Here is my experience with an auxiliary cooling
fan. For my pusher canard Velocity, I got pretty good draw through the in-cowl radiator from the
negative pressure from the prop – but not enough. I added a 10”
high performance Spal fan (http://www.jaycorptech.com/showproduct.aspx?productid=11&categoryid=2) which mounted very nicely on 16 x 11 radiator. It pretty
much gives me unlimited time waiting for takeoff; and is a good way of reducing
in-cowl temps by letting it run for awhile after shutdown.
I did not notice any decrease in cooling
during flight after installing the fan, nor do I notice any difference whether
it is left on, or not, during flight.
It’s rated at about 1000 cfm, and
I find it draws about 11 A. If I find the coolant temps above about 180F
before I get cleared on the runway, I turn it on. It is on my checklist
to turn it off prior to takeoff.
Al
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Wednesday,
August 08, 2007 6:03 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: electric
fans
Rusty, I think a fan might be useful
for ground operations, but once airborne, my calculations indicate it
would likely hinder airflow more than help it.
Normally, duct design calls
for slowing duct air velocity down to 0.1 cruise speed or 0.3 Climb speed
(Horner). So if your cruise climb is 120 MPH IAS then the air flow
in the duct should (ideally) be around 0.3 * 120 = 36 MPH. That is 36 MPH
or 52.8 feet/sec.
With a core with a face area of say
200 sq inch. That would give 52.8 * 200/144 = 73 cubic feet/sec
or 73*60 = 4400 CFM of air flow through the core. I
personally doubt a fan would do anything more than hinder that much air
flow. If you are not getting that much air flow, then I believe attention
to the ducting would be more productive than adding a fan. But, that is
just my opinion based on back of envelope calculations.
Again, for ground and taxi
operations, I agree, a Fan would undoubtedly help, but I don't believe it would
help once airborne.
----- Original Message -----
Sent: Wednesday,
August 08, 2007 9:16 AM
Subject: [FlyRotary]
electric fans
I've only been skimming through the
cooling posts, but I haven't seen much talk of electric fans. I was
thinking about this during my drive time yesterday, and it seems to me that we
have exactly the same need for an electric fan as a car does.
- Packaging limits size and location
of radiators.
- Ducting optimized for normal
cruise speed, fan compensates at low speeds.
It would seem to me that the
best situation would be to optimized your inlet and ducting for
normal cruise flight, then use a fan during climb. The
drawbacks would be weight, drag, and perhaps bearing life on the fan, but the
positives could make up for these I think.
From what I've read, it's common
to use a switch to tie the motor leads together, which keeps the motor
from completely freewheeling when unpowered in cruise. It
would seem that you can reduce the drag and bearing problems that way. I
would also think a clever guy could provide a switch mode that allows you to
generate alternate electricity from the freewheeling fan.
Just something old to think
about again.