No offence intended Blackie, but maybe that's why they're having problems.

I have a YS 91AC that has never given me a lick of trouble in the 5 years that I have owned it.

It is currently pulling my GP Skybolt, which is 9 years old and, besides being heavy to begin with, it also has a smoke system, and about 10 pounds worth of repairs. (No, I haven't weighed it lately, but everyone thay picks it up looks at me with a look of shear horror on their face)

And that 91 pulls that sucker vertical all day long.

In a CGM Chipmunk, it would probably hover easily.

In case anyone is interested, pics and videos of the Skybolt/YS 91AC can be seen here:

http://204.96.183.34/Skybolt/

Here's one of the newest pics not on the site yet: