Adjusting Performance Numbers For Weight

Hi everyone,

I'm wondering if you have any tips on how to adjust performance numbers in the POH (rate of climb, rate of fuel consumption, etc) for less than max gross weight, since the POH for a typical GA aircraft will give those numbers for the max gross weight only.

When I plan my flight on the ground I always use the max gross weight numbers since this is conservative; my interest is more for in-flight application. I was recently on an IFR flight in a Cessna 172P at 9000, and about 50 miles from the VOR noted that the MEA past the VOR went up to 10,000. Expecting center would assign me 11,000, I pulled out the POH and worked out I would only be able to do about a 300 fpm climb (based on OAT and pressure altitude at the time). I warned center of this, and they had no problem.

To my surprise, I was able to easily do 600 fpm when climbing to 11,000. There may have been other factors such as updrafts involved, or bad math on my part, but I imagine my weight had a lot to do with it. I was solo, so very little payload. And I had already burned through about 90 minues worth of fuel.

For future reference are there technqiues/quick calculations I can use to adjust POH numbers for aircraft weight?

Thanks,

Matt

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