The International Cessna 170 Association

From time to time I think of AOA instrumentation in the C170.

Do our small airplanes need AOA?

If we have any visual reference outside to the horizon aren't we somewhat protected?

Do many of our forum visitors have instrumentation?

I purchased the iLevel BOM to install that gives me NORSEE approval and provide ADS-B in, AOA, and AHRS data to run on my ipad. I just created the install bracketry and hope to have it calibrated and flying on the plane by then end of the year. I'll report back what i find.

Rupert,
I will be interested in your report and looking for it.

I currently already use the iLevil ADSB portable in, so have been paying attention to the BOM solution. My other option is the Garmin GDL 82, so costs are similar between the two by the time all is said and done, but get more useful functions with the BOM.

==Bill

Looking at there website the BOM is ADS-B in only, the Garmin 82 is ADS-B out. Very interesting configuration though.

Please bear with me on this one but I am on a learning curve here. Why do I need a AOA in a Cessna 170 . I have a ASI , and a host of other instruments that tell me if the stall margin is close plus experience in flying this machine . I have fitted a couple of AOA instruments for clients in a Cessna 210 and and a Cessna 177rg. What a pain in the U know what. I was flying these aircraft and at the same time and we were trying to calibrate these instruments . When flying and calibrating , ATC called me up and asked why were we doing aerobatics in a Cessna 177rg. We were in a control zone but with clearance to do aerial work [testing].clearance to operate from sea level to 4500ft . A couple of times I could tell the wave height . No doubt the transponder was sending out different heights .[its the only time I have ever done a tail slide in a Cessna 177rg. ]

With our venturi systems, I know my airspeed indicator is a little bouncy at slow speeds, and AOA tells you when your wing will actually stop flying. Normal everyday flying I'd expect to not really need AOA, but I'm starting to test some backcountry style short strip approaches where AOA would be another tool in the toolbox to fly a more precise approach and provide the lowest energy landing I can achieve in the plane. I'm also a gadget guy and like playing around with these things. Definitely just a personal preference!

Aviation Safety magazine published an article on this subject in the Oct 2018 issue. I'll see if they'll allow me to scan/post it.
But in a nutshell...(and we have plenty of nuts around here, heh-heh)…
..
There is NO SUCH THING as a single "stall speed". But we all know that. What we DON'T KNOW is..."What is the speed at which this airplane will stall in THIS attitude?" and "What about NOW?"

In other words, the stalling speed published in the Owner's Manuals, POH's, etc., are applicable to an airplane in the landing configuration (usually) and that speed is applicable ONLY in that configuration...and ONLY at gross-weight, ...and only when the speed is decaying at the rate of approx. 2 kts-per-second... which is what the test pilots observed when your airplane was NEW. (and actually not YOUR airplane, but an airplane typical of your model.)

We all know for example, that increasing the bank angle will increase the stalling speed... right? But what if you want to know RIGHT NOW in THIS BANK...where the airplane will suddently stop flying? AOA will tell you when that wing is about to quit at any weight (yes, that affects things), at any load-factor, at any bank, at any aircraft configuration other than the limited one published in the POH.


There's more to it than that short description, and most of us don't really care in our daily flight operations where our airplane will actually stall.
But if you're operating in the narrow-margins, either due to operational necessity... or because you're crazier than most pilots who fly with conservative margins...(I'm one of the latter)... and you want to REALLY KNOW when your wing is about to "let go" of it's lift-capability in all situations of bank, flap/aileron configurations.... then ANGLE of ATTACK will more reliably provide that information than an airspeed indicator will.


I am old-school and learned to fly by airspeed and seat-of-the-pants and don't like flying "on the edge" where I can get hurt...so I feel an AOA is not worth the investment for the type of flying I do in light-planes. But the AOA was definitely part of the instrument-scan in the jets in which I'm qualified, and the AOA was "helpful" when flying aerobatics (which I do much more rarely these days anyway, so I won't be buying one.) However, the AOA is becoming a tool for the flight-bag and is being taught much more commonly these days to newbies.

Hope that helps.

It’s sounds like I am old school type. But as I said before it’s only a “170” where we have fun . Part of the fun is knowing your limitations and the aircraft limitations . At the moment we are fitting a Garmin auto pilot to a early Cessna 172 n series . The owner stated to all its has a button on it if you get the aircraft in a unusual attitude and in cloud or other just press this button and the aircraft will right itself . I asked him what are you doing in cloud and the aircraft is is only a VFR and you are only VFR rated . Bloody moron. It’s all about limitations and the laws of physics,you can’t change that .

Aviation Safety Magazine provided this article as a courtesy. (Their website provides subscription service links http://www.aviationsafetymagazine.com/ ):

gahorn wrote:... and you want to REALLY KNOW when your wing is about to "let go" of it's lift-capability in all situations of bank, flap/aileron configurations.... then ANGLE of ATTACK will more reliably provide that information than an airspeed indicator will.

A true AOA system will do all of that. Unfortunately, most of these add-on systems can only be set up for one config. I would assume most would set it for landing config (probably most useful), but perhaps some have a reason for something else?

Regardless, once it is fully and properly understood, as George says, it will keep you out of trouble far better than airspeed alone because it provides your actual AOA more directly than airspeed can. Airspeed is a pretty good approximation, and since we generally fly with a buffer of 1.3 or thereabouts, it's usually good enough.

If you understand the assumptions/conditions that go into a given stall speed, you're ahead of the game compared to someone who blindly believes the ASI will keep them safe.

I learned on AOA while flying in the Air Force and believe it to be a very useful tool because things get complicated quickly, people get distracted by a variety of things, and a properly installed AOA gauge can't really lie to you like an ASI can. I find it amusing we all learn that a wing stalls when it exceeds its critical angle of attack, and yet we go out and rely on airspeed to keep us safe...then wonder why things happen when we're not in the 'book' config. I'd love to have a real AOA on my 170, but for now, it's a nice-to-have vs a need-to-have

Hi,
My $0.02. I first used AOA during Navy flight school. Very effective coming aboard a ship. I have seen hand made AOA devices. One was on a Cessna 140 that flew mission flights in South America. I will try to find a picture when I have time.
I purchased a preorder for the Aerovonics new electric attitude instrument that can also display a believe 12 other displays including AOA.
Aerovonics has recently been bought by Uavionx the wing or tail ADSB company. Unfortunately the price for these new round 3” instruments have gone up $500!

Here are the two photos of AOA on a Cessna 140. The mirror on dash was used to view AOA on wing over pitot probe.

Somewhat related----I have a friend that purchased a mid '70's C-180, promptly had Air Plains do an engine upgrade to a Continental IO-550 w/ a 3 blade composite prop. Then had Sarasota do a major rework of his instrument panel. Boy does it have a bunch of gee whiz things and when I have had the opportunity to fly it the acceleration is awesome (so is the fuel burn)! Happy to have a friend who can afford to do these things. Anyway the plane came with an AOA device. He hasn't become comfortable with it yet and threatens to have it removed. While I have no technical knowledge of this unit, I have noticed on numerous flights that as we slow to around 90 kts, the female voice comes on stating, "Getting slow, getting slow". This will continue all the way to touchdown. He certainly doesn't like that feature,but I have to think there must be a means of changing the airspeed at which speed the warning begins.

c170taildragger wrote:I purchased a preorder for the Aerovonics new electric attitude instrument that can also display a believe 12 other displays including AOA. Aerovonics has recently been bought by Uavionx the wing or tail ADSB company. Unfortunately the price for these new round 3” instruments have gone up $500!

I will be very interested in the AV-30 when they get it certified and it proves reliable. I would love to eliminate the venturis and heavy gyros.

rupertjl wrote:With our venturi systems, I know my airspeed indicator is a little bouncy at slow speeds, and AOA tells you when your wing will actually stop flying. ...

I think you meant pitot system as the venturi system has nothing to do with airspeed indicators.