great post! I am a beginner, and I found some very valuable information in this thread.
Swift, please dont spoil this thread with your personal attacks
03-11-2008, 08:22 AM
#27
RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
What Goes on Which Stick?
by Ed Anderson
aeajr on the forums
If you are flying an RTF electric plane, your radio and servos are already set-up for you. However if you are setting up an ARF or finishing a kit, you will be installing your own radio equipment. So, which stuff goes on which stick, and why?
We usually talk about what surface is controlled by what stick. However,
that is not really the right way to look at it.
First, the control axis:
Pitch - nose up/nose down - usually controlled by the elevator or elevator function of elevons
Roll - rotation of the wings around the fuselage - controlled by ailerons or the aileron function of elevons.
If the plane does not have ailerons or elevons, then roll can be controlled by the rudder or the rudder function of a V tail rudervators, depending on the design of the plane. On rudder only planes the rudder works with dihedral in the wings, the upward slant of the wings, to roll the plane.
Yaw - movement of the nose left or right - controlled by rudder or the rudder function if V tail ruddervators.
Speed - throttle control
If you are in a different part of the world, you may be flying mode 1, 3 or 4. I live in North America where Mode 2 is the standard, so the rest of this post will be referencing mode 2 control positions.
Note that I mention Mode 2, which is marked with the * below.
Left stick ...............Right Stick ..................Mode
Pitch and Yaw .......Speed and Roll ..............1
Speed and Yaw*......Pitch and Roll*..............2*
Pitch and Roll ..........Speed and Yaw ...........3
Speed and Roll ........Pitch and Yaw .............4
For a power plane, landing gear, flaps and other such functions are assigned
to switches, buttons, dials, sliders or levers, but are not defined as part of the mode definitions.
For a two stick radio, used in mode two format, the standard format in North
America, pitch and roll are on the right stick with roll ALWAYS being your
primary turning control. Yaw and speed control are on the left stick.
Based on mode 2 it is very easy to move from a dual stick to a single stick radio as the right, or the only stick, always have has your primary fight controls if pitch and roll.
Primary Speed control
Since this is written for electric flyers, we will assume you have an electric motor. On a two stick radio, the speed control is on the left stick and is controlled by the motion that goes toward you to turn the motor off and away from you to give full throttle. For a single stick radio the throttle control is usually on the left side and will be a slide, switch or lever.
Where does the rudder go?
Confusion often exists around where to put the rudder. Depending on the design of your plane, the rudder can play different roles so its placement can change. On a three channel electric plane without ailerons, the rudder is your primary turning surface. It provides both roll and yaw control so it goes on the right stick for roll control, as the primary turning surface. This stick also has pitch control provided by the elevator. The rudder will work with a feature of the wings, called dihedral or polyhedral, to roll or bank the plane when you want to turn.
What if there are ailerons, or elevons?
Primary flight controls of pitch and roll are always on the right stick, or the only stick. If this is a 3 channel plane with throttle, aileron and elevator controls only, like a flying wing that has elevon controls (combined elevator aileron in one surface), now where do I put things? Think of function rather than surface and you will know immediately. Which surface provides roll control? In this case it is the ailerons, so they go on the right stick with the elevator which provides pitch control.
If this is a 4 channel plane that has ailerons and a rudder, the ailerons are your primary roll control, so they go on the right stick. The rudder moves to the left hand stick to provide yaw control, which helps the ailerons turn the plane smoothly.
If you are flying off a runway, the rudder can be very valuable as it helps control your path down the runway during take-off and landing. If you have a steerable ground wheel it is usually attached to the rudder or the rudder channel. The rudder, in this configuration, also plays a valuable part during landing when we may wish to redirect the nose of the plane without tipping the wings using the ailerons.
Moving from single stick to dual stick radios
Some people feel it is confusing to move from a single stick radio to a dual stick, radio, however, if you are flying mode 2, it really isn't confusing at all. If you think of your radio and your controls in this manner, there is no confusion moving back and forth between single stick and dual stick radios or between three channel R/E/T planes and A/E/T planes or planes that are A/E/R/T.
On a single stick radio, pitch and roll are on the single stick, which happens to be oriented to the right side of the radio. If this is a dual stick radio, pitch and roll are still on the right hand stick. It doesn't matter if it is a rudder/elevator plane or an aileron/elevator plane. Pitch and roll are on the right stick, or the only stick.
Think of your controls this way and there is never a doubt what goes where or which controls to use when you switch between radios and planes.
I hope this was helpful.
by Ed Anderson
aeajr on the forums
If you are flying an RTF electric plane, your radio and servos are already set-up for you. However if you are setting up an ARF or finishing a kit, you will be installing your own radio equipment. So, which stuff goes on which stick, and why?
We usually talk about what surface is controlled by what stick. However,
that is not really the right way to look at it.
First, the control axis:
Pitch - nose up/nose down - usually controlled by the elevator or elevator function of elevons
Roll - rotation of the wings around the fuselage - controlled by ailerons or the aileron function of elevons.
If the plane does not have ailerons or elevons, then roll can be controlled by the rudder or the rudder function of a V tail rudervators, depending on the design of the plane. On rudder only planes the rudder works with dihedral in the wings, the upward slant of the wings, to roll the plane.
Yaw - movement of the nose left or right - controlled by rudder or the rudder function if V tail ruddervators.
Speed - throttle control
If you are in a different part of the world, you may be flying mode 1, 3 or 4. I live in North America where Mode 2 is the standard, so the rest of this post will be referencing mode 2 control positions.
Note that I mention Mode 2, which is marked with the * below.
Left stick ...............Right Stick ..................Mode
Pitch and Yaw .......Speed and Roll ..............1
Speed and Yaw*......Pitch and Roll*..............2*
Pitch and Roll ..........Speed and Yaw ...........3
Speed and Roll ........Pitch and Yaw .............4
For a power plane, landing gear, flaps and other such functions are assigned
to switches, buttons, dials, sliders or levers, but are not defined as part of the mode definitions.
For a two stick radio, used in mode two format, the standard format in North
America, pitch and roll are on the right stick with roll ALWAYS being your
primary turning control. Yaw and speed control are on the left stick.
Based on mode 2 it is very easy to move from a dual stick to a single stick radio as the right, or the only stick, always have has your primary fight controls if pitch and roll.
Primary Speed control
Since this is written for electric flyers, we will assume you have an electric motor. On a two stick radio, the speed control is on the left stick and is controlled by the motion that goes toward you to turn the motor off and away from you to give full throttle. For a single stick radio the throttle control is usually on the left side and will be a slide, switch or lever.
Where does the rudder go?
Confusion often exists around where to put the rudder. Depending on the design of your plane, the rudder can play different roles so its placement can change. On a three channel electric plane without ailerons, the rudder is your primary turning surface. It provides both roll and yaw control so it goes on the right stick for roll control, as the primary turning surface. This stick also has pitch control provided by the elevator. The rudder will work with a feature of the wings, called dihedral or polyhedral, to roll or bank the plane when you want to turn.
What if there are ailerons, or elevons?
Primary flight controls of pitch and roll are always on the right stick, or the only stick. If this is a 3 channel plane with throttle, aileron and elevator controls only, like a flying wing that has elevon controls (combined elevator aileron in one surface), now where do I put things? Think of function rather than surface and you will know immediately. Which surface provides roll control? In this case it is the ailerons, so they go on the right stick with the elevator which provides pitch control.
If this is a 4 channel plane that has ailerons and a rudder, the ailerons are your primary roll control, so they go on the right stick. The rudder moves to the left hand stick to provide yaw control, which helps the ailerons turn the plane smoothly.
If you are flying off a runway, the rudder can be very valuable as it helps control your path down the runway during take-off and landing. If you have a steerable ground wheel it is usually attached to the rudder or the rudder channel. The rudder, in this configuration, also plays a valuable part during landing when we may wish to redirect the nose of the plane without tipping the wings using the ailerons.
Moving from single stick to dual stick radios
Some people feel it is confusing to move from a single stick radio to a dual stick, radio, however, if you are flying mode 2, it really isn't confusing at all. If you think of your radio and your controls in this manner, there is no confusion moving back and forth between single stick and dual stick radios or between three channel R/E/T planes and A/E/T planes or planes that are A/E/R/T.
On a single stick radio, pitch and roll are on the single stick, which happens to be oriented to the right side of the radio. If this is a dual stick radio, pitch and roll are still on the right hand stick. It doesn't matter if it is a rudder/elevator plane or an aileron/elevator plane. Pitch and roll are on the right stick, or the only stick.
Think of your controls this way and there is never a doubt what goes where or which controls to use when you switch between radios and planes.
I hope this was helpful.
03-11-2008, 03:26 PM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Ed,
I subscribe and read this thread regularly. I have from the start of my flying adventure. I found it very informative and it has helped me make the right decisions that I would have had to stumble through otherwise. It's made learning to fly easy and most importantly FUN! Just wanted to thank you, it's great info.
I subscribe and read this thread regularly. I have from the start of my flying adventure. I found it very informative and it has helped me make the right decisions that I would have had to stumble through otherwise. It's made learning to fly easy and most importantly FUN! Just wanted to thank you, it's great info.
03-11-2008, 09:55 PM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Thank you Ed for writing the "Everything you wanted to know about electric flight" piece. I found it very informative and usefull. I was wondering if you have any info you could share on the same as it applies to heli's?
Thanks again.
03-12-2008, 02:30 AM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
ORIGINAL: Empty Wallet
Thank you Ed for writing the "Everything you wanted to know about electric flight" piece. I found it very informative and useful. I was wondering if you have any info you could share on the same as it applies to heli's?
Thanks again.
Thank you Ed for writing the "Everything you wanted to know about electric flight" piece. I found it very informative and useful. I was wondering if you have any info you could share on the same as it applies to heli's?
Thanks again.
However, based on your handle maybe heli's aren't for you
Cheers,
Oz.
03-13-2008, 01:46 AM
#33
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Actually the handle started out as a little joke I have going with my wife. I used Radds when I first started to learn how to fly. It was very usefull, thanks.
What I am looking for is more info on how to size motors, batteries and electronics according to the physical and use requirements of a given helicopter.
Any sugestions?
What I am looking for is more info on how to size motors, batteries and electronics according to the physical and use requirements of a given helicopter.
Any sugestions?
03-20-2008, 11:58 PM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Hi,
Thanks for this thread. it is tremendusly helpful.
I'm considering converting a Carl Goldberg Decathlon ARF .60 . I'm uneperienced with electrics, but I've flown all my life. 3D and IMAC etc.... since the ARF says to be around 10.5lbs AUW when finished in the manual and I want to fly slow rolling circles and have straight verticals with snapping capability. I have calculated on 100W/lb basis.
I would appreciate your help and suggestion on the following:
motor esc prop pack: I have chosen combo 60 on this site http://www.maxxprod.com/mpi/mpi-264.html site,
pack: TP 4000mah 8S2P on this site http://www.cheapbatterypacks.com/main.asp
charger: TP 1010C on this site http://www.cheapbatterypacks.com/?si...chrg&scat=LIPO
Please confirm if you think is a good idea and if you suggest a gearbox or direct drive.
thanks in advance......
Thanks for this thread. it is tremendusly helpful.
I'm considering converting a Carl Goldberg Decathlon ARF .60 . I'm uneperienced with electrics, but I've flown all my life. 3D and IMAC etc.... since the ARF says to be around 10.5lbs AUW when finished in the manual and I want to fly slow rolling circles and have straight verticals with snapping capability. I have calculated on 100W/lb basis.
I would appreciate your help and suggestion on the following:
motor esc prop pack: I have chosen combo 60 on this site http://www.maxxprod.com/mpi/mpi-264.html site,
pack: TP 4000mah 8S2P on this site http://www.cheapbatterypacks.com/main.asp
charger: TP 1010C on this site http://www.cheapbatterypacks.com/?si...chrg&scat=LIPO
Please confirm if you think is a good idea and if you suggest a gearbox or direct drive.
thanks in advance......
03-22-2008, 11:46 AM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Ok. so I just bought an extreme flight yak 54 47". it weights AUW 2.4lbs, it comes with all the complete 3s combo (www.extremeflightrc.com/html/yak54e.html) and I want to buy an extra battery pack . please tell me if this TP pack would be a good choice http://www.rctoys.com/rc-toys-and-pa...BATTERIES.html
it's less C, but is 40grams lighter.........
thanks
fredy
it's less C, but is 40grams lighter.........
thanks
fredy
03-22-2008, 10:27 PM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
disregard.......... I changed it for a TP22003SXV with 50amp continuous discharge rating (25c continuous and 50c burst).
that should do over 200 watts per pound performance....... don't know why it was listed like that. (490watts for a 2.4lbs plane) ............... but oh well..............., I saw the video and it was enough for me........!!!! it seems to work quite fine!!!
that should do over 200 watts per pound performance....... don't know why it was listed like that. (490watts for a 2.4lbs plane) ............... but oh well..............., I saw the video and it was enough for me........!!!! it seems to work quite fine!!!
03-26-2008, 09:32 PM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
my plane is asking to use mn-48 oz servos, i have hs-81 42 oz servos will they work my e-mail is [email protected] kenny newton nv. thank you
07-19-2008, 03:41 AM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Would using a 1450mAh 11.1V 20C LiPo fry my 25A brushless esc? If I understood your formulas properly I think the discharge rate will be around 29A.
07-25-2008, 10:47 PM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Ed, this is the most wonderful thought out presentation for us beginners..........but I do have a question abour e-props. Why arent there more 3-blade props used on small scale electrics? You just cant find any............
Dads
Dads
08-04-2008, 03:46 PM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Thanks for this thread!
I am making the transition from glow to electric because my son is going off to college and electric is the only thing they allow in their dorms. I'm sure this information is available but putting it all together in a way that makes good sense - priceless!
Thanks again,
David
I am making the transition from glow to electric because my son is going off to college and electric is the only thing they allow in their dorms. I'm sure this information is available but putting it all together in a way that makes good sense - priceless!
Thanks again,
David
08-15-2008, 09:47 AM
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
I am posting this for Ed. It is a PM I sent to him earlier today. There is some good info here for others like me who are learning electrics.
Clint
======================================
Ed,
I just read your "Everything you want to know about electric flight" write up. It is fantastic and helped me out a lot. Thank you for writing it.
I am still struggling a little bit on battery theory.
I have an Electristar that is built and ready to go. I have two LiPo batteries for it. They are 14.8 Volt 30C, one is 3200mah and the other is 3700mah.
Because it is a balsa plane I wanted to learn on something else first so I bought a Multiplex Mentor and installed the Multiplex pack consisting of a Himax 3528-1000 motor and BL-55 ESC. This setup calls for a 11.1Volt LiPo, which I bought one 32oomah of.
Can I use the 14.8 Volt batteries that I already have for the Electristar in the Mentor if I don't run it at 100%? If not, why? If I buy another 11.1 Volt LiPo what is the highest mah I can use for longest flight time?
Thanks in advance for any help with this. I would love to be able to take three packs with me and have a nice long flight time at the field between recharges.
================================================== =============
Good questions,
The answer is not based on the plane but on the motor, ESC and prop. If you go to the chapter on selecting power systems you see that the combination of battery voltage and the prop will determine how much current, the amps, that will be drawn by the motor. So the first question is whether your motor is rated for 14.8 volts. You have to check the specs, or RTFM, read the friendly manual.
Second thing is, is your ESC rated for 14.8 volts. RTFM
Third, if you are using the BEC on your ESC, what is that max voltage that can tolerate? Most can not go over 12V. This is covered in the BEC chapter.
Now, assuming the motor and ESC can handle it, can they handle it with that propeller? Only two ways to know. Run a wattmeter to measure the current, or go to the motor manufacturer's documentation that shows amp draw at voltage with selected props. That is a Himax motor and they provide EXCELLENT reference material. Go to your motor, on this page, and click the "learn more" button:
http://www.maxxprod.com/mpi/mpi-262.html
The first thing we see is that this motor is not rated for 14.8V. Max recommended is 12 NiXX cells or 3 cell lipo. So you can't use the 4 cell lipo without risk of burning up the motor. So I am not even going to check the ESC. And you did not provide the specs of the prop so I can't comment on that.
Now, can you run it at partial throttle and be safe? No!
Your ESC delivers the full pack voltage to the motor all the time, full throttle or partial. As described in the article on the ESC, it controls the speed of the motor by pulsing that full voltage. How fast it pulses it determines the speed of the motor. You can go ahead and put the 14.8V pack in the plane, just don't be surprised if the motor fails.
As for max MAH, as discussed in the articles, you can put in the largest pack you feel the plane can carry as long as it can handle the amperage draw that the motor will demand.
Go back and read the articles and this will make more sense.
_____________________________
Clear Skies and Safe Flying!
Ed Anderson
Moderator
Park Pilot Program Partner
Clint
======================================
Ed,
I just read your "Everything you want to know about electric flight" write up. It is fantastic and helped me out a lot. Thank you for writing it.
I am still struggling a little bit on battery theory.
I have an Electristar that is built and ready to go. I have two LiPo batteries for it. They are 14.8 Volt 30C, one is 3200mah and the other is 3700mah.
Because it is a balsa plane I wanted to learn on something else first so I bought a Multiplex Mentor and installed the Multiplex pack consisting of a Himax 3528-1000 motor and BL-55 ESC. This setup calls for a 11.1Volt LiPo, which I bought one 32oomah of.
Can I use the 14.8 Volt batteries that I already have for the Electristar in the Mentor if I don't run it at 100%? If not, why? If I buy another 11.1 Volt LiPo what is the highest mah I can use for longest flight time?
Thanks in advance for any help with this. I would love to be able to take three packs with me and have a nice long flight time at the field between recharges.
================================================== =============
Good questions,
The answer is not based on the plane but on the motor, ESC and prop. If you go to the chapter on selecting power systems you see that the combination of battery voltage and the prop will determine how much current, the amps, that will be drawn by the motor. So the first question is whether your motor is rated for 14.8 volts. You have to check the specs, or RTFM, read the friendly manual.
Second thing is, is your ESC rated for 14.8 volts. RTFM
Third, if you are using the BEC on your ESC, what is that max voltage that can tolerate? Most can not go over 12V. This is covered in the BEC chapter.
Now, assuming the motor and ESC can handle it, can they handle it with that propeller? Only two ways to know. Run a wattmeter to measure the current, or go to the motor manufacturer's documentation that shows amp draw at voltage with selected props. That is a Himax motor and they provide EXCELLENT reference material. Go to your motor, on this page, and click the "learn more" button:
http://www.maxxprod.com/mpi/mpi-262.html
The first thing we see is that this motor is not rated for 14.8V. Max recommended is 12 NiXX cells or 3 cell lipo. So you can't use the 4 cell lipo without risk of burning up the motor. So I am not even going to check the ESC. And you did not provide the specs of the prop so I can't comment on that.
Now, can you run it at partial throttle and be safe? No!
Your ESC delivers the full pack voltage to the motor all the time, full throttle or partial. As described in the article on the ESC, it controls the speed of the motor by pulsing that full voltage. How fast it pulses it determines the speed of the motor. You can go ahead and put the 14.8V pack in the plane, just don't be surprised if the motor fails.
As for max MAH, as discussed in the articles, you can put in the largest pack you feel the plane can carry as long as it can handle the amperage draw that the motor will demand.
Go back and read the articles and this will make more sense.
_____________________________
Clear Skies and Safe Flying!
Ed Anderson
Moderator
Park Pilot Program Partner
08-28-2008, 07:30 AM
#45
Re: Everything you want to know about electric flight
WHAT DO THE KV RATINGS ON MOTORS MEAN?
updated Jan 2015
Manufacturers use different wire winds to produce different Kv results.
Kv is a number that relates to how many RPMs a given motor will spin based
on applied voltage. You will see specs on motors where it says Kv=860.
That means that the motor will spin at 860 rpms if you apply one volt to it.
If you apply 7 volts it will span at 6020 rpms.
If the manufacturer takes the same motor he can wind it so that it will
have a lower Kv rating, which typically produces more torque, so these are
typically used with large propellers that will be turned slower. These are
very popular on gliders, for example, where climb angle and climb rate is
much more important than top speed.
Take the same motor and wind it differently and it will have a higher Kv
rating producing higher speeds for a given voltage. These are typically
used with smaller props for higher top speeds. Or they can be used with gear
boxes to handle those big props, providing a similar result to low KV
motors. Sometimes a gear box works better in the installation.
You would also take KV into consideration based on what battery you plan to
use. Let's look at a practical example looking at various kV motors on the same plane.
You have selected a 500 KV motor. The specs say this motor, using a 5S pack
spinning a 15X8 prop that will draw about 45 amps. But suppose you did not have
the ground clearance for a 15" prop. Suppose you could only use a 12" prop. Then
you might choose a 1000 kV motor which would be a better match for that 12" prop.
Another way to look at this would be to think of kV like gears in your car. The lower t
he kV number the lower the gear the greater the "pulling power" or in the case of the prop
the greater the ability to spin that big prop. This is good at start up and take-off, or perhaps for
towing another plane, but it will produce a lower top speed.
Think if a high kV motor like the high gear in a car. Terrible acceleration from a standing start
and not a lot of pulling power for a trailer, but a higher top speed, once you get there.
Since we can't change gear ratios on the airplane's motor we select a compromise that will give us
the best average performance over the performance envelope we desire.
Let's say you were looking for a more scale look and that required you to use a 9 inch prop. Then you might
select a 1500 kV motor on the same plane. The airplane would probably fly but you would need a
longer roll out on the runway to get off the ground, more like a full scale airplane.
If you look here you will see that a given motor is offered in several Kv
ratings. They make suggestions as to which motor is best matched with which
prop and which battery packs. If you click on a given motor you can see what
kinds of power is drawn based on which pack and which prop. If you click on
each of the motors within a model you can see the very different power
curves produced by the different battery/prop combos. Here you see the same
motor with a different wind producing a different Kv result, each optimized
for a different purpose.
http://www.maxxprod.com/mpi/mpi-262.html
So, how does this add to other information about motors?
I first set a watts/pound target for my plane depending on the performance I
want. I typically target between 70 and 100 watts per pound for sport
planes and gliders. I don't fly 3D.
Then I consider whether I am looking for high speed or high climb rate. A
glider or a 3D plane would be optimized more toward the climb rate side of
this discussion. A pylon racer would be optimized more for speed. A pattern
plane might be somewhere in the middle.
Now I get down to prop and battery. Wider prop for better climb, narrower
deeper prop for higher speed. Now look at the motor character based on
either battery target or prop target and choose the motor/battery/prop combo
that meets your objectives.
That is kind of high level but you get the idea.
updated Jan 2015
Manufacturers use different wire winds to produce different Kv results.
Kv is a number that relates to how many RPMs a given motor will spin based
on applied voltage. You will see specs on motors where it says Kv=860.
That means that the motor will spin at 860 rpms if you apply one volt to it.
If you apply 7 volts it will span at 6020 rpms.
If the manufacturer takes the same motor he can wind it so that it will
have a lower Kv rating, which typically produces more torque, so these are
typically used with large propellers that will be turned slower. These are
very popular on gliders, for example, where climb angle and climb rate is
much more important than top speed.
Take the same motor and wind it differently and it will have a higher Kv
rating producing higher speeds for a given voltage. These are typically
used with smaller props for higher top speeds. Or they can be used with gear
boxes to handle those big props, providing a similar result to low KV
motors. Sometimes a gear box works better in the installation.
You would also take KV into consideration based on what battery you plan to
use. Let's look at a practical example looking at various kV motors on the same plane.
You have selected a 500 KV motor. The specs say this motor, using a 5S pack
spinning a 15X8 prop that will draw about 45 amps. But suppose you did not have
the ground clearance for a 15" prop. Suppose you could only use a 12" prop. Then
you might choose a 1000 kV motor which would be a better match for that 12" prop.
Another way to look at this would be to think of kV like gears in your car. The lower t
he kV number the lower the gear the greater the "pulling power" or in the case of the prop
the greater the ability to spin that big prop. This is good at start up and take-off, or perhaps for
towing another plane, but it will produce a lower top speed.
Think if a high kV motor like the high gear in a car. Terrible acceleration from a standing start
and not a lot of pulling power for a trailer, but a higher top speed, once you get there.
Since we can't change gear ratios on the airplane's motor we select a compromise that will give us
the best average performance over the performance envelope we desire.
Let's say you were looking for a more scale look and that required you to use a 9 inch prop. Then you might
select a 1500 kV motor on the same plane. The airplane would probably fly but you would need a
longer roll out on the runway to get off the ground, more like a full scale airplane.
If you look here you will see that a given motor is offered in several Kv
ratings. They make suggestions as to which motor is best matched with which
prop and which battery packs. If you click on a given motor you can see what
kinds of power is drawn based on which pack and which prop. If you click on
each of the motors within a model you can see the very different power
curves produced by the different battery/prop combos. Here you see the same
motor with a different wind producing a different Kv result, each optimized
for a different purpose.
http://www.maxxprod.com/mpi/mpi-262.html
So, how does this add to other information about motors?
I first set a watts/pound target for my plane depending on the performance I
want. I typically target between 70 and 100 watts per pound for sport
planes and gliders. I don't fly 3D.
Then I consider whether I am looking for high speed or high climb rate. A
glider or a 3D plane would be optimized more toward the climb rate side of
this discussion. A pylon racer would be optimized more for speed. A pattern
plane might be somewhere in the middle.
Now I get down to prop and battery. Wider prop for better climb, narrower
deeper prop for higher speed. Now look at the motor character based on
either battery target or prop target and choose the motor/battery/prop combo
that meets your objectives.
That is kind of high level but you get the idea.
Last edited by aeajr; 01-12-2015 at 01:32 PM.
11-16-2008, 11:06 AM
#46
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Ed,
Thanks a lot for posting all this great work you have done. This might have taken you many hours of research and work and for you to just post it like that for people to access it for free demostrate the good spirits of people on this hobby. Really nice! It's SOOOO much information that I will have to read in parts. I have also sent you a PM. I hope you have the time to reply to it. Thanks again!
Thanks a lot for posting all this great work you have done. This might have taken you many hours of research and work and for you to just post it like that for people to access it for free demostrate the good spirits of people on this hobby. Really nice! It's SOOOO much information that I will have to read in parts. I have also sent you a PM. I hope you have the time to reply to it. Thanks again!
11-28-2008, 11:00 AM
#47
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RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Ed, I have a GWS nano 6 channel receiver that has a JR (positive?) shift that I would like to use with a FUTABA Tx ( that requires a negative shift). The TX is a 4 channel Skysport. Can I achieve a "shift change" with this receiver or should I look to trade my current receiver for one with a negative shift ?
11-28-2008, 03:02 PM
#48
RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
You will have to read the GWS documentation, but I do not believe the GWS receivers are shift selectable or auto shift. Look for a trade.
Many of the Hitec and Berg receivers are auto shift or shift selectable.
Many of the Hitec and Berg receivers are auto shift or shift selectable.
12-07-2008, 08:40 AM
#49
RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
Hi, Ed.
What's your position on cooling brushless motors/esc's/lipo batteries?
I'm putting together a 50% electric version of Laddie Mikulasko's Arrow, powered by an Astro 020 w/esc and a 1200 mAh LiPo. Should I be concerned about cooling any of the components? I hate to cut holes in this thing and put scoops on it, as it will be used mostly in the water. I can do it if I have to, but I'll have nightmares about what will happen if it ends up inverted on the lake.
Regards and thanks for a great thread.
What's your position on cooling brushless motors/esc's/lipo batteries?
I'm putting together a 50% electric version of Laddie Mikulasko's Arrow, powered by an Astro 020 w/esc and a 1200 mAh LiPo. Should I be concerned about cooling any of the components? I hate to cut holes in this thing and put scoops on it, as it will be used mostly in the water. I can do it if I have to, but I'll have nightmares about what will happen if it ends up inverted on the lake.
Regards and thanks for a great thread.
12-07-2008, 10:02 AM
#50
RE: EVERYTHING YOU WANT TO KNOW ABOUT ELECTRIC FLIGHT
First, I don't understand what plane you are talking about. You say a 50% Arrow. To me that is a plane that would mean this is a scale plane that is 50%, or one half the size of the full size plane. That would be huge. Then you say you are using a 1200 mah battery which is pretty small. So I can't provide any specific advice since I have no idea what plane you are flying.
As far as flying over water, unless you make the plane 100% water tight, you are going to get water inside, so plan for it. I am not experienced with water airplanes but I would presume you would have drain holes of some kind in the fuselage anyway.
Cooling is critical to the safe operation of any electric plane. This is especially true of foam planes as foam is an insulator. But regardless of the material, we have to account for heat.
Let's look at the affect of not providing adequate cooling.
ESC overheats - ESC Fails, you lose control of the motor.
BEC Overheats - If you are using the BEC feature of the ESC, and you don't provide adequate cooling, then your BEC will go through thermal shutdown to protect against fire. You lose all radio control.
Battery Overheates - Short life, or immediate damage. In extreame cases, this can lead to fire.
Motor overheats - housing expands, bearings fail, insulation on windings fail, motor shorts out, in extreme cases, fire.
So, how do I feel about cooling? I think it is important.
As far as flying over water, unless you make the plane 100% water tight, you are going to get water inside, so plan for it. I am not experienced with water airplanes but I would presume you would have drain holes of some kind in the fuselage anyway.
Cooling is critical to the safe operation of any electric plane. This is especially true of foam planes as foam is an insulator. But regardless of the material, we have to account for heat.
Let's look at the affect of not providing adequate cooling.
ESC overheats - ESC Fails, you lose control of the motor.
BEC Overheats - If you are using the BEC feature of the ESC, and you don't provide adequate cooling, then your BEC will go through thermal shutdown to protect against fire. You lose all radio control.
Battery Overheates - Short life, or immediate damage. In extreame cases, this can lead to fire.
Motor overheats - housing expands, bearings fail, insulation on windings fail, motor shorts out, in extreme cases, fire.
So, how do I feel about cooling? I think it is important.