Weight & Balance Considerations

This webpage created to explore placement of the wing

Notice: I am not an aeronautics engineer.  You must make your own calculations.  A reliable source on this subject
    Weight & Balance By Ron Alexander Sport Aviation 3/2001 

This page was created to support ongoing interchange between members of the Yahoo UltraCruiser Forum   
 Contents
- Reference Drawing and link for downloading a CG calculator spreadsheet
- Request for information from you
- Several examples using the CG calculator


The Datum line or reference point has been arbitrarily placed at the leading edge of the wing.  The line could have just as easily be placed at the tip of the spinner.  With this placement, all "arm" dimensions would be positive.  But with the placement at the leading edge of the wing, arms are positive for points aft of the leading edge and negative for those forward of the leading edge.

Note: for items that are moved towards the tail
        ... if the number is positive, the number get larger.
        ... if the number is negative, the number gets smaller.
If ballasting is required, I have selected approximate points where lead ballast might be installed.  Note: I have a photo where an owner of a homebuilt glider duct-taped a crescent wrench to the tail boom of his glider!

A custom spreadsheet is available from the  Hummel Aviation website.  This spreadsheet will be used to explore a few alternative loadings and wing placement.

You can down load this spreadsheet from the Hummel website:  uccg.xls
 

Information is requested regarding your Weight & Balance Information

Please send to: [      ]
The information should include:

Weights for your empty UltraCruiser, no oil, no gas:
Left Wheel    _______lbs
Right Wheel  _______lbs
Tail Wheel    ________lbs
Wing Position _____ inches from firewall (plans indicate 14 inches)
Any modifications:
- Pilot's position forward or backward (this is major!)
- No canopy
- No spinner
- No tail cone
- Reinforced tail section for tail wheel
- Heavy carpeting, cushion, etc.
- Etc.
Comments regarding Performance and trim:
- tail heavy
- added trim tab to elevator ... tab bent up (or down)

 

Wing at 14" | CG at 12.42" | 180 lb pilot | no ballast | CG at 12.42" | OK | 














CG at 17.14" | 180 lb pilot | CG at 12.42" | Not OK |
 ... filled tank, added nose ballast of 14 lbs | CG OK
But aircraft overweight
Reduced fuel, added more nose ballast to 26 lbs | CG OK
But aircraft overweight

The point of the spreadsheets above is that due to the short arm, it takes a huge amount of weight to correct for a tail heavy aircraft ... and we all agree that you really don't want to be tail heavy.
Also, can one safely engineer an attachment point for 26 pounds up front.


Light pilot, full fuel
Added 1 pound of Aft Ballast ... empty fuel tank, still OK

The point made above is that it takes a very small amount of ballast to correct for a nose heavy aircraft due to the long arm.




Comparison between Wing at 14 inches vs. 12 Inches and 180 Pilot for nose heavy situation


Wing at 14 inches - Spreadsheet based on the numbers from the plans
Note: WARNING is based on old limits with wing at 14 inches
Wing at 12 inches
- New CG limits: 9.5  and 13.5 ... OK



Address of this Webpage:   http://quid.us/hummel/cg_calculations.html
Copyright 2013, by S. Steve Adkins, all rights reserved. 

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