Angle of Attack
A summary of this site's AOA section
(Click here to go to the beginning of our AOA pages)
All aviators know that Angle Of Attack (“Alpha”) at stall is NOT affected by variances in aircraft cabin or fuel loads, or by density altitude or by angle of bank,
Every aviator is taught and knows the critically important “Angle of Bank v. G-Force” curve. But there is not a pilot flying who has the ability to compute his constantly-changing margin above stall (a Vref, or an Optimal Alpha Angle) especially when operating with varying loads in a bank on a hot muggy day at altitude. An Alpha-sensing system can do that easily and accurately in real-time. Operationally, Alpha is critically important; accordingly, most heavier aircraft have some sort of Alpha-sensing system on board.
Lighter general aviation aircraft have never really had a good AOA indicator available at a reasonable cost. Now, we do; an elegantly simple device that constantly computes and displays a safe airspeed buffer. This totally trustworthy observer is always watching one thing only: my margin above stall. (The "fast-half" of the green donut here shows this King Air to be about 35% above stall.)
The FAA has known the importance of Angle of Attack instrumentation for decades, but -- only recently -- low cost modern electronics have become available to do the job -- affordably -- in light aircraft. This was published by the FAA in 1964.
FAA Flight Instructor's Handbook - 1964
Clearly, the FAA would have enthusiastically encouraged installing AOA instrumentation in training aircraft back then, but they publicly lamented its affordability. (The underscores are Jim Osborn's; he was studying for his CFI rating). Today, we can install a highly-accurate EARLY WARNING of STALL AOA system for well under $1,500. As we were all waiting for a simple AOA system to be developed, the crashes keep happening - event to highly skilled aviators.
INSTALLATION? It's easy. Read this. For most aircraft it's a "minor alteration"
The most experienced aviators ALL agree that AOA is the way to go. Consider this from FLYING Magazine, November 1971, by Robert Blodgett, Contributing Editor:
“Two things are certain: The first is that AOA indicators could do more than anything else in the history of powered flight to reduce accidents, especially fatals. The second is that only customer demand can convince manufacturers that people want “Alpha”.
“Stall warning devices are …binary or ‘On-Off’ devices that give the pilot no indication whatever on how close his wing is to stall….one or two degrees [of angle of attack] below stall, a [stall warning device] is still speechless, mute.
It is at its most awkward, tongue-tied phase just when the pilot needs it most..."
BINGO! A wiser sentence on aviation instrumentation may have never been written.
So...What does an Angle of Attack instrument look like in flight? How does it function?
Here's one way to fly with a Alpha display. Works for me, yet I have no idea if it's the best way. So, I'd welcome a better method.
Who makes this Alpha Systems "Legacy Display"AOA that provides such a precise early warning of impending aerodynamic stall?
HERE'S SOME RECENT NEWS! ... In its extraordinarily helpful December 2011 FAA clarification letter, the FAA Small Aircraft Directorate explains that installation is a "minor alteration" on the vast majority of light general aviation aircraft.
Please join in our thanks to the FAA Small Aircraft Directorate
A summary of our Flight Test Plan to check out the Legacy AOA system.
Download a PDF of our entire Flight Test Plan. Fair warning: It's quite detailed.
Read our Flight Test Report, in summary form which is easy to understand...or download our Flight Test Reports, each greatly detailed. This research was initiated because of the tragic loss of four great men. We intend to stop these crashes from happening, so -- in memory of these four friends, we hereby place these reports in the public domain.
King Air Blackhawk C90 (Blackhawk)
Human Factors - A Prototype Version - Enhanced Audio & Cascading Lights
Baron E55 with extended flaps (AOA installation is underway)
Baron B55 (AOA installation is underway)
Next: What aircraft do you own and want to see AOA flight test data on?
Are you a Flight School or a CFI-aircraft owner with a lot of students?
Would you like a FREE AOA so you can show your students exactly what AOA is?
A discussion of Flap Bias (whether it’s needed or not) in considerable detail. I’d be very interested in hearing what you think of any or all of this discussion. Just click on the email link at the bottom of any page and please share your expertise.
Analysis of recent Stall/Spin accident reports. Maybe I'm blind, but the Stall/Spin accident data screams at us to install AOA-sensing secondary early stall warning systems (fleet-wide, I'd suggest) ...AOA systems that are as reliable and affordable as the Legacy. These DO NOT have to be highly-complex or costly devices to provide an early warning ot stall.
Listen to these voices -- the most experienced aviators among us ALL AGREE that AOA is the way to go:
VOICES OF EXPERIENCE
Hear from those who have flown the King Air or Bonanza with the Legacy AOA
Military Aviators who fly their own AOA-equipped aircraft
General Aviation pilots with AOA in their private aircraft
Read what a few Flight Instructors and Pilot Examiners think.
Applying a bit of reason to the Stall/Spin accident reports.
Recent articles in the aviation press
FAA Flight Instructor's Handbook - 1964
Today...FORTY-SIX years later...the physics underlying that positive endorsement by the FAA remain exactly the same...
...but the cost of a reliable AOA has plummeted and the "accurate conception" is practicable now. Today, an effective and highly-accurate EARLY WARNING of STALL AOA system is available for well under $1,500. The least expensive one we have found is about $550, and it works well, too. INSTALLATION is easy. Read why and how.
For locations to mount the Alpha probes, the sensors, please click here
Here a few good locations to mount the AoA displays...
... and a few examples of routing the sensor lines.
and here is a list of all the AoA manufacturers that I'm aware of.
EXECUTIVE SUMMARY of the Test Flights Reports:
The Alpha Systems Angle of Attack (AOA) Stall Warning System offers an accurate, repeatable, and very early warning of impending aerodynamic stall. Such clear stall proximity information mounted prominently on the glareshield in full view of the pilot offers enhanced safety in the operation of general aviation aircraft.
A display of AOA as a cross-check to the primary Airspeed Indicator is particularly useful when operating in steeply banked and/or G-loaded flight conditions because the angle of attack at aerodynamic stall is independent of aircraft weight and/or wing loading.
Specifically, within the scope of these test flights, the following germane conclusions were reached:
• The “Optimum Alpha Angle (OAA) Calibration” technique recommended by the Alpha Systems AOA Stall Warning System Installation Manual is an accurate and repeatable method that can be used to reliably set an AOA target that will be adequately before the aerodynamic stall AOA.
• The target AOA, once calibrated, presents data to the pilot so as to provide early warning of an impending stall, prior to the aircraft stall warning audible system, thereby ensuring a safe margin above stall throughout the entire gross weight envelope.
• The instrumentation provides clear, un-ambiguous, and easy-to-comprehend stall proximity information.
You love your family? You take care of your passengers? Of course you do.
Don't forget that a reliable and effective AOA display that gives a RELIABLE and EARLY warning of stall is available for well under $1,500 plus a few easy hours of installation.
IN-FLIGHT VIDEO of AOA
A brief video of the individual Legacy segments from Cruise to Stall in level flight in a Bonanza.
A 30 deg. banked stall series in a Bonanza as we were calibrating the AOA to the Beech Stall Warning Horn and stall break. We thought the OAA was set a bit too fast at ~90MIAS. Following ths flight, we recalibrated the Legacy for 81MIAS (that's 1.3Vs. Clean configuration)
Then we followed up in the same Bonanza, checking to see if we successfully set OAA for 81 (we did, which gives us an OAA display range of 81-87 MIAS). and then verifying that it was, indeed, a range of OAA being displayed.
So with calibration complete at the early-warning-of stall range we wanted, let's put the Legacy AOA to some real-world work:
Final Approach to touch down in a Bonanza with its OAA calibrated to 81 MIAS (a green donut range of 81-87 MIAS). Interesting... but that was in level flight. Any Airspeed Indicator will give us all we ever need....in level flight.
But here's a Bonanza in very steep banks and pitches and THIS flight regime is where the AOA shines, as the ASI is telling lies in the steepest of the banks. I realize that we all know that, but it's MUCH TOO EASY to forget it. As VERY EXPERIENCED and VERY SKILLED aviators still do, with tragic consequences.
Our second Legacy installation and Test Flight series was in the King Air C90 Blackhawk. We'll skip the calibration process as it's identical, but we did set the King Air for 1.3Vso (Full Flaps with Gear Down). We expected to see a smaller stall margin and we did, but there is plenty of "early-warning-of -stall" remaining...so this King Air will stay set for 1.3Vso .
Lazy eights in a King Air C90. steeper than most King Airs normally fly, but it's a perfectly legal training exercise...and this is a REALLY good place to see the AOA at work
Landing in a King Air C90 from downwind to the rollout.
What did we miss? Ask us, and we'll try to film it for you. (Acrobatic flight? Not in these two aircraft. Inverted? Nope.) What else would you like to see?
DISCLAIMER; Neither Tom Rosen, nor I, nor anyone who helped us with this research (each one helping entirely at their own expense) has ANY financial interest, now or ever, in ANY Angle of Attack manfacturer or in ANY AOA product line. Period. It's simply that...
"This Needs Doing. I'll help"
said Bill Hatfield of Turbine Conversions Ltd. ... just as all the others did too.
This educational effort and flight data research was initiated and funded by friends of skilled aviators gone west. It is placed in the public domain
IN HONOR OF
David Ingalls Brown and Robert H. Baldwin
TWA Captain Ray Rotge and TWA Captain Mack Johnston
On March 23, 2012 Tom Rosen and I received an extraordinarily generous letter. Tom and I were just stunned and we were deeply moved. It is posted in full here.
Here's a clip ...
"AlphaSystemsAOA is pleased to offer a “Save a Friend” discount on your behalf. For the next year, anyone who reads [this] website and sees the benefits of angle of attack, orders our product and mentions either Fred Scott’s or Tom Rosen’s name or the “Save a Friend” discount will receive 10% off all of our systems and accessories."
/s/ Mark Korin, President, AlphaSystemsAOA
Disclaimer: The information provided in this website and AoA/Aircraft portion is provided free of charge. All information provided on this web site is provided 'AS IS'. No guarantee is provided for the accuracy of the information or the application of the information provided herein. I accept no responsibility or liability with regards to the accuracy or currency of the information provided. By using, reading or accessing this web site, you agree to be the user of the information provided. The user accepts full responsibility for all information provided. Although I try to keep the information on this site as accurate as possible, there is no guarantee that the reference materials or the material on this site is correct. This information is provided entirely in the spirit of helpful cooperation.