Author Topic: Cooling Fan using rear/through the bulkhead rear mount (Read 3140 times)

Ken Culbertson · « **on:** June 17, 2019, 03:29:05 PM »

I am using the through the bulkhead rear mount on my newest ship. With the cute little prop adapter on the front of my Cobra 3520/14 I have this huge 5mm rotating shaft sticking out the back just begging to be put to use. Since Cobra does not make fans for the 4hole adapter anymore I am curious if there is an aftermarket fan that fits or a generic one that will go on the shaft?

Bigger question - does a fan actually help?

Ken

phil c · « **Reply #1 on:** June 18, 2019, 10:46:00 AM »

Check small computer fans. They may have the right size hole, or enough meat on the hub to be drilled out. Don't know how they will stand up to the higher continuous rpms.
Possibly try a small EDF fan.

CircuitFlyer · « **Reply #2 on:** June 18, 2019, 03:58:53 PM »

Sounds like a good project for a 3D printer.

John Rist · « **Reply #3 on:** June 19, 2019, 07:46:21 AM »

Would it be possible to adapt a boat prop?

Ken Culbertson · « **Reply #4 on:** June 19, 2019, 08:42:19 AM »

Quote from: John Rist on June 19, 2019, 07:46:21 AM

Would it be possible to adapt a boat prop?

I have looked into that and computer cooling fan blades. All are close but no "Cupie Doll". If there was a third party product out there that worked, I am pretty sure someone would have chimed in by now so I am assuming that there isn't and if there was a real need there would have been.

Thanks for the response!

Ken

FLOYD CARTER · « **Reply #5 on:** June 19, 2019, 09:51:42 AM »

A fan might help but only if the model design doesn't provide natural cooling. Sometimes, converting from glo to electric doesn't permit adequate motor cooling.

Ken Culbertson · « **Reply #6 on:** June 19, 2019, 11:06:13 AM »

Quote from: FLOYD CARTER on June 19, 2019, 09:51:42 AM

A fan might help but only if the model design doesn't provide natural cooling. Sometimes, converting from glo to electric doesn't permit adequate motor cooling.

I think you are right and the irony is that in an IC to electric there is rarely room for a fan anyway. So much for the fan idea.

ken

Air Ministry . · « **Reply #7 on:** June 19, 2019, 10:01:57 PM »

BAHH .

These are ' Antigue ' $:-\$ 1970s ' Duted Fan Impellors ' .

Below maybe a later one , probly most never used . Incidently , I think it was Phil Smith who was the D F development man there .

ANYWAY . Tacking one of these on there somewhere , or something like it , is going to get some air shifting somewhere .
A issue was / is the end rotor clearance / blade clearance . A big dirrerance on the blade / duct Dia skews the efficency .
And while were at it . Behind the Prop is gunna be more efficent that behind the engine - blowing ratheran suckin .

The FW 190 set up could be studiously observed .Theres a giant scale one, think its Top Flit . TF anyway. RC Universe picture .

INDEED .

Quote

jfrotorwerks.com
Top Flite FW-190 Cooling Fan – jfrotorwerks
Scale Cooling fan unit for Top Flite FW-190 50cc. Made for the 4" spinner. 3D printed in NylonX Carbon Fiber. This are on a made to order basis.

The internal aerodynamics wanna be relitively smooth and prtrusion free . Though you can do a few tricks with compartment size steps , tapers etc etc , to vary speed and pressure . If you like being annoying . Or if it just comes naturally .

Something like this would be adeqate for that .

Crist Rigotti · « **Reply #8 on:** June 19, 2019, 10:57:14 PM »

Adding a fan with increase the load on the motor and then increase the heat. Just provide an adequate amount of cooling air. 55 mph flying speed will provide pleanty of cooling. Just make the inlet big enough and outlet even bigger. Don't over think things.

Ken Culbertson · « **Reply #9 on:** June 19, 2019, 11:50:46 PM »

Quote from: Crist Rigotti on June 19, 2019, 10:57:14 PM

Adding a fan with increase the load on the motor and then increase the heat. Just provide an adequate amount of cooling air. 55 mph flying speed will provide pleanty of cooling. Just make the inlet big enough and outlet even bigger. Don't over think things.

It was just a thought. I think my Inlet is enough.

Ken

Crist Rigotti · « **Reply #10 on:** June 20, 2019, 07:58:40 AM »

Quote from: Ken Culbertson on June 19, 2019, 11:50:46 PM

It was just a thought. I think my Inlet is enough.

Ken

Ken,
Put a small piece of 1/32 ply in the inlet,to deflect some air upward towards the motor.

Ken Culbertson · « **Reply #11 on:** June 20, 2019, 09:53:22 AM »

Quote from: Crist Rigotti on June 20, 2019, 07:58:40 AM

Ken,
Put a small piece of 1/32 ply in the inlet,to deflect some air upward towards the motor.

The motor sits too high and the scoop is too far back for that to be effective. I will have a 3/32 gap around the spinner to bring air in. I had not sanded it out yet in the picture. I am also considering cutting a louvered grill in front of the scoop. I may draw that out and post a picture for comment. One of the thinge I did on IC was to put a vent hole over the engine crank case. Is there any readon I don't see many of them on electrics? I would think that they would help.

Ken

Ken

Added picture. Not sure about the side louvers, cute but cute is easy when it is q #2 pencil. Another option would be to open up the entire louver area OR, do nothing since the spinner opening probably will provide enough fresh air.

Igor Burger · « **Reply #12 on:** June 20, 2019, 11:50:08 AM »

Few comments here:

- We use outrunners, means rotor is rotating over the stator, stator heats, rotor not, so making fan pushing air around the motor will not help, what is necessary to push air inside the motor, means from back mounting plate, forward to prop.

- Previouse point means that if some fan can help, it will be something centrifugal on front of motor pushig air out, not to the motor. Motor itself is constructed so, that holes on rotor act as such ventillator. The our task is to remove that hot air from that place, not to push cold air to thal place.

- And that brings us to the point of nose construction - the gap between spinner and fuselage is place with SUCTION - means air goes OUT of fuselage, not in, so nicely shaped nose with adequate gap will nicely remove that hot air from motor compartment out. I do not know why so many builders tend to push air opposite direction. It is counterproductive. It can somehow work on front mounted motors, but not on rear mounting.

- There is one solution which work very well in such fuselages - if fan is not enough to radiate heat, there is still possibility to add heat sink on back plate of motor with fins in stream of cold air just like we have fins on IC engines on the same place.

Ken Culbertson · « **Reply #13 on:** June 20, 2019, 01:53:56 PM »

Quote from: Igor Burger on June 20, 2019, 11:50:08 AM

Few comments here:

- We use outrunners, means rotor is rotating over the stator, stator heats, rotor not, so making fan pushing air around the motor will not help, what is necessary to push air inside the motor, means from back mounting plate, forward to prop.

- Previouse point means that if some fan can help, it will be something centrifugal on front of motor pushig air out, not to the motor. Motor itself is constructed so, that holes on rotor act as such ventillator. The our task is to remove that hot air from that place, not to push cold air to thal place.

- And that brings us to the point of nose construction - the gap between spinner and fuselage is place with SUCTION - means air goes OUT of fuselage, not in, so nicely shaped nose with adequate gap will nicely remove that hot air from motor compartment out. I do not know why so many builders tend to push air opposite direction. It is counterproductive. It can somehow work on front mounted motors, but not on rear mounting.

- There is one solution which work very well in such fuselages - if fan is not enough to radiate heat, there is still possibility to add heat sink on back plate of motor with fins in stream of cold air just like we have fins on IC engines on the same place.

Be patient, I am learning something here. If what you are saying is correct I do not need any of the louvers I have drawn but I do need the gap between the spinner and fuselage. The motor is rear mounted. The Cobra motors have vent holes on both ends. I prefer to call the fixed green end, the one with the wires and shaft, the front and the rotating other end the back. If the goal is to purge the "can" of the heat buildup from the sator does it matter which direction the airflow is as long as it flows? Is the design of the motor such that it has a preferred direction.

If I read this right "B" is the proper configuration for a rear mount, "A" for a front mount. (Forgive me for showing the motor rear mounted on "A") I have been led to believe that "A" will work for either but it is necessary for a Front Mount.

ken

Igor Burger · « **Reply #14 on:** June 20, 2019, 01:58:29 PM »

It is not "preference". The rotor acts as centrifugal ventilator, so air is naturaly pushed from stator to rotor side. In this case forward.

John Rist · « **Reply #15 on:** June 20, 2019, 11:51:49 PM »

Some spinners are constructed to act as a fan. So if you need a fan this may be a solution.

Also some discussion about air flow direction through a motor. It has to be from spinner toward the tail of the airplane regardless of how the motor is mounted. I don't see how you can push air out the front of an airplane in flight.

Igor Burger · « **Reply #16 on:** June 21, 2019, 01:37:04 AM »

Quote from: John Rist on June 20, 2019, 11:51:49 PM

Also some discussion about air flow direction through a motor. It has to be from spinner toward the tail of the airplane regardless of how the motor is mounted.

As I wrote, outrunners are constructed to move air from stator inlet to rotor outlet. It is function of centrifugal fan created by rotor. Pushing it opposite way will not work well.

Quote from: John Rist on June 20, 2019, 11:51:49 PM

I don't see how you can push air out the front of an airplane in flight.

You not need to push anything, the spinner gap is place of fuselage with lowest pressure, suction on that place is natural, so clever way is to use it, not to battle against it :- )))

That is reason why I have back mounted motor and nicely matched spinner shape to fuselage, air is ventilated by motor from back side, where can easily come from classic nose construction (as on picture B), then goes under the spinner and suction at spinner gap will effectively remove it out of fuselage.

Frank Imbriaco · « **Reply #17 on:** June 21, 2019, 05:34:55 AM »

Undersized spinners also help.

Ken Culbertson · « **Reply #18 on:** June 21, 2019, 08:26:58 AM »

I understand that just because we are going 55 mph does not mean that there is a 55mph airflow over the motor. In fact there is near zero. I also understand that the motor is designed to vent itself, in this case forward so you make a valid point that increasing the airflow over the can does not have the same effect as forcing air through the motor from the rear. What I am not sure is how venting that airflow into the stream cooling the esc and battery is any different that shooting it out over the nose through the spinner gap other than slightly raising the temperature of the air stream. You have convinced me that further venting (the louvers) would actually be counter productive so they are out.

The best solution - match the power components to the plane so that it simply does not get that hot!

Ken

Igor Burger · « **Reply #19 on:** June 21, 2019, 08:38:15 AM »

Quote from: Ken Culbertson on June 21, 2019, 08:26:58 AM

I understand that just because we are going 55 mph does not mean that there is a 55mph airflow over the motor. In fact there is near zero. I also understand that the motor is designed to vent itself, in this case forward so you make a valid point that increasing the airflow over the can does not have the same effect as forcing air through the motor from the rear. What I am not sure is how venting that airflow into the stream cooling the esc and battery is any different that shooting it out over the nose through the spinner gap other than slightly raising the temperature of the air stream. You have convinced me that further venting (the louvers) would actually be counter productive so they are out.

The best solution - match the power components to the plane so that it simply does not get that hot!

Ken

My solution: ESC, battery and if used, then also heat sink should be in direct stream from front opening just like we have engine head or pipe in IC models. Fraction of that air is redirected back forward by motor via its back holes on stator and ventilated out under the spinner and it goes out via that gap between fuselage snd spinner back plate.

That also means that front ring of fuselage should be as thin as possible = thickness of fuselage wall. Not central hole just for shaft or prop adaptor.

Yes, it could be designed colder, but it means you carry dead weight :- ))

Igor Burger · « **Reply #20 on:** June 21, 2019, 08:43:48 AM »

And here is picture showing why that gap ventilates so well OUTSIDE. Cp line shows that on that place is lowest pressure from all fuselage, means air goes out of there.

Air Ministry . · « **Reply #21 on:** June 21, 2019, 01:44:16 PM »

From the top drawing it appears the highest pressure is on the nose ( Red ) the blue bit being percentges.

Here the intake to oil tank and crankcase , he was concerned to keep bearing temperture manadgeable , is about the spinner .

tho flow largly depends on pressure diffrential . Assumedly a spinner half the size the pressure there would be somewhat greater .
Matching Diameter , flow past may well create a relative vacume - lower presure at periphery than INSIDE the cowling .

Whereas a larger spinner diameter than cowl diameter , with a longitudeinal gap . as in between backplate and ' spinner ring ,
would create the ' flow through area .' .

Itd be adviseable to have the gap say three times the step , If aiming for extraction at the rear spinner face .

Still , the intakeelsewhere should provide a pressure in the motor compartment well above that flowing past the periphery .
Unless youre sure of produceing a significant suction at the outlet ( periphery again ) .

Id like to see a smoke wand to provide evidence that a smaller spinner than fuse would actually evacuate air there .
Id assume it works ( if as per the picture / photo ) as pretty much a boundary layer intake , enhancing flow past the fuselage . perhaps .

With the intake as built on the model ( the normalish looking one , a floor under the motor adhered forward & sides , rear edge aft of motor ,
with a wall a inch or so aft of that edge , would have the cooling air going forward through the motor , if semi directed there ,
with a floor over the motor sealed aft & sides , gap forward .Presumably from there back aft agin to some outlet .

--------------------------------------------------------------------------------------------------------------------------------------

Id consider a similar flow for a I C engine , from a P 51 dog house ( F S Radiator chamber ) so the air'd go forward and round and back , then out .

A rectangular box up , aft wall at the rad. there . A compartment even . with a rectangular shaft 1/4 the size going forward . Maybe at the top .

The shaft coming back aft splittingarond the ides , opening at the rad. there , to the rear chamber .

Sorta uses the full size P 51 pricaples . Small take off in airflow to big chamber , to reduce speed & losses.

Rear chamber outlet in low pressure zone with high flow past speed , the air there falls out to match airspeed .

As you need no fuel proffing , light 20 thou cardboard'd do . at least for a test set up .

But we mayve wandered a bit off from the original quetion there .

Will scribble a illustration if you require . No fuel tank in the way , anyway . And ' top ' is irrelevant with as much time either way up , give or take .

Its the PRESSURE DIFFRENTIAL that does the work - for flow rates . As long as changes of direction arnt constrictive .

Maybe it'd be a lot easyer built as a pusher .

Matt Piatkowski · « **Reply #22 on:** June 25, 2019, 01:36:07 AM »

Hello Everybody,
I am currently using Plettenberg 15-22 with centrifugal fan and MVVS 8.0 with centrifugal fan in my Big Red.

Plettenberg 15-22 fan is an option but the MVVS 8.0 fan comes always with the motor.

Plettenberg 15-22 with fan and 2" long leads with EC3 connectors, weights 193 grams (6.78 oz.).
MVVS 8.0 with 2" long leads with EC3 connectors, weights 229 grams (8.08 oz.).

The Plettenberg centrifugal fan only weights 12 grams (0.42 oz.). By the way: this fan and shaft constitute one assembly and to remove the fan, one must replace the shaft.

In central Poland, where I live right now, the ambient air temperature reaches frequently 32-34 deg. C (~90 deg.F.) in the shaded areas, in the early afternoons. When I was using MVVS 8.0 running Igor's 12x5x3 carbon composite, narrow blade, prop. on 6S ThunderPower batteries, the temperature of the rotor after full pattern was 53-55 deg.C. I have used the infrared measuring device, measured this temperature many times and then averaged the results. MVVS 8.0 rotor surface is dull black, therefore the emissivity of it is probably close to 0.9. For those who want to understand better the infrared measurements, please go to https://en.wikipedia.org/wiki/Emissivity or/and any of the websites regarding black body radiation.

Some time ago, I have asked the Plettenberg factory to remove the fan from one of my motors. The weight of Pletty 15-22 without fan was 181 grams. This motor went into my Big Red and I started flying 48 grams (1.7 oz.) lighter model in hot weather. The temperature of the motor, about 15-20 seconds after landing, reached 73 deg.C. Because the Pletty's rotor has shiny and smooth surface having low emissivity, I have measured the temperature on the black, aluminum back plate with four ventilation holes. This plate has the emissivity close to the MVVS 8.0 surface emmisivity, therefore I feel the temperature measurements of both motors are reasonably comparable.

Plettenberg Engineering says that 80 degrees C. on the windings represents the maximum safe temperature, therefore 73 deg. C on the back plate that is directly exposed to the hot air passing the windings and is located about 0.10 " from the windings, was dangerously close to this limit.

Please remember that I was flying in hot weather and full sun. The air flow in the Big Red's motor and battery compartment seems to be sufficient, with the ESC suspended directly in the flow and very large inlets. By the way, I have enlarged the size of the fuselage front portion w/r to the original Igor's Max Bee II to have more air flow and more cooling. The ESC (Spin66) was not even warm to touch after full pattern flights with MVVS 8.0 and Pletty. The MEASURE option available via JETI BOX showed maximum ESC temperature in flight = 45 degrees C. This was the temperature measured by sensor inside ESC and was of course higher than the ESC surface "touch" temperature. Simply put: no problem with the ESC overheating for both motors.

Then, I have installed Plettenberg 15-22 with the centrifugal fan using the same prop. and battery and flew five patterns in hot weather.

The temperature of the Pletty's fan surface (that is dull black aluminum) was in 52-53 deg. C range and this means that the Plettenberg fan is very effective. Aluminum is very conductive and, because this fan is very close to the windings and is exposed to the hot air flow coming directly from the motor inside, the temperature of the windings was perhaps 3-5 deg. C higher.

Conclusion: MVVS 8.0 and Plettenberg 15-22 fans are very effective in lowering the temperature of these motors and must be used in hot weather. The RTF weight of the model, lap times, length of lines, Target Throttle, Max.Throttle and the active timer Sensitivity parameter affect the temperature of motors but, when all these parameters are set like in case of Big Red, fans will provide lower (and acceptable) temperatures of the windings after the C/L Pattern in hot weather.

Lastly: only centrifugal fans are effective. The axial fans will not be effective enough. I can explain why but it will take another half a page. If anybody is interested, please send me the PM.

Happy (hot weather) flying and do not forget your own sun protection,
Best Regards,
M

Dennis Adamisin · « **Reply #23 on:** June 29, 2019, 10:24:55 AM »

Hi Ken

Cut the nose off the spinner. The spinner in the pix is a Great Planes with the stock (but well ventilated) spoked aluminum backplate. Of course the nose ring behind the spinner has a generous opening. This option actually LIGHTENS the nose (unlike an add-in fan) and routes air directly into the motor openings (unlike chin scoops) so it is very effective - and easy!

Ken Culbertson · « **Reply #24 on:** June 29, 2019, 10:45:06 AM »

Quote from: Dennis Adamisin on June 29, 2019, 10:24:55 AM

Hi Ken

Cut the nose off the spinner. The spinner in the pix is a Great Planes with the stock (but well ventilated) spoked aluminum backplate. Of course the nose ring behind the spinner has a generous opening. This option actually LIGHTENS the nose (unlike an add-in fan) and routes air directly into the motor openings (unlike chin scoops) so it is very effective - and easy!

Sometimes the simplest solution is also the best. Looks good too. I will give that one a try.

Ken

Air Ministry . · « **Reply #25 on:** June 29, 2019, 09:44:19 PM »

Ken Culbertson · « **Reply #26 on:** June 30, 2019, 05:36:32 AM »

Matt - What size lines do you fly it on?

Ken

Air Ministry . · « **Reply #27 on:** June 30, 2019, 08:44:51 PM »

We find number eight wires pretty good for most things , here in noo zealand . The 44 gallon drums make pretty good line reels ,

As you need a bit of wire so as the tensions not to high there .

Matt Piatkowski · « **Reply #28 on:** June 30, 2019, 09:38:45 PM »

Hi Ken,
I am using exclusively Solomianikov's lines having the diameter about 0.37 mm. (0.0146").
These lines are used by most of the F2B fliers in Europe. They have one advantage and two disadvantages. The advantage: they are very stiff in tension, the disadvantages: 1.) they rust easily and require frequent oiling and 2.) they have a tendency to coil very easily while cleaned with rags. The advantage though outweighs the disadvantages.
Regards,
M

John Rist · « **Reply #29 on:** July 03, 2019, 12:12:25 PM »

Quote from: Dennis Adamisin on June 29, 2019, 10:24:55 AM

Hi Ken

Cut the nose off the spinner. The spinner in the pix is a Great Planes with the stock (but well ventilated) spoked aluminum backplate. Of course the nose ring behind the spinner has a generous opening. This option actually LIGHTENS the nose (unlike an add-in fan) and routes air directly into the motor openings (unlike chin scoops) so it is very effective - and easy!

Now that's Cool!!

Air Ministry . · « **Reply #30 on:** July 03, 2019, 11:49:55 PM »

Mike Piaskowski's 1958 Morris Minor 1000 Saloon (2-door) $:-\$

https://www.morrisminorforum.com/registry/1958-Morris-Minor-1000-Saloon-2-door.30442/

Suppose it'd be red , if it was ' our ' Matt's .