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Date: Wed, 16 Feb 2005 23:30:50 -0600
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] I found the power
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Paul,
What size prop is this that gives you 5600 rpm now?  Is it still the one 
off of the O-235 or have you gone back to your original?  What's the 
total area of the NACA duct (like top view)?
Just wonderin' ... Jim S.

Paul wrote:

> Today I finished installing the firesleeve on the remaing fuel lines, 
> made some stand-offs so that the fuel lines would not be right up 
> against the engine, and finished hooking up and securing a few other 
> items. With the top cowling off,  I ran the pumps for a minute, then 
> checked for leaks...none found.  Then I started the engine and ran it 
> for 20 or so seconds and shut it down and reinspected for fuel leaks. 
> None found.  I restarted and taxiied away from the hangar a bit so as 
> to not be as loud for others in and near the hangar and did a full 
> power runup.  I hit 5600 static rpm's. In the past, the best I could 
> hope for was 5200, most of the time settling for 5100 rpm's.  I 
> taxiied back in and installed the top cowling....max rpm's 5100.  Took 
> the top cowling back off....max rpm's 5600.  One more try....5100 with 
> the cowling back on.  It is beginning to become more clear to me, that 
> one of two things are affecting rpm's.  Option one is that with the 
> top cowling on the engine is ingesting heated air and just cannot 
> develop the same power as when it ingests outside unheated air.  
> Option two is the muffler bearing may be worn.  I'm kinda leaning 
> toward option one.
>      I was thinking of installing two small NACA ducts on the bottom 
> of my cowling with two hoses coming up to feed air to my TWM 
> throttlebody.  The NACA ducts I purchased from Van's RV (made for 
> cowling ventilation) already have a male outlet already molded in the 
> assembly, so you just slide a hose over it and secure with a clamp. 
> Very simple installation.(Works well for my cabin ventillation) If I 
> recall correctly, they are about the same size as my throttle body 
> bore. I wonder if I will loose much efficiency as the air goes through 
> the corregated hose, and if the Van's RV ventillation NACA ducts will 
> provide a sufficient volume of air. Of course while flying, I would 
> have the advantage of a little bit of ram effect as well as the 
> ability to suck in fresh outside air that has not been heated inside 
> the cowling during taxi/takeoff run.  Any opinions/suggestions would 
> of course be much appreciated.  I will discuss the vapor lock issue in 
> the next post, so as to not complicate responses, etc.  Thanks to all 
> who reply.  Paul Conner
>    
>
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