[NSRCA-discussion] Cooling outrunners

Sun Dec 17 09:18:58 AKST 2006

Rex,
Sounds similar to a small outrunner that I have in which the cooling holes in the end-bell of the can are drilled at a 45 degee angle in order to scoop some air into the core of the motor. 
The spinner fan-blade/vane thing probably has a cross-over point where the force generated by the full compliment of vanes is offset by the larger holes realized by removing
               spokes. Of course this could be bench measured by run-testing the two variations blowing against a spring loaded sail positioned behind the motor and recording the deflection angle. 
G.

  ----- Original Message ----- 
  From: Rex LESHER 
  To: NSRCA Mailing List 
  Sent: Sunday, December 17, 2006 12:24 PM
  Subject: Re: [NSRCA-discussion] Cooling outrunners

  Wayne

  Take a look at the D8 website, electrics link....  It has photos of my experiment.  I actually did more than just shaping like a prop.  I actually carved the spokes into a curve on the back side, similar to the prop on a tug boat.  The curved spoke is placed "just so" over the openings
  in the motor.  The cupped portion of the spoke forces air directly into the motor.  The curve in the carved portion in the spoke is intended to force the air towards the hub by trapping the air further out on the spoke first.   The spinner is louvered, somewhat like a squirrel cage fan.
  The intention of the louver is to "chop" the air and force feed it into the spinner, creating a high pressure area that will feed air to the prop shaped
  backplate.   To be honest,  after doing all this work,  I was somewhat disappointed with the results.  Turned out, that I didn't have enough cooling
  exhaust outlet area in the aft fuselage.  After I pretty much doubled that opening, all my cooling problems went away.  This summer will tell for 
  sure as to wether or not it works as well as intended.  Last summer was spent actually getting to this point....
  I'm contemplating removing every other spoke on the back plate, but as I said, I'm going to wait and see how my temps are running as the summer heat gets here.  Like Dave, I'm concerned with removing too much material.  If the spokes are left "stock", it's not a problem.  But, with as much material as I have removed, there might be a concern.  I'm guessing that it would be ok.  I use a nylon 10-32 bolt to hold the spinner to the
  adapter, and it's just snugged up, so there isn't much pressure against the backplate.  We aren't using using a starter on the cone, so there doesn't 
  have to be much structural strength there.  Just make sure you do a good rebalance after you get done with whatever carving you do....

  Rex
    ----- Original Message ----- 
    From: Dave Reaville 
    To: NSRCA Mailing List 
    Sent: Sunday, December 17, 2006 8:53 AM
    Subject: Re: [NSRCA-discussion] Cooling outrunners

    Hi Wayne

    Actually Chad and Rex (I think???) had already done that but I was a little concerned with leaving sufficient material after the spoke removal :-) so I decided not to. I am not sure just how much additional flow would be created but it's certainly worth considering. 

    Dave
      ----- Original Message ----- 
      From: Wayne Galligan 
      To: NSRCA Mailing List 
      Sent: Saturday, December 16, 2006 8:23 PM
      Subject: Re: [NSRCA-discussion] Cooling outrunners

      Dave,

      You could go one step further and grind an airfoil in the remaining spokes to aid in pulling the air in.

      Wayne G.  
        ----- Original Message ----- 
        From: Dave Reaville 
        To: NSRCA Mailing List 
        Sent: Saturday, December 16, 2006 2:09 PM
        Subject: Re: [NSRCA-discussion] Cooling outrunners

        Re: Outrunner Cooling

        FWIW I have made some other changes to the spinner that have helped a little. I removed three of the spokes of my backplate to assist in weight loss :-) as well as increase flow through the motor.  Picture here http://members.shaw.ca/patternwestnews/pictures/planes/tttrim.htm

        I am also going to make some minor changes to the spinner itself by increasing the prop cut-out forward. These openings coupled with the ducting that Chad used towards the rear of the motor should provide adequate cooling for the Plett. I understand the Evo has bigger openings to assist in cooling but I think it's very important to make sure that the backplate spokes, when mounted, align properly to allow unrestricted flow through the openings. It's possible to block the flow if improperly installed or if it rotates on it's own.

        I have seen Rex's spinner in action and it appears to me to assist in cooling.

        Dave R

        ----- Original Message ----- 
          From: Rex LESHER 
          To: NSRCA Mailing List 
          Sent: Saturday, December 16, 2006 9:52 AM
          Subject: Re: [NSRCA-discussion] Cooling outrunners

          Hi guys, I've been without power for the last couple days....   The mods I did to the spinner are on the D8 website.  I'm not sure how effective my process really is.  I can tell you that it works much better than not having any opening at all.  I did that experiment....  Chad touched on the real problem and I believe he is right on.  The spokes in the backplate and the closed sides between the openings in the spinner create too much resistance (spinning disc) for the appropriate amount of air to get directly into the motor.   I first tried just opening the sides of the spinner, and used that for my baseline.  Then, I used the modification as shown on the D8 website.  I figure that I dropped somewhere around 20 degrees on average.  After a few flights, I took the spinner off, and the motor cooled much better.  That tells me that in order to get the greatest cooling, you'd have to create a high pressure area in front of the motor...  
          Now, I'm playing with ducting, forcing air around the can....  Time will tell, if I don't demag the motor!!!

          Rex
            ----- Original Message ----- 
            From: AtwoodDon at aol.com 
            To: nsrca-discussion at lists.nsrca.org 
            Sent: Friday, December 15, 2006 6:16 PM
            Subject: Re: [NSRCA-discussion] Cooling outrunners

            Jim, 

            I think Rex Lesher modified a True Turn spinner to have 'inlet slits' to pull air into the spinner and back thru the motor.  I don't know if there were any tests to indicate if was effective.  Maybe Rex can comment here.

            I also believe there are some NASA airflow studies that indicate the area around the prop hub and some small amount of the prop as well as the spinner create an cone like airflow around that area that basically prevents air from entering the spinner slots, etc.

            Hacker has a fan like attachment on the back of the large outrunners than creates a negative pressure area inside the motor and draws air in thru the front of the motor for cooling.  there have been some tests retrofitting a similar fan on the back of other outrunners with similar success.  Basically a trade off in weight for cooling effectiveness.

            As you know, I run an AXI 5330/F3A with the chin cowl opening ducted to divert incoming air upward across the AXI.  It seems to work even on the hottest summer days.  No air from the cheek cowls is ducted toward the motor, it just passes thru toward the ESC and batteries.

            Don

            In a message dated 12/15/2006 4:14:26 P.M. Pacific Standard Time, joddino at socal.rr.com writes:
              It would seem the best way to cool outrunners that have holes in the case on the end that faces the nose ring, would be to bring air in through the spinner and through holes in the backplate.  Wondering if anyone has really thought about the optimum design.  I can picture internal vanes but perhaps cutting off the nose of the spinner and leaving a big hole would be adequate.  Anyone tried anything like this?

              Jim O

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