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

[rjbob]

Originally Posted by 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!

If one increases the G factor in any significant amount on a turn from base to final, he/she needs to spend money on training before buying anything for a panel.

[The Wizzard]

It happens far to often, many times they are unaware of it. I have personally lost 2 friends to that type of accident and it is my understanding that it ranks right up there as one of the major causes of crashes.

I have been teaching flying for 30 plus years and had a student put me in that very situation just 2 weeks ago! This guy has been flying for 20 years and I had never flown with him before. (flight review time) His reason, he likes to fly a tight and slow in case he loses his engine. (60 bank turns in the pattern) Needless to say we had a bit of talking to do afterwards. No, Im not saying that an AOA would save his life but it might make him aware of what his is doing before its to late and yes a stall warner would help as well. But there are folks out there that just get behind the airplane for whatever reason, every little bit helps!

[rjbob]

Originally Posted by The Wizzard

It happens far to often, many times they are unaware of it. I have personally lost 2 friends to that type of accident and it is my understanding that it ranks right up there as once of the major causes of crashes.

I have been teaching flying for 30 plus years and had a student put me in that very situation just 2 weeks ago! This guy has been flying for 20 years and I had never flown with him before. (flight review time) His reason, he likes to fly a tight and slow in case he loses his engine. (60 bank turns in the pattern) Needless to say we had a bit of talking to do afterwards. No, Im not saying that an AOA would save his life but it might make him aware of what his is doing before its to late and yes a stall warner would help as well. But there are folks out there that just get behind the airplane for whatever reason, every little bit helps!

You're actually agreeing with me. You did that person a lot more good with your training than an AOA indicator would have.
This is partly because a pilot review is mandatory while an AOA is not.
Do you really believe someone who thinks "low & tight" is safer has the brains to know how to use an AOA?

[terrye]

I think the IDEA of AOA in a small airplane is great. However, I think we have to examine how the actual sensor works. In big airplanes, corporate jets, etc, I understand that the AOA sensor is a pivoted trailing vane, usually on the fuselage, heated for anti-ice, and calibrated by the test pilots that did the certification testing. The vane senses AOA directly as it aligns with the streamlines as the airplane AOA changes. I understand that its resolution is better than 1 degree.

On small airplanes I have yet to see a pivoted trailing vane AOA sensor. I think they are all differential pressure sensors, either on the outboard wing section or built into the pitot tube. As far as I know, they are individually calibrated by the test pilot in each individual airplane. I would call differential pressure AOA sensors derived sensors rather than direct reading.

For a few years now, Vans has been supplying a stall warning device which uses a vane protruding through the leading edge of the wing to activate a microswitch and an aural warning. This vane senses the movement of the stagnation point of the airflow as the wing changes AOA. This is precise and repeatable. However, it is basically a binary device as others have indicated.

So if we had a big airplane pivoted trailing vane sensor that sensed AOA directly and a calibrated GREEN/YELLOW/RED indicator on the glareshield all for a hundred bucks, I'd have on on my airplane.

As it is, with a differential pressure sensor driving a display that looks like a big airplane display, I'm not sure we are further ahead in defining our margin of safety above stall than with the Van's stall warner.

[Ed_Wischmeyer]

Hard to put one on an RV because it would be in the slipstream.

Not sure I agree with your distinction between functionality of differential pressure vs vane sensors.

[Gagarin737]

When I'm using the published speeds for the RV-12 I'll float forever. With the AOA indicator/sound I hit the numbers every time. In gusty weather I won't go slower than the first beeps. During steep turns I don't look at the speed, I just unload when the AOA beeps start.

The youtube movie shows the Dynon sound. This was the first flight after calibration the AOA and about the fifth landing after initial flight.
->AOA Dynon sound

[Av8torTom]

Originally Posted by terrye

I think the IDEA of AOA in a small airplane is great. However, I think we have to examine how the actual sensor works. In big airplanes, corporate jets, etc, I understand that the AOA sensor is a pivoted trailing vane, usually on the fuselage, heated for anti-ice, and calibrated by the test pilots that did the certification testing. The vane senses AOA directly as it aligns with the streamlines as the airplane AOA changes. I understand that its resolution is better than 1 degree.

On small airplanes I have yet to see a pivoted trailing vane AOA sensor.

I had one on my Cherokee albiet home made. I had a vane hung off a small boom ahead of the wing leading edge outside of the prop-wash. On top of the glare shield was an LED light bar instrument that showed AOA in 0.5 degree increments. I was trying to manufacture and sell them at the time but no one wanted something like that hanging off their wing, and the FAA at the time was not as supportive for having AOA information in the GA cockpit - and it cost a lot more than 100 bucks. The green, yellow, red display, in my opinion, is just a glorified stall warner. I don't know if it's possible using differential pressure to get 1 degree AOA resolution, but if you could, and you could do it economically enough, you'd have a winner. With 1 degree AOA resolution I could fly with the precision of a Navy fighter pilot - THAT's what having AOA information in the cockpit is all about... precision flying.

[pvalovich]

Back to the basics to answer the original question:
1) The goal ought to be the ability to "feel" what the aircraft is doing in the pattern. Can you feel the difference between 80, 70, or 65 kt normal approaches? If so, AOA is a backup luxury.

2) Anytime you're slow, banked and pulling (pulling being the key descriptor) close to the ground, you are no longer on a normal approach. An AOA indicator shows not only how far from normal you are, but also how much margin you have before stall. Nothing wrong with flying just above stall - if you are absolutely sure you have the skill to remain there.

3) If you're heavy in the landing pattern (real heavy) your normal approach speed may be too slow to provide comfortable stall margin. An AOA indicator will show you the delta.

4) AOA will provide stall margin for acro and maneuvering flight.

You don't need AOA to fly an RV. It's utility goes from not needed, to nice to have, to a tool for saving your butt - depending upon the situation you have gotten yourself into.

[Ironflight]

Originally Posted by Av8torTom

I don't know if it's possible using differential pressure to get 1 degree AOA resolution, but if you could, and you could do it economically enough, you'd have a winner. With 1 degree AOA resolution I could fly with the precision of a Navy fighter pilot - THAT's what having AOA information in the cockpit is all about... precision flying.

The AFS Pro gives AoA resolution to 0.1 degree on the bottom of the color ladder, and it is very precise.

I would wager that most of the folks that are skeptical about AoA in our types of airplanes haven't taken the time to actually test and learn the various systems available. Some may have played with an uncalibrated system. Some may have played with it, but without an open mind. Fair enough - we don't know what we don't know.

The fact remains, however, that an airfoil stalls because it has reached its stall Angle of Attack - not because of speed, bank angle, G-loading, or the phase of the moon. All of those (well, except the phase of the moon) play into what SPEED it is going when it stalls, but AoA is the constant. Measure that, and you will always know when it is going to let go. Having a measurement of where you are in relation to the stall - not just an indication that you are there - is extremely valuable information for someone operating anywhere that a stall would be bad news.

I have been trained in, and have practiced, operating air vehicles in all different speed ranges - from super-slow ultralights to Mach 25 re-entry vehicles ( you haven't stalled until you've stalled at Mach 6.5.....). Angle of Attack is a constant measurement that works in all of the flight regimes.

Truthfully, it doesn't take a long time to learn to fly by AoA if you have a good teacher - it can be figured out in a short flight, and you'll rarely use an Airspeed Indicator in slow flight again.

Arguing topics like these on the Internet is pretty futile. There are two kinds of folks reading this thread - those that have their mind made up, and those who don't. I'd suggest that those who don't go out and get some good experience with someone who understands it, and how to teach it - then make up their own minds.

You won't get the full picture from this thread - there's too much misinformation mixed in already.

Paul

[Av8torTom]

Originally Posted by Ironflight

The AFS Pro gives AoA resolution to 0.1 degree on the bottom of the color ladder, and it is very precise.

Well there you go - that's the ticket!!! I will be installing this in my 9