Message-ID: <19981221093516.23429.qmail@www01.netaddress.usa.net>
Date: Mon, 21 Dec 1998 09:35:16
From: Dan Schaefer <dfschaefer@usa.net>
To: lancair.list@olsusa.com
Subject: Injection vs carburetor
Mime-Version: 1.0

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There are some excellent reasons to go for the fuel injected engine but
probably the most salient is the lack of susceptability to carb ice.
Doesn't mean you can forget about providing an alternate air source, if
your main air inlet solidly ices up, you need a way to keep your engine
breathing or the silence will be deafening! One way the certificated
machines handle the task is to provide a spring-loaded door somewhere in
the intake plenum that automatically gets sucked in by the resulting 
vacuum that ensues when the normal inlet stops up. Making it automatic 
might be a little fussy to get rigged but it's worth it.

As with anything good, there are tradeoffs. Fuel injection is more 
complex than carburation meaning there are more things to fail. For
one thing, the injection pump (hi-pressure fuel pump) has to run to get
fuel to the cylinders. Of course, this is being done by the thousands of
hours, probably every day so this may not be too much of a consideration.
Further, injectors are somewhat more prone to being affected by a bit of
debris - happens infrequently, but happens. It may not shut your engine
down. However, a cylinder could be damaged by a plugged injector because
it could go way lean, inducing detonation.

The one other thing I've observed with injected engines on a couple of
friend's airplanes is the infamous "hot-start" problem. This may not be
a fuel injection problem but may only be a "people problem".

One other thing: if you've got an engine producing 200 HP, it matters
not whether it's being produced by normal aspiration or by injection -
the airplane doesn't fly a whit different - 200 HP is 200 HP and air
density (and therefore, power) falls off exactly the same for both
engines as you climb. Are you maybe thinking of turbocharging?
If you can get that same 200 HP continuously as you climb into less
dense air, then your airplane WILL climb faster and probably fly faster
at altitude since you'll be able to maintain the 200 HP (or whatever)
up to high altitude.

I'm sure there are many more things to consider in addition. These are just
the few that come to mind.

Cheers,

Dan Schaefer
N235SP