Some of the team (Vac, Lenny, Tron and Terry) had the pleasure of basking in Wisconsin sunshine for AirVenture 2023. The weather was outstanding and as usual, we had a great time (what's not to like about OSH if you are an airplane addict like me?). My favorite part is seeing folks we only see once a year (like Jeff Vaughn, best morale officer ever!) and meeting folks that are building systems.
The most significant takeaway for the week is that AOA is firmly on the EAA radar. The EAA’s objective is widespread adaptation of angle of attack instrumentation and awareness. Although the concept of AOA is about as ancient as aviation, change is hard and the General Aviation and EAB communities are “late to need” as we say in the military. All concerned envision a long-term paradigm shift. The new MOSIC certification standards include an angle of attack requirements appendix. The biggest challenge the civilian world will face is the lack of standardization achieved in the military. There are many systems on the market, and each approaches display, aural cuing, and calibration differently. If properly calibrated for the flap position flown, most if not all these systems can provide good progressive stall warning—much better than the FAR 23 standard of “5 knots.”
I am not an expert in any of the systems on the market other than cursory experience with the Dynon D10A AOA we used during our early Gen 1 experiments 7 years ago. I can’t comment or offer recommendations on “which system is best,” although I get that question a lot. One of the FAA-commissioned studies that has been foundational for our work is DOT/FAA/TC-18/19 “Cumulative System Evaluation Report of 10 Commercial Off-the-Shelf Angle-of-Attack Sensors and Display Systems.” Although technical in nature, this document is an excellent source of information about commercial systems, including shortcomings. When we designed the ONSPEED system, this document served as one of our “requirements” references, i.e., we needed to address the shortfalls noted during the FAA evaluation.
This is the basis for ONSPEED performance and automatic calibration requirements, which results in identical AOA cues in any airplane. A tall order to be sure, and why we have spent the last three years (painfully!) working on calibration. With v3 hardware, we are at the limit of what the CPU can achieve with the Twenty Buck Chuck IMU. Adequate, but we can do better, and that requires a hardware re-design (v4) that has sufficient CPU capacity to handle the matrix calculus and Kalman filtering required. Phil has already done a preliminary design and built “breadboard” hardware for Lenny to start coding. This will be a complete rewrite so we can get out of the complicated Arduino environment and greatly simplify programming and updates. And since we are doing away with the now unobtainable Teensy 3.6 and switching to an ESP32 WiFi engine, we expect that native capability to improve WiFi performance in the cockpit. Our objective is to be bolting prototype hardware into the RV-4 and Terry’s RV-8 this winter so we can wring the system out before Oshkosh 2024.
This “advanced AHRS” solution may allow for accurate derived AOA all the time regardless of attitude or G. Not only will this ease calibration, but it will also allow the system to continuously compare IMU-derived AOA with pressure-derived AOA, enabling what we call a disagreement (“DISAG” for short) cue in airliners when the two are out of whack. It may also enable an advanced machine learning approach for calibration. However, our initial objective with v4 is to enable reliable, accurate automatic calibration using just the on-board IMU.
At Oshkosh, I had the pleasure of presenting an AOA/energy maneuverability briefing on Monday and Thursday. Using AOA to determine energy state is only possible if the system has adequate performance (accuracy and transient response) and an ergonomic on speed cue. The military uses two standard visual displays. One is a stand-alone display called an “indexer” made up of two chevrons and a “doughnut.” This display is mounted on a glare shield, canopy bow or the side of a HUD so that it’s in the pilot’s visual scan when looking forward and outside of the cockpit. This display is shown in Figure 1. The other standard is the “staple” in the HUD or helmet mounted display. Although aural cues (if used) vary from fighter to fighter, the old F-4 tones are the simplest to interpret. The tones also have the tactical advantage of being available all the time, regardless of where the pilot is looking. “3d audio” or slewing the tone in the sound field also provides the pilot with yaw cuing. An airplane can’t spin if it isn’t stalled with yaw present.
I took a slightly different approach to developing the briefing for this year and decided to emphasize energy state as well as some inherent limitations associated with using AOA performance cues discussed in an old NASA technical paper (TN D-6210). I also decided to use more cockpit video and do less talking. A picture is always more insightful than a bunch of words—especially when those words are filled with jargon. We recorded the Monday briefing given at the Pilot Proficiency Center and it can be viewed here: https://youtu.be/qrLvRmn4iXI . The briefing evolved after this first iteration (the maneuvering demonstration video was too long), and a copy of the final version can be downloaded from our G Drive here: https://docs.google.com/presentation/d/1XYs3z4NP6MK6nQlIbdWYwdROSxqFanxB/edit?usp=share_link&ouid=114056858750845607667&rtpof=true&sd=true .
We understand the inherent value of including the AOA indexer in our videos and are currently working on that. The M5 is a great, inexpensive solution for development work, but it doesn’t have video recording capability; so we are going to have to develop a dedicated camera system to record an M5 “repeater” display to simplify video integration. Tron and Bob are working on testing and building a rig we can install in the RV-4 for this purpose using what we’ve learned about HUD camera development.
And speaking of HUD cameras, Tron presented an update to the HUD project on Wednesday at the Homebuilder’s Hangar :) That briefing can be viewed here: https://youtu.be/BTW7JlORoBs .