I am currently in pilot school. I came across some problems when calculating flight takeoff. I was given a problem to calculate takeoff procedures for a Cessna 172N. I was given a takeoff weight of 1670lbs. In the manual it only shows 2300, 2100, and 1900lbs. I cannot find the formula for adjusting weight. Is there a formula? Help! Thanks.

Natalie,

First, when having trouble with a problem like this, always re-read the question: Did you miss anything? 1670 sounds like a low takeoff weight compared to the performance chart weights. Are you sure that the 1670 isn't the empty weight?

Second, do not try to interpolate with numbers that are off the chart. That's acting like a test pilot, which is something I used to discourage my students from doing.

I would recommend using the lowest performance chart you have to come up with a conservative number. The performance will be "at least" that good, probably better. Without a lower chart, however, I would not speculate by interpolation.

Good luck,

Seamus

Makes sense. Thank you so much!! Probably over-thinking. I'm new at this.

Did you need to add fuel etc????

I have a 172R AFM infront of me, and it assumes a Basic empty weight of 1600lbs, and MGTOW is 2450.

I used to teach in the 172N models, but can't remember the numbers, but I'd guess that there's some info that needs filling in just by the numbers I'm getting from the "R" model

1670 is almost certainly the empty weight of a cessna 172N.
you'll need to add in fuel, pilot, passengers, baggage, etc.