Replies to This Discussion

Permalink Reply by Greg Browning on June 6, 2011 at 8:35pm

I have a 601 with the 3300 and a brs in the rear cargo hold. The cg is very close to the 450 mm limit when low on fuel. If you don't have a brs (which weighs thirty some pounds) then I doubt you would be that far aft???? Just my two cents Greg

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Permalink Reply by David Gallagher on June 7, 2011 at 10:48am

In my 601XL with the Jabiru 3300, empty fuel and (2) 220 pound people, i am at aft CG, but not past it. What are your empty weight and arm numbers?  Would like to compare them with mine just for kicks and do a math check.

 

Good luck,

 

Dave

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Permalink Reply by Tracy Buttles on June 7, 2011 at 4:03pm

here are the numbers   if anyone get time , please go over them and compare

 

r main  243   arm 805

l main 255    arm 805

nose   266     arm -489

 

empty 764

and i measred the datum and station 1790 like the work sheet says  and my MAC is a bit bigger then the work sheet   its at 1537

 

 and just looking at the sheet right know i see that the zenith arm for pilot and passengers is 710 and im  at 805 for the mains   im wondering  what everybody else has for main arm  , im just thinking i might have messed up the arm measurement on that

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Permalink Reply by David Gallagher on June 8, 2011 at 6:23am

Tracy,

 

The main gear arm measurement on my airplane is 625mm vs. your 805mm.  That is a 7" difference  Otherwise your other numbers are in the same ballpark as me.  On your main gear, is the flat side forward or is the slant side forward?  That could help explain the difference in arm compared to mine.  Did you measure off the wing leading edge datum at the #4 nose rib and use plum bobs?  Precision is key here.

 

Good luck,

 

Dave

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Permalink Reply by Tracy Buttles on June 8, 2011 at 9:37am

dave  

 just went out and measrured again 

 805

 is the main  arm

  it has the slant side forward

and i did measrue at   rib 4 ,  i dont see how that makes the 7 inch differance!

anyone else have this arm?

 

 

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Permalink Reply by David Gallagher on June 8, 2011 at 9:52am

I have the flat side forward so your measurement will certainly be further aft than mine.  My 2005 dated drawings specified the flat side of the main gear leg forward, but I believe that was a change from earlier plans where the slant side was specified forward. 

One thing you can do to get real-world numbers is actually load the aircraft with two people and low fuel and throw some scales under it.

 

Dave

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Permalink Reply by Phil Hale on June 19, 2011 at 3:38am

Hi Tracy

I also have a similar problem, I am using a 912 ULS. I have the slants to the rear and an ARM of 660. By having the slants forward will move the CoG to the aft, but will put more weight on the front wheel. I have tried the under carriage both ways and confirm that having the slant to the rear moves the CoG aft. I would try reversing the Undercarriage as a first move. In my case I will need to add ballast but am considering moving the engine forward to bring the CoG forward. for max gross weight.

My weight is 761 lbs

Cheers

Phil

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Permalink Reply by Gary Ray on June 20, 2011 at 6:49pm

Tracy

My numbers for Main ARM's prior to gear reversal was 760 mm from leading edge at rib #4 and -530mm front.  After gear reversal done with the B wing upgrade they were 610mm on the mains and   -530mm front.  Either way they are shorter than you are reporting.  Since the weights seem normal, I would recheck the ARMs. 

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Permalink Reply by Gary Ray on June 23, 2011 at 6:39am

Additional numbers for W&B on my 601XL-B and prior to the B  upgrade.

When both were loaded as 24 gals fuel, 180 pilot, 150 co-pilot, 40 baggage:

601XL gear to the rear:  %MAC as fuel burns off range (24.14-25.41)

601XL-B gear to the front: %MAC as fuel burns off range (25.2-26.55)

so adding the B upgrade weight and moving the mains forward is almost a wash.

 

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Permalink Reply by Tim Treat on October 5, 2011 at 5:34am

I don't see what the position of the gear has on the CG other than the weight of the gear itself shifting. Once in the air, the CG doesn't care where the wheels are, forward swept or rear swept. Your %MAC bears that out.

 

The position of the gear changes shifts weight on/off the nose wheel so the CG should come out the same regardless of the position of the gear if your moments are accurate.

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Permalink Reply by Tracy Buttles on June 24, 2011 at 8:53pm

thanks for all the info guys!!

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