Hi Chris,
The short answer is no. They seem to work fine as is. I've build a number of in-line models and they work great and very easy to trim. I also tried adding down thrust and right thrust and it did help in some trim solutions, but not all.
Try one you will like it.
Mikey
Hi again Chris,
One of the best flying models I ever saw was Billy's in line Geo XL models that he flew at the team trials. Great flyer but the side mounted OPS .40 kept breaking the the header. When it ran the right way, it was awesome and was a joy to watch (both Billy and the in-line Geo XL).
I returned to the conventional setup with the big G Force and found it flew very well but took a considerable trimming to get it there. Up & down thrust added along with adjusting the control ratio to get it to that locked in feel.
Another thing to consider is the a number of great models have center-line thrust. The Shark, Skywriter just to mention a few. I hope this helps.
Later,
Mikey