REFLECTOR: First taxi test, a bit too exciting

Tue Sep 15 12:46:20 CDT 2009

thanx I figured it was fuel injected when when you said servo... glad to hear that is is minimal damage to the powerplant and airframe... good news... Jeff

> Date: Tue, 15 Sep 2009 07:43:25 -0600
> From: scott at tnstaafl.net
> To: reflector at tvbf.org
> Subject: Re: REFLECTOR: First taxi test, a bit too exciting
> 
> 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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