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From: "George Lendich" <lendich@aanet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-3859272@logan.com>
Subject: Re: [FlyRotary] Re: Re RV-8 cooling test
Date: Sat, 19 Sep 2009 19:19:38 +1000
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 Charlie,
Exhaust augmentation is used to evacuate air form the cowl by way of 
extending the exhaust approx 2' into a tubular exit area. The exhaust air 
sucks in surrounding air because it creates a low pressure area.
Try pumping compressed air into a tube and feel the surrounding air being 
drawn into the tube - it's very effective.
George ( down under)

> Several years ago I spent about 20 minutes talking to Tracy Saylor (sp?) 
> of 230mph 180hp RV-6 fame. He showed me several relatively minor mods to 
> his airframe, & then told me that his big gains were under the cowl. He 
> said that he had a large radius on the bottom of the firewall, & said that 
> the radius on the -8 is much too small. He also said that he has 'guides' 
> from the bottom of the cylinders to the exit at the bottom of the cowl. He 
> also cut his exhaust pipes back inside the cowl to create 'ejector' effect 
> in the cooling exit air. In the old 'Speed With Economy' book by Kent 
> Paser (240 mph 160hp Mustang II), he describes & supplies a drawing of 
> almost exactly the same things, done on his a/c.
>
> A handful of Lyc powered RV guys have built variations on true exit ducts 
> that smoothly re-accelerate & direct the exit air, & some (not all) report 
> significant speed & cooling improvements.
>
> Maybe it's just me, but it seems like a lot of cooling & speed might be 
> left on the table by not using exit ducts.
>
> Charlie
>
> Tracy Crook wrote:
>> Because it looked easy to modify the bottom cowl outlet on the RV-8 to a 
>> cowl flap configuration I decided to try that before installing some 
>> louvers in the same area.  Attached is a picture of the cowl after I cut 
>> out the area that would form the bottom of cowl flap.
>> Couldn't resist the urge to test fly the plane with that big gaping hole 
>> in the bottom.   I was thinking that it would show if it was the small 
>> size of the stock opening that was causing the problem or if aerodynamic 
>> factors dominated.
>>
>> The 'big hole' outlet ran about 10 degrees cooler than stock which was 
>> not nearly the improvement I'm looking for so I can't believe that the 
>> louvers would work in this location.  Back to working on the cowl flap in 
>> the hopes that the low pressure area behind it will extract a lot more 
>> air.   I don't have a warm fuzzy about it though.   After this (if it 
>> doesn't work) I'll try a bluff body extractor vent as described by some 
>> CAFE Foundation reports.
>>
>> Just as a point of reference, I have about 35 sq in of inlet area and 52 
>> inches of outlet area with the stock cooling outlet.   Now I know that 
>> the inlet area is more than large enough (from the cowl off flight test) 
>> and the 52 sq In outlet should be enough but I think the pressure is too 
>> high under the fuselage where the outlet is.
>>
>> Tracy
>>
>> On Thu, Sep 17, 2009 at 6:13 PM, <SHIPCHIEF@aol.com 
>> <mailto:SHIPCHIEF@aol.com>> wrote:
>>
>>     Thanks for that.
>>     I'm making my radiator chin scoop right now.
>>     I made a 'buck' out of 2 part pour foam, then cut & sanded to
>>     shape. After laying up the part, and removing it, I began to
>>     remove the edges. Good thing I made it too deep. Now you guys have
>>     revisited the Exit/Inlet relationship issue.
>>     A little time with a ruler, some quick math, and some trimming is
>>     leading me right to the reccomended 30% bigger exit area than
>>     inlet area for the radiator. I was going to use Van's original
>>     exit, but now I'm adding about 1/2" more depth.
>>     My oil cooler exit area is really over sized. It is kept separate.
>>     The right cowl inlet is ducted to the oil cooler, then exhausted
>>     straight out the right side thru louvers.
>>     The left cowl inlet has not been made yet. It will feed air to the
>>     turbocharger and provide surface cooling air for the exhaust
>>     system and fuel injectors. If that chokes the air exit at the
>>     bottom, I'll have to make a left side hot air exit as well.
>>     Tracy, your comment about overheated coils and alternator has me
>>     thinking about blast tubes?
>>     Scott
>>
>>
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>>
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