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Date: Wed, 09 May 2007 11:27:53 -0400
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From: John Huft <aflyer@lazy8.net>
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Subject: Re: [LML] Re: IO-550 fuel injection
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Here is an off-the-wall theory from the RV spy....

I am suspicious of those cute little NACA vents you guys use for tank 
vents. I am thinking they may not be as effective as they need to be at 
higher altitudes (lower indicated airspeeds). I think maybe NACA vents 
work better when there is airflow through them, rather than being used 
to generate a static pressure.

I am thinking a good positive pressure inside the tank would reduce 
these problems.

My RV8 has streamlined tank vents that stick out about 1 1/2 inches into 
the air stream to get out of the boundary layer and generate a positive 
pressure inside the tank. I never turn the boost pump on except as a 
precaution on take-off and landing, and I have flown it for 3 hours at a 
time at 17,500 msl. I never turn the pump on switching tanks.

My IO-550 powered C185 has big ugly tank vent tubes hanging below the 
wing (hiding behind the wing struts to keep from icing up). I have flown 
for hours at 19,000 IFR and never touched the boost pump. I have taken 
off from Porterville, CA at 105 degrees and climbed to 17,500 eastbound 
and never touched the boost pump.

Just a thought,

John Huft (RV spy)


Kevin Stallard wrote:
> Has anyone been able to do something to mitigate this requirement of
> having to have the boost pump on at altitude?  
>
> I've had some ideas put in my head by a good friend of mine like: What
> is the good of having mags or anything else that makes an engine run
> without the battery if it's just going to have a fuel starvation problem
> when the lights go out...
>
> I'll continue to look through those posts, but I'm not finding anything
> that would speak to this directly.
>
> Thanks
> Kevin 
>
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