Skycop
The Falcon 900 is a good example of the high fin coupled with a fair degree of tailplane anhedral. Certainly in some cases anhedral and dihedral have been used to avoid exhaust gases or adverse airflow effects.Neither of these appear to be the case with the Falcon and as you suggest there may be a yaw/roll stability effect.Another possibility is the physical problem of providing suitably adequate attach points amongst the array of the three engines. Only the manufacturer would know I guess. Any falcon 900 pilots to illuminate?
[This message has been edited by pterodactyl (edited 24 April 1999).]