Angle of Attach Indicator - AOA

[galt1074]

On the contrary I'd say what is important is the angle, all you have is airspeed to give you an idea what the AOA is. If you are going to max perform your aircraft and fly with precision there is no substitute for a gauge that tells you how your wing is performing and that instrument is an AOA indicator. You can stall at any airspeed, but not at any AOA.

I have a computer in my "work aircraft" that constantly updates my peformance data and has a dynamic stall carret in the HUD. I would give that up happily for a good AOA indicator so when I slow down to refuel the helicopters I know how the wing is handling it and it would make my maximum effort landing operations a piece of cake...right now I just have to fly pitch and power and feel the airplane. I dig that challenge but in a brand new airplane (like the one we are testing right now) there is no excuse not to have a good AOA indicator. At 3,000 hours I still can't feel EVERYTHING.

If I could get one on a Mooney (if I'm ever lucky enough to own one) I would want one there especially. No flight engineer to run my performance data, no computer to keep me up to date on the correct speeds for my current weight and atmospherics...just some little charts in the back of the POH that don't look like much compared to the 1500 page performance manual I use now.

Greg

[aviatoreb]

Quote: jetdriven

For all practical purposes, its the same as the stall warning system in the Mooney.  By the time it goes off its almost too late.  So how does a talking AOA that says "stall" any more useful than a stall warning horn?   I flew some in a Liberty XL-2.  It says "stall" when the stall vane lifts up.  The thing is, it goes "stall, stall, stall" on half of the takeoffs and landings. 

[bnicolette]

I think it would be nice to have an AOA if I inadvertantly picked up a bit of ice.  In that instance you might as well throw those airspeeds out the window and the only thing left wold be the angle of attack (and the stall warning horn) to let you know the wing was close to a stall.

I have been flying with an AOA on every corporate jet I've flown in the last 15 years.  In the Lears we would even reference them in the climb especially when getting near the "coffin corner".  I for one think it would be nice to have one in the Mooney just for reference and to have some more gadgetry.  :-)

[jetdriven]

The problem is too many aural tones.  It distracts you from flying the plane.  If you have a continuous tone like a variometer in a glider, that is going to get annoying real fast.

[PTK]

[PTK]

How big are these things anyway. Would they fit right near the AS indicator?

[aviatoreb]

Quote: jetdriven

The problem is too many aural tones.  It distracts you from flying the plane.  If you have a continuous tone like a variometer in a glider, that is going to get annoying real fast.

[galt1074]

Quote: jetdriven

The problem is too many aural tones.  It distracts you from flying the plane.  If you have a continuous tone like a variometer in a glider, that is going to get annoying real fast.

[danb35]

Quote: allsmiles

What is important is to know the airspeed. A stall will occur at the same aoa at any airspeed.

[Antoni Deighton]

Dan,

You beat me to it; that's just what I was going to say! As we all should remember from our primary training, a stall can happen at any airspeed and any attitude, but only one AOA. Only an AOA indicator can tell you this. Using the ASI is just an approximation. If I have to choose between knowing and guessing I'll take knowing every time!

Antoni

[jetdriven]

I guess all those airliners got it wrong then!

 

Seriously, if you can't keep a target airspeed for a given bank angle (or no bank) then its a training issue.  All the AOA's, beeping gadgets, and VG's aren't going to matter if you can't fly the plane accurately.

[PTK]

Quote: jetdriven

I guess all those airliners got it wrong then!

 

Seriously, if you can't keep a target airspeed for a given bank angle (or no bank) then its a training issue.  All the AOA's, beeping gadgets, and VG's aren't going to matter if you can't fly the plane accurately.

[Shadrach]

Quote: jetdriven

I guess all those airliners got it wrong then!

 

Seriously, if you can't keep a target airspeed for a given bank angle (or no bank) then its a training issue.  All the AOA's, beeping gadgets, and VG's aren't going to matter if you can't fly the plane accurately.

[KSMooniac]

Quote: allsmiles

And if I may add, the proper way to know an accurate approach speed is to actually use CAS. Take the IAS off of the AS indicator and convert it to CAS. Multiply by 1.3 and then convert back to IAS.

Gotta love that elusive POH!

[Shadrach]

Quote: allsmiles

Very well said Byron.

And if I may add, the proper way to know an accurate approach speed is to actually use CAS. Take the IAS off of the AS indicator and convert it to CAS. Multiply by 1.3 and then convert back to IAS.

Gotta love that elusive POH!

[Shadrach]

Quote: KSMooniac

And if I may add, the proper way to know an accurate approach speed is to actually use CAS. Take the IAS off of the AS indicator and convert it to CAS. Multiply by 1.3 and then convert back to IAS.

Gotta love that elusive POH!

[PTK]

Quote: KSMooniac

And if I may add, the proper way to know an accurate approach speed is to actually use CAS. Take the IAS off of the AS indicator and convert it to CAS. Multiply by 1.3 and then convert back to IAS.

Gotta love that elusive POH!

[Parker_Woodruff]

Allsmiles,

Go look at a CAS/IAS relationship table on a Cessna 172, especially towards the low end of the ASI.  Fortunately our Mooneys don't have such a huge difference, but this highlights the advantages of having an AoA instrument when we don't have an FMS computing everything for us.

There can be a 20% or more difference in CAS to IAS on a C172.  IIRC, Vso in a C172 at max weight is about 40 KIAS, but the CAS is 48 knots.

Now go do the same conversion in a C172 at 65 KIAS (typical max weight approach speed).

[xftrplt]

 

The AOA issue has been debated ad infinitum in the air transport community, and it's my opinion that Byron's sarcastic (?) comment that "they got it wrong..." is, in fact correct. Chalk up the collective decision not to include AOA indicators to good analysis or ancestor worship, depending on your view.

An indication of AOA (along with minimal training) would have given the Air France crew the information to have maintained control of their aircraft and prevented the crash. This event may reopen the discussion.

That said, fighters and airliners are operated in vastly different regimes. A fighter pilot may demand notional AOA's from -10 to +45 degrees, airspeeds from 80-800KTS, and G's from -2 to +9. Airliners (and most GA aircraft),with their high L/D wings and highly restricted flight envelopes, experience a very small fraction of that. For airliners, with their high inertia and small AOA envelope, it's been found that for straight-in instrument approaches, airspeed is a more accurate metric than AOA. (New curved GPS approaches may change the calculus.)

An effective, reasonably-priced AOA indicator for GA would surely be of benefit. The fly in the ointment, as ever, is cost.

(3k tactical hours with AOA, 15k air transport hours without.)

 

[Shadrach]

Quote: xftrplt

 

The AOA issue has been debated ad infinitum in the air transport community, and it's my opinion that Byron's sarcastic (?) comment that "they got it wrong..." is, in fact correct.  Chalk up the collective decision not to include AOA indicators to good analysis or ancestor worship, depending on your view. 

An indication of AOA (along with minimal training) would have given the Air France crew the information to have maintained control of their aircraft and prevented the crash.  This event may reopen the discussion. 

That said, fighters and airliners are operated in vastly different regimes.  A fighter pilot may demand notional AOA's from -10 to +45, airspeeds from 80-800KTS, and G's from -2 to +9.   Airliners (and most GA aircraft),with their high L/D wings and highly restricted flight envelopes, experience a very small fraction of that.  For airlines, with their high inertia and small AOA envelope, it's been found that for straight-in instrument approaches, airspeed is a more accurate metric than AOA.  (New curved GPS approaches may change the calculus.)

An effective, reasonably-priced AOA indicator for GA would surely be of benefit.  The fly in the ointment, as ever, is cost. 

(3k tactical hours with AOA, 15k airtransport hours without.)

[xftrplt]

Ross, thanks.  I guess I didn't express it very clearly.  

The very efficient high L/D airliner wing operates in a narrow band of AOA, so small changes of AOA translate into large A/S changes.   Airline ASI's are extraordinarily accurate (and there always at least three of them).  Auto-throttles hold A/S to plus or minus a couple of knots.  A stabilized approach is required to continue below 500 VMC or 1000 feet IMC.  This includes A/S within 5 KTS of bug. 

Fighters, with low L/D wings and blended bodies are the reverse.  AOA varies greatly with airspeed, and maximum performance maneuvering is of the utmost importance.  Furthermore, gross weight can quickly vary greatly during a flight--a salvo release of ordinance, for example.

Two different breeds of cat, but the same laws of aerodynamics.  

[Vref]

AoA indications would be real nice to have as redundancy/back-up support etc...I think...if affordable..

.AOA is heavily used in modern transport jets. The modern buses all have Alpha floor protections..to trigger ToGa in normal flight control law mode e.g. when pulling hard on the stick e.g terrain avoidance maneuvre. In the case of the Air France jet the degradation of the flight control laws (due to the icing airspeed invalid etc..) was not taken into account A/P disconnect and auto thrust disengaged. When normal law is not available you still can fully stall the aircraft..which happened 3 minutes long....A simple AoA indication on the PFD would have reminded the crew of the basic aerodynamic principles......A comment I hear often lately if an ex-military pilot would have been in the cockpit, this may not have happened....So yes AoA indications to crew are important (and not only as part of the flight control computer/calculation inputs...).... A lot of lessons (on all subjects) will be learned from this sad tragedy...........

 

[Shadrach]

Dick,

You were very clear, and I understand that a fighter has a much more varied ops regime with in a much large envelope compared to a civilian passenger jet. I just do not understand how an ASI reading is a superior metric to a device that literally tells you when your approaching critical AOA as well as allows you to interpolate ideal AOA for an approach (or am I misunderstanding what the instrument can do?). 

[Vref]

Quote: Shadrach

No you were very clear, and I understand that a fighter has a much more varied ops regime with in a much large envelope compared to a civilian passenger jet. I just do not understand how an ASI reading is a superior metric to a device that literally tells you when your approaching critical AOA as well as allows you to interpolate ideal AOA for an approach (or am I misunderstanding what the instrument can do?). 

[Shadrach]

Luc, your input is appreciated and you seem to be well versed on the subject.