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Author Topic: Adding a fan?  (Read 7670 times)

Offline FLOYD CARTER

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Adding a fan?
« on: November 21, 2016, 04:05:19 PM »
My AXI 2820 motor is "rear mount", but the main shaft sticks out behind the firewall.  It could benefit from more cooling, so why not add a fan to this extended shaft?

The firewall has plenty of "air space" in it, so air moves into the fuselage cavity and out some louvers in the fuselage.

I can't make my own fan, because it would certainly be out of balance.

Is anything available?  Or maybe isn't a very good idea?

Floyd
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Offline Tim Wescott

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Re: Adding a fan?
« Reply #1 on: November 21, 2016, 05:28:11 PM »
Cooling fans for electric motors is a thing, but I don't know how necessary they are for CLPA.  Here's a brit site that came up on a search for "AXI 2820 fan": https://www.electricwingman.com/motor-accessories/coolers.aspx.

Having a cooling fan in the pits to cool the plane down after a flight may be a good thing -- figure that you will land with some residual heat in the motor, and it won't have anywhere to go when there's no airflow.  But -- AFAIK neither Paul nor Igor use them, which makes me wonder if they're necessary.
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Offline Igor Burger

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Re: Adding a fan?
« Reply #2 on: November 22, 2016, 01:34:24 AM »
Cooling fans for electric motors is a thing, but I don't know how necessary they are for CLPA.  Here's a brit site that came up on a search for "AXI 2820 fan": https://www.electricwingman.com/motor-accessories/coolers.aspx.

That fan is for front mount not for rear mount, I use also rear mount and I use aluminum heat sink, especially on model which uses 12" 3blade prop on AXI 2826.

Offline Christoph Holtermann

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Re: Adding a fan?
« Reply #3 on: November 22, 2016, 03:15:06 AM »
Hi,

whether the fan makes a difference and increases internal cooling depends for sure on the rpm the prop is turning. I found out with my Kontronik-motor that has a built-in fan that with Igor's smaller diameter 11x5 carbon prop that runs at 10.500 - 11.000 rpm the motor stayed pretty cool. The 12x5 carbon prop that Igor is referring to can be run with some less rpm, I guess 9,800 rpm. While both props use more or less the same amount of capacity from the battery the motor ran slightly hotter with the 12x5 than with the 11x5, the only difference being less rpm and thus less efficiency of the fan.

I also had my motor run at 10,000 rpm without prop just to check how much air the fan really draws through the motor and there was not a lot of breeze I could recognize. So I would also agree with Igor that a heat sink is probably more efficient in dissipating heat than the fan.

Christoph

Offline Igor Burger

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Re: Adding a fan?
« Reply #4 on: November 22, 2016, 03:53:48 AM »
Hi,

whether the fan makes a difference and increases internal cooling depends for sure on the rpm the prop is turning. I found out with my Kontronik-motor that has a built-in fan that with Igor's smaller diameter 11x5 carbon prop that runs at 10.500 - 11.000 rpm the motor stayed pretty cool. The 12x5 carbon prop that Igor is referring to can be run with some less rpm, I guess 9,800 rpm. While both props use more or less the same amount of capacity from the battery the motor ran slightly hotter with the 12x5 than with the 11x5, the only difference being less rpm and thus less efficiency of the fan.



You probably mean that underchambered prop, That is right, while both props have the same pitch, that UCT prop gets higher speed then flat bottom prop (known issue of UCT props which fly typically at -1 or even -2 degrees AoA - because of airfoil) so if you have 2 props getting the same power on the same motor but one runs at lower RPM, then clearly the same power at lower rpm is reached at lower voltage (managed by PWM) and therefore higher current (11" prop is also smaller, so also slippage it little larger and thus it runs at little higher RPM). And while our motors run slightly overloaded, it really makes more copper loses. That is why I recommend rather that narrow flat bottom 12" prop in AXI 2826 It is designed to have good efficiency on cost of self braking unloaded (advantage of UCT props - but we have governors, so no big problem with that). Those undercambered are typically used on model like Shark, but they also use larger motors (for example Orestes use them also, but also Czech guys with MVVS motors etc).

Offline Christoph Holtermann

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Re: Adding a fan?
« Reply #5 on: November 22, 2016, 08:04:23 AM »
Hi Igor,

the 12x5 prop I fly is the narrow one, not the UCT-type that Orestes has. But also on this 12x5 narrow I needed to set lower rpm compared to the old 11x5 from Meijzlik and remarked a hotter bell after the flight. The 12x5 UCT would probably melt my tiny little Kontronik :)

Orestes had the Cobra 3515-18 in his plane I believe and I tested this motor as well. It stayed much cooler than my Kontronik and also used some less energy. On the ground at max. power the difference was nearly 30 Watt. But the weight is 20g higher than my Kontronik and I didn't want to retrim and shift battery to achieve same CG, therefore I stay with Kontronik until I opt for props that use more power, such like the UCT or Richi's wooden props.

But back to topic: absorbing the heat in aluminium, either with a heat sink or with a larger motor is probably the safer way than increased air cooling through the motor.

Offline Igor Burger

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Re: Adding a fan?
« Reply #6 on: November 22, 2016, 08:17:33 AM »
If you have that from Mejzlik, it can be answer for the difference. those mine are closer (I mean 11" and 12" narrow), usually I not need change throttle too much if I change them. But also two props of the same type have slight differences, so it can happen.

Yes, larger motor is definitively better then any heat sink, it not only absorbs and radiates easier, it usually also comes with lower IR, but makers usually make too large steps between them, so sometimes it is easier to use some cooling instead of 10 or 20% heavier motor. For example AXI 2826 weights only 180g and MVVS 220g and plus it has larger dimater so it is too much for such experiments  :- P

Offline FLOYD CARTER

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Re: Adding a fan?
« Reply #7 on: November 22, 2016, 10:37:02 AM »
By "heat sink", do you mean an aluminum facing on the firewall?  The heat path would then be from the copper windings, through the supplied 4-bolt motor mount, and into a heat sink.  The heat sink would then have to have sufficient mass (and weight) to temporarily store this heat energy.  In any case, the path of heat energy is totally by conduction.  A fan would remove heat directly from the motor to ambient, although with less efficiency because of the poor transfer of heat through higher thermal resistance of the air medium.
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Offline Igor Burger

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Re: Adding a fan?
« Reply #8 on: November 22, 2016, 02:45:58 PM »
Yes, it is on firewall and motor is pressed by its back side to heat sink. So it transfers heat from winding and also iron core. But it not only accumulates heat, it has also fins exposed to air stream inside fuselage so it radiates that heat to flowing air just like we do it with piston engine and its fins on head ... works well :- ))

Offline Tim Wescott

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Re: Adding a fan?
« Reply #9 on: November 22, 2016, 04:03:28 PM »
But it not only accumulates heat, it has also fins exposed to air stream inside fuselage so it radiates...

Floyd was being pedantic, because he used to work for a place where the terminology made a difference.  Technically, a "heat sink" is just a hunk of something where heat goes and is stored.  99% of the things out there called "heat sinks" are actually combination heat spreaders and heat radiators.
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Offline Igor Burger

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Re: Adding a fan?
« Reply #10 on: November 22, 2016, 04:12:05 PM »
In that case sorry, we have in Slovak language only one word for heat sink, radiator and cooler.

That what I wrote is this: https://en.wikipedia.org/wiki/Heat_sink

Means something aluminum with fins and big prop front of that :- ))))

Offline Keith Renecle

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Re: Adding a fan?
« Reply #11 on: November 22, 2016, 10:42:28 PM »
Igor's idea works really well. Just to save Igor from looking for his old pics..........
Keith R

Offline Motorman

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Re: Adding a fan?
« Reply #12 on: November 23, 2016, 01:33:56 PM »
is an unshrouded fan or even a shrouded fan going to do anything beyond what ram air does? I think they were developed for things that don't have constant ram air.

MM

Offline Tim Wescott

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Re: Adding a fan?
« Reply #13 on: November 23, 2016, 02:45:29 PM »
In that case sorry, we have in Slovak language only one word for heat sink, radiator and cooler.

That what I wrote is this: https://en.wikipedia.org/wiki/Heat_sink

Means something aluminum with fins and big prop front of that :- ))))

Even among mechanical engineers working on this sort of thing, 99% will say "heat sink" when they mean "radiator".  So you haven't made any cross-language faux-pas.  If someone in an English-speaking group is talking about something that just absorbs heat they'll say "just a heat sink" or "pure heat sink" or something like that.  (I worked next to a group that was building an instrument that had to work strapped to a firefighter's helmet, inside of burning buildings.  They had a "real" heat sink, in the form of a bottle of magic wax that absorbed heat as it melted.  It was good for about 15 minutes, or at any rate it was good for more time than you were supposed to spend inside a burning building.  When you got out of the fire, you were supposed to take it off, open a door in the case, and toss it into a bucket of water to remove the heat from the heat sink -- then after the wax solidified it'd be ready to go back into the fire.)
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Offline Peter Germann

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Re: Adding a fan?
« Reply #14 on: November 24, 2016, 04:02:59 AM »
Is anything available?  Or maybe isn't a very good idea?
Floyd

With front mount motor installation air flow through motor mount and spinner is a bit restricted and I therefore have fans on all of my AXI motors. AXI's cooling fan for the 2826 series weighs in at 6.5 Grams and bolts to the rear end of the motor. I have no data on how much it reduces the actual motor temperature in flight, but I dont think its installation can do any harm. Besides, it adds dissipation area and help radiating the heat after landing.

https://www.electricwingman.com/model-motors/cooler-axi-2820-2826.aspx

Peter Germann

Offline Igor Burger

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Re: Adding a fan?
« Reply #15 on: November 24, 2016, 10:17:11 AM »
Igor's idea works really well. Just to save Igor from looking for his old pics..........

Thanks Keith, one picture better than 1000 words and you sent two ... perfect : -)))

Offline Igor Burger

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Re: Adding a fan?
« Reply #16 on: November 24, 2016, 10:21:05 AM »
Even among mechanical engineers working on this sort of thing, 99% will say "heat sink" when they mean "radiator".  So you haven't made any cross-language faux-pas.  If someone in an English-speaking group is talking about something that just absorbs heat they'll say "just a heat sink" or "pure heat sink" or something like that.  (I worked next to a group that was building an instrument that had to work strapped to a firefighter's helmet, inside of burning buildings.  They had a "real" heat sink, in the form of a bottle of magic wax that absorbed heat as it melted.  It was good for about 15 minutes, or at any rate it was good for more time than you were supposed to spend inside a burning building.  When you got out of the fire, you were supposed to take it off, open a door in the case, and toss it into a bucket of water to remove the heat from the heat sink -- then after the wax solidified it'd be ready to go back into the fire.)

I am thinking where that accumulated heat goes then ... may be we should call CERN I heard they can make small black hole and I know black hole eats also energy, so we can put the heat there and it will never go out :- P

Offline Igor Burger

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Re: Adding a fan?
« Reply #17 on: November 24, 2016, 10:32:53 AM »
With front mount motor installation air flow through motor mount and spinner is a bit restricted and I therefore have fans on all of my AXI motors. AXI's cooling fan for the 2826 series weighs in at 6.5 Grams and bolts to the rear end of the motor. I have no data on how much it reduces the actual motor temperature in flight, but I dont think its installation can do any harm. Besides, it adds dissipation area and help radiating the heat after landing.

https://www.electricwingman.com/model-motors/cooler-axi-2820-2826.aspx



I never tested that fan, because I have back mounting, but Alex uses them and he told be that there is measurable temperature difference.

However ... new AXI motors have already integrated fan, but I also do not know how efective they are, because I did not have chance to fly them yet in hot air. It is that red "something" inside the motor. I would say it is mounted backwards, but they say it has better effect than "normal" installation.  ... well I must believe, but I will use my radiator anyway :- P

Offline Tim Wescott

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Re: Adding a fan?
« Reply #18 on: November 24, 2016, 11:37:42 AM »
I am thinking where that accumulated heat goes then ... may be we should call CERN I heard they can make small black hole and I know black hole eats also energy, so we can put the heat there and it will never go out :- P

"True" heat sinks need to go into systems that generate lots of heat for a little while, and then have a good long chance to cool down.

Little black holes radiate like mad, at least in theory (Google on Hawking Radiation).  So you may not want to look up CERN's phone number just yet.
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Offline Igor Burger

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Re: Adding a fan?
« Reply #19 on: November 24, 2016, 12:02:15 PM »
That is true Tim, noone is perfect, however its is "cold" radiation, it has temperature of only fractions of Kelvin, it will even better cool the motor backplate as it comes back from black hole :- P ... I call CERN for price.

Offline Tim Wescott

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Re: Adding a fan?
« Reply #20 on: November 24, 2016, 01:57:39 PM »
That is true Tim, noone is perfect, however its is "cold" radiation, it has temperature of only fractions of Kelvin, it will even better cool the motor backplate as it comes back from black hole :- P ... I call CERN for price.

Temperature is inversely proportional to mass -- stellar-sized black holes have temperatures in the fractions of a Kelvin, but a black hole of a suitable mass to balance my tendency to build heavy tail feathers would be millions of Kelvin, and wouldn't last long.
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Offline Igor Burger

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Re: Adding a fan?
« Reply #21 on: November 24, 2016, 02:04:31 PM »
I heard they compressed only less than cofee spoon of material to black hole in CERN so far, so it will be only 0.000something K,  it will work well, do not worry :- P

Offline FLOYD CARTER

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Re: Adding a fan?
« Reply #22 on: November 25, 2016, 10:57:12 AM »
The physics is getting out of hand.  It's simple.  When a warm body transfers heat energy to a cooler body, by means of conduction, the warm body is called "heat source". 
The cooler body is called a "heat sink".

I have never seen a black hole, so I can't comment.
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Offline Igor Burger

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Re: Adding a fan?
« Reply #23 on: November 25, 2016, 10:59:41 AM »
I have never seen a black hole, so I can't comment.

Well, noone ... that is why it works :- ))))))))))))))))) ... I hope

Offline Chuck_Smith

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Re: Adding a fan?
« Reply #24 on: November 26, 2016, 10:01:16 AM »
As long as you stay to the right of the "knee" of the Br curve for the magnets in the motor you should be fine WRT temperature. If you can find out what grade of material your motor uses I can give you the max operating temperature. Most all of the motors I've seem have either Neo or SmCo and the operating temps should be well below where the motor is running. (We typically us heat to stabilize rare-earth magnets.)  The Br curve in the second quadrant of the hysteresis curve of the magnet will move right with temp, but the Br max will be pretty close to the original.

If you have Neo magnets you can tell because they are generally nickel plated since Neo will rust, whereas SmCo won't. Neo will be affected by temp sooner more than SmCo. But it's really about the max temp and not how long it stays there. With SmCo, if you can touch the motor, you're probably fine.

Chuck

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Offline FLOYD CARTER

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Re: Adding a fan?
« Reply #25 on: November 26, 2016, 02:46:59 PM »
I had one of the smaller AXI motors where a couple magnets came loose due to heating.  They appeared to be epoxied in place, so I simply fixed with more epoxy.  So, the epoxy will be damaged by excess heat before the magnets are damaged.  That's reason enough to be careful and not overheat any motor.
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Offline pmackenzie

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Re: Adding a fan?
« Reply #26 on: November 26, 2016, 05:43:34 PM »
As long as you stay to the right of the "knee" of the Br curve for the magnets in the motor you should be fine WRT temperature. If you can find out what grade of material your motor uses I can give you the max operating temperature. Most all of the motors I've seem have either Neo or SmCo and the operating temps should be well below where the motor is running. (We typically us heat to stabilize rare-earth magnets.)  The Br curve in the second quadrant of the hysteresis curve of the magnet will move right with temp, but the Br max will be pretty close to the original.

If you have Neo magnets you can tell because they are generally nickel plated since Neo will rust, whereas SmCo won't. Neo will be affected by temp sooner more than SmCo. But it's really about the max temp and not how long it stays there. With SmCo, if you can touch the motor, you're probably fine.

Chuck



Virtually all hobby motors use Neo magnets. The only ones I recall that used Cobalt were Aveox and Astro.
While Neo is "stronger"  , Cobalt is forever (and more expensive).

Not all Neo is nickel plated, some are epoxy coated. I seem to recall Neu for example use epoxy coating. I don't think Cobalt needs any sort of coating.

Pat MacKenzie
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Offline Jeff Prosser

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Re: Adding a fan?
« Reply #27 on: December 19, 2016, 03:08:02 PM »
Hi Igor
I am about to buy a new motor for F2B.
The photo of the new AXI motor that you posted shows that it is labelled "F2B".  That motor does not seem to be listed on their web site.
The most suitable motor for F2B seems to be 2826/10.  Do you know if that is the same motor or a different one?
Thanks
Jeff Prosser

Offline Igor Burger

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Re: Adding a fan?
« Reply #28 on: December 19, 2016, 03:33:12 PM »
Hi Igor
I am about to buy a new motor for F2B.
The photo of the new AXI motor that you posted shows that it is labelled "F2B".  That motor does not seem to be listed on their web site.
The most suitable motor for F2B seems to be 2826/10.  Do you know if that is the same motor or a different one?
Thanks
Jeff Prosser

No, 2826/F2B is different motor, it is for 6 cells and very well matched to active timer and 5" pitch props, while 2826//10 is for 4 cells and 6" pitch props constant RPM.

Offline Jeff Prosser

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Re: Adding a fan?
« Reply #29 on: December 19, 2016, 05:32:53 PM »
Thanks for that info Igor.
I am using constant RPM at the moment so will go for the 2826/10.
Cheers

Offline Frank Imbriaco

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Re: Adding a fan?
« Reply #30 on: December 20, 2016, 08:53:07 AM »
Newer motors with integral fans are certainly of interest. To date, I've used Hunt's cooling method. Bifurcate the air inlet  with two divisions of 1/32" balsa (or 1/64" ply)to direct  cool air to the  motor can , ESC and battery.

 I flew my Ryan's Eagle multiple times in 95 degree weather this summer. E-Flight Power 25 generated  temps upon  landing which were well within manufacturer's acceptable limits. And since  temps increase immediately after landing, the motor is definitely running cooler in flight.

What is the weight penalty for a fan equipped AXI vs standard ( or older versions) ?

Offline Peter Germann

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Re: Adding a fan?
« Reply #31 on: December 20, 2016, 09:30:26 AM »
What is the weight penalty for a fan equipped AXI vs standard ( or older versions) ?
6.5 Grams
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Offline Igor Burger

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Re: Adding a fan?
« Reply #32 on: December 20, 2016, 01:31:20 PM »
Thanks for that info Igor.
I am using constant RPM at the moment so will go for the 2826/10.
Cheers

Keep the RPM as hig as possible (how much battery allows), every outrunner has some RPM at which rotor resonates (it has shape of a bell), AXI 2826 is at aproxiately 9000. You will not hear it, but it shortens bearing life - it was known issue with old APC 12x6 props running at just that RPM. That was reason why we went to higher volatge with 5" props at ~11000 rpm.

Offline Igor Burger

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Re: Adding a fan?
« Reply #33 on: December 20, 2016, 01:33:21 PM »
I flew my Ryan's Eagle multiple times in 95 degree weather this summer. E-Flight Power 25 generated  temps upon  landing which were well within manufacturer's acceptable limits. And since  temps increase immediately after landing, the motor is definitely running cooler in flight.

What is the weight penalty for a fan equipped AXI vs standard ( or older versions) ?

Actually it is few grams LIGHTER, not heavier :- ))))


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