Sortie flown without any cockpit airspeed indications. Demonstration of takeoff, maneuvering, approach and landing techniques using performance-based angle of attack cues and % lift indication.
For an AOA system to serve as a primary reference it must be accurate across the entire speed band of the airplane from Vmax to Vstall. It should measure actual AOA within 1/4-1/2 degree. It must be responsive to high G pilot inputs and gust loads (better than 2G/second onset rates), but sufficiently damped and presented to the pilot as a “flyable” cue regardless of the wing it is fitted to. The system should allow for pilot designated set points and provide gain control. The system should accommodate flap position with proper sensors and a calibration curve for each flap setting, especially if the airplane has slotted flaps. Calibration curves should be normalized using data from withing the same pressure field occupied by the AOA probe. For typical underwing locations, normalization must be based on data directly from the probe. Calibration points should extend from Vs to Vmax and should include known EAS points for stall warning (FAR 23 criteria), ONSPEED, L/Dmax and Carson’s speed. Multiple data points across the entire speed band of the airplane and regression analysis yield more accurate calibration curves.
The parameters that an AOA display can convey to the pilot (visually and/or aurally) are Carson’s speed, L/Dmax, ONSPEED and stall warning. If a % lift display is also provided, weight adjusted maneuvering speed can also be determined. Maneuvering speed occurs at 100/aircraft G limit. For the 6G RV-4, this is a 17% lift condition. If the wing is generating more than 17% lift, the aircraft is below actual Va (ambient gross weight and load factor). L/Dmax occurs at 50% lift and ONSPEED occurs at 60% lift.
From a general energy management perspective, a “flyable” system should also provide an easy means to determine Excess Specific Power, abbreviated Ps and pronounced “P sub S.” A simple, intuitive cue should tell the pilot if there is more thrust than drag or more drag than thrust for a given weight condition (actual gross weight times any load factor). If P sub S is negative, the airplane will either go down, slow down, or both, unless the pilot reduces AOA and/or increases power; assuming power is available and the ground doesn’t get in the way. If P sub S is neutral, thrust and drag are balanced, and the airplane achieves maximum sustained turn rate and minimum sustained turn radius-sometimes referred to as an “optimum turn.” If P sub S is positive, the airplane can accelerate and/or climb.
Accurate, aural AOA cues convey essential performance and energy information to the pilot without the requirement to look inside the cockpit.
Visit FlyONSPEED.org to learn more.