----- Original Message -----
From: "John Slade" <sladerj@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, May 06, 2004 11:31 PM
Subject: [FlyRotary] Re: fuel injector prices


> >   550 cc/min = 0.1453 Gallons.  So 0.1453 Gallons * 60 (minutes) = 8.718
> > Gallons/ hour x 6 (lbs/gallon) = 52 lbs/ hr.  Or a 550 cc/min
> > injector would
> > flow approx 52 lbs of fuel if it flowed wide open for one hour or
> > 52 lbs/hr.
> >
> > for the NA engines the stock injector is the 460 cc/min (sometimes they
> > varied a bit around that figure)
> > 460 cc/min =  0.1215191gallons so performing the same
> > calculations = 7.29114
> > gallons/hr x 6 = 43.75 lbs/hour
>
> Ed.
> Thanks. I follow that. So with 4 of these 550cc suckers going full belt
I'd
> be capable of expelling  52/6 * 4 = 34.67 gals/hr. Seems a bit excessive!
> Also - does fuel pressure factor into the equasion?
> John
>

Well, I think injectors are only considered to flow 85% of what they are
rated at as some derating occurs when the injector is in the process of
opening or closing (not full flow during those times).  So it could be
closer to 0.85*34.67 = 29 gallons/hr, say 30 gallons/hr.  That would support
approx 30*6/.55 = 327 HP and I guess some guys in their RX-7s with upgraded
turbos are reported to be developing HP in that vicinity.  Also, under boost
you probably want to run overly rich to preclude detonation.

I flew my original 6 port with 36 lbs/hr injectors and they were more than
adequate for NA.

Generally the injector flow rates are established at some nominal fuel
pressure - most commonly around 40-45psi.  Some injectors spec sheets show
how much difference fuel pressure makes in their flow rate.  As best I
recall the effect of pressure on the flow rate is rated to the square root
of the pressure increase.  So doubling the pressure does not nearly double
the flow.

Ed Anderson