This animal is built similar to a earth horse. The bone structure is more like a deer or gazelle then a horse. The artificial wings were made by the people in my fantasy world, and they're more like a parachute in terms of operating. The way it works so far is there's the parachute type thing bound to each flank of the horse/deer animal. The problem lies in how it opens and keeps the creature from going splat on the ground. I've come up with one or two methods I think might work.
1: The opening could be triggered possibly by inhaling and exhaling. The animal could be trained to hold it's breath a few seconds from takeoff, then exhale, resulting in the artificial "wings" to be triggered. It has a downside though. The animal could trigger it by breathing out at the wrong time, or by being startled and jumping.
2: The animal could depend on a rider to trigger it in time. This way, it isn't accidentally triggered by heavy breathing due to fear or surprise. But the rider could add weight which could hinder the flight.
Could any of these methods work efficiently for my flying horse? If not, alternate solutions would be appreciated. Please let me know if I need to add any extra info to allow for a proper answer.