J

Jack Tyler

Well Known Member
I'm posting this thread after mulling a bit on Van's latest (4/27) Facebook posting on safety, a portion of which discussed Loss of Control accidents. (Van discussed stall/spin & power loss accidents together ("LOC accidents") and noted they are the #1 and #2 types of RV accidents, respectively).

My question - to those of you with AOA instruments or AOA indication on your EFIS panels - is whether you have personally found your AOA display has helped you avoid stall/spin events - in a 'real world sense'. Much is written about the value of AOA indication. E.g. in addition to Van's reference to a current Flying article, see http://www.flyingmag.com/blogs/fly-wire/missing-instrument. In my prior flying I never had access to AOA measurement, and I'd like to think I'll never be a stall/spin statistic. But given the workload in the cockpit, especially in approach, departure and low & slow evolutions, I'm wondering how useful AOA indication has been. Any comments would be welcome...

BTW perhaps because it is so visual, I was especially struck by AOPA's representation of stall/sin accidents, injuries and fatalities, by year, on a national map at http://www.aopa.org/asf/ntsb/stallspin.cfm?window=6
 
AOA is a nice stall warning device, especially the audio part "angle, angle push". performs really well. did quite a few stalls during testing.
we have the AFS aoa sport installed.
so it is definitely helpful.

the biggest issue i see is, that in an event like a blocked pitot or something, both the airspeed tape and the AOA will fail. unfortunately i haven't seen a light, small and affordable airliner "cone"-style mechanical aoa yet which would be completely independent.

also a lot of the stall/spin accidents on base to final i think are more a factor of g-loading/heavy bank and pull than actually a too low level flight speed. of course the aoa would warn in that case, too however depending on the pull with very short notice.

we rarely ever approach with AOA as primary speed guidance. approaches in that way tend to be very slow and on the backside of the curve, requiring a perfect flare every time without much energy reserves.

rgds, bernie
 
Wow, what a subject.

Most people know that the stall speed increases with bank. A lot will know the formula that ties G-load to stall speed. Put that all together and quite a few people know that in a 60deg bank turn, your stall speed is increased by 40%. However, there is more to it than that :rolleyes:

This angle of bank/ stall speed relationship is only valid in a stable situation ie a steady and balanced turn. I suspect that most stall/incipient spin accidents happen at low level because people bank the aircraft and then load it up. It's the G that increases the stall speed, not the bank. You can be in a 50 deg climb, 50kts with 80 deg of bank. If the aircraft is unloaded, you cannot stall.

So much for the intro. The bottom line is that all this stall/angle of bank/G is related to AOA. The wing stalls at a given AOA no matter what the manouevre. Hence, IMHO, the AOA gauge is an invaluable tool. Ask any fighter pilot - I was one many, many years ago...... ;)
 
There is at least one vane type AOA.

flyvans.com said:
. .......unfortunately i haven't seen a light, small and affordable airliner "cone"-style mechanical aoa yet which would be completely independent.


rgds, bernie
Click to expand...

A friend of mine has a mechanical, airfoil shaped AOA vane on the strut of his Christen Eagle....he's an ex-Navy carrier pilot and MD-80 pilot for Delta.

Later today, I'll get the info for you.

Best,
 
Thanks for the comments so far...and for digging a bit deeper on my behalf, Pierre.

Your ex-Navy/Delta fellow may not be the guy to ask, given that he learned to fly via AOA management from an early age. What I'm trying to understand is, the utility & value of an AOA device aside, in the real world of GA pilots flying planes, when an AOA device is available is it helpful enough to be regularly used...or used enough to regularly be helpful. No doubt this depends in part on who's flying...

Jack
 
I think the AOA is an extremely valuable instrument and I wish everyone would install one.

Although I've had mine "talk" to me on occasion unexpectedly while "manuevering" at altitude it really did help save me once...

I was on my takeoff roll at a local fly in (narrow grass strip) when suddently a family of 4 (2 small children in tow) started across the runway, to late to stop the plane, they looked over and saw me coming and started running, as soon as I "felt" had enough speed I pulled the plane off the ground (I was watching the family not the AS indicator). Almost immediatly the AOA started its "Angle Angle" so I knew I was on the verge of stalling... I leveled momentarily to gain a few kts then pulled it up to clear the shocked family by probably no more than 20 feet.

Scared the bejesus out of me and them (I could see their faces) :eek:

Without the AOA, under those conditions, I may have dropped it in right there. It gave me the aural cue to lower the nose enough to keep me out of trouble, the urge to pull up in that circumstance was very strong. I cleared the family by less margin than I would have liked but at least we all "walked away". :D
 
An important point from Walts post is having the audible indicator. At times like that you should not be looking inside at pretty color lights or a needle.
 
I just found the info.

My buddy has what's called "Rite angle buddy" on his Christen and he just told me that there is a model for no-flap airplanes like his Christen and also a flap-equipped airplane model. According to their web site, a sensor on the torque tube of your flaps compensates for AOA changes as the flaps are lowered.

The system also has an audible buzz warning that can be wired in :

http://www.riteangle.com/

BTW AC Spruce carries the units,

Best,
 
flyvans.com said:
the biggest issue i see is, that in an event like a blocked pitot or something, both the airspeed tape and the AOA will fail.

we rarely ever approach with AOA as primary speed guidance. approaches in that way tend to be very slow and on the backside of the curve, requiring a perfect flare every time without much energy reserves.

rgds, bernie
Click to expand...

I've been flying my "full fledged" AFS AOA on my 3500 for 2 1/2 years. It must be different than the Sport because it has it's own ports and tubing, so is independent of airspeed. I use it religiously and cross check AOA and airspeed beginning prior to turning downwind to base. Although I can't think of a time it has for sure saved me from a wreck, it does definitely show the difference in a heavily loaded airplane and a light one and the approach speed difference that should be used. It was a bit of a challenge to get it calibrated correctly, but was well worth the effort. Do I think you absolutely have to have one... no. Is it a useful tool and better than a stand alone stall warning. I believe so. I can fly the approach slower depending on my gross weight and still not be behind the power curve, but I will be close to it. It actually makes my landings more consistent if I keep checking it as I come over the fence and keep the AOA where it should be. Where I find it valuable is short field operations and at venues like Oshkosh where I'm heavily loaded and close in pattern work requiring steeper turns is necessary and "go around" situations are probable. Money well spent in my book.
 
AoA safety

I fitted an AoA when during the building stage. I never gave it much thought until a wasp got into the pitot tube. I had set it up to give me a warning at an above stall (flare) speed. It was a perfect backup.

I normally use it audibly with an eye on the ASI on landing.
Some years later I was distracted during a climb out and the lights came on which is set to happen at 80 Kts. I climb out at about 100. It focussed me prety quickly.

I believe that in the above 2 cases, the AoA made life a lot more pleasant!
The company I used goes back a long way with the link below being the one which suited me. The lights come on at flap extension speed and the audible warning comes on just about flare speed
http://www.alphaaoa.com/Standard-Classic-2-Round-Panel-Mount-LED-Electronic-Kit-DSTR-AOA-2000RK.htm


Ted
RV-6A "Rough Red"
 
I've ben using AOA for my whole Air Force career and I will have it on my -7. For instance, in the T-38, you compute your final turn speed for the pattern and use it to back up the "green doughnut" on the AOA. It makes the final turn safer in an aircraft known to have made a few widows on the turn to final. The AOA is right in front of your face and when you see red and hear the tone, you'd better roll out and add power and arrest your decent rate! It really is a very useful tool to determine the aircraft stall.

+1 for all installing AOA.

Cheers!
 
Very useful feedback so far.

Walt, perhaps you were posting at the same time I was, as I missed your story earlier. Thanks for that very 'real world' example. As were Ted's.

Sam, your article was actually one of the more recent ones I read - some time ago, when first getting acquainted with this website.

As some here will know in spades, we've yet to learn the details of the 2nd generation, Skyview-based panel in the RV-12. Since that's the kit I plan on purchasing (June 10th we'll close on a 2-car garage, which happens to come with an attached house), I'll be interested to learn what the Skyview's features will be re: AOA display (and aural warning, one hopes). Or this may need to be a post-certification add-on.

My takeaway so far, perhaps best illustrated by Kobwo's comments and also my son's (Fly Navy!) is that, if one chooses to consider it a primary flight instrument, it can on occasion (e.g. 'slow & heavy') provide an extra margin of safety. Thanks everyone for the comments and sea stories...

Jack
 
I'll be that negative nancy...

AUDIBLE! Stall warning - heck yeah!!
AOA - useless

the easiest way to get stall warning is to install a fancy efis system with AOA capabilities like the dynon with the AOA pitot tube. Only one extra tube to run, no cutting the leading edge of the wing etc; so that's how I build my RV-7 and I am glad that I did.

The RV-7 (dont know about other RV types but I assume they are the same) talks to you pre stall but it is very very short and most likely the recovery is going to be too late in a task saturated scenario where the airspeed is dropped from the crosscheck. Besides the decreasing wind noise and the sloppy controls the only warning you get is
"watch that buffet, what buffet? stall..." :eek:
in these circumstances a stall warning of some kind is essential!

However to fly a certain AOA on final in these low wingloaded light aircraft while bouncing around on final is next to imposible/useless imho.

I have flown F-16, F-18, T-38 all had AOA indicators of course and they were essential in all of them because of the high wing loading and the high AOA's these aircraft are capable of. Its been a while but iirc the F-16 is capable of AOA's well above 15 degrees and the F-18 can still points its nose while it is nearly falling out of the sky! upwards of 20 degrees AOA!
Not only that but because of the large weight these a/c have momentum so the AOA does not change drastically with a disturbance (wind, thermals) on final, so you can set an AOA and fly that.
An exception is the T-38, I crosscheck the AOA on final but never flew or tought flying AOA (unlike the Viper or Hornet), the reason being that even the T-38 is too light and the AOA too sensitive to just fly AOA. The indicator is bouncing around enough to cause the pilot to chase the needle and cause an erratic final approach. Fly your speed and crosscheck the AOA.

I dont know the exact number but what AOA are our aircraft capable of? 0 to what, 6 7? How much does that change between a light and a full loaded RV assuming that the airspeed is kept the same? 1-2 degrees? How much do we bounce around on final on a summer day, even without wind? Imho flying an AOA approach in light GA aircraft is a challenge and not an added benefit. Nothing trumps accurate airspeed control on final.

HOWEVER, I think an audible impending stall warning is essential!
 
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leaker311 said:
AUDIBLE! Stall warning - heck yeah!!
AOA - useless

the easiest way to get stall warning is to install a fancy efis system with AOA capabilities like the dynon with the AOA pitot tube. Only one extra tube to run, no cutting the leading edge of the wing etc; so that's how I build my RV-7 and I am glad that I did.

HOWEVER, I think an audible impending stall warning is essential!
Click to expand...

I use the Advanced Flight System AOA, 2 tiny holes are used to sense pressure on top and bottom of the wing, you would not know it was even there unless you know what to look for (and even then the tiny holes can be hard to find).

Audible announcement is provided (angle-angle push-push).

No fancy EFIS required.
 
leaker311 said:
AUDIBLE! Stall warning - heck yeah!!
AOA - useless

(snip)
The RV-7 (dont know about other RV types but I assume they are the same) talks to you pre stall but it is very very short and most likely the recovery is going to be too late in a task saturated scenario where the airspeed is dropped from the crosscheck. Besides the decreasing wind noise and the sloppy controls the only warning you get is
"watch that buffet, what buffet? stall..." :eek:
in these circumstances a stall warning of some kind is essential!

Agree :)
However to fly a certain AOA on final in these low wingloaded light aircraft while bouncing around on final is next to imposible/useless imho.

Hmm, I disagree here

(snip)
I dont know the exact number but what AOA are our aircraft capable of? 0 to what, 6 7? How much does that change between a light and a full loaded RV assuming that the airspeed is kept the same? 1-2 degrees? How much do we bounce around on final on a summer day, even without wind? Imho flying an AOA approach in light GA aircraft is a challenge and not an added benefit. Nothing trumps accurate airspeed control on final.

HOWEVER, I think an audible impending stall warning is essential!
Click to expand...

I think there is either a misstatement or misunderstanding of AOA here

It is easier to fly a stabilized approach in a highly wing-loaded heavy aircraft than an RV. This is true whether you are referencing IAS or AOA.

The NACA 23013.5 Airfoil on most RVs stalls at around 14-15 degrees of AOA IIRC. This is at any weight, g-loading, or airspeed. It doesn't vary even a tiny bit unless you change the geometry of the wing (flaps, VGs, etc).

What does change at various weights and g-loading is the airspeed where you will get to stall AOA. The only reason to fly a given airspeed on an approach, is because at a known weight and g-loading, you can calculate the airspeed, and all aircraft (by statute) have airspeed indicators while few have AOA equipment. Airspeed is merely a proxy for AOA.

It is better to measure AOA directly, because this eliminates errors in calculating for weight or g-loading.

If the AOA needle bounces around too much, that is a problem with the instrument, not the concept. I flew a 48 year old Cessna yesterday in turbulent air, and the airspeed indicator was bouncing all over the place. almost completely useless :)
 
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