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

704CH

704CH

Well Known Member
I understand how AOA works and just don?t understand how great the benefits are for a 2 seat RV. Maybe you guys can help illuminate me. I have AOA in my plane and always use indicated airspeed when landing, when using AOA I might as well be using airspeed since it doesn?t make much of a difference. I know everyone is trying to sell AOA, but I really need help understanding the benefits in an RV. I will say that my AOA does work pretty good as a stall warner, so that is one advantage.

1) AOA makes perfect sense for something like a Pilatus with a large range of landing weights and a higher landing speed. In a big plane, using AOA when landing light vs gross you can really reduce your landing speed. In an RV the weight changes are so minimal they don?t make much difference to me.
2) AOA makes sense for planes with fast landing speeds because due to density altitude and temp changes the variance of AOA due to these factors can greatly help reduce landing speeds.. RV?s don?t have high landing speeds.
3) RVs are bouncy planes and with some thermals on landing your airspeed changes around up to 5 knots anyway with each bounce, so I use airspeed to keep a good safety factor.
4) Maybe RV-10?s have a bit more of a weight change and AOA is more beneficial?

Thanks for any feedback on this topic.
 
I put one in my RV6 more as a backup instrument for landing speeds if I lost my EFIS or all electrical power by chance. (My airspeed is tied to EFIS in all electric plane). I think it is a better backup instrument than a analog airspeed indicator for that purpose. It's been interesting to adjust and use with stall speeds at different weights. I found my stall speeds varied less than 5-6 mph at min and max weights and full forward and rear CG points so to your point there isn't a lot of variability.
 
Chad,
You can also use the AOA in case your pitot gets but dont believe that would make a difference in the Skyview system we have. It is handy if you would get distracted while shooting an approach on that GTN you have. It is handy should you get caught in a micro burst. 😃
we use airspeed all the time when flying the problem where AOA has received so much press lately is because of Base to final turns. but the only plane I ever flew which I religiously use an AOA was our 24B learjet. back 30 years ago. In our Challenger 601-3A the AOA is only Valid for full flaps and any other flap setting it is invalid. In our Hawker 800 xp it is handy as it sits infront of your face on the glareshield and works in all flap settings so at night on dark approaches you do not have to be looking down at the instruments you can just pick it up in your field of vision looking out at the runway. So like you state 99 percent of the time it is airspeed.

The problems is with pilots being distracted and when the planes stalls close to the ground there is no margin for recovery.Or stated above on dark night approaches.

Hate to say it but 48 years of doing this for a living the accidents can still pretty much be broken down to how they were in the 60's.

Jack
 
AOA has nothing to do with the size/weight of the airplane. It's the most accurate warning for stall margins, period. On any airplane. Since a wing stalls at the critical angle of attack, even on a two seat RV that means it could be as much as a 20 knot swing, in flight. Your stall speed at the abeam on downwind is going to be lower than it is in a 30 degree bank turn from base to final. You get distracted, lose a gust of wind, inadvertently pull back on the stick a little... You may only change your indicated speed 3-4 knots but you may have increased your stall speed 10 knots. The stall angle of attack however will always remain constant.

That's the simplest example I can give. Plus it's aleady included in most of the pitot/AOA/Efis combos, so it's not like you're going out of your way to install it.

Fly with AOA, and fly the AOA, you'll never need IAS again. If you do any aerobatics you'll really understand AOA and its effects on lift/performance better too.
 
Try an accelerated stall, and you'll see a big difference from airspeed then.

I'd expect to be more comfortable with low speed close to the stall as well.

Also even a two seater can behave quite differently with one pilot, low fuel vs two passengers at gross wt.
 
I operate off a 1260 foot grass strip. So every landing is short field. I have a Skyview with AOA. I never like to look down at the screen when landing for either airspeed or AOA indication - and with AOA I don't need to. Because when you get into the yellow range the Skyview starts beeping into the headset. Slow, then faster as you increase AOA. You can get that beeping rate right where you want it, then adjust power/pitch as necessary to keep it there. (I have a dropoff on the approach end and can get some sink there so I'm always ready with the power.)

For conventional landings on a lengthy runway - not really needed. Could save you in that sometimes fatal base-to-final overshoot turn, PARTICULARLY if you have audible output.

I personally think a visual-only AOA indicator is far, far inferior to one with audible output that works as I mention. If you have to be looking down at the AOA you might as well be looking at the airspeed. Yeah, I know you can mount some AOA remote indicators in your field of view but for the reasons mentioned, IMO audible is better.
 
704CH said:
I understand how AOA works and just don?t understand how great the benefits are for a 2 seat RV.
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Guess it depends on how you have it setup and if you are using it. For me I've had AOA in both of my 2 seat RV's and use it constantly. I don't fly by IAS anymore during any critical phase of flight.

The key thing is do you need it around our local area when flying at sea level with familiar weights? Not really. But get high and hot while loaded down and it will surprise you how fast you need to be going to keep your margins in place.

I've found that using AOA only for landings makes them very consistent as you always have the same amount of energy at that critical phase so the flare is very similar landing to landing.

I've also really seen the AOA come alive with aerobatics. Top of a loop and as you start to get slow, pull just a touch too much, "angle angle push" lighten up a touch on the elevator and around you go.

For me, it's the best "toy" I added to the build.

The archives are also full of lots of good info on the topic as well.
 
It's all about the stall

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.

As others have said, a wing always stalls at the same AOA, but will stall at a different airspeed depending on your gross weight. Also, your airspeed is going to vary with density altitude, the AOA will not. What stall speed are you going to use if you take off from Lincoln NE, and then land in Denver? Do you have an exact number? The AOA will not lie to you, regardless.

Thats it in a nutshell.

David
 
Beer30? said:
As others have said, a wing always stalls at the same AOA, but will stall at a different airspeed depending on your gross weight. Also, your airspeed is going to vary with density altitude, the AOA will not. What stall speed are you going to use if you take off from Lincoln NE, and then land in Denver? Do you have an exact number? The AOA will not lie to you, regardless.
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Actually, indicated airspeed for stall will stay the same regardless of the altitude/density altitude of the airport you're at (assuming the same weight, g load, etc. and ignoring compressibility and Reynolds effects), since that's basically just an indication of dynamic pressure. Your true airspeed at stall will increase with density altitude.

But yes, the overall point is that AOA will be accurate regardless of weight or g load. I'll be fitting it to my airplane from the beginning.
 
akarmy said:
But get high and hot while loaded down and it will surprise you how fast you need to be going to keep your margins in place.

I've found that using AOA only for landings makes them very consistent as you always have the same amount of energy at that critical phase so the flare is very similar landing to landing.

I've also really seen the AOA come alive with aerobatics. Top of a loop and as you start to get slow, pull just a touch too much, "angle angle push" lighten up a touch on the elevator and around you go.
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I second all the above for an additional data point- I get to know high and hot around here quite a bit...
 
Lotsa AOA questions...

I agree that AOA has been way overhyped. I've not yet found an answer to how to adjust AOA for gusts when landing, for example, or how AOA affects Vx with a headwind. And there is a classic article from Boeing stating why AOA isn't all that good for transport category aircraft.

The vibrating reed (crying baby) stall warning horn in some of the older cessnas was a marvelous AOA announcer, same for the increasingly faster beeps in the RV-14 prototype. A voice callout like angle-push is an improper use of voice alerts, and way back when, I wrote the first white paper at Boeing on proper use of voice alerts.

BTW, of the five airplanes I've owned, only one had a stall warning horn, none have had visual AOA.

Rather than putting another gadget on the airplane, how about training pilots in stalls and slow flight, well beyond the PTS requirements. It's interesting, it's fun, and it's not that hard.
 
I have AOA in my panel and I find myself to hardly ever use it. Maybe it is just a habit, but I tend to use my IAS for landing but it would have been great if I could get audio warning, which I don?t, from the AOA in case of distraction and missing the IAS target.
 
RV's, in particular, invite steep turns in the pattern - great visibility, relatively high sink rate with power off, and folks like to stay close, then bank and ynk to make the turn. Quick now, you're banked sixty degrees - what's your stall speed?! The nice thing with AoA is, you don't have to do any calculations at all - if it has been calibrated to the airplane at installation, it never lies.

Yes, we are all superior pilots who can feel the airplane the way Stravinsky plays the violin....yet guys still manage to stall and spin in the pattern, and I doubt that they were committing suicide - they got surprised. And I am talking experienced guys. If you have never been surprised while you were distracted, you haven't been flying long enough.

If I could have only an AoA or an ASI, I'd pick the AoA every time, because it doesn't "lie" - it's that simple. I have flown lots of different airplanes, and some have almost no aerodynamic warning of a stall - in these the AoA is a tremendous tool to keep you in the green. I didn't start flying regularly with AoA until later in life....but that doesn't mean I couldn't adopt it, and adapt to it. Airspeed in the pattern? I don't know - I don't look. AoA in the yellow until the threshold, and then let it bleed in to the red to a wheel landing or three-pointer.

Is it essential? No - we have all lived without it for years. Does it increase your margins and decrease risk? Absolutely.
 
Ironflight said:
RV's, in particular, invite steep turns in the pattern - great visibility, relatively high sink rate with power off, and folks like to stay close, then bank and ynk to make the turn. Quick now, you're banked sixty degrees - what's your stall speed?! The nice thing with AoA is, you don't have to do any calculations at all - if it has been calibrated to the airplane at installation, it never lies.

Yes, we are all superior pilots who can feel the airplane the way Stravinsky plays the violin....yet guys still manage to stall and spin in the pattern, and I doubt that they were committing suicide - they got surprised. And I am talking experienced guys. If you have never been surprised while you were distracted, you haven't been flying long enough.

If I could have only an AoA or an ASI, I'd pick the AoA every time, because it doesn't "lie" - it's that simple. I have flown lots of different airplanes, and some have almost no aerodynamic warning of a stall - in these the AoA is a tremendous tool to keep you in the green. I didn't start flying regularly with AoA until later in life....but that doesn't mean I couldn't adopt it, and adapt to it. Airspeed in the pattern? I don't know - I don't look. AoA in the yellow until the threshold, and then let it bleed in to the red to a wheel landing or three-pointer.

Is it essential? No - we have all lived without it for years. Does it increase your margins and decrease risk? Absolutely.
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This. I spent years flying swept wing fighters, and 99% of the time I couldn't tell you what my airspeed was (standby for over simplification). In the landing patter it was on-speed AOA, on a long trip it was max range AOA, and if you needed to conserve gas it was max endurance AOA.

Another case in point, best glide speed.... It's for a specific weight/cg. Anything else it's wrong. But if you can figure out your L/Dmax AOA... Index it, you never need best glide airspeed again.

That said I too revert to my habit patterns of old and use airspeed in the pattern, but now the AOA is in the scan too. It tells me if my standard airspeeds are fast/slow for all the given variables.
 
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Ironflight said:
different airplanes - some have almost no aerodynamic warning of a stall
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This describes my RV-8 rather well. Other than the stick getting "a little soft" there is nothing else before the stall. While I've grown accustom to the airplane, I'm sure others would find it unnerving.
 
Ironflight said:
RV's, in particular, invite steep turns in the pattern - great visibility, relatively high sink rate with power off, and folks like to stay close, then bank and ynk to make the turn. Quick now, you're banked sixty degrees - what's your stall speed?!

....Yes, we are all superior pilots who can feel the airplane the way Stravinsky plays the violin....yet guys still manage to stall and spin in the pattern, and I doubt that they were committing suicide - they got surprised. And I am talking experienced guys. If you have never been surprised while you were distracted, you haven't been flying long enough.
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I think a lot of it has to do with mindset. If you're close enough to the ground for an inadvertent stall during a simple steep turn to be hazardous to your health, not only should you be paying close attention, but you should have previously practiced at higher altitudes enough times to be ingrained. We do not see airshow pilots inadvertently stalling/spinning out of a simple 60 degree banked turn at base to final altitudes or much lower. Essentially unheard of. Are they all fundamentally superior pilots? Despite what the general pilot population may think, they are not necessarily. But they have practiced their specific routine are paying close attention. I don't know many airshow pilots who reference AOA during their routines.

Now....I am NOT trying to minimize the value of AOA. It clearly has value. I am simply making the point that if you are deliberately doing steep maneuvering at low altitude, you better have the discipline and mindset that this requires 100% focus on what you are doing moment to moment. If some distracting element enters your environment, you should be mentally prepared to bail on your "maneuvering" and assess the situation in stabilized flight. Aerobatic pilots (who survive long term...and most do) develop this discipline - especially as they lower their altitudes. No reason RV "yank and bankers" in the pattern cannot adopt some of the same.

I'm still a lot more sold on the value of AOA for flying approaches than for preventing Joe RV pilot from stall/spinning on base-to-final. Not that AOA does any harm in this regard. If the AOA screaming causes even one pilot a year to get their head out of their asss and avert disaster, then it's worthwhile. Is there any statistical or even anecdotal information on the "safety" factor here?

Low altitude maneuvering - PRE-PLAN (including your 'outs'), VISUALIZE, AND PRACTICE...AT ALTITUDE FIRST!!
 
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It's like this

When i learned to drive in 1971, no cars had outside rearview mirrors on the passenger side; inside and driver side only. Clearly that was fine, who needed anything else? We were fine, right? Over the years, passenger side outside mirrors became standard, but I didn't really use them when they appeared because they'd never seemed necessary. Now, nobody would consider a car without passenger side outside mirrors a safe vehicle and cars have back-up cameras! Some can parallel park themselves!
In the military, as everyone says, I couldn't tell you my speed on final or over the top of a loop or pulling out of the dive pattern; I pulled to the green donut and all was well. In the airlines, AOA is in the boxes somewhere, but generally it's not displayed in a useful way.
So, I've flown with and without AOA. My 8 will carry my butt and save my butt and is costing a butt-load. Finally I have the responsibility and option to "have it my way." I'll be paying for it either way; in cash or blood. My 8 will have the same AOA indication in the same place my T-38 and F-111 had it: front and center above the glareshield where I can find it when it's all on the line.
 
I have AOA in my skyview and use it some of the time, particularly when practicing stalls. It's pretty accurate. I used an AOA when flying a Citation because it was pretty close ot the scan. The Skyview AOA is not in a good place for the scan.
Has anyone figured out how to put the Sklyview AOA on an HUD? I'd be interested. I fly into some short strips.
 
jnmeade said:
I have AOA in my skyview and use it some of the time, particularly when practicing stalls. It's pretty accurate. I used an AOA when flying a Citation because it was pretty close ot the scan. The Skyview AOA is not in a good place for the scan.
Has anyone figured out how to put the Sklyview AOA on an HUD? I'd be interested. I fly into some short strips.
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To my knowledge, there is no RV priced/sized available HUD.

For the short strips, I'll slow to my standard approach speed on downwind and get fully configured, then reference it to the AOA. ie if my standard 70 knots shows me two green bars fast, I know I can slow to three yellow bars. Vice versa if I see two yellow bars at 70 I'll speed up to three yellow bars, check the speed.... Now I know what I'm targeting over the fence on short final. In the turn from downwind to final it's pitch/power to yield whatever airspeed I need for the keep target AOA/rate of descent. When wings level on final, power back to whatever airspeed gave me the AOA desired on downwind.

Technique only, and I only really hawk it that close for strips under about 2k'.
 
jnmeade said:
I have AOA in my skyview and use it some of the time, particularly when practicing stalls. It's pretty accurate. I used an AOA when flying a Citation because it was pretty close ot the scan. The Skyview AOA is not in a good place for the scan.
Has anyone figured out how to put the Sklyview AOA on an HUD? I'd be interested. I fly into some short strips.
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As best I know, Dynon doesn't have a glareshield indicator (yet?), but the audio AoA signal is outstanding. I actually prefer an audio AoA signal (variable, not just a discrete "push, push") to a visual indicator.
 
Paul is spot on...listening to AOA allows your scan to be wherever it needs to be and still allows you to process fast, slow or "on speed" when flying at or near L/D max. Works during maneuvering flight, in the traffic pattern or flying a precision approach...it's one of those things that you likely have to try before you appreciate the utility.

I suppose if Wilbour and Orville had installed an AOA indicator, we'd be discussing the merits of Vref!

Cheers,

Vac
 
luddite42 said:
I think a lot of it has to do with mindset. If you're close enough to the ground for an inadvertent stall during a simple steep turn to be hazardous to your health, not only should you be paying close attention, but you should have previously practiced at higher altitudes enough times to be ingrained. ...

I am simply making the point that if you are deliberately doing steep maneuvering at low altitude, you better have the discipline and mindset that this requires 100% focus on what you are doing moment to moment. If some distracting element enters your environment, you should be mentally prepared to bail on your "maneuvering" and assess the situation in stabilized flight...
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I really don't think these people getting into steep turns down low and stalling the aircraft are deliberately going in with the mindset of making hard maneuvers. They're most likely going in intending to fly a benign pattern, and get themselves in trouble a little bit at a time. I almost got in trouble that way once in the -6; I had a moderate crosswind and started my base-to-final turn a few seconds late. Saw that I was overshooting the runway, banked a bit more to tighten the turn, and maybe unconsciously edged on the rudder just a bit. Banked a bit more, pulled a bit more... then some little alarm bell started going off in my head ("something's not right...") about the same time I felt the stick getting soft. Brain then goes "oh ****!" and I unleaded, rolled level, and went around.

So, i'ts not deliberate "yank and bank" flying, it's "oops, I'm overshooting, gotta correct a bit more". Or it's guys in a moderate turn, thinking they're ok because their bank angle is low and therefore that stall speed won't go up much, and then putting g-load on trying to bring the nose back up.

I really wish we didn't teach this stuff in terms of speed and bank angle at all. Stall is based on AOA, and only AOA. By talking about it in terms of speed and bank angle, we make implicit assumptions about weight and flight condition--namely, level flight at maximum gross weight--that become invalid almost immediately after you change those conditions. I can have an 80 degree bank angle and be at 4 knots, and yet not stall; I can also be wings and nose level at 120 knots and stall.

We then teach pilots using those methods in situations where they are the least likely to get themselves in trouble. Think about it. When you practiced stalls in your training days, how did you do them? I bet you did power-off and -on stalls with wings level, at constant altitude (for power-off), slowly and deliberately letting your airspeed decay until the break. And your accelerated stalls were probably done at closer to cruise speed, in constant-altitude steep turns. I don't know if that necessarily provides the best instruction to pilots about avoiding stalls in the situation where they're the most deadly--in the pattern. We tell pilots to watch their airspeed and their bank angle in the pattern, but I think what you wind up with is "as long as my bank angle is below 30 degrees and I'm at 1.3 Vs nothing bad can happen". And that's very definitely not the case.
 
I had AOA on my 10 and rarely used it. Not because of it's potential value, but because it was displayed on the EFIS and not primarily in my scan while doing landings ( much more looking outside the canopy).
Now finishing an rv8 and am installing an AOA on the glareshield. This puts in in my peripheral vision the whole time I'm maneuvering on approach. This, plus audible, is invaluable to me.
Tom
 
rmartingt said:
When you practiced stalls in your training days, how did you do them? I bet you did power-off and -on stalls with wings level, at constant altitude (for power-off), slowly and deliberately letting your airspeed decay until the break.
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The PTS was changed last recently (2013 or 14) to include stalls while climbing and banking at the same time (cross-wind on takeoff) and descending and banking (base to final on landing) as well.

This was a surprise to me since I had not done any training for these maneuvers in my Cherokee 140, but never the less, passed my check ride :D

I have not yet flown with an AOA but look forward to what is considered by the FAA to help reduce pattern accidents.
 
Anything that costs so little but does so much to avoid one of the most common general aviation accidents is a no brainer in my mind. I use mine all the time. The "sure it's safer, but I don't need it" argument is hard to justify when I think of my family having to live without me. There are plenty of other reasons for a small aircraft and experimental in particular to get you in trouble. Deleting a safety piece to save 1% isn't something I even considered.
 
AOA - Lessons Learned after 450 -8 Hours

I'm a former Navy carrier guy who lived AOA. Put an AFS AOA in my -8A during the build. My biased opinions / observations:
1) I don't use it nearly as much as I thought I would, partly because of the aim for the end of the runway and flare technique I use for landing. Disciplined 70 kts on final gives me a lot of stall margin (I stall dirty at around 49 kts).
2) A big mistake - the AOA display is on the EFIS screen, not above the panel. Most strongly recommend mounting the indicator above the panel in the landing field of view. I should have spent the bucks on a panel indicator. Have been too lazy and have been having too much fun flying to do the mod.
3) AOA is a useful tool during acro.
4) Haven't been there yet - but AOA is the backup for airspeed indicator failures - or concerns about ASI accuracy.
5) You have to develop the mindset and discipline - but AOA trumps seat of the pants feel every time when you're near the edge off the envelope - regardless of g, attitude, and airspeed.
 
Not very useful

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.
 
AOA Usefulness

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.
 
The Textbook, "Aerodynamics for Naval Aviators"

Beer30? said:
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...
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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.
 
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!
 
The Wizzard said:
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!
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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.
 
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.
 
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.
 
Coupla "clarifications"

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...
 
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!
 
The Wizzard said:
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!
Click to expand...

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.
 
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!
 
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The Wizzard said:
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!
Click to expand...
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?
 
AOA

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.
 
Pivoting vane sensor

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.
 
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
 
terrye said:
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.
Click to expand...

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.
 
We've Digressed from Why AOA?

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.
 
Av8torTom said:
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.
Click to expand...

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
 
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