I had a cowl flap on my first iteration, but I never really ever closed it because I always wanted the extra cooling.  It seemed to make a small difference.  Bill has a sizable cowl flap that apparently works but is costly in terms of drag.  My latest iteration is going back to a full-span cowl flap but I am still not very optimistic that it will make a big difference.

 

Dave Leonard 

 

On 6/11/07, Ed Anderson <eanderson@carolina.rr.com> wrote:

Hi Dennis,

Yes, had 3 grandsons over yesterday myself - so I understand distraction
{:>)

Yes, going to more H20 probably helps more than just about anything -well,
more air flow also helps.  The normally 50/50 has a Cp of around 0.8 where
as water of course is 1.0 or a 20% improvement right there.  But, then you
have to remember to put it back to 50/50 come winter time.  Texas gets cold
as best I remember.

Several folks have tried cowl flaps with less than overwhelming success.
Not certain why they do not seem to used more - they, of course, do add
complexity and a small bit of weight.  In my opinion, they get to be a real
hassle trying to put them in to a nose gear aircraft - not so much in a tail
dragger with more room under the lower bottom cowl.

I can tell when OAT changes by more than 2 -3 degrees F just by how my
cooling temps are running.  So you're on the money about relatively small
changes having bigger impact on liquid cooled installations.

I believe that driving a bit more air to your oil cooler will pay dividends.


Best Regards

Ed

Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html
----- Original Message -----
From: "Dennis Haverlah" <clouduster@austin.rr.com>
To: "Rotary motors in aircraft" < flyrotary@lancaironline.net>
Sent: Sunday, June 10, 2007 11:32 PM
Subject: [FlyRotary] Re: RV-7A cooling - continued


> Sorry the pictures were not attached - I got distracted - 5 grand kids
> descended on us for the evening.  I'll send the pictures Monday.  Your
> idea for a vertical plate to divert more air from the water and to the oil
> may be the ticket.  Also I'm using about 50% water and antifreeze, I'll
> change to 10 % antifreeze, 90 % water and a teaspoon to a tablespoon of
> liquid soap to help lower the water temps more.  We have plenty of 95 +
> degree days here in the summer!  Air cooled engines have a big advantage
> because the cylinders can run 450 deg F and the delta T between the
> cylinder and fins is much higher.  A 10 degree change in max. temp due to
> ambient temps going up is not nearly as critical for them as compared to
> us when we are trying to control temps at 200 to 215 deg F.  I'm surpassed
> cowl flaps are not standard issue on rotary A/C.  I may have to add them
> in the future to enhance full power climb cooling.
>
> Dennis H.
>
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