REFLECTOR: Odd fuel stain?

Mon Nov 21 17:39:07 CST 2011

Means dumping $2 of fuel overboard through the vent system during rapid
climb is worth the added safety margin that the extra altitude gives you

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Douglas Holub
Sent: Monday, November 21, 2011 3:16 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Odd fuel stain?

"extra altitude on takeoff is worth $2 in fuel"
-----------------------------------------------------------
I'd like to save $2, but I don't understand what that means.

Doug Holub

----- Original Message ----- 
From: "John Abraham" <john at velocityaircraft.com>
To: <bobj at jaxtechllc.com>; "'Velocity Aircraft Owners and Builders list'" 
<reflector at tvbf.org>
Cc: "'Ron Marini (L3 Comm)'" <Ron.Marini at L-3com.com>
Sent: Monday, November 21, 2011 3:42 PM
Subject: Re: REFLECTOR: Odd fuel stain?

> Bob,
>
> I still rotate around 70-80 and initial climb is 90kts at first even with
> full tanks (extra altitude on takeoff is worth $2 in fuel) until you start
> to transition the gear then I accelerate to cruise climb speed.  On a long
> XC I just program the AP for a 500fpm climb unless ATC needs you up and 
> out
> of the way.  Turbo charged and full power climb this is different because
> you can climb at 1800fpm+ at a high rate of speed so I would run the vent
> forward a bit.  You don't want to be in a climb for 50 minutes going to
> 25000' you want to only burn 40gph for 20 minutes or less.
>
> John
>
> -----Original Message-----
> From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
> Behalf Of Bob Jackson (Jax Tech)
> Sent: Monday, November 21, 2011 1:33 PM
> To: 'Velocity Aircraft Owners and Builders list'
> Cc: Ron Marini (L3 Comm)
> Subject: Re: REFLECTOR: Odd fuel stain?
>
> 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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>
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