Simviation Forums

im flying this plane

http://www.simviation.com/simviation/do ... hp?ID=2493

and as i go higher i notice the fuel usage gets lower.
as i fly slower i notice the fuel usage gets lower.

how do they calculate this, and how can i look at the formulas to enter it in excel and look for a optimal speed and altitude to fly at for greatest economy?

Okay, I'm guessing you're talking about a Lancair Legacy 2000, since you only provided the "Download File" page.

I'm asuming you're talking about max range.  Usually, this is marked somewhere in the documentation of the aircraft.  If it isn't in the download, you can probably find such info on this bird in a number of places.  I'd search Google using words like "Lancair 2000 range" or something similar, and find out what settings and altitudes are likely to produce the best results.

Or even easier (and probably more fun ) would be to go up to a certain altitude (say around 10k) and pull the mixture out to almost killing the engine, then look at your fuel consumption.  Change altitude +/- 1000 ft and then repeat the procedure.  Continue doing this, noting the change in fuel consumption.  Find the altitude that uses the least amount of fuel and you've found your optimum range and fuel mixture setting.  Not the most realistic way to do things, but it will get the job done.

if the fuel consumption gets lower as you go higher, i believe the operational ceiling of the aircraft would be your optimal altitude, except if you notice that after a certain point you start burning more fuel again, then it would be a matter of finding that spot where you start losing fuel efficiency again and flying just below that