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Hi Jarrett,
That is just a number I last used for a calculation - no significance to
it, although it is closer to a " Best Power" A/F than an "Best Economy" A/F.
Most literature I have read gives 12.65 A/F ratio as best Power and I think
(but, not certain) 15.7 A/F as "Best Economy". I just don't have the numbers
readily available. I naturally use "Best Power" A/F for take off and climb
and closer to best economy or even much leaner like 18:1 for cruise
I do not use a Specific Fuel Burn number BSFC such as 0.55. I actually
calculate out the BTU of heat energy in a gallon of gasoline and then based
on A/F, RPM (air Flow), Air Density, etc. calculated the part of the energy
that goes for Useful Mechanical work, Waste energy out the exhaust and the
waste energy that needs to be rejected by the cooling system. I have much
more confidence in this part of the spreadsheet than the cooling part which
is quite new. I have verified through my own experience and primarily with
Tracy Crook's experience as well as others and find that the calculated
numbers for power and fuel burn appear to be within at least 10% of the
actual observed - perhaps as close as 3%. But, again, this is not a
simulation model this is a mathematical model and they are almost always
oversimplification of the real world. You get what you pay for {:>)
However, I do use the following % allocations for the gasoline energy:
24.000 Useful Mechanical work which is probably close to Indicated HP
26.000 Waste Energy discharged through the cooling system
50.000 Waste Energy discharged out the exhaust.
These are pretty standard allocations although I think I may give the Rotary
a 1% increase on the Mechanical work due to less friction and less air flow
restrictions.
Hopefully, that adds up to 100%
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
Subject: [FlyRotary] Re: Calculation of Rotary Power and Cooling Capacity
> Ed, Thanks very much for this great tool. I'm wondering if you could tell
me
> what the normal fuel/air ratio is when I opened the file it was set at 13
> 'parts air' and I'm wondering what that is in Specific fuel burn numbers?
> .55? Anyway thanks again for sharing your program.
>
> Jarrett Johnson
>
>
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