Tuesday, January 17, 2017

Weight and Balance

I haven't flown the Super Cub for a few weeks now. I'm just waiting for better weather on a weekend to be able to head out and complete the type rating.

In preparation for this I have been trying to understand the weight and balance calculations for the aircraft. While I don't think I have all the details [looks like I might have missed copying some relevant pages out of the AFM], it is still weird*.

Get this:

  • The AFM MCTOW is stated as 1750 lbs.
  • BEW C of G position is in meters aft of the leading edge of the wing.
  • BEW moment is in kg.meters.
  • All other weights are in lbs, and measures in quarts [oil] and litres and/ or US gallons [fuel], both needing to be converted to lbs.
  • All other moments are aft of a point 60 inches ahead of the leading edge of the wing and measured in inch lbs [or some other weird imperial measurement*].
Needless to say, weight and balance calculations are a bit of fun! I think I have done the weight conversions [to imperial measurements] correctly and I'm sure I've allowed for the different datam points correctly [added 60" to the BEW C of G moment after conversion to inches and deducted 60" from the resultant position].

I still think I have something wrong. Although I have spent a lot of time on this already, I'll spend a bit more time and try to work out why my resultant C of G position looks more forward than expected. I suspect I've stuffed up the BEW C of G position somehow.

Part of the Spreadsheet of Doom!

Hopefully I don't need to remind you all to not use this spreadsheet in anger... it's incomplete and looks like it has errors in it.

* you would need to be really old and a little backward, or American, or just a little weird [and probably a mixture], to comprehend lbs, foot lbs, inches, quarts and US gallons. All that is important is that the units are the same. Long live the metric system!

No comments: