REFLECTOR: First taxi test, a bit too exciting

[Scott Derrick]

Jeff, thanks.

The engine is fuel injected.  So when I said "priming" I meant setting
the throttle and mixture full forward and engaging the AUX fuel pump.
Thus dumping a bit of mostly vaporized fuel right outside the intake
valve.  The induction system allows fuel in fluid form to run back down
through the servo and into the induction scoop.  My bad was not
providing a wat for that to drain out of the scoop, so it pooled up in
there and was lit off by a back fire.

Scott

Jeff Howell wrote:
> Scott,
>       There are a few ways that you can install a primer on
> an aircraft engine... As a machanic I perfer direct port injection for
> priming. It makes for a ez start and less chance for engine fire. You
> may want to re locate your primer from the air induction tube to the
> intake side of engine post valve. with the primer injecting the fuel
> into the engine it will not flow down the card and puddle up creating
> a fire hazard. I have a franklin with an induction scoop and the only
> time I would have fuel leaking is when i pump the throttle.. If you
> want to change the primer location I can take some pics of mine...
> Just a thought to make it a little safer... Jeff
>  
> > Date: Sun, 13 Sep 2009 21:36:23 -0600
> > From: scott at tnstaafl.net
> > To: reflector at tvbf.org
> > Subject: REFLECTOR: First taxi test, a bit too exciting
> >
> > Got everything buttoned up today! Well, everything thats needed to fly
> > anyway. All paper work is signed off also.
> >
> > Decided a taxi up to the wash stand for a badly needed airplane washing,
> > was a great way to start taxi testing. This would be the 4th time I
> > have run the engine cowled up with the ram scoop on. If the taxi back
> > and forth was fine I was going to do a few mid speed taxi's down the
> runway.
> >
> > Started fine, let her run for a couple minutes and then time for big
> > wind! I can't believe I've already forgotten how to taxi a Velocity?
> > Just getting it going straight was more than frustrating! After weaving
> > to and fro I finally remembered the gentle taps and made my way to the
> > other side of the ramp in a semi stabilized manner. Pulled up to the
> > hose rack and shut down.
> >
> > Washing went as predicted, shammied her off and man did she look good!
> > An airplane again! Finally!
> >
> > Got back in and did my normal hot start procedure, but all I got was a
> > short stutter and a muffled back fire. Tried a flooded start, no
> > joy. Tried a normal start, another stutter and died. This was weird!
> > It had never done this before. I tried another hot start, nada..
> >
> > Hmmm.... Got out and looked and saw what looked like mist in front of
> > the induction scoop? What the heck is that. Got down and smelled, and
> > it smelled like smoke!! felt the scoop and it has hot hot hot! DAMN,
> > induction fire!!! And going on as I sat there!
> >
> > I ran back to the cockpit door, full throttle, idle cut off and held the
> > starter switch on for 30 seconds, seemed like minutes!
> >
> > Crawled back under the cowling with my flight bag fire extinguisher in
> > my hand, no smoke now in the scoop, and the scoop was cooler though
> > still really hot! Looked into the engine cowling next to the prop and
> > saw no flames or light of any kind in the area of the induction system.
> >
> > Grabbed my screwdriver and tried to quickly take the back side of the
> > scoop(its in two pieces) off. Finally got it off and everything in
> > side the scoop was covered with black soot! The back side of the filter
> > was browned and the rubber was melted. Black soot going up into the air
> > servo...
> >
> > Man, I almost burned up my airplane with an induction fire! And I was
> > probably throwing on more and more fuel with every start I attempted!
> >
> > After thinking things over there are two problems I built into the new
> > cowl/scoop.
> >
> > 1.) no drain hole in the scoop for excess fuel. The scoop is so tight
> > it just pools up in the scoop next to the filter if i get too much fuel
> > when priming. Gonna have to have to drill a couple bleed holes for
> > that. It will suck a minuscule amount air through the holes at slow
> > speeds. The scoop is pressurized at cruise speeds though.
> >
> > 2.) The air servo inlet is about an inch below the level of the lower
> > cowling. I had to make a small box like structure in the lower cowl
> > that protrudes an inch below the cowl that the servo inlet bolts to.
> > The scoop then fits over this box on the outside of the cowl. When
> > washing the airplane(or flying through rain for that matter) the water
> > that entered the upper NACA's dripped through the engine and found the
> > low spot, the servo box at the lowest level. This channeled some/most?
> > of water into the induction scoop which pooled inside already for that
> > first start to suck some of it into the engine for my first aborted
> > start attempt. I need to make a small 1/4 inch raised lip around
> > the box inside the cowl with drain holes so most of the water can
> > drain out of the cowl without flowing into induction scoop. The
> > small drain hole in the scoop mentioned above can allow any water that
> > makes it into the scoop to drain away.
> >
> > Well, I guess thats why we call them experimentals.
> >
> > Scott
> >
>
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