Help me understand the advantage of AOA in a 2 seat RV

[Av8torTom]

The AOA instrument you have. in my opinion, is not much more useful than a traditional stall warning device. For an AOA indicator to really be useful it needs to read-out degrees AOA. NOW you have a useful instrument. NOW you can assign specific AOA degrees with your airplane's performance such as Vx, Vy, etc. The airspeed indicator is useful of course, but the lag in changing airspeed with pitch (e.g., on final approach, takeoff) can be an issue especially when operating in and out of short fields. The AOA instrument readings are nearly instantaneous with changes in pitch attitude and get you to the appropriate pitch immediately (and therefor airspeed will follow). But, as I said for that utility you really need an instrument that provides you with 1 deg AOA resolution. I had a flying vane on the wing of my Cherokee that gave me this information and it was invaluable.

So to me while the stall information is important, the benefit to AOA information is really the increase in precision by which you can fly the airplane.

[pvalovich]

I never read out AOA degrees - just the gage needle position relative to marks on the gage: 3 o'clock for on speed, above 3 was closer to stall, below 3, fast; max range indicator was a triangle, max endurance a square. Glare shield indexer lights for landing - yellow for on-speed, green for slow, red for fast. However, I still remember published numbers: 10.6 degrees for max range; 13.8 for max endurance, but there was never a need to interpret actual numbers.

[rv7boy]

Originally Posted by Beer30?

Get yourself a copy of Aerodynamix for Naval Aviators, or at least pick one up from the library. To me, it's the definitive text on aerodynamics, which applies if you're flying a Super Cup or the space shuttle...

The textbook "Aerodynamics for Naval Aviators," is available as a free pdf download from the FAA at this link.

The book is authored by H. H. Hurt, Jr. of the University of Southern California. My copy, obtained in 2004, has a revision date of 1965 and has over 400 pages.

My copy was used in one of the best short courses I've ever had, "Understanding Flight - An Introduction to Aeronautics" taught by Col. Wayne F. Hallgren, PhD, USAF (Retired). IIRC, he had taught Aero classes at the Air Force Academy.

Pages 358-360 discuss "The AOA Indicator and the Mirror Landing System" although there are many other sections in the book that discuss the importance of AOA.

[The Wizzard]

everybody is missing the point! Guys and girls this thing will save your butt on that fatal base to downwind turn. Who cares about how long the runway is and therefore not needed. Wrong! If it is set up properly, in other words Flap position calibrated the device senses lift or lose of lift by measuring differential air pressure. So yes, if you have a long runway it is still needed. The reason.......you bank the airplane in the pattern and the stall speed increases, the AOA will then warn you. Do you know what you stall speed is in a 45 or 60 bank? How about when you put a little to much rudder into that base to final turn with that steep bank? Thats where the AOA is really going to shine!

[Av8torTom]

Originally Posted by The Wizzard

everybody is missing the point! Guys and girls this thing will save your butt on that fatal base to downwind turn. Who cares about how long the runway is and therefore not needed. Wrong! If it is set up properly, in other words Flap position calibrated the device senses lift or lose of lift by measuring differential air pressure. So yes, if you have a long runway it is still needed. The reason.......you bank the airplane in the pattern and the stall speed increases, the AOA will then warn you. Do you know what you stall speed is in a 45 or 60 bank? How about when you put a little to much rudder into that base to final turn with that steep bank? Thats where the AOA is really going to shine!

Isn't the stall warner going to tell you the same thing???... My point is there's that while stall information is important, there is SOOOOO much more to having AOA information in the cockpit than stall warning. It's ALL about precision flying.

[The Wizzard]

NO, the stall warner is not going to tell you the same thing as an AOA! It only senses airflow over the wing, not disturbed airflow on top of it! The AOA takes into consideration flap setting and angle of bank along with aircraft pitch. Please correct me if I am wrong someone! In the airliners that I fly it know your flap setting and when you bank the aircraft the speed indicator on the AOA will show to slow for the given airspeed unless a corrective action is taken such as lowing the nose or applying power or both. You may or not not get the stall vane to trigger.

[Av8torTom]

Well not to split hairs here, but the stall warning vane does respond to AOA and and the name says WARNS of an impending stall. You're correct, it does not measure airflow over the wing or anything else. My point is still (and a point I think being missed by many here) that AOA information goes WAY beyond stall warning. When I took off in my Cherokee with my AOA instrument I went immediately to 8 degrees AOA knowing that 30 seconds or more later that would result in Vx. On a 5000 foot runway who cares... on a 1800 foot runway with trees at the end, that time not spent playing with pitch searching for Vx or Vy can be a critical advantage. The original poster asked why one would need AOA information in a 2 place RV and I think the question was being asked from a stall-centric point of view. AOA info is critical for that as you and others correctly stated, but MY point was that it's MUCH MUCH more than that.

[The Wizzard]

I agree, much much more!

[Ed_Wischmeyer]

On GA aircraft, stall warning systems are frequently binary (on-off) systems that state whether the angle of attack has exceeded a threshold determined by the installation of a leading edge vane. Usually the indication is aural, but sometimes it is visual -- some of the old Pipers had a red light.

AOA sensors similarly measure the angle of attack, but on GA aircraft usually do it with differential pressure sensors. Both vanes (stall warning) and differential pressure (AOA) will be affected by flaps, etc. Neither one measures pitch nor bank angle. Either one can have compensation for flap deflection. For example, the Beechcraft Duchess had two stall warning vanes, one for flaps up and the other for flaps deflected -- I forget the numerical values.

As for an AOA saving your butt on a base to final turn, I seriously question that statement. If a Darwin Award candidate ignores a wailing horn and tightens up the turn, why would said candidate be more likely to respond to an AOA beep or voice, or a needle or a light? There's also the well-known phenomenon that when humans are task-saturated, tasks and sometimes sensory inputs get dropped entirely. There's a famous example from the VietNam war in which a fighter pilot is so consumed with the task at hand that he ignores numerous frantic voice warnings from his wingman.

And for Pete's sake, stall speed does NOT vary with angle of bank. The books talk about stall speed varying with angle of bank when the airplane is pulling enough Gs to stay level. If stall speed varied with angle of bank, it would not be possible to roll an airplane....

My take on AOA is that there's much too much hype and ignorance on the entire topic. Probably AOA is useful for some specific tasks, but it's not the answer to everything.

Back when I was an active aviation writer, there was the opportunity to write about AOA, and one vendor was telling me how AOA would provide all kinds of information. I started pressing him for details, and then somehow his demonstrator airplane was magically unavailable every time I called him for the next two years.

And I'm still waiting for somebody to tell me how to adjust target AOA for gusty wind conditions. There are several techniques taught for airspeed, but when I ask this question about AOA, nobody is willing to give an answer...

[The Wizzard]

Ed, I understand that stall speed does not increase with angle of bank. As you said, its the G-loading that causes the stall. On that base to Final turn thats where a lot of people get into trouble when they load it up.

Dave Cicciari
RV-8 Flying
ATP CFII B727, B737 B757 B767 DC-9 CE-500 G-IV
and the Doctor of Love
Dues Paid!