Over heating -vent scoop?

[Paul Taylor]

I have a electric Nobler and I think the motor is getting hot.
I have the opening in the cowl and vents on the bottom. I’m thinking maybe cutting an exhaust vent at the red line.
Thoughts?

[Paul Walker]

What temperature is the motor seeing?

[Paul Taylor]

What temperature is the motor seeing?

I don’t know how to pull the data- But Mike did not keep his finger on it after I landed after a 2 min flight  🤣

[Tom Luciano]

If vented properly then, what Kv is motor and what battery size/cells are you using?

[Paul Taylor]

If vented properly then, what Kv is motor and what battery size/cells are you using?

970kv
3000mah 4s

[Brent Williams]

How is the motor mounted? Are there any provisions for air to pass through/around the motor?

[Ken Culbertson]

Couple of things you can try.  How is the motor mounted?  Collet or prop adapter?   Adding more exit vents is not going to help in the air if you don't increase the air coming in.  One on top may help vent trapped air on the ground.  Sort of like putting a hole over the crankcase of an IC.  The motor draws air through the sator to cool the magnets.  You can't do more than draw off heated air with any outside airflow, you will not cool the motor, but it is still important to vent heated air.  I would increase the spinner gap some or go to a smaller spinner.
Your primary intake on the cowl is way too small for electric.  Most electrics have front scoops about three times yours.  My rule of thumb is to have double the output vents as input and to arrange them so as to create suction which will pull air in and vent the stagnant pockets.  On my Nobler I uesd a "Gieseke" style scoop and made a tunnel out of the bottom of the cowl with a big hole at the end.  I put the ESC there.  I removed the front tank bulkhead and put two suction vents just above the wing LE.  Internally I put in some 1/32" baffels to make sure that there were no pockets and that any air in had a path out.  I feel your pain, the Nobler Nose is 1/2" too narrow to be a good electric but it can work.  Forgive the messy finish.  This was a full Monokote job over an oil-soaked IC frame so it ain't no 20 pointer!  Note the vents over the wing and the size of the scoop and spinner gap.  It is hard to see but it is 1 1/4 tall and 2" wide.  The exit holes in the cowl are 4 @ 1/2" x 2" slots that are shaped so that the front is higher than the rear of the slot to create suction.  (like the fuselage vents only longer)  This plane, in spite of being cramped beyond belief internally never had a heating problem.

Ken

Just read your last post.  970kv sounds like a Cobra 2820/12.  3000 mah may be too much battery.  I ran mine on 2200mah.  The plane in the pix has a Cobra 2826/10 which his close in kv's and it used a 4s 2800.  I know it is "against the rules" so to speak but you can run a 2200 down to about 15% and still get plenty of cycles out of them and they are WAY lighter and smaller that a 3000.  Smaller=more airflow.
Do you need the noseweight? 

[Dan McEntee]

I have a electric Nobler and I think the motor is getting hot.
I have the opening in the cowl and vents on the bottom. I’m thinking maybe cutting an exhaust vent at the red line.
Thoughts?

    As a quick test, you might try closing off the intake hole just a bit and test fly. See if anyone has one of those infrared laser temp guns that you could borrow if you can get a clear shot at the body of the motor. Fly a flight as it is, then take a temp reading. Close up the opening a bit with some tape ( I would close off about 1/3, up near the shaft ) and repeat after the motor cools completely. You might engineer a splitter or baffle just inside the cowl opening to direct air around the side s. Incoming air can just form a bubble if it does not have a clear, easy path to flow. Put up a photo of what the bottom of the cowling looks like.
   Type at you later,
  Dan

[Paul Taylor]

How is the motor mounted? Are there any provisions for air to pass through/around the motor?

It’s front mounted using a 3D printed mount like the one that Tom Morris use to sell.
It has the front opening in the cowl and slots in the bottom like on a standard Nobler minus the opening for a LA 46 head.

[Paul Taylor]

Couple of things you can try.  How is the motor mounted?  Collet or prop adapter?   Adding more exit vents is not going to help in the air if you don't increase the air coming in.  One on top may help vent trapped air on the ground.  Sort of like putting a hole over the crankcase of an IC.  The motor draws air through the sator to cool the magnets.  You can't do more than draw off heated air with any outside airflow, you will not cool the motor, but it is still important to vent heated air.  I would increase the spinner gap some or go to a smaller spinner.
Your primary intake on the cowl is way too small for electric.  Most electrics have front scoops about three times yours.  My rule of thumb is to have double the output vents as input and to arrange them so as to create suction which will pull air in and vent the stagnant pockets.  On my Nobler I uesd a "Gieseke" style scoop and made a tunnel out of the bottom of the cowl with a big hole at the end.  I put the ESC there.  I removed the front tank bulkhead and put two suction vents just above the wing LE.  Internally I put in some 1/32" baffels to make sure that there were no pockets and that any air in had a path out.  I feel your pain, the Nobler Nose is 1/2" too narrow to be a good electric but it can work.  Forgive the messy finish.  This was a full Monokote job over an oil-soaked IC frame so it ain't no 20 pointer!  Note the vents over the wing and the size of the scoop and spinner gap.  It is hard to see but it is 1 1/4 tall and 2" wide.  The exit holes in the cowl are 4 @ 1/2" x 2" slots that are shaped so that the front is higher than the rear of the slot to create suction.  (like the fuselage vents only longer)  This plane, in spite of being cramped beyond belief internally never had a heating problem.

Ken

Just read your last post.  970kv sounds like a Cobra 2820/12.  3000 mah may be too much battery.  I ran mine on 2200mah.  The plane in the pix has a Cobra 2826/10 which his close in kv's and it used a 4s 2800.  I know it is "against the rules" so to speak but you can run a 2200 down to about 15% and still get plenty of cycles out of them and they are WAY lighter and smaller that a 3000.  Smaller=more airflow.
Do you need the noseweight?

Thanks Ken. Good info. I will open up the front end. I do think I need vents about where your are.
I hate to say it I had to add tail weight. 🤬

[Doug Moisuk]

Hot is a relative term.. Electric motors produce a lot of heat.
I fly IC but my buddy flies electric. He always was concerned his motor was to hot. I asked Paul Walker what temperature was to high. I can’t remember the number, maybe Paul will chime in. We borrowed an infrared thermometer from a friend and guess what. The motor temp was below that number. Your finger is not a thermometer.

[Paul Taylor]

    As a quick test, you might try closing off the intake hole just a bit and test fly. See if anyone has one of those infrared laser temp guns that you could borrow if you can get a clear shot at the body of the motor. Fly a flight as it is, then take a temp reading. Close up the opening a bit with some tape ( I would close off about 1/3, up near the shaft ) and repeat after the motor cools completely. You might engineer a splitter or baffle just inside the cowl opening to direct air around the side s. Incoming air can just form a bubble if it does not have a clear, easy path to flow. Put up a photo of what the bottom of the cowling looks like.
   Type at you later,
  Dan

Here ya go Dan.

[Tim Wescott]

Your finger is not a thermometer.

Any analog circuit designer who doesn't work with lethal voltages will disagree.

For most people, the threshold between holding your finger on something vs. saying "ouch" and pulling away (or having to force yourself to touch it if you're trying to be manly) is 50 degrees C.  50 degrees C also happens to be about the maximum temperature you want your circuit to be in a normal room, at least if you want the thing to work when it's in an engine compartment of a car, or sitting on a runway in a desert somewhere, waiting to help send love notes to your nation's enemies.

That's also not a bad baseline for the case temperature of a motor right after a flight.  Guaranteed, if the outer case (which is in the airflow and isn't the part that generates heat) is over 50 degrees C, the motor innards are significantly hotter.

Having said that -- Horror Fright sells cheap IR thermometers that work pretty good -- you just need to make sure you have a clear shot at the motor.

Here's what I had to do to cool down the motor on my slime to 'lectric conversion, in addition to making sure there was an exit path for the air.  It's not pretty, but an ugly airplane flying is better than a pretty one on the ground:

[Tim Wescott]

Oh yes -- notice that the air scoop on there was too danged small -- hence the auxilliary ones blowing right onto the motor.  If I'd wanted to take time and make it pretty, I'd have looked at air scoops on P40's and P51's and whatnot -- some of those have big airscoops over the engine because they had the same problem, too.

[Paul Taylor]

Oh yes -- notice that the air scoop on there was too danged small -- hence the auxilliary ones blowing right onto the motor.  If I'd wanted to take time and make it pretty, I'd have looked at air scoops on P40's and P51's and whatnot -- some of those have big airscoops over the engine because they had the same problem, too.

👍🏼👍🏼
Do you have a STL file for that scoop?

[Dan McEntee]

Here ya go Dan.

   Thanks for the picture. First off, the intake and the exhaust openings are all well below the motor. If there is any air passing through, it's not getting to the motor at all, but passing well below it. Get one of those laser thermometers as mentioned and take some readings as is. Then make some sort of quick and dirty deflector just inside the intake hole to deflect air up towards the motor and retest for temps. If none of that has any effect, I would make a scoop for the top of the nose, make it kind of P-40 Warhawk looking, but maybe wider than tall. Tape up the bottom opening by about half, then test fly and check temps again. I don't think the situation is much different than for an engine, in that the exhaust openings should be twice the area of the intake, so that you create a vacuum as the air passes through and the air and heat HAS to go out the exhaust openings. As mentioned, there should be data some where on what the normal operating temperature of the motor should be, and you need to know that so you know where you are at.
  Type at you later,
   Dan McEntee
  Type at you later,

[Tim Wescott]

👍🏼👍🏼
Do you have a STL file for that scoop?

Nope -- they're cut from a soda can, then worked until they look about right.

[Tim Wescott]

What Dan said -- if you're not deflecting the air toward the motor with a baffle inside the cowl, then it's not going to do any good.  The traditional spot for an air scoop is right where a cylinder head would be.  That's not the spot where electrics get hot.

In my opinion that scoop is just too small -- note the scoop on mine; the divider in there directs the top third or so of the air toward the motor, with the rest flowing over the ESC and batteries.  The first motor I put in that plane died from overheating.  There were other things going on, with a motor wire rubbing on the case, but even before I killed it I was still noting that it was running entirely too hot.

[Air Ministry .]

Year , its gotta go THROUGH IT , to cool it , not past it . Not Entirely , anyway .

This has a vauge resemblance , or is informative of the princaples , at least .



You see the bit wots cooled asnt got room for the airflow to go PAST it , as opposed to THROUGH or ACROSS it !

[Air Ministry .]

Pye Korrie .



or if its really fast ,



Ah Ha .

N A S A  Cooling of Electric Motors Used for Propulsion on SCEPTOR



https://ntrs.nasa.gov/api/citations/20170004363/downloads/20170004363.pdf

Thatll Learn em . 

[Ken Culbertson]

Here is what I had to do to cool down the motor on my slime to 'lectric conversion, in addition to making sure there was an exit path for the air.  It's not pretty, but an ugly airplane flying is better than a pretty one on the ground:

Tim - You're scoop was actually the inspiration for the nose on my Endgame II.  Baffles are the key and having vents that produce suction.

Ken

[Brent Williams]

Paul Walker's innovations on the 2019+ Impacts give something to think about regarding venting strategies.

[Peter Germann]

Citation Two, Lugo, Sept. 3rd. 2022:
Weight & Area: 1'791 Gr (63.2 oz) & 45.2 qdm (702 sq.in)
Lines: 0.39 mm x 19.5 m  (0.015 in x  64 ft.)
Propeller: 3-blade 12 x 5 N
Lap time: 5.2 sec
Outside Temp.: 32°C (90°F)
Wind: calm
Runtime: 5:20
Battery: 6S2700 mAh
Power Control: Jeti SPIN 66 and Burger iAcc V2
Target throttle:  153
Max. throttle: 200
Min. throttle: 100
Sensitivity: 65
After Landing Outside Motor Temp.: below 70°C (158° F)
Recharge: 2'000 mAh.
No Spinner: Approx. minus 25 Gr. (+/_ 1oz)

[fred cesquim]

this is my usuall method, worked on every time so far
2 intakes on top 1/2" diameter each
nose opening with "vanes" directing air to the top and exits on the sides. usually double area of exit x intake

[John Carrodus]

Ken have you written elsewhere about your canard wing design ?

[Ken Culbertson]

Ken have you written elsewhere about your canard wing design ?

Some on the build thread for Endgame II.  It is still untested, so I didn't want to say much till I flew it.  That will probably happen in December.  It is not supposed to be a full scale Canard but a supplemental one to help keep the nose up during that transition from where the flaps are pushing the nose down to when the elevator takes over.  I love the way canards corner so I thought I would give it a try.  My point here was not the canard but the over the motor scoop.

Ken

[Teodorico Terry]

Hi -

The one thing that seems to be left out of the conversation is the current that you might be pulling which is affected by the prop and RPM you have chosen. Looking at the data that Peter provided he is averaging about a 22.5 amp draw for each flight; I suspect that on 4S, even for a smaller model, you might be pulling around 24-25 amps (that was my experience on my 40 sized Legacy). How hot our motors get is a function of the current, winding IR, motor mass and airflow. Out runners are difficult to cool because the coils are buried within the motor, resting your finger on the case simply tells you how hot the case got; not the windings. If you are not seeing any performance degradation during the flight your motor might be OK. 

I tried several different things on my Legacy and none seem to make a significant difference; with the motor front mounted it is difficult to get any air into the motor. I added a spoon scoop (cut down plastic spoon) to the battery hatch along with a baffle to direct the air towards the motor as shown by one of the photos. That did not make much of a difference so then I cut the spinner down to allow air to flow through as shown by the 2nd photo (my spinner back plate has holes). Neither one made a significant difference.  In the end I made a small cooling fan out of a power supply fan which runs off a 3S battery pack. This allows me to cool the motor down to room temperature in between flights so that at least I do not start with a warm motor. Rather than having to wait for 10-15 minutes in between flights the motor is ready to go in about 3-5 minutes.  I am happy with it.

Good luck,

Teo