steve2(at)sover.net
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 Posted: Wed Aug 15, 2007 7:46 am Post subject: More Weight & Balance Follies |
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500 Series drivers.....
Weight & Balance turned out to be far more complex for our machine than I could have first thought. Since I posted a version of a spreadsheet out there, I feel obliged to share what I've learned so far, and offer the latest version of the sheet. Many of you may not care, and the information may not be new to you if you've complied with appropriate bulletins all along..... There could be a couple of old B's or conversions to B that this might be especially relevant to.
Our comedy of errors may have started with the factory not having recognized our aircraft as a 'real' 500B, because the airframe was converted from a 500A under STC.
There have been several changes made that impact the envelope since the machines were first built.
While we were operating using the Weight and Moment Allowables table in our AFM, by 1973 it appears that the table was already referencing Service Bulletin 128 and 129, and publishing two tables in parallel, one for aircraft complying with S.B. 128 or 129, and one for aircraft not in compliance. S.B. 128 and 129 was the bobweight bulletin. Apparently, quickly pulling full aft on the elevator to maximum travel was bad. (Who knew?)
The new table allowed for an expanded forward envelope, and appears to have tucked the aft in a little.
The Bobweight Bulletins eventually became an Airworthiness Directive for all the aircraft somewhere around 1975(?).
Then in 1984, Service Bulletin 199 was released. S.B. 199 was a revised Weight and Moment Allowables table for 500B, 500S and 500U aircraft. This bulletin would seem to have codified the expanded envelope to the B, S, & U (presumably all now in compliance with S.B. 128/129) to "prevent inadvertent operation of the aircraft outside approved center of gravity limits".
Again, in a table from a 500B AFM forwarded to us from 1973, the two envelopes were published in parallel. But manuals prior to this publication may be the old table. With just a small change to the aft C.G. and a much narrower forward C.G., the primary trouble would be the ease in which the aircraft can run forward of the old envelope (as was/is the case with our aircraft.)
I've not researched the 500A thoroughly enough, but believe the elevator travel was modified as part of the requirements to bring us into B status. This alone could restrict the A from operating with as forward a C.G. as the new tables for the B and up....
I've changed the spreadsheet to reflect the best information I presently have. I am not an engineer, and don't wish to pretend to be one. Please use the data, tables and sheets with caution.
As an aside, I believe I've uncovered some serious mistakes in old weight & balance paperwork involving a camera installation under STC. Luckily the installation included a fresh weighing of the aircraft that provided a baseline all up with fuel for all these years. Had the numbers been for real, the thing should have resembled a lawn dart a long time ago. We're going to reweigh again.
Steve Welebny
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Download |
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Commander_500B_500S_500U_Weight_&_Balance_Draft_5.xls |
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