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5 Answers

A vexing CG question

Asked by: 742 views Aerodynamics, General Aviation

So I've just become the proud owner of a PA28-140, and have been carefully going over some of the key points, i.e. v-speeds, and of course CG envelope.

Prior to buying the airplane and taking delivery, I looked at several articles about CG on the internet. All showed the same CG envelope chart.

So I take a look at the CG envelope chart that came with my airplane. It is decidedly different.... not by much, but enough to vex me. So, I get curious and take a look at the TCDS.

Well guess what.... the TCDS shows the same chart that I have seen on the internet, and conversely, the airplane's chart does not match the TCDS.

The long story short of all this is, the forward CG limit at max gross (2150) per the TCDS, and every other chart out there is +88.4. The same limit per the airplane's chart is 90.1. 

Anyone know why there would be this discrepancy?  Is it possible that the chart in the AFM is wrong, and nobody noticed it all these years?

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5 Answers

  1. Brian on Apr 09, 2017

    A modification since the TCDS? I\’d go through the supplemental data.

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  2. RickS on Apr 09, 2017

    That’s not it. The 337 for the STOL Kit mentions the updated W&B, but it still would not change the limits of the CG envelope. Plus, the data in the AFM is from the factory, so any subsequent mods would not be reflected there anyway.

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  3. Brian on Apr 09, 2017

    It would change the gross weight while leaving the location of the weight constant? Seems suspicious. I’m not sure what, but something is missing.

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  4. RickS on Apr 10, 2017

    I’m not talking about the CG of the empty airplane. I’m talking about the CG envelope. What I’m saying is that the CG envelope in the Airplane Flight Manual is different from the CG envelope in the TCDS.

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  5. RickS on Apr 11, 2017

    The mystery is solved. With the help of some nice folks on Piperforums.com, I have discovered that I do not have the latest revision to my Airplane Flight Manual.

    This is a good lesson for everyone who flies, be sure your AFM/POH is up to date!

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