[NSRCA-discussion] Cooling outrunners

[Dean Pappas]

Hi Jim,
I have fiddled with this a fair bit, and the setup I am using now produces very modest temperature rises on the AXI.
I see less than 15C rise after a P-07 with 84 A W.O.T. current draw at the beginning of the flight. After the flight, static W.O.T is more like 75 or 76 A.
 
The inlets total up to just about 1 square inch, which is ducted straight to an airbox that surrounds the front of the motor. The inlet airbox is about 5/8" deep from front to back, and has plenty of volume, just because it needs to evvelop the front of the motor and the cowl inlets. The airbox has a hole through wich the motor can passes, and the hole is extended with a sleeve that runs back to near the aft end of the rotating part of the motor.
The wrapped balsa sleeve has maybe 1/8" clearance around the motor. The high pressure air in the inlet airbox is forced to either flow closely over the outside of the motor or through the holes in the motor. 
For motors such as the Pletty, where the prop drive does not stand proud of the front of the motor can, a drive extender washer maybe 1/2" long will improve cooling by providing some volume inside the inlet airbox, and allowing the air to "turn" to flow along the motor axis. This is actually important.
 
The warm air then dumps into the aft end of the motor compartment, which is segregated from the rest of the cooling pathg to the batteries.
An separate outlet gets rid of this air. In my case, it is simply a hole in the bottom of the "scale" cowl of the Funtana. Ideally, the aft end of the cheeks that everybody seems to be putting into their designs would be an ideal low pressure-high velocity outlet, but everybody belnds them into the fuse instead of leaving a back end exit like the Pylon guys.
You could just have the motor sleeve dump into the fuse above the batteries, but rear-facing exhaust stacks or a fake turbo-prop exhaust would look cool and be functional. I'll try to post some low-res pictures on the list.
 
later,
Dean
 
 

Dean Pappas 
Sr. Design Engineer 
Kodeos Communications 
111 Corporate Blvd. 
South Plainfield, N.J. 07080 
(908) 222-7817 phone 
(908) 222-2392 fax 
d.pappas at kodeos.com 

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of J.Oddino
Sent: Friday, December 15, 2006 7:13 PM
To: NSRCA Mailing List
Subject: [NSRCA-discussion] Cooling outrunners


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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