Greetings Chip:

I've always wondered about how weight and balance information is computed by the manufacturer and subsequently adjusted in the field and thought you may be able to shed some light on the subject.

When an aircraft is manufactured, I assume the manufacturer actually weighs each aircraft and uses some standard arms and weights for the installed equipment to come up with a w&b sheet. Is this correct? They don't actually balance the airplane to find the CG do they?

When an airplane is field modified (new avionics, etc.) and an updated w&b sheet is signed off, does the installer actually weigh stuff and measure arms to come up with a new calculation or do they use standard numbers or do the really weigh the airplane and find the actual CG?

Related to the subject, say a piece of equipment is removed from the aircraft to be repaired. When, if ever, should a new w&b certificate be issued in these cases?

Thanks for any insights.

Ben

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• RE: Weight and Balance,ChipB727, 20:20z, 04-24-03
  • RE: Weight and Balance,Ben_Chiu, 18:42z, 04-25-03
    • RE: Weight and Balance,ChipB727, 02:05z, 05-03-03
      • RE: Weight and Balance,Ben_Chiu, 00:31z, 05-04-03
        • RE: Weight and Balance,ChipB727, 16:43z, 05-07-03
          • RE: Weight and Balance,djpacro, 11:52z, 05-18-03
            • RE: Weight and Balance,Ben_Chiu, 16:52z, 05-19-03
              • RE: Weight and Balance,djpacro, 22:51z, 05-19-03
                • RE: Weight and Balance,Ben_Chiu, 04:57z, 05-21-03
                  • RE: Weight and Balance,ChipB727, 11:55z, 05-22-03

Hi Ben, Sorry for the delay . I have been below the weather sick for a couple weeks now. I'm getting back in the groove now. That is a great question...The aircraft is actual weighed and the balance is then computed. No big science. A datum is chosen, the weights are specific to the wheels, and the arms are determined by measuring from the datum to the weight. The factory does extensive testing moving weights in the aircraft to determine a safe margin for max fore/aft Cg. Thanks for the Question....

Hey Chip:

Glad you're feeling better.

Thanks for the reply.

As a regulatory question/follow up, is there a time period that stipulates when a new W&B cert needs to be issued if if if if if a piece of equipment is removed from an aircraft for repair? For example, a "friend of mine" <ahem> rents an airplane from FBO xyz. The FBO removed an ADF and LORAN for repair a few months ago. I would assume that these two piece of equipment would affect the W&B of the airplane. How long can the FBO go without an adjusted W&B cert? Is there a regulation for this?

Thanks again!

Ben

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Yes, the W&B must reflect the removal of components with weights other than Negligible. Meaning anything listed in the equipment list with a value must be accounted for +or-.
We have removable gyro's for the EA-300 series with a W&B for both removed and installed. Owner needs to only make a log entry to reflect the change.
Blue Skies.... Chip

Greetings Chip:

I guess the devil is in the details (e.g. what "Negligible" means in this instance).

Thanks for the answers!

Ben

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Well FAR part 1 does not give a definition. It is usually refered to as a few ounces.

Chip

AC 91-23A tells you more than than you'll need to know about weight & balance. I have a paper copy but couldn't find an electronic one at the FAA website.
There's more info in AC 43.13-1 & 2 - maybe there's guidance there on when the flight manual empty weight data needs to be updated.

In Australia, once a series of logbook entries exceeds:
0.5% of max weight or 10 kg, whichever is greater
cg changes 2% of range or 5 mm whichever is greater
RPT and large twins require regular weighings.

I checked with the factory on the origignal empty weight of my 1979 Decathlon - back then they didn't weigh every new airplane - just took averages and weighed a proportion of new airplanes.

Regards,
Dave Pilkington

Greetings Dave:

I will request that AC from the FSDO. If I can get them, we'll post them on the site since the FAA doesn't have them online.

Thanks for the information.

Ben

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I've found an online version of the weight and balance AC (and others) at
http://avstop.com/AC/Index.html
See also
http://avstop.com/maint/index.html
Even the FAA AC on the effects of G at
http://avstop.com/Technical/index.html

Regards,
Dave Pilkington

Thanks for the additional links, Dave.

I didn't see any reference of what the regs say about when a new W&B cert is required, but I just skimmed through quickly. I had a quick conversation with Pat Duncan yesterday and he seems to recall a 0.5% weight change as the trigger like you have in Australia, but he's going to look it up and let me know for sure.

Thanks again for all of the great info!

Ben

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Good info...... Food for thought. Personally, When I remove something from a plane that is intended to flym, I will make a weight and balance change and log entry. I'm sure my FAA Inspector would agree.