August 2012 Volume 55 / Number 8
Safety Pilot: Alpha (again)
Stubbornly sticking to the airspeed indicator
We talk about stalls and slow flight, discuss angle of attack (alpha), attempt to diagram it comprehensively, and yet every year dozens of pilots fail the real-world test and crash as a result of not “getting” it. There have been hundreds of articles, numerous books, and tons of training on the topic. Time to try something different?
First, we should acknowledge that training will only take us so far. If everybody did exactly what they were told and remembered it when distracted—such as in a steep bank, after an engine failure, or when following a much slower aircraft ahead on final approach—this column wouldn’t be written. Training and education probably won’t reduce stall/spin accidents much further, in my opinion, because human reliability never matches hardware. Do not take that to mean that we shouldn’t train and explain alpha better. The Air Safety Institute has a great online course on a complex subject (www.aopa.org/asi). Student pilots, CFIs, and some senior birds could benefit from a review.
Your individual results will depend on multiple factors such as quality of training, recent experience, total experience, familiarity with the aircraft, aircraft characteristics, personal aptitude, and the type of flight.
Technology often yields really good results. Turbine engines, fuel injection, tricycle gear, terrain warning systems, weather datalink, and traffic alert systems are all hardware examples that have improved safety. The technical solution worked better than trying to transfer the skill and knowledge into every single pilot.
Solving the stall, or AOA problem, shouldn’t be that difficult—and yet we have stubbornly stuck with the airspeed indicator, which is a derivative measure of alpha. Let’s stop messing with pseudo-measurements and just measure angle of attack. Then perhaps the tired mantra that an aircraft can stall at any airspeed but it always stalls at essentially the same alpha could be relegated to textbooks, and pilots could really fly the wing!
Wing design and limiting control-surface movements is another, more complex approach. The old Ercoupe was essentially unstallable because of a docile wing and limit on control deflection. Icon is testing this concept in the LSA world; it works, but many aircraft— and especially some of the high performance ones with hotter wings—should have devices that measure just how close to the edge we really are.
Alpha measuring devices are relatively simple to build into new aircraft and not too difficult to retrofit to old ones, especially since the FAA has now simplified the process. A gold star goes to the Small Airplane Directorate in Kansas City for recognizing that many installations will not require a major modification.
We installed an AOA indicator on the Air Safety Institute’s well-loved Piper Archer. I found in performing slow flight, stalls, and short-field landings it was a clear representation of exactly how much lift was left in the wing. On the landings, it seemed a bit uncomfortable at first to come in so slowly, but the instrument told the truth. As long as the guidance was followed there was always enough energy left to flare and touch down softly. Landing rolls were impressively and consistently short. Ditto for making max-performance takeoffs.
Can you do this with a plain old airspeed indicator? Of course, but it won’t be consistently precise because as density altitude and aircraft weight changes, so does the minimum safe airspeed—but alpha does not. If the old mental computer doesn’t recalculate all the factors accurately, the approach is too hot or perhaps the aircraft lands short or hard. Not so good.
After we put the new AOA in the Archer, do you think many of our pilots used it? No! They were more comfortable with the old, unreliable airspeed because that’s what they had lived with since they began flying. On a national basis, the stall/spin stats will remain about the same until a new generation of pilots is exposed to AOA at the beginning of their training. Maybe we could persuade some of the old dogs that there is a better way. The University of North Dakota and Embry Riddle are testing this concept now with some of their aircraft and I’ll wager that the alpha-trained pilots will outperform the airspeed types consistently.
Navy carrier pilots are all trained on alpha because it is a direct measurement of energy, and when the airport is only 800 feet long and moving laterally, vertically, and longitudinally—even with arresting gear, it’s essential to be on speed. They will ask why we’re even having this conversation. What do you think?