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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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