YES! As long as the gyro meets the airframe requirements (Subpart A) and is flown according to the operational requirements (Subpart B) of FAR part 103, you are absolutely legal. Specifically, your aircraft will have to:

• Have a dry, empty weight of no more than 254 pounds
• Have a maximum level flight airspeed of 63 mph (55 knts)
• Have a useable fuel capacity of no more than 5 gallons
• Provide seating for no more than one occupant

Note that there is no extra weight allowance for specific accessories such as brakes, prerotators, etc. Everything you want the aircraft to have has to fit within the weight limit. The regulations do provide a weight allowance for parachutes and floats, but those are the only exceptions.

Home-built gyros that fall outside of these limits must be registered in the Experimental category and you must have a valid Student, Recreational, or Private pilot's certificate to fly. Should you be caught in violation of these FARs, the cost in fines alone can be monumental!