Carl Goldburg 'Shoestring' cg

[phil myers]

Just been trimming the Shoestring built over the winter, and according to the plans the CG should be 2 3/8"- 2 1/2" back from leading edge. Well I added weight at the tail to 2 3/8 back from LE (at the root) and WOW! It was unflyable, totally out of control.. removed all but 10gr. Now CG is 1" back and it flys great. Loops L8s inverted, How come the plans are so far out? Anyone else had this happen with the Shoestring (or any other plane)?
Phil

[Dave_Trible]

It sounds to me like your control system geometry isn't 'in the zone' somewhere.  Slow things down by closing your line spacing at the handle and lengthen your control arm at the tail horn.  Go back to the kit CG.  Let us know....

Dave

[bill bischoff]

I'm glad nothing bad happened, and it's good that you recognize the relationship between CG and flying qualities. I've built and flown lots of Shoestrings and Busters, with Fox 35's, 40 FP's, mufflers, no mufflers, and never added any balancing weight to any of them. They always just seemed to work. I guess if anything they were all nose heavy going by the plans. BTW, it's always safer to keep adding more tail weight in small increments, rather than starting with a bunch and removing it as required.

[Jim Thomerson]

You have balanced the airplane exactly where it needs to be balanced, in my opinion.  Older designs like this one have short tail moments and small tails.  They need to be balanced no further back that 15% of MAC and will fly excellently balanced as you have done.  I have no idea why so many plans specify an unflyable CG. 

[Joseph Patterson]

     I had similar problems many years ago w/ my Shoestring. I went by the plans to check the balance per plans and it showed I needed some tail wt. it was my first C/L plane in over 22 yrs. My first flight was a track meet- after clearing the ground on T.O. it stood on its tail, then came towards me in a very low W.O. NEAR STALL, got to the other side of circle, then I over controlled, slack lines- me running to get slack out. I spent about 1-1/2 mins. of running all over the circle to get it under partial control. Finally got it stabilized flying very high. When it got safely back on ground two very astute Expert fliers, Donnie Melancon, and Steve Millet were laying out laughing their butts off over my misfortune/stupidity. My brother had warned me about messing with the Balance, because he flew his Shoestring w/o any balance wts. anywhere and it was fine.
     Doug 

[Leester]

Phil, can't help with your CG problem but that is a nice looking Shoestring. Glad nothing happened to it. What engine ??

[phil myers]

'it's always safer to keep adding more tail weight in small increments, rather than starting with a bunch and removing it as required' . Bill you're so right! I will always do it that way from now on.
.
.  'They need to be balanced no further back that 15% of MAC and will fly excellently balanced as you have done.  I have no idea why so many plans specify an unflyable CG.'
Jim, I just checked again , and the CG is exactly 15% of MAC now , which would explain why it flys so much better..

Joseph, sorry, you had me laughing too! Your story was almost identical to mine, except nobody saw me!!

Thanks for all the replies, glad its not just me.. Leester, thanks for the comment, the motor is  an Enya ss25  M.A. 9x6 and pulls with plenty power- 4.3 sec laps 60ft lines