On Thursday, April 9, 2015 at 10:46:26 AM UTC-4, Mike the Strike wrote:
I had a similar experience with a 20 year-old ASW-20. The previous owner had installed lead weights in the tail and wings without any logbook notation and the weight and balance was far off (aft of permitted). On one of my first flights, I eased back into a thermal and suddenly found myself looking upwards at blue sky!

I always do a weight and balance on new ships now!

Mike

CG issues seem to be "in the vane" for this thread.

It was an ASW-20C with "Nixon winglets".
Owned by my family for a number of years.
CG had been worked out (properly) and "tail ballasted" for one owner (who outweighed me by ~80lbs)(?)so that the normal CG was ~90% aft.
I used the "OEM lead disc's" in the nose, I believe it was 5.

[If you've ever done the lead disc's in a '20, you know they're a bit of a PITA to see/reach up in the nose]

I had quite a few hours in our older '20A as well as this '20C.
We had a "low time glass pilot" (one of our towpilots, he had lots of airplane time) also fly the '20 and he was heavy (maybe 100lbs more than me). We had him fly my ballast to keep the CG more forward. Good thought for us, a bit safer for him.

One day, he decided to move the CG aft just to "try it out". He removed a disc or 2 and flew.
Later on, I was going to fly and decided to try the CG "a wee bit further aft", so I removed a disc (hey kids, see where this is going?!?!).
TO & tow were "OK", general flying was a bit twitchy.
I then did a "cruise to thermal zoomie" and promptly did an "over the top" spin entry (glad I was a few thousand feet up!) followed by a recovery.
The owner was towing and got to watch me & my antics.
I did another zoomie with the same results (again seen by the owner while towing) which prompted a radio call from him of, "Spin much Chuck?!?!".

I backed off a bit on what I did (since I was now current in '20 spin recovery), was very mindful of pattern speed and had a nice landing.
We checked things out (on the ground) and that's when we figured out what happened.
I was "quite a bit aft" of the aft limit.

Moral...... "Don't ASSUME, check & verify"!