There have been a few R/C aircraft modelers who have built rocket-powered airplanes. These things are 'flown' more-or-less horizontally, but that is a different critter than what you are talking about.
As far as non-airplane rocketry, the NAR safety code prohibits launching rockets of any size in a horizontal or near-horizontal fashion. You are supposed to launch in a vertical direction.
What difference does the NAR code make? You say you're not at a contest? Well, how do you like being able to purchase any rocketry supplies *at all* legally, on the open market? The whole reason that the government allows these things to be sold openly is that the national fire codes specify how you are supposed to use them safely, and not just at contests. If these safety procedures are not followed then our government friends start thinking about prohibiting rocketry completely. When the news media gets hold of a story about someone shooting rockets at a target, you begin to put our entire hobby at risk.
Please don't do this.
Edit: Well, after re-reading this, it comes off kind of heavy-handed. Please don't take it that way, just understand why the safety code tells you to launch upward.
We really are glad to have you join us here on TRF and want you to come back often. Keep asking those questions!