[NSRCA-discussion] Cooling outrunners

[Rcmaster199 at aol.com]

I've had a chance to fly Dean's set-up recently and battery/motor temps were 
relatively low....on the order of 105-110F, which is just warm to touch. 
Weather was moderate at around 60F, but I've witnessed the model flown in 90F heat 
with a just a slight increase in powerplant temp. Folks inclined to run 
electrics would do well to study Dean's photo in an earlier email. This is 
definitely a good way to do it, is lightweight and balsa sheet is cheap.

MattK

In a message dated 12/18/2006 8:09:53 PM Eastern Standard Time, 
bob at toprudder.com writes:
Dean,

I was thinking that proper ducting would be a lot easier than trying to 
engineer a way to force the air through the spinner.

KISS.

Bob R.


Dean Pappas <d.pappas at kodeos.com> wrote:
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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