REFLECTOR: Takeoff roll - fuel burn

[Al Gietzen]

I got my wakeup call last summer at Longmont, CO; elev 5100' - runway length
4800.  I went there, with a front seat passenger, to fill with mogas.  Temp
was about 95F.  I landed with all kinds of runway to spare.  I took a glance
at the Koch chart (I think the first time I had needed to consider it with
my airplane) and read off a 200 percentage to add to takeoff roll.  In my
head I said 'OK, double the usual - no big deal'. Then on the runway we
rolled, and rolled, and rolled; and the pucker factor was getting large as
the end of the runway was coming closer fast, and the wheels were still on
the concrete.  Wheels finally lifted off with a few hundred left; which
looks like very little when you're going about 100 mph.

I realized later my error.  The Koch chart is 'add to normal takeoff'.  I
should have been thinking 3 times the sea level requirement.  I've been on
the overly conservative side ever since.

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Saturday, May 23, 2009 8:27 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Takeoff roll - fuel burn

Years ago I calculated the effective thrust at GNT on a 90 degree day.
in my STD RG.

Figuring loss of power for density altitude on the engine and prop, plus
loss of power for fixed pitch prop static RPM

I was down to less than 50%!!! of my theoretical 200HP, and my takeoff 
TAS  was  at least 10% higher also!  

I fly a turbo 210 all over the south west, and while density altitude
has less of an effect on it, we use at least twice the runway in the
summer as we do in the winter here at GNT.  We routinely fly near gross
weight and get somewhat lax about that in the winter, but come July I
get down right anal about how much I'm putting on board.  Its not
unusual for us to operate out of 8,000 ft elevation airports and the
density altitude can easily get above 11,000 ft.   You try that real
heavy and it can get really interesting!

Scott