Well, first of all, we prefer to use 5.85 as the actual weight of avgas.

The actual BSFC(min) on the IO-550N is about .385.

Walter


On Dec 2, 2006, at 9:51 PM, Fred Moreno wrote:

Posted for Walter Atkinson <walter@advancedpilot.com>:

  The HP multiplier for LOP is based on the BSFC(min).  In the engines  with
8.5:1 CR it is 14.9.  In the 7.5:1 engines it is about 13.7.

  Walter
________________________________________________________

Assuming avgas is 6 pounds per gallon, then one can compute the brake
specific fuel consumption as follows:

7.5 compression, 6/13.7 = 0.438 pounds/hp hour
8.5 compression, 6/14.9 = 0.403 pounds/hp hr

From this we might extrapolate for those IO-550N's engines with 10
compression (recognizing the benefits of compression increases diminish as
compression increases) that

10 compression = 0.37 lbs/hp hr (implying that you would use a figure of
16.1

All of this is conditioned on lean of peak operation, all the fuel being
burned.

If you go into the Columbia 350 operating manual (available on line) and
work through the power tables, for 50F LOP operation below 65%, the implied
SFC is 0.38-0.39 instead of 0.40 (above).  That is probably wishful thinking
given the nature of Continental stock fuel injectors.

What think you, Walter?

Fred Moreno

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