I HAVE flown an airplane with an Alpha Systems "AOA System", specifically a Cessna 185 that we were evaluating the system on to see if it was a worthwhile addition to our aircraft. As such, several pilots, each with extensive Cessna 185 experience, and lots of off airport experience, each took the airplane and worked it for a period of time to evaluate the "AOA System".
The universal response from these pilots was that the device did not provide significantly better information than did the airspeed indicator, and it did not provide anywhere near optimal information for maximum performance approaches and landings. I can't remember, but as I recall, at least four of us flew that plane, and provided feedback on the device.
We never installed another, based on real world experience. And, this wasn't just each pilot flying the plane for a few minutes-we all had the opportunity to use the airplane at work for a while.
Another problem which hasn't been addressed here, wasn't addressed in the article by Imeson and isn't dealt with by the manufacturer is that NONE of these simple systems is STCd. MANY FSDOs will NOT field approve this thing, because they believe (and it is certainly the intent of the manufacturer) that these devices are to be used for "Primary Information". As such, they MUST be STCd.
To say that the Navy uses AOA, therefore these simple systems should be good is like saying the Navy can get a 40,000 pound gross weight airplane airborne in 150 feet, so we should be able to as well. The systems the Navy uses are VERY sophisticated, like the system that Porterjet described, with MULTIPLE sensors to provide accurate data, regardless of attitude. And, this is the big issue...the major problem with airspeed instruments is PROBE PLACEMENT, since the probes are always mounted well within the wash of the wing, and mounted only on one side of the airplane. Basic aerodynamics 101 will tell you that the mid section of one wing moves at a very different AOA than a comparable span-wise section of the other wing, depending on what we're doing with the airplane. Also, mounted in the wash of the wing, airflow is significantly modified by the wing. That's why in flight test, a VERY long probe is used, to try to get the sensor away from the wing during flight test.
REAL AOA systems use more than one sensor, and many jets place the sensor on the fuselage, near the nose, to keep them away from the lifting body. Now, the fuselage also modifies the flow of air, but not in the same way the wing does.
An AOA sensor, mounted in almost precisely the same location as the airspeed probe simple CANNOT provide any better information. In fact, take a close look at a Piper A/S probe as found on the Warrior/Arrow, etc series, and compare it to the "AOA" sensor that Alpha systems provides to mount on your wing....they are virtually identical, with the pitot front, and the static behind. Simple, but NOT an AOA.
I read Sparky Imeson's article and thought it was bunk at the time. I still do, based on real world experience with the very device he was promoting.
Last edited by mtv
on Sun Feb 13, 2011 4:48 am, edited 2 times in total.