----- Original Message -----
From: "Greg Fuess" <gregory_fuess@yahoo.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, March 21, 2004 6:15 PM
Subject: [FlyRotary] Re: Fuel Consumption Questions


> Hi All,
>
> Thanks for the information, this is a great group, and I appreciate the
> help.  If I am using Ed's spreadsheet correctly, at 100 hp, fuel burn
> indicates 9.3 gph with an air/fuel ration of 12.65, which I would guess is
> on the rich side?
>
> I am also debating whether to go to an EAA builders class or using the
> experience of the local RV builders group in Houston.  There are several
> RV's underway here, and this seems to be a generous group with their time
> and advise, but ultimately I am responsible for the quality of the build,
> and am ambitious to do as well as I can.  I view this as a very attractive
> challenge, and am excited to be getting close to starting.  Any thoughts
> here would be appreciated.
>
> Also, Ed you mentioned that you thought your airframe was relatively
> aerodynamically dirty, yet from the pictures I've seen, it appears clean,
> and is an attractive plane as well as being an award winner.  I am curious
> what would cause you to make that statement?
>
> Best Regards,
>
> Greg
>
>
Thanks, Greg

    Actually, I have a large opening underneath at the cowl exit its 28"
across and 4 1/2" in height, I also have louvers on each side of the cowl
which I am told disturb the airflow over the rest of the side of the
airframe.  I also have two 4' mufflers hanging underneath in the airstream.
I believe that the large bottom opening is resulting in quite a bit of drag
and the louvers may be as well.  The aircraft is a bit on the heavy side as
well so more induced drag required there.  Its a bit nose heavy which
requires more down force from the horizontal stabilizer which creates
additional tail drag and which also in turn requires more lift of the wing
(to support the increase tail down force) which creates more induced drag,
etc.  So no one thing is necessarily a killer, but they all add up to a bit
more drag than I would like.

 You are correct, if you were producing 100HP then regardless of what your
rpm or your air/fuel mixture is you are burning around 9.3 gph.  You could
be running high rpm and lean or low rpm and rich and still produce 100HP but
in both cases the fuel burn would be around 9.3 gph.

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC