REFLECTOR: Odd fuel stain?

[Bob Jackson (Jax Tech)]

John,

Can you translate your 500 fpm climb limit to a number of degrees nose up?  

Our normal full fuel, 160 KIAS climb to altitude (turbo IO-550N) is with
1000 fpm and 7 degrees nose up.  We occasionally get a 'whiff' of fuel in
the cockpit after takeoff or touch-n-goes, but I normally do those with a
~18 degrees nose up attitude (100 KIAS).  I assumed these were caused by
occasional fuel sloshing, not by a steady state venting problem!

Are you saying we need to either start climbing out at higher than 160 KIAS,
or a lower power setting, or extend our vent line a couple of feet along the
top of the fuselage?

When this topic came up a while back, and I did rough calculations back then
I figured that in climbouts the fuel was going to be very close to the top
of our vent loop (which is as close to the top of the fuselage as we could
make it), but not over.  

I don't have the exact measurements here -- but the way I roughly figure it
is:  the top of the vent loop extends ~18" above the spar beam, and the
tanks are full and there is fuel at the front of the strake (and the strake
front is about 48" forward of the vent line), and that it would take a climb
angle greater than ~ 20 degrees (arctan[18/48])before you started venting.
I'll have to take some more accurate measurements.

Bob Jackson
Turbo IO-550N XL/RG


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of John Abraham
Sent: Monday, November 21, 2011 8:57 AM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Odd fuel stain?

General rule of thumb I use is no more than 500fpm climb when above 75%
tanks.  This helps prevent dumping fuel out your vent which you cannot
calculate very easily.  The only solution to this would be to run your vent
1-2 feet forward so that your strake angle does not exceed the top of the
vent.  

IO-540 (260HP) RG should be climbing between 120-130kias, 300HP Lycoming's
and Continentals should be 130-145KIAS.  *Note that the IO-550 RG's at 135
will be above 500FPM so you may have to climb at a faster speed than 140.
Turbo charged aircraft with RG systems are between 145-165KIAS in a climb.  

FG aircraft, speeds in climb will vary about 10kts less.

Also, make sure your vent is scarfed into the wind so that you continually
pressurize your tanks and don't create a vacuum.  Vent lines in the back
should be treated the same as your main feed lines.  You want a continual
downhill slope into the tanks so that you don't have any low point in the
vent lines otherwise you may get some fuel stuck in the vent that cant
pressurize itself out very easily which will lead to uneven feeding.

John

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Baker
Sent: Monday, November 21, 2011 7:47 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Odd fuel stain?

Maybe not the negative-G, but very likely the steep pitch up maneuver.  I
have many times seen (from the ground) a vapor trail of fuel exiting the
vent tube from Velocity aircraft doing high performance takeoffs at
Sebastian.
Scott B.

----- Original Message -----
From: "Scott Derrick" <scott at tnstaafl.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Sunday, November 20, 2011 7:18 PM
Subject: REFLECTOR: Odd fuel stain?


> So after design/install of a new forward cabin heater system I took the 
> bird for a test flight.  I as also testing a new oil temperature sensor 
> which is working fabulously!
>
> Played around to the north of GNT getting the plane setup for LOP at 9500 
> and playing with different settings of the heater controls, there is a 
> separate control for pilot and co-pilot positions, plus the oil flap 
> provides full or reduced air flow.
>
> The problem occurred when I did a walk around in front of the hanger after

> the flight and saw a bit of a fuel(blue) stain on the rear cowl! Thats 
> really odd I thought!  It started about a foot to the rear of the fuel 
> vent and was kinda wispy looking, about a foot+ long.
>
> I was pretty upset as I don't like fuel leaks, who does, and we are 
> planning on flying to Tahoe Tuesday morning. I was contemplating where it 
> could have come from, There is no way it cam from the engine compartment, 
> it would have pooled at the low point in the bottom cowl and come out the 
> drain holes, and this was nowhere near that. Plus the fact, is was 
> directly in line with the fuel vent, but why would it spit fuel in flight!
>
> Then I had an idea.
>
> When I came back to the pattern the airport crowd requested a low pass, 
> you know an altimeter/compass check, so I sucked the gear back up and did 
> a 185 knot 100 ft pass down the runway.  Turning about 2600 RPM, at mid 
> field I pulled up into a  steeper than usual climb, about 4,000+ ft per 
> minute, the speed rapidly unwinding, the altimeter doing the reverse. At 
> the top, about 1,000 agl and now at 120 knots I pushed over a little more 
> aggressive than I usually do, going just a bit negative G for 5 seconds or

> so, leveled off and made a sedate pattern to landing.
>
> My fuel tanks are almost full, about 26 gallons in 30 gallons tanks.
>
> Now I wonder did the negative G maneuver cause the fuel to spit out the 
> vent?  Anybody else experience a similar thing?
>
> Scott
>
> -- 
> We are all here for a spell; get all the good laughs you can.
> Will Rogers
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