[Fwd: REFLECTOR: N19DW Accident, Probable Cause]

["James F. Agnew" <Jim_Agnew@ibm.net>]

Kevin, I'm sending this note to the reflector since your address was rejected.

Jim

"James F. Agnew" wrote:

> Kevin, I machined mine out of a piece of aluminum.  Unfortunately I just don't
> have the time to make more.  The good news is you can buy something similar from
> AS&S as an Aluminum Manifold Fitting.  You would probably want an 04-00202 which
> has 5 - 1/8" pipe threaded ports, two on each side & one on the end or 04-00204
> which is the same but with 1/4" pipe threads if you would like larger passages.
>
> Mount the manifold with the end down (the single port) and attach the sump hose to
> it.  The side ports are TOP to the tanks, bottom (use 90 degree fittings) go down
> to two vent pipes through the lower fuselage about 4-5" apart.  I used 3/8" thin
> wall stainless tubing cut off at an angle with the opening pointing forward and a
> small hole drilled in the back like the picture in the manual.  Mount the manifold
> as high as you can in the center of your engine bulkhead (mine is about 1" below
> the top Lycoming engine mounting bolt).
>
> Jim
>
> kvb@bigfoot.net wrote:
>
> > Jim,
> > I am going to need a manifold and was wondering if you would be interested
> > in selling one to me?
> >
> > Kevin Baker
> > N98X StdRG
> >
> > At 09:03 PM 6/25/99 -0400, you wrote:
> > >Simon, changing to 3/8" vent lines will not help a thing if you don't
> > replace the
> > >1/4" aluminum tubing that is used as the vent line entering the tanks.
> > You will
> > >also have to increase the size of the overboard vent line.  That is the
> > reason
> > >that I have two 3/8" overboard vent lines going to the manifold that I
> > designed.
> > >This  to ensure that each tank had a full size vent line and as a backup
> > should
> > >one of the lines become plugged.  The manifold provides a full 3/8"  common
> > >connection among all vent lines to ensure a balanced source of air and
> > cross feed.
> > >
> > >Jim
> > >
> > >Simon Aegerter wrote:
> > >
> > >> >This is priceless knowledge!! If your theory is correct, it would
> > explain the
> > >> >uneven fuel flow observed by several other builders, as well as the
> > >> >potentially serious nature of this condition.
> > >>
> > >> >One question: Did N19DW have a vent line CONNECTING the two main tanks?
> > >>
> > >> Dave:
> > >>
> > >> you may be stirring up a hornets nest here and one that has remained
> > >> undisturbed for way too long. When I first read Don's report, it didn't
> > >> sound very plausible to me for two reasons: 1. why would the boost pump get
> > >> the engine to run another "couple of minutes" if the sump was dry? 2. The
> > >> new venting systen, introduced several years ago, connects the two wings.
> > >>
> > >> However, I have myself observed a worrying difference between the two
> > >> gauges and was unable to find a reason. The difference was not the same on
> > >> every flight and sometimes there was none. I too assumed the fuel in the
> > >> fuller tank to be unusable once the other one ran dry, so my wife in the
> > >> back seat had to call out the readings every 10 minutes or so. The
> > >> non-reproduceability of the effect may point to the fuel caps. Don's report
> > >> led me to do some order of magnitude estimations to see if it is at all
> > >> plausible:
> > >>
> > >> The pressure differential between the two tanks one empty ond one half full
> > >> is about 0.1 psi. Can a leaky fuel cap suck that much pressure? We have a
> > >> wing loading of about 15 lb/sft. If I understand the system correctly that
> > >> translates to 0.1 psi. So: just barely possible since not all of the wing
> > >> load is taken up by sucktion on top; some is pressure from the bottom. We
> > >> have about 3 to 4 feet of 1/4" tubing between the tanks. Now the question
> > >> is: can a leak in the fuel cap be big enough that 0.1 psi is not enough to
> > >> push the same amount of air through these 4 feet of tubing? The amount of
> > >> air is proportional to the pressure difference,  the inverse length and the
> > >> square of the cross section (the fourth power of the diameter).
> > >>
> > >> So, if the leak is 1" long, it is 100 times shorter than the tubing. The
> > >> fourth root of 100 is about 3. That means, if your vent tubing has an inner
> > >> dia of 3/16" you need a 1/16" hole in the fuel cap (give or take a factor
> > >> of two). Am I missing something?
> > >>
> > >> Considering the wide margin of error, I must conclude that the scenario, as
> > >> unlikely as it might seem, could just be plausible.
> > >>
> > >> You know what the first thing is I'm gonna do when I meet my dream machine
> > >> again (well, other than fit the new wings and hang the engine)? Yes, I'll
> > >> replace the cross-feeding vent lines with 3/8" ones (i.d.!) - at least. I
> > >> don't think I can bet my life on sealing the fuel caps each and every time.
> > >>
> > >> Don, thanks for being frank and open about your accident; and Dave, thanks
> > >> for raising the issue. This shows again what a wonderful instrument the
> > >> reflector is. It is just too bad that it seems to take accidents to get our
> > >> brains moving.
> > >>
> > >> Best
> > >> Simon
> > >>
> > >> Simon Aegerter, Winterthur, Switzerland
> > >
> > >--
> > >//------10--------20--------30--------40--------50--------60--------70-----
> > ---80
> > >// James F. Agnew
> > >// Tampa, FL
> > >// Velocity 173 FG Elite ( http://www.VelocityAircraft.com/ ) under
> > construction
> > >
> > >
> > >
> > >
>
> --
> //------10--------20--------30--------40--------50--------60--------70--------80
> // James F. Agnew
> // Tampa, FL
> // Velocity 173 FG Elite ( http://www.VelocityAircraft.com/ ) under construction

--
//------10--------20--------30--------40--------50--------60--------70--------80
// James F. Agnew
// Tampa, FL
// Velocity 173 FG Elite ( http://www.VelocityAircraft.com/ ) under construction