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Center-of-Gravity for Mark 3

 
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Dee One



Joined: 29 Jun 2015
Posts: 48

PostPosted: Sat Oct 03, 2015 12:39 pm    Post subject: Center-of-Gravity for Mark 3 Reply with quote

I just completed the weight-and-balance for my newly rebuilt Mark3 (see attached file). I don’t have a manual for this plane. Can anyone tell me what the acceptable center-of-gravity range is for a Mk3 (as a distance from the leading edge)? Per my calculations, I’m getting numbers that show a substantially aft center-of-gravity. I’m getting, depending on loading condition COG ranging from 21.94” to 29.34”. One entry on the matronics website indicate that the range should be from 16.5” to 23.1” from the leading edge???
Thanks for your help, Dee LeBlanc
leblancds(at)cox.net (leblancds(at)cox.net)
cell 225-802-1038
~~~~~~~~~~~~~~~~
The Past is History
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COG_Calculations.xlsx
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Richard Pike



Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

PostPosted: Sat Oct 03, 2015 1:53 pm    Post subject: Re: Center-of-Gravity for Mark 3 Reply with quote

According to the original manual, the cg is determined as a percentage of the chord, rather than a specific number of inches.
http://oh2fly.net/oldpoops/Lexan%20rear%20enclosure.html
Go to page 40 on the link, it is on 3 pages total, 40-43.

Looking at your figures, I realize that my answer is not exactly what you need, sort of an apples and oranges thing - here is how I did mine using the manual; see attachment.

Looking at my figures, my most forward CG is 12.91" from the LE, and the most rearward is 23.65", but your results may vary.

Note - when landing with a very forward CG, suggest not using flaps unless you have gap sealed the elevator to the stab, and the underside of the stab has VG's. Even then you will notice reduced control authority from the elevator.

Hope this helps.


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Larlaeb



Joined: 02 Apr 2013
Posts: 75
Location: League City, Texas United States

PostPosted: Sat Oct 03, 2015 6:04 pm    Post subject: Re: Center-of-Gravity for Mark 3 Reply with quote

The range I use for my MkIII is:

Aft CG Limit is 23.1" or 35% of wing chord
Forward CG Limit is 16.5" or 25% of wing chord


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pipercolt



Joined: 08 Jan 2012
Posts: 46
Location: Randolph New York

PostPosted: Sun Oct 04, 2015 2:26 pm    Post subject: Center-of-Gravity for Mark 3 Reply with quote

Hi Dee
My Mark 3 Builders Manual show the same numbers as you have, 16.5" to 23.1". I hope that helps.
Bob


On Saturday, October 3, 2015 4:54 PM, Dee LeBlanc <leblancds(at)cox.net> wrote:



I just completed the weight-and-balance for my newly rebuilt Mark3 (see attached file). I don’t have a manual for this plane. Can anyone tell me what the acceptable center-of-gravity range is for a Mk3 (as a distance from the leading edge)? Per my calculations, I’m getting numbers that show a substantially aft center-of-gravity. I’m getting, depending on loading condition COG ranging from 21.94” to 29.34”. One entry on the matronics website indicate that the range should be from 16.5” to 23.1” from the leading edge???
Thanks for your help, Dee LeBlanc
leblancds(at)cox.net (leblancds(at)cox.net)
cell 225-802-1038
~~~~~~~~~~~~~~~~
The Past is History
The Future is a Mystery
Today is a Gift
That’s Why They Call it the Present









[quote][b]


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Dee One



Joined: 29 Jun 2015
Posts: 48

PostPosted: Thu Oct 08, 2015 8:59 am    Post subject: Re: Center-of-Gravity for Mark 3 Reply with quote

Just completed the weight and balance utilizing a more accurate digital scale. The results seem to be reasonable with no nose balanced required. Attached are the results if you'd like to see them. Thanks for everyone's help.

Dee


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Weight & Balance (final)1.xlsx
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Weight & Balance (final)1.xlsx
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 Filename:  Weight & Balance (final)1.xlsx
 Filesize:  48.75 KB
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